Abstract:Based on the high spatio-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, we comparatively analyze 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 was no obvious synoptic scale system dominating the three local sudden heavy rainstorms, but the ambient atmosphere had high convective available potential energy and low convective inhibition energy. The lifting condensation height was only 0.2-0.4 km, with a certain wet layer in the lower level. Generally, the occurrence of local sudden rainstorm is mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the three local sudden rainstorms, the differences in temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious nonuniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of the local convection. In addition, before the occurrence of the local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened. The converged thermal low pressure of the urban heat island and the converged sea breeze jointly made the mesoscale convergence intensity significantly strengthened, which was the main cause for the occurrence of local sudden rainstorm. The meso-γ scale convective cells were triggered at the edge of the strong convergence center.