Causative Mechanisms of Low-Latitude Mesospheric Inversion Layers
Previously Published Material: Published onlline in Journal of Geophysical Research: Space Physics on 19 May 2014. doi:10.1002/2013JA019750.
Abstract ID#: 33531
Mesospheric Inversion Layer (MIL) refers to the inversion of temperature gradient from negative to positive superposed upon the characteristically decreasing mesospheric thermal structure. Though morphological characteristics of MIL events have been known for several decades, their causative mechanisms are still unknown. Gravity wave breaking, panetary wave critical level interaction, Gravity wave tidal interaction and chemical heating have been suggested as possible causative mechanisms of the MIL events. However, their relative importance and seasonal and altitude dependences are relatively unknown. Considering several case studies, all the dominant causative mechanisms for the occurrence of MILs over a low latitude region, Gadanki (13.5°N, 79.2°E) are investigated using mainly the Rayleigh lidar temperatures over Gadanki, MF radar winds over Tirunelveli (8.7°N, 77.8°E), TIMED-SABER temperature, volume mixing ratios of O, H, O3 etc and the chemical heating rates of various exothermic reactions. Based on the detailed investigation, it is found that the lower MILs (~70 km) are due to planetary wave-critical level interaction, the middle MILs (~80-85 km) are dominantly caused either by chemical heating due to H+O3→OH+O2 or by gravity wave breaking. The upper MILs (above 90 km) are found to be due to the exothermic chemical reaction, O+O+M→O2+M.