Techniques for High - Level Analysis and Forecasting of Wind - and Temperature Fields

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'"'re i·r,)

S ER WORLD

METEOROLOGICAL

ORGANIZATION

TECHNICAL NOTE No. 35

TECHNIQUES FOR HIGH· LEVEL ANALYSIS AND FORECASTING OF WIND· AND TEMPERATURE FIELDS

PRICE: Sw. fr. 8.-

I WM 0 • No. 106. TP. 45 I Secretariat of the World Meteorological Organization • Geneva • Switzerland

1961

III

TABLE OF CONTENTS

Foreword

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Contributions* I

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A detached table of contents of each contribution is given at the beginning of the text provided by each couhtry.

v

FOREWORD

The introduction of jet-propelled aircraft into commercial airline operations has given rise to demands for meteorological services beyond those previously provided for aeronautical purposes. Questions such as forecasting for the high levels at which these aircraft operate and the various other meteorological requirements for their safe and economical operation., have to be studied. The national meteorological services of certain countries have for some time given attention to these questions. There is, however, a need for international co-ordination in this new meteorological field and the World Meteorological Organization, being mindful of its responsibility in this respect has also been giving consideration to the problems involved. In 1957, the Executive Committee of the World Meteorological Organization established a small panel of experts under the chairmanship of Mr. Luis de Azc~rraga, director of the Spanish Meteorological Service, with the following terms of reference: (i)

to examine the implications for meteorology of future requirements for routine commercial operations of jet aircraft~

(ii)

to examine how far existing meteorological techniques and facilities will allow these requirements to be met;

(iii)

to define clearly any short-time developments in meteorological techniques and facilities that may be required for the operation of jet aircraft.

The Executive Committee, at its tenth session (April/May 1958), examined the report of the panel and noted inter alia the importance of developing forecasting techniques for high-level operations. As a first step in the further study of this latter question, the Committee decided that Members of the World Meteorological Organization which have experience in this field should be invited to forward to the Secretary-General a description of themethods they use for analysis and forecasting, and that such information should be incorporated in a WMO Technical Note on this subject. In compliance with the above decisions, a provisional version of the Technical Note was published in 1958 and submitted to Members of the World Meteorological Organization for their comments. This provisional edition comprised contributions from the following eight Members of WMO: Canada Federal Republic of Germany France French Equatorial Africa Israei Union of Soviet Socialist Republics United Kingdom of Great Britain and Northern Ireland United States of America The provisional Technical Note together with the comments received from Members were studied by a new panel of expert§ during ~ meeting ~n Bru§sels (lB-22 Marcb~ 1959) under the chairmanship of Mr. Meyer (Federal Republic of Germany). The panel noted that the provisional Note had been met with an exceptionally good reception by Members and that undoubtedly its publication had filled an important gap. The panel also considered that it was highly desirable that a final revised version of the Note be published. The panel favoured the layout used in the provisional Note in which the contributions of Members are presented

FoREwORD

VI

separately and stressed that in accordance with the Executive Committee's resolution contributions Should be in a sufficiently detailed form to permit the practical use of these methods for routine forecasting work. With a view to achieving the highest possible degree of homogeneity, the panel furthermore developed a plan for the contents of each contribution to serve as guidance to the individual contributors to the final Note. The Executive Committee during its eleventh session (April-May 1959) approved the recommendations of the panel and decided to invite Members who had already contributed to the provisional Technical Note to revise their contribution along the principles proposed by the panel; the Committee also invited other Members to contribute, if they so desired, to the final version of the Technical Note. As a result, contributions in original or revised forms became available from following 12 Members:-

the

British East African Territories Canada Federal Republic of Germany France French Equatorial Africa (*) Israel Netherlands Norway Sudan Union of Soviet Socialist Republics United Kingdom of Great Britain and Northern Ireland United States of America These contributions, reproduced in full, constitute the present Technical Note. The Note is thus a comprehensive and up-to-date review of the high-level analysis and forecasting techniques which have so far been developed by Members of WMO. As such, it is believed it will be useful to all Members of WMO (both those who have contributed to it and to others) in reviewing and developing their respective techniques and procedures for the provision of meteorological services for high-altitude flight. The contributions are presented in alphabetical order of the titles of the respective Members, each contribution being preceded by a detailed table of contents. The Note also includes at the beginning a subject index based on the proposals of the panel. Thus rapid reference may be made to any section of the Note. The Note is being published in full in the English and French languages, each version of which includes translations of the Foreword in Russian and Spanish. In conclusion, it is wished to express the gratitude of WMO to the Members of the Organization who have contributed to the Note and also to the experts who have served on the two panels established by the Executive Cummittee and whose guidance and advice have contributed greatly to the compilation of this pres,ent Note.

(D. A. Davies) Secretary-General

(*) The title and status of this Member have been changed subsequent to the contribution being received.

VII

AVANT-PROPOS

A la suite de la mise en service par llaviation commerciale d1avions a reacteurs, de nouveaux beoins sont apparus dans le domaine de llassistance meteorologique a llaeronautique. 11 slest revele necessaire dletudier des questions telles que la prevision aux hautes altitudes atteintes par ces aeronefs, ainsi que divers autres problemes meteorologiques inherents a llexploitation sQre et economique de ce type d1appareils. Les services meteorologiques de certains pays se sont penches depuis plusieurs annees sur ces problemes. 11 est, toutefois, necessaire d1assurer une coordination internationale dans cette nouvelle sphere dlactivite et 1lOrganisation meteorologique mondiale, consciente de ses responsabilites dans ce domaine, a egalement accorde toute son attention a ces questions. Clest ainsi que le Comite executif de 1lOrganisation meteorologique mondiale a cree, en 1957, un groupe dlexperts restreint place sous la presidence de M. Luiz de Azc~rraga, directeur du Service meteorologique espagnol; ce groupe avait les .attributions suivantes: i)

examiner les incidences que comporteraient dans le futur, pour la meteorologie, les besoins de llexploitation courante des avions commerciaux a reaction;

ii)

examiner dans quelle mesure les techniques et moyens meteorologiques actuels permettront de repondre aces besoins;

iii)

definir clairement to~s progres qui pourraient @tre realises a breve echeance, en matiere de techniques et moyens meteorologiques, afin d1assurer llexploitation des avions a reaction;

A sa dixieme session (avril-mai 1958), le Comite executif a examine le rapport de ce groupe dlexperts et a souligne, entre autres, llimportance de mettre au point des techniques de prevision pour les vols a haute altitude. Le Comite a decide qu1avant d1entreprendre une etude plus approfondie du probleme, il fallait inviter les Membres de 1lOrganisation meteorologique mondiale ayant une certaine experience dans ce domaine a faire parvenir au Secretaire general un expose des methodes utilisees pour llanalyse et la prevision, et que les renseignements ainsi recueillis devaient @tre rassembles dans une Note technique de 1IOMM. Conformement a ceS decisions, une version provisoire de la Note technique a ete publiee en 1958 et soumise aux Membres de 1lOrganisation, pour commentaires. Cette version provisoire comprenait les communications des huit Membres suivants: Afrique equatoriale frangaise Canada Etats-Unis dlAmerique France Israel Republique federale dlAllemagne Royaume-Uni de Grande-Bretagne et dlIrlande du Nord Union des Republiques socialistes sovietiques La Note technique provisoire ainsi que les commentaires formules a son sujet par les Membres ont ete etudies par un nouveau groupe dlexperts, au cours d1une reunion qui a eu lieu a Bruxelles du 18 au 22 mars 1959, sous la presidencede M. Meyer (Republique federale dIAllemagne). Le groupe d1experts a constate que la Note technique avait ete extr@mement bien accueillie par les Membres et que sa publication avait sans aucun doute comble une importante lacune. Le groupe d'experts a egalement estime qulil etait tres souhaitable de faire paraltre une version definitive de cette Note, apres llavoir revisee. 11 slest prononce en faveur de la disposition utilisee pour la Note technique provioire, dans laquelle

