Midlatitude Disturbances in the Martian Atmosphere: A Second Mars Year

Abstract

Viking Lander 2 meteorological data from the fall and winter seasons of a second Mars annual cycle have been subjected to time spectral and cross-spectral analysis, so as to determine important characteristics of the observed transient disturbances having periods longer than one Mars solar day (a Sol). Phase relationships between the highly coherent pressure, wind, and temperature oscillations are found to be very similar to those previously determined from first-year data, and thus consistent with those expected for eastward traveling, baroclinic waves centered to the north of the Lander 2 site. Wave-numbers (both zonal and meridional) and phase speeds also are estimated and are similar to those of the first year, though there is relatively less variance at low zonal wavenumbers (1.5–2.0) and the phase speeds are slightly larger. It is proposed that the reduced long wavelength disturbance amplitudes are a general consequence of a less dusty, second-year atmosphere characterized by lower static stabilities. Composites of the waves for two highly regular subperiods were constructed. No sharp frontal structures are apparent in these composites, though the pressure and temperature waves are distinctly asymmetric. Wavenumbers and phase speeds were also estimated from the composited wind and pressure data and agree very well with those obtained from the spectral analysis.