HR: 08:45h
AN: A21H-03    [Abstracts]
TI: Aerosol Optical Depth Tendencies Over the United States Over the Last Decade
AU: * Augustine, J A
EM: john.a.augustine@noaa.gov
AF: NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
AU: Michalsky, J J
EM: joseph.michalsky@noaa.gov
AF: NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
AU: Dutton, E G
EM: ellsworth.g.dutton@noaa.gov
AF: NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
AB: A recent decadal study of aerosol optical depth (AOD) over the U.S. reveals a general nationwide decrease, but also geographic differences. These new data from NOAA's SURFRAD surface radiation budget network show high AOD in summer and low AOD in winter. The western stations have the lowest AOD and the eastern stations have the highest. Western stations also show a secondary springtime maximum caused by Asian dust. The abundance of aerosols in the east and their relatively small size is attributed to organic emissions, high humidity, and the predisposition for stagnant air in summer. These characteristics agree with previously published results, however, national and station decadal AOD tendencies show interesting features that may have climate change implications. Nationally, 500nm AOD decreased from 1997 through 2006 by about 0.02, which is similar to recent results reported for the oceans. However, all U.S. stations do not share this tendency. Results show that aerosols are decreasing in the eastern U.S., however, in the west a decrease is only observed at Desert Rock, Nev. Fort Peck, Mont. and Boulder, Colo. show a very slight increase over the past decade that is likely caused by an upsurge in wildfires from 2000 through 2006. When the four years with the most abundant wildfires are removed, decadal tendencies at Boulder and Fort Peck are steady. If climate change is causing drier conditions in the western U.S., then higher than normal numbers of forest fires are likely to occur, and the observed AOD increase should be considered part of the background. In that case, the additional blockage of sunlight by direct and indirect effects of the fire-induced aerosols would act to slightly offset the warming attributed to increasing greenhouse gases. If the increasing trend in western wildfires does not continue, then the recent AOD increase in the intermountain western U.S. can be considered temporary, and western AOD should be expected to remain steady, as suggested by the observed tendencies of the low-fire years. The only way to answer these and other questions related to aerosols and climate is to continue to build AOD times series into future decades so that tendencies can be determined with more certainty.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1640 Remote sensing (1855)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting