Spatiotemporal gradients in aerosol radiative forcingand heating rate over Bay of Bengal and Arabian Seaderived on the basis of optical, physical, and chemicalproperties

摘要

Spatiotemporal heterogeneity in aerosol radiative forcing and heating rate have beenstudied over Bay of Bengal and Arabian Sea during premonsoon (March–May 2006) usingaerosol optical depth (AOD), total mass, aerosol chemical composition, and radiativetransfer model. Mean 0.5 ,um AOD over Bay of Bengal and Arabian Sea is 0.36 and 0.25,respectively. Water-soluble aerosols, sea salt, and mineral dust constitute –98% of totalaerosol mass while black carbon aerosols contribute <2% over the two oceanic regions.Sensitivity tests reveal that (1) curvature effect in AOD spectra has insignificant impact inmodifying the aerosol radiative forcing and heating rate and (2) the net Earth-atmosphereenergy content shows minor differences when aerosol vertical profiles are used. OverBay of Bengal the average aerosol forcing is estimated to be –12.0, –22.4, and 10.4 W m~(-2)at the top of the atmosphere (TOA), at the surface (SFC), and in atmosphere (ATM),respectively. The average aerosol radiative forcing is less negative over Arabian Sea and is–10.5, –15.8, and 5.3 W m~(-2)at TOA, SFC, and ATM, respectively. Aerosol radiativeforcing decreases in magnitude from north to south over Bay of Bengal whereas anopposite trend is noteworthy over Arabian Sea. The average atmospheric heating rate overBay of Bengal is –0.3 K/d, a factor of 2 higher than that over Arabian Sea. Furthermore,ATM warming and associated heating rate are the lowest compared to earlier resultsas scattering aerosols are dominant during premonsoon (March–May). These results haveimplications to the assessment of regional and seasonal climate impacts.