VIII

AVANT-PROPOS

les contributions des Membres etaient presentees separement et il a souligne le fait que, conformement a la resolution du Comite executif, les communications devaient §tre suffisamment detaillees pour permettre llemploi pratique de ces methodes dans les travaux de prevision courants. Afin de parvenir a une presentation aussi homogene que possible, le groupe d'experts a egalement mis au point un plan relatif a la teneur de chaque communication a titre d'indication pour les Membres qui devaient contribuer a la Note technique definitive. Lors de sa onzieme session (avril-mai 1959), le Comite executif a approuve les recommandations du groupe dlexperts et a decide d'inviter les Membres qui avaient deja contribue a la Note technique proviso ire a reviser leurscommunications selon les directives suggerees par le groupe d'experts; le Comite a egalement invite dlautres Membres a contribuer, slils le desiraient, a la version definitive de la Note technique. Clest ainsi que les 12 Membres suivants ont fait parvenir au Secretariat les textes originaux ou revises de leurs communications: Afrique equatoriale frangaise* Afrique orientale britannique Canada Etats-Unis dlAmerique France IsralH Norvege Pays-Bas Republique federale dlAllemagne Royaume-Uni de Grande-Bretagne et d'Irlande du Nord Soudan Union des Republiques socialistes sovietiques. Ce sont les contributions de ces pays qui, reproduites integralement, composent la presente Note technique. La Note contient donc un expose detaille des techniques modernes d'analyse et de prevision a haute altitude mises au point jusqu1ici par les Membres de l'OMM. De ce fait, nous croyons qulelle aidera tous les Membres de l'Organisation, aussi bien ceux qui y ont contribue que les autres, a reviser ou a perfectionner leurs propres methodes et techniques d'assistance meteorologique aux vols a haute altitude.

Les contributions sont presentees selon llordre alphabetique des noms des Membres qui en sont les auteurs; chacune d'entre elle est precedee par une table des matieres detaillee. On trouvera egalement au debut de la Note technique un index des sujets traites, etabli selon les propositions du groupe d'experts. 11 est donc possible de se referer rapidement a nlimporte quelle partie de la Note technique. La Note est publiee integralement en anglais et en frangais; dans chaque edition, l'avant-propos est traduit en russe et en espagnol. Pour conclure, je tiens a exprimer la reconnaissance de 1lOMM aux Membres de 1lOrganisation qui ont pr§te leur concours pour llelaboration de la Note technique, ainsi qu'aux experts qui ont fait partie des deux groupes etablis par le Comite executif et qui, par leurs directives et leurs conseils, ont contribue dans une large mesure a la composition de la presente Note technique.

~ (D.A. Davies) Secretaire general

*

Le nom et le statut de ce Membre ont change apres reception de sa communication.

IX

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XII

INTRODUCCION

La entrada en servicio de aviones a reaccion en las lineas .aereas comerciales plantea necesidades nuevas a los servicios meteorologicos, que tienen que realizar prestaciones superiores a las que se hacian para la aeron~utica. Es necesario estudiar cuestiones tales como las predicciones del tiempo alas grandes altitudes que alcanzan esas aeronaves, as! como otros varios problemas meteorologicos inherentes a la explotacion, con seguridad y econom!a, de ese tipo de aparatos.

Los servicios meteorologicos de algunos paises se han ocupado ya de esos problemas desde hace anos. De todas formas, es necesario asegurar una coordicacion internacional en este nuevo campo de actividades meteorologic as y la Organizacion Meteorologica Mundial, consciente de sus responsabilidades en esta materia, presta igualmente su atencion a estos problemas. En 1957, el Comite Ejecutivo de la Organizacion Meteorologica Mundial creo un pequeno grupo de expertos, bajo la presidencia del Sr. Luis de Azc~rraga, Director del Servicio Meteorologico espanol. Las atribuciones de ese grupo eran las siguientes: i)

examinar las repercusiones que han de tener en 10 futuro, para la meteorologia, las necesidades de explotacion normal de los aviones comerciales a reaccion;

ii)

examinar en que medida se pueden satisfacer esas necesidades con las los medios meteorologicos actuales;

iii)

definir con claridad todos los progresos que se podr!an realizar en breve plazo en materia de tecnicas y medios meteorologicos, a fin de asegurar la explotacion de los aviones a reaccion.

t~cnicas

y

En su decima reunion (abril-mayo de 1958), el Comite Ejecutivo examine el informe de ese grupo de expertos y subrayo, entre otras cosas, la importancia de preparar tecnicas de prevision para los vuelos a gran altitud. El Comite decido que, antes de emprender un estudio m~s detallado del problema; seria precise pedir a los Miembros de la Organizacion Meteorologica Mundial que posean experiencia en esta materia que envfen al Secretario General una descripcion de los metodos que emplean para el an~lisis y la prevision, y que los datos asi recogidos deber!~n ser reunidos en una Nota Tecnica de la OMM. De acuerdo con esas decisiones, en 1958 se ha publicado una version provisional de la Nota Tecnica, que ha sido sometida a los Miembros de la Organizacion Meteorologica Mundial para que hagan los comentarios que estimen oportunos. Esta version provisional estaba formada por las comunicaciones de los ocho Miembros siguientes de la OMM: ~

Africa Ecuatorial Francesa Canad~

Estados Unidos de America Francia Israel Reino Unido de Gran Bretana e Irlanda del Norte Rep~blica Federal de Alemania Union de Rep~blicas Socialistas Sovieticas. La Nota Tecnica provisional y los comentarios formulados al respecto por los Miembros han sido objeto de estudio por parte de otro grupo de expertos reunido en Bruselas del

•

INTRODUCCION

XIII

18 al 22 marzo de 1959, bajo la presidencia del Sr. Meyer (Republica Federal de Alemania). El grupo de expertos ha comprobado que la Nota Tecnica provisional habia sido muy bien acogida por los Miembros y que su publicaci6n habia servido indudablemente para colmar una importante laguna. El grupo de expertos ha estimado tambien que era muy conveniente publicar una versi6n definitiva de dicha Nota, una vez revisada. Se ha mostrado partidario de conservar la misma disposici6n de la Nota Tecnica provisional, en la que las comunicaciones de los Miembros se presentaban por separado, y ha subrayado el hecho de que, de conformidad con 10 dispuesto en la resoluci~n del Comite Ejecutivo, las comunicaciones deberian ser 10 bastante detalladas para permitir el empleo pr~ctico de esos metodos en los trabajos normales de previsi6n. Para conseguir una presentaci6n 10 m~s homogenea posible, el grupo de expertos ha preparado adem~s un plan relativo al contenido de cada comunicacion, que ha de servir de orientaci6n a los Miembros al hacer sus aportaciones a la Nota Tecnica definitiva. Con ocasi6n de su undecima reuni6n (abril-mayo de 1959), el Comite Ejecutivo ha aprobado las recomendaciones del grupo de expertos y ha decidido invitar a los Miembros que ya han.hecho aportaciones a la Nota Tecnica provisional a que revisen sus comunicaciones, siguiendo las instrucciones sugeridas por el grupo de expertos; el Comite ha invitado igualmente a otros Miembros a que hagan aportaciones, si 10 desean, a la version definitiva de la Nota Tecnica. Como consecuencia de ello, los doce Miembros que se indican a continuacion han enviado a la Secretar!a los textos originales 0 revisados de sus comunicaciones:

• Africa Ecuatorial Francesa* Canad~

Estados Unidos de America Francia Israel Noruega Pa!ses Bajos Reino Unido de Gran Bretana e Irlanda del Norte Republica Federal de Alemania Sud~n

Territorios Brit~nicos de Africa Oriental Union de Republicas Socialistas Sovieticas. Las aportaciones de estos pa!ses, reproducidas integramente, componen la presente Nota Tecnica. La Nota esta, pues, formada por una exposicion detallada de las tecnicas m~s modernas de an~lisis y prevision a gran altitud, elaboradas hasta ahora por los Miembros de la OMM. Creemos, por 10 tanto, que ayudar~ a todos los Miembros de la OMM, tanto a los que han hecho aportaciones como a los demas, a revisar 0 perfeccionar sus metodos y tecnicas de asistencia meteorologica a los vuelos a gran altitud.

