HR: 0800h
AN: A11A-0029 [WITHDRAWN] [Abstracts]
TI: Quantification of the Direct Aerosol Effect Using Ground Based Radiative Flux Measurements at Cabauw (The Netherlands)
AU: * Los, A
EM: alexander.los@knmi.nl
AF: Royal Netherlands Meteorological Institute (KNMI), PO Box 201, De Bilt, 3730 AE, Netherlands
AU: Knap, W H
EM: wouter.knap@knmi.nl
AF: Royal Netherlands Meteorological Institute (KNMI), PO Box 201, De Bilt, 3730 AE, Netherlands
AB:
Aerosols affect the Earth's climate profoundly by changing the amount of sunlight at the surface due to both, the
direct and indirect aerosol effects. Mishchenko et al. (2007) showed that the aerosol optical thickness (AOT)
decreased on a global scale since the beginning of the 1990s, even though regional aerosol column densities
vary considerably due to both, natural events and especially anthropogenic activities. The decreasing global AOT
will likely increase the surface solar radiative heat flux which eventually reduces the counterbalance to
greenhouse gas warming and potentially contribute to the warming trend of the last decade.
Using surface solar radiative flux measurements and AOTs derived from sun-photometer measurements at
Cabauw we show the magnitude of the aerosol effect for cloud free conditions. This so-called direct aerosol effect
is quantified by subtracting modelled radiative fluxes for cloud-free and aerosol-free conditions from radiative
fluxes as measured at the BSRN station Cabauw (The Netherlands). To exclude measurements where clouds
are visible above the horizon we applied several (longwave and shortwave) cloud detection algorithms and
examined sky images taken by an 2-π hemispheric camera. The mean direct aerosol effect was in 2006
about -30 W/m2. During the same period the direct aerosol effect accounted for a reduction of the surface
solar radiative flux on average by about 120 W/m2 per unit AOT. The poster presentation will contain an
uncertainty analysis of the direct aerosol effect and an airmass trajectory analysis to determine the aerosol origin
and some information about its composition. From these results we will derive an aerosol climatology for The
Netherlands, which is useful for validation purposes of the regional climate model RACMO.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting