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# The Role of Initial Cloud Condensation Nuclei Concentration in Hail Using the WRF NSSL 2-moment Microphysics Scheme

• The effects of the initial cloud condensation nuclei (CCN) concentrations (100-3000 mg-1) on hail properties were investigated in an idealized non-severe hail storm experiment using the Weather Research and Forecasting (WRF) model, with the National Severe Storms Laboratory 2-moment microphysics scheme. The initial CCN concentration (CCNC) had obvious non-monotonic effects on the mixing ratio, number concentrations, and radius of hail, both in clouds and at the surface, with a CCNC threshold between 300 and 500 mg-1. An increasing CCNC is conducive (suppressive) to the amount of surface hail precipitation below (above) the CCNC threshold. The non-monotonic effects were due to both the thermodynamics and microphysics. Below the CCNC threshold, the mixing ratios of cloud droplets and ice crystals increased dramatically with the increasing CCNC, resulting in more latent heat released from condensation and frozen between 4 and 8 km and intensified updraft volume. The extent of the riming process, which is the primary process for hail production, increased dramatically. Above the CCNC threshold, the mixing ratio of cloud droplets and ice crystals increased continuously, but the maximum updraft volume was weakened because of reduced frozen latent heating at low level. The smaller ice crystals reduced the formation of hail and smaller clouds, with decreased rain water reducing riming efficiency so that graupel and hail also decreased with increasing CCNC, which is unfavorable for hail growth.
摘要: 本研究基于WRF模式理想的冰雹对流云实验, 使用NSSL双参数云微物理方案, 探究初始云凝结核浓度(CCNC, 100–3000 mg-1)对冰雹的影响. 实验结果表明, CCNC对云中以及落在地面的冰雹的混合比, 数浓度以及等效半径均有明显的非单调作用, 并且存在一个“阈值”浓度介于300-500 mg-1. 当低于(高于)该“阈值”时, 增加云凝结核浓度将会促进(抑制)地面的降雹量. 这种非单调的结果是由于热动力和云微物理两方面所导致的. 当云凝结核浓度低于“阈值”时, 云滴以及冰晶的混合比会随着CCNC的增加而快速增加, 这便会使得在4千米和8千米高度的凝结潜热和冻结潜热大量释放, 进一步的会增加上升气流体积, 同时冰雹增长的淞化过程也会得到加强, , 使得冰雹得到快速增长; 当云凝结核浓度高于“阈值”时, 云滴和冰晶的混合比会进一步增加, 但是由于他们的半径急剧减小而很快被带到更高的地方, 使得在较低处的冻结潜热释放减少从而上升气流体积也减少, 冰晶半径较小会使得雹胚形成的效率变低, 另外, 更小的雨滴和混合比降低的雨滴不利于冰雹和霰的淞化过程.

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## Manuscript History

Manuscript revised: 30 March 2017
Manuscript accepted: 10 April 2017
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## The Role of Initial Cloud Condensation Nuclei Concentration in Hail Using the WRF NSSL 2-moment Microphysics Scheme

• 1. Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China

Abstract: The effects of the initial cloud condensation nuclei (CCN) concentrations (100-3000 mg-1) on hail properties were investigated in an idealized non-severe hail storm experiment using the Weather Research and Forecasting (WRF) model, with the National Severe Storms Laboratory 2-moment microphysics scheme. The initial CCN concentration (CCNC) had obvious non-monotonic effects on the mixing ratio, number concentrations, and radius of hail, both in clouds and at the surface, with a CCNC threshold between 300 and 500 mg-1. An increasing CCNC is conducive (suppressive) to the amount of surface hail precipitation below (above) the CCNC threshold. The non-monotonic effects were due to both the thermodynamics and microphysics. Below the CCNC threshold, the mixing ratios of cloud droplets and ice crystals increased dramatically with the increasing CCNC, resulting in more latent heat released from condensation and frozen between 4 and 8 km and intensified updraft volume. The extent of the riming process, which is the primary process for hail production, increased dramatically. Above the CCNC threshold, the mixing ratio of cloud droplets and ice crystals increased continuously, but the maximum updraft volume was weakened because of reduced frozen latent heating at low level. The smaller ice crystals reduced the formation of hail and smaller clouds, with decreased rain water reducing riming efficiency so that graupel and hail also decreased with increasing CCNC, which is unfavorable for hail growth.

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