The occurrence altitudes of middle atmospheric temperature inversions and mesopause over low-latitude Indian sector

M Sivakandan,D Kapasi,A Taori

doi:10.5194/angeo-32-967-2014

M Sivakandan, D Kapasi + Show 1 more

Open Access

https://doi.org/10.5194/angeo-32-967-2014

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Abstract

Abstract. We study the occurrence characteristics of mesospheric inversion layers (MILs) in the 60–105 km altitude region over the low-latitude Indian sector. We note that lower inversions in the mesospheric temperatures occur in the 70–75 km altitude regions while the upper inversions occur in 90–95 km altitude regions. The mesopause altitude is mostly noted to be ~ 98 km with the night-time mesopause (particularly in the year 2002) showing a small peak in the mesopause occurrence at ~ 75 km altitude. We note higher occurrence rate of MILs during high solar activity year compared to low solar activity year. It is also observed that night time MILs show a systematic seasonal variability, with higher occurrence of single and double temperature inversions during equinoxes.

Highlights

The mean thermal structure of the Earth’s middle atmosphere is characterized by a negative temperature gradient
We note that during daytime, the mesospheric inversion layers (MILs) occur uniformly in 70–95 km altitude regions and most of the times MILs occurring above 96 km are nothing but a signature of the mesopause altitude
We find that MILs tend to occur either near to 75 km altitudes or 96 km altitudes

Summary

Introduction

The mean thermal structure of the Earth’s middle atmosphere is characterized by a negative temperature gradient. It is understood that gravity wave, tides and planetary waves govern the middle atmospheric variability These dynamical processes contribute significantly to the variability noted in the mesospheric structures and may influence the mesopause altitude (Hargreaves, 1992). There are several reports showing positive temperature gradients in the mesosphere which are in contrast to the ideal situation of negative gradients (Meriwether and Gardner, 2000; Gan et al, 2012, and references cited therein). This kind of phenomenon is known as “mesospheric inversion layer (MIL)”. Szewczyk et al (2013) reported the turbulence-triggered double mesospheric inversions at altitudes of 71–73 km and 86–89 km respectively

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