e
weather, and therefore do not show the features of the actual south
polar climate.

During the three years of the "Fram's" drift depressions passed on all
sides of her, with a preponderance on the west. The direction of
progression averaged nearly due east, and the hourly velocity 27 to 34
m., which is about that in the United States. For the higher latitudes,
most of the cyclones must pass by on the equatorial side of the
observer, giving "backing" winds in the northern hemisphere. The main
cyclonic tracks are such that the wind characteristically backs in
Iceland, and still more so in Jan Mayen and on the eastern coast of
Greenland, these districts lying on the north and west of the path of
progression. Frightful winter storms occasionally occur along the east
coast of Greenland and off Spitzbergen.

For much of the year in the polar zones the diurnal control is weak or
absent. The successive spells of stormy or of fine weather are wholly
cyclonically controlled. Extraordinary records of storm and gale have
been brought back from the far south and the far north. Wind direction
and temperature vary in relation to the position of the cyclone. During
the long dreary winter night the temperature falls to very low readings.
Snowstorms and gales alternate at irregular short intervals with calmer
spells of more extreme cold and clearer skies. The periods of greatest
cold in winter are calm. A wind from any direction will bring a rise in
temperature. This probably results from the fact that the cold is the
result of local radiation, and a wind interferes with these conditions
by importing higher temperatures, or by mixing upper and lower strata.
During the long summer days the temperature rises well above the winter
mean, and under favourable conditions certain phenomena, such as the
diurnal variation in wind velocity, for example, give evidence of the
diurnal control. But the irregular cyclonic weather changes continue, in
a modified form. There is no really warm season. Snow still falls
frequently. The summer is essentially only a modified winter, especially
in the Antarctic. In summer clear spells are relatively warm, and winds
bring lower temperatures. In spite of its lack of high temperatures,
the northern polar summer, near the margins of the zone, has many
attractive qualities in its clean, pure, crisp, dry air, free from dust
and impurities; its strong insolation; its slight precipitation.

_Twilight and Optical