Research On Different Types Of El Nino Events And Its Possible Causes For The Intraseasonal Variations Of Following Summer Precipitation In Eastern China

By using1950-2011global reanalysis monthly mean sea surface temperature (SST)data, the ONI (Oceanic Nino Index) series, SODA monthly various elements, NCEP/NCAR reanalysis wind field, height field, humidity field and monthly rainfall of160stations of China, El Nino events are classified in several ways, the main characteristics of different types of El Nino events and the influences of all kinds of El Nino events on east Asia circulation and the monthly and seasonal precipitation in following summer are investigated. The main results are as follows:(1) The analysis on the definition and characteristics of different types of El Nino event indicate:1) according to the regions of the biggest positive sea surface temperature anomaly (SSTA) during El Nino events, El Nino events can be categorized into three patterns, namely, the nino3, nino4and nino3.4pattern.2) The linear warming trend of sea surface temperatures had no significant effect on classification of El Nino event.3)The distribution of each type El Nino events’subsurface SSTA are different.The big value area of subsurface SSTA is located within the scope of the each type of El Nino longitude-defined.4) During nino3type events, there is an abnormal in the eastern equatorial Pacific, while in the west of the Pacific Ocean has an exception of sinking airflow. The distributions of nino3.4pattern are similar to nino3pattern. The distributions of nino4pattern are differences form other two kinds of types, as it exists two abnormal updraft in Pacific area, at the same time there are also a rising air over the Indian Ocean.(2) The analysis on the classification and characteristics of three phases which including development mature and attenuation of different types of El Nino events indicate:1) In the period of development,both positive SSTA and subsurface SSTA (Unity is called as the sea temperature anomaly) are first appeared in the southeast of equatorial Pacific region in nino3pattern. While in nino4pattern,they are first appeared in the central and western equatorial Pacific, which called nino4area.In the nino3.4pattern, the positive sea temperature anomaly are first appeared in south-eastern equatorial Pacific and the eastern of nino3.4region.When maturity comes, the intensity of sea temperature anomaly strengthened.In the period of attenuation, nino3pattern the positive sea temperature anomaly in the eastern equatorial Pacific is significantly reduced, the other two types of events have the negative sea temperature anomaly in the eastern equatorial Pacific.2) In the three stages,three types of El Nino have some differences in the distribution of walker circulation anomalies. Nino3pattern from development stage to decline stage, there maintain an abnormal walker circulation loop in the tropical Indian Ocean and Pacific, just its strength become strong from weak then to weak, position has a little change. Nino4pattern in the stage of development, the Pacific region has two abnormal updraft, when mature period comes, in the Indian Ocean-Pacific Ocean there form two reverse walker circulation loop. There have not obvious sinking airflow in attenuation period.Nino3.4pattern in each phase has the similar distribution, only strength become strong from weak then to weak.(3)The analysis on different types of El Nino events in the following summer including monthly and seasonal precipitation indicate:1) the influences on the following year June, July and August’s precipitation anomaly field distribution in eastern China are obviously different in the different types of El Nino events.2) For the whole summer, the main rain belt in the pattern of nino3, nino4and nino3.4have the features that it moved gradually from the south to the north. In nino3pattern, main rain belt is mainly located in the eastern part of southwest to the Jiangnan area, In nino4pattern, the main rain belt mainly located between the Yangtze river and Yellow River basin, In nino3.4pattern, main rain belt is mainly located in the southwestern province of Sichuan, the bend of the Yellow River and north China. The rainfall is strongest for nino4pattern and is the weakest for nino3.4pattern for both the monthly and summer precipitation.(4) The analysis on different types of El Nino corresponding to circulation characteristics in the following summer or monthly indicate:1)For the South Asia High, it becomes stronger and moves eastward and northward corresponding to the climatological field after the events of nino3and nino4patterns and the latter is even stronger than the former. For the nino3.4pattern,it is weaker and withdraw westward. For the western Pacific Subtropical High, it is stronger and moves westward and northward corresponding to the climatological fields and the latter is even stronger and more obvious than the former. For the nino3.4pattern,it retreats eastward and moves move northward.2) The following summer, the main source of nino3pattern’s warm current is an anticyclonic water circulation over the west Pacific Ocean and Indochina type. In nino4pattern, mainly comes from the anticyclonic water circulation over the northwest Pacific Ocean, and its location more north than the nino3. In nino3.4pattern, warm current is mainly composed of two, one come from the east over the low latitude atmosphere flows through the Philippine islands and hainan island, another is the anticyclonic water circulation over the bay of Bengal.For each month in the summer, the nino3and nino4pattern, their warm current source is similar, while nino3.4pattern appear more water circulation, they work together to transport warm moist air to the territory of China.3) Look from anomalous zonal-vertical circulation and meridional-vertical circulation, in next summer of nino3pattern, the configuration at of vertical movement and water vapor content is the most favorable for the formation of precipitation at25°N～30°N. While in nino3.4pattern,the configuration which most favorable for the formation of precipitation at35°N-40°N.For nino4pattern, both at25°～30°N and35°～40°N have precipitation anomalies. Look from each month in the summer, Three types of events’ abnormal updraft and the area of maximum water vapor content mainly in south of30°N in June. July,both the abnormal updraft and the area of maximum water vapor content. In August, nino3pattern have no obvious vertical movement,and nino4pattern’s updrafts further north towards, nino3.4pattern’s updraft stronger and the scope is bigger compared with July.