Vertical Wind Shear in the Lower Layers of the Atmosphere

Citation preview

WORLD METEOROLOGICAL ORGANIZATION

TECHNICALNOTE NOTENo. No.93 2 TECHNICAL

METHODS OF OABSERVATION AT SEA VERTICAL WIND SHEAR IN THE LOWER LAYERS OF THE ATMOSPHERE PART I – SEA SURFACE TEMPERATURE

WMO-No. 26.TP TP. 8 WMO-No. 230. . 123 Secretariat of the World Meteorological Organization – Geneva – Switzerland

WORLD

METEOROLOGICAL

ORGANIZATION

TECHNICAL NOTE No. 93

VERTICAL WIND SHEAR IN THE LOWER LAYERS OF THE ATMOSPHERE

I WMO· No. 230. TP.123 I Secretariat of the World Meteorological Organization .. Geneva .. Switzerland

1969

----- - - - - - - - - - - - -

© 1969, World Meteorological Organization

NOTE The designations employed and the presentation of the material in this publication do not the expression of any opinion whatsoever Oll the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country or territory or of its authorities, or concerning the delimitation of its frontiers. imp~y

TABLE OF CONTENTS

Foreword ••••••••••••.•••••.••.•..••••••..•.••••••••••••••..••.•••.•.••...••••

V

Contributions

I

II

Canada Vertical wind shear in the boundary layer - by R. ·B. Pettitt and R. G. Raot •.••••••••••••••••..••••••••.••.•••...•.••••.••.•••.•••••

1

Preliminary analysis of Canadian wind-shear data - by F. B. Muller and C. M. Mushkat •..•••••••.•••••••..••..••...••..••.•.••••••••••••

31

France Etude dynamique de la couche 0-100 m sur Ie site de Paris-Nord par J. Sarssac •..••.••••...•.••••••••..•.•.•••...••..•••.•••..•••.•

37

Etude dynamique de la couche 0-100 m sur Ie site de Roissy-en-France par J. Sarssac ••••••••••.....••••.....•••...•.•.•..•••.••••.•.•.•••

59

III

India A report of the statistical investigations on vertical wind shear in the lower layers at Thumba ••••••••••.•.•••••..•.•••••••••..•••••••• 103

IV

Japan Vertical wind shear in the lower layers at the Tokyo International Airport - by Kazuo Kusano, Yoshio Suzuki and Hisanari Takei ••..•••• 169

V

Netherlands Dependence of observed low-level wind shear on averaging period and

lapse rate - by P. J. Rijkaort VI

VII

Unian af Soviet Sacialist Republics Wind shear in the lower atmasphere - by K. G. Abramovic V. G. Glazunav

185 and 195

United States of America A preliminary analysis of some observations of wind shear in the

lawest 100 feet af the atmosphere far applicatian to the problem of the control of aircraft on opproach - by Charles F. Roberts

203

Estimatian of the 90 m wind from low-level abservations by Steven R. Hanna and Hans A. Panofsky •••.•••.•••••••...•.•••••••• 219

v

FOREWORD

The vertical wind shear in the lawest 100 metres layer of the atmosphere is a meteorological parameter of importance to aircraft during the take-off and initial climb and of even greater importance during the approach and landing. The third session of the WMO Commission for Aeronautical Meteorolog~ which was held simultaneously with the Meteorology and Operations Divisional Meeting of ICAO in Paris in 1964, accordingly recommended that WMO should invite Members to carry out studies relating to the occurrence of vertical wind shear in the layer between 10 and 100 metres above ground level at appropriate locations, preferably at international aerodromes. Subsequently the ICAO All Weather Operations Panel recommended that the abave-mentioned studies should be representative of conditians at international aeradromes on a worldwide basis, and should include data on the nature and intensity of vertical wind shear and its relation to aircraft operations at aerodromes.

At its sixteenth session (Geneva, 1964) the Executive Committee approved the CAeM-III/MET-OPS recommendation referred to above and urged Members who are in a positian ta do so to carry out the necessary studies and to keep the Secretary-General informed of the progress of such studies. In response to this request of the Executive Committee, seven Members of WMO - namely, Canada, France, India, Japan, Netherlands, the Union of Soviet Socialist Republics and the United States of America forwarded to the Secretariat papers reporting recent research in this field. Although these studies are generally of a preliminary nature, they constitute a very interesting sample of investigation into the occurrence of vertical

wind shear in different geographical areas and under varying climatological conditions. They are accordingly being published together in the present Technical Note, in accordance with a suggestion of the President of CAeM. It is hoped that it will be useful to meteorologists engaged in investigations into these very important phenomena,

and to the aeronautical bodies concerned. I wish to express the gratitude of WMO to the Members who contributed to this note.

(D. A. Davies) Secretary-General

CANADA

VERTICAL WIND SHEAR IN THE BOUNDARY LAYER By R. B. Pettitt and R. G. Root

PRELIMINARY ANALYSIS OF CANADIAN WIND-SHEAR DATA By F. B. Muller ond C. M. Mushkot

VERTICAL WIND SHEAR IN THE BOUNDARY LAYER by R. B. Pettitt and R. G. Root*

INTRODUCTION

1.

This paper presents the results of a short study on baundary-layer vertical wind shear, i.e. the rate of wind velocity with height, in the first 200 feet above the graund. Important applications of such work are faund in the fields of structural engineering (in determination of wind loadings on buildings, masts, bridges, etc4) and

aviation (where wind changes wi th height are relevant during landing and especially when near the stalling speed).

take-off,

Vertical wind shear was investigated at two towers: one in Montreal, Quebec, the other at Whiteshell, Manitaba. These particular sites were selected because they represent widely varying topographical lacations. The Mantreal tawer is in an urban district; the Whiteshell site, an the other hand, is on a relatively flat plain with an exposure typical of many airports.

Fallowing a discussion of relevant theary, the data, first from Montreal, then from Whiteshell, are examined separatelYi a comparison of the two sets of results is then given. The Montreal data (Section 3) were investigated by R. Bruce Pettitt; the Whiteshell data (Section 4), by Robert G. Root. The two analyses were performed independently, and then the results combined, for convenience of the

paper.

2.

reader,

into

one

This explains why the types of treatment and display of the results differ. THEORY Vertical wind shear d

Vertical wind shear is strictly defined as az

~

i~

(li). where u is the

wind

vela city vector and z is the height above the ground. In this paper, however, the scaLar u (magnitude oft) has been used, the angular shear being analysed separately. du ., the scalar 5 hear at one pOlnt; ' h ereln, ' h owever, th e t erm '" W1n d 5 hear '" 15 us e d --:.1.5 ¥~ express (U - u ), the !Iaverage wind shearn between heights z1 and z2 fro~ which I 2 (zl - z2) the data were reported. *

This study was undertaken in the summer of 1965 while Mr. Pettitt, an Honours Mathematics and Physics Student at McGill University, and Mr. Root, an Honours Mathematics and Physics Student at the University of Manitoba, were employed as student assistants with the Meteorological Service of Canada.

CANADA

2

In the height range cansidered .here, the vertical wind prafile is empirically described by equation (l~ namely,

=

G~)

(1)

p

where subscripts 1 and 2 refer to two different heIght levels above ground and p is an index dependent on the terrain over which the wind blows, geostraphic wind speed, and the lapse rate. For example,De Marrai. (1959) has presented extensive summaries of p-values for the Brookhaven meteorological tower. In strong-wind.engineering applicatians, a value of 1/7 for p is often used. It can be seen from equation (1) that the limiting case af no wind shear corresponds to a value of zero far p. The wind at the top of the planetary boundary layer is produced by synoppressure gradients. B~cause air is. a viscous fluid, the surface of the earth exerts frictional drag and momentum is transferred downward from the geostrophic wind level to the ground. This produces a surface shearing stress and a vertical wind shear. Turbulence is the primary mechanism for momentum transfer, and tic and meso$cale

wind shear decreases (i.e. the index p decreases) with increasing turbulence.

Turbulrnce is produced in the boundary layer in two ways: :."".;,

.(a) (b)

.;-~

Forced canvection, caused by the roughness af the underlying surface. Free convection, caused

~y

buoyancy forces.

Unstable air tends

enhancing vertical mixing and .reducing the wind shear.

to

rise,

During inversions,

on the other hand, vertical mati on is damped and the wind shear may become very large.

In th,e

cas~

of a strong nocturnal radiation inversion, a low--

level jet stream (Blackadar, 1957) tends to develop at toe top of the inversion, a phenomenon· that has been observed at the Whiteshell site (Munn, 1963), for example. Forced convection may be subdivided into two cases. (i)

Where the lowest level of wind measurement is much higher than the surface roughness elements;

(ii) Where the lowest level of wind measurement is of the same order of magnitude as the surface roughness elements, e.g. wind-shadow effects in the wake af buildings. In this latter case, the flow becomes very disturbed and the wind shear may vary greatly with slight upstream changes in building orientation. Far example, if several 50-ft buildings were not far from a tower, the 200-ft level wind might be accelerated while the 20-ft wind were diminished, creating a large

VERTICAL WIND SHEAR

3

wind shear; with certain wind directions, however, wind channelling between buildings might accelerate the flow at the 20-ft level.

3.

WIND SHEAR AT THE MONTREAL BOTANICAL GARDENS SITE Data source _ Instrumentation The data consist of measurements of hourly ten-minute mean values of wind

speed and direction, for the period from June 1962 to May 1963 (inclusive), from Bendix Friez 120 anemometers at the 35 and 200- ft levels of a micrometeorological tower in the Rosemount Batanical Gordens in the City of Montreal (Wilson et al., 1965: The ~ower is owned and operated by the Province of Quebec, Division of Industrial Hygiene. directions

The wind speeds are chart-scaled to the nearest mile per hour; to 8 compass points.

the wind

Local topography The tower is immediately surrounded by an ope~ grassed field (at elevation 185 feet above sea-level) near the western corner of the Maisonneuve Park (Montreal's Rosemount Botanical Gardens).

There follows a description of the terrain over which most of the winds blow in each directional class: N-class winds

0-500 yards ~

500 yards

Open, grass field;

land falling awoy gently

Lines of trees 50 to 60 feet high

500 yds - 1 mile

Golf course (fields with scattered trees)

';;-1 mile

Land elevation drops to 110-120 feet ond then gradually further drops off; surface: fairly low, mixed, residential, commercial buildings

E-class winds

0-300 yards

Open fields, Q few scattered small trees, hedges, small buildings

300 yds - 1 mile

Partly open field to about 600 yards then fairly dense trees ~ 50 feet high, partly law two-storey buildings (residential)

1 mile

Steep drap of

:> 1 mile

Mixed commercial and residential buildings, to the St. Lawrence River about two miles from tower

AJ

80 feet in land elevation

4

CANADA S-class winds ----------.---

0-300 ft

.:> 300

ft

Small hedges, cultivated fields Residential buildings (two storey) on land somewhat higher than tower base

W-cla-ss winds 0~150

ft

5150 ft

Open field and street Two-storey residentiol-type buildings

Treotment of the doto The only doto considered were those cases in which u 200

'>

20 mph;

winds are not likely to concern structural engineers and aviation interests.

lighter Aiso l

the wind direction wos token to be thot of the 200-ft wind. Grouping of the dato The data were grouped in an attempt to have a significant number of cases (approximately 10) in each class. The data were divided into four seasons:

Summer

- June, July, August (1962)

Autumn

- September, October, November (1962)

Winter

- December (1962), January, February (1963)

Spring

- March, April, Moy (1963)

ond also into day (0800-1900 EST) and night (2000-0700 EST).

are listed;

In Table 1 the numbers of cases occurring at various directions and speeds on this basis the data were grouped as follows:

directionolly to four compass-points:

N - (north and north-east winds) E - (east and south-east winds) S - (south and south-west winds) W - (west and north-west winds)

and spee.dwise

into

4 groups:

A - (u B - (u C - (u

200 200 200

= 20, 21, 22 mph) = 23, 24, 25 mph) = 26, 27, 28 mph)

D - (u 200 :;;

29 mph)

5

VERTICAL WIND SHEAR TABLE l Seasonal distribution by wind direction and wind speed (200-ft winds) of wind-shear caseS studied- Montreal

Summer

DAY

NORTH EAST

lllh 9 10

TOTAL

TOTAL 9

3 27

15

1 3

6

32

1

1 34

1

22

4

96

1 25

3

13

6 2

67

29

lllh

3·

SOUTH WEST

~

26-28

NIGHT

3

8

1

41

Autumn 20-22

23-25

lllph

NORTH EAST SOUTH WEST TOTAL

8

13

6

23

29

14

9

10

20

11

10 34 17 65

18 18 59

... 29

26-28

lllh

TOTAL

lllh 11

18

17

63

1

26

5

70

1 12 64

is

8 56

7 42

5 1 18

70 15

2

6

42

30

201

40 27

19

152

winter lllh

NORTH EAST SOUTH WEST TOTAL

10

12

23-25

2 -28

lllh

lllh

10

5 61

40

11

18

1

18

11

9

75

7

29

TOTAL

lllh 5

11

12 3 4

21 94

33 17 70

2

16 5

49

12 33

38

~-7

2 52

39

8

9

7

5

31

17

147 44 265

8 5 195

Spring

20-22

23-25

lllph

NORTH EAST

4 15

17 9

19 23

SOUTH

9

WEST TOTAL

1

70

52

~ 29

26-28

lllph

lllh

TOTAL

mh

5

5 15 20 12 52

1 14

9 24

5 20 2 27

1 15

1 4

36 93

22 30 69

10 26

14

182

163

6

CANADA Calculatian af index p The index p may be faund in a particular case fram equatian (1) thus:

p

=

(2)

A p-value representative af a given wind class (say, N winds in the 23 ta 25 mph speed range far winter nights) was calculated by first finding the average of the upper winds in the class (u ) and that af the lawer winds (U ) , and then using 2 l equatian (2). Results In this sectian of the paper, an attempt is made ta paint aut impartant features af the various graphs which have been prepared, and also to present an explanation of these features by relating them to relevant causal conditions. Wind-shear frequency distribution Figure 1 represents the frequency of shears of various magnitudes using

011 cases under study, and indicates that the modal value of 8 mph/165 feet. Furthermore, Figure 1 shows that the wind shear in 165 ft in just over 99% of all the 1,295 cases studied.

wind was

shear is 15 mph




0.17

V/D

29

0.25

Probably the difference between autumn and spring as compared with winter

lies in the fact that in autumn and spring there is: (1) less stability, ground (as opposed to smooth snow cover), and (3) some foliage

on

the

hence, there is more low-level turbulence affecting the 35-ft tower wind.

