Abstract
Abstract. A new sulfate aerosol hygroscopicity parameter (κSO4) parameterization is suggested that is capable of considering the two major sulfate aerosols, H2SO4 and (NH4)2SO4, using the molar ratio of ammonium to sulfate (R). An alternative κSO4 parameterization method is also suggested that utilizes typical geographical distribution patterns of sulfate and ammonium, which can be used when ammonium data are not available for model calculation. Using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), the impacts of different κSO4 parameterizations on cloud microphysical properties and cloud radiative effects in East Asia are examined. Comparisons with the observational data obtained from an aircraft field campaign suggest that the new κSO4 parameterizations simulate more reliable aerosol and cloud condensation nuclei concentrations, especially over the sea in East Asia, than the original κSO4 parameterization in WRF-Chem that assumes sulfate aerosols as (NH4)2SO4 only. With the new κSO4 parameterizations, the simulated cloud microphysical properties and precipitation became significantly different, resulting in a greater cloud albedo effect of about −1.5 W m−2 in East Asia than that with the original κSO4 parameterization. The new κSO4 parameterizations are simple and readily applicable to numerical studies investigating the impact of sulfate aerosols in aerosol–cloud interactions without additional computational expense.
Highlights
Aerosols impact global climate by directly scattering and absorbing radiation
The simulated sulfate and ammonium distributions are compared with the observational data that were measured onboard the NASA DC-8 aircraft during the KORUS–AQ campaign in and around the Korean Peninsula in May and June of 2016
The performance of the new κSO4 parameterizations was evaluated by comparing it with observational data obtained from a field campaign in East Asia, and it was demonstrated that the new parameterizations could produce more reliable aerosol and cloud condensation nuclei (CCN) concentrations than the previous method, which used a single κSO4 value (i.e., κ(NH4)2SO4 )
Summary
Aerosols play an important role as potential cloud condensation nuclei (CCN). The aerosol-induced changes in cloud microphysical properties can alter the Earth’s radiation budget and hydrological cycle. Such aerosol–cloud interactions possibly cause the greatest uncertainty in the estimation of climate forcing due to their complexity (Myhre et al, 2013). Understanding the role of aerosols as CCN (CCN activation) is important for predicting future climate. CCN activation depends on the chemical and physical properties of aerosols (Köhler, 1936; Abdul-Razzak et al, 1998; Dusek et al, 2006; Fountoukis and Nenes, 2005; Khvorostyanov and Curry, 2009; Ghan et al, 2011). Soluble aerosol species have high potential to become CCN, and differences in aerosol solubility could exert a considerable impact on CCN activation (Nenes et al, 2002; Kristjánsson 2002)
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