Open AccessNonmigrating tides in the thermosphere of Mars
Author(s) -
Forbes Jeffrey M.,
Bridger Alison F. C.,
Bougher Stephen W.,
Hagan Maura E.,
Hollingsworth Jeffery L.,
Keating Gerald M.,
Murphy James
Publication year - 2002
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001je001582
Subject(s) - thermosphere , solstice , mars exploration program , atmospheric tide , atmospheric sciences , geology , longitude , martian , northern hemisphere , atmosphere of mars , geophysics , geodesy , ionosphere , physics , latitude , astrobiology
The vertical propagation of nonmigrating (i.e., longitude‐dependent or non–Sun‐synchronous) solar diurnal and semidiurnal tides into the thermosphere of Mars is investigated through numerical simulation. The waves are generated in the NASA Ames Mars general circulation model (MGCM) through solar radiative, topographic, and nonlinear processes using a comprehensive physics package and including a diurnal cycle. At an altitude near 70 km, zonal wave number decompositions of the diurnal and semidiurnal tidal fields are performed, and each wave component is extended from 70 to 250 km using a linear steady state global scale wave model for Mars (Mars GSWM). Conditions representative of aerocentric longitudes L s = 30 (near equinox) and L s = 270 (Southern Hemisphere summer solstice) are considered. Modeled total relative density variations of order ±10–40% near 125 km are analyzed in terms of the zonal wave numbers ( k s ) seen from the Sun‐synchronous perspective of the Mars Global Surveyor (MGS) accelerometer experiment, and yield reasonable agreement in amplitude and phase with the density measurements. The model indicates the two most important waves responsible for k s = 3 to be the eastward‐propagating diurnal and semidiurnal oscillations with zonal wave numbers s = 2 (∼15–40%) and s = 1 (∼8%), respectively. The eastward‐propagating diurnal component with s = 1 (∼15%) and the semidiurnal standing ( s = 0) oscillation (∼4–23%) are concluded to be the main contributors to the k s = 2 longitudinal density variation seen from the Mars Global Surveyor (MGS). The standing ( s = 0) diurnal oscillation (∼4–5%) and the westward‐propagating semidiurnal component with s = 1 (∼5–8%) emerge as the most likely contributors to k s = 1. Other waves that may make important secondary contributions include the westward‐propagating semidiurnal oscillations with s = 3 (∼4–6%) and s = 4 (∼3–9%). In addition, above 100 km the wind and temperature fields associated with the above waves represent ∼15–30% perturbations on the Sun‐synchronous wind and temperature fields driven in situ by EUV and near‐IR solar radiation absorption. Nonmigrating tides primarily arise from zonal asymmetries in wave forcing associated with Mars' topography; our results show for the first time that the dynamical effects of Mars' topography extend throughout the atmospheric column to Mars' exobase (∼200–250 km).