Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG35] Global Carbon Cycle Observation and Analysis

Tue. May 22, 2018 10:45 AM - 12:15 PM 301A (3F International Conference Hall, Makuhari Messe)

convener:Kazuhito Ichii(Chiba University), Prabir Patra(Research Institute for Global Change, JAMSTEC), Toshinobu Machida(国立環境研究所, 共同), David Crisp(Jet Propulsion Laboratory), Chairperson:Ichii Kazuhito, Patra Prabir, Machida Toshinobu

12:00 PM - 12:15 PM

[ACG35-06] Large decrease in CH4 emissions due to the Mount Pinatubo triggered atmospheric CH4 stabilization in the 1990s

*Naveen Chandra1, Akihiko Ito, Prabir Patra1, Masayuki Takigawa1, Shingo Watanabe1 (1.JAMSTEC)

Keywords: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.