Index Geophysics

On the discrepancies between theoretical and measured below-cloud particle scavenging coefficients for rain – a numerical investigation using a detailed one-dimensional cloud microphysics model

Existing theoretical formulations for the size-resolved scavenging coefficient &Lambda;(<i>d</i>) for atmospheric aerosol particles scavenged by rain predict values lower by one to two orders of magnitude than those estimated from field measurements of particle-concentration changes for particles smaller than 3 μm in diameter. Vertical turbulence is not accounted for in the theoretical formulations of &Lambda;(<i>d</i>) but does contribute to the field-derived estimates of &Lambda;(<i>d</i>) due to its influence on the overall concentration changes of aerosol particles in the layers undergoing impaction scavenging. A detailed one-dimensional cloud microphysics model has been used to simulate rain production and below-cloud particle scavenging, and to quantify the contribution of turbulent diffusion to the overall &Lambda;(<i>d</i>) values calculated from particle concentration changes. The relative contribution of vertical diffusion to below-cloud scavenging is found to be largest for submicron particles under weak precipitation conditions. The discrepancies between theoretical and field-derived &Lambda;(<i>d</i>) values can largely be explained by the contribution of vertical diffusion to below-cloud particle scavenging for all particles larger than 0.01 μm in diameter for which field data are available. The results presented here suggest that the current theoretical framework for &Lambda;(<i>d</i>) can provide a reasonable approximation of below-cloud aerosol particle scavenging by rain in size-resolved aerosol transport models if vertical diffusion is also considered by the models.

Wang, X.

Zhang, L.

Moran, M. D.

2018-01-15

Text

application/pdf

10.5194/acp-11-11859-2011

https://acp.copernicus.org/articles/11/11859/2011/

eISSN: 1680-7324

eng