山东半岛两次海风锋引起的强对流天气对比

Comparative Analysis of Two Strong Convections Triggered by Sea-breeze Front in Shandong Peninsula

利用常规地面和高空观测资料、烟台和青岛多普勒天气雷达资料、加密自动气象站等资料分析2014年7月14日("7·14")和2009年6月29日("6·29")山东半岛两次海风锋引起的强对流天气。结果表明:"7·14"强对流天气发生于冷涡后部前倾槽的环流形势下,明显的静力不稳定层结、中等大小的对流有效位能及垂直风切变相对偏弱,是此次对流风暴持续时间短且降雹范围较小的原因;"6·29"过程是东北冷涡影响下的强对流天气。海风锋、阵风锋、地面辐合线是两次过程的触发机制,两次过程都出现了高悬的强回波、弱回波区、回波悬垂、钩状回波、中气旋等超级单体回波特征;大冰雹形成期表现为中气旋垂直伸展较大和旋转较强,两次过程的超级单体风暴均由海风锋触发的靠近山脉的风暴发展加强而成,即地形与海风锋结合导致的更强抬升在加强对流风暴并演化为超级单体风暴中起了关键作用。但"6·29"强对流天气过程出现了强中气旋,"7·14"强对流天气过程出现了弱中气旋,因此,前者对流范围更大、强度更强。

Using surface and high conventional observations, radar echo data and automatic weather station data of Yantai and Qingdao, two strong convections triggered by sea breeze front in Shandong Peninsula on 14 July 2014 and 29 June 2009 are analyzed. The convection on 14 July 2014 occurs under circulation patterns of forward-tilting trough in the back of cold vortex, where dry and cold air at middle and upper layer is strong, warm and humid air at low layer is weak, leading to obvious static instability stratification and moderate convective available potential energy. The vertical wind shear is from weak to moderate, there- fore the duration of supercell is short, and the range of hail is small. The convection on 29 June 2009 ap- pears under circulation patterns of a typical northeast cold vortex, and strong vertical wind shear is a prin- cipal factor in the maintenance of supercell. Sea breeze front, gust front and convergence line of surface are triggering systems. The high convective available potential energy, temperature and pseudo equivalent po- tential temperature difference between 850 hPa and 500 hPa, average wind speed of storm bearing layer, wind indices, and potential downside indices are indicative to the intensity of convection. Both processes have supercell storms, showing similar echo characteristics, such as hanging strong echoes, weak echoes regions, echo pendency, hook echoes and mesocyclones. The difference is that there is a strong mesocy- clone on 29 June 2009, while the mesocyclone on 14 July 2014 is much weaker, so the former has a larger convection range and stronger intensity. The collision process between sea-breeze front and gust front en- hances the mesocyclone, and when one factor weakens the mesocyclone weakens too. Two hail processes appear in the decline phase of cell top and echo top, maximum period of a storm with maximum reflectivi- ty. The strong radar echoes over 50 dBZ in both processes extend to much higher than the height of -20℃. Lower melting level, suitable height of 0℃, thick depth of negative temperature layer are impor- tant to large hails. In addition, the formation period of large hails are in the period of low base height, deep thickness, severe rotation intensity of mesocyclone and is simultaneous with the strong period of mesocyclone. Therefore, the size of hail is related to base height, thickness, and rotation intensity of meso- cyclone. Supercell storms of two processes occur to storms of the sea-breeze front which is close to the mountains. The stronger uplift triggering caused by combination of terrain and sea-breeze front is critical to strengthen original convective storms and evolve into supereell storms.