Atmospheric densities derived from measured acceleration of several Mars orbiters reveal large amplitude Sun‐synchronous longitudinal density variations at altitudes of about 100–160 km. These variations are associated with vertically‐propagating nonmigrating solar thermal tides that are excited near Mars' surface and propagate into the thermosphere. Excitation of these waves is associated with the zonally asymmetric component of the near‐surface heating distribution and is commonly attributed to topographic modulation of solar heating. However, there are other possible contributors to the excitation of nonmigrating tides, including zonal variations in surface properties and wave‐wave nonlinear interactions, whose relative contributions remain unexplored. In this study we use a general circulation model in combination with the Mars Global Surveyor accelerometer measurements to isolate the different waves responsible for the observed density structures. While it is evident that topography accounts for most of the waves' amplitudes, the surface thermal inertia and albedo are found to have a nonnegligible contribution to the eastward‐propagating diurnal tide with zonal wave number s = −1 and the standing s = 0 diurnal tide. Previous studies have reported the dominance of wave numbers 2 and 3 in the resulting Sun‐synchronous aerobraking density maps. We show that wave number 1 has a comparable amplitude and is mostly the result of mapping the diurnal standing wave into a near Sun‐synchronous orbit. While most of the nonmigrating tides at thermospheric altitudes are generated by an interaction between the migrating solar radiation and the dominant topography harmonics, we also find that wave‐wave interaction is necessary to explain some of the observed density features.

[1] In this paper, we globally characterize the solar terdiurnal tide in the 80-110 km region of Earth's atmosphere through analysis of 10 years of temperature measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics spacecraft. The Sun-synchronous ("migrating") component (TW3), which is longitude-independent and achieves maximum amplitudes of order of 5 K (10 K) at 90 km (110 km), not too different than the 7-15 K amplitudes that are typical of the migrating diurnal and semidiurnal tides in this region. Significant longitude variability ( 20-25%) in terdiurnal temperature amplitudes also exists, which is decomposed into zonal wave number components. The largest of these (TE1, TW4, and TW5) reveal distinct seasonal-latitudinal and height versus latitude patterns and interannual consistency. In addition, it is demonstrated that these particular components vary in ways that suggest that they originate from nonlinear interactions between diurnal and semidiurnal tides, specifically between DE3 and SW2 for TE1, between DW2 and SW2 for TW4, and between DW1 and SW4 for TW5. We also demonstrate that the terdiurnal tides derived here are not influenced to any significant degree by aliasing due to the presence of other waves.

[1] This study presents a new interpretation of Mars aerobraking density observations in terms of planetary wave-tide interactions. Mars Global Surveyor and Mars Reconnaissance Orbiter provide invaluable information about tidal activity in the lower thermosphere of Mars through the longitude structure that they reveal in near-Sunsynchronous frame of reference. However, this same perspective does not permit one to uncover the origins of day-to-day variability of these structures. Herein, by employing a new arrangement of the data and understanding the relationship between spectral features in longitude space versus UT space, we are able to attribute a significant amount of density variability in the aerobraking region to the effect of tidal modulation by planetary waves in the 5-20 day period range.

[1] A new global model for the Martian atmosphere with a vertical domain extending from the surface into the thermosphere (at about 160-180 km) is presented with some preliminary results. The model is a grid point model with a semi-Lagrangian semi-implicit dynamical scheme that is used for weather forecasting by the Meteorological Service of Canada. The physics includes a comprehensive radiative transfer scheme for heating, a boundary and surface layer parameterization. The design of the model allows for different grid configurations that include a globally uniform grid as well as the possibility of zooming over an area of interest with a locally uniform grid. The performance of the model is shown both in global uniform-resolution simulations as well as high-resolution simulations over the Tharsis Montes region. The simulated temperatures are compared with the Thermal Emission Spectrometer's measured profiles and the Mars Pathfinder entry data. Both the agreement with the data and the depiction of known features of the Martian atmosphere indicate that the Global Mars Multiscale Model has a good potential for modeling the atmosphere of Mars.

In this paper we employ Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry temperature measurements from 20 to 120 km and between about ±72° latitude to investigate several aspects of the quasi‐two‐day wave (QTDW) during the 2002–2011 decade, including interannual variability of its seasonal‐latitudinal structure, its penetration into the lower thermosphere, and various wave‐wave interactions. We focus on two components of the QTDW: the westward‐propagating component with zonal wave number s=3 (TDW3), and the eastward‐propagating component with s=−2 (TDE2). TDW3(TDE2) has maximum amplitudes during 2003, 2004, and 2011(2006 and 2011) and both waves have their lowest amplitudes during the deep solar minimum years of 2008–2009. TDW3 and to some degree TDE2 penetrate with significant amplitudes up to 120 km altitude, well into the region where neutral winds generate electric fields through the dynamo mechanism. A new “longitude subdivision method (LSM)” is presented that enhances temporal resolution of TDW3 and enables the determination of 9.6 h and 16 h waves that result from nonlinear interaction between TDW3 and/or TDE2 and diurnal migrating (DW1) and semidiurnal migrating (SW2) tides. Evidence is presented for westward‐propagating 9.6 h and 16 h waves with s=5 and s=4, respectively, and a zonally symmetric (s=0) 9.6 h wave. The s=5(s=0) wave only occurs as a result of nonlinear interaction between SW2 and TDW3(TDE2), whereas the s=4 wave can result from interaction of TDW3 with DW1 or of TDE2 with SW2. We payed special attention to possible aliasing between different waves.