THE ATMOSPHERES OF THE OTHER PLANETS 
If the cyclonic shear in the dark belts and the anti- 
cyclonic shear in the light zones are permanent features, 
it is possible to speculate further. In that case, the 
bright zones would be high-pressure regions; further- 
more, due to lateral friction, they would be regions of 
horizontal divergence. Since we are looking at a high 
level in the atmosphere, regions of divergence would be 
regions of upward vertical motion. It is then possible 
to explain the light color of these zones by the ammonia 
erystals formed in rising currents. 
Jupiter is observable for about eight out of every 
thirteen months. In the remaining five months it is 
too near the sun. For each of these eight-month periods, 
average speeds of the different currents are available. 
Usually, the periods in these different observing “sea- 
sons” are based on different markings, and represent 
averages over a number of spots; variations from year 
to year may not be due to real variations of the cur- 
rents but to more or less random variation between 
spots, since the difference of the periods of individual 
spots in given currents is usually much larger than the 
change of the average speed from “‘season”’ to ‘‘season.” 
Occasionally variations in speed of as much as 10 m 
sec! occur from one season to the next, especially in 
the south equatorial current. These jumps affect all 
visible spots and are certainly not statistical accidents. 
Also, gradual changes which are real occur over periods 
of the order of 40 years. 
Whatever the physical nature of the Red Spot, the 
variations of its speed of rotation from year to year are 
certainly real. The period of rotation has varied from 
9 hr 55 min 33 sec to 9 hr 55 min 42 sec, with changes 
from year to year never exceeding 3 sec (1 m sec~). 
Two different, but not independent, methods showed 
correlations of 0.61 and 0.62, respectively, between the 
speed of the Red Spot and the speed of the surface 
westerlies on Harth at moderate north latitudes, based 
on 37 pairs of observations [6]. Little is known concern- 
ing the significance of correlation coefficients between 
time series. Perhaps a correlation of this type might be 
accounted for if variations in the radiation from the 
sun would affect the intensities of circulation both on 
Jupiter and on Earth. Several objections may be raised 
against such a hypothesis. The distance of Jupiter from 
the sun varies by 10 per cent during its orbital period 
of 12 years. Yet there is no correlation between the 
period of the Red Spot and the distance of Jupiter from 
the sun. This means that changes of total radiation of 
20 per cent have no effect on the general circulation of 
Jupiter. The possibility remains that the ultraviolet 
radiation of the sun may vary by 100 per cent or more, 
and this large change may produce variations of the 
speed of air currents both on Jupiter and on Earth. 
Another objection against the reality of the correla- 
tion is the fact that there is a negligible correlation 
between Red-Spot period and easterly index on Earth. 
It is hard to see why the Red Spot, which is located in 
the south tropical regions of Jupiter, should exhibit 
variations in motion similar to those in moderate ter- 
restrial latitudes in the Northern Hemisphere. 
Little information is available concerning the general 
397 
circulation of the other major planets. The few spots 
observed on Saturn indicate the shortest periods near 
the equator with a gradual increase toward higher 
latitudes. The distribution of rotational velocities deter- 
mined spectroscopically agrees with this picture [5]. 
Suggestions for Future Work 
For Venus the outstanding meteorological problems 
are (1) determination of the nature of the variable light 
and dark bands observed in the ultraviolet, and (2) 
determination of the cause of the variability of the 
emission from the planet’s CO, at 10 u. These two phe- 
nomena may well be related, and a concerted attack 
should be planned, involving simultaneous observations 
with the spectrograph, the ultraviolet camera, and the 
radiometer. Once such basic data have been gathered, 
further interpretation may prove possible. 
For Mars one would most like to see a verification 
and extension of the work on the temperature field and 
general circulation. This could best be done at the good 
oppositions coming in 1954, 1956, and 1958. It would 
require a coordinated program of radiometric observa- 
tions of the temperature distribution combined with 
careful visual and photographic determination of the 
drift of clouds. This is an observing program of con- 
siderable magnitude, but is worth while in view of the 
basic nature of the result to be derived. We also need 
further observations of such fundamental quantities 
as the atmospheric pressure, the amount of water vapor, 
the height and composition of the blue haze layer, and 
the value of the nocturnal temperatures. 
Additional information concerning Jupiter can be 
obtained from a study of the latitudinal variation of 
ammonia and methane absorption. If ammonia is satu- 
rated near the cloud surfaces, such a study should 
indicate the latitudinal variation of temperature and of 
cloud level. Studies of limb darkening in the zones and 
belts have so far been carried out without consideration 
of the extremely important selective absorption of meth- 
ane and ammonia. Careful investigations of this type 
are necessary to determine the relative optical depths 
of light and dark areas. Finally, the correlation between 
the motion of the Red Spot and the zonal index on the 
Earth should be verified on observations since 1939, 
since standard tests of significance of correlation coef- 
ficients do not apply here. 
For Saturn, similar investigations might be suggested, 
especially as far as the evaluation of the limb darkening 
is concerned. 
REFERENCES 
1. Huss, S. L., “A Meteorological Approach to the Question 
of Water Vapor on Mars and the Mass of the Martian At- 
mosphere.” Publ. astr. Soc. Pacif., 60: 289-302 (1948). 
2. —— ‘Some Aspects of the Meteorology of Mars.” J. 
Meteor., 7: 1-13 (1950). 
3. Kurppr, G.P.,ed., The Atmospheres of the Earth and Plan- 
ets. Chicago, University of Chicago Press, 1949. 
4. Lampranp, C. O., ‘‘On the Observable Radiation from the 
Carbon Dioxide in the Atmosphere of Venus.” Astrophys. 
J., 93: 401-402 (1941). 