Las divers as comunicaciones se presentan por el orden alfabetico de los nombres de los Miembros que las han enviado. Cada una de ellas va precedida de un sumario detallado. Al principio de la Nota Tecnica figura igualmente un Indice de materias preparado a base de las instrucciones del grupo de expertos. Resulta, pues, facil encontrar cualquier seccion de la Nota Tecnica.

*

El nombre y la condici6n jur!dica de este Miembro han cambiado despues de recibida su communicacion.

XIV

.

INTRODUCCION

La Nota se publica !ntegramente en ingles y en frances. introducci6n se ha traducido al ruso y al espanol.

En ambas ediciones, la

Para terminar, conviene manifestar la gratitud de la OMM a los Miembros de la Organizaci6n que han hecho aportaciones, a la Nota Tecnica, as! como a los expertos que han formade parte de los dos grupos estab1ecidos por el Comite Ejecutivo y que, con sus orientaciones y consejos, han contribu!do grandemente a la compilaci6n de la presente Nota Tecnica.

~

D.A. Davies Secretario General

xv

INDEX

SUBJECT

..,... "" " I

..,en

'".

70"1

120·

115-

SO"

70'

Form

902":~46

FIGURE 3. Comparison of Long. Wave Pattern obtained by avera~ing two 500-mb charts one half short wave period apart in time with the Long Wave Pattern obtained by a four day average of 500 mb charts. The heavy solid line is the long wave pattern for 1500 GMT 14 Dec. 1953 obtained from averaging the 18,000 foot contour for 0300 GMT 14 Dec. 1953 (light solid line) and for 0300 GMT, 15 Dec. 1953 (light dashed line). The heavy dashed line is the long wave pattern for 2100 GMT 14 Dec. 1953, obtained from the mean position of the 18,000 contours for the 0300 GMT and 1500 GMT 500 mb charts for 13, 14, 15 and 16 Dec. 1953.

METEOROLOGICAL DIVISION-DEP~RTME~T OF TRANSPORT- CANADA

Cl

~

:J=o

Form 9021-5"-46

FIGURE 4. Motion of centres of 24 hour height changes on 500 mh ch .. rt with respect to long w..ve p .. ttern. Solid line long wave p .. ttern for 0300 GII7I. 14 Dec. 1953. D.. shed line long w..ve p .. ttern for 0300 GMT 15 Dec. 1953. D..shed dotted line long wave pattern for 0300 GMT 16 iDec. 1953. Long wave p .. ttern obt .. ined from mean position of 18,000 foot contours from two 500 mb charts 24 hours ap .. rt. Ci1"cles m.. rk the centres of 24 hour height ch"nges, l ..·belled R for rises ..nd, F for f .. lls with ..... gnitude in feet. 1 in the circle denotes height ch ..nge for 0300 GilT 14 Dec. 1953, 2 for 0300 GHT 15 Dec. 1953 and 3 for 16 Dec. 1953. The dotted lines indic .. te the direction of motion of the height ch ..nge centres.

\.>I \J1

CANADA

36

a short-wave trough or ridge, respectively is in phase with it, When the long waves move slowly and their intensity changes little, the height changes aloft will be largely due to the motion of the short waves. It has been found that the trajectories of the centres of the 24-hour height changes delineate the long-wave pattern. The fact that they do indicates that the long-wave current is more or less the path for the short waves. More will be said about the rises and falls of the upper-level contours as they are a very useful aid in both analyzing and prognosticating upper-level charts (Figure 4), 3,2,2 There is' a close association between the upper short waves and surface highs and lows, but whether the surface features appear as minor perturbations or as intense cyclones and anticyclones depends on other considerations. Surface pressure waves usually consist of warm troughs and cold ridges. At 500 mb however, the phase is reversed so that the short waves, as well as the long waves, are characterized by cold troughs and warm ridges. 3.2.3 Although the short waves usually have small amplitudes, the~ can frequently be spotted by an inspection of a series of upper-level charts due to their rapid motion. Association of upper-level features with surface systems also helps. A chart of the height changes aloft usually makes them stand out sharply.

Long

WQves

G.-atldes onde5

P~ttern at time GOhfi 9 '-4r'at;on d

t L'''cure

---

Short waves, Onolc.s courtes

.,.

LOl1g Wc.1Ve pattern

C"",(igurg tiQn cJe ottd e$

,, /

La~

9ues

"

"Contour

::... _ / at time t+24

L;gne de

HI"vequ

;, l heHre t ... 2 4-

3.3

Figure 5 Schematic 24-hour height rises and falls due to slow-moving long waves and fast-moving short waves

The use of geopotential change charts

3.3.1 An analysis of the height rises and falls on the upper-level constant pressure charts offers a solution to the problem of locating the day-to-day positions and motions of the short and long waves 1117. It is convenient in practice to consider the 24-hour changes in the contour heights-at 500 mb. The observed areas of rises and falls (Ro and Fo) of the contour heights are considered to be mainly a combination of the rises and falls of the moving long waves (R L and FJ) and of the faster moving short waves (R s and F s )' When the long waves are stationary, the observed rises and falls are mainly due to the moving

CANADA

37

short waves. It has been noted in the latter case that the motion and intensity of the rise and fall areas can usually be followed consistently from chart to chart. 3.3.2 To clarify the above, consider the areas of 24-hour rises and falls associated with a slow-moving long wave of large amplitude and a faster short wave of smaller amplitude, both separately and combined, as shown in Figures 5 and 6. The rises and falls due to the long waves will be elongated and lie along latitude circles. Those due to the short waves will be more cellular in shape and lie along the long wave current. The observed height changes on the upper-level charts are, of course, a combination of both. 3.3.3 In working with upper-level charts it is the observed height contours and height changes that are obtained directly. In order to study the behaviour of the long waves and short waves, it is necessary to break down the observed pattern into the long-wave and short-wave patterns. This may be done in several ways, but two methods appear to be most practical. 3.3.4 In general, the centres Rs and F s will correspond closely to the centres of Ro and F o , but their intensities differ due to the motion of the long waves. From the Ro and Fo , then,it is possible to obtain the approximate wave length and speed of the short waves, and from these their period. If two charts, one-half the short-wave period apart in time, are averaged, the short-wave pattern will be largely cancelled and the long-wave pattern for the mid-period of the two charts will be obtained. The RL and FL may be obtained from these charts, and these subtracted from the Ro and F o will also give the Rs and F s • History and Rossby's equation for wave motion may then be u'sed to prognosticate the height changes, and consequently, the upper-level chart. 3.3.5 Alternatively, the approximate position and wave length of the long wave may be determined by inspection. The distortion of the long-wave streamlines by a short wave can result in an error in the exact location of a long-wave ridge or trough larger than the 24-hour motion of the ridge or trough. However, knowing the approximate wave length and the zonal· speed, the 24-hour motion of the long wave can be obtained by Rossby's equation to a close approximation. The zonal speed can be computed in a few minutes, using the "planimetric method" ~11. By moving the upper-level chart along a distance equal to this 24-hour motion, the RL and FL may be obtained. The Rs and F s may then also be obtained and a pro_ gnost:ic chart prepared as by the previous method. 4.

