Aircraft Measurements of the Radiative Effects of Tropospheric

Abstract

The size distribution and the complex refractive index of tropospheric aerosols have been retrieved from the simultaneous observations of solar radiation and aerosols described in Part I of this study (Asano and Shiobara, 1989). Three sets of observations over the Tsukuba area have been analyzed, for which the aerosol optical thicknesses were available from ground-based spectral attenuation measurements of direct solar radiation.The bimodal size distribution for tropospheric aerosols was approximated by a composite powerlaw distribution function. The parameters of the distribution function were determined by fitting the function to the columnar size distributions inverted from photometrically measured spectral optical thicknesses. Estimation was made of wavelength-mean effective values of the complex refractive index m*=mr-mii which optimally simulate the observed solar fluxes and heating rates for the total solar spectral region. In the simulated calculations, the observed profiles of aerosols and water vapor were considered. The single scattering properties were computed from Mie theory for the determined size distribution and for a reasonably assumed real part of the index of refraction of mr=1.52. The optimal value of mi=0.03*0.02 was estimated for the imaginary part of the index of refraction of the tropospheric aerosols.