Understanding atmospheric methane sub-seasonal variability over India

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.