Stratospheric distribution of methane over a tropical region as observed by MIPAS on board ENVISAT

PR Nair, M Kavitha - International Journal of Remote Sensing, 2020 - Taylor & Francis
PR Nair, M Kavitha
International Journal of Remote Sensing, 2020Taylor & Francis
The paper essentially deals with the stratospheric distribution of methane (CH4) over the
Indian region, based on satellite-borne Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS) data as observed during 2003–2012 period. The inter-dependence of
CH4 and other trace gases such as Water vapour (H2O), Ozone (O3), and Nitric oxide (NO),
variation of the equivalent water and long-term trends in CH4 and H2O is also presented.
The CH4 mixing ratio exhibits significant latitudinal and altitudinal dependence. The mixing …
Abstract
The paper essentially deals with the stratospheric distribution of methane (CH4) over the Indian region, based on satellite-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) data as observed during 2003–2012 period. The inter-dependence of CH4 and other trace gases such as Water vapour (H2O), Ozone (O3), and Nitric oxide (NO), variation of the equivalent water and long-term trends in CH4 and H2O is also presented. The CH4 mixing ratio exhibits significant latitudinal and altitudinal dependence. The mixing ration of CH4 varies in the range that goes from [1.8, 2.1] Part per Million by Volume (ppmv) to [1.2, 1.4] ppmv in the upper troposphere to the lower stratosphere. An out of phase relationship is observed between CH4 and H2O in the stratosphere in all the three-latitude regions (0° to 10° N, 10° to 25° N, and 25° to 40° N) addressed in this analysis. It is estimated that about 2.7 molecules of H2O are produced as a result of oxidation of CH4 and the excess in H2O molecules is attributed to other production photochemical process, most important one being the oxidation of H2. The dependence of CH4 to O3 and NO is altitude dependent, exhibiting an exponential decrease in the lower stratosphere and linear relation in the upper stratosphere. The analysis of the equivalent water in the mid-stratosphere shows an irregular variation in the altitude of 23–35 km and a gradual increase as the height increases. The overall change in equivalent water in the stratospheric region is [1, 2] ppmv. No consistent trend is observed in stratospheric CH4. On the other hand, H2O depicts an overall increase.
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