Delayed Impacts of the E1 Nino Episodes in the Central Pacific on the Summertime Climate Anomalies of Eastern China in 2003 and 2007

In the summers of 2003 and 2007, eastern China suffered similar climate disasters with severe flooding in the Huaihe River valley and heat waves in the southern Yangtze River delta and South China. Using SST data and outgoing longwave radiation (OLR) data from NOAA along with reanalysis data from NCEP/NCAR, the 2002/03 and 2006/07 El Ni(n)o episodes in the central Pacific and their delayed impacts on the following early summertime climate anomalies of eastern China were analyzed. The possible physical progresses behaved as follows: Both of the moderate E1 Ni(n)o episodes matured in the central equatorial Pacific during the early winter. The zonal wind anomalies near the sea surface of the west-central equatorial Pacific excited equatorial Kelvin waves propagating eastward and affected the evolution of the E1 Ni(n)o episodes. From spring to early summer, the concurring anomalous easterly winds in the central equatorial Pacific and the end of upwelling Kelvin waves propagating eastward in the western equatorial Pacific, favored the equatorial warm water both of the SST and the subsurface temperature in the western Pacific. These conditions favored the warm state of the western equatorial Pacific in the early summer for both cases of 2003 and 2007. Due to the active convection in the western equatorial Pacific in the early summer and the weak warm SST anomalies in the tropical western Pacific from spring to early summer, the convective activities in the western Pacific warm pool showed the pattern in which the anomalous strong convection only appeared over the southern regions of the tropical western Pacific warm pool, which effects the meridional shift of the western Pacific subtropical high in the summer. The physical progress of the delayed impacts of the E1 Nifio episodes in the central equatorial Pacific and their decaying evolution on the climate anomalies in eastern China were interpreted through the key role of special pattern for the heat convection in the tropical western Pacific warm pool and the response of the western North Pacific anomalous anticyclone.     

Relationship between persistent heavy rain events in the Huaihe River valley and the distribution pattern of convective activities in the tropical western Pacific warm pool

Using daily outgoing long-wave radiation （OLR） data from the National Oceanic and Atmospheric Administration （NOAA） and the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data of geopotential height fields for 1979-2006, the relationship between persistent heavy rain events （PHREs） in the Huaihe River valley （HRV） and the distribution pattern of convective activity in the tropical western Pacific warm pool （WPWP） is investigated. Based on nine cases of PHREs in the HRV, common characteristics of the West Pacific subtropical high （WPSH） show that the northern edge of the WPSH continues to lie in the HRV and is associated with the persistent ＂north weak south strong＂ distribution pattern of convective activities in the WPWP. Composite analysis of OLR leading the circulation indicates that the response of the WPSH to OLR anomaly patterns lags by about 1-2 days. In order to explain the reason for the effects of the distribution pattern of convective activities in the WPWP on the persistent northern edge of the WPSH in the HRV, four typical persistent heavy and light rain events in the Yangtze River valley （YRV） are contrasted with the PHREs in the HRV. The comparison indicates that when the distribution pattern of the convective activities anomaly behaves in a weak （strong） manner across the whole WPWP, persistent heavy （light） rain tends to occur in the YRV. When the distribution pattern of the convective activities anomaly behaves according to the ＂north weak south strong＂ pattern in the WPWP, persistent heavy rain tends to occur in the HRV. The effects of the ＂north weak south strong＂ distribution pattern of convective activities on PHREs in the HRV are not obvious over the seasonal mean timescale, perhaps due to the non-extreme status of convective activities in the WPWP.     

COMPARISON OF THE EFFECTS OF ANOMALOUS CONVECTIVE ACTIVITIES IN THE TROPICAL WESTERN PACIFIC ON TWO PERSISTENT HEAVY RAIN EVENTS IN SOUTH CHINA

The different effects of anomalous convective activities in the tropical western Pacific on two persistent heavy rain events in South China in 2005 and 2006 have been compared in this study. The dataused consist of NOAA Outgoing Longwave Radiation (OLR) data, the NCEP-NCAR reanalysis and precipitation from meteorological stations in South China. Results show that the persistent heavy rain in 2005 was related to the 10-25-day westward propagation of convective activities in the tropical western Pacific from about 150 °E. The physical mechanism is interpreted as a Gill-type response of subtropical anticyclone westward extension during weak convective activities period over the Philippine Sea. Our researches also show that the persistent heavy rain in 2006 has longer period than that in 2005, and the subtropical anticyclone persists westward in the earlier summer which is possibly related to the lasting anomalous strong convective motion in the southern branch of Intertropical Convergence Zone (ITCZ) in the tropic western Pacific. The anomalous convective activities affect the local Hadley circulation over the western Pacific with anomalous ascending motion south of the equator and anomalous descend motion north of it, in favor of the westward extension of the subtropical anticyclone for a long time. Comparison between the two persistent heavy rain events indicates different physical effects of convective activities in the tropical western Pacific, though both effects are helpful to the subtropical anticyclone westward extension as a common character of large-scale circulation backgrounds for persistent heavy rain events in South China.