The Research On The Impact Of Two Types Of ENSO Evnets On Precipitation In Eastern China

Eastern China is located in the East Asian monsoon region.The abnormal precipitation in eastern China not only has an important impact on industrial and agricultural production and social infrastructure construction,but also threatens the safety of people's lives and property.As the strongest signal in the inter-annual variation of tropical sea-air coupling system,ENSO has an important effect on the precipitation in eastern China.Therefore,studying the impact of ENSO on the precipitation in eastern China has scientific and practical significance for precipitation prediction over this region.Using the Daily Precipitation Grid Data(CN05.1)in China,Global Sea Surface Temperature Data,and Meteorological Reanalysis Data from 1979 to 2010,the paper systematically analyzes the abnormal distribution characteristics of tropical Pacific sea surface temperature(SST)and the abnormal response of Hadley circulation when the Eastern-Pacific ENSO(EP ENSO)and Central-Pacific ENSO(CP ENSO)occur.The influence characteristics of two types of ENSO on the precipitation in eastern China is also analyzed as well as its influencing mechanism.Meanwhile,the effects of the two strongest CP El Ni?o/La Ni?a events from 1979 to 2010 are selected and their different impact on precipitation in eastern China are explored from the general events.Finally,from the perspective of atmospheric circulation and Wave Action Flux(WAF),the influence mechanism of the strongest El Ni?o/La Ni?a events on precipitation in eastern China is analyzed.The main conclusions are as follows:(1)When the EP El Ni?o/La Ni?a occurs,the tropical Pacific SST anomaly exhibits dipole oscillation in the latitudinal direction and a equator symmetrical structure in the meridional direction.When the CP El Ni?o/La Ni?a occurs,the tropical Pacific SST anomaly is characterized by tripolar distribution in the latitudinal direction;while in the meridional direction,the SST anomaly is a equator symmetrical structure in autumn and winter,but asymmetric about the equator in spring and summer.Because of the different structures of the tropical Pacific SST anomalies when the two types of El Ni?o/La Ni?a occur,there are different effects on the Hadley circulation.When the EP El Ni?o/La Ni?a occurs,the Hadley Circulation anomaly maintains the characteristics of equator symmetry in the whole year.When the CP El Ni?o/La Ni?a occurs,the Hadley Circulation anomaly is symmetrical about the equator in autumn and winter,but asymmetric in the spring and summer.This is consistent with the meridional structural characteristics of the SST anomaly when two types of El Ni?o/La Ni?a events occur,indicating that the abnormal forcing of SST has a significant impact on atmospheric circulation.(2)At all stages of the two types of El Ni?o/La Ni?a,their effects on precipitation in eastern China are quite different.During the mature period of EP El Ni?o in winter,precipitation in southeastern China is relatively high and precipitation in central and northeastern regions is less.During its decayed period in spring,rainfall is excessive in most areas of Eastern China.During its decayed period in summer,the precipitation area mainly exists in the middle and lower reaches of the Yangtze River basin and the northeastern region of China.When the CP El Ni?o occurs,the location of rain belt in eastern China is northward than that in EP El Ni?o,while during the period of maturity in spring,less precipitation in South China and more precipitation in the Yangtze River Basin.During the period of maturity in summer,rainfall belts are mainly concentrated in the Huang-Huai River Basin,while drought occurs in the south of the Yangtze River.The effect of two types of La Ni?a on precipitation in eastern China is basically opposite to that of the corresponding El Ni?o events.In this paper,the mechanism of two types of El Ni?o/La Ni?a affecting precipitation in eastern China is analyzed from the perspective of atmospheric circulation.The result shows when the EP El Ni?o occur,the atmospheric circulation is characterized as a positive geopotential height anomaly in the equatorial Western Pacific,the stronger Western Pacific Subtropical High(WPSH),and an abnormal anti-cyclone circulation exists in the Philippine Sea.The southwester transports moisture from Pacific to eastern China,combined with the seasonal movement of WPSH and moisture convergence zone,which can lead to the seasonal variation of the precipitation in eastern China.In the case of the CP El Ni?o incident,the atmospheric circulation anomalies are different due to the difference of the SST anomaly distribution in the equatorial Pacific region between CP El Ni?o and EP El Ni?o,the overall performance is that the position of the WPSH and the anti-cyclone circulation is further north than that during the EP El Ni?o.In addition,the Pacific-Japan wave train(PJ wave train)caused by the CP El Ni?o event is weaker than that by the EP El Ni?o and is located eastward,which may be the reason that the CP El Ni?o has a weaker impact on the precipitation in eastern China than that of the EP El Ni?o.When two types of La Ni?a events occur,the abnormal structure of SST is opposite to that of the corresponding El Ni?o events,so the precipitation anomaly in eastern China is also opposite to the latter.In addition,the cumulative extreme precipitation in eastern China is increasing from northwest to southeast,and the cumulative extreme precipitation accounts for a large proportion of total precipitation in each season.When the EP and CP El Ni?o/La Ni?a occurs,the spatial distribution characteristics of the extreme precipitation anomalies in eastern China are consistent with the total precipitation,but the abnormal distribution of weak precipitation does not change significantly.Therefore,the two types of El Ni?o/La Ni?a mainly affect the anomalous distribution of total precipitation by affecting the extreme precipitation anomalies in eastern China.(3)The paper selects the El Ni?o event in 2009/10 and La Ni?a event in 1998/99 as the two strongest CP El Ni?o/La Ni?a events from 1979 to 2010,and analyzes their influence on the precipitation in eastern China.During the maturation period of the strongest CP El Ni?o,the precipitation anomaly is negative in southwest China,but positive in East and North China,which is different from that in the general CP El Ni?o.During the maturation period of the strongest CP La Ni?a,the precipitation in most parts of eastern China are uniformly less.While the north of the Yangtze River has more precipitation in the general CP La Ni?a events,showing different distribution characteristics from the strongest events.In the decayed period,the influencing characteristics on precipitation in eastern China are similar to that in the general CP El Ni?o/La Ni?a events,but with a stronger intensity.When the strongest CP El Ni?o occurs,the anomalous anticyclone circulation and WPSH are stronger than the general events,and the WPSH is located more westerly and northerly.When the strongest CP La Ni?a occurs,the anomalous cyclonic circulation is stronger than the general event,and the WPSH eastward retreat more obvious,so the impact of the strongest events on the precipitation in eastern China is stronger than that of general events.In addition,during the maturation period of the strongest CP El Ni?o,moisture can be transported to northern China because most of eastern China is controlled by cyclonic circulation.Therefore,the precipitation anomaly in eastern China in winter of 2009 is different from the general CP El Ni?o events.During the maturation period of the strongest CP La Ni?a,the Outgoing Longwave Radiation(OLR)is positive anomaly in most areas of eastern China,indicating the convective activity is inhibited,which is not conducive to precipitation occurrence in this area,which is different from that of the general events.The strong convection will stimulate stationary waves and the WAF is stronger in regions with stronger convective activity.During the decayed period of the strongest El Ni?o in summer,there is a clear spread of WAF from the equatorial region to the south of China,accompanied by the spread of PJ wave trains.When the strongest CP La Ni?a occurs,due to the strong convective activity in the western Pacific,there is a clear WAF spreading northward from Southeast Asia.