ANTARCTIC ATMOSPHERIC CIRCULATION 
sounding, on 12 July, gave —79.38C. At 15 km, the 
coldest value, —79.5C, was reached on 24 June in a 
sounding ending at 15,770 m, —82.1C, and was almost 
3C lower than the next coldest reading (on 12 July). 
At 14 km, the coldest reading, —82.1C, was reached on 
19 August; only one other August sounding reached 14 
km, finding —80.7C, a temperature colder than found 
at this level in any other month. 
Thus it seems that at 14 km and for an unknown 
distance above, winter temperatures must often be below 
—80C. Consequently, the absolute ranges of tempera- 
tures given in the diagram for each kilometer level are 
valid only up to about 13 km, where they attain the 
phenomenal value of 50.6C. They are misleading at 
higher levels: at 20 km, where the warmest temperature 
was —28.4C on 28 November, the lowest im late winter 
was probably colder than —100C, for an absolute range 
of more than 70C in three months. In the mid-tropo- 
sphere, however, the absolute range was only about 29C 
and the range between extreme monthly means is only 
some 15C, about 40 per cent of the greatest such range 
in North America, over Hudson Bay [131]. 
This wide variation of temperatures in the lower 
stratosphere, unparalleled in the Northern Hemisphere, 
is for a station not in the interior of Antarctica, but for 
one several hundred miles from the continent proper, at 
the very edge of the thick Ross Shelf Ice with open 
water four miles away In summer and not more than 
twenty or thirty miles distant in winter. Conditions 
over the continent can only be inferred from the Little 
America data, until soundings from the interior are 
actually available. And inference, with so many factors 
unknown, can be very misleading. 
For instance, Grimminger [49] deduced from the 969 
pilot balloon ascents of the first two Byrd expeditions 
that the tropopause was about 1 km higher in summer 
than in winter and averaged 7.7 km; his computation 
assumed that, with increasing latitude, troposphere 
temperatures decrease and stratosphere temperatures 
increase, as they do in middle latitudes. Later measure- 
ments, however, showed the tropopause lower in sum- 
mer than in winter, and about 2 km higher than the 
level of strongest winds, which was around 8 km in 1940 
as in 1928 and 1933. 
Summertime. Temperatures do decrease with lati- 
tude all the way to the Pole in winter, m both tropo- 
sphere and stratosphere, as Grimminger assumed. This 
is shown in the first meridional atmospheric cross sec- 
tion [60] to use winter data from high southern latitudes, 
those for Little America already discussed as well as one 
year’s values for Macquarie Island. But the swmmer 
diagram, for which in addition the Highjump data were 
used, is open to question: not only do stratosphere 
temperatures zimcrease continuously from Equator to 
Pole, as it shows, but im the troposphere it is more 
probable that the lowest temperatures in midsummer 
occur at about the margin of Antarctica, and that 
toward the interior temperatures actually increase 
again. 
Poleward increase of temperature in summer in the 
upper troposphere and in the stratosphere is indicated 
931 
by the downward progress of the springtime warming 
over Little America, from October at the upper limit of 
observation, in the mid-stratosphere, to December in 
the lower troposphere. The pattern is revealed clearly in 
the individual observations: at 4 km warming does not 
start until December, at 8 km (just below the tropo- 
pause) it occurs chiefly in November, at 12 km in late 
October and November, and at 16 km in October and 
early November. At 20 km the warming had already 
occurred by the time the lower layers became warm 
enough for a balloon to reach that height on 1 Novem- 
ber. The trend is shown even in monthly means (C): 
Height (km)| Aug. Sept. Oct. Nov. Dec. Jan 
20 ag roe oe —3l —33 —34 
16 as 79 65 37 38 37 
12 —74 —75 —69 —46 —43 —42 
8 — 64 —63 —62 —53 —49 —49 
4 —38 —38 —33 —32 —25 —25 
Obviously, advection cannot be the major cause of 
the stratospheric warming, since the temperatures be- 
come warmer than those at the same elevations farther 
north. The warming at 16 km of about 1C per day could 
be caused by subsidence of some 100 m per day, about 
one-third the rate of the downward progress of the start 
of the warming, which is around 2 km per week. How- 
ever, the most plausible explanation of the rapid warm- 
ing is that it is due chiefly to absorption of solar radia- 
tion: in the summer half-year, the duration of sunlight 
increases not only with latitude, but with elevation 
[130]. At 16 km over Little America, continuous sun- 
shine is received from 10 October onward, but at the 
surface it does not start until 20 October; at the South 
Pole, it starts about 10 September at 16 km, and about 
20 September at the surface. 
This downward progress of available solar energy 
can explain the apparent heating from above of the 
atmosphere over Little America, provided the energy is 
absorbed. Presumably, it is absorbed by ozone, which is 
known to exist in greater concentrations and at lower 
levels in the arctic atmosphere than in lower latitudes, 
and to have its maximum concentration in spring. No 
measurements of ozone concentration have been re- 
ported from Antarctica, but the atmospheric tempera- 
ture regime seems to indicate that it may be higher than 
in arctic regions. 
This explanation of the springtime warming over 
Little America implies that farther south, where con- 
tinuous sunshine begins earlier, the temperature rises 
sooner, and thus that in spring and up to the solstice 
the temperature increases poleward at all levels above 
the surface layer. Consequently, any diagram of sum- 
mer temperatures over Antarctica, such as those of 
Loewe and Radok [60] and Flohn [91], should show the 
—50C isotherm as sloping downward from lower lati- 
tudes to about 60° or 70°S, then bending upward verti- 
cally; likewise the —40C isotherm probably does not 
reach the pole, but bends upward similarly around 
85°S. At lower levels, the warmer isotherms extrapo- 
lated poleward from Little America (78°30’S) should 
