Understanding atmospheric methane sub-seasonal variability over India

Abstract

Atmospheric methane (CH) is considered to be one of the most important greenhouse gases due to its increasing atmospheric concentrations and the fact that it has a warming potential 28 times that of atmospheric carbon dioxide (CO). Over the Indian sub-continent, fluxes and transport both contribute towards CH seasonal variability. Its intra-seasonal variability however is more complex as it is additionally influenced by monsoonal activity during the Asian Summer Monsoon (ASM) period. In this study, the intra-seasonal variability of atmospheric CH is examined using ground-based observations at two sites located in the Southern Indian Peninsula, Sinhagad (SNG) and Cape Rama (CRI); and outputs from three different model simulations. Both, the ground based observations and multi-model simulations show that the dominant spectral variability of CH is coherent with 20–90 day oscillations in the dynamics of the monsoon (termed hereafter as Intra-Seasonal Oscillations, ISOs). The multi-model analysis revealed that CH is heavily influenced by advection due to this intra-seasonal variability. The simulations also display a clear northward propagation of CH anomalies over India. The co-evolution of CH, outgoing long wave radiation (to represent convection) and OH radicals (proxy to CH sinks) is presented. The study quantifies CH variability at intra-seasonal timescales and also its spatial extent. The results suggest that the effect of ISOs on CH needs to be considered along with the corresponding observations for future inverse modeling.