EXAMPLE OF LONG-WAVE ANALYSIS

4.1 The 500 mb charts for 14, 15 and 16 December 1953, in Figures 7, 8 and 9, have been chosen to illustrate most of the points brought out in the foregoing discussion. On these charts the centres of height rises and falls correspond closely with the short-wave ridge and trough locations respectively. The long-wave ridge and trough positions were obtained by the methods outlined above and have been marked ~ and respectively.

Lr

4.1.2 Several features of these charts are particularly noteworthy. An inspection of the charts would indicate that the deep long-wave trough over southeastern U.S.A. moved eastward rapidly from 14 December to 15 December and then apparently westward from 15 December to 16 December. The charts of the long-wave pattern indicate that this trough had a steady eastward motion of about 6 de~rees longitude Fer day. The short wave "fall" area moving northeastward to the east of this eastward moving long-wave trough intensified. The surface low associated with this short-wave trough deepened 21 mb from 14 December to 15 December, and by 16 December the open wave of 14 December had completely occluded. Conversely, the short wave "fall" area moving southeastward behind the long-wave trough decreased in intensity and its associated surface wave filled and almost completely disappeared.

\>1

CO

METEOROLOGICAL DIVISION-DEPARTMENT OF TRANSPORT- CANADA SIl"

I'""it-

I

...

,""~I

I

I" I

"

I

I

80'

7!5D

70·

GilD

60· 55"

150· 45"

I~

o

:»

~:»

70-!

120·

1115"

10'

70' Form

9021-!5~46

FIGURE 6. Observed 24 hour Height Rises and Falls at 500 mb from 0300 GHT 14 Dec. 1953 to 0300 GHT 15 Dec. 1953. Light dashed lines are isolines of 24 hour height changes at 200 foot intervals. Heavy solid line is 18,000 foot contour on 500 mb chart for 0300 GMT 15 Dec. 1953. Dashed heavy line is the long wave pattern at 1500 GHT 14 Dec. 1953 obtained by taking the mean position of 18,000 foot contours from the 0300 GHT 500 mb charts for 14 and 15 Dec. 1953.

METEOROLOGICAL DIVISION-DEPARTMENT OF TRANSPORT- CANADA

Cl

I

Form

902~:'46

FIGURE 7. 500 mb cltlar't f"or 0300 GMT 14 Dec. 1953. Solid lines are height contours a.t 400 foot intervals •• Hea.vy solid line is central contour of ~esterly current. Heavy da.shed l~ne is the long w~ve p~ttern for 0300 GMT 14 Dec. 1953 obta.ined by taking the mean position o~ the 18,000 foot contours from the 1500 GMT charts for 13 and 14 Dec. 1953. Light da.shed lines a.~e isolines of 24 hour height c'hanges at 200 foot intervals, labelled ill hundreds of feet.

'->l

\0

~

o METEOROLOGICAL DIVISION-DEPARTMENT OF TRANSPORT- CANADA

o

i

ForIllIOl~.

FIGURE 8,.

500 mb Chart f'or 0300 GilT 15 Dec. 1953. Solid lines are height contours at 400 foot interv·als. Heavy solid line is central contour of' westerly current. Heavy dashed line is the long wave pattern for 0300 GilT 15 Dec. 1953 obtained by taking the mea~position of' the 18,000 foot contours from the 1500 GMT charts for 14 and 15 Dec. 1953. Light dashed lines are isolines of 24 hour height changes at 200 foot intervals, labelled in hundreds of' feet.

METEOROLOGICAL DIVISION-OEPARTMENT OF TRANSPORT- CANADA

o

:x>

~

:x>

FIGURE 9. 500 mb Cbart t'or 0300 GilT 16 Dec. 191>:l" Solid lines are height contours at 400 foot interv ..1s. Heavy solid line is central contour of westerly current. Be ..vy dashed line is the long "' ..ve patt'ern for 0300 GilT 16 Dec. 1953, obt .. ined by taking the mean position 01' the 18,000 t'oot contours t'rom the 1500 GilT charts for 15 and 16 De~. 1953. Light dashed lines .. re isolines ot' 24 hour height ch ..nges at 200 foot intervals, labelled in hundreds of feet.

-l:=" I-'

42

CANADA

4.1.3 On 16 December a short-wave trough moved into the long-wave trough ~ver the eastern Atlantic and deepened the trough to such an extent that a cut-off low was formed. It will be noted that the westerlies split in this area, part of the westerly current continued in a northeasterly direction over the ridge, "and part of the current went south to include the cut-off low. This set up a "blocking" situation in this area. It is int,eresting to note that "blocking" features prevailed on the upper-level charts for the remainder of the winter. REFERENCES 1.

Riehl, H., and collaborators, 1952 - Forecasting in middle latitudes. Meteorological Monographs, ~, 5. American Meteorological Society.

2.

Anderson, R., Boville, B.W., and McClellan, D.E., 1953 - An operational frontal contour analysis model. Meteorological Division, Department of Transport, Technical Circular, CIR-2359.

3.

Rossby, C.G., and collaborators, 1939 - Relation between variations in the intensity of zonal circulation of the atmosphere and the displacement of the semi-permanent centre of action. J. Marine Res., ~, pp. 38-55.

4.

Rossby, C.G., 1940 - Planetary flow patterns in the atmosphere. Quart. J. R. Met. Soc., 66, (SuPP.), pp. 68-87.

5.

Namias, J., 1947 - Extended forecasting by mean circulation methods. U.S. Dept. of Commerce, Washington, D.C.

6.

Sutcliffe, R.C., 1951 - Mean upper contour patterns of the northern hemisphere - the thermal synoptic viewpoint. Quart. J.R. Met. Soc., 77, pp. 435-440.

7.

Charney, J.G., and Eliassen A., 1949 - A numerical method for predicting the perturbations of middle latitude westerlies. Tellus, 1, pp. 38-54.

8.

Cressman, G.P., 1948 - On the forecasting of long waves in the upper westerlies. J. Meteor., 2, pp. 44 -57 .

9.

Robertson, G.W., and Cameron, H., 1952 - A planimetric method for measuring the velocity of the upper westerlies. Bull. Amer. Meteor. Soc., 33.

10.

Namias, J., and Clapp, P.F., 1944 - Studies of the motion and development of long waves in the westerlies. J. Meteor., ~, pp. 55-57.

11.

Cameron, H., and Robertson, G.W., 1954 - Short period and long period components of the geopotential change at the 500 mb level. Meteorological Division, Department of Transport, Technical Circular, CIR-2416.

43

CANADA APPENDIX

IV

300 MS FROGS - A SHORT METHOD (by B. W. Boville)

1.

INTRODUCTION

The general approach is based on the use of an equivalent on-level model for specifications of synoptic scale conditions in the troposphere, i.e. independent and co-ordinated progs for the surface and 500 mb (or total thickness) levels theoretically specify the conditions at other levels. The charts for the other levels may thus be obtained by the application of statistical or model formulae. 2.

