An Analytical Model of Aerosol Optical and Microphysical Properties with Account for Hygroscopic Growth
Khvorostyanov, V.I., Central Aerological Observatory; Curry, J.A., University of Colorado
Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting
A microphysical model of aerosol size spectra that includes hygroscopic growth is presented. In the presence of atmospheric humidity, an aerosol size spectrum of the Junge-type transforms into a superposition of two equilibrium power law spectra with indices determined by the original Junge index and the fraction of soluble material contained in the aerosol. Based on this model of aerosol hygroscopic growth, the Twomey cloud condensation nuclei power law is then derived so that its coefficients are related to the aerosol microstructure and humidity dependence under subsaturation. The aerosol model is used to calculculate the aerosol scattering and absorption coefficients of solar and longwave radiation. This model provides a theoretical interpretation for the empirical Angstrom wavelength relation. An explanation is offered for the spectral behavior of the scattering coefficient and its variation with relative humidity for various types of atmospheric hazes. This model explains the negative temperature dependence of atmospheric absorption in the atmospheric winding without requiring the presence of water vapor dimers. The importance of the aerosol absorption relative to water vapor absorption in the atmospheric window increases with deceasing temperature and becomes particularly important for the polar radiation balance. Hence, aerosol absorption is a negative feedback which may be of particular importance in the Arctic during winter.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