(2)

bare

vegetation;

The effect

is a lowering of the 35-ft wind speed; i.e., a raising of p-values. The maximum values stay much the same, but the off-maximum values do indeed increase (relative to winter), and, hence a less sharply defined maximum results. Less order in autumn and spring than in winter is explicable by the fact that the ground is bare (as opposed to a smooth snow surface), and trees and other vegetation near the tower have foliage; hence, more localized factors become important as obstacles, each direction having more pronounced peculiarities. Furthermore, in Table 3(0, b, c)there is a definite directional trend for p-values to increase from

north to east to south to west. Shear changes at night (Table 4 (a, b, c» Inversion conditions usually exist during the night, and inhibit recovery

of the wind to the upstream value. Thus, for example, the shadow effects for a few trees near the tower will be magnified at night, while during the day their effects

CANADA

10

are reduced by better mlxlng of the air. The foregoing is exhibited by the relative lack of order in the night data (Table 4) as compared with day data (Table 3). Winter, however, does show more regularities than autumn and spring nights.

This may be explained by the relative absence of vegetation effects, the ground presenting a smooth snow surface, and thus the effects of nearby obstacles be~ng minimized. Nevertheless, p-values increase from north to east to south· to west, very consistently in all seasons, under night-time as well as day-time conditions. Wind shear versus direction

It has been noted that all the data indicate a general p-value increase from north to east to south to west, for all wind speeds and all seasons, day and night. This can be explained reasonably well by analysing the topography relevant in each case.

West winds When winds are westerly, the air blows over

two-storey residential build-

ings to within 150 feet of the tower; the last 150 feet consists of a six-lone street and an open field. A wind-shadow effect is to be expected, with reduced speeds at 35 feet. The wind-shear index p is therefore large. . North winds Most of the winds in this class were actually from the north-east rather than the north (see Table 1). The upwind exposure is excellent in this sector and the surface roughness is relatively low. It is perhaps surprising that the resulting. p-volues ore smaller than in any other direction, despite the fact that the turbulence should be least with north-east winds. We can only infer that the local wind-shadow effects are more important than the general level of turbulence in affecting the vertical wind shear. The resulting p-values with north-east winds are likely to be similar to those that might be found at a relatively open airport. East winds Almost all winds in this class were south-eost rather than east (see Table 1). The immediate upwind exposure within 300 yards of the tower is open but there are relatively large, rough, surface elements beyond to introduce a wind shadow. South winds Here again the directional classification was biased with many more southwest than south cases (see Table 1). Beyond an upwind distance of about 300 feet, the wind is blowing over a built-up area.

VERTICAL WIND SHEAR

4.

11

WIND SHEARS AT THE WHITESHELL SITE

The Whiteshell tower, one of the installations in Canada's micrometeorological tower network, is located an the Atomic Energy of Canada Limited site in southeastern Manitoba (Wilson et ah,1965). The Health Physics and Safety Division of Whiteshell Nuclear Research Establishment (WNRE) owns and operates the tower. In general, the mesometeorological environment consists of a gently rolling

wooded landscape interspersed with lakes. The WNRE property consists of a cleared area of approximately half a square mile. The tower is located near the mid-point of the western half of the clearing, which is bounded on the west by the Winnipeg River flowing north. The opposite bank area is cleared for 3/4 mile, except for a strip of trees 900 feet wide bordering the river to the south-west. A description of the small-scale features of each directional sector follows:

350-030 degrees 0-300 feet

Cleor and flat

at 300 feet

Small raw of bushes oriented approximately east-west

> 300 feet

Generally open country

030-120 degrees 0-250 feet

Open ploin

250-750 feet

Seven scattered buildings, ranging in height from 24 to 58 feet

750-2,500 feet

Open flat land

120-180 degrees 0-650 feet 650-700 feet

> 700 feet

Open, level ground Construction camp trailers, about 12-ft high 30-ft trees for several thousand feet except due south, where they extend only to the river which is about 1/4 mile away

180-220 .degrees 0-150 feet

Clear ground

150 feet to river

300-ft high trees (the river varies from 400 to 800 feet oway)

Across river

30-ft high trees for 350 feet then clear. (river approximately 1,500 feet wide)

12

CANADA

220-290 degrees 0-200 feet

Open, flat ground

200-300 feet

30-ft high trees

300-1,500 feet

River

1,500-1,700 feet

> 1,100 feet

30-ft high trees Open for 1/2 mile

290-320 degrees 0-400 feet 400-1,600 feet 1,600-1,750 feet

> 1,150 feet

Open clearing

River

30- ft high trees _ Open land for 1/2 mile

320-350 degrees 0-350 feet

Open land

350-500 feet

Trees 30 feet high

500-2,000 feet

River

> 2,000 feet

Open land for 3/4 mile

Grouping of data Wind speed and direction data for the 20- and the 200-ft levels and also the temperature difference (T - T ) between the levels from the Whiteshell tower 200 20 were used. The data were available from September 1963 to May 1965, excluding December 1963. The speed and direction of the wind were ten-minute means from each hour

recorded to the nearest mph and ten degrees. to the nearest 0.1 0 F.

The temperature difference was measured

Only cases when the upper_wind speed equalled or exceeded 20 mph were considered t since at lower speeds wind shear becomes insignificant for both building design and aviation. The data were then subdivided according to speed, season, direction, and lapse rate (Table 5). For examination of the effect of speed, the mean values of both the upper and lower winds in 3-mph groups were used. The lapse rate wind divided into only two categories - inversion when the temperature at 200 feet was greater than or equal to the temperature at 20 feet and non-inversion when T - T was < O. 200 20

VERTICAL WIND SHEAR

13

TABLE 5 Seasonal distribution by wind direction and wind speed (200-ft winds) of wind-shear Cases studied _ Whiteshell

April and October ~ . '-I'e~&\. "'S'-O

"

'Ie

NORTH

20-22

23-25

26-28

29-31

lilh

mh

mh

mh

38

7

54 EAST SOUTHEAST

47 53

SOUTH

38

~ORTH-

42

49 10

9

19

9

"4-

14

5 1

9

9

74

SOUTHWEST WEST

77

17

6

7

2....-....... _.....

32-34

35-37

38-40

9

3

2

41-43

2

1

20 21

1

14

20

Summer mph

mph NORTH

2

B

mh 1

47

mh 1

mh

NORTHEAST SOUTHEAST

1

Winter

NORTH NORTHEAST SOUTHEAST SOUTH SOUTHWEST NORTHWEST

23

5 10

41

18

3

5

3

9

1 2

CANADA

14

For classifying coses into seasanal and directional groupings, the only criterion was that each division would have a comparable

number

of

cases.

This

approach yielded the following groups. TABLE 6 Directionol distribution of Whiteshell data Directions Angular sector

North

North-east

South-east

South·

South-west

North-west

340-010

020-130

140-170

180-210

220-290

300-330

536

939

615

457

520

609

included No. of cases

Throughout the remoinder of Section 4 ond in Figures 6-10 when reference is made to particular wind directions

(e.g. north, north-east, etc.1 the sector as

defined in TobIe 6 will be implied. TABLE 7 Seasonal distributions of Whiteshell data Seasons

Months - inclusive

Terrain

Summer

May - September

Leaves;

Winter

November - March

Snow

Transition

April and October

Transition period

No. of cases

foliage

1,106 1,148 872

Combinations of the above two groupings were employed whenever the number of cases in eoch sub-group exceeded ten cases. For each group and sub-group, ·both p and wind shear were studied. Distribution of shears The distribution of wind shears is given in Figure 2, which indicates that only 0.75% of all cases equalled or exceeded 20 mph/180 ft. Small shears, i.e., where l!. u is less than 4 mph, are also unusual, totalling only 2.7% including five cases of no shear and

three cases where the scalar shear was negative.

The

most

probable shear was 10 mph/180 ft. Eighty per cent of the cases occurred from 6 to 14 mph per 180 ft, and 50 per cent were included in the group 8 to 12 mph/180 ft.

VERTICAL WIND SHEAR

15

Although 80 per cent of· the volues would seem to foIl within

0

relotively

narrow range, it is nevertheless a broad range when compared with that associated with p-values normally observed. For instance, if 22 mph were used as on average

upper-wind speed, 8 mph/180 ft sheor correspond to 12 mph shear requires a p-value of 0.33.

0

p-volue of 0.175 whereos

0

In other words, for aviation pu-rposes, where large di fferenc6s in the wind speed and wind direction between the upper and lower levels ore the main concern, the range of the probable shear is quite small. On the other hand, for construction purposes, where high winds mean added costs to strengthen the building against the larger wind stresses, the· range of both p and upper-wind speed is quite large.

Extreme values

Table 8 displays the maximum scalar category of speed and direction;

shear per 180 feet observed in each

thus it provides an indication of the magnitude of

the shears which may be encountered -- for example, the extreme was 28 mph per 180 feet For 200-ft winds between 20 and 28 mph, the extremes occurred almost always during inversions and were probably associated with a low-level jet stream. When the 200-ft winds were greater thon 28 mph, the extremes were mostly with lopse conditions. However, the magni tude of the extremes did not seem to depend on the strength of the 200-ft wind, although there was a directional effect (larger volues with south and south-west winds). TABLE 8 Maximum observed wind shears for various wind direction and speed closses (200-ft winds) - Whi teshell 20-22 mph

23-25 mph

26-28 mph

29-31 mph

32-34 mph

35-37 mph

38-40 mph

41-43 mph

all speed

1l0RTl1

11

18

16

19

20

21

11

18

21, 1..1

NORTH-EAST

22

l2.

l2.

13

.!.§.

1£

19

11

22

SOUTH-EAST

22

!.l

14

19

18

SOUTH

11

17

.!.§.

19

24

25

28

24

28

SOUTH-WEST

.!.§.

25

12

18

12.

18

10

22

12

NORTH-WEST.

14

1£

17

21

17

20

.!.§.

13

21

ALL IoIRECTIONS

22

12.

12

21

24

25

28

24

28

NOTE:

22

Maximum shears occurring under inversions are underlined.

CANADA

16 Angular di stri bution

One can justify the treotment of wind sheor as a scalar in the layer of air from 20 to 200 feet by an examination of the distribution of angles of deviation between 200~ft and 20-ft wind directions, as shown by Figure 3. For over 59 per cent of all cases no deviation was recorded. ~

Moreover,

unless the ·angular shear is equal to or larger than 30 0 , the change of magnitude is 'not significant.

Only 1.9 per cent of the cases demonstrated such angular variation;

thus, treatment as a scalar is valid. Examples of the effect of angular shear greater than or equal to 50 degrees are given in Table 9 •. It is also evident from Figure 3 that veering with height is seven times more common than

backing~

TABLE 9

-

A few examples of the effect of angular shear at Whiteshell. 8U is the shear as IH

usually calculated whereas ~ is the shear I1z

) and lower (u ) when directional differences in upper (u 20 200 wind speeds are included

--

u 200

u 20

21

10

11

14.6

30

16

14

19.7

22

07

15

17.5

20

13

07

11.6

20

11

09

14.5

28

11

17

22.5

700

20

13

07

15.5

1000

20

13

07

22.0

22

14

08

24.5

Angular shear 500

600

l1u (mph/180ft) I1z

~ I1z

(mph/180ft)

.

Variation of shear and index p with various parameters

~~:~~!~~~_~~!~_!~~~~_:~!~_~~~_~~~:i!_~~~~_~~~~~ Figure 4 displays averaQe values of (u u

200

.

200

- u ) for various ranges of 20

A separation according to lapse or inversion conditions is also included.

VERTICAL WIND SHEAR

17

As might be expected, the mean wind· difference increases with increasing 200-ft wind. In addition, the differences are larger for inversion than for lapse cases.

The index p is given in Figure 5. There was a trend for decreasing p with increasing 200-ft wind during inversion, probably becaus~ the inversion intensity was decreasing, although this was not investigated. During lapse conditions, on the othel hand, there is li tte variation of p wi th wind speed. It is also significant to note that all p values are larger than the 1/7 empiricol formula. Variation with 200-ft wind ·di.rection

--------------------------------~---

The variotion of the index p with different directions is displayed by Figure 6. The'plots of p against direction for the two lapse rates investigated ore also included~ The changes in p due to different directions ore of the same order of magnitude as the inversion/non-inversion change. Figure 7 shows a similar plot for the quantity (u

200

- u ). 20

The trends

of Figure 7 ore essentially similar to those of Figure 6. However, there ore a few secondary variations in Figure 7 which are not shown in Figure 6. For example,

NE (020-130°) has a higher wind-speed difference than SE (140-170 0 ), p values for the two are similar.

although

the

This is almost certainly due to higher wind speeds

in the case of NE winds. Thus, because wind speed does affect the values of p, the cumulative effect due to directions, seasons, and stability will be discussed for a specific 200-ft wind

speed (20-22 mph).

