Spatio-temporal variation of methane over Indian region: Seasonal and inter-annual variation .

Abstract:

Methane (CH₄) has an important role in the radiation budget and chemistry in the lower and middle atmosphere as a greenhouse and reactive trace gas. The rapid developments in the agriculture and industry over India have lead to the emission of many pollutants like CO, O₃, CH₄, CO₂, SO₂ etc into the atmosphere. However, their sources, sinks and concentration levels are poorly understood because of the lack of systematic sampling and monitoring. The advent of satellite remote sensing has helped to analyze the chemical composition of atmosphere with good spatial coverage especially over tropical region which was poorly sampled with the existing surface network. This work attempts an analysis of spatial distribution, seasonal cycle and inter annual variation of CH₄ over Indian region during 2003-2009 using SCIAMACHY data onboard ENVISAT. Column CH₄ varies from 1740-1890 ppbv over Indian region with distinct spatial and temporal features. We observed a dependence of seasonal CH₄ variation on rice cultivation, convective activities and changes in boundary layer characteristics. The comparative study using satellite, aircraft and surface measurement shown CH₄ has non-homogeneity in its distribution and seasonal variation in different layers of atmosphere. A comparative study of CH₄ at different hot spot regions over the globe was carried out which showed prominent hemispherical variations. Large spread in column CH₄ was observed at India and Chinese region compared to other regions with a significant seasonal variability. This study points to the blending of satellite, aircraft and surface measurements for the realization of regional distribution of CH₄.