海风锋及低压环流对闽东一次暴雨过程的影响分析

Analysis of a heavy rainfall event triggered by sea breeze front and cyclonic circulation in the eastern coast of Fujian

利用常规气象观测资料、NCEP再分析资料与WRF数值模拟资料,以2014年8月11日闽东沿海一次大暴雨天气过程为例,分析了该过程中海风锋、低压环流的形成、移动及其在暴雨区上空的结构演变与热力、动力特征。结果表明:(1)该过程午后强降水的主要影响系统是海风锋,夜间强降水的主要影响系统是低压环流。(2)数值模式较好地模拟出海风锋的生消以及低压环流的形成和移动。海风能深入到内陆70~90 km,并与山谷风形成海风锋。在海风锋的前端是东南风和东北或西北风交汇的辐合带,对应其南侧海风气旋性曲率最大处,降水越强。(3)海风锋在向内陆推进的过程中呈现出湿度增大、湿层增厚、气温下降的特征;海风最强时刻对应低空辐合最强、地面降水最强;海陆气压差日变化与海陆温差呈反位相分布。(4)闽东沿海午后强降水主要由海风锋造成;夜间,再次增强的偏南气流与随冷空气南下的偏北气流汇合,激发气旋性涡度增大,使得低压环流强烈发展,导致闽东沿海夜间大暴雨。

Using datasets of conventional observations, NCEP/NCAR reanalysis and numerical simulations by WRF model, we have investigated the formation and motion of sea breeze front（SBF） and cyclonic circulation, as well as their thermodynamic and dynamic structure characteristics, for a heavy rainfall event occurred in the eastern coast of Fujian on 11 August 2014. The results indicate that（1） the main weather systems leading to the severe rainfall is SBF in afternoon and cyclonic circulation in nocturnal.（2） The generation and dissipation of SBF and the formation and motion of cyclonic circulation are reasonably simulated by the numerical model. Sea breeze invades interior territory for70-90 km and encounters valley wind triggering SBF. A convergence zone is in front edge of the SBF caused by southeast wind and northeast wind or northwest wind, corresponding to the maximum cyclonic curvature of sea breeze in the south side convergence zone where rainfall intensity is the strongest.（3） The characteristics of increasing humidity, thickening wet layer and decreasing temperature are presented in the process of sea breeze advancing inland. When the sea breeze reaches the strongest, both low-level convergence and ground-level precipitation reach the strongest, too. Diurnal variations of pressure difference and temperature difference are reversed phase distribution between sea and land.（4） Severe rainfall in the afternoon in the eastern coast of Fujian is mainly caused by SBF. At night, the converge of the southerly air flow increased further and the northerly air flow with the cold air moving southwards triggers the increase of cyclonic vorticity, which makes the low-pressure circulation developed vigorously, and eventually resulting in extremely heavy rainfall in nocturnal in east coast of Fujian.