Spatial–temporal variation of mid-upper troposphere methane based on twenty-year atmospheric infrared sounder observation

The 20-year spatio-temporal variability of atmospheric methane (CH4) and its trends are presented using the CH4 volume mixing ratio (CH4 VMR) retrieved from Atmospheric Infrared Sounder. These data have a 1 deg×1 deg spatial resolution and cover pressure levels between 600 and 200 hPa, latitudes 67°S–67°N, and the time interval from March 2003 to February 2023. The vertical distribution of the CH4 VMR showed a definite decrease with altitude and a long-term increase in time. There was an obvious gradient with latitude, which increased from south to north. The horizontal distribution released strong regional signals. In the Northern Hemisphere, the high values of the CH4 VMR were mainly distributed in the northern temperate zone and most of the northern subtropic, and the low values were mainly observed in tropical Africa. The spatial distributions of seasonal growth rates presented clear climatic zone characteristics for all four seasons. Empirical orthogonal function analysis further illustrated a significant increase of CH4 VMR during the past 20 years and predicted a continued increase in the next few years. The comparative analysis between the Oceanic Niño Index and ΔCH4 VMR indicated that CH4 emissions are restrained under the influence of El Niño-Southern Oscillation.