Oleg Dubovik

Single-Scattering Albedo and Radiative Forcing of Various Aerosol Species with a Global Three-Dimensional Model

Global distributions of the aerosol optical thickness, Angstrom exponent, and single-scattering albedo are simulated using an aerosol transport model coupled with an atmospheric general circulation model. All the main tropospheric aerosols are treated, that is, carbonaceous (organic and black carbons), sulfate, soil dust, and sea salt aerosols. The simulated total aerosol optical thickness, Angstrom exponent, and single-scattering albedo for mixtures of four aerosol species are compared with observed values from both optical ground-based measurements and satellite remote sensing retrievals at dozens of locations including seasonal variations. The mean difference between the simulation and observations is found to be less than 30% for the optical thickness and less than 0.05 for the single-scattering albedo in most regions. The simulated single-scattering albedo over the Saharan region is, however, substantially smaller than the observation, though the standard optical constant of soil dust is used in this study. The radiative forcing by the direct effect of the main tropospheric aerosols is then estimated. The global annual mean values of the total direct radiative forcing of anthropogenic carbonaceous plus sulfate aerosols are calculated to be 20.19 and 20.75 W m22 under whole-sky and clear-sky conditions at the tropopause, respectively.

Synergetic retrieval of atmospheric aerosol from a combination of lidar and radiometer ground-based observations

The new algorithm that simultaneously inverts co-incident ground-based observations by AERONET radiometer and multi-wavelength lidar is presented. The retrieval uses an assumption that a mixture of fine and coarse aerosol modes with vertically constant spectral optical properties can satisfactorily describe the vertical variability of aerosol spectral optical properties. In this model the shape of size distribution and complex refractive index are assumed to be height independent for each mode, while the vertical profiles of aerosol concentrations can change arbitrarily for each mode. Consequently the inversion algorithm retrieves the size distribution, complex refractive index, single scattering albedo and vertical distribution of both fine and coarse aerosol modes. The concept of the method is presented and illustrated by the application of the developed method to the actual combined observations of lidar and radiometer.

Influence of sky radiance measurement errors on inversion-retrieved aerosol properties

Remote sensing of the atmospheric aerosol is a well-established technique that is currently used for routine monitoring of this atmospheric component, both from ground-based and satellite. The AERONET program, initiated in the 90’s, is the most extended network and the data provided are currently used by a wide community of users for aerosol characterization, satellite and model validation and synergetic use with other instrumentation (lidar, in-situ, etc.). Aerosol properties are derived within the network from measurements made by ground-based Sun-sky scanning radiometers. Sky radiances are acquired in two geometries: almucantar and principal plane. Discrepancies in the products obtained following both geometries have been observed and the main aim of this work is to determine if they could be justified by measurement errors. Three systematic errors have been analyzed in order to quantify the effects on the inversion-derived aerosol properties: calibration, pointing accuracy and finite field of view. Si...

Aerosol and Surface Properties Characterization from Joint Inversion of Ground-Based and Satellite Observations

A method for simultaneously retrieving aerosol and surface parameters from ground based and satellite observations collocated in space and time is presented. The improvements in aerosol and surface reflectance characterization are discussed.