Determination of ice clouds and water vapor in Venus atmosphere from balloon observation

Strong, J. D.

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BALLOON TELESCOPE STUDIES OF VENUS
John Strong
Johns Hopkins University
Baltimore, Maryland
In this presentation I intend to review the work on
Venus carried out by the Johns Hopkins University
balloon astronomy group. This work has been reported
by Bottema et al. (1964a and 19641)).
My approach to the problem of Venus represents a
minority opinion about the interpretation of the available
data, the radio emission data in particular. I would like
to keep open the question of the origin of the radio emis-
S_lk.beeause I believe that it is not entirely surface
_ion but that some nonthermal process such as that
suggested by Tolbert and Straiton (1962) is active. How-
ever, before going into this question, I wish to describe
the evidence for the existence of ice-crystal clouds in the
upper Venusian atmosphere as obtained by our balloon
astronomy group.
I. Determination of Water Vapor in the
Atmosphere of Venus
Venus was observed with a 30-cm telescope suspended
from a balloon at an altitude that was above 99.9% of
the Earth's water vapor and 97% of the Earth's CO2. The
telescope was oriented with a Sun tracker and a star
tracker. Radiation was measured in the band at 1.13 t_,
with a grating spectrometer of 2 A resolving power. This
portion of the spectrum was scanned once every 10 see
with a set of 21 exit slits arrayed to match 21 H20
absorption line groups. The radiation passing through
was received by a chilled photomultiplier with S-1 sur-
face, and its response was recorded on paper.
From 120 such records we have determined that the
modulation produced by the water absorption, when
the line groups were scanned, was 1021 _ 0.5 %. By
calibration, this modulation is the same as that produced
by 9.8 × 10 -s grn/cm 2 of water vapor at atmospheric
pressure. We were also able to measure the influence of
the doppler shift on our recorded data. At one point in
each scan cycle a mercury-discharge spectral line at
11287 A was passed through one of the exit slits and was
recorded as a modulation in the reference-level spectrum.
Measurements from this fiducial line to the Venus water
dips, taken from 20 scans, exhibit a doppler shift of
0.49 _ 0.05 A, in agreement with a shift of 0.495 A
calculated from the orbital motions of Venus and the
Earth.
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https://ntrs.nasa.gov/search.jsp?R=19660022173 2020-03-16T20:42:16+00:00Z
VENUS
The pressure at the cloud level is poorly known but is
thought to range between 90 and 600 mb. The amounts
of water vapor calculated from our data for gravitational
atmospheres at these base pressures are:
22.2 x 10 -s gm/cm 2 for the 90-mb case
5.2 X 10-s gm/cm 2 for the 600-mb case
The respective mixing ratios would be 2.5 x 10 -4 and
0.87 × 10 -5.
II. Determination of the Existence of Ice Clouds
A second balloon experiment was carried out in
October 1964 with a low-dispersion grating, utilizing
three detectors in place of slits. The following scans were
carried out:
40 scans of the Venus spectrum
12 scans of the spectrum of adjacent sky
10 scans of a tungsten lamp
18 scans of the solar spectrum
The spectra, which covered a range from 1.7 to 3.4 /z,
were corrected for water vapor using the results of our
previous measurements to obtain an absorption spectrum
of water vapor above the cloud tops. The work of Kuiper
was used to correct for the CO,,. Our observed and cor-
rected spectra are indicated by the solid line in Fig. 1.
Also shown in Fig. 1 is the reflection spectrum of a
-39"C laboratory ice cloud. The agreement is excellent!
These corrections not only strengthen our inference
that the Venus clouds consist of ice but also confirm our
prior determination of the quantity of water vapor above
them.
The existence of water vapor and ice clouds allows an
explanation of one of the mysteries of the observations of
Venus: namely, that the temperature of the shady side
of the planet does not fall more than a few degrees
short of the temperature of the sunny side as measured
in the 8 to 14/_ band, even though the shady side has
several months to cool off. This is a circumstance that
model builders have been somewhat more complacent
about than we have. The failure to cool is due to the
-- GROSS REFLECTIVITY OF VENUS (I)"TF -- VENU CLOUD LAYER (2)
i • • • LABORATORY ICE CLOUD (3)
I 'TR'ANSMISSIONOr-I_ HIGH VE_NU_;A'FMOs_PHI_R_E_ ---r-_T "7
Ir_',,= -_.< ,, ---,, ........
'COz _ t
i COz t |
OI t i J * J * , I I i _. ./ i I L i L -t-- I
1.5 2.0 2.5 3.0 /
WWAVELENGTH, H-
Fig. 1. Reflection spectrum of Venus clouds, showing
correction for upper Venusian atmosphere. (From
the Journal of Geophysical Research)
liberation of latent heat of H=O vapor, of about 620 calo-
ries per gram, as that vapor condenses to form clouds.
Menzel and Whipple (1955) have pointed out in their
discussion of the atmosphere of Venus that the Schaefer
point is -39* C, the temperature below which saturated
water vapor cannot be cooled without spontaneous nu-
clearization and crystalization. This temperature is pre-
cisely the temperature assumed by many high-level
cumulus clouds on Earth. Menzel and Whipple calculate
13.0 X 10-3 gm/cm 2 of saturated water vapor above the
Venus clouds.
We interpret the work of Clark and Kuzmin on the
radio emission of Venus assuming that the measured
brightness temperature is due in part to surface emission
and in part to emission of the clouds. Our calculations
show that Tb would be reduced by 168"K and the aver-
age temperature would be 238* C.
In summary, it seems to us that Venus is becomin
more interesting planet now that the Mariner IV photo-
graphs have lessened the romance that Lowell had fas-
tened so securely on Mars. The data that are now coming
in must be criticized harshly, and modem methods
should be used to consider all possibilities, or we will not
be on time or even live to see the day when the mysteries
of Venus are resolved.
148
WRONG
REFERENCES
Bottema, M., Plummer, W., and Strong, J., 1964a, Asfrophys. J., VoL 139, No. 3.
• , , and Zander, R., 1964b, Astrophys. J., Vol. 140, No. 4.
Menzel, D. H., and Whipple, F. L., 1955, Publ. Astron. Soc. Pac/fic, Voh 67, p. 161.
Tolbert, C. W., and Straiton, A. W., 1962, J. Geophys. Res., Voh 67, p. 1741.
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Balloon telescope studies of Venus

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