The Interhemispheric transport pathway of methane observed by the GOSAT/TANSO-FTS thermal infrared sensor

Abstract:

Interhemispheric transport is crucial for the global distribution of long-lived trace gases in the troposphere. Large disagreement exists on the role of Hadley circulation and intertropical convergence zone (ITCZ) oscillation on the interhemispheric exchange efficiency, and locations in different longitude bands or at heights.

The difference in methane emissions in the Southern and Northern Hemispheres is the main cause of the meridional gradient, which is increased further by the greater loss of CH₄ by hydroxyl (OH) radicals in the tropics. Thus 3-dimendional CH₄ distribution provides unique opportunity to study the inter-hemispheric transport of long-lived gases as it has a lifetime about 10 years in the troposphere.

We use CH₄ measurements from the thermal infrared (TIR) band observations by the Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observation SATellite (GOSAT). This study identifies the transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) the Southern Hemisphere during northern summer. This transport pathway is linked to the boreal summer monsoon that is characterized by the lower level convergence and upper level divergence. Presented results confirm the role of monsoon zonally asymmetric heating on interhemispheric transport and highlight that the monsoon-induced eddy circulation plays an important role in the interhemispheric transport of long-lived chemical constituents.

Figure shows latitude-longitude distributions of CH₄ at the levels of 800 (a--b), 500 (c--d), and 300 (e--f) hPa respectively, observed by GOSAT-TIR (left panels) and modeled by ACTM (right panels) for JAS period of 2010.