Abstract
In this work, the effect of the aerosol vertical distribution on the local shortwave aerosol radiative forcing is studied. We computed the radiative forcing at the top and bottom of the atmosphere between 0.2 and 4 microns using the libRadTran package and compared the results with those provided by AERONET (AErosol RObotic NETwork). Lidar measurements were employed to characterize the aerosol vertical profile, and collocated AERONET measurements provided aerosol optical parameters required to calculate its radiative forcing. A good correlation between the calculated radiative forcings and those provide by AERONET, with differences smaller than 1 W m−2 (15% of estimated radiative forcing), is obtained when a gaussian vertical aerosol profile is assumed. Notwithstanding, when a measured aerosol profile is inserted into the model, differences between radiative forcings can vary up to 6.54 W m−2 (15%), with a mean of differences = −0.74 ± 3.06 W m−2 at BOA and −3.69 W m−2 (13%), with a mean of differences = −0.27 ± 1.32 W m−2 at TOA due to multiple aerosol layers and aerosol types. These results indicate that accurate information about aerosol vertical distribution must be incorporated in the radiative forcing calculation in order to reduce its uncertainties.
Highlights
The response of the earth–atmosphere system to the perturbation created by growing concentrations of greenhouse gases is nowadays the subject of intense research
We computed the radiative forcing at the top and bottom of the atmosphere between 0.2 and 4 microns using the libRadTran package and compared the results with those provided by AERONET (AErosol RObotic NETwork)
Simultaneous ground-based remote sensing measurements were carried out at the site with the following instruments: the vertically resolved aerosol profile was provided by a multiwavelength advanced lidar system (Madrid-CIEMAT ACTRIS station) and the column-integrated optical properties were derived from sky and direct sun measurements provided by an automatic photometer (AEMET-AERONET station)
Summary
The response of the earth–atmosphere system to the perturbation created by growing concentrations of greenhouse gases is nowadays the subject of intense research. The radiative influence of aerosols is globally comparable to that produced by greenhouse gases but opposite in sign [1] This effect of aerosols on radiative fluxes bears the largest uncertainty in the Earth’s radiation balance estimations [2], mainly due to their large temporal and spatial (horizontal and vertical) variability [3]. Many new satellite sensors have been deployed with spectral, viewing and polarization capabilities better suited to extract aerosol properties (e.g., MISR, PARASOL, CALIPSO, or ATSR). They provide useful information on spatial and temporal distribution of aerosols, especially over regions where ground monitoring is sparse (developing countries) or not available (over many ocean regions). The satellite data do not yet provide the required representativeness needed to assess aerosol temporal and spatial variability due to their long overpass times
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