Nitric Oxide Abundance in the Martian Thermosphere and Its Diurnal Variation

Abstract

AbstractAs an important species of the Martian thermosphere, NO is chemically and radiatively active. However, its abundance is poorly constrained due to difficulties in both remote sensing and in situ measurements. In this study, we use the Neutral Gas and Ion Mass Spectrometer measurements made onboard the Mars Atmosphere and Volatile Evolution to derive the N(4S), N(2D), and NO abundances in the Martian thermosphere based on time‐dependent odd N chemistry. At a reference altitude of 160 km, our calculations suggest that the NO abundance is maximized in the afternoon whereas the N(4S) and N(2D) abundances maximized in the morning, both driven by the variation of the ambient N2 mixing ratio. The difference in chemical loss time scale implies a strong diurnal variation for NO and N(2D) but a weak variation for N(4S).