11:00 〜 11:15
[ACG35-08] The influence of global atmospheric circulation and chemical reactions (OH) on the redistribution of methane fluxes between the mid-latitudes and the tropics
キーワード：methane, hydroxyl radical, inverse modeling, climate change, greenhouse gases
This study investigates the impact of the hydroxyl radical (OH) on the global and regional methane budget from 2001 to 2020. Despite relatively low interannual variability (within ±6%), OH significantly influences methane oxidation, altering its atmospheric lifetime and radiative forcing. Using MIROC4-ACTM inverse model simulations, we evaluate two prescribed three-dimensional OH fields: one with climatological variability and the other with interannual variability. Through a comprehensive analysis of observations and numerical simulations, we unravel the dynamic interplay between OH and methane emissions, reveal regional patterns and temporal variations in the methane budget, and identify the driving factors behind these changes.
Our results show that OH-inverted CH4 emissions are in good agreement with global total estimates (~566 Tg-CH4 yr-1) but exhibit notable differences across latitudinal bands. These differences result in significant shifts in CH4 fluxes from the tropics to northern mid- and high latitudes, driven by enhanced OH activity and robust mixing facilitated by the global circulation. In particular, the influence of OH interannual variability is particularly pronounced during 2005-2010, resulting in a decrease in emissions of more than 20 Tg-CH4 yr-1. East Asia has the largest impact, with OH interannual variability contributing an additional 10 Tg-CH4 yr-1 (20%) of emissions for 2000-2020. Other regions significantly affected by OH include Boreal North America (16.2%), Europe (-16.4%), North Africa (-8.6%), and Central Africa (-11.8%).
To investigate the latitudinal redistribution of CH4 fluxes, we performed forward modeling with optimized emissions, focusing on OH effects. Using the same model version and setups, we examined the period 2006-2016, which was characterized by substantial OH variability and CH4 flux changes. The complex interplay of CH4 fluxes, enhanced OH activity, and the global circulation has a significant impact on CH4 levels, especially around 35°N. The near-surface Hadley circulation shapes the tropical atmospheric circulation, driving methane migration from higher latitudes to the tropics. This transport mechanism requires upward compensation of methane emissions at northern mid- and high latitudes, resulting in increased methane influx to the tropics and subsequent emission adjustment. Transient responses to shifts in OH concentration in 2008 and 2012 underscore the uneven changes in methane concentrations across atmospheric layers, driven by broader global atmospheric circulation patterns. Changes in OH affect the upper atmospheric layers via the deep branch of the Brower-Dobson circulation, which is central to the exchange of air masses and chemical constituents between the tropics and the northern mid- and high latitudes, providing critical insights into the mechanisms that shape CH4 flux dynamics.
Our results show that OH-inverted CH4 emissions are in good agreement with global total estimates (~566 Tg-CH4 yr-1) but exhibit notable differences across latitudinal bands. These differences result in significant shifts in CH4 fluxes from the tropics to northern mid- and high latitudes, driven by enhanced OH activity and robust mixing facilitated by the global circulation. In particular, the influence of OH interannual variability is particularly pronounced during 2005-2010, resulting in a decrease in emissions of more than 20 Tg-CH4 yr-1. East Asia has the largest impact, with OH interannual variability contributing an additional 10 Tg-CH4 yr-1 (20%) of emissions for 2000-2020. Other regions significantly affected by OH include Boreal North America (16.2%), Europe (-16.4%), North Africa (-8.6%), and Central Africa (-11.8%).
To investigate the latitudinal redistribution of CH4 fluxes, we performed forward modeling with optimized emissions, focusing on OH effects. Using the same model version and setups, we examined the period 2006-2016, which was characterized by substantial OH variability and CH4 flux changes. The complex interplay of CH4 fluxes, enhanced OH activity, and the global circulation has a significant impact on CH4 levels, especially around 35°N. The near-surface Hadley circulation shapes the tropical atmospheric circulation, driving methane migration from higher latitudes to the tropics. This transport mechanism requires upward compensation of methane emissions at northern mid- and high latitudes, resulting in increased methane influx to the tropics and subsequent emission adjustment. Transient responses to shifts in OH concentration in 2008 and 2012 underscore the uneven changes in methane concentrations across atmospheric layers, driven by broader global atmospheric circulation patterns. Changes in OH affect the upper atmospheric layers via the deep branch of the Brower-Dobson circulation, which is central to the exchange of air masses and chemical constituents between the tropics and the northern mid- and high latitudes, providing critical insights into the mechanisms that shape CH4 flux dynamics.