Seasonal differences,

i.e. variations due to leaves and snow, are indi-

cated by Figure 8 which is a plot of u - u against 200-ft wind speed 200 20

for

the

lapse CDses in the three seasons. Wind-shear effects due to changes in ground cover are of a smaller magnitude than variations due to inversions and wind directional changes. From Figure 10, the transition season, April and October, has the highest shear values whereas winter (snow) has the lowest. Summer is intermediate. Discussion of possible causes of this trend will be considered below.

Variation of index p with direction, stabili tyand season for the 200-ft ~~~~:~E~~~=~!~~~=~!=~2:~~=§E~-------------------------------------------

In order to simplify discussian, cases in the 200-ft speed class of 20-22 mph have been analysed separately. Figures 9 and 10 show the resulting variations in p values with 200-ft wind direction, stability and season. Non-inversion cases (Figure 9) The relatively large number of cases in each group in Figure 9 and the reproducibility of the main trends from season to season lend weight to the reality

of the results.

18 Consider.first the seasonal trends.

The p-vo!ues are lowest in winter,

except in the case of northerly winds (340-010 0 -) for which p-values are higher in winter than at other times of the year. The most open, exposure at Whiteshell is to the north, and winds from that direction are most likely to approximate hamogeneous flow. Th~ smoother snow surface in winter reduces forced convection; in addition, the high albedo of snow diminishes the frequency of free convection cases. Both of tnese factors reduce turbulence and increase wind shear in winter.

it must be

Since all other wind directions have their smallest p-valu6s in winter, that the effect of local obstacles and changes in surface rough-

assu~ed

ness have a major influence.

In general, high p-values are associated with northerly (340_010 0 ) and southerly (180-2100 ) winds, low p-values occur with winds from the sectors 020_1700 ond 300-3300 , while intermediate values are in the sector 220-2900 • Some speculative theories have been proposed to account for these remark-

able differences but it would not be possible to substantiate them without more data or perhaps even a scale-model wind-tunnel study of the area. Certainly, the p-value veri.otion must reflect the influences of wind-channelling, building wind-shadows, and discrete roughness chonges from forest to grass or snow.

Inversion cases (Figure 10) The seasonal trends in Figure 10 are not as reproducible as those in Figure 9. This may be due in part to the few cases in some classes, e.g. northerly winds, seven cases in April and October, eight cases in summer. However, it is' readily apparent that average p-values are higher during inversion than lapse conditions with all wind directions. For those groups containing large numbers of data, the directional trends of Figure 9 are more or less r~produced in Figure 10. High ·p-values occur with

"northerly and southerly winds; low values are associated with the sectors 020-1700 ond 300-3300 , while the directions 220-2900 give intermediate p-values. Many of the inversion cases are associated with low-level jet streams in which the 20-ft wind is

light. It is, therefore, remarkable that the lapse-condition directional variations of Figure 9 are reproduced in Figure 10. Figures 9 and 10 invite further analysis with larger samples of data.

5.

COMPARISON OF THE MONTREAL AND WHITESHELL RESULTS The towers, as previously mentioned, are located at highly contrasting

sites. One, the Montreal tower, is in a large city and is bordered on three sides by two-storey buildings; therefore, it is representative of a residential area.

The Whiteshell tower, on"the other hand, is on a flot, relatively open area, in many ways similar to the locations of most large airports. Thus, it was felt that, along with a comparison of values of p found by other researchers, a comparison of the two

sites would be valuable from the standpoint of (a) aviation and (b) building design.

VERTICAL WIND SHEAR

19

Aviation

When landing a large aircraft, particularly near the stall speed, consideration must be given to the vertical wind shear. The largest scalar shear observed at Montreal (12 months' record) was 19 mph/165 feet (11.5 mph/IOO feet); at Whiteshell (20 months' record), 28 mph/180 feet (15.5 mph/IOO feet). At Whiteshell 0.9 per cent of all cases had shears equol to or greater than 20 mph/180 feet (11.1 mph/IOO feet). Only 9 per cent of Montreal cases exceeded or equalled (61 cases) 16 mph/165 feet (9.7 mph/IOO feet), whereas 2 per cent of Whiteshell cases were 18 mph/180 feet (10 mph/IOO feet) or more. The most probable shear at Whiteshell was 10 mph/180 feet (5.5 mph/IOO feet), at Montreal 8 mph/165 feet (4.85 mph/IOO feet). In Montreal the highest average shear was with winds from the west, the most built-up area; the extreme shear occurred in both the north and west. In Whiteshell, the highest average shear and highest extreme shear were from the south and south-west. It is interesting, however, that north, the open direction at Whiteshell, has high average shear but low extreme values.

Building design Modern high-rise buildings must be designed to withstand strong wind stress. For this reason, the magnitude of the 200-ft wind speed is important. As observations are not regularly made of 200-ft winds, they must be estimated from 20-to 30-ft wind speeds, usually by use of the power laws. the 200-ft

Whiteshell had, in 20 months, 3,000 winds of 20 or more mph recorded at level; Montreal only had 1,200 in 12 months.

Montreal also had a smaller maximum 10-min wind speed (40 mph) than Whiteshell (43 mph), as well as a smaller number of high winds. For example, in only 64 cases were the 20D-ft winds aver 30 mph at Montreal; velocities at 200 feet at Whiteshell over 34 mph in 70 ob~atians. For strong 200-ft winds, the value of p was lower than for light winds. In Whiteshell the p~value for all winds greater than 31 mph was 0.2. Listed below are the p-values at Whiteshell for high 200-ft wind speeds in which there were eight cases or more. 200-ft wind speed

No. of cases

Direction and season

32 - 34

10

North~

35 - 37 38 - 40

15 12 9 8

NW, summer NW, winter NW, winter NW, winter

Apr. Oct.

p value

.20 .18 .155 .161 .12

CANADA

At Montreol the mean value of p for all 200-ft wind speeds equal to greater than 30 mph was .185.

or

Values of p and wind shear and their dependence on wind speed, season,

direction and stability were alike at both Montreal and Whiteshell, although values at Whiteshell tended more to extremes. The trends shown in p in this paper are similar to those found at BrQokhaven by De Marrais (1959).

6;

CONCLUSION

Wind speed, direction, and temperature data, available from both the 200-ft and 35-ft levels of the tower in urbon Montreal, and from the 200-ft and 20-ft levels of the WNRE's tower in a flat, sparsely wooded area. of Whiteshell, were used ta calculate wind shear and values of the exponent p as given in·equation (1). The shear magnitudes and exponent p showed distinct trends at both Montreal and Whiteshell. The variations can be well related to 200-ft wind speed and direction, stability and season, the main dependence being on terrain and lapse rate. Both maximum scalar shear and frequency distribution of shear were distinguishing characteristics of each tower.

REFERENCES (1)

Blackadar, A. K., 1957:

Boundary layer wind maxima and their

significance for the growth of nocturnal inversions.

Meteor.

Bull.

Amer.

Soc., 5, pp. 283-290.

(2)

De Marrais, G. G., 1959: Wind-speed profiles at Brookhaven National Laboratory. J. Meteor, Vol. 16, No.2, pp. 181-190.

(3)

Munn, R. E., 1963: Somme winter temperature profiles in the boundary layer at Lac Du Bonnet, Manitoba. Meteorological Branch, Department of Transport, CIRcular-3856, TEC-472.

(4)

Wilson, H. J., McLernon, J. S. and Bradt, P., 1965: Micrometeorological installations in the Canadian National Air Sampling Network -Paper presented at 1965 Annual Meeting of A.P.C.A.

VERTICAL WIND SHEAR

20

~ e.-

15

w

u

0

z

W 0:: Il: ::::l U U

0

....0

10

>u z w

:::>

CJ

w

Il:

LJ..

5

o

LJ2~LJ4-L.J6LL.Je~.l...---:1'=-0---l.---:1~2---l.--;1~4--l~1~6:::::l1L....:I~e---l WIND SHEAR

(mph/165 ft.)

Figure 1 - Wind-shear frequency distribution - Montreal

21

'"'" IS~

-

EXTREMES

..

15

(471)

l\

~/

180 FT.

-

NO. of CASES

24

5

14

25

J

13

27

I

28

I

-

>- 12 u

z

UJ

II

o

10

::>

UJ II: lL. UJ l.!l rovided in the following table.

VERTICAL WIND SHEAR

33

Site

Temperatures

Wind

Ottawa

la-min averages centred on

Hourly averages centred on

the hour (tenths of a degree Fahrenheit)

the hour (directions to 16 points, speeds to 1 mph)

As for Ottawa

Sarnia

Whites hell

5.

IO-min averages centred on

la-min averages centred on

the hour. (Resolution as for Ottawa)

the hour. 'Resolution as for Ottawa) Direction 36 points

RESULTS The over-all discrete frequency distributions for the wind shear are

tabulated below.

The shear computed was the vector wind that must be added to the

lower-wind vector to obtain the upper. The cross-wind component of this shear is indicated as positive if the ~-wind direction represents a clockwise rotation of the lower_wind direction (i.eo, wind veering with increasing height). The down-wind component is the component of the shear in the direction of the ~-wind vector.

Positive indicates a wind increasing with increasing height.

(If only the upper wind

is calm, the down-wind shear is given as negative, and the cross~wind shear as zero.) The magnitude of the vector shear is of course always positive, and therefore cases when the down-wind speed increases with height are grouped with those cases when it

decreases with increasing height.

Although this latter happens less frequently, the

figures do show a not inconsiderable number of such cases.

6.

DISCUSSION OF RESULTS Table 1 presented below includes a distributian aver all sites taken to-

gether. This distribution should be treated with caution as it represents a mix from different sites in different climatic regions for widely differing sample sizes, and with differing data averaging times. It may, however, provide an over-all small sample indication of conditions typical for Canada.

Striking differences appear between the sites, and one may conjecture For the magnitude of the shear, it appears that at Whiteshell, wind shears of large magnitude are far more frequent than at Ottawa or about the cause of some of them.

Sarnia. However, in a record substantially shorter than that of Sarnia or Ottawa, Whiteshell shows a far greater number of cases of shear of any given magnitude greater

than about 13 mph.

This difference gives the immediate impression of being due to

the greater frequency and intensity of night-time inversions at Whites hell in a climatically much colder region of the country. However, the much smaller averaging interval is also responsible, and to an extent which must be determined by further study. In respect to cross-wind shear, the Whiteshell site shows very many fewer negative cases of any magnitude, The occurrence of a substantial population of negative shears, particularly at Ottawa and Sarnia, is a striking result. Unfortunately,

CANADA

34

it was not anticipated, and the detailed distributions were cut off at 7 mph.

How-

ever, it is evident that at bath sites the wind backs with height mare cammonly than it veers. The figures are approximately: Ottawa 3 ta 2, Sarnia 8 ta 7, Whiteshell 1 to 4. Presumably this reflects the strong influence of local terrain in relation to the direction af the prevailing wind, although it is conceivable that climatological factors may be operative, such as the frequency of warm or cold frontal inver-

sions.

7.

(See below.) INTERPRETATION OF DISTRIBUTIONS FOR AVIATION

For aviation, there is special interest in the frequency of occurrence of shears exceeding a figure corresponding roughly to 12 mph in one hundred feet. As-

suming a uniform shear, this might correspond roughly to

between 20 and 200 ft.

a~hear

of 20 mph or over

Out of the roughly 95,000 hours exomined, 78 fell in this

category, or about one in a thousand.

It is to be noted that the wind averaging period for all stations is much longer than the interval taken for an aircraft to descend along an approach path from 200 to 20 feet, which is less than 1 minute. For Whiteshell, the averaging time is ten times this; and for Sarnia and Ottawa, sixty times. To interpret the distributions obtained in terms of risks of shears of a given magnitude to be experienced in one minute will require a study of data obtained under conditions of high wind-shear and averaged dver not more than IS-second intervals. Large wind shear can be expected in either one of two circumstances: (i) When there is a large difference of direction between two levels; this is likely to occur only when an inversion is present; (ii) When the wind is very strong; in this case an inversion is unlikely, and the direction will usually be nearly the same

at both levels. In deciding whether 10-minute or 60-minute averages of wind provide the essential information required, some further considerations should be borne in mind.

(a)

It is known that laminar atmospheric flow breaks down intermittently into turbuflow, and the onset of this break-down need not necessarily occur simultaneously

at two levels separated by one to two hundred feet. (b)

Under inversion conditions, there may be little relationship between the changes with time of the wind at the two levels, and over short periods the magnitude of the shear may be greater than that found from averaged winds.

(c)

An aircraft senses a shear measured over a considerable horizontal as well as

vertical separation. The shear that should be studied for aircraft operations is that measured between two sensors separated by a horizontal distance of about one mile as well as with a vertical separation of one to two hundred feet. (d)

Inhomogeneities in the horizontal field of vertical wind shear just mentioned in

(c) above may not be propagated with the meon wind, and may never be even suggested by the wind records on a single tower.

VERTICAL WIND SHEAR

35

For these reasons, it is felt that the probability of an aircraft at a given airport in Canada experiencing a wind shear of a specified magnitude on descent or take-off may exceed that indicated by the results obtained from this study. What the extent of the excess may be is a matter which can only be settled by a special observing and analysis

progromme~

SUMMARY AND CONCLUSIONS

8.

Records of hourly values of wind shear between 20 and 200 ft at three instrumented towers in Canada, studied over three or"four years, show the following: (1) (2)

For about eight hours a year, such wind shears may reach or exceed 20 mph. The three sites may not be typical of conditions at Canadian airports, and con-

ditions at one airport may differ widely from thase at another. (3)

The risk that an aircraft may encounter shears of this magnitude on landing or

take-off is probably greater than indicated by (1). (4)

Additional analysis of the above and similar data from other towers is needed and planned to obtain distributions under various conditions of season, time of day, vertical temperature difference, wind direction and speed at upper and lower

levels. (5)

In arder to obtain a complete assessment of the problem of wind variability for an aircraft in the process of landing, it is necessary to study the space and

time variability as well.

This would imply additional observations to get the

possible change near the ground with space and more frequent observations to relate the question to the time-scale involved in an aircraft landing.

CANAOA:

36

TABLE

1

DISTRIBUTION OF WIND SHEAR BETWEEN 20 AND 200 FT ABOVE TERRAIN AT THREE CANADIAN TOWER SITES

Class

Ho.

~~;h 1

D> .......

~.

I

.J, ._. -_.-

-

,

-

__ .

. __.• ..J..•_

-1

I,

I I

,

D"

-~

=e"]

VERTICAL WIND SHEAR

Pal..

vu~

d~

FOCI>

(m.ottt';..

a.

45

45·)

G4n,

Ll:'

:t±--ft" -t-ttb

: : ;: : ;: ; :,~:

·,:·.",. ' ;.-l

.,.1

".,

::::::t:

:i..,.,,''.'+r='",-'-:,,-:--: c:I.~

"=:,,:

,.,.,.-

..0"

~-

.... ." .

.. ".

,•

"":

~

. ..,. :::J

..

'-"-' ,

::;::::'

"" .... :.:. i :

:: :::: :::i

,;

. , .. :.,

:::: ~::: ::i::i!i

.. ,.

H_.·I

:: ~ : ',-,'1'-'

........

~

~

. ~~.~ ~,~: dfi !±.: " j l : : ,,:

=_ _

:-::--s_~~:: .... :;:: :::: :-:.:: ::~:: "::: ~::

:1'7::: :

·~fr:.:,.. f""+:4"ti=... ·±i':-·P.':;",J:+:fi.-T.'-'-~;t:c!-;=:';"I;: '-:"c'~-":-t":+"4'~"',,!'

: ,":,"8:':;::ii

*.

;:l:

I 1'=+0£: "-'-'+:'-'-"~'+,-,'-'-"-'-~H::+"+::"'i:: :::""+3":-"8"-F,e.:',-".:.:f"-'.'LC·.'~"'i:'''-'-''-:--'''-j

_ ~~::;

,:.: •. :,.,.:..·.1..-.' .' . ',. ,. ,.~.

: ::~~{:: r

, ;':T

.. ~;~-. ~-l=i~:

.d.. ..... ::"

.

.-., ,

" ,.

:i;,I~,.II:.i.tl--ll=' ,'., - ~ '~:: :::,' :::: :.:::: ' :::: :U:t'l:±!tt:: r:; . . :':=c-- ::t::t++- :::: .:;i :;l~ :l~: :

".,'. , ' ; : •• c. .". :::;

.... :::: ~:::,

~;~ ~;~ 1:D+I:g~:~-la~ E~ ~~~ ~~ g~~ ~5~

'-+---"'::::::: ~::I!::

~:;',;

:-:'.1

_. :::! ';-'r

;' ~s~ill ::: ," "j;

-.......

.

.. ~ ~:

.... ....- -, --::;~

..

•

I

:: d

I

•

! .

~:: I ,J: ~~ I

I

,

:; : .

: : 1 : : ' 1++" :',', J

IT!! ~ ~: i !!T ,., I

I

.... ....

',-

.... I...

+~Y

,:~:~ ~~L

:/i~ iii!

, ..

: ~ J-1

!

I::: .... .... ,

.'

..

!-~

.". :1;: .::; ~::: j ....... "

;: ~l--'-' '·.:.J'+-'-'c.;"':'-I:;::;:;';;::: :..:.:.: Iii! I'" ". "t· .. ·,

I'"

:._1 ~ • _---l- .• _I---,._ j.

..

. '-1-

._.. , ..

••••.• j':";'

, ,

....

h

••

-

!!t:.

. .~

-1-+ ••

-----.-.

"

::!~

,

" ." 11 ....""II

:; m: iW ::. II.: :::!

.... :;.;.0

....-.

•~.+ _ • .L.-__

c", ::t;::1:

;:

hI~

:! ::::1::--:

._ ..

~"';"'::1::P.'~:t';;-:::::~::C::'i#·~'''h:t~''·ffi11~I:~I;';'~':i': 't:1:1 ~'.I$'=:'='gJ·j·"t::::::lttd:t: :1:: ,.,. :--;::.::r.:-: .::: ::j; iit~~' #-i ~;:~··f:r~:

:':"'''''':1-'1":,..:""

; . . . : ' " , :' ' - 1 '.:...'

---:-.;::1.;.:~;-~8F-

.:,;=!=:...:.- ~~~ ::;~ 8: jliiliJ. ~~~ I ;illlH~ t I"',,' ct±:." :::: i:; ;~~; gg tif: ~~ Hi: ;:i11~

:~tt J+:::~ .~

~

"I' ;- IJ TRTHjJ+ __r n:n :_1-_ '-.J- :::: iii; Iii; lilt iii :Ii iii! iiH HI ' ~

·t·· ....

- _:ff~

• ..••• 't••

.:~:LS-:l:- :::~ ~~ ~~~ l;::: ~ ~~~~~illI

-:::~ :;~ :m f:t ::; :;~ ±: •:,"" ,,; :1"1' :11: :t'~, r,,,,h 1+0 • ~

'::at: "h~ltI

VERTICAL WIND SHEAR

87

'," d.-

", ••• 11

... ::':: ... : --;,.:

.". :::: :[T:

'.::

::::1 ••• 1

,

......... .. : .. ::~

.

.::10:.

• • • 1••

'0

.::~:'

...

... :':::::

;Li."

-

t:n:~

"

.-- --,- ...

.... :::: ::1:

n

·,,·t---·

• oj'

, :::: " .. ,. ......... ,,,

"'

"I'

.. ::::

~~- ";~:' ~F~C

...

.. '. ,." .... , ~:::

o

-..

....

-ffff ~:~'-: ~~i-1" ::.'::: :.:.

•• 1,

:

••

! _, ~;:

j.

~:t;

I, _

r-

""'"

. :::!:::: .,,,,,,.

...

~:-,~_L::_:

._-~

;-::H. ltt

~::

:;:1-::-

~

:i::

>----!-:::

..

......

... :::: ;~;; ~ :c··'.'"...~.f".+'..C,_+'::iC:"_rt"11"~'o.'~. ·c.::+=+:==-c..:"-I'4=F+'.,"..+ 'FEE ,-.~...,

- -'-

,.- -

"

: ~ :.

:::: :;::

:.:: :::':h;;;';f:' ::.: . *:

..

.••.• h ·

.". '

,

......

::::1::.

~=

::::1::::

:c:: ::" "t: 7C:,

:.:.;.;,;:.:...-

...... -- ......... --

,I

,;,;;..-_

... ----

00 .....

.:>".. OJ

' ....

"-

88

FRANCE

...........

,..,

'Iv": '''... .... /0 c: 2 -.'"1"'+""1+'~"'+'c;..':-:.".j-.:-:.~-l"' _ :-:::::::::: ::: . . , i::' .' ..

;:: ; ':';':';-I-C."-.'-.'+--',0: ,,'

.

,.

I

:; .:;:

. 'c.:t::;: c:.:'~

+~, ~~: :: ::

~_::

t-~ _~ ~"

....

.C:

i

;~:

...........

"

"" "" C'" .': ::c

.... '. '. '

'1;": '+:~''''-'-i-'-'-'-'-i-'-'.-'-'.-+ "c'

-":':1:::.F'F-l ",' ''f'';:f'' ",''j;c''"' 1 ;::':4:"":.C'I":1--";..;-''c.;-::I-="=,,-+++'d'"....

....

.

+'

:.. 1_ .

'"....

•

,

::::::::::::1:"

~-~_-;_j_ :~:~ :-:: .j";

1-: :::: .::: :::: :::: :., '.',:,.. :=-:_ ','., - ,;,.,:.' Cl

........

90

FRANCE

,':: ::::I~" ;::: ':;,

:

::::: :'it ,.:,.,.

"'f-'"::-;'1~I';';1::'4

... -.

::::::::

....

:~::

~

.:"

.. :..::: ::::

.......... ,.

:: ~:

.,

••••• 1"

.....

-

........ ::::

......,.

....

::::::1:

,",.'1"':I~::: .!.-.

:;::-h~

.11. ", .• ;.,

.... :::: :;:::!::

::••::: .::: J. .::::... .::: ,,:.

",i_.,

titl

:,:::::: ,~,·n· 't'

1'" .l. ,'"

" •• i •• , •• ,,~ 1

...... ," .,..

-,_

>

.:.:j:'::, .. ,

q,t :~~:~ m~ :iD Snr nij ::::: : . . ~ ~H~ -npE-:£ 11ft- f·t . :::: :1;: ::::

