Interannual variability and trends of atmospheric methane over the western Pacific
Abstract
We presented interannual variability (IAV) and trends of atmospheric methane (CH4) over the western Pacific between 55°N and 35°S from 1994 to 2008, observed by the National Institute for Environmental Studies (NIES) Center for Global Environmental Research (CGER) volunteer observation ships sailing between Japan and Australia/New Zealand and between Japan and North America, on which maritime air was sampled quasi-monthly with high resolution in latitude. The large CH4 increases of 15-18 ppbv/yr were observed in 1997-1998 during the El Niño event. Our observation indicates that the increase initially occurred in the northern tropics in mid-1997 and then in midlatitudes in the Northern Hemisphere (NH) after a half year and in the Southern Hemisphere (SH) after 1 year. Then, the large CH4 increase was observed from the beginning of 2006, with the growth rate of 12 ppbv/yr in NH and 8 ppbv/yr in SH in 2007. We show that the recent increase in the northern midlatitudes is partly attributed to the atmospheric transport, however, additional CH4 emission and/or decrease of hydroxyl radicals are required for the global increase of CH4. The higher growth rates by 4 ppbv/yr in the NH than those in the SH may imply larger increase of surface emissions in the NH. We found no CH4 increase in the northern tropics (5-15°N) throughout 2006-2008. The simulation indicates that the suppression of the CH4 growth in the northern tropics is a local phenomenon in the western Pacific and is caused by atmospheric transport, probably associated with the enhanced vertical transport during La Niña event over this region.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A53C0282T
- Keywords:
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- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0368 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: constituent transport and chemistry;
- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling