Evidence of baroclinic waves in the upper atmosphere of Mars using the Mars Global Surveyor accelerometer data

Abstract

Here we use accelerometer data of 115 orbits (#P0670–P0789) from 1–30 November 1998, between latitude ranges (50–70°N), and of 57 orbits (#P0588–P0648) from 30 September 1998 to 24 October 1998, between latitude ranges (50–70°N), both under spring equinox and medium solar activity conditions. The neutral densities of different gases are derived from their mixing ratio. From these neutral densities, the longitudinal distribution of total peak ionization rates of CO2+, N2+, O2+, O+, and CO+ are obtained for solar zenith angle 78° because of solar EUV and soft X‐ray (1–102.57 nm) radiation using Analytical Yield Spectrum approach. These calculations are made at different altitudes and longitudes starting from 115 to 220 km and from 0 to 360°E using intervals of 0.1 km and 5°, respectively. These conditions are appropriate for Mars Global Surveyor Phase 2 aerobraking period from which the accelerometer data is used. The Fourier analysis is carried out on the calculated total peak ionization rates for different gases both at midlatitude (17–42°N) and high‐latitude (50–70°N) range in the upper atmosphere of Mars. This analysis at high latitude indicates the presence of two dominant harmonic regions, in which the first is a class of long planetary‐scale waves, associated with the fixed topography of Martian surface, while the second is a class of rapidly moving transient disturbances associated with baroclinic instability processes. The similar analysis carried out at midlatitude (17–42°N) region indicates the absence of second peak at higher wave number, confirming that the baroclinic instability is almost absent at this latitude region.