12:00 〜 12:15
[ACG35-06] Large decrease in CH4 emissions due to the Mount Pinatubo triggered atmospheric CH4 stabilization in the 1990s
キーワード：Atmospheric Methane, MIROC model simulations, VISIT terrestrial ecosystem model, Mount Pinatubo eruption
Atmospheric methane (CH4) growth rates varied greatly in the past 3 decades, at about 12ppb/yr (range 8.8 – 14.3 ppb/yr) increase during 1988-1991, 0-5 ppb/yr during 1992-2005, and 7 ppb/yr (range 4.5 – 12.5 ppb/yr) during 2007-2016 (WMO bulletin, 2017). The causes of these variabilities still puzzling to the research communities. We use the MIROC atmospheric general circulation model (version 4.0; Watanabe et al., 2011) for simulating atmospheric CH4 and other long-lived greenhouse gases. The MIROC-AGCM has a spectral dynamical core and uses a flux from the semi-Lagrangian scheme for the tracer advection. The simulations were conducted for the period of 1988-2016, after a spin-up for 29 years. The CH4 emissions consist of anthropogenic and animals (EDGARv4.3.2), wetland and rice paddies (VISIT terrestrial ecosystem model), and biomass burning (GFEDv4s; period: 1997-2016) and others (TransCom). Two different cases of a-priori emissions are discussed here for varied biogenic emission modeled by VISIT using CH4 emission schemes, Cao et al. (Cao) and Walter-Heimann (WH).
Both the model simulations show remarkable performance in reproducing the observations along with the year-to-year variability, in particular during the transient and constant period from 2000-2006. The model simulates more than 70% of the observed variability successfully over the southern and mid-latitudes (below 45oN). The Cao-scheme performs well in simulating the seasonal amplitude over the tropical sites (15oS-15oN), however, over the southern hemispheric sites (~ below 45oS), the WH-scheme performs better in simulating the amplitude compared to the emissions using the Cao scheme.
It was reported that a major difficulty in producing beginning of the reduction in CH4 growth rate could only be overcome by a decrease in CH4 emissions (Ghosh et al., 2015). Here we show the VISIT model simulated a decrease in CH4 emission by about 20 Tg/yr during June 1991 – May 1993, following the Mount Pinatubo eruption. Anomalous cooling over tropical (~20-25 oN) and extratropical (~60-65 oN) wetlands lead to more or less decrease in CH4 emission. Further, we investigate the sensitivity of CH4 concentrations to these emission perturbations during the pre- and post-Pinatubo eruption.
Both the model simulations show remarkable performance in reproducing the observations along with the year-to-year variability, in particular during the transient and constant period from 2000-2006. The model simulates more than 70% of the observed variability successfully over the southern and mid-latitudes (below 45oN). The Cao-scheme performs well in simulating the seasonal amplitude over the tropical sites (15oS-15oN), however, over the southern hemispheric sites (~ below 45oS), the WH-scheme performs better in simulating the amplitude compared to the emissions using the Cao scheme.
It was reported that a major difficulty in producing beginning of the reduction in CH4 growth rate could only be overcome by a decrease in CH4 emissions (Ghosh et al., 2015). Here we show the VISIT model simulated a decrease in CH4 emission by about 20 Tg/yr during June 1991 – May 1993, following the Mount Pinatubo eruption. Anomalous cooling over tropical (~20-25 oN) and extratropical (~60-65 oN) wetlands lead to more or less decrease in CH4 emission. Further, we investigate the sensitivity of CH4 concentrations to these emission perturbations during the pre- and post-Pinatubo eruption.