Nonmigrating tides in the thermosphere of Mars: a quasi-empirical description

A methodology is proposed for using sparsely-distributed data to calibrate physics-based tidal functions, that can then be used to reconstruct global wind, temperature and density patterns associated with diurnal and semidiurnal tides throughout Mars' upper atmosphere (i.e., 25-200 km). The functions, called Hough Mode Extensions, maintain self-consistent internal relationships between winds, densities and temperatures, and account for changes in vertical and latitudinal shape within the dissipative thermosphere. In the present work, total mass densities from the Mars Global Surveyor accelerometer experiment during Phases I and II of aerobraking are separated into zonal wavenumber components (k(s)) viewed from the satellite reference frame. Fits are performed to two of the wavenumber components to illustrate how the technique works, and to provide insight into its potential for analysing more comprehensive datasets anticipated for the future. Results indicate Phase-11 wind and temperature amplitudes for the eastward-propagating diurnal tide with s = -1(k(s) = 2) to be of order 10-40 ms(-1) (eastward) and 2-10 K, maximizing in the equatorial region above 120 km. Similar values are found for the westward-propagating semidiurnal tide with s = 1 (k(s) = 1) during Phase I at polar latitudes, a wave that is identified for the first time in MGS aerobraking data. This is the same oscillation that appears prominently in the terrestrial lower thermosphere over south pole, and is thought to be excited by nonlinear interaction between the terrestrial migrating semidiurnal tide and the stationary planetary wave with s = 1. The above wind and temperature estimates must be viewed as preliminary, however, as more data are required to more definitively constrain the fits. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.