Anomalous Dawn Enhancement of Atomic Oxygen in the Martian Upper Atmosphere During Type C Dust Storms

The Martian upper atmosphere exhibits prominent dawn–dusk asymmetries, traditionally characterized by dusk-side enhancements of atmospheric gases or ions driven by daytime solar heating and thermal expansion. Utilizing Neutral Gas and Ion Mass Spectrometer (NGIMS) measurements from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft spanning Martian Years (MY) 32 to 36, an anomalous inversion of this asymmetry in atomic oxygen (O) during the dusty season is observed. While heavier species like CO₂, N₂, and Ar exhibit typical dusk enhancements, atomic O shows significant dawn uplift during Type C dust storms. Analysis of Local Solar Time (LST) versus altitude profiles, multi-species asymmetry indices, and O/ CO₂ mixing ratios at altitudes of 180-220 km are performed. This abnormal dawn-uplift of atomic oxygen might be driven by altered day-to-night global circulation and gravity wave breaking induced by lower atmospheric dust heating, which dynamically sweeps lighter species toward the dawn terminator, overcoming the localized dusk thermal expansion. In addition, although there have been studies of diurnal variability in the Martian upper atmosphere in different seasons, there has been very less comprehensive study of its behaviour during the Type C dust storms which mainly occur during Ls 310-350, and are a great source of information on dust storm behaviours. In this paper, a highly unusual dynamic seen during the Type C dusty season of atomic oxygen (O) is documented that breaks the standard thermal paradigm and has exhibited a profound dawn enhancement, while heavier species like CO₂, N₂ and Ar maintained standard dusk enhancements. This unique observation suggests a mass-dependent dynamical forcing mechanism tied to dust activity, providing a new missing link in the understanding of Martian atmospheric circulation.