Meteorological impacts of El Niño on tropospheric ozone distribution during 1970-2006
Abstract
This study investigates the effects of El Niño on global tropospheric ozone distribution using a global chemical transport model. We particularly focus on the roles of the meteorological condition change caused by El Niño in tropospheric ozone distribution, aside from the El Niño induced emission changes. To evaluate the meteorological impacts of El Niño, we assess composite pattern of the past El Niño impacts on tropospheric ozone in our performed simulation that covers the period from 1970 to 2006 including four strong El Niño events. The composite shows significant positive anomalies (1-3DU) in ozone over the tropical western Pacific including Indonesia, and the subtropics in the central to eastern Pacific in December to February. The ozone increases over Indonesia and the tropical western Pacific are caused by downward motion, suppressed convection, and decreases in water vapor. Over the subtropics in the central to eastern Pacific, about half of the simulated ozone increase is attributed to enhanced chemical ozone production in the troposphere with the remainder to increased ozone transport from the stratosphere. This ozone change over the subtropics in the central to eastern Pacific is found to be linked to the enhanced meridional circulation (local Hadley cell) and the changes in transport pattern of ozone precursors (CO, NOx). Enhanced meridional circulation causes increased downward transport of ozone rich air from the stratosphere and the upper troposphere to the lower troposphere. In addition, the model result shows large positive anomalies of CO (5 ppbv at 1km) and NOx (10 pptv at 3km) over the subtropics in the central to eastern Pacific reflecting changes in transport pattern and water vapor in the troposphere. The changes in transport pattern of ozone precursors play a significant role in the ozone increases as well as the changes in transport pattern of ozone. Composite pattern of the past El Niño impacts on tropospheric column ozone in our performed simulation. unit is Dobson unit.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A54B..03S
- Keywords:
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- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0368 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: constituent transport and chemistry;
- 1009 GEOCHEMISTRY / Geochemical modeling;
- 1616 GLOBAL CHANGE / Climate variability