:!~~

~~~ :~~ m~

+--

"

::::;; :~: Hi' '-':: ::; 'f S' '? ~ :c'c:: ":E':

~-'"":++ddl:;.c-::t~-"I;; ""::.::{'-"I"",,""F::+.:'!;: ;': ~F.s:-.:=;' Fg;;;;:;:.btcE::::E=:::~t~:::-_:="c=L~::!,+': i:::'~:t=~-"1~+-::j'::::j:"".: c~.~: .... " , I.ir:":." :~j.fl?.?i~:=";;t==:::'::•• ? • :;;1:

=;::.

. •.•. ··f-

=fr':

::= 11=: ••:::: ::G

~I:E'

....

:~r.

..,' ,.. _ ". -'" ::~ l:t ~~E: :::: £

.,~

.. ::.,;: .

~

:::: :E:-::-t:

4:..::.~-~;...

1----,0-

~

:~~'l_t ~-= -:::.:..-=E~~

•••••••• _

,

.,_ ••

.

.. '-" ..p-

... , ....

•••••• ±'

:!:: ::~ ~~~ :::.

..... ..

"_ ...... _

"" ",. " "" , "

..

........."

• .0-.-. ~

If··

, ':':It:o:t:: "::-h"" ~ -0 .-". 'i

FRANCE

92

...... i,

:::: ::-:~ ••••• >1.

::,"Ii'~,~

j-

....::!: ........

j-,--,"_:'_.+--F~' --"':;+.' ' '.:;.H:::: ·"'·",·c:."c:.·I'·~····::·f·"·:""7· i j'h·";'' ;·',,··+' ,,':-'rH':::"",' '::j::::j,,··,,"t:·-ii""·ji::,,::s::m r ::.I__ _. .,.,,1, ...............

.......

""'"'.'

~

,

'

~'

_,-,.,..1-

.:tt:·~·~ =-~::~::;--

~.

"

,.,.,.;

..

,:::::::,,:;> :F"''X

2··::::: z-""":: .. ,. fF.;.c:-I---B?,", ••

.11.

./:

:i::

:,'."" ......•.: ::.:/ ::;:I,L;-: ·"·'~1...L.,.

:

.;, • •

~..;..-

,~. ~;!: ;~::Ii:

::i:

: .• ;id0 tffi"=ttrk -~b~~B:-

.... .... ~~~~ i~~~ =/

"::; ~1~~ ~~-~~

,

.·.Fi--'~

.... " " " j -

::;,J

:,

l7'

:!:; :::;

.,.,

•

:;:: ::;: ::~:

:::-1 :i:: .......::::"

............... :::::;;: ;;!:,.

::::::::

.... " j

"":l::

'!".

"".

::::,

...... ;:,: :::: I-:+,'~'",'.... r-~~ - ,- t -. - .~ -;.-r'-+- -t--;--,...L" • ,.:.:-'It..:.. ••• ~

,'~

...

!'"

.

:!:: :~~:

"".;;;;10

:. -=-~=.:--::- .. ::"

.1,

.......:::!: ;!;; ..... -::;:: :::: .:::

FP!?V

::!:

d._,

:::::!:: :1:: .,. :.:.:.:..:;.;:.

-;- :!li

,

.."lo,'

!:~l ::::

,~

:;:: 0

:,1: ::::

.. ::

- ....'" "-

FRANCE

100

II

d

!I

. ,. . " . . .. ¥:

.

.. .1\ 'C:::lt'~ 7' :::' _... -

-

I'f cc :: ~ -_

::'/

..•...... -

.

--

:}

'I:

,-

::8

.J\

····:::t

L:.·:,:'

~

..... M

" ....'" H

...."

.... :::; .... :;b . . ···1 .... · ": :::"i:::-:"::!:::: :::: :., ::'+:-"- ~: :

j.i

,~.

~

.... :::. :i;: ::~2

.. "::1:'" .... ::(.

;!

:::::::: :::;

im

mr

~ ~~ ~;? l;~ Wi ~;~~ :!~~ i~ -;-m~- ~1f-,~~:~:. ~~~ ~~;~ !!~~~:~ t ::::~~E~:~~t~i-~~~~m~#h1T§E:+Fi';E~'---: '::;;:::' -,.. - ~ ~~-~-~ ~ ~~ ::;~ Tr~~ _~~ ~~I~~~: ?~ t-~ .~, ;~:-:. -:~_~" :~: :~: ;:g f:~~ :

im m

~

..l§:~" h:: ; ,; , :.j ::l:thi; Hlt! I." .. ll 1;11 ... , ~1., '·;·1',·, ,,,' I I', "'- .,..; '''j t'p 'j~ i-ll"W!" I'" I

=t~t:± ::~ ~;:

=i

,~,t~.'L

::::

:~ l~~,

,tt.:

zr.-±1:::~Il1.j;

.:.it-l-

::::';:'1',',::1",'"111",,1::'1'1"1'''111' _I ",iii: lIilll1. illilli II l! I t J.",!.

;j;;

~

~:'S::" ::::. "

::::::::':": " ,

+ ·.... ·1

VERTICAL WIND SHEAR

,: ,:,: I: : : :

,:I:::: :::: t::

101

,:, I : : : .

_. .•··IH 8#; HiP- fl:·~ M%:1:

f~'+-H=-'-'

I".': ,': .~ .. V~"'T:k:-:tJ'":' :·:.:I..':::.:.:.·.r.·.:·. r,::, :, '... '.1.:I ·u. J-I r: I. :'-..'C:LC '~._': / ·Ie.'-' ~ :.It>. _ H:'•. j. I :.•..'.: ' : : i:::: ..:-': . k :: . Y'..

, . . I .. 6- I" j. : . -

: :

I

:

:

. I

1·'··1..··

~'''~'_:~·IT)ZIC::I~· :1-.;: ~-J.-.~.

.

!

':: .. ,!:.c:

.

.. : . 1:::1:'" :::: -::: .:,. .,..

1 .'. ,:,

..

~lr::!T:C ,:

:.;c

c..:.:c.

I' : :

•• : .

:i!: . " .

,.. ::.·1:;: --+-::·•• 'lrr .•.....

"1'" .--,

.

' .

':.' .:'. +,-.-l;'" 0F

,.. , '.1.::"

",

.::::::: \: .

-,-i": : :fiSpcH "f'-. :,:.:.:.'+"7"7-1-"-:=:',7:ce.-t'::j:::",::::/'-:::"1:::",::+:H+

I.::' .;. -

l r L:

~:y: ...

: i:l_ :.-.·.-.:'-·.:.:.·""'. .--.·ecc.•.·:.::...:.~.•·.,I,:.:.·. :,.1.:'.:.' .·.·.·,1.,1;,·'·.·•·. . '.: ,'. '.~ ..•• _~~~ ••.

. E ;'•.: ' :": ,•• " " . . , . ... - .• • -.-'-_ . '--'1 , --. .. . .-. _.- -. - .

i.:

.... : :::::::1

u

........

::::

::::

=c'::~'

.::. :::: :::: :":: .:.· . •.

'."

s.•. · ...~·. . '.•.-.:. .

~

:-::-

; !~~ j::" I"

.. - . . : : .:' ii" ~.~;' ••::. I"T :,'" :··;i. :-. ":1"+:';-::;:'+'+"-'-1=+'-::: .. =+:.c:.e;-'-'-I:. • . : ." . · . . : .N:. • . T.'''''.\.•.•. : F : : :-1-:--: : -: ... -.- ..•. . . " . ,... . _. . .•_. _ _ .,." -'1,

I., ..

~, , ,.

;~:~l~~j~

I..

• I

,

........ . ............ ::,:::; ;i:;

.• ,

::' t

:::.:: '" ': ::+••

'" M

Q)

H :>

....'"

"-

102

FRANCE

M M

.":>.. .....'" u..

I NDI A

A REPORT OF THE STATISTICAL INVESTIGATIONS ON VERTICAL WIND SHEAR IN THE LOWER LAYERS AT THUMBA

A REPORT OF THE STATISTICAL INVESTIGATIONS ON VERTICAL WIND SHEAR IN THE LOWER LAYERS AT THUMBA

INTRODUCTION

1.

A 200-ft meteorologicol tower hos been erected ot Thumbo Rocket Lounching Focility, at a distance of 7 km from Trivandrum Aerodrome. This report presents the results of statistical investigotions bosed on wind data obtained from this tower, over a period of two years.

The third session of the Commission for Aeronautical Meteorology (1964) recommended the study of verticol wind sheor. Such study is importont for deoling with the problems of both manuol and automatically controlled opproaches by aircraft. In

particula~

values of shear are necessary for applying

compensation

matic control of "all weather" landing systems. It is hoped that this in India, at a systematic study of wind shear, will help the design

in

the

auto-

first ottempt, and operation

planning of supersonic aircraft.

2.

DATA COLLECTION

The meteorological tower at Thumba is located on the seashore. The terrain is sandy, and on the landward side a semi-circular area of radius 250 ft has been cleared of trees and other obstacles. The Met tower instrumentation was done in stages,

starting with instruments at three levels. Now, the Distant Indicoting Wind Equipment are installed at 33', 83', 100', 136', 156' and 200' levels. Additional self-recording facilities are available at 58', 136' and 200' (since March 1966). Surface wind is obtained from a standard equipment, installed ot a height of 8' above ground, in a Met enclosure, 400 ft away from the tower. Hourly observations are being taken from the indicating instruments from OOOOZ to 1500Z and the recorders run continuously.

3.

METHOD OF ANALYSIS Vertical wind shear may be defined

~:

where v is

the

horizontal

vector

wind and z the height. It is, however, convenient to study the easterly and northerly components of shear separately. Accordingly, the wind velocity values at each of these levels were resolved into the north and east components and the shears between successive levels worked out. Frequency tables were then constructed indicating shear

mognitudes exceeding 10 knots per 30 metres. This procedure CAeM III recommendotions.

is

in

conformity

The results are presented in the tables and diagroms at the end

of

with this

article.

4.

DISCUSSION

Very close to the surface, it follows from the logarithmic law of wind profile, that shear should be lorge. At higher levels it is to be expected that the

. INDIA

104

=k

log z, ddv =

~

• It will be seen from the present z study that shears are indeed large in the slab nearest to ground. shear value diminishes. For, if v

z

When the lopse rate is high, shear may be expected to be minimized by turbulence. The diurnal as well as seasonal variations studied in this paper generally bear this out. It may be pointed out that as Thumba is a coastal station, close to the equator] the important variation is from the cloudy monsoon months to monsoon months; the change from summer to winter is far less marked.

the

clear non-

The present anolysis is canfined to the following timings: OOOOZ, 0300Z, 0600Z, 0900Z, 1200Z ond 1500Z. From the results the following picture emerges. Let us first consider the layer from surface to 58'. Before 0830 1ST (0300Z) the winds in this layer are light. (less than 4 knots) throughout the year. They strengthen as the day advances and reach a maximum at about 1430 1ST (0900Z). At levels above 58', the pattern of wind is as follows. Before 0830 1ST, the winds are less than 5 knots, although during the monsoon season they attain about 7 knots. The winds generally increase up to 1430 1ST, after which there is a diminution in speed. The seasonal variation is as follows: During the winter months almost all the occasions of significant shear occur only in the lowest layer. As the season advances, the frequency of significant shears in the higher layers increases, reaching

a maximum in July at the altitude 136' - 100' and 156' - 136'. After July, there is

a

general change, once again, towards the winter conditions.

The results may be summarized as follows: 1. In the layer 8' - 33' the shear magnitude attains a maximum around 1430 1ST in all seasons. The shear vector 33' - 8' is seen to veer with change of season from winter to monsoon, backing again from monsoon to winter. Shear

values

exceeding

10 knots per 30 metres (significant from the point of view of SST operations according to CAeM III) occur at times and months given below: 1130 1ST - All months of the year

2.

1430

"

All months of the year

1730

"

Nearly all months of the year.

In the layer 58' - 33' significant shear occurs

mainly during

autumn, as given below:

1130 1ST - April, May and August to October 1430

"

May and August to November

1730

"

May to November.

summer and

VERTICAL WIND SHEAR 3. In the layer 136' - 58' the mean shear becomes significant manths given belaw:

105 at

times and

1130 1ST - March ta May

4.

1430

"

All manths of the year

1730

"

July to September

In the layer 200' - 136' significant wind shear occurs as follows: 0530 1ST - June and August

0830 " to - July to August 2030 " During the winter months, the sea-breeze effect is markedly noticeable by a short change in wind direction, at all levels, at about 1000 hrs IST (0430Z); also, as should be expected, the transition becomes less marked during the monsoon months when, due to cloudiness, the antitriptic component diminishes. In conclusion it may be stated that shear components have been worked out here for thin layers (average thickness 27 ft). If we content ourselves with computation over thicker layers (e.g., 100 ft), as the components are to be added algebraically, the shear magnitudes would be appreciably less than the figures given in the accompanying tables.

. .

.

INDIA

106

TABLE I Frequency table showing Nand E component shear values in different slobs in the layer 0 - 58 ft over Thumba - February 1964 Time ~f on pbserva . (GMT)

Shn

Height intervals

r kts 30m

8'-33'

33'-58'

N

E

N

E

0000

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24

13 3 2 1 4 0 0

.8 5 7 1 1 0 1

15 5 2 0 1 0 0

13 7 1 1 0 0 1

0300

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24

5 8 2 4 2 1 1

9 9 2 1 0 1 1

17 3 2 1 0 0 0

18 3 2 0 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

1 2 2 4 8 2 2 1

17 3 0 0 1 0 2

16 2. 0 2 0 1 1

0

0 3 1 1 3 2 9 1 1 1

0 0 0

0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

2 0 2 1 6 2 2 4 0 0

0 0 0 0 2 0 1 10 5 1

0600

0

0

-

0900

15 2 1 1 0 0 0 0 0 0

12 4 3 0 0 0

0 0 0 0

VERTICAL WIND SHtAR

107

TABLE I (continued)

Time of o bserva tion (GMT)

1200

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 0- 3 4- 6 7- 9 10-12 13-15

1500

Height intervals

Shear kts/3Om

16-18 19-24 25-30 31-36 37-42

8' -33'

33'-58'

N

E

N

E

3 3 3

1 3 1

19 2 1

16 5 0

4 2 3 3 1

1 2 1 9 5

0 0 0 1 0

2 0 0 0 0

1 0

0 0

0 0

0 0

13 5 2 1 0 2 1 0 0 0

6 1 2 6 1

19 3 0 0 1

14 6 3 0 0

3 2 2 1

0 0 0 0 0

0 0 0 0 0

0

INDIA

108

TABLE 2 Frequency table shawing Nand E camponent shear values in different slabs in the layer a - 58 ft over Thumba - March 1964

Time of observation ( GMT)

0- 3

0000

4- 6 7- 9 10-12 13-15 16-18

N

E

21

19

19

3 3 4

4 3 3 1

6 4 1

N

E

20 2 2 4

a a a

a

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

15 4 3 6

