Non-homogeneous vertical distribution of methane over Indian region using surface, aircraft and satellite based data

The upper tropospheric methane (UCH4) data from Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC), the column average mixing ratio of methane (XCH4) from SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and near-surface methane at two locations- Cape Rama, Goa, a Commonwealth Scientific Industrial Research Organization (CSIRO) network station and Ahmedabad (23.03 degrees N; 72.45 degrees E) were analysed to understand vertical inhomogenities in methane mixing ratio and the seasonal changes in the latitude sector 13 degrees-24 degrees N over India. XCH4 and UCH4 were found to follow more or less similar pattern over all the three latitude sectors, with the peak occurring in July-August, and minimum in late winter. The seasonal amplitude in XCH4 is less at low latitude sector (similar to 64 ppbv) compared to that of high latitudes (similar to 101 ppbv at 18 degrees-22 degrees N and 88 ppbv at 22 degrees-24 degrees N). On the other hand, the near surface methane shows opposite pattern peaking in winter attaining low in monsoon. During monsoon when methane sources are active at the surface, XCH4 > UCH4 and during other seasons UCH4 > XCH4 indicating presence of high altitude layers. This analysis revealed non -homogeneous distribution of methane in the troposphere indicative of stratified layers. The role of convective activity, boundary layer meteorology and long-range transport in controlling the seasonal changes in the vertical distribution of methane are examined in this study. (C) 2016 Elsevier Ltd. All rights reserved.