Open AccessSensitivity of aerosol indirect effects to cloud nucleation and autoconversion parameterizations in short‐range weather forecasts during the May 2003 aerosol IOP
Author(s) -
Chuang Catherine C.,
Kelly James T.,
Boyle James S.,
Xie Shaocheng
Publication year - 2012
Publication title -
journal of advances in modeling earth systems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.03
H-Index - 58
ISSN - 1942-2466
DOI - 10.1029/2012ms000161
Subject(s) - aerosol , cloud forcing , shortwave , atmospheric sciences , environmental science , cloud albedo , precipitation , cloud feedback , climatology , climate model , liquid water content , radiative forcing , cloud physics , meteorology , liquid water path , climate sensitivity , climate change , cloud computing , cloud cover , radiative transfer , physics , geology , computer science , oceanography , quantum mechanics , operating system
Aerosol‐cloud interactions begin with the direct involvement of aerosols in cloud nucleation followed by its indirect contribution to the formation of precipitation through autoconversion. Since the treatments of cloud microphysics in climate models are highly parameterized, a thorough study is needed to examine the range of simulations associated with different parameterizations of aerosol‐cloud interactions. Unlike previous studies focused on climate‐mode simulations, our interest is in short‐range model response before the development of model bias and the compensation of multiple feedback mechanisms. In this study, we modified CAM4 to explore model sensitivity to treatments of cloud nucleation and autoconversion over the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility during the May 2003 Aerosol Intensive Operations Period (IOP) under the Cloud‐Associated Parameterizations Testbed framework. Simulated liquid water path and low cloud fraction were sensitive to the choice of parameterization; however, change of modeled precipitation was insignificant with varying parameterization in short‐range (∼3 day) simulation. In general, simulated cloud properties were more sensitive to the treatment of autoconversion than nucleation. Calculations of sulfate indirect effects indicate that the change of shortwave fluxes from cloud lifetime effect is much more sensitive to cloud parameterizations than cloud albedo effect. Microphysical feedbacks complicate the local response of the climate system and can yield a positive 2 nd indirect sulfate forcing that counters the expectation that increases in aerosol concentration decrease the shortwave fluxes. As a result, the calculated total sulfate indirect forcing over SGP varies widely ranging from −0.1 to −2.1 W m −2 during the IOP.