BASIS FOR THE METHOD

2.1 Correlation data for height changes at a number of Canadian stations yielded values near unity for the 300 and 500 mb levels. 2.2

Simple extrapolation techpiques are in use at the NAWAC at Washington.

2.3 Correlation of actual wind speeds at 300 and 500 mb for a month at three U.S.A. stations yielded a coefficient of 0.75 with a regression equation 13.5 kts

+

1.16

V500

2.4 It is thus presumed that simple extrapolation from 500 mb supplemented by the known behaviour of the jet stream relative to surface and 500 mb developments will yield 300 mb progs with the same accuracy as the 500 mb prog.

3.

METHOD

3.1 A standard graph such as shown by the dashed curve in Figure 1 is obtained by plotting the 500 and 300 mb heights from observed data in the area of concern. The basic graph can be prepared on a weekly or monthly basis depending on the range and detailed accuracy of the prog required. For prognostic periods of the order of 48 hours or more the accuracy is such that a standard graph could probably be used for at least a season. 3.2

Modification to the basic table can be done in several ways.

3.2.1 In the example shown the actual 300 and 500 mb values at observation time in the Atlantic sector were plotted (crosses) and the graph amended for a better usual fit. The usual 300 mb contours were then tabulated to give an amended Table 11. The 300 mb prognostic contours are obtained by drawing them to correspond to the 500 mb prognostic values as given in Table 11. This is probably the simplest method where 300 mb charts are not drawn on a routine basis. 3.2.2 A continuity method may be somewhat simpler for the routine production of progs. A standard table, such as Table I, is used and ~he compu~ed and actual positions of selected 300 mb contours, at times t 0, are drawn on a chart (see Figure 6). A similar amendment to the computed positions of these contours on the prog is made by visual adjustment when tracing.

44 4•

. CANADA THE JET STREAM

4.1 Place the 300 mb prog over the surface prog then sketch the jet axes and maxima in the strong flow at 300 mb to fit the known relationship of the jet to the surface fronts and developments (Riehl,1952) taking into consideration the 300 mb history and the observed tendency for the axes to persist near the same 500 mb contour height and (500 - 300 mb) thickness value (McClellan, 1954). 5.

ISOTACHS

5.1 The 60 and 80 kt isotachs are established using the geostrophic wind scale. Curvature corrections can be made subjectively for extreme values. The maximum value on the axis is set by combining geostrophic measurement, history and development. The remaining isotachs can then be filled in rapidly. The use of normal shear values (Lee, 1953, 1954; Murray and Johnson, 1952) from the tables or scales will be of material assistance, particularly to those with little experience in jet-stream analysis.

6.

EXAMPLE

l200Z, 11 JUNE 1957

6.1 Figure 1 shows the 500-300 mb height relationship determined the previous week. Actual heights for the Atlantic area at l200Z, 10 June 1957 were then plotted and a new curve determined for best visual fit and convenience of use. 6.2 The 300 mb contours were drawn directly as shown on Figure 2 over Figure 4 (500 mb actual) on a light table. Time about 10 minutes. 6.3 . This chart was placed over the surface chart (Figure 5) and the jet axis drawn and maxima entered. 6.4 The isotachs were then drawn using the geostrophic wind scale on the 400 ft contours plus knowledge of expected relations to surface and 500 mb maps. Time about 20 minutes. 6.5 No 300 mb history or data were available so the chart was based solely on the surface and 500 mb charts plus the empirical height relationship established 24 hours previous~. 6.6 Comparison with the actual 300 mb chart (Figure 3) shows that the chart is synoptically accurate both in jet location and isotach speed. In practice the 500 mb and surface progs would be used rather than actuals. Actuals were used here to test the extrapolation relationship without having to discuss the merit of a particular surface and 500 mb prog. A considerable number have been done using 36-hour prognostics with quite satisfactory results. 7.

CONCLUSION The foregoing provides an adequate basis for 300 mb prognosis on the synoptic scale.

REFERENCES 1.

Lee, R.,

1953 - Principles of isotachs analysis, Tec.-162.

2.

Lee, R.,

1954 - A method of jet-stream analysis at 300 mb, Tec.-198.

3.

McClellan,

D. E., 1954 - Jet-stream analysis, Tec.-179.

4.

Murray, R., and Johnson, D.H., 1952 - Structure of the upper westerlies, Quart. J. R. Met. Soc., 78 p. 186.

5.

Riehl, H., et al, 1954 - The jet stream. Meteorological Monographs. Amer. Met. Soc., ~' 7.

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mb .

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12••••••• 9().5 08••••••• 88 04 ••••••• 85.5 00 ••••••• 83 296 ••••••• 80 92••••••• 77.5 88 ••••••• 74.5 284 •••••••172

188

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300 mb

180 Actual station values Atlantic sector. 1200Z, 10 June,1957. s. Valeurs reelles aux stations de sondage de la zone atlantique, 1200Z, 10 juin 1957

500 mb 176

Q ~

~

Table I I .Tableau I I

iO ~

~

500 mb

316 ••••••••192.5 12 •••••••• 90 08 •••••••• 87 04 •••••••• 84 00 •••••••• 81.5 296•••••••• 78.5 92 •••••••• 76 288 ••••.••••173.5

;£)0 mb height, hundreds of feet geopotentiel de 300 mb, en centaines de pieds I 111 I I1I I I I I 1 I 1 I 11 1 I I

280

-

-

:f-! Atlantic prog. ~~~H:j:H=BlEta Recommandee pour lletabliSSement~B:tiE ' de la carte prevue dans la zone ::) atlantique

184

172

+.

I

P=r- t ' '".

284

288

2'92

296

r

1 I I 11 I I I I1 I I

300

304

308

312

Figure 1.

Distribution of 500 and 300 mb heights.

Figure 1.

Distribution des geopotentie1s de 500 et 300 mb.

31i

-l=" V1

~

0\ (1

40'

(1

~>

Slatil)n.• ~.f:.:.Q

, ,

I.!.1.1:'i 7. H, . ..I2.o0.z '". of cho".300.m.l1... E~'nlP.QI.Qlj.Qn ......... Do
-->"Pg' Pg

= 2: Ji" = 2" a;- =

-->-",,-->Pg Pg' () Z

=

0

'

Substituting for equations (2.1) and (2.2) yields 1 ).2T

whence

-->-

-->-

(k X Vptp)· (k X VpT)

= 0

Vptp· Vp T = 0

The result states that in an isobaric surface the intersection s with a surface of maximum wind joins the points where isothermals cut ~he contour lines perpendicularly (Figure 1).

Figure 1 Line of intersection between surface of maximum wind and isobaric surface The line of intersection of an isobaric surface and the surface of maximum wind plays an important part with'respect to changes of flight altitude, similar to the "isobaric" axis of the jet stream which is of importance for horizontal deviations of the flight track. The point of intersection of the line s and the isobaric axis of the jet stream is a point of the real axis. From experience it is known that at least in jet-stream conditions the variation of wind direction with height appears to be small. If then we assume the variation to be negligible, the condition in a surface of maximum wind becomes

Whence from equation (2.2) The isobaric temperature gradient is zero at every point of the surface of maximum wind. From a geometrical point of view this is only possible if the line of intersection s of the surface of maximum wind and an isobaric surface is a double isothermal c.q. if along the line of intersection s an isothermal surface is tangent to an isobaric surface (Figure 2). This result is somewhat misleading inasmuch as in general an isothermal surface will be tangent to isobaric surfaces not along a whole line but in some isolated points only. Although the above reasoning leads to an inconsistency it tends to indicate that alQn~ the line s the variation of temperature will be very small.

