Aerosol Impacts on Earth’s Energy Budget: What we know, and what we don’t
Ralph Kahn [Ralph.Kahn@nasa.gov], NASA Goddard Space Flight Center, Greenbelt, MD
Aerosols play a significant role in the global energy balance, and especially in atmospheric
and surface energy balances regionally. A combination of surface direct radiative cooling,
atmospheric warming through diabatic heating, and indirect effects of aerosols on clouds, all
contribute to the net aerosol effect. They are represented in modern climate models, yet their
magnitudes are highly variable in space and time, and all are highly uncertain. Space-based
remote sensing is a key tool for constraining aerosol impacts on Earth’s energy budget, due to
the frequent, global coverage it provides. However, information from such observations about
aerosol amount (i.e., aerosol optical depth or AOD), and especially about aerosol type, is limited.
The current generation of aerosol remote-sensing instruments, including NASA’s MISR and
MODIS, offer vast improvements over previous instruments. MODIS provides AOD over water
and darker land surfaces, and fine vs. coarse particle type over ocean. MISR contributes AOD
over bright desert, discrimination of about a dozen aerosol types under good retrieval conditions,
based on particle size, shape, and single-scattering albedo (SSA) constraints, and near-source
aerosol layer heights for wildfire smoke, desert dust, and volcanic ash plumes. The CALIPSO
lidar complements the MISR plume heights, providing vertical distributions of aerosols globally,
downwind of sources. This presentation will briefly summarize capabilities and expected
improvements to the currently available aerosol products, in light of required energy budget
constraints. Ways of addressing the need for detailed information about particle microphysical
properties, especially SSA, unobtainable from current or planned space-based instruments, will
be discussed.