Record Details
A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds |
| Names |
Marshak, Alexander
(creator) Wen, Guoyong (creator) Coakley, James A. (creator) Remer, Lorraine A. (creator) Loeb, Norman G. (creator) Cahalan, Robert F. (creator) |
| Date Issued | 2008 (iso8601) |
| Note | This work was supported by the Department of Energy (under grant DE-AI02-95ER61961 to NASA’s GSFC) as part of the Atmospheric Radiation Measurement (ARM) program, by NASA’s Radiation Program Office (under grants 621-30-86 and 622-42-57); by the National Oceanic and Atmospheric Administration Climate Program Office’s Atmospheric Composition and Climate program (under grant NA06OAR4310083); and by NASA’s CALIPSO Project (under grant NAS1-99104). |
| Abstract | In determining aerosol-cloud interactions, the properties of aerosols must be characterized in the vicinity of clouds. Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3-D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. The paper only addresses the cloud-clear sky radiative transfer interaction part. It provides a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. This assumption leads to a larger increase of AOT for shorter wavelengths, or to a ‘‘bluing’’ of aerosols near clouds. The assumption that contribution from molecular scattering dominates over aerosol scattering and surface reflection is justified for the case of shorter wavelengths, dark surfaces, and an aerosol layer below the cloud tops. The enhancement in Rayleigh scattering is estimated using a stochastic cloud model to obtain the radiative flux reflected by broken clouds and comparing this flux with that obtained with the molecules in the atmosphere causing extinction, but no scattering. |
| Genre | Article |
| Identifier | Marshak, A., G. Wen, J. A. Coakley Jr., L. A. Remer, N. G. Loeb, and R. F. Cahalan (2008), A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds, J. Geophys. Res., 113, D14S17, doi:10.1029/2007JD009196. |
