Solar Monte Carlo Radiative Transfer Simulations in Saharan Dust Plumes.

Torge, Antje (2012) Solar Monte Carlo Radiative Transfer Simulations in Saharan Dust Plumes. Open Access (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 140 pp.

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Radiative fields of three-dimensional inhomogeneous Saharan dust clouds have been calculated at solar wavelengths by means of a Monte Carlo radiative transfer model. Scattering properties are taken from measurements in the SAMUM campaigns, from light scattering calculations for spheroids based on the MISCHKA code, from Mie Theory for spheres and from the Geometric Optics Method assuming irregular shaped particles. Optical properties of particles with different projected area equivalent shapes are compared. Large differences in optical properties are found especially in the phase functions. Modelled scattering properties are compared to laboratory measurements with good agreement. Results of radiative transfer calculations based on the Monte Carlo Method are shown exemplarily for one dust cloud simulated by the cloud resolving atmospheric circulation model COSMO-MUSCAT. Shape induced differences in the radiation fluxes are pronounced, for example, the domain averaged normalized radiance is about 20% lower in the case of a dust plume consisting of spheroids or irregular particles compared to spheres. Further the modelled radiative fields are compared to simulated fields from COSMO-MUSCAT and to satellite measurements with the SEVIRI instrument onbord the MSG satellite. In some cases the patterns of the radiative fields agree quiet well, especially with the simulated fields from COSMO-MUSCAT. But because by uncertainties in particular in the input data, the modelled radiative fields do not agree very well with most of the satellite measured fields. The satellite measurements are also used to compare with the measured radiances from an aircraft. There good agreements are found. In the Monte Carlo radiative transfer calculations the horizontal photon transport can be switched of, which was used for investigations on its effect (3D-effect) on the reflected radiance fields. The 3D-effect is only notable at the largest gradients in optical thickness. For example, the reflectance at low sun position differs locally about 25% when horizontal photon transport is accounted for. 'Sharp edges' due to 1D calculations are smoothed out in the 3D case.

Document Type: Thesis (PhD/ Doctoral thesis)
Thesis Advisor: Macke, Andreas
Keywords: Saharan Dust, Radiative Transfer, Particle Shape Saharastaub, Strahlungstransport, Partikelformen
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Open Access Journal?: Yes
Date Deposited: 31 Jan 2013 14:10
Last Modified: 26 Jul 2023 05:53

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