| Based on various data such as Chinese ground stations,NCEP reanalysis data,and satellite observation data,the variations of East Asian summer monsoon circulation,precipitation,and cloud of different types of El Ni?o events in the following summer are discussed,as well as the relationship between the variations of cloud and precipitation.The results show that in the eastern El Ni?o decaying summer,China experienced large-scale precipitation increases,forming two abnormal rain belts under the combined action of the East Asia-Pacific teleconnection and the mid-high latitude double-resistance circulation;while in the central El Ni?o decaying summer,there is only an abnormal rain band formed in the Yangtze River-Yellow River basin under the action of the Philippines anomalous anticyclone;the distribution of cloud amount anomalies and precipitation anomalies are roughly the same,and they show a positive correlation well across the country.For stations those passed the significance test,the linear relationships between cloud amount and precipitation anomalies are obvious.The abnormal rain belts corresponding to the two types of El Ni?o events are mainly formed by the increase of precipitation duration and of precipitation intensity.The total precipitation days increases in the El Ni?o decaying summer,which is mainly manifested by the increase of long-lasting precipitation days.In abnormal rain areas,the frequency of low cloud forms such as cumulonimbus calvus,stratus or stratus fractus,fractonimbus,cumulus and stratocumulus has increased significantly;total cloud amount,optical thickness and cloud water path,as well as the cover of cirrostratus and deep convective cloud is basically positively correlated with precipitation anomalies;both convective precipitation and stratospheric precipitation have increased in both types El Ni?o decaying summer,and the increase in convective precipitation is more obvious in the eastern part of the rainy area,while in the western part of the rainy area it is the stratus precipitation has increased significantly,and the increase of precipitation in the East Asian monsoon region is mainly due to convective precipitation.We use the reanalysis data of NCEP / NCAR(National Centers for Environmental Prediction / National Center for Atmospheric Research)to test the simulation capability of the Community Atmosphere Model V5.1(CAM5.1)to simulate multiple meteorological elements of Asian summer monsoon using and the results show that it could reproduce the main features of Asian summer monsoon well.Then,sensitivity experiments,which adopt greenhouse gases emission scenarios of 2000 and 1850 respectively,are carried out to study the response of the Asian summer monsoon to increases in greenhouse gases using CAM5.1 model.The results show that the increase in greenhouse gases lead to an increase in summer monsoon in the East Asian,and the total summer precipitation in the central and northern Indian Peninsula,the central and northern Indochina Peninsula and eastern China increased.The increase in greenhouse gases has caused more uneven heating of the atmosphere over land,the decrease of atmospheric stability,the enhancement of convective activity,the increase of convective cloud amount and thickness,and the increase of convective precipitation.Meanwhile,the increase of convective precipitation is the main reason for the increase of total precipitation.Correlation analysis of atmospheric energy budget and conversion shows that increased greenhouse gases concentration causes the atmospheric heat sources to enhance by the means of increasing the convective condensational latent heat.The increase in atmospheric heat sources results in an increase of full potential energy.Thus,there are positive transformations of full potential energy to the kinetic energy of divergent wind,the transformation of kinetic energy from divergent wind to nondivergent wind is increased,too,which leads to the non-divergent wind enhancing,and ultimately enhancing the summer monsoon over East Asian. |
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