Two types of regional daily precipitation extremes over fujian-jiangxi of China and their related anomalous circulation patterns during boreal summer

Abstract:

Based on daily rainfall data from CMA, best track data of Tropical Cyclones (TC) from JMA, and the NCEP-NCAR reanalysis from NOAA, regional mean daily precipitation extreme (RDPE) events over Fujian-Jiangxi Region (FJR) of China and the associated circulation anomalies have been investigated. During summers of 1979-2011, totaling 105 RDPE events are identified; out of which 35 are TC-influenced (TCIn-RDPE) and 70 no-TC-related (TCFr-RDPE). Distinct differences between these two types of RDPEs are found in both their statistical features and the related circulation patterns, except they all occurred more frequently with stronger intensities in recent two decades other than in 1980s. TCFr-RDPEs usually occur in June while TCIn-RDPEs mainly do in July-August. When TCFr-RDPEs happen, a center of the departure cyclonic circulation is observed over FJR, with an anomalous anticyclonic circulation to the south of this region. The warm/moist airflows from the South-China-Sea (SCS) and western Pacific meet with colder air from the north to form a narrow convergent belt of water vapor over FJR. Simultaneously, positive diabatic forcing anomalies are observed over FJR whereas negatives over both its south and north sides, facilitating the formation and maintenance of the cyclonic circulation anomaly as well as the upward motion of the atmosphere over FJR. As TCIn-RDPEs occur, southeastern China is dominated by a TC-related stronger anomalous cyclonic circulation. An anomalous anticyclonic circulation in mid- and high-latitudes north of the FJR exist in mid and lower troposphere, which looks opposite as compared to that of TCFr-RDPE events. The abundant warm/wet air is carried into the FJR from both the Indian Ocean and SCS, leading to large amount of latent heat to release over FJR, inducing strong ascent of air there. Furthermore, large differences are also found in ways of Rossby wave energy propagation between these two type RDPE events. These results are helpful for us to deepen understanding of mechanisms behind these two types of RDPE events.