Retrieval of Mean Cosine of Aerosol Phase Function from Extinction and Sky Brightness Measurements
Zhuravleva, T.B.(a), Sviridenkov, M.A.(b), and Anikin, P.P.(b), Institute of Atmospheric Optics SB RAS, Tomsk, Russia (a), A.M. Obukhov Institute of Atmospheric Physics RAS, Moscow, Russia (b)
Thirteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting
Asymmetry of the aerosol phase function together with optical thickness drive the magnitude of the aerosol radiative forcing. Two approaches are usually used to obtain the mean cosine of the phase function retrieval of the single scattering phase function from sky brightness measurements or calculations for the given aerosol size distribution and refractive index. We studied the possibility to determine the mean cosine directly from extinction and solar almucantar measurements at low sun elevations. Simulations were made for different aerosol models using Monte Carlo method. It was found that a simple relation exists between the products of aerosol optical thickness by mean cosine of the aerosol phase function and integral of the sky brightness by its mean cosine, similar to the known relation, valid for the near-forward approximation of the radiative transfer equation. So, the mean cosine can be estimated from brightness measurements for the known aerosol optical thickness. No information concerning the surface albedo is needed. In situations, when the submicron aerosol fraction is predominant in scattering, the mean cosine can be estimated for the known aerosol refractive index by inversion of the data on spectral extinction and recalculation of the phase function for the size distribution obtained. Two methods of the retrieval of the mean cosine are in a satisfactory agreement, and their comparison allows one to make a rough estimate of the refractive index.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
