Optimization of the sulfate aerosol hygroscopicity parameter in WRF-Chem

A new sulfate aerosol hygroscopicity parameter (inline-formula $M1inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimg622dc9929597c20909d24ffc7eafcadd gmd-14-259-2021-ie00001.svg23pt12ptgmd-14-259-2021-ie00001.png ) parameterization is suggested that is capable of considering the two major sulfate aerosols, inline-formulaH₂SO₄ and inline-formula(NH₄)₂SO₄, using the molar ratio of ammonium to sulfate (inline-formulaR). An alternative inline-formula $M5inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimg350642aa3ea7fb10e1a963dc56ac717d gmd-14-259-2021-ie00002.svg23pt12ptgmd-14-259-2021-ie00002.png 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 inline-formula $M6inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimg0f3761c00885f50ffc65c527b771c5c4 gmd-14-259-2021-ie00003.svg23pt12ptgmd-14-259-2021-ie00003.png 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 inline-formula $M7inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimge2f3251b358b44a6f8d3a15ba0086037 gmd-14-259-2021-ie00004.svg23pt12ptgmd-14-259-2021-ie00004.png parameterizations simulate more reliable aerosol and cloud condensation nuclei concentrations, especially over the sea in East Asia, than the original inline-formula $M8inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimgd9220de5bf940efc6e3431cf9a6062be gmd-14-259-2021-ie00005.svg23pt12ptgmd-14-259-2021-ie00005.png parameterization in WRF-Chem that assumes sulfate aerosols as inline-formula(NH₄)₂SO₄ only. With the new inline-formula $M10inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimg258510d1afdd1d0b6104fa69eb87bb78 gmd-14-259-2021-ie00006.svg23pt12ptgmd-14-259-2021-ie00006.png parameterizations, the simulated cloud microphysical properties and precipitation became significantly different, resulting in a greater cloud albedo effect of about inline-formula−1.5 inline-formulaW m⁻² in East Asia than that with the original inline-formula $M13inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimgd99655f1c2dd3e716efadbc1d2115c45 gmd-14-259-2021-ie00007.svg23pt12ptgmd-14-259-2021-ie00007.png parameterization. The new inline-formula $M14inlinescrollmathml{\mathrm{italic\; \kappa }}_{chem{\mathrm{normal\; SO}}_{\mathrm{normal\; 4}}}$ 23pt12ptsvg-formulamathimg49d4a39662b4c1417d54bf9e92b95264 gmd-14-259-2021-ie00008.svg23pt12ptgmd-14-259-2021-ie00008.png parameterizations are simple and readily applicable to numerical studies investigating the impact of sulfate aerosols in aerosol–cloud interactions without additional computational expense.