103

NETHERLANDS

From inspection of a number of 300 mb charts in winter this statement is confirmed;

Figure 2 Intersection of surface of maximum wind, isothermal surface and isobaric surface the variation turns out to be 1 or 2°C only. Further inspection reveals that the temperature distribution shows a complicated "cellular" pattern in the vicinity of the line s with small temperature gradients (Figure 3).

c / -XfC/ .1./ Figure 3 Temperature distribution in isobaric surface in the vicinity of line of intersection between surface of maximum wind and isobaric surface

3.

of>

/, I

, I

I

\

\

\,

THE ANALYSIS OF THE WIND FlEW IN THE SURFACE OF MAXIMUM WIND

Considering the somewhat heuristic arguments in the preceding paragraph the surface of maximum wind is characterized by the property that it is generated by (almost) coinciding isobars-isothermals. This feature has an interesting bearing on the analysis of the wind field in the surface of maximum wind. To comment on this it is recalled that under the assumption of geostrophic flow the wind field may be described by a stream function not only in isobaric surfaces but also in isentropic surfaces (Montgomery's stream function).

;-3

In 7 it is shown that the same holds in all surfaces in the atmosphere which are generated by c'O"inciding isobars-isothermals, c.q. in all "barotropic" surfaces within which the temperature is a function of pressure only.

104

NETHERLA.NDS

Accordingly the surface of maximum wind may be interpreted as a barotropic surface with a corresponding stream function ~ defining its wind field. It follows that the wind field in a surface of maximum wind may be obtained along the same lines as in isobaric analysis, i.e. by drawing stream-lines ~ = constant at fixed intervals and measuring the wind speed by means of a geostrophic scale. The stream function ~ is a rather complicated function of the existing temperature distribution in the atmosphere and should be determined empirically. The analyses must be such that the gradient surpasses those of all isobaric surfaces beneath and above the surface of maximum wind. The real axis of the jet stream joins

Figure 4.

Analysis wind field in surface of maximum wind. Increment stream function 200 ft. Dotted lines represent some contours.

the points of steepest gradient. In Figure 4 a portion of the wind field in a surface maximum wind has been schematically drawn using data from~I-7.

of

REFERENCES

1958 - The layer of maximum wind. Journal of Meteorology, 15, Pp. 27-43.

I.

Reiter, E.R.,

2.

Bericht Uber die Vorbereitung des Dlisenluftverkehrs beim Zentralamt des Deutschen Wetterdienstes. Offenbach a.M. (1958).

3.

de Jong, H.M.,

1959 - Geostrophic flow. Med. en Verh., 74

(to be published).

105

NORWAY

TABLE OF CONTENTS

Page Introduction

It

Cl

•

D

Cl

•

Cl

Cl

Cl

Cl

Cl

It

..

Cl

0

Cl . . . Cl 0 at top and base of layer. Northern hemisphere flow. Vorticity < 0 at top and base. Southern hemisphere flow.

vo)

-Vb

- (-v) 0

Vc

Anti-flow at the base of the layer.

Vd

Anti-flow at the top of the layer.

ve

Vorticity zero at the base.

(-v l ) v

0

Vo

Here vc' Vd and v e are the correct thermal winds when the absolute vorticity differs in sign at the top and the base of the layer. Normally only one will fit the thickness pattern. In practice the thermal winds are worked out by an assistant on the assumption of constant vorticity with height. That is, simply the vector difference is taken. During the analysis of the thickness chart the forecaster will find winds in isolated areas, which seem to be inconsistent with the most likely thickness pattern. With some experience the analyst is nearly always able to determine from the lower and upper flow on chart B, which of the adjusted thermal winds vc' Vd or v e to select. In the case of Vd' anti-flow at the top of the layer, the station circle is marked on charts C and A. The kinematic Equator as the line where the temperature gradient suddenly reverses, is normally immediately apparent from the plotted thermal winds and the thickness values from radiosonde stations. When constructing the thickness pattern, a clear understanding is necessary of the errors introduced by the assumption (4.1) IVORI = constant, in equation (2.2). If this assumption is not fullfilled, that is, the value of absolute vorticity varies with height, the thermal winds computed with equation (4.1) are approximate only. One easily sees that the possible error will increase with decreasing differences of the wind direction at the lower and upper surface. Thermal winds derived from winds which differ by less than 30° are rather unreliable and must be used with reserve. Constant reference to chart B therefore is necessary to base the thickness pattern on the most representative thermal winds available in an area. Furthermore, the fact that for East and South African stations the thermal winds present wind shear between 700 and 500 mb instead of 900 to 500 mb for most other stations, must be borne in mind. With these precautions the construction of thickness pattern near and across the Equator is quite possible. In fact the thickness pattern and the thermal winds tend to show less variations and irregularities than the actual flow. To the final draft of the 1000-500mb thickness pattern the 1000 mb contours are added to obtain the first draft of the 500 mb

SUDAN

122

contours. This is done on a plastic overlay with a light coloured grease pencil. The overlay is then placed on top of chart A. On chart A, the following corrections are applied to the reported height values : (a)

Type of sonde. Values from Finnish sondes are corrected by - 20 metres at 500 mb level.

(b)

Corrections for differences in barometric standard in Lamy + 10 metres.1

(c)

Corrections for the diurnal pressure variation for OOOlz TEMPs. Here the height changes of the 1000 mb or 850 mb surface are added to the 500 mb height reports.

adja~ent

areas. (Fort

This last correction is clearly most important. The large diurnal pressure yariation in the tropics makes a direct use of non-simultaneous soundings practically impossible. Mainly for this reason uniform times for ascents in RA I are so desirable. The first draft of the contours on the overlay is adjusted to fit the corrected heights and the observed winds at 20,000· feet. As mean errors of radiosonde heights are of the same order of magnitude as the pressure gradient over wide areas, bias is normally towards the more numerous wind observations. The position of the kinematic Equator and areas of antiflow are copied from chart C onto A. The position of these zero lines of absolute vorticity must necessarily be the same on both charts. If on the final draft of the contour pattern, these lines must be shifted and adjusted, the thickness pattern should also be re-examined in that area. Finally the contour pattern obtained by differential analysis for Africa is linked with the OOOlz pattern obtained by direct analysis in Europe. Differential analysis on a routine basis has been carried out since April 1959 at Khartoum. The experience gained up to now suggests that contour analysis shows much more consistency than flow analysis. Due to the scanty upper-air information and reception difficulties, extrapolation over wide areas and long periodp is often necessary in Africa. As thickness gradients and thermal winds normally differ from pressure gradients and actual winds, the final contour pattern is defined in much larger areas than when using winds only for an always more or less subjective drawing of flow lines. Furthermore in areas of antiflow, even the most careful flow analysis must fail to present the general pressure and circulation pattern. Such areas are easily extended to form secondary closed circulations, which in this sense do not exist and certainly do not show in the pressure distribution.

5.

300 mb CONTOUR ANALYSIS

No correlation between 1000-500 mb and 500-300 mb thicknesses seemed to exist in the tropics. It is therefore necessary to build up the 300 mb level from the 500 mb contours. The same technique as outlined in section 4 above is used. The only differences introduced are corrections for dynamic heights. The equations (2.1) and (2.2) on which the analysis is based refer to dynamic pressure. With wind speeds below 50 knots the dynamic corrections are less than the inherent errors of radiosonde reports. At the 300 mb level higher speeds are quite possible and common. It is therefore advisable to correct heights of radiosonde stations if the reported wind speed is large. No corrections are necessary for thermal winds. It follows from equation (2.2) that the temperature gradient given by the thermal winds applies to dynamic temperature. That is, the thermal wind is related to the gradient of the mean (virtual) temperature between two dynamic surfaces.

