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

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 for 70-90 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.