Polar warming in the Mars thermosphere: Seasonal variations owing to changing insolation and dust distributions

Abstract

[1] Warming of the martian lower thermosphere (100-130 km) at north polar latitudes near the perihelion/winter solstice (Ls = 270) was recently observed. No analogous warming has been observed within the south polar thermosphere during its aphelion/winter season (Ls $ 90). Detailed global model simulations are required to investigate the physical processes driving these seasonal variations. New simulations are conducted for conditions approximating the atmosphere during these Mars Global Surveyor (MGS) and Odyssey (ODY) aerobraking periods. Strong northern winter polar warming features are calculated near 120 km, yielding nightside mean temperatures 10 -15 K warmer than observed ODY values. No southern winter polar warming trend is simulated; however, nightside mean temperatures are 20-30 K warmer than observed by MGS. The stronger interhemispheric circulation during northern winter is clearly driven by stronger insolation and dust heating near perihelion, resulting in subsidence and warmer temperatures in the northern polar night.

Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

“…There is no hydrostatic assumption in this model; thus, it can deal with large vertical velocities [Ridley et al, 2006;Deng et al, 2008]. It is noteworthy that the previous Mars Thermospheric General Circulation Model (M-TGCM) is based on the hydrostatic assumption [ Bougher et al, 2000Bougher et al, , 2006 and thus cannot deal with large vertical winds appropriately, especially when experiencing extreme events, such as interplanetary coronal mass ejections (ICMEs) and solar energetic particles (SEPs) heating.…”

“…Recently, Dong et al [2014] successfully employed a one-way coupling between the MF-MHD model and the 3-D M-TGCM model [Bougher et al, 2000[Bougher et al, , 2006 along with a 1-D spherically symmetric hot corona model [Kim et al, 1998] to study the effects of the 3-D cold neutral atmosphere on ion escape rates. However, Dong et al [2014] did not investigate the effects of varying inhomogeneous crustal field orientations and seasons on the Martian upper atmosphere ion loss.…”

Ion escape fluxes from Mars

“…We use photoionization rates which take into account optical depth effects. The one important change we made recently is that instead of assuming a spherically symmetric neutral atmosphere, we use the results of the appropriate density and ionization rate from the 3D neutral atmosphere model of Bougher et al [2000Bougher et al [ , 2006. This model predicts significant variations of the density and temperature with solar zenith angle, as well as solar cycle; the model is constrained by observations from MGS (Mars Global Surveyor), Mars Odyssey and MRO (Mars Reconnaissance Orbiter).…”

On Forcing the Winter Polar Warmings in the Martian Middle Atmosphere during Dust Storms

“…Recently, a warming in the Martian thermosphere (between 100 and 130 km) was detected in high latitudes near the winter solstices (Keating et al 2003;McCleese et al 2008). It was recognized that these phenomena in both the middle atmosphere and thermosphere are induced by adiabatic heating (e.g., Barnes and Haberle 1996;Wilson 1997;Bougher et al 2006;Medvedev and Hartogh 2007). They arise due to a convergence of the meridionally transported air, and the associated downwelling over winter polar regions.…”