Spatial Variation of Stratospheric Aerosol Acidity and Model Refractive Index: Implications of Recent Results

Philip B. Russell NASA Ames Research Center, Moffett Field, CA 94035

Search for other papers by Philip B. Russell in
Current site
Google Scholar
PubMed
Close
and
Patrick Hamill Physics Department, San Jose State University, San Jose, CA 95192

Search for other papers by Patrick Hamill in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

Recent experimental results indicate that little or no solid ammonium sulfate is present in background stratospheric aerosols. Other results allow straightforward calculation of sulfuric acid/water droplet properties (acidity, specific gravity, refractive index) as functions of stratosphere temperature and humidity. We combine these results with a variety of latitudinal and seasonal temperature and humidity profiles to obtain corresponding profiles of droplet properties. These profiles are used to update a previous model of stratospheric aerosol refractive index. The new model retains the simplifying approximation of vertically constant refractive index in the inner stratosphere, but has sulfuric acid/water refractive index values that significantly exceed the previously used room temperature values. Mean conversion ratios (e.g., extinction-to-number, backscatter-to-volume) obtained using Mie scattering calculations with the new refractive indices are very similar to those obtained for the old indices, because the effect of deleting ammonium sulfate and increasing acid indices tend to cancel each other.

Abstract

Recent experimental results indicate that little or no solid ammonium sulfate is present in background stratospheric aerosols. Other results allow straightforward calculation of sulfuric acid/water droplet properties (acidity, specific gravity, refractive index) as functions of stratosphere temperature and humidity. We combine these results with a variety of latitudinal and seasonal temperature and humidity profiles to obtain corresponding profiles of droplet properties. These profiles are used to update a previous model of stratospheric aerosol refractive index. The new model retains the simplifying approximation of vertically constant refractive index in the inner stratosphere, but has sulfuric acid/water refractive index values that significantly exceed the previously used room temperature values. Mean conversion ratios (e.g., extinction-to-number, backscatter-to-volume) obtained using Mie scattering calculations with the new refractive indices are very similar to those obtained for the old indices, because the effect of deleting ammonium sulfate and increasing acid indices tend to cancel each other.

Save