江淮气旋影响下的山东降雪过程相态特征

利用常规的地面观测资料、高空探测资料、自动气象站1 h间隔观测资料、NCEP/NCAR再分析资料（1°×1°，6 h）和ERA5再分析资料（0.25°×0.25°，1 h），针对1999—2013年山东省12例江淮气旋降雪过程，总结了降水形态类型及时空分布、相态转换等特征并讨论了降水相态“逆转”现象的物理机制。结果表明：1）江淮气旋降雪过程的降水形态种类多样，可出现雨、雪、雨夹雪、冰雹、冰粒、霰、米雪和雨凇，降水相态转换过程中，除了雨夹雪，冰粒也是一种过渡形态；2）冰雹、冰粒、霰、米雪和雨凇5种特殊降水形态最易出现在2月和3月，“雷打雪”现象亦多发于2月和3月；3）鲁东南和半岛南部地区以降雨为主，鲁西北地区多出现降雪，雷暴集中出现在鲁中的中西部和鲁南地区，尤其是鲁东南地区；4）江淮气旋降雪过程相态转换的基本形式为雨转雪，以有无明显雨雪分界线为依据，可分为“典型雨转雪”和“无明显雨雪转换”两类，二者的影响系统特点显著不同；5）范围较大的相态逆转现象易发区域在地面雨雪分界线附近，位于地面倒槽后部，走向与地面倒槽槽线走向一致。气旋生成前低层暖温度平流增强引起低层增温以及气温日变化导致的中午前后近地层浅薄增温均可引起相态逆转，上述两个因素均与地面倒槽的发展态势关系密切。

Feature of precipitation phase in snowfall process in Shandong induced by Changjiang-Huaihe cyclone

By using conventional surface observation data, sounding data, automatic weather station data with an interval of 1 h, NCEP/NCAR reanalysis data (1°×1°, 6 h), and ERA5 reanalysis data (0.25°×0.25°, 1 h), the types and spatial-temporal distribution of forms of precipitation, transformation of phases, and physical mechanism of phase inversion are discussed and summarized based on 12 cases of snowfall processes induced by Changjiang-Huaihe cyclone from 1999 to 2013 in Shandong Province. The results are shown as follows. 1) There are various forms of precipitation in snowfall processes induced by Changjiang-Huaihe cyclone, such as rain, snow, sleet, hail, ice particle, graupel, snow grain, and glaze. Ice particle also acts as a transition form of precipitation in transformation of phases besides sleet. 2) Hail, ice particle, graupel, snow grain, and glaze appear most frequently in February, followed by March. Thundersnow occurs often in February and March. 3) Rain often occurs in the southeast of Shandong Province and the south of Shandong Peninsula, while snow often appears in the northwest of Shandong Province. In addition, thunderstorm occurs in the middle and western part of central Shandong Province and the south of Shandong Province, especially the southeast of Shandong Province. 4) The transformation from rain to snow is the basic phase change in snowfall process by Changjiang-Huaihe cyclone. Based on existence of rain and snow boundary, the transformation of phases can be categorized into two kinds, one is typical transition from rain to snow, the other one is without obvious transition from rain to snow. There are significant differences in synoptic systems. 5) Large-scale phase inversion phenomenon tends to occur near the boundary between snowfall area and rainfall area. The zone of phase inversion, with the same orientation of surface inverted trough, is located behind surface inverted trough. Phase inversion can be caused by temperature increase resulted from warm temperature advection at lower troposphere and shallow warming resulted from diurnal variation of temperature near surface around noon before cyclogenesis. The two factors both are closely related with the development of surface inverted trough.