Martian Weather Correlation Length Scales

Abstract

Spring and fall equinox Viking infrared thermal mapper 15-μm channel atmospheric brightness temperature (T15) observations are used to estimate the weather correlation length scale of Mars in the pressure range 0.5–1 mbar. The results provide a better understanding of martian atmospheric dynamics, a benchmark for validating martian general circulation models (GCMs), a guide to the optimal placement of a network of landers, and information for use in data assimilation efforts for orbiters and landers. Observations of atmospheric temperature are used to compute an atmospheric mean state as a function of time-of-day, latitude, longitude, and altitude, which is then subtracted from the observations to yield weather temperature residuals. These residuals are correlated with each other to determine (1) the weather temperature correlation length scale (∼1000 km) as a function of latitude and (2) the weather temperature variance (∼4 K^2 global average for L_S∼ 0°, ∼3 K^2 for L_S ∼ 180°). Good general agreement is found in comparing the length scales to the Rossby radius of deformation and to inferences made from other data sets. The weather temperature variance results are also compared with GCM results, yielding satisfactory agreement, with some differences in the magnitudes of the variances.