Abstract:

This study aims to understand the mechanism of rainstorm events and the difference of precipitation characteristics of cold air at different heights combining with landing typhoons. The unusual rainstorm events on October 7 - 8, 2013 and July 11, 2016 in southeast Jiangsu caused by the landing typhoon No. 1323 “Fitow” and No. 1601 “Nepartak” respectively were used for comparative analysis. The results showed that during the “10·7 - 8” rainstorm, the low-level cold air intruded into the “Fitow” residual low pressure, combined with the easterly jet on the north side of “Danas”, the atmospheric stratification changed from convective instability to conditional symmetric instability. The frontogenesis and convergence of the low-level baroclinic increased, the high-level strong divergence and the inclined convection developed, those led to the stratigraphic and cumulative mixed heavy precipitation with uniform distribution and long duration, the center of the rainstorm had the same location with the frontogenesis and MPV2 in the lower troposphere. The “7.11” rainstorm was caused by the development of mesoscale low pressure induced by the lower layer near the top of the residual low pressure inverted trough of “Nepartak”. The cold air intruded into the middle level, the strong convective instability stratification was established, and the release of the convective effective potential energy formed a strong vertical upward movement, those resulted in strong convective heavy precipitation with uneven distribution, short duration and strong short-term rainfall, the rainstorm center was located near the surface mesoscale convergence line and temperature ridge. During the “10·7 - 8” rainstorm, the easterly jet on the north side of the typhoon provided sufficient water vapor. Water vapor in the process of “7.11” rainstorm mainly came from the easterly transport of the right side of the local and mesoscale low pressure. Different heights of cold air intruding into the landing typhoon system could result in different formation mechanisms of atmospheric stratification stability and ascending motion causing significant differences in precipitation characteristics, and deserves attention in the operational forecast.

Key words: typhoon rainstorm, cold air, stability, ascending motion