uting the
"circumpolar whirl," which are so well developed over the southern
portions of the southern hemisphere oceans, blow all the way home to the
South Pole. The steep poleward pressure gradients of these southern
oceans end in a trough of low pressure, girdling the earth at about the
Antarctic circle. From here the pressure increases again towards the
South Pole, where a permanent inner polar anticyclonic area is found,
with outflowing winds deflected by the earth's rotation into easterly
and south-easterly directions. These easterly winds have been observed
by the recent expeditions which have penetrated far enough south to
cross the low-pressure trough. The limits between the prevailing
westerlies and the outflowing winds from the pole ("easterlies") vary
with the longitude and migrate with the seasons. The change in passing
from one wind system to the other is easily observed. This south polar
anticyclone, with its surrounding low-pressure girdle, migrates with the
season, the centre apparently shifting polewards in summer and towards
the eastern hemisphere in winter. The outflowing winds from the polar
anticyclones sweep down across the inland ice. Under certain topographic
conditions, descending across mountain ranges, as in the case of the
Admiralty Range in Victoria Land, these winds may develop high velocity
and take on typical _fohn_ characteristics, raising the temperature to
an unusually high degree. _Fohn_ winds are also known on both coasts of
Greenland, when a passing cyclonic depression draws the air down from
the icy interior. These Greenland _fohn_ winds are important climatic
elements, for they blow down warm and dry, raising the temperature even
30 deg. or 40 deg. above the winter mean, and melting the snow.

In the Arctic area the wind systems are less clearly defined and the
pressure distribution is much less regular, on account of the irregular
distribution of land and water. The isobaric charts published in the
report of the Nansen expedition show that the North Atlantic
low-pressure area is more or less well developed in all months. Except
in June, when it lies over southern Greenland, this tongue-shaped trough
of low pressure lies in Davis strait, to the south-west or west of
Iceland, and over the Norwegian Sea. In winter it greatly extends its
limits farther east into the inner Arctic Ocean, to the north of Russia
and Siberia. The Pacific minimum of pressure is found south of Bering
Strait