Disentangling the dominant drivers of gravity wave variability in the Martian thermosphere

Abstract

In this study, we extracted the amplitudes of the gravity waves (GWs)from the neutral densities measured in situ by the neutral gas and ion mass spectrometer aboard the Mars atmosphere and volatile evolution mission. The spatial and temporal variabilities of the GWs show that solar activity (the F10.7 cm solar flux corrected for a heliocentric distance of 1.66 AU), solar insolation, and the lower atmospheric dust are the dominant drivers of the GW variability in the thermosphere. We developed a methodology in which a linear regression analysis has been used to disentangle the complex variabilities of the GWs. The three dominant drivers could account for most of the variability in the GW amplitudes. Variability caused by the sources of GWs and the effects of winds and the global circulation in the mesosphere and lower thermosphere are the other factors that could not be addressed. The results of the present study show that for every 100 sfu increase in the solar activity, the GW amplitudes in the thermosphere decrease by ~9%. Solar insolation drives the diurnal, seasonal and latitudinal variations of ~9%, ~4% and ~6%, respectively. Using the historical data of the dust opacity and solar activity, we estimated the GW amplitudes of the Martian thermosphere from MY 24 to MY 35. The GW amplitudes were significantly reduced during the maximum of solar cycle 23 and were highest in the solar minimum. The global dust storms of MY 25, 28, and 34 lead to significant enhancements in the GW amplitudes.