ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Comparative Analyses of Two Persistent Extreme Rainstorms in Sichuan Basin
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Abstract:
Two persistent extreme rainstorms occurred in Sichuan Basin on August 10-13 and 14-18 in 2020 resulting in secondary disasters,casualties,and huge economic losses.To deeply understand the development mechanism of extreme rainstorms and its disaster causing mechanism using various observations and ERA5 reanalysis data,the precipitation characteristics of these two rainstorms, as well as the development,evolution,and trigger mechanism of MCSs in the heaviest precipitation stage of these two rainstorms were analyzed. The results showed that the two processes occurred under the Ω type circulation background with “two troughs and one ridge”? in the middle and high latitudes.Besides, they were typical rainstorms accompanied by “east-high-pressure and west-low-pressure” in the basin.And both had precipitation over 250 mm/day(or 100 mm/h). The hourly rainfall of the “8.10-13” rainstorm exceeded the historical extremes,while that of the “8.14-18”rainstorm was equivalent to the historical statistical value. The strongest precipitation stage of the “8.10-13” rainstorm was a warm-sector rainstorm,which was caused by a MCC occurrence-development-maturation-weakening process. The radar echo areas greater than or equal to 40 dBZ in this rainstorm were wide and long-lasting.And the echo centroid was low and the intensity was more than 50 dBZ. The heaviest precipitation phase of the “8.14-18” rainstorm was a mixed precipitation induced by a two α-MCS occurrence-development-merger-weakening process.The radar echo areas greater than or equal to 40dBZ were narrow and short-lived.The echo centroid was low and the intensity reached 50 dBZ.Convection in the "8.10-13" rainfall was produced by horn mouth terrain flow, windward slop uplift and high temperature gradient zone，and sustained with strong warm advection at low level，weak cold advection at high level at the same time.The “8.14-18” rainstorm convection was triggered by the convergence of the lower troposphere cold,warm currents and the left convergence of the low-altitude jet stream in the warm zone.The shear formed by the intersection of the cold and warm currents caused the precipitation lasting.
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