6.

200 mb CONTOURS

200 mb contours are drawn up by the direct method. The 300 mb contours obtained by differential analysis serve as a guide. This chart as well as the 300 mb contours are again

SUDAN

123

composite charts combining the OOOlz reports from Europe with the 0600z observations in Africa. This is unfortunately necessary, as few services in Africa can afford for a variety of reasons to start radiosondes at OOOlz.

7.

PROGNOSIS OF UPPER-Am CHARTS

When forecasting upper-level contour charts for 24 hours the best results were obtained with forecasts of surface pressure and of the thickness pattern. Past tracks of 24 hourly surface pressure changes in conjunction with the current 500 mb contours (steering) were used for the prognostic surface pressure distribution. Two other methods which are less laborious must be used in practice due to the limited time and staff available. One is Defant's method, which north of 25° latitude gives often quick and useful results, except on occasions with standing waves, which are comparatively common between 20° and 30° North. The other method, which is the least time-consuming and least exact method, is displacing troughs and ridges together with their possible development by extrapolation. South of 20° latitude both methods can not be used. Here a slow displacement of pressure (height) centres seems to be the main feature. The interaction of moving troughs and ridges further polewards with a displacement of centres near the Equator can result in appreciable changes in the contour pattern on account of the small pressure gradients prevailing in the equatorial zone. For forecasts of the kinematic Equator and areas of anti-flow, the position on the current chart is used. They are only displaced whenever a marked change in curvature is likely to occur. Anti-flow is found to be rather stable and tends to persist over periods of 24 to 48 hours.

8.

FORECAST WINDS SUPPLIED TO AmCRAFT

Two sets of prognostic flow-charts are prepared daily and supplied to operators and crews. For north-bound flights 500 mb charts for the time interval 2l00z to 0600z are constructed covering the area from l5°N to 45°N. For south-bound flights prognostic charts for 700 mb and 500 mb are prepared for the area from 20 0 N to 05°S valid from 0300z to 0900z. These prognostic charts are based on forecasts of the contour charts but are drawn as fiow charts. This is necessary as the large variations of the pressure gradient corresponding to a given wind-speed on these charts are inclined to be misinterpreted by the users. From these charts mean sector winds are extracted, taking the latest available wind reports and the anticipated changes in the pressure gradient into account. Generally there is a tendency for an increase of the wind-speed at night. As only aircraft reports are available after midday for levels above 12-14,000 feet, this increase is difficult to check directly. Neverth~less this increase of approximately 50 per cent is normally taken into account when forecasting mean sector winds for flights by pressurized aircrafts between 2l00z and 0300z. Local variations of absolute vorticity will produce variations of the wind-speed for the same pressure gradient. Nevertheless for sectors 200-300 miles across, mean sector winds can be extracted from the contour charts with tolerable accuracy. The contour scale designed by Matthews ;-3 for this purpose is especially useful. Mean sector winds together with temperatures-are plotted for two flight levels along the track on the prognostic flow chart for documentation. No special method to forecast temperatures has been developed.

7

EXAMPLEB

Figure 1.

1000-500 mb thickness analysis for 20.3.59. With adjusted thermal winds.

Figure 2.

Unadjusted thermal winds for 20.3.59.

Figure 3.

500 mb contours for 20.3.59 with the position of the kinematic Equator and antiflow areas.

SUDAN

124

1.000-500 mb thickness analysis fo!' With adjusted thermal winds.

2O.~.1959.

Topographie relative de la couche 1.000-500 lIlb. le 20.).19591 (vents thermique corriges).

Thermal winds Vents thermiques ~

Southern hemisphere flow Flux de 1 'hemisphere Sud

G-'J Anti-flow Flux inverse _ . _ VOR = 0 Line Ligne de tourbillon nul HEIGHT At1SL ,

,

20000

FEET

MBS

,"

,,' Figure 1

1.000-500 mb thickness analysis for 20.3.59. With adjusted thermal winds.

SUDAN

125

NOTES

;0-'--

Thermal winds 20 .3.1959 1.000-500 mb thickness unadjusted Vents thermiques le 20 .3.1959, topographie ~elative de la cou~ che 1.000-500 mb, non corriges , . -------------

sf"'"'I""'--,t----t----------i-••

HEIGHT AMSl ..................... 16000

FEET

...........................

.MBS

·10'

Figure 2 Unadjusted thermal winds for 20.3.59.

126

SUDAN

Figure :; 500 mb contours for 20.3.59 with the position of the kinematic equator and anti-flow areas.

SUDAN

127

REFERENCES

1.

A. Grimes - Compendium of meteorology, Amer. Met. Soc., 1951.

2.

WMO Publication No. 67.RC.14. Ninth Session of the Executive Committee, Geneva, 1957. Abridged Report with Resolutions.

3.

L.S. Matthews - A direct reading geostrophic wind-scale. Met. Mag., Sept. 1956, 85, 1011.

4.

E. Kruger - Generalized gradient wind equation and upper-air contour analysis in the tropics. (In preparation).

129

UNION OF SOVIET SOCIALIST REPUBLICS

TABLE OF CONTENTS Page 1.

Numerical method of forecasting the absolute topography of isobaric surfaces •••••

131

2.

Construction of prognostic charts by the subjective method •••••••••••••••••••••••

132

2.1

Prognostic chart of surface pressure distribution ••••••••••••••••••••••••••••••••

132

2.2

Prognostic charts AT

132

References

Cl

••

00 0

0

Cl 0

0

0

0

0

0

0

0

700

Cl • • 0

0

, AT 0

Cl 0

•

SOO I)

0

and AT

000 000

0

0

300 •

0

0

••••••••••••••••••••••••••••••••••••••••• 0

0

0

0

0

0

0

•• 0

0

0

000 00 •

0

o ••• "

0

•

000 0

•

0

0

00

0

000 0

0

133

131

UNION OF SOVIEr SOCIALIST REPUBLICS

The USSR Hydrometeorological Service worked out numerical and subjective methods of forecasting the .pressure distribution at different levels which are used for providing meteorological services for civil aviation. 1.

NUMERICAL METHOD OF FORECASTING THE ABSOLUTE TOPOGRAPHY OF ISOBARIC SURFACES

A non-divergent geostrophic model of baroclinic atmosphere ~4-7 is used for twentyfour-hour forecasts. The basic equation for forecasting the geopotential of the isobaric surface is as follows : 2

c

dH

7,2 L1 at

where

d H) + nd (2' d' dt = 2

c' (

gL1H

-If. H, - l -

+ l)

-

g (

Cl

dH) H, J[

(1)

H = geopotential t

=

time p

'=p p

pressure

P

1000 mb

x,y

horizontal co-ordinates

1

=

Coriolis parameter

g

=

acceleration of gravity

2 C

= (Ya - Y) R2 1'1 , g

Ya = dry adiabatic lapse-rate

Y = lapse rate of temperature of the air Tl = mean temperature ~ = Laplace operator

~ db _ da db . (a, b) -- J (a , b) -_ dX dy dy dX For the boundary conditions, 2

d H d'dt

and'

,=

1 :

dH + a Jt =

0

The solution of this equation is :

g (" dH) H, ~ ,

-, T

(2)

132

UNION OF SOVIEI' SOCIALIST REPUBLICS

In this equation, Gi and G are Green's functions, the analytical expression of which will be found in publication No.~listed under References. Variations of the forecasting model were applied in the case of data selected for two levels rS 7, three levels 7, and four levels ~~. Under present operating conditions, prognostj[c ~harts for AT8S0,-AT~0 and AT are constructed. 3S0

r3

2.

