MARTIAN WEATHER CORRELATION LENGTH SCALES

Spring and fall equinox Viking infrared thermal mapper 15-mu m channel atmospheric brightness temperature (T15) observations are used to est imate the weather correlation length scale of Mars in the pressure ran ge 0.5-1 mbar. The results provide a better understanding of martian a tmospheric dynamics, a benchmark for validating martian general circul ation models (GCMs), a guide to the optimal placement of a network of landers, and information for use in data assimilation efforts for orbi ters and landers. Observations of atmospheric temperature are used to compute an atmospheric mean state as a function of time-of-day, latitu de, longitude, and altitude, which is then subtracted from the observa tions to yield weather temperature residuals. These residuals are corr elated with each other to determine (1) the weather temperature correl ation length scale (similar to 1000 km) as a function of latitude and (2) the weather temperature variance (similar to 4 K-2 global average for L(s) similar to 0 degrees, similar to 3 K-2 for L(s) similar to 18 0 degrees). Good general agreement is found in comparing the length sc ales to the Rossby radius of deformation and to inferences made from o ther data sets. The weather temperature variance results are also comp ared with GCM results, yielding satisfactory agreement, with some diff erences in the magnitudes of the variances. (C) 1996 Academic Press, I nc.