[A-AS03] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS03-P07] Multiscale Influences on Persistent Extreme Precipitation Events in North China

*Xiaojun Guan¹, Jianyun Gao¹, Tim Li², Lan Wang¹, Xiaoxiao Chen³ (1.Fujian Institute of Meteorological Sciences, 2.Department of Meteorology, University of Hawaii at Manoa, 3.Pingtan Meteorological Bureau)

Keywords:multiscale influences, persistent extreme precipitation events,, low-frequency oscillations, atmospheric circulation anomalies

PEPEs pose a great threat to social and economic development due to their longer duration and wider spatial coverage. This study attempts to investigate PEPEs in North China from the perspective of large-scale control by multiple climate modes. The main purpose is to gain a general understanding of PEPEs in North China and reveal their precursor signals. In this study, we classify PEPEs in North China into two types in accordance with variance contributions and significance of different periodicities of summer rainfall variability. It is found that type 1 PEPEs are dominated by the 10–20-days oscillation, whereas type 2 PEPEs are mainly influenced by the 30–60-days oscillations.On an interannual timescale, La Niña states in the preceding winter are more favorable for the occurrence of PEPEs. The major difference in tropical SST between the two types of PEPEs lies in the SST transition in the central and eastern equatorial Pacific from the preceding winter to the concurrent summer. Type 1 PEPEs tend to occur when SST anomalies in the regions persist, while type 2 PEPEs tend to occur when tropical Pacific SST anomalies transition from a cold to a warm anomaly in the concurrent summer. Features of atmospheric circulation anomalies of the two types of PEPEs share some similarities and differences. For instance, upper-level divergence is favorable for both types of PEPEs. A major difference lies in the wave train pattern. A zonally oriented wave train is dominated in the mid–high latitudes for type 1 PEPEs, while a meridionally oriented wave train is clearly seen over the East Asia for type 2 PEPEs. The water vapor sources for type 1 PEPEs are mainly from the East China Sea in association with an anticyclone downstream of North China, while for type 2 there is an additional moisture source from the tropical Indian Ocean, the South China Sea, and the tropical western Pacific.The comparison between two types of PEPEs indicates that both types result from combined effects of low-frequency oscillations in mid–high latitudes and the tropics. The EU-like (EAP-like) pattern with the 10–20-day (30–60 days) oscillation is more pronounced in type 1 (type 2) PEPEs, which suggests their different origins. The current study suggests that monitoring the 10–20-day oscillation in mid-latitudes may help set up a statistical model for conducting an extended-range forecast of type 1 PEPEs. For type 2 PEPEs, special attention should be paid to the 30–60-day signals from the tropics.