Abstract:Based on the high spatial-temporal resolution data such as ERA5(0.25°×0.25°) reanalysis data, automatic weather stations data, doppler weather radar data and the retrieval data from Variational Doppler Radar Analysis System(VDRAS), we compared and analyzed the mesoscale characteristics and triggering mechanism of three local sudden rainstorms in the urban area of Tianjin on 22 July 2018, 18 July 2019 and 23 August 2021.The results show that there is no obvious synoptic scale system leading the three local sudden heavy rainstorms, but the ambient atmosphere has a high convective available potential energy (CAPE) and a low convective inhibition energy (CIN). The lifting condensation height (LCL) was 0.2~ 0.4 km, and there was a certain wet layer in the lower level. The occurrence of local sudden rainstorm was mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the local sudden rainstorm, the difference of temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious non-uniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of local convection. In addition, before the occurrence of local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened, resulting in the convergence of wind speed. The thermal low pressure of the urban heat island and the disturbance of sea breeze made the mesoscale convergence intensity significantly strengthened, which was the main reason for the occurrence of local sudden rainstorm. γ-mesoscale convective cells were triggered at the edge of the strong convergence center.