The recent focus in Mars research was in the area of the seasonal behavior of water in the atmosphere, surface, and polar caps, and exchange of water between these reservoirs. Results of recent work is summarized

Jakosky, Bruce M.

English

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THE BEHAVIOR OF WATER ON MARS 
NAGW-552 
PROGRESS REPORT 
25 MAR 1987 
BRUCE M. JAKOSKY 
LABORATORY FOR ATMOSPHERIC AND SPACE P H Y S I C S  
U N I V E R S I T Y  OF COLORADO, BOULDER, CO 80309-0392 
(NASA-CR-180249)  TEE E E f i A V I C E  CE WAITEf CN NE7- 193 24 
EARS €.zoqress 6egcrt (Colcraac Grriv-) b p 
CSCL 038 
Unclas 
63/91 43762 
https://ntrs.nasa.gov/search.jsp?R=19870009891 2020-03-20T11:29:46+00:00Z
Our recent focus in Mars research has been in the area of the seasonal 
behavior of water in the atmosphere, surface, and polar caps, and exchange of 
water between these reservoirs. Below, we summarize some of our recent 
results. 
We have analyzed the behavior of water in the atmosphere and on the 
surface in the vicinity of the Viking-2 lander on Mars, with an emphasis on 
understanding the stability of H,O and CO, frosts. The analysis consisted of 
examining surface and atmospheric temperatures measured by the Viking Infrared 
Thermal Mapping experiment in order to constrain the physical properties and 
processes in the vicinity of the lander site, followed by modeling of the 
sublimation rates of CO, and H,O frosts based on these properties. We show 
via an equilibrium surface energy balance calculation that C02 frost is not 
stable when frost is observed on the surface. We estimate the stability of 
H,O frost based on sublimation rates controlled by the surface temperature; 
water frost was stable during the period when frost was actually observed, but 
was not stable after the frost actually disappeared. Results on these 
calculations, estimates of the amount of water actually involved in exchange 
with the surface, and discussion of  the implications for the seasonal cycle of 
water in the atmosphere are contained in a paper by Hart and Jakosky (1986). 
The relationship between atmospheric water and ozone is an especially 
interesting one. Both species can play a role in impacting the seasonal 
weather patterns and current-epoch climate. Therefore, computer simulations 
of the behavior of ozone have been conducted. Photochemistry in the winter 
polar atmosphere of Mars has been examined for several latitudes, cloud types, 
and dust abundances. Computer simulation reproduces the ozone abundances 
observed by the Mariner 9 ultraviolet spectrometer experiment. Clouds change 
ozone abundances by only a few percent; however, typical dust abundances 
induce 10 to 30% increases in ozone abundances, primarily because 
photodissociation rates are drastically reduced by dust absorption. 
Furthermore, annual, latitudinal, and seasonal variations in dust opacity 
cause variations of 30% or greater in the ozone abundance. Results of these 
calculations have been reported in a paper submitted for publication by 
Li ndner (1987). 
Interactions between subsurface and atmospheric water play a major role 
Observations of the subsurface water in controlling the seasonal water cycle. 
abundance can constrain both the interactions between the surface and the 
atmosphere and the physical state of any near-surface water. The gamma-ray 
spectrometer on the upcoming Mars Observer spacecraft will contain a neutron 
spectrometer mode which will allow estimates of subsurface hydrogen to be 
made. 
water can be measured by such an investigation. 
We have done a preliminary study of the efficacy with which subsurface 
Results of these calculations 
have been reported in a paper submitted for publication by Drake et al. 
(1987). 
Our ongoing research is currently centered on two specific areas. First, 
a re-analysis of the radiance data obtained by the Viking atmospheric water 
detection experiment will provide updated information on the atmospheric water 
abundance. Second, physical modeling of the sublimation and transport of 
water from the summer residual north polar cap will constrain the physical 
processes which control the seasonal water cycle. 
The radiance data consist of measurements of the solar flux reflected 
from the martian surface in five channels, two of which are in continuum 
regions and three of which are in water vapor absorption bands. We are 
pursuing the goal of using the three band absorption measurements to derive 
simultaneously the column water vapor abundance as well as the effective 
temperature and pressure of line formation. Error analyses provide us with 
the information that we need in order to properly choose the data which can be 
averaged together to improve the signal-to-noise ratio enough to allow 
successful inversion. Additionally, the role o f  dust scattering and 
absorption must be taken into account at the level of accuracy desired. 
Finally, we are correcting problems in the earlier inversions of the MAWD data 
in terms of failing to correct properly for the variations of the solar flux 
with wavelength. The end result will be a better estimate o f  the abundance of 
water vapor in the martian atmosphere, an estimate o f  the vertical 
distribution of the water, and, perhaps most importantly, a better estimate of 
the uncertainties in the data inversion and analysis. Preliminary results 
have been reported by Hart and Jakosky (1987). 
Physical modeling of  the sublimation and transport of water from the 
vicinity o f  the north polar cap during northern hemisphere summer season on 
Mars is important in order to understand the processes which control the 
current seasonal cycles on Mars. Previous analysis suggests that water 
appears in the atmosphere over the north polar cap as the cap heats up during 
summer and is transported equatorward by the circulation o f  the atmosphere. 
We have used Viking IRTM measurements of the temperature of the cap to 
calculate the amount of water sublimed into the atmosphere, using previously 
described models of the sublimation process. For realistic estimates of the 
boundary layer properties, it is possible to sublime sufficient water to 
explain the global increase in atmospheric water content. Interestingly, i f  
the dark lanes or the circumpolar debris deposits contain water which is 
capable of subliming into the atmosphere, this source of water could dominate 
the polar behavior of water. Calculations of the transport equatorward of 
this polar water, using the two-dimensional, axisymmetric model developed by 
R. Haberle, cannot explain the apparent migration o f  water, however. This 
results due to the sluggish circulation in the polar region; once water can be 
moved to the region near 60" latitude, the cross-equatorial Hadley cell can 
move the water efficiently. Aspects o f  the seasonal cycle o f  water can be 
reproduced if the atmosphere contains a non-axisymmetric source of mixing; the 
only currently known mechanism f o r  such eddy mixing is the near-polar cyclonic 
motions suggested by spiral wave clouds seen at these seasons. Preliminary 
results of these investigations have been presented by Jakosky (1987) and 
Haberle and Jakosky (1987). 
REFERENCES 
Drake, D.M., W.C. Feldman, and B.M. Jakosky, Martian neutral albedo spectra, 
submitted for publication, 1987. 
Haberle, R.M. and B.M. Jakosky, Transport of water from the residual north 
polar cap on Mars (abstract), Lunar Planetary Science Conference, 1987. 
Hart, H.M. and B.M. Jakosky, Composition and stability o f  the condensate 
observed at the Viking Lander 2 site on Mars, Icarus, 66, 134-142, 1986. 
Hart, H.M. and B.M. Jakosky, Vertical distribution of water vapor in the 
atmosphere of Mars: Error analysis and preliminary results (abstract), 
Lunar P1 anetary Science Conference, 1987. 
Jakosky, B.M., Sublimination o f  water from the residual north polar cap on 
- Mars (abstract), Lunar Planetary Science Conference, 1987. 
Lindner, B.L., Ozone on Mars: The effects of clouds and airborne dust, 
submitted for publication, 1987. 


The behavior of water on Mars

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