Abstract
Abstract. As one of the most abundant atmospheric aerosols and effective ice nuclei, mineral dust affects clouds and precipitation in the Earth system. Here numerical experiments are carried out to investigate the impacts of dust aerosols on summertime convective clouds and precipitation over the mountainous region of Taiwan by acting as ice-nucleating particles. We run the Weather Research and Forecasting model (WRF) with the Morrison two-moment and spectral-bin microphysics (SBM) schemes at 3 km resolution, using dust number concentrations from a global chemical transport model (GEOS-Chem-APM). The case study indicates that the long-range-transported mineral dust, with relatively low number concentrations, can notably affect the properties of convective clouds (ice and liquid water contents, cloud top height, and cloud coverage) and precipitation (spatial pattern and intensity). The effects of dust are evident during strong convective periods, with significantly increased ice water contents in the mixed-phase regime via the enhanced heterogeneous freezing. With both the Morrison and SBM schemes, we see the invigoration effects of dust aerosols on the convective intensity through enhanced condensation and deposition latent heating. The low-altitude dust particles are uplifted to the freezing level by updrafts, which, in turn, enhance the convective cloud development through immersion freezing and convective invigoration. Compared to the Morrison scheme, the SBM scheme predicts more realistic precipitation and different invigoration effects of dust. The differences are partially attributed to the saturation adjustment approach utilized in the bulk scheme, which leads to a stronger enhancement of condensation at midlatitudes to low altitudes and a weaker deposition increase at the upper level.
Highlights
In order to investigate the influences of dust aerosols on clouds and precipitation, the simulation results of the six runs are compared and evaluated with available observations and reanalysis
One of the possible reasons is that the contributions of other natural and anthropogenic aerosols to cloud condensation nuclei (CCN) and ice nucleating particle (INP) are not considered in the Morr2 or spectralbin microphysics (SBM) schemes in this numerical study, and another factor could be the relatively coarse resolution (3 km), which cannot resolve the orographically forcing and mountain–valley circulation well
This study explores the influences of long-range-transported mineral dust on the convective clouds and precipitation
Summary
Due to the enormous global emission rate (Zender et al, 2004; Textor et al, 2006), relatively long lifetime (days up to weeks) (Penner et al, 2001; Prospero, 1999), and the longrange transport ability (Husar et al, 2001; Perry et al, 2004; Engelstaedter et al, 2006; Liu et al, 2008; Uno et al, 2009), mineral dust is one of the most abundant aerosol components in the atmosphere (Andreae et al, 1986; Carslaw et al, 2010; Kok et al, 2017). Mineral dust is suggested to have important impacts on the radiation budget of the Earth system through direct effects (scattering and absorbing shortwave and longwave radiation) Besides the effects on radiative properties of the atmosphere, dust aerosols are suggested to influence cloud properties and enhance or suppress clouds and precipitation by serving as cloud condensation nuclei (CCN) and ice nu- 2019) and semi-direct effects through changes in the atmospheric temperature structure and cloud lifetime (Hansen et al, 1997; Koren et al, 2004; Huang et al, 2006).
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