Hints to Northern Pilots

Citation preview

HINTS TO NORTHERN PILOTS k -J O . J4.v\ir.e£jf

CANTIS G~1

Ottawa, April, 1947

NUNC COCNOSCO EX PARTE

TRENT UNIVERSITY LIBRARY PRESENTED BY TREVOR LLOYD

HINTS TO NORTHERN PILOTS

CANTIS G-l Ottawa, April, 194?*

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This first edition of "HINTS" is provisional only, subject to modification in th8 light of experience.

Geographers and

airmen are invited to send criticisms and suggestions, through such authorized channels as may be necessary, to

Chief, I.S.T.S., Department of National Defence, Ottawa, Ont

Digitized by the Internet Archive in 2019 with funding from Kahle/Austin Foundation

https://archive.org/details/hintstonorthernpOOOOjenn

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1, In regions of low relief lakes are likely to be shallow and full of reefs* Mountain lakes are usually deep* but subject to sudden gusts and dangerous down drafts, especially where nearly bare rock descends to a lake at a steep angle. These downward gust3 occur most Mountain frequently on the afternoons of bright lakes sunny days, when the rocky cliffs around the lakes have become strongly heated, while the air masses high above remain at a relatively low temperature, 2, In August many .hikes at the heads of valleys shrink in sis© and even dry up, especially if their valleys are wide and Headwater open, A fair number of those lakes in southern Canada, e,g,, hake M&au&n in Quebec, have been dammed for storage, but in more northern regions very few. Generally speaking, therefore, northern pilots should avoid headwater lakes unless they have definite information of their safety, 3, The dates of freeze-up and break¬ up of any Xeke or river may vary from Freeze-up year to year by as much as a month, and Wherever possible, the mean date should Break-up be given, using the records of several years,

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4. A week averaging 29°F. or lower will start the formation of ice along the shores of lakes and rivers*» A lengthier period with temperatures between 29°F. and 32°F« will allow time for water of near freezing density to accumulate along the surface of a lake or sluggish river, after which freeze-up can occur with startling rapidity, often within 24 hours, if there is a severe drop in temperature. Broadly speaking, however, there is in most years an interval cf from two to four weeks between the time when the mean temperature of the air falls below 32°F0 and the freeze-up of adjacent lakes and rivers. In the spring rivers generally begin to break out from two to four weeks after the mean temperature of the air has risen above BE0]?. However, the break-up period is much more uncertain than the freezeup one, because it is more influenced by temperatures at the headwaters, which may be several hundred miles away. A long river coming from a region that has experienced early warmth may break out much earlier than one would expect from the temperatures nearer its mouth. After a mild winter and early spring in the Yukon, the Peel River has been known to break out before the Mackenzie, which it joins above the Arctic Circle, although the letter river heads much farther south.

3 A cold way© following an early warm period at the headwaters of a riyer may check the break-up process and create an ice jam lower down its course. Then the recurrence of very warm weather at the headwaters may send such a torrent downstream that it will overrun the ice and flood the country until, finally, all the ice breaks up and goes out„ 5» Lakes of a mile or less in diameter, being as a rule rather shallow and not greatly disturbed by winds, usually freeze over and break up about the same time as rivers in the vicinity» The larger and deeper lakes in the sa,me district, however, do not usually freeze over or break up until two or three weeks after the riverso Speaking generally, the summer season during which float planes can land on freshwater lanes and rivers, and on bays and Mr hours along the coast, decreases .Float-plane in length as one goes northward, or, season more accurately, northeastward, since the isotherms do not run parallel to the lines of latitude, but roughly from northwest to southeasto 60

Thus float planes can generally land on Lake Laberge, in the Yukon (61° 00s N„, 135° 15? tfo)s from the last week in May until midOctobero 100 miles farther north and ?0Q miles

4 east, in the lake district around Yellowknife (62° 28* N., 114° 20* W.) the season does not usually open before mid-June, though it ends about the same time in mid-October* In the same latitude ss Yellcwknife, but east of it another 800 miles, Yathkyed Lake (62° 45* N., S7° 32* W.) seems rarely open to float planes before tie end of June, and to freeze about the beginning of October. The Mackenzie River is open longer than one would expect from its latitude, because its largest tributary, the Liard, has sources in the west that encounter warm air masses from the North Tacific Ocean. It is open, indeed, longer than Great Slave Lake. On the other hand, many coastal bays are liable to obstruction at any time during the summer months by ice flees which drift in from the open sea. It should be noted that the float¬ plane season does not necessarily coincide with the season of open water. Wind, currents, or high salinity may prevent the formation of ice even though the air temperature remains con¬ sistently below the freezing point. Planes can then alight without trouble, but may be unable to take off again because of tie weight of the ice which forms on the pontoons, or of the spray which freezes on the ailerons. It is for this reason that float planes do not

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use the harbour of Go&thaab in Greenland during the winter, although it ha3 frozen only rarely during the last fifty years. 7. In a normal year all lakes on the mainland of Canada appear to be free of ice by the last week of July, or, at the very latest, the first week in August. But in the archipelago north of the mainland, and particularly north of Victoria Island, some lakes may retain their ice

ell summer. 8. Ice forms most slowly, and disappears earliest, where there is most movement in the water. The rapids of many rivers never freeze except at their banks. Sven in the Arctic Ocean lanes of water may persist all or nearly Hazards all winter off certain promontories, and of between certain islands, where there are thin ice strong currents. In general, therefore, pilots should avoid Ice landings off capes and promontories, in bays where rivers enter and flow out, and in narrow channels connecting larger bodies of water. Such places are likely to carry strong currents, and the ice covering them may be treacherously thin. In any case, pilots should not land in such places before mid-January, or after mid-March.

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9. Ice on the surface of lakes and rivers often, causes currents below it to change their courses. Hence, wherever currents or springs are known to occur in the vicinity of any ice landing-strip, it is advisable to check the ice from time to time during the winter* 10. Many factors affect the strength of ice, e.g., the salinity of the water, its movements, and the air temperature at the time of freezing. Ice formed at air temperatures of zero and below is stronger than ice farmed at temperatures near the freezing point. Lake ice is usually a little stronger than river ics, and both are nearly threes Strength times a3 strong, on the average, as ox ice sea ice, although old sea ice gains strength as it loses its salinity. Shore ice near the mouths of rivers, being less salty, is generally stronger than ice in the open sea; and ice under an air temperature of, let us say, -30°F» is stronger than ice at 10°F, Allowing for both the static weight of a plane and its impact at landing, the Russians have evolved the following formulae for calculating the minimum thickness of ice necessary for landing on skiss

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