科研之友
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摘要
One year (June 2006-May 2007) of the Clouds and the Earth's Radiant Energy System (CERES) top of atmosphere (TOA) shortwave (SW) and longwave (LW) fluxes are used with Ozone Monitoring Instrument-Aerosol Index (OMI-AI) data to assess the direct radiative effects of ultraviolet (UV)-absorbing aerosols. We show that TOA SW aerosol radiative effects from UV-absorbing aerosols alone are almost double that compared to when considering all aerosols. These aerosols account for nearly all of the seasonal variation in direct SW radiative effect (SWRE) over the oceans and a significant portion of that over land.
Overall, TOA clear-sky SWREs over ocean and land surfaces were estimated to be -4.3 and -4.9 W m(-2), respectively, with both values being in line with previous estimates. When only regions where UV-absorbing aerosols are considered, the SWRE over the ocean becomes more negative between March and August, when the concentration of dust aerosols in the North Atlantic is greatest. Larger concentrations of UV-absorbing aerosols generally exist over land surfaces, increasing the OMI-AI to 0.54 compared to 0.20 over ocean, increasing SW cooling estimates over land. The SWRE also varies as a function of land-surface type and surface albedo. The lowest concentration of absorbing aerosols and therefore the least SW cooling occurs over forests, with the OMI-AI 0.36 and the non-bias-adjusted SWRE -1.45 W m(-2). Over other surfaces, the concentrations of absorbing aerosols are greater (AI. 0.5), thereby increasing the SWRE to between -2 and -3 W m(-2). However, as surface brightness increases, the correlation between the AI and the SWRE decreases, and it becomes more difficult to attribute the SWRE estimates to absorbing aerosol concentrations. In particular, the SWRE estimates over bare-soil regions were found to be negative, but completely uncorrelated with the OMI-AI. We concluded that the uncertainty of the SWRE estimates increases as a function of increasing albedo.
The TOA radiative effects of absorbing aerosols to longwave radiation (LWREs) are also examined over North Africa and the North Atlantic, where substantial concentrations of elevated dust aerosols exist. LW warming was found to offset SW cooling over the ocean 20-30% during the spring and summer months. Even greater LW warming was found over land in North Africa and South Asia, with a mean value of +3.8 W m(-2) between March and August, representing an increase of over 100% compared to the other seasons. Our analysis indicates that the OMI provides complementary information to the Moderate Resolution Imaging Spectroradiometer (MODIS) for studying aerosol radiative effects.
- 出版日期2011
