THE ATMOSPHERES OF THE OTHER PLANETS 
this basis the data of Table II indicate somewhat lower 
wind velocities than on Harth. This is consistent with 
the results of observation of the motion of clouds on 
Mars, which also indicate relatively low wind-speeds. 
Tasie II. Mean VALUES oF THE VERTICAL WIND-SHEAR ON 
Mars ComMpureD FROM THE Data or Fia. 1 
Latitude 0U/dz (msec km™) 
15° N-50°N 4.0 
15°S-47°S 0.8 
47°S-78°S 1.6 
The last value in Table II, however, is appreciably 
larger than the corresponding value on Harth. Never- 
theless, this does not mean higher wind-speeds than on 
Earth, because this value is from the most poleward 
zone considered in the summer hemisphere, and the 
temperature at the southernmost boundary (lat. 78°S) 
393 
part to force the pattern into a familiar shape. An 
examination of the winds will show that the broader as- 
pects of this map could not be altered very much by 
another independent analysis. The existence of a more 
or less broad belt of westerlies in both hemispheres is 
clearly indicated, and there are observations to support 
the drawing of a pair of subtropical high-pressure belts 
which are broken up into individual cells. The pairs of 
winds which form the basis of the two cyclonic storms 
indicated in the Southern Hemisphere are synchronous 
in one case, and in the other case were observed on 
successive nights. Thus there is no way of avoiding an 
analysis which involves sharp cyclonic shears, that is, 
fronts, without ignoring the data. 
The cyclonic circulation at lat. 35°S, long. 345° is 
indicated by an easterly cloud drift in a latitude where 
one would expect to find west winds. But this is the same 
region in which the temperature distribution indicated 
an abnormally warm spot. It is probable that we have 
fo) 
IB 
esa) cae ae 
\~ 
ZI 221) If ees 15 2977 28 W 
UV —-19: 
— 24717Q 3573036Q 72: 
5 ie A = 
20 
ee eS 
Bae 
-30 
2 li As 2033 44—- 40 
-50 Cc 
—s 
90 120 150 180 210 240 270 300 330 360 30 
Fie. 1—The distribution of temperature (°C) on Mars in Northern Hemisphere winter. This is the normal telescopic 
view with south at the top. To obtain the usual meteorological view, merely invert the page. The observations marked “Q”’ 
are questionable either because they are interpolated values or because of the presence of clouds. A fifth row of data 
at 78°S was available for the analysis but does not appear on this projection. Taken from [2]. 
is probably influenced by the proximity of Mars’ polar 
icecap. This depresses the temperature at the surface 
and makes the gradient seem quite high. If one could 
measure the temperature at, let us say, one kilometer 
above the surface, the effect of the polar ice would be 
diminished and the north-south temperature gradient 
reduced. This is to say that more stable lapse rates pre- 
dominate near the icecap than elsewhere, a common 
situation on Harth. 
Figure 2 is a streamline map for Mars drawn in a 
fashion as consistent as possible with the temperature 
distribution of Fig. 1, eighteen wind directions deduced 
from the observed drift of clouds, and general mete- 
orological principles. While these did not suffice to 
define the flow pattern uniquely, the amount of imagi- 
nation required was quite small. 
The most striking aspect of Fig. 2 is its marked re- 
semblance to terrestrial weather maps. Mars has an 
atmospheric circulation very similar to Harth’s. This is by 
no means due solely to a tendency on the analyst’s 
here an example of a “heat low.” This is all the more 
remarkable because the two pieces of evidence are a 
cloud-drift direction observed in 1894 and a temperature 
field determined in 1926. This persistence points to a 
local peculiarity of the surface which is conducive to 
high summer temperatures and the formation of a heat 
low. Examination of a map of the normal surface mark- 
ings of Mars reveals no visible feature that can explain 
this phenomenon, but there is a large dark area which 
forms seasonally in this region. It is present in Southern 
Hemisphere summer (when these measurements were 
made) and disappears in winter. It would be valuable 
to obtain radiometric measures of this area at other 
Martian seasons to see if the high temperatures vanish 
with the dark coloration. 
Despite these similarities the circulation on Mars 
differs in important respects from that on Harth. Fac- 
tors contributing to such differentiation are: (1) the 
absence of oceans and sharp mountain ranges, (2) the 
lesser water-vapor content, and (3) the longer year on 
