Martian Climate Variability: Multi-Year, In-Situ Observation & Requirements

J. E. Tillman, (Dept. of Atmospheric Sciences, Box 351640 University of Washington, Seattle, Wa., 98195-1640, USA), Ari-Matti Harri, (Finnish Meteorology Institute, Dept. of Geophysics, Vuorikatu 15, P.O. Box 503, FIN-00101 Helsinki, Finland), Søren E. Larsen}, (Meteorology Dept., Risø, Danish National Laboratory, Postbox 49, DK-4000, Roskilde, Denmark)

Multi-Year meteorological observations at the same site on the surface of Mars are necessary to define the ``Martian Climate'', understand atmosphere - surface interactions and interpret orbital observations. Weather conditions will also have a significant impact on spacecraft design and operations, especially to guarantee safe landings. Prior to the Viking Lander Meteorology Experiments 3.3 Mars years observations at the Lander 1, 22° N site and 1.5 years at the 48° Lander 2 site, it was thought that Mars had ``great'' dust storms each year at perihelion. However, from atmospheric pressure measurements alone, Tillman, 1988, demonstrated that the first 1.5 years strongly suggest that this is not the case, the third year at Lander 1 confirmed it, while the fourth year produced an intense dust storm, differing in timing from the intense 1977 B storm.

Figure 1 illustrates hourly average minimum, mean, and maximum atmospheric temperature at 1.5 meters, and the sol standard deviation of the pressure. During this first Viking year, transient normal modes are observed, along with the 1977 A and 1977 B great dust storms. By comparing all available VL-1 pressure data and these unpublished temperature data during the 3.3 Mars years, we will describe inter annual differences during dust storm seasons and show that the daily average temperature is a poor indicator of major changes in solar insolation; this may be important in looking for signatures of terrestrial climate changes. We demonstrate the necessity of permanent, (e.g., > 5 Mars year), observations, preferably at the VL-1, "climate" site, to describe the dramatic inter annual variations and to help distinguish orbital spatial from temporal variations.