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 0- 3 4- 6 7- 9 lel-12 13-15 16-18 19-24 25-30 31-36 37-42

19-24

0300

Height intervals 33'-58' 8' -33'

Shear kts/30m

-

0

a

a

1

11 12 1 2

26 4 1

a

a 1

0

I

a

0 0

a

0

0 0

5 3 3 3 3 5 3 0 2

3 2 3 4

22 2 1 0 0

5 7 2 1

a

2 0 0

2 0 0

a a 0

8 1 1 2 4 3 5 2 4 0

1

27 2 1 0 0 0 0 0 0 0

24 4 2 0 0 0 0

1 2

a

I

0600

0900

a

a 2 2 1 2 5 3 9 5

I

24 6 0 1 0 1

2 3 0

a a

j

20 3 n

G

a 0

a

I I!

VERTICAL WIND SHEAR

109

TABLE 2 (continued)

Time of o bserva ti on (GMT)

1200

1500

Height intervals

Shear kts/30m

8' -33'

33'-58'

N

E

N

E

0- 3 4- 6 7- 9 10-12

6 2 2 4

2 4 3

15 5 3 6

20 4 4 1

13-15 16-18 19-24

5 3 3

6

6

0 0 1

0 0 1

25-30 31-36

3 2

3 3

0 0

0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

11 7 3 4

9 3 3 5 0 2 7 1 0

23

a 2 2 0 1

1

2

a

a a

25 4 1 0 0

0 0 0 0

0

5 2

a a a

J

;

110

INDIA TABLE 3 Frequency table showing Nand E component shear values in different slabs in the layer 0 - 58 ft over Thumba ~ April 1964

Time of o bserva tion (GMT)

0300

0600

0900

8'-33'

33'-58'

N

E

N

E

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24

18 8 4 0 0 0 0

18 9 2 0 0 0 1

23 5 2 0

23 3 3 1

0 0 0

0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24

13 9 4 1 1 1 1

12 11 4 2 1 0 0

23 5 1 0 0 0 0

17 4 4 2 2 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 43-48

e 3 5 3 1 2 3 0 1 0 0

2 0 2 3 1 3 4 4 3 3 1

6 3 2 4 4 3 4 0 0 0 0

7 12 3 2 1 0 0 1 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

8 5 0 4 2 2 5 1 1 0

1 1 1 1 3 1 8 6 4 2

6 4 6 2 7 1 2 0 0 0

-

0000

Height intervals

Shear kts/3Om

9

11 5 2 1 0

0 0 0 0

VERTICAL WIND SHEAR

111

TABLE 3 (continued)

Time of observation (GMT)

Height intervals

Shear kts/30m N

E

N

E

7 7 5 1 3 1 2 2 0 0

4 0 4

10 2 7

10 11 3

2 1

2 4

1 2

3 5 5 3 1

2 0 0 1 0

0 1 0 0 0

11 7 4 4 0 0 1

10 4 3 5 1 0 3

16 5 3 3 1 0 1

0 0 0

0 0 1

0 0 0

18 5 5 1 0 0 0 0 0 0

0- 3 4- 6 7- 9 10-12 1200

13-15 16-18 19-24 25-30 31-36 37-42

1500

~-

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

33'-58'

8'-33'

"--

---_.-

INDIA

112

TABLE 4

Frequency table showing Nand E component shear values in different slabs in the layer 0 - 58 ft over Thumba - May 1964 Time of o beerva tion (GMT)

Height intervale

Shear kta/3Orn

8'-33'

0000

0300

0600

E

21 4 2 0 0 0 0 1I

10 8 6 3 1 1 1 0

14 11 4 1

8 5 3 9 2 1 0 0 0 0 1

13 7 4 2 1 1 1 0 0 0 0

12

0 2 3 1 1 0 4 5 7 1 4

1 3 5 7 4 4 5 0 0 0 0

E

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

10 9 5 2

0- 3 4- 6 7- 9 10-12 13-15 16'-18 19-24

5 11 5 2 1 3 2

25-30 31-36 37-42 43-48

0 0 0 0

,0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

4 8

2 1 1 0

, 2 5 0 1 1 0 0 0

31~6

37-42 43-48

-

33'-58' N

N

----

I-

-

--

0 0 0 0

11 1 4 1 0 0 0 0 0 0 12 8 5 2 1 i.1 0 0 0 0 0

VERTICAL WIND SHEAR

113

TABLE 4 (continued)

-

Time of observation (GMT)

0900

1200

1500

------

Height intervals

Shear kts/3Om

-

8'-33'

-

33' _58'

N

E

N

E

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

8 8 6 2 2 3 1 0 0 0

0 0 1 1 1 3 3 4 8 9

0 2 4 5 7 7 4 1 0

14 4 6 5 1 0 0 0 0

0

0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 43-48

5 9 3 7 2 2 2 0 0 0 0

3 0 1 2 0 1 9 4 5 4 1

2 6 7 7 4 2 2 0 0 0 0

8 17 3 1 0 0 1 0 0 0 0

0- 3 4- 6 7- 9 10-12

12 6 6 2

8 5 5 4

9 8 5 2

20 7 0 1

13-15 16-18 19-24' 25-30 31-36 37-42

1 1 0 0

2 1 1 1 1 1

1 2 2 0 0

1 0 0 1

0

1

-

0

0 0

------

INDIA

114

TABLE 5 Frequency table shawing Nand E component shear values in different slabs in the layer a - 58 ft over Thumba - June 1964 Time of obee'rvation (GMT)

Haight intervale

Shear kte/3Om

33'-58

8'-33 E

N

E

17 8 1 2 1 0 0 0' 0 0 0 1

23 4

13 6 3 2 2 3 0 0 1 0 0 0

23 3

19-12 1 -15 16-18 19-24 25-30 31-36 37-42

12 5 2 5 2 1 2 1 0 0

12 8 3 4 0 1 1 0 0 1

14 6' 4 5 0 1 0 0 0 0

18 8 2 1 0 0 1 O· 0 0

0-3 4-6 7-9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

10 8 6 3 1 0 1 0 1 0

2 4 4

6 4 8 5 2 3 2 0 0 0

14 3 10

N

0-3 4-6 7-9 10-12

i~:ig

0000 ~

19-24 25-30 31-36 37-42 43-48 49-54 0-3 4-6 7-~

0300

0600

a 0 0 0 0 1 0 1 1 0

S 1 4 5 1 3 3

a

1 1 1.

a 1 a

0 0 0

0 1 0 0 0 0

,

VERTICAL WIND SHEAR

115

TABLE 5 (continued)

Height intervals

Time of

pbserva tion (GMT)

0900

1200

1500

Shear ktsj30m

R'_33'

33' _58'

N

1';

j\j

1';

0-3 4 - 8 7 - 9 10 -12 13 -15 16 -18 19 -24 25 -30 31 -36

4 10 6 3 2 3 2 0 0

2 2 4 4 2 8 5 2 1

4 2 11 2 1 1 0 1

8 11 6 2 1 0 1 0 0

0-3 4 - 6 7 - 9 10 -12 13 -15 16 -18 19 -24 25 -30

12 6 4 4 3 0 1 0

6 6 2 2 2 3 4 5

2 6 7 7 4 2 2 0

8 17 3 1 0 0 1 0

0-3 4 - 6 7 - 9 10 -12 13 -15 16 -18 19 -24 25 _30

16 10 2 1 0 1 0

12 6 4 5 1 0 2 1

9 8 5 2 1 2 2

20 7 0 1 1 0 0 1

0

8

0

-

INDIA '

116

TABLE 6 Frequency table showing Nand E component shear values in different slabs in the layer 0 - 58 ft over Thumba - July 1964

Time of pbserva t on (GMT

1

Height intervals Shear Kts/30m

33' "- 58'

8' - 33' N

E

N

.6

0000

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

16 6 1 6 0 0 1 0

18 6 4 0 0 1 0 1

15 7 4 4 0' 0 0 0

19 7 4 0 0 0 0 0

0300

0- 3 4-6 7- 9 10-12 13-15 16-18 1.9-24 25-30 31-36

13 10 3 2 0 1 2 0 0

15 5 2 3 1 3 0 2

14 6 4 6 0 1 0 0 0

21 8 0 1 0 0 1 0 0

0- 3

10 7 2 6 1 2 1 0 0 1

3 3 3 3 3 4 5 6 0 0

8 5 l5 8 3 1 2 0 0 1

18 7 3 0 0 0 2 1 0 0

4-

0600

(I

7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

O'

117

· VERTICAL WIND 'SHEAR TABLE 6 (continued)

Time of

pbserva.tion (GMT)

0900

1200

1500

Height intervals Shear Kts/3Om

8' - 33'

33' - 58\, E,

N

E

N

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 43-48

8 7 9 2 1 1 0 0 0 0 0

2 6 0 1 1 1 4 10 3 0 0

0 2 6 9 5 1 2 1 1 0 1

0- 3 4- 6 7-9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 43-48 49-54

11 10 4 2 0 0 3 0 0 0 0 0

5 4 2 5 1 5 4 2 1 1 0 0

8 3 6 4 2 3 0 2 1 1 0 0

18 5 2 0 1 0 2 0 1 0 0 1

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

10 10 5 0 2 1 1 0

10 12 5 1 0 0 0 1

12 5 6 5 1 0 0 0

16 8 2 1 2 0 0 0

91

7!

6, 5 0 O. 1; 0' 0 0 0

INDIA '

118

TABLE 7 Frequency table shawing Nand E camp anent shear values in different slabs in the layer 0 - 58 ft over Thumba - August 1964

Time of o beerva tion (GMT)

0000

0300

Hei.gbt intervals Shear Kte!3Elm

E

N

E

11"

15 4 5 3 0 0 3 1

17 4 4 1 1 2 2 0

25 3 2 1 0 0 0

10 8 4 2 2 2 2 0

15 5 5 2 2 1 1 0 0 0 0

5 12 2 1 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 43-48

12 5 5 :3 1 1 0 0 0 1 0

5 7 5 4 1 1 3 1 0 0 1.

0- 3 4- 6

10 12 4 1 2 2 0 0 1

2 5 1 6 3 3 6 4 1

10-12 13-15 16-18 19-24 25-30 31-36

33'-58'

N

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

7- 9 0600

8' -33'

o·

0 0

2

7 6 9 4 1 2 0 0

0

18 8 1 2 2 0 0 0 0

VERTICAL WIND 'SHEAR

119

TABLE 7 (continued)

Time of obeervation (GMT)

Height intervale

Shear Kte/30m

33"- 58'

8' - 33'

E

N

-

0900

1200

1500

If

E

,--

0- 3 4- 6 7- 9 10-12 ' 13-15 16-18 19-24 25-30 31-36

9 8 6 2 3 0 2 1 0

3 2 1 3 0 0 11 9 2

6 4 1 6 7 3 3 1 0

16 9 3 0 2 1 0 0 0

0- 3 4- 6 7-9 10-12 13-15 16-18 19-24 25-30 31-36

11 5 7 3 3 1 1 0 0

7 4 3 3 2 5 4 2 1

0 12 5 8 3 1 2 0 0

10 12 7 1 1 0 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

12 8 3 3 3 0 1 0

12 5 4 5 0 0 3 1

11 6 6 3 2 0 2 0

13 9 5 2 1 0 0 0

-

INDIA '

;20

TABLE 8 Frequency table showing Nand E component shear values in di fferent slabs in the layer 0 - 200 ft over Thumba - September 1964

Time· of observation ( GMT)

8'-33'

136' -200'

N

E

N

E

N

.ill

11 6 5 6 0 0 0 0 0

12 . 4 3 5 2 1 0 0 0 1

21 4 2 0 0 0 0 1 0 0

22 3 2 0 0 0 0 0 0 0

16 6 4 1 0 0 0 0 0 0

23 5 0 0 0 0 0 0

0

13 6 3 3 0 0 0 2 1 0

0

14 5 1 0 5 3 0 0 0 0

7- 9 10-12 13-15 16-18 19-24 25-30 31-36

6 5 5 4 2 3 0 1 1

9 4 4 3 0 1 4 2 0

7 5 8 4 1 2 0 0 0

13 7 4 0 0 0 0 0

14 8 4 0 0 0 0 0 0

13 6 6 1 0 0 0 0 0

16 8 1 1 0 0 0 0 0

5 8 4 1 5 1 2 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

10 3 5 2 3 3 1 0 0 1

3 4 3 1 1 1 10 3 0 2

1 3 5 5 6 0 6 1 1 0

8 8 3 5 2 0 1 0 1 0

10 8 2 6 1 0 0 0 0 0

16 6 3 2 0 0 0 0 0 0

14 11 0 1 1 0 0 0 0 0

10 2 0 6 3 3 2 0 1 0

4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 0- 3

0600

58' -136'

E

4- 6 0300

33'-58'

N

0- 3

0000

Height intervals

n~730m

3

d

/

VERTICAL WIND SHEAR

121

TABLE 8 (continued)

Time of o be erva tion (GMT)

Height intervals· 8' -33'

33'-.58'

58' -136'

136'-200'

If

E

N

E

N

E

N

E

.0900

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

11 4 5 2 1 1 3 0 1

1 0 2 3 1 2 10 4 5

2 2 5 5 6 2 3 2 1

6 7 5 4 3 2 1 0 0

6 10 8 1 2 1 0 0 0

19 8 0 1 0 0 0 0 0

9 14 1 2 1 1 0 0 0

13 7 5 1 2 0 0 0 0

12 5 3 6 1 0 1 1 0

4 4 3 2 2 4 5 4 1

4 6 5 5 4 3 1 1 0

11 8 4 2 3 1 0 0 0

11 7 6 3 1 0 0 0 0

14 8 3 2

1200

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

1 0 0 0

13 13 2 0 0 0 0 0 0

7 8 7 4 1 1 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

7 10 4 2 1 4 0 1 0 0

11

10 7 2 5 4 1 0 0 0 0

14 11 2 2 0 0 0 0 0 0

15 8 6 0 0 0 0 0 0 0

15 10 3 0 0 1 0 0 0 0

17 8 2 0 0 0 0 0 0 0

5 8 4 8 2 0 0 0 0 0

1500

.

Shear Kts/3Om

4 4 4 1 2 1 1 0 1

0

~

TABLE 9

Frequency table showing Nand E component shear values in different slabs in the lay'er 0 - 200 ft over Thumba ~ October 1964 Time 'of o bserva tion (GMT)

-

--

. Height interva.ls

Shear' kts/30m

N

-

0000

0300

0600

'--

-

33'_58'

8' -33' E

E

11

E

N

E

25 4 0 1 0 0 1 0

22 8 1 0 0 0 0 0

16. 6 3 0 0 0 0 0

14 10 1 0 0 0 0 0

21

10 2 3 3 6 2

20 6 2 2 1 0 0 0

17 4 5 0 0 0 0 0

17 4 4 1 0 0 0 0

18 7 1 0 0 0 0 0

12 5 3 1 3 2 0 0

12 10 2 4 3 0 0 0

7 9 9 1 0 0 0 0

19 6 1 0 0 0 0 0

15 6 2 1 0 0 0 0

10 8 4 2 0 0 0 0

15 7 4 3 1 1 0 0

18 7 3 1 0 1

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

12 6 5 5 1 1 1 1

14 8 5 3 1 1 0 0

15 6 9 1 0 0 0 0

0- 3 4- 6 710-1 ~ 13-15 16-18 19-24 25-30

:l,1

1 1 5 0 2 7 So 6

3 1 12 6 7 0 1 1

7 4 3 2 0 3 1

136' -200'

N

0- 3 4-6 7- 9 10-12 13-15 16-18 19-24 25-30

0 1

58'-136'

-

- - - - --- -- - - _ . _ - - - - - - - - - - - -

3

2 0 0 0 0 0

--

0 0

.... z

.... »

TABLE 9 (continued) ,----- Time of observa tion (GliI T)

---- --

Height intervals

Shear' kts/30m

, 8'-33' N

33' _58'

58' -136'

136'-200' '

E

N

E

N

E

N

E

0 5 0 3 2 1 5 5 6 4

3 3 2 5 9 6 2 1 0 0

16 10 2 3 0 0 0 0 0 0

1 9 14 1 0 0 1 0 0 0

20 6 0 0 0 0 0 0 0 0

18 4 4 0 0 0 0 0 0 0

14 7 2 2 0 1 0 0 0 0 9 10 4 1 2 0 0 0

'"

0900

1200

1500

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42

8 3 7 1

0- 3 4- 6 7- 9 10-"12 13-15 16-18 19-24 25-30 , '0'

16 9 4 1 1 0 0 0

10 3 5

6 5 5

21 6 2

6 9 10

20 5 1

1 2 3 5 2

5 6 2 1 1

2 0 0 0 0

1 0 0 0 0

0 0 0 0 0

15 11 0 0 0 0 0 0

14 10 2 4 0 0 1

14 7 4 3 1 1

14 7 2 2 2 1

23

:1

3

1.5 7 5 1 0 0 0

25 2 1 0 0 0 0

19 5 3 0 0 0 0

0- 3 4- 6 7- 9, 10-12 13-15 16-18 19-24

6

2 3 0 1 0

.

...

-'

-

4 4 0 0 0 0

,

7 9' 5 4 2 0 0

--

< TTl

'"-i .... j; ..... z ~

o

(J)

::J: TTl

~

.... l::l

f-e

TABl.E

""....

10

Frequency table showing Nand E component shear values in different slobs in the layer 0 - 200 ft over Thumbo - November 1964

_._---.----.-....-.-----,.--..--.

t-'-

Time of a bserva ti on (GMT)

She:lr kts/30rn

. Height 8'_33'

--.

-~---

interv~ls

33'_58'

58'-136'

E

N

E

N

E

13

16 11 1 0 1 0 0 0

15 8 4 2 0 0 0 0

25 2 0 0 1 0 0 0

20 6 2 0 0 0 0 0

136' -200'

N

E

N

0- 3 4- 6 7_ 9 10-12 13-15 16-18 19-24 25-30

16 7 5 1 0 0 1 0

18 8 3 0 0 0 0 1

16 5 5 3 0 1 0

5 1 0 0 0 0

0300

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

13 10 3 :l. 0 2 1 0 0

12 10 1 2 1 2 0 0 2

18 9. 2 0 0 0 0 0 0

22. 2 2 0 1 3 0 0 0

26 2 0 1 0 0 0 0 0

22 6 0 0 0 1 0 0 0

28 0 0 0 0 0 0 0 0

27 1 0 0 0 0 0 0 0

13

Z4 6 9 5 0 2 0 0

19 5 2 0 2 0 1 0 0

17 8 0 0 0 0

1.8 :i 1 3 0 0

16 9

