Understanding atmospheric methane sub-seasonal variability over India

Atmospheric methane 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. Over the Indian sub-continent, fluxes and transport both contribute towards atmospheric methane's 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, Yogesh K. Tiwari and colleagues examine the intra-seasonal variability of atmospheric methane 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 methane 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 methane is heavily influenced by advection due to this intra-seasonal variability. The simulations also display a clear northward propagation of methane anomalies over India. The co-evolution of methane, outgoing long wave radiation (to represent convection) and OH radicals (proxy to methane sinks) is presented. The study quantifies atmospheric methane variability at intra-seasonal timescales and also its spatial extent. The results suggest that the effect of ISOs on atmospheric methane needs to be considered along with the corresponding observations for future inverse modeling.

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