一次伴有雷暴大风的飑线天气过程分析及数值模拟研究

利用常规观测资料，多普勒天气雷达产品，基于多源数据的RMAPS模拟结果等，对2017年7月9日发生在河北顺平县的一次由下击暴流引发的极端大风过程进行了分析和模拟。结果表明：（1）对流云中及云下方的西北气流受降水影响，动量下传且伴有地面的辐散风，近地层的下沉中心位于地面大风区上空。（2）云中水成物微物理特征模拟结果显示雨水和霰/冰雹的比含水量大，雹胚生长主要与雪和云水有关，而霰/冰雹融化后增加了雨水粒子。（3）比较不同水成物的等效冷却温度，发现雨水蒸发冷却对大风形成的贡献最大，冰雹的融化机制和拖曳作用贡献量相当；在700 hPa以下，随着高度降低雨水拖曳的贡献逐渐大于冰雹融化与冰雹拖曳贡献之和。（4）下沉气流叠加在地面辐散风场和冷池密度流上，导致地面辐散中心的东南侧出现了43.1 m·s^-1的极端强风。极端强风的下游，由于云水凝结、雹胚生长等凝结潜热释放过程抵消了部分水成物的冷却效应，以及冷出流减弱等因素，使得地面风速有所减弱。

Observational and numerical study of a microburst line-producing storm

Using conventional surface observations, Doppler radar imagery and products of the RMAPS model, a gust caused by a downburst event occurred on July 9, 2017, in Shunping of Hebei Province was studied. The results showed that: (1) The northwesterly flow from the convective cloud and below the cloud is affected by precipitation, which resulted in the downward momentum transport accompanied by surface divergent winds. The subsidence center near the surface is above the gust region. (2) Simulation showed the rain and graupel/hail with high mixing ratio. The moisture contribution to the growth of hail embryos was mainly from snow and cloud water. Rain drops increased with graupel/hail melting. (3) Compared to equivalent cooling temperature with the cloud and rain water, rainfall evaporation contributes the most to the gust, followed by the equal contribution from the melting mechanism of hail and the dragging effect, and the contribution of rainfall dragging is greater than that of hail melting below 700hPa. (4) The downdraft, together with surface divergence of cold pool flow led to an extreme gust with a new record in downstream of the surface divergence center. In addition, the surface wind speed was reduced downstream of the extreme winds due to the heating effects of latent heat release by cloud water condensation and hail embryo growth, which offset partly cooling effects of water, as well as weakened outflow at surface.