0600

0- 3 4- 6 7- 9 10-12 13..:.15 16-18 19-24 25-30 31-36

0 1 0

18 . 4 4 0 0 .0

0 0 0

0 0 0

0 0 0

0 0 0

-

0000

2 6 2 1 4 1 0 0

2.

1 1 8 3 2 8 3 1

a

11

1

------

.... z

S l>

(continued)

TABLE 10

Time of observa tion (GMT)

0900

Height intervals

Sh~r kts 30m

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 ·25-30 31-36 37-42

8'-33'

33'.-58'

58' -136'

---

136' -200'

N

E

N

E

N

E

N

E

8 6 6 2 1 3 2 1 1 0

2 1

2 0 5 11 7 2 1 0 1 1

14 10 2 2 1 0 1 0 0 0

23 4 2 0 0 0 0 0 0 0

13 9 5 2 0 0 0 0 0 0

24 3 2 0 0 0 0 0 0 0

22 6 1 0 0 0 0 0 0 0

ci

1 3 2 1:5 7 1 0

~

'"-l H

~

r

~ H

Z

1200

1500

0- 3 4- 6 7- 9 10-12 13-15 16.-18 19-24

7 3 4 4 7· 3 2

13 8 5 2 1 1 1

7 3 4 4 7 3 2

13 8 5 2 1 1 1

23 4 0 1 0 0 ·0

20 6 1 0 1 0 0

26 0 2 0 0 0 0

23 4 1 0 0 0 0

0- 3 4- 6 7-.9 10-12 13-15 16-18

18 9 2 0 1 0

19 5 2 1 2 1

14 5 7 3 0 1

19 4 3 4 0 0

19 9 1 0 0 0

25 2 2 0 0 0

21 5 0 0 0 0

23 3 0 0 0 0

"

'"

:I:

~

..... ~

.... TABLE

~

11

Frequency table showing Nand E component shear values in different slabs in the layer 0 - 200 ft over Thumba - December 1964 Time· of observa tion (GliIT)

Shear kts/30m

0- 3

0000

0300

4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36 37-42 0- 3 4- 6 7- 9 10-12 13-15 16-18

~E:~~

31-36 37-42

0600

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 ·31-36

Height intervals 8'-33'

33'-58'

58' -136'

136' -200'

N

E

Il

E

N

E

N

E

14 11 4

16 6 7 0 0

19 6 4 1 1 0 0 0 0 0

13 7 4 2 2 1 2 0 0 0

21 6 2 0 t 0

15 9 2 3

20 4 1

20 2 2 0 1

24 3 1 1 0 0

19 6 2 2 0 0

0

1 0 0

0

0

1

0 0 0 0 0

0 0

0 0 0 1

14 6 2 1 1 1 1 0 2 0

12 6 6 2 0 0 1 0 0 1

22 3 2 2 0 0

0

0

0 0

20 6 3 0 0 0 0 0 0 0

5 10 1 4 6 1 3 0 0

9 5 8 3 4 0 0 0 1

8 11 4 2 0 2 1 2 0

13 9 2 3 0 1 1 0 0

17 3 4 2 3 0 0 0 0

0

1 0 2 5 6· 4 8 4 0

80 80

0 0 0

8

0

0 0

0 0

0 0 0

0 0

0 0

29 0 0 0 0 0 0 0 00 0

28 1 0 0 0 0 0 0 0 0

7· 8 1. 1 0 0 0 0 0

19 5 3 0 0 0 0 0 0

.... z o .... »

TABLE 11

(continued)

-, Timeo! o bserva tion (GMT)

0900

1200

'Shear kts/30m

8'-33'

33' -58'

58' '-136'

136' -200'

N

E

N

E

N

E

N

E

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

2 1 1 0 1 2 11 8 3

1 5 4 0 3 3 9 4 0

1 4 6 6 6 1 1 3 0

4 7 5 7 3 1 2 0 0

18 9 2 0 0 0 0 0 0

15

24 3 2 0 0 0 0 0 0

23 5 0 1 0 0 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30 31-36

6

8

11

7 5 3 2 0 1 1 0

26 4 0 0 0 0 0 0 '0

23 7

0 0 0 0

24 2 2 0 0 0 0 0 0

23 3 2 0 0 0 0 0 0

19 5 3 2 1 0

27 2 0 0 0 1

26 4 0 0 0 0

21 8 0 0 0 0

27 1 1

~- 3 - 6

1500

Height intervals

-,----------

7- 9 10-12 13-15 16~18

7 4 1 1 0 0

2 4 3 1 0 0

12 6 3 4 3 0 1 0 1

14 8 5 2 0 1

14 10 2 1 2 1

16 8 3 2 1 0

g

~

11 1 2 0 0 0 0 0

80

--


l

12

Frequency table shawing Nand E campanent shear values in different slabs in the layer 0 - 200 ft aver Thumba - January 1965

-Time of o bserva tion (GMT)

Sh~5 kts 3 m

Height intervals 8'_33' N

E

33'-58'

58'-136'

N

E

N

E

N

E

20 7 2 1 0 0 0

11 13 3 2 0 0 1

21 6

0 0 0 0

16 8 1 2 0 0 0

18 4 2 0 0 0 0

19 4 1 0 0 0 0

136'-200'

21

0000

0- 3. 4- 6 7- 9 10-12 13-15 16-18 19-24

3 1 0 0 0

17 6. 6 1 0 0 0

0300

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24

14 5 5 1 2 2 1

10 7 8 3 0 2 0

20 8 1 0 1 0 0

15 10 4 0 1 0 0

24 2 2 0 0 0 0

18 7 3 0 1 0 0

25 5 0 0 0 0 0

26 4 0 0 0 0 0

0600

0- 3 4- 6 7- 9 10..12 13-15 16-18 19-24 25-30 31-36 37-42

4 2 2 8 4 2 5 0 0 0

1 2 5 4 5 4 5 0 0 1

12 8 2 3 1 0 0 0 0 0

19 5 1 1 0 0 0 1 0 0

15 6 2 1 0 1 0 0 0 0

13 8 1 0 1 2 0 0 0 0

18 5 1 0 0 0 0 0 0 0

14 8 2 0 0 0 0 0 0 .0

5

a

'"'

TABLE 12

Time

of observa tion (GMT)

0900

1200

1500

Height intervals

Shear kts/30m

0- 3 4- 6 7- 9 10-12 13-'15 16-1~

19-2 25-30 31-36 37-4& 4349-54

(continued)

8'-33'

33'-58'

58'-136'

N

E

N

E

N

0 0 4 1 3 3 9 6 0

1 1 1 0 0 2 7 9 4 1

6 11 5 0 2 0 0 1 0 0

19 4 1 2 0 0 0 0 0 0 0 0

0 0 0

8

£

-

136' -200'

E

N

E

13 10 3 0 0 0 0 0 0 0 0 0

5 17 4 0 0 0 0 0 0 0 0 0

24 5 0 0 0 0 0 0 0 0 0 0

26 3 0 0 0 0 0 0 0 0 0 0

0- 3 4- 6 7- 9 10-12 13-15 16-18 19-24 25-30

5 3 3 3 3 5 5 0

1 1 3 3 6 5 4 4

12 11 2' 1 0 0 1 0

15 9 3 0 0 0 0 0

18 9 0 0 0 0 0 0

18 8 1 0 0 0 0 0

28 0 0 0 0 0 0 0

26 1 1 0 0 1 1 0

0- 3

13 5 3

5 5 4

18 6 2

17 6 5 0

22 7 0

19 9 1

29 2 0

27 4 0

~

4 4 1

0 0 0

0 0

0 0 0

0 0 0

0 0 0

~: ~

19:15 16-18

19-24 25-30

~ 0

~

g

81 0

80

8

8




+'

....0

....u ....00

Ol

...0

" "E " +' +'

.J::

------ ...

Ol

"

....... C

"

\' '\

">0 +'...

'I

(.

U

\\ \\

0

....0"

~ 1\,

11 - ........... II

" I

0

E

" "... +' ."

.J::

.... ,

II \ 11_------,

0

a. .......

... -

« UJ

4-

0

Vl

C 0

....>

a. ...

Of-

I

E

z

« « 0:: «

CD

'"

.J:: .J::

~

:IE

U+' +'

"

c -" en 0

." OJ ..J

oC

0

'"

."

'""...

......."

Ol

r 3

2

·1 -1 lCm: 10 Sec

A

4

A

A

A

6

..}.

B

AA

5

/'6

6

6iii

'"..... -I

,...£?

Figure 30 - Distribution of mean vertical wind shear for Feb. 1964

::e:: ..... z



r

-1 -1 1 Cm: 10 Sec

'A

3

2

.,

(A B

I

.,

A

5

6

~

A

j-A B

AI.

B

B

B

B

Figure 3d - Distribution of mean vertical wind shear for May 1964

r 2

B~A

B/",.A

1 em

,~c

6

5

4

3

., .,

= 10

~A~A

r

~A

A

B

;;i

""-i

B

1-1

Figure 3e - Distribution of mean vertical wind shear for

Jun~

~

1964

:E:

1-1

B VI

:c ~

r r

B

A

~A

B

I B

5

4

3

2

.1

, em = 10

~A

/

.A

B

fA

""

.,

S~c

6

r:

B

r-'

Figure 3f - Distribution of meon vertical wind shear for July 1964

t7.

-.0

.....

eO

r t

jA

A

B

4

3

2

r'"

B

1 em

I

5

•

A

.1

= 10

.1

Sec

6

~B

\A' B

...,

Figure 3g - Distribution of mean vertical wind shear for Aug. 1964

z .....

'" l>

r 2

3

A fo:o c B

0

B~A

lCm

4

crA fic B

0

5

rA

crA

Figure 3h - Distribution of mean vertical wind shear for Sept. 1964

B

= 10-1 Sec·1 6

~A

Bc

r 3

2

c

;>--0

k

4

o

o

1 Cm

5

o

.1 Sec 6

,~

.. A

1.-

CfA

B

_1

=10

r

O

B

c B




0

A

OK B C

c

B B

Figure 3j - Distribution of mean vertical wind shear for Nov. 1964

B

.....

'".....

I-'

r 3

2

R; 1 em

.1

= 10

.1

S~c

A

5

4

6

A

/A

/ B

e~O A

A

~

A

e\

O·

O\B

B

A

C'¥.:;.S

S

....z

Figure 3k - Distribution of mean vertical wind shear for Dec. 1964

o ....

r 2

e."..O /l.B

.

3

A

e oA-B A

o~B

o e B

» .1

1

em = 10

.1

"~c

5

A

,~'

Figure 31 - Distributian of mean vertical wind shear for Jan. 1965

S

6

o

J-

e

S= 0

A

...

r A.JC

0

C

5

,.

Dr

8 8 A"r'- 0

,.

4

3

2

., .1 ICm: 10 Sec

c

0

o \8

,

,.

~

°'f"C

... ,.

8 B

B

;;i

'" -I

H

~

Figure 3m - Distribution of mean vertical wind sheor for Feb. 1965

::E: H

Z

o

r C,

~~.

0

Sf'"

»

.1

5

'"

6

c. c.

C.

2

Cs ,. C,

•1

1 em= 10 S.ec

4

3

c..

-

0>

/

~

r

.1

5

4

3

2

.1

1 cm: 10 !>ec

6

0,

0,

0,

C.

C.

C.

C.

D.

C.

A

B

B

'.

B

c,

C.

C,

'A "·CI

0,

A

C,

C. 0,

0,

C.

C.

A

A

Figure 3s - Distribution of mean vertical wind shear for Aug. 1965

H

Z

o

~

r r;L'

Brt\\'C'

C. K

c,

B

C A

•

D•

6

~

D.

A

.1

5

4

3

2

CIt D.

.1

1 em: 10 !>ec

~

Figure ~t _ Distribution of mean vertical wind shear for Sept. 1965

A

B

A-!f;;:C.

•

B

A

'

r 4

3

2

1

em=

.1

.1

10 !>ec

5

6

C,

e.,LA

B~~

0

1

e~

A

~

D.

e.

o

o. e.~

P' C,

e. '"?Jo~

8

8

ot..

C,

e, \fa~. Da~A

.8 A

0,

A

8

..

,

B~.' c.,1lI: G.r.




::t:

~

r 5

4

3

2

.1 .1 1 Cm =10 !>ec

O. e~A I

0, •

C,~

"'-Ca ~Ol

c, • Do~CJ,P .. B e.

el'~8A 01

6

c.~ c, A

(I~/t Dol-rei

D,

I

I

D.

8

C.

D.

8

C... 0

Figure 3v - Distribution of mean vertical wind shear for Nov. 1965

f-'

0',

"

....

~

r . •

- 6 m/sec (253-107 m); B: 3-5 m/sec; Cj :::: 2 m/sec.

180

VERTICAL WIND SHEAR

continued for the period more than 12 hours, indicated by smoll circles. The isopleth of visibility was drawn in Figure 6. It is mentioned that the poor visibility is accompanied by weak wind speeds at the surface and weak wind shear, and good visibility appears when wind speeds and shear are strong. It must be noted that samples for days of weak wind shear with good visibility were not chosen in this figure; thus, .Figure 6 is applicable to derive only maximum value of the wind shear from the mean surface wind velocity and the mean visibility. (2) Correlation between wind shears and surface winds Figure 7 indicates the correlation between surface winds and wind shears in division of regions A, Band C. In region A, wind shears are stronger than 6 m sec- l /(253-107 m), in B, 3-5 m sec- l /(253-107 m) and in C, weoker than 2 m sec- l /(253107 m). Wind shear values more than 9 m sec- l /(253-107 m) ore indicated by cross marks in Figure 7. It is found that wind shears stronger than 6 m sec- l /(253-107 m) occur associated with wind as weak as 4 m sec-l when wind directions are north-north-west at the surface; however, wind shears are weak in the case of so-called north-easterly flow pattern. Wind shear values can be estimated from Figure 7, with accuracy as shown in Table 5.

4.

EXAMPLES OF SYNOPTIC ANALYSES OF STRONG WIND SHEAR OCCURRENCES

Several considerations were made on the development of strang wind shear related with synoptic situation for each particular case.

(a) This is an example of strong wind shears associated with the frontal system. The low pressure with central pressure 1005 mb moved eastward in the Japan Sea; the warm front and cold front extended from the centre of low pressure passed Tokyo at around 10 LST and 22 LST, respectively. The wind shear increased early in the morning, decreased temporarily at the time of cold front passage, increased again after the frontal passage and continued strong while covered by the warm sector, and

Figure 8 - Surface chart for 0900 JST 28 November 1961

Figure 9 - Surface chart for 0900 JST 27 November 1961

181

JAPAN

then it decreased abruptly at the same time af passage of the cold front. The wind shear stronger than 5 m sec- l /(253-107 m) continued for about 14 hours with the maximum wind shear 11.7 m sec- l /(253-107 m). The variations of the wind shear and the visibility in this period are somewhat alike.

( b) This is the case in which a strong wind shear occurred in the high-pressure area. The high pressure was centred in the southern area of the east China Sea on 26 November, at 9 LST, then it moved slowly eastward and crossed the southern Kyushu. Its centre approached the south of Tokyo at 9 LST of 27 November (Figure 9). The strong wind shear occurred at 17 LST of 26 November, when the eastern edge of the migratory high approached the Jopanese Islands. Then it intensified rapidly to 20.0 m sec- l /(253-107 m), when a sea breeze changed to a land breeze. The wind shear stronger than 5 m sec- l /(253-107 m) continued for about 11 hours.

(c) The cold front passed over Tokyo at 6 LST, 24 November; consequently, a steep pressure gradient from west to east over the Japanese Islands has brought about pronounced monsoonal activity (north-westerly winds in winter) over Japan. The strong

north-westerly winds were blowing by 24 LST on the 24th. Then, the pressure gradient became rather gentle sa that the surfoce wind was weakened. Intense wind sheor occu~red 2 hours before the cold-front passage, then the wind shear stronger than 5 m sec- l ; (253-107m) continued for 22 haurs, except for an interruption at around 15 LST. The maximum intensity af 13.8 m sec- l !(253-107m) occurred at 5 LST just before the coldfront passage; at which wind direction and speed at "each level af the TV tawer (253 m,

WM~ "H..

!~~ I.lI

:'~. ::.) £1. t1 U)

U,

,,~

Q)

•• ::>

.m... ~.,

I,~

..

'N

..... 0-

10 r6V

t::,.Z

:~~t ...

.1

o

1rz'

.0

4

.~

Vi

'".... ....

~

.

2' 0

I~

'-..

a,l -

I

lO?H( (WORLD BROADCAST MAST) -. YlEAR 1959 N=7920

