An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this at...An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.展开更多
依据常规高空、地面观测及雷达资料,对2014年6月22日滨海新区的强对流天气(短时强降水、冰雹)过程进行分析。结果表明:1)500 h Pa低涡位于40°N,滨海新区上游有冷空气侵入,并且700 h Pa和850 h Pa也有切变线存在,是滨海新区地区发...依据常规高空、地面观测及雷达资料,对2014年6月22日滨海新区的强对流天气(短时强降水、冰雹)过程进行分析。结果表明:1)500 h Pa低涡位于40°N,滨海新区上游有冷空气侵入,并且700 h Pa和850 h Pa也有切变线存在,是滨海新区地区发生强对流天气的环流背景。2)对流层低层水汽充沛,探空CAPE、SWEAT等指数指示意义较好,存在较好的不稳定能量和弱的垂直风切变,尤其是地域性的海风过程提供了触发条件和底层水汽。3)雷达回波演变上可以清晰看到出流边界(阵风锋)和海风锋共同作用触发单体回波及单体发展、旺盛、消亡演变过程。该过程中,冰雹移动路径沿滨海新区地面辐合线(海风锋)呈东北—西南向移动,该路径是滨海新区的强对流天气常有的移动路径之一。展开更多
The evolution of a sea-breeze front （SBF） in parallel and offshore environmental flows was investigated by using high-resolution simulations of two SBF cases from the Bohai Bay region, China. The results show that t...The evolution of a sea-breeze front （SBF） in parallel and offshore environmental flows was investigated by using high-resolution simulations of two SBF cases from the Bohai Bay region, China. The results show that the combination of a distinct vertical wind shear caused by the sea-breeze circulation with a neutral or slightly stable atmospheric stratification associated with the thermal inner boundary layer promoted the occurrence and maintenance of a Kelvin-Helmholtz billow （KHB）. In a parallel environmental flow, the SBF evolved into a few connected segments because of the inhomogeneity of the sea-breeze direction and intensity as it penetrated inland. A significant upward vertical motion occurred at the two ends of the SBF segment owing to the sea-breeze convergence and was accelerated by the KHB. The KHB made a notable contribution to the intensity at the ends of the segment, whereas the intensity at the middle segment was primarily attributed to the convergence between the sea breeze and the parallel flow. In the offshore environmental flow, the clockwise rotation of the offshore flow varying with time increased the downstream convergence of the interface between the sea breeze and the offshore flow and pushed the downstream convergence zone to an orientation consistent with the offshore flow. The air parcels ascending from the downstream part of the SBF were continuously lifted by the downstream convergence zone during their advection, leading to a significant downstream development of the SBF. The significant upward vertical motion caused by the sea-breeze convergence behind the upstream end of the SBF was shifted to the upstream end of the SBF by the KHB, which enhanced the intensity of the upstream end of the SBF.展开更多
对2007年8月13日天津多普勒天气雷达（CIN RAD WSR/98D）探测的雷暴天气个例进行分析,结果表明：此次雷暴天气是由渤海湾海风锋与阵风锋碰撞形成的;碰撞后,在海风锋前端、阵风锋前部有新的雷暴单体形成;阵风锋后部的对流回波主体加强,...对2007年8月13日天津多普勒天气雷达（CIN RAD WSR/98D）探测的雷暴天气个例进行分析,结果表明：此次雷暴天气是由渤海湾海风锋与阵风锋碰撞形成的;碰撞后,在海风锋前端、阵风锋前部有新的雷暴单体形成;阵风锋后部的对流回波主体加强,对流回波主体由椭圆状加强为典型的弓状。应用天津36个自动气象站的地面六要素资料和北京850 h Pa以上探空资料,组成新的诊断资料,对该个例进行诊断分析,结果表明：雷达探测的海风锋前端具有较强的低层垂直风切变梯度和露点温度梯度大值区,海风锋前沿与0~3 km垂直风切变梯度密集区相对应,且与露点温度梯度变化较快的区域基本吻合;海风锋与阵风锋相互碰撞时,0~3 km垂直风切变在2 h内变化较快,且有明显的增加趋势,CAPE（convective available potential energy,对流有效位能）值在雷暴形成前有较明显增加;随着雷暴天气结束,上述特征随之消失。展开更多
基金supported by the National Research Fund for Public Welfare (Grant No.GYHY200906011)the National Key Technology R&D Program of China (Grant No.2009BAC51B01)the National Fundamental 973 Research Program of China (Grant No.2013CB430100)
文摘An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.
