Science Briefs

Simulating Martian Weather with the GISS GCM

The Mars-adapted version of the NASA/GISS general circulation model (GCM) has been applied to the hourly/daily simulation of the planet's meteorology over several seasonal orbits. The current running version of the model includes a diurnal solar cycle, CO2 sublimation, and a mature parameterization of upper level wave drag with a vertical domain extending from the surface up to the 6µb level. The benchmark simulations provide a four-dimensional archive for the comparative evaluation of various schemes for the retrieval of winds from anticipated polar orbiter measurements of temperatures by the Pressure Modulator Infrared Radiometer (McCleese et al. 1992).

Sample frame from Quicktime video

A sample frame from an animation of modeled temperatures and wind vectors.
+ View Quicktime video (14 MB)

The accompanying Quicktime animation for the southern summer solstice season on Mars as displayed on this page represents a small sample of the animated time-lapse sequences of the simulated global Martian weather. The bright colors plotted over a brown-shaded surface feature map correspond to surface temperature contours as indicated by the horizontal bar scales graduated in 10K intervals. Arrows show the surface wind vectors scaled in relation to the 10m/s reference shown just above the color bars. The "areocentric longitude" Ls shown in the upper left corner of each map is the Mars seasonal index, progressing at a somewhat variable rate of approximately 0.5°/Mars solar day. The numbers plotted at the top of each chart mark the Local Mean Solar Time, at this season only 15min ahead of the Local True Solar Time (Allison 1997; see also "Time on Mars").

The diurnal solar tide is the single most obvious feature of the sequence, as indicated by the bightest red contours following the mid-afternoon meridian. Certain locations show an accompanying diurnal rotation of the surface wind vector, as in the Tantalus Fossae region to the north of the Tharsis ridge and the Thaumasia Fossae region to the south of the Solis Planum. Others exhibit instead a semi-steady flow structure, as in the sinuous core of thesurface westerly at 30°S latitude, apparently strongest in the GISS simulations between 100 and 200°W longitude, and in the region extending from Noachis west to the Nirgal Vallis. The meridional flow is variably northerly at almost every longitude just to the south of the equator, consistent with a rising branch of the Hadley circulation near the sub-solar latitude.

Also of interest is the steepening evolution at Ls = 272° of an apparent baroclinic wave in the northern (winter) hemisphere, as revealed by the slowly moving, comma-shaped green contour bordering the colder polar region just above 60°N latitude in the Utopia Planitia, at 260°W longitude in the final frame. The associated cyclonic vorticity of this feature is clearly indicated by the plotted wind vectors, as is the anticyclonic swirl to the southeast over the northern tip of Syrtis Major. Recently recorded images from the Mars Orbiter Camera on the Mars Global Surveyor spacecraft have revealed similar cloud structures near the planet's polar region.

Reference

McCleese, D.J. et al. 1992. Atmosphere and climate studies of Mars using the Mars Observer Pressure Modulator Infrared Radiometer. J. Geophys. Res. 97, 7735-7757.

Allison, M. 1997. Accurate analytic representations of solar time and seasons on Mars with applications to the Pathfinder/Surveyor missions. Geophys. Res. Lett. 24, 1967-1970.

Allison, M., J.D. Ross, and N. Solomon 1999. Mapping the Martian meteorology. In Fifth International Conference on Mars. LPI Contribution No. 972. Lunar and Planetary Institute. Houston.

Contact

Please address all inquiries about this research to Dr. Michael Allison.