Insight into the atmospheric methane gas cycle in India over thirteen years using Hilbert Huang transformation
摘要
Thirteen years of atmospheric methane fluctuations over India have been analyzed using a novel Hilbert Huang transformation methodology. The decomposition of the time series into intrinsic mode functions reveals several cyclic components embedded within the data. Different characteristic timescales of the intrinsic mode function (IMF) show various methane-emitting sources contributing to atmospheric methane over India. Fluctuations of CH4 observed in each intrinsic mode function reveal the highest CH4 emission during and at the end of the annual monsoon period, i.e., June to September. Methane emissions from biogenic sources are attributed to this large fluctuation. To emphasize on the emission sources, a region in the northern part of India has been selected, and the atmospheric methane data from that region have been analyzed in the Hilbert Huang transformation framework. Similar periodic fluctuations have been observed through the intrinsic mode functions for the entire India. Comparison of the results with EDGAR data further strengthened the finding that emissions from rice cultivation and biomass burning contributed to the observed variation in IMF5, and the variation observed in IMF6 can be attributed to emissions from biofuels used in residential settings. The residue obtained after the decomposition process shows an increasing trend in atmospheric methane concentration in both datasets. Comparison with EDGAR data shows that emissions from wastewater treatment, solid waste disposal, enteric fermentation, and manure management could have contributed to the observed trend. The time period of each mode shows an exponential variation with the mode number. Reconstruction of the data from the intrinsic mode functions establishes the completeness of the Hilbert Huang transformation method. Volatility and reconstruction analysis also establishes the fact that the Hilbert Huang transformation can be used as both a high-pass and low-pass filter in the frequency domain.
Research highlightsAtmospheric methane gas cycle over India for 13 years has been revealed and the possible contributors to those cycle have been linked.