Causative mechanisms for the occurrence of a triple layered mesospheric inversion event over low latitudes

AbstractThe temperature profile obtained from the space borne instrument “Sounding of Atmosphere by Broadband Emission Radiometry” instrument onboard “Thermosphere Ionosphere Mesosphere Energetics and Dynamics” shows a triple layered mesospheric inversion event on the night of 23 September 2011, when there is an overpass near the low‐latitude sites Gadanki (13.5°N, 79.2°E) and Tirunelveli (8.7°N, 77.8°E). The three mesospheric inversion layers (MILs) are formed in the height region around ~70 (lower), ~80 (middle), and ~90 km (upper) with amplitudes ~11, ~44, and ~109 K and thickness of 3.4, 4.9, and 6.6 km, respectively. The formation of the lower and middle MILs can only be observed in the Rayleigh lidar temperature profiles over Gadanki due to upper height limitation of the system. Nearly all the dominant causative mechanisms are examined for the occurrence of the MIL event. The lower MIL at ~70 km is inferred to be due to planetary wave dissipation, as there is a sudden decrease of planetary wave activity above 70 km. Further, it is demonstrated that the middle MIL at ~80 km is due to the turbulence generated by gravity wave breaking which is in turn due to gravity wave‐semi‐diurnal tidal interaction, though the height of the middle MIL descends at the rate of ~1 km/h, which is nearly the vertical phase speed of diurnal tide, whereas the upper MIL at above 90 km is due to the large chemical heating rate (~45 K/day) generated by the dominant exothermic reaction O + O + M → O2 + M.