Contribution of large‐scale circulation anomalies to variability of summer precipitation extremes in northeast China

摘要

We propose a short‐lived extreme precipitation event, which is identified by the definition of 75th and 95th percentile using gauge observations across northeast China (NEC). Atmospheric variables from reanalysis dataset are then composited to examine the contribution of synoptic‐scale circulations to variations in extreme events. Results show that the divergence aloft combined with lower pressures at surface lead to upward vertical motion of circulations, along with flow around low‐pressure area and high pressure to east NEC derived from associated wavetrain conveying efficient moisture, providing favorable environment for occurrence of precipitation extremes. The northwestward shift of western Pacific subtropical high, together with northward shifted position of upper‐level westerlies over NEC, results in the strengthened southwesterly, which transports more moisture into NEC and produces extreme rainfall. Moreover, the stronger anomalies of dynamical quantities present for 95th percentile cases. The roughly same percentage of summertime short‐lived extreme events related to cut‐off lows (COLs) is found for both percentile composites, 21.2% (79 out of 373) and 21.1% (77 out of 365) for 75th and 95th percentile events, respectively. Overall, the contribution of COLs to short‐lived extreme precipitation is insignificant during 1960–2015 in NEC, although COLs have been documented to be more active in summer over NEC. The time series of COL‐induced events exhibits inter‐annual variability with not statistically significant linear trend, suggesting that COLs play a tiny role to the slightly decreasing trend of short‐lived precipitation events over NEC. Short‐lived rainfall events show insignificant decreasing trends in NEC. Large‐scale circulation anomalies contribute remarkably to extreme rainfall. Short‐lived precipitation extremes are not significantly affected by COLs. In the figure, contribution of moisture fluxes and cut‐off lows to precipitation extremes in NEC.