The Regional Climate Response to Absorption-Driven Solar Dimming over East Asia

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Thursday, 8 January 2015: 11:30 AM
122BC (Phoenix Convention Center - West and North Buildings)
Geeta G. Persad, Princeton University, Princeton, NJ; and Y. Ming, D. Paynter, and V. Ramaswamy

East Asia—a region of global dynamical importance with large anthropogenic aerosol emissions—has experienced strong, aerosol-driven reductions in surface solar radiation (SSR) over the last several decades, colloquially referred to as “solar dimming.” The regional climate response to this dimming can be expected to differ depending on whether the attenuated solar radiation is being trapped within the atmosphere (i.e. absorbed) or reflected back out of the surface-atmosphere system (i.e. scattered), but few studies have analyzed the relative contribution to dimming from aerosol absorption versus aerosol scattering. We recently demonstrated in a pair of atmospheric general circulation models (AGCMs), however, that as much as half of the clear-sky SSR trend over East Asia is attributable to increased aerosol absorption. We here analyze the regional climate response to absorption-driven dimming over East Asia in AM3, the Geophysical Fluid Dynamics Laboratory's latest generation AGCM. We find that, although the aerosol absorption constitutes a large, positive radiative perturbation in the atmosphere, the SSR-driven surface cooling dominates the response of the regional circulation, suppressing large-scale ascent and convection and reducing the land-sea contrast and monsoonal on-shore flow. This can be contrasted with past AGCM studies over ocean surfaces, which find that aerosol absorption promotes large-scale ascent due to increased atmospheric heating in the presence of fixed sea surface temperatures. This work sheds new light on the relative importance of absorbing aerosols' atmospheric vs. surface radiative perturbation for regional circulation changes, the implications of which will be discussed.