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Based on dual-polarization radar observations, surface data and ERA5 reanalysis product, an extensive propagation high wind event in Hubei province triggered by squall line is studied. Results show that in the environment with typical thunderstorm temperature and humidity profiles (wet downburst), the squall line originating in Southwest Henan province significantly enhanced after crossing Tongbai mountain, and resulted in a Derecho event in Hubei province. The direct reason for the enhancement of the squall line is that several isolated storms on the south side merged into the squall line. Further analysis reveals that the key mesoscale systems for the enhancement of the squall line included a shallow cold outflow from another squall line, an boundary-layer jet forced by the topography and the cold pool outflow of the squall line. The topographic effects include the blocking of cold pool outflow, the valley penetration of outflow, and the orographic uplift, which triggered isolated storms and provided a mesoscale ascending environment. After the squall line crossed the mountain, extreme winds in Guangshui were mainly caused by downward momentum transfer and divergence of strong downdrafts. The intense convective cells in the squall line were composed of graupels or small hails above the melting layer, and many small solid particles melted into large water droplets or water-covered ice cores near the melting layer. Significant evaporation under the melting layer significantly reduced the diameter of raindrops and liquid water content. This indicates that significant melting and evaporation are the main mechanisms for the formation of strong downdrafts in the storm. The results enhance our understanding of the effects of mesoscale topography on storms and physical processes of the formation of extreme winds.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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