~~~ I

4 -. ,

WiND MEASUREMENT 10 AND 30M

.

t::,. I 1 I- . ->- t::,.Z I DEGREES CliOO MHERS)

HEiGHT TENIPERATURfE MEASUREMENT AT 2 AND SSM HEiGHT

I

. -6

-4' -2

0

2

4

6

S

10' 12·

14

16

1S

20

Figure 3: RHA TlVE FREQUENCiES ON P.ERCENT) Of WiND SHEAR AND iEMPERATURE DIFFERENCE ACCORDiNG TO RAMSEY [3J

~

::E:

.... E5 VI

:J:

~

'"

UNITED STATES OF AMERICA

217

(I)

F'Il

Z

0 0

l~

~

0

~

' r-

'. "-

C

:E:

.... z

8.0

0-

E

Ul

:x: > '" ::0

III I-

0.15

0.20 0.25 Ri c ->-

0.30

Figure 5: MAXIMUM WIND SPitED OIHtRENCE· (knots/laO feet) BETWEEN SURFACE . AND 110 FT. FORVARIOUS TEMPERATURE

GRADIENTS AND CRITiCAL RICHARDSON NUMBERS

.. --~

ESTIMATION OF THE 90m WIND FROM LOW-LEVEL OBSERVATIONS by Steven R. Hanna and Hans A. Panafsky, Project Director Prepared for United States Deportment of Commerce, Weather Bureau

ABSTRACT Hourly overages of temperature and wind were collected from 0 90m tower From these observations, an empirical method was developed for the estimation of the wind at 90m from wind and temperature at 30m and below. The method accounted for about 80% of the variance of the 90m-30m wind ratio. at Tyson's Corner, Virginia.

Monin and Obukhov similarity theory was modified by

th~

inclusion of the

effects of Coriolis and pressure gradient forces in order to arrive at a theoretical equivalent to the empirical estimation process. Agreement between observations and

theory was quite good. Due to the varying roughness characteristics of the terrain around the tower a dependence of roughness length on wind direction could be demonstrated; further, roughness decreased significantly when the ground was snow-covered. The roughness length during the summer voried from 50 cm for SW winds ta 10 cm for NW winds; during the winter the value for NW winds decreased to 1 cm over open ground and .01 em over snow-covered ground.

The theoretical and practical relationships were valid for unstable, neutral, and slightly stable stratificotion. In very stable air, no sucessful method was found for the estimation of the 90m wind. An attempt to use the geostrophic wind as a predictor was not successful.

1.

INTRODUCTION

1.1

Purpose

The purpose of this investigation was to develop and test a means of estimating wind speeds at heights above the surface boundary layer from stability and wind measurements near the surface. The objective was the construction of a nomogram, sufficiently simple ta be usable by any observer; the nomogram was to contain values af the estimated wind speeds at a certain height as a function of a wind speed near the surface and a stability parameter near the surface. This nomogram was to be based on empirical evidence, but was to be justified in terms of wind profile theory.

VERTICAL WIND SHEAR

220 '

1.2

Importance of the investigation

Often it is desirable to have an estimate of the wind speed at heights in the order of 50 to. 1000m, when only surface abservations are available. Such information is useful to pilots of aircraft landing or taking off, to fog and air pollution forecasters, to construction personnel, or to anyone whose work requires a knowledge

of the boundary layer wind distribution. Since most locations do not have the expensive and complicated instrumentation necessary for such higher-level wind measurements, these winds must be estimated from the limited instrumentation available, usually consisting af the standard U~S.

Weather Bureau anemometer at ten metres and a thermometer at one or two metres.

An additional thermometer at anemometer height would complete the instrumentation necessary for wind estimations of the type described in this study. 1.3

Historical background

Although wind profile theory is fairly well established for the constantstress layer of the atmosphere, the literature is noticeably void of investigations similar ta the type undertaken here. The most extensive theory regarding the farm of the wind profile in the layer from 50 to 1000m has been developed by A.K. Blackadar (1965}•._ However, no attempt was mode to find a means of estimating .the ·wind at any height in this layer from parameters near the surface, although his theory, modified by the effects of buoyancy, can be used as a basis for a wind estimation. In 1957, Reiter developed an objective, but purely statistical, method of estimating wind shears in the lowest 1000m of the atmosphere. As predictors he employed the wind direction, wind speed, lapse rate, and cloudiness. He obtained a 60% skill score from data at Tulsa, Oklahoma. This method is of use in making qualitative estimates of wind shear but does not provide a physical basis for making wind predictions. Blackadar (1957) also investigated the problem of high wind shears caused by the nocturnal low-level jet. During the night an inversion builds and releases the constraint imposed on the wind by day-time mixing. As a result the wind at the inversion top accelerates, becomes supergeostrophic, and osc~llates inertially. This type of behaviour should be predictable from surface winds, stabilities, and time of day. In order to find a scientific basis for estimation of winds in the 50 to 1000m level, the theory of wind profiles in the constant stress layer must first be considered, then extended to higher layers and statistically tested an data. 1.4

Wind profile theory

1.4.1 Simil~rity theory; According to the similarity theory of Monin and Obukhov (1954J-the-surrace-Soundary layer (z10 and ~w are calculated by means of Eq. (22). For stable conditions, ~ was determined to be (1 + 3Ri). This estimation was obtained by testing various expressions for ~ in Eq. (31) until the theoretical WR distribution corresponded most nearly to Fig. 7. Results of these ~ calculations may also be found in Table 4. Wi th the \t and q; different values of Ug • Then WR as a function of R~(4) and

functions, WR can be evaluated at a given Ri(4) for Ug is converted to U30 and the theoretical nomogram of U30 is drawn (Fig. 8). , ,

238

VERTICAL WIND SHEAR

TABLE 4.

Ri(4) +.030 +.020 +.(1]0 -.lIOj

af 'fI fun cti o'l~"_an

,-

:6m/s), near-neutral recards far NW wind directions were processed, including 239 hours fram winter 1965 and 40 hours from winter 1964. These records indicate that the roughness has decreased by appraximately an order of magnitude from the value for NW winds during the summer. 3.5.1 Construction and statistical anolysis af empirical nomogram. Hourly values of WR-~ere-plotted-a;-a-f~~~tIo~-of-D30-a~d-the-~aI~~Iated-RI{5;, resulting in the namogram in Fig. 11. In contrast to the data from SW and NW wind directians during the summer, the values of WR are concentrated around near-neutral stabilities. The over-all variance is therefore relatively small and the percentage of variance explained by the nomogram is cansiderably less than that explained far the previous two categories of data.

Deviations from the over-all mean wind ratio, 1.19, give an

over-all sample variance of sA = 2.8299/279. Deviations from the isopleths of the empirical nomogram yield a sample variance of ? = 1. 2313/279 and a sample standard deviation af about .06. The decrease in standard deviation can be attributed to the smoother, more homogeneous terrain in winter.

The percentage of variance explained

by the nomagram is: % Variance

=

100 X 2.8299 - 1.2313 2.8299

=

56%

If one or two hundred diabotic cases from this season and with these wind directions could be analysed and included in the above calculations, the-percentage of variance

explained should increase and approach the previous value of about 85%.

At the

moment, however, no comparisons can be made with the other results.

3.5.2 Determination of the roughness length. Of all the periods analysed, the data from NW-wI~ds-durI~g-t~e-wI~ter-allowed-t~e-most accurate determination of the roughness length.

In order to insure against varied roughness conditions, snow

periods were first excluded from the data. The resulting high-wind neutral cases indicated a wind ratio of 1.18 for U30 = 12 m/s •. Substi tution of Ug = 19 m/s and WR = 1.18 into Eq. (30) yields a raugnness length of about 1 em. This value of Zo is smaller than the Zo for NW winds during the summer by a factor of 10, indicating that the pasture grass is aerodynamically smoother in the winter. 3.5.3 Determination of theoretical nomogram. The application height of the lower-level RI-Is-IdeaIIy-V36 X .6I~;-:55m:--f~us the calculated Ri(5) is about eight times larger thon the actual Ri(.55).

For linear extrapolation purposes it is as-

sumed that Ri(30) = 50Ri(.55) and Ri(90) = 150Ri(.55). As before,Ri(.55) and the calculated Ri(5) will be included on the abscissa of the nomogram.

I;:

....

8.

i

i

i

.

I

I

7 1.1 1.2

•

6

•

11