A02: Aerosol wet removal by convective clouds in E3SMv2

What causes the weakened convective scavenging of aerosols in E3SMv2?

• Kai Zhang

• kai.zhang@pnnl.gov

Kai Zhang¹, Xiaoliang Song², Po-Lun Ma¹, Hailong Wang¹, Hui Wan¹, Shaocheng Xie³, Xue Zheng³, Wuyin Lin⁴, Chris Golaz³, Phil Rasch¹, Ruby Leung¹ 1.PNNL 2. UCSD 3. LLNL 4. BNL

Atmospheric aerosols; E3SMv2; model development and evaluation

E3SM

Convective clouds can efficiently remove aerosols from the atmosphere. Compared to E3SM version 1, the aerosol wet removal by convective clouds is substantially decreased in v2, while the wet removal by stratiform clouds increased. This shift causes overall weakened aerosol wet removal, larger burden, and longer lifetime for all species (if everything else remains unchanged). Consequently, the simulated aerosol optical depth has large positive biases. To identify the reasons why there is such a shift in aerosol wet removal pathways, we have performed short nudged simulations with individual parameterization modifications reverted to the original v1 settings. We find the modifications that cause 1) a substantial change of the ratio between stratiform and convective precipitation, and 2) a large change in the cloud fields that determine the first-order loss rate (the conversion from cloud condensate to precipitation) can well explain the weakened convective scavenging of aerosols in E3SMv2. These two changes are also expected to happen when the model is running at much higher resolutions or with substantially changed/tuned parameterizations, so this study offers useful information for future model development and evaluations.

Yes

kai.zhang@pnnl.gov