文摘依据常规高空、地面观测及雷达资料,对2014年6月22日滨海新区的强对流天气(短时强降水、冰雹)过程进行分析。结果表明:1)500 h Pa低涡位于40°N,滨海新区上游有冷空气侵入,并且700 h Pa和850 h Pa也有切变线存在,是滨海新区地区发生强对流天气的环流背景。2)对流层低层水汽充沛,探空CAPE、SWEAT等指数指示意义较好,存在较好的不稳定能量和弱的垂直风切变,尤其是地域性的海风过程提供了触发条件和底层水汽。3)雷达回波演变上可以清晰看到出流边界(阵风锋)和海风锋共同作用触发单体回波及单体发展、旺盛、消亡演变过程。该过程中,冰雹移动路径沿滨海新区地面辐合线(海风锋)呈东北—西南向移动,该路径是滨海新区的强对流天气常有的移动路径之一。
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund(GYHY201306009)Fundamental Research Funds for Chinese Academy of Meteorological Sciences(2013Y008)
文摘The evolution of a sea-breeze front （SBF） in parallel and offshore environmental flows was investigated by using high-resolution simulations of two SBF cases from the Bohai Bay region, China. The results show that the combination of a distinct vertical wind shear caused by the sea-breeze circulation with a neutral or slightly stable atmospheric stratification associated with the thermal inner boundary layer promoted the occurrence and maintenance of a Kelvin-Helmholtz billow （KHB）. In a parallel environmental flow, the SBF evolved into a few connected segments because of the inhomogeneity of the sea-breeze direction and intensity as it penetrated inland. A significant upward vertical motion occurred at the two ends of the SBF segment owing to the sea-breeze convergence and was accelerated by the KHB. The KHB made a notable contribution to the intensity at the ends of the segment, whereas the intensity at the middle segment was primarily attributed to the convergence between the sea breeze and the parallel flow. In the offshore environmental flow, the clockwise rotation of the offshore flow varying with time increased the downstream convergence of the interface between the sea breeze and the offshore flow and pushed the downstream convergence zone to an orientation consistent with the offshore flow. The air parcels ascending from the downstream part of the SBF were continuously lifted by the downstream convergence zone during their advection, leading to a significant downstream development of the SBF. The significant upward vertical motion caused by the sea-breeze convergence behind the upstream end of the SBF was shifted to the upstream end of the SBF by the KHB, which enhanced the intensity of the upstream end of the SBF.
文摘对2007年8月13日天津多普勒天气雷达（CIN RAD WSR/98D）探测的雷暴天气个例进行分析,结果表明：此次雷暴天气是由渤海湾海风锋与阵风锋碰撞形成的;碰撞后,在海风锋前端、阵风锋前部有新的雷暴单体形成;阵风锋后部的对流回波主体加强,对流回波主体由椭圆状加强为典型的弓状。应用天津36个自动气象站的地面六要素资料和北京850 h Pa以上探空资料,组成新的诊断资料,对该个例进行诊断分析,结果表明：雷达探测的海风锋前端具有较强的低层垂直风切变梯度和露点温度梯度大值区,海风锋前沿与0~3 km垂直风切变梯度密集区相对应,且与露点温度梯度变化较快的区域基本吻合;海风锋与阵风锋相互碰撞时,0~3 km垂直风切变在2 h内变化较快,且有明显的增加趋势,CAPE（convective available potential energy,对流有效位能）值在雷暴形成前有较明显增加;随着雷暴天气结束,上述特征随之消失。
