Mesospheric Temperature Inversions Observed in OH and O2 Rotational Temperatures From Mount Abu (24.6°N, 72.8°E), India

Abstract

AbstractWe present a detailed investigation of upper mesospheric temperature inversions (MTIs) based on around 4.5 years of data of O2 and OH nightglow emission intensities (I(O2) and I (OH)) and temperature (T(O2) and T (OH)) corresponding to 94 and 87‐km altitudes. These measurements were carried out using Near‐Infrared Imaging Spectrograph from a low‐latitude location, Mount Abu (24.6°N, 72.8°E), in India. A total of 745 nights of Near‐Infrared Imaging Spectrograph observations is used, which showed the mean of T(O2) and T (OH) to be 199.6 and 203.0 K. However, there are nights that showed T(O2) greater than T (OH), which is considered as an indicator of upper MTIs. Among these nights, around 28% (209 out of 745) showed MTIs. It is found that 75% and 25% of MTIs occurred during premidnight and postmidnight hours. It was noted that maximum number of nights showed MTIs for a duration of around 4 hr followed by 3, 2, 5, and 6 hr. Investigation of causative mechanism for the upper MTIs revealed that although both wave dynamics and chemical heating by the exothermic reactions do work together, the in situ chemical heating process seems to be a more probable cause as compared to the vertical transport of energy from lower below. So far, such detailed statistics on MTIs does not exist in the published literature, and thus, the information presented in this work provides the necessary input for a greater understanding of the atmospheric temperature structure through modeling and simulation studies.