New Background Stratospheric Aerosol Model for Use in Atmospheric Radiation Models

摘要

The current background stratospheric aerosol model is based on laboratory measurements of indices of refraction for a solution of H2SO4 taken at 300 K and a size distribution based on a modified gamma distribution. Stratospheric temperatures are considerably colder than this. Also, recent satellite measurements indicate that a log normal size distribution is more representative of stratospheric aerosols. Therefore, a new background stratospheric aerosol model is presented based on temperature dependent indices of refraction and a log normal size distribution that is consistent with the literature. A set of indices of refraction have been calculated using Lorentz-Lorenz corrections and interpolated values of the available laboratory measurements of the index of refraction of a mixture of 75% H2SO4 in water. Indices of refraction at 215 K have been taken as representative of an averaged, midlatitude stratosphere. The log normal size distribution based on recommendations from an experts meeting on aerosols and climatic effects held by the World Climate Programme. The proposed extinction coefficients are essentially unchanged for wavelengths up to about 5 micrometers. Above 5 micrometers, the proposed values are smaller than that in LOWTRAN 6. The differences are due almost entirely to changes in the absorption coefficient as a result of the smaller imaginary components of the index of refraction. Also, the results are insensitive to changes in size distribution. (JHD)