Abstract:Using the data obtained by conventional observations, the data collected at a 255 m tower during an atmospheric boundary layer experiment in Tianjin, Doppler radar observations, VDRAS data and mesoscale TJ WRF model data, we analyze the heavy rainfall which occurred on 16 August 2010 in the urban area of Tianjin and highlight the superimposition of urban heat island and sea breeze front and trigger mechanism of local heavy precipitation caused by it. The results show that the local severe precipitation occurs under weak anti circulation conditions after low level trough, and precipitation has obvious characteristics of meso γ scale convection. Urban heat island effect can cause uneven distribution of local thermal, which is very favorable for the formation of the ground mesoscale convergence line. When moving from the shore to the urban, the sea breeze front encounters the ground mesoscale convergence line, being able to stimulate the local unstable energy release and resulting in severe convective weather. Urban heat island can block the movement of the sea breeze front. When the sea breeze front moves near the area with obvious urban heat island effect its rear airflow will be changed into branch flows, climbing. Meanwhile in the meeting place, the convergence and upward motion get strengthened rapidly, providing favorable dynamic and thermodynamic conditions for unstable energy to release and thunderstorm to develop. The mesoscale TJ WRF model can simulate this phenomenon very well.