Mesospheric Temperature Inversions Observed in OH and O-2 Rotational Temperatures From Mount Abu (24.6 degrees N, 72.8 degrees E), India

摘要

We present a detailed investigation of upper mesospheric temperature inversions (MTIs) based on around 4.5years of data of O-2 and OH nightglow emission intensities (I(O-2) and I (OH)) and temperature (T(O-2) 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 degrees N, 72.8 degrees E), in India. A total of 745 nights of Near-Infrared Imaging Spectrograph observations is used, which showed the mean of T(O-2) and T (OH) to be 199.6 and 203.0 K. However, there are nights that showed T(O-2) 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 4hr followed by 3, 2, 5, and 6hr. 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. Plain Language Summary Earth's mesosphere lower thermosphere (MLT) region (60-110 km) is very dynamic and least explored region. It responds to forcing from above due to solar influences and from below due to various upward propagating waves that are generated in the troposphere. Understanding the vertical coupling of the atmosphere under varying geophysical conditions is an emerging field of research. One of the methods to investigate dynamics of the MLT region is by measuring nightglow emission intensities and temperatures corresponding to the different airglow emission altitudes. We have investigated upper mesospheric temperature inversions (MTIs) that are the narrow thermal layers showing an inversion in the vertical temperature gradient from negative to positive. This work is possible due to around 4.5 years of high cadence ground-based observations of O2 and OH nightglow emission intensities and corresponding temperatures from, Gurushikhar, Mount Abu (24.6 degrees N, 72.8 degrees E) in India. Results on the statistics in terms of the percentage and duration of occurrences and possible formation mechanisms for the upper MTIs have been discussed. Such detailed investigations on the occurrence characteristics and possible causative mechanism of MTIs provides the necessary inputs for a greater understanding of the mesospheric temperature structure through theoretical and simulation studies.