CONSTRUCTION OF PROGNOSTIC CHARTS BY THE SUBJEx:TIVE METHOD

The Central Forecasting Institute constructs the following prognostic charts and transmits them by facsimile and also in coded form: Surface charts (12, 18, 24 and 36 hours), 700 mb (24 hours), SOO and 300 mb (12, 18 and 24 hours). The method adopted for their construction is set forth in the manual of short-range forecasting published by the Central Forecasting Institute of the Hydrometeorological Service of the USSR ~6-l7. 2.1

Prognostic chart of surface pressure distribution

When constructing prognostic charts of surface pressure distribution, the principle of a steering by a medium level of the troposphere (700 and SOO mb surface) is applied, together with the laws of the hydrodynamic theory of pressure variation (vorticity di~place­ ment and divergence influence~. Extrapolations of the trajectories are also made, and account is taken of the evolution of the pressure configuration, fronts and frontal areas, pressure tendenoies and variations in the geopotential of isobaric surfaces (isallohypses). 2.2

Prognostic charts AT700 , AT and AT SOO 300 Prognostic charts AT700 , ATSOO and AT300 are constructed as follows :

(a) The height of the 1000 mb surface is calculated at selected points on the basis of prognostic chart of surface pressure distribution; (b) At-each of the selected points, the forecast thickness of the layer between the 700 and 1000 mb, SOO and 1000 mb, and 300 and 1000 mb surfaces is determined. The prognostic values of the thickness 700 - 1000 mb layer are determined by displacement, at the selected points, according to the directions of the isohypses and the real wind speed given on the initial AT chart. The values calculated for this layer are then 700 corrected in accordance with changes in the directions of the isohypses resulting from the variations of the surface pressure distribution during the period of forecast. The corrections are usually carried out in areas Where, according to the prognostic surface chart, the greatest variations in pressure and in pressure gradients, in comparison with the initial chart, are expected to occur. The prognostic values of the thicknesses SOO - 1000 mb and 300 - 1000 mb are determined by displacement at the selected points according to the direction of the isolines of function worked out by Dr. N.r. Buleev ~4 and

g.

where H SOO ~HSOO

initial geopotential of the SOO mb surface

= Laplace

operator

()2 H60Q (

dX'

+ dd~

H 6OQ)

calculated according to the initial geopotential

of the SOO mb surface. m

non-dimensional coefficient, equal to 4.

UNION OF SOVIET SOCIALIST REPUBLICS

133

The calculation of the Laplace operator is based on four points situated 1000 km from the selected points. The B function in each case is equal to the arithmetic mean value for H500 for the four points at a distance of 1000 km.

This function varies less than the geopotential in relation to time. The displacement speed according to the B isolines is proportional to the density of these lines and may be determined by means of the same gradient scale as that used for calculating the gradient wind according to baric topography charts. (c) By adding respectively the values obtained for the thicknesses 700 - 1000 mb, 500 1000 mb, and 300 - 1000 mb to the geopotential of the 1000 mb surface, the forecast value for H700' H500 and H300 is obtained. , AT (d) When drawing the isolines on the AT and AT prognostic charts, the fore500 300 700 caster makes the necessary corrections and adjustments to take account of variations in the geopotential corresponding to variations in the mean temperature of the layer situated between the isobaric surfaces mentioned above and 1000 mb, such temperature variations being the result of vertical air movements, caused by the evolution of the pressure distribution (cyclones and anti-cyclones) on the weather prognostic charts in relation to the initial charts. REFERENCES

1.

Belousov, S.L., - Theoretical calculation of pressure at various atmospheric levels. Meteorology and Hydrology, 1957. No. 9.

2.

Buleev, N.I. and Mar~uk, G.I., - Dynamics of large-scale atmospheric processes. Work carried out by the Institute of Atmospheric Physics, 1958. No. 2.

3.

Du~kin,

4.

Kibel, I.A., - Introduction to hydrodynamic methods for use in short-range weather forecasting. State Technical Publishing House (Gostecizdat), Moscow, 1957.

5.

Ma~kovi~,

6.

Manual of short-range weather forecasting, Part 1. Hydrometeorological Publishing House.

P.K" Lomonosov, E.G. and Tatarovsajia,M.S., - Cyclone and anti-cyclone formation forecasting by means of computers. Meteorology and Hydrology, 1959. No. 6.

S.A., and Gromova L.G., - Some results of numerical forecasting of pressure distribution at sea level and in the middle troposphere. Work carried out by the Central Forecasting Institute. 86, 1959.

135

UNITED lITNGDOM OF GREAT BRITAIN AND NORTHERN IRELAND TABLE OF CONTENTS Page 1.

Introduction.

2.

Charts and construction procedures.o.oo ••

2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7

Charts for 000.1. 1200 GMT. 1000 mb chart .. 500 rob chart. 300 mb chart. 200 rob chart 400 mb 11

Maximum

wind

Aircraft

3.

Wind

500

III 11 0

11 11 11 • •

0

0

11 •

at

0

0 0

1800 GMT

and

11 •

11 •

isobaric

•

Cl Cl

e

Cl •

11 11 0

•

Cl 0

Cl 0

0

0

11 11_ 0

III 0

0

0

Cl

"

11 0

0

0

Cl Cl

200 mbo

Cl 11 0 11 0

0

• • 11 11.0 e

0

0 11 e

500 rob ·300 200

0 •

charts 0

0 0

Cl • • Cl 11 11 0 •

0

0

0

11

(I

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Cl •

Cl Cl Cl 0

Cl 0

•

Cl •

0

•

11

•••

• • 11 •

•

11

0

11:I

Cl 0

Cl

prontour

c h a r t . Cl 0 0

pront o u r

c h a r t 11 11 •

mb

prontour

chart. 0

Cl Cl 11 •

0

11 Cl 0 11 0 • 11 •

e Cl Cl 11 11 •

11 0

0

0 0

0 0

0

0

0

0

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0

0

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11 0

11 11 0

0

a

Cl Cl 0

ell Cl •

0

Cl •

0

11 0

e •

11 0 0

•

•••••• 0

•

0 0

11 • • 0

11 Cl

11 11 11 11 0

•

0

0

11

0

0

•

11 11 Q

Cl •

Cl Cl Cl •

Cl 0

11

11

•

11

••

••

11 •

•

11

11 0

•

11 0

11 11

11 11 11 • • • 11

11 11 11 0

0

(I

11 •

0

• • • 11

•.0

•• 0

11 •

0

0

11 11 11 11 11 11

e 0

0

•

Cl Cl Cl Cl e Cl

•

11 11

•

•

Cl •

Cl Cl •

11 Cl Cl Cl Cl Cl Cl •

Cl Cl Cl e Cl 11 11 11 11 0 11 0

0

11

11

Cl •

11 11 •

a

11

0

Cl Cl Cl Cl Cl Cl • • • e Cl 11 •

11 11 11 Cl 11 11 Cl to

0

11 •

0

0

e

0

11 •

11 0' •

11 •

e

0

11 Cl 0

O •• 0

Cl Cl Cl Cl 0

Cl 0

0

Cl 11 •

0

11 11 0

11 0

Cl. 0

11 Cl 11 11 11 •

11 0 • • 11 Cl 0 Cl 0 0

11 0

0

00 11 0

11 11 Cl 011 0

11 11 0

Cl 0

0

11 0

0

0