Trans-Pacific transport of Asian dust and CO: accumulation of biomass burning CO in the subtropics and dipole structure of transport 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, 30332, USA
2NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
Received: 01 November 2009 – Published in Atmos. Chem. Phys. Discuss.: 19 January 2010 Abstract. In May 2003, both MODIS aerosol optical depth (AOD) and carbon monoxide (CO)
measurements from MOPITT show significant trans-Pacific transport to North
America. We apply the global chemical transport model, GEOS-Chem, to analyze
the main features of the long-range transport events. Enhancements of MOPITT
CO over the tropical Pacific are much broader than MODIS AOD enhancements. We
find in model simulations that a major fraction of the CO enhancements in the
subtropics in May is due to biomass burning in Southeast Asia in April.
Biomass burning CO was recirculated into the subtropical high-pressure system
and lingered for a much longer period than aerosols transported at higher
latitudes. Simulated AOD enhancements are due to a combination of dust,
sulfate, and organic and elemental carbons. Dust contribution dominates the
AOD enhancements in early May. Model results indicate that dust transport
takes place at higher altitude than the other aerosols. MODIS observations
indicate a bias in model simulated pathway of dust transport in one out of
the three cases analyzed. Sensitivities of dust transport pathways are
analyzed in the model. The dipole structure of transport, consisting of the
Aleutian Low to the north and the Pacific High to the south, over the Pacific
is found to be a key factor. The placement of the dipole structure relative
to model parameters such as up-stream wind field and source location may lead
to the high sensitivity of simulated transport pathways.
Revised: 23 March 2010 – Accepted: 31 March 2010 – Published: 06 April 2010
Citation: Nam, J., Wang, Y., Luo, C., and Chu, D. A.: Trans-Pacific transport of Asian dust and CO: accumulation of biomass burning CO in the subtropics and dipole structure of transport, Atmos. Chem. Phys., 10, 3297-3308, doi:10.5194/acp-10-3297-2010, 2010.