Low Frequency Oscillations Of East Asia/Pacific Teleconnection And Their Impacts On Persistent Heavy Precipitation In The Yangtze-huai River Valley

Based on the daily reanalysis dataset from NCEP/NCAR, the daily OLR dataset from NOAA and the daily precipitation data from National Meteorological Information Center, the Ensemble Empirical Mode Decomposition(EEMD) method and composite analysis method ar e applied to investigate characteristics of the persistent precipitation extremes(PPEs) in the Yangtze-Huai River Valley(YHRV) and East Asia/Pacific teleconnection(EAP) oscillation on intra-seasonal timescale. This study conducts a further research on t he evolution of EAP at the key band of low-frequency and how the EAP leads to the occurrence of PPEs in the YHRV. Through studying both the tropical convection and the extratropical circulation systems related to the formation of EAP on low-frequency, the understanding of the formation of EAP is deepened.Results show that EAP affects the precipitation in southeastern China at intra-seasonal time scales. It mainly influences the PPEs in the YHRV, and also can affect rainfall in south of the YHRV. There are two reasons why the EAP event which does not produce the PPEs happen in the YHRV: one is that the western pacific sub-tropical high(WPSH) is located in a southward position, with result that it transports the water vapor southerly, and the other is unstable and small moisture vapor transportation during which the WPSH moves westward unstabl y early event due to active high frequency part of EAP.The precipitation in the YHRV and the EAP both exhibit the property of 10-30 days and 30-60 days low-frequency oscillations. Two bands are present the EAP effect on PPEs in the YHRV. The events of 10-30 day oscillations account for 60% of total, and the second accounts for 20%. At the key low-frequency scales, the anomalous cyclonic circulation controlled by the trough of EAP in the mid-latitude, encounters with the anomalous anticyclonic circulation in the YHRV which is controlled by the WPSH, carrying large amount of warm atmospheric water vapor. Such type of combination system lasts more than three days, and leads to the occurrence of the PPEs event.The formation of the EAP at low-frequency scales is investigated. In the low latitudes, suppression of convection in the middle and lower troposphere dominates in the South China Sea and the Philippines region. It results in the subtropical high anomalies. The northward propagating wave energy produces from the subtropical high form a complete EAP in the middle and lower troposphere. In the upper troposphere, extratropical system s of EAP evolve under the influence of the upstream system. Both the low-frequency system in equatorial easterlies and the low-frequency circulation in extratropical westerlies act on the middle troposphere, causing a phase lock between those two systems of the EAP along the coast of East Asia, thus it forms a typical EAP structure.