HR: 1340h
AN: A23C-0829    [Abstracts]
TI: The Nature and Effects of Background Aerosols
AU: * Halthore, R N
EM: halthore@nrl.navy.mil
AF: Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375-5320 United States
AU: Caffrey, P F
EM: caffrey@nrl.navy.mil
AF: Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375-5320 United States
AB: Accurate, world-wide, long-term measurements of aerosol optical thickness (AOT) in continental and remote marine boundary layer reveal an absolute minimum in AOT ($\sim 0.02$ at 550 nm and an Angstrom exponent $\sim -1$) at most low-altitude locations but one. At this AOT magnitude the aerosols could have significant consequences on climate and remote sensing by the direct effect alone. For example, if all the optical thickness is due to aerosol absorption, as sometimes required for surface irradiance closure, an optical thickness of just 0.02 would increase atmospheric absorptance by about 4%, a significant fraction of the approximately 20% absorptance currently assumed for the shortwave. Likewise, satellite sensor calibration by ground-look methods would be severely affected. To better understand the nature of this background aerosol in the remote marine environment (i.e., sources, sinks, and lifetimes), Naval Research Laboratory's dynamic microphysical aerosol model MARBLES has been used with hourly meteorology input provided by COAMPS, the Navy's mesoscale meteorological model. Full specification of boundary layer profiles, including turbulent mixing, boundary layer height, wind speed, humidity, cloud cover, rain rates has been provided along COAMPS derived $\sim10$ day back trajectories from specified AERONET (NASA's sunphotometer network) sites. Calculated optical properties are compared with AERONET measurements for selected periods representative of remote background conditions and for several distinct aerosol events. Some comparisons show good agreement, indicating that marine aerosol sources, primarily sea-salt and sulfate, explain the AOT minimum well. Detailed results of calculated vertical aerosol concentration, composition and extinction profiles are provided. Implications will be discussed.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting