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

• Published in: International journal of remote sensing 2020-11, Vol.41 (21), p.8380-8405
• Main Authors: Nair, Prabha R., Kavitha, M.
• Format: Article
• Language: English
• Subjects: Altitude; Atmospheric sounding; Dependence; Distribution; Equivalence; Gases; Indian spacecraft; Lower stratosphere; Methane; Michelson interferometers; Mixing ratio; Nitric oxide; Oxidation; Ozone; Photochemicals; Photochemistry; Stratosphere; Trace gases; Tropical climate; Tropical environments; Troposphere; Upper stratosphere; Upper troposphere; Water chemistry; Water vapor; Water vapour
• ISSN: 0143-1161; 1366-5901
• DOI: 10.1080/01431161.2020.1779376

The paper essentially deals with the stratospheric distribution of methane (CH 4 ) 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 CH 4 and other trace gases such as Water vapour (H 2 O), Ozone (O 3 ), and Nitric oxide (NO), variation of the equivalent water and long-term trends in CH 4 and H 2 O is also presented. The CH 4 mixing ratio exhibits significant latitudinal and altitudinal dependence. The mixing ration of CH 4 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 CH 4 and H 2 O 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 H 2 O are produced as a result of oxidation of CH 4 and the excess in H 2 O molecules is attributed to other production photochemical process, most important one being the oxidation of H 2 . The dependence of CH 4 to O 3 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 CH 4 . On the other hand, H 2 O depicts an overall increase.