Causes And Prediction Of June Rainfall Anomaly In Jiangxi

Based on the monthly reanalysis data of NCEP/NCAR from 1959-2016 and precipitation data of 82 stations in June provided by Jiangxi Meteorological Information Center and the global monthly mean sea surface temperature data reconstructed by NOAA,the temporal and spatial distribution characteristics of June rainfall in Jiangxi and the characteristics of circulation anomalies are analyzed,the relationship between rainfall and atmospheric vertical circulation over South Indian Ocean and the reasons for the interdecadal changes of the relationship are explored,and a prediction model for the June rainfall in Jiangxi is established.The conclusions are as follows:(1)The June rainfall in Jiangxi has obvious interannual variations and the spatial distribution characteristics is dominated by the whole region,with the south-north-opposite and the north-south-central opposite.When there is more than normal rainfall in Jiangxi,the water vapor is mainly composed of the westward airflow from the Indian Ocean and the southwest warm and moist airflow on the northwest side of the Western Pacific Subtropical High,there are more blocking hight activities at high-latitudes and Western Pacific Subtropical High is stronger and southerly,there are positive vorticity abnormality on the 500 hPa and north-south wind anomalies are convergent on the 850 hPa over the Jiangxi area.(2)The atmospheric vertical circulation over Southern Indian Ocean affects the circulation anomalies in East Asia,thus affects the June rainfall in Jiangxi.There is a good coupling relationship between the vertical circulation over the Southern Indian Ocean and the vertical circulation over the Pacific Ocean.When the vertical circulation index I is greater than 0,the western Indian Ocean and its north and south sides are all anomalous vertical upward movements,which have an important impact on the western Pacific circulation through the “atmosphere bridge”,making the Western Pacific Subtropical High is stronger,and leading to more rainfall in Jiangxi.(3)The vertical circulation over South Indian Ocean is closely related to the June rainfall in Jiangxi,when the anomalous descending(ascending)motions occur over South Indian Ocean,there is more(less)June rainfall in Jiangxi.However,their interannual relationship has interdecadal changes.During 1969-1989,the southern Indian Ocean vertical circulation has no significant correlation with June rainfall in Jiangxi;while it becomes significant positive phase.(4)Dynamic diagnosis shows that during 1969-1989 the interannual anomaly of vertical circulation over the southern Indian Ocean contributed positively to the local vorticity in Jiangxi,but the interdecadal anomaly contributed negatively,weakening the role of interannual anomalies.The interannual anomalies during 1990-2016 contributed positively,and the interdecadal anomalies also contributed positively,strengthening the role of interannual anomalies,making it positively correlated with precipitation in Jiangxi in June.(5)The precipitation prediction model for Jiangxi is established by the multi-variable regression ensemble,and five evaluation parameters(such as prediction score(P),etc.)are selected to evaluate the prediction results.Results show that the model has a certain skill for the prediction of precipitation in Jiangxi.After the independent forecast of 2012-2016,it is found that the average P score is 70.67,72,70.67,51.33,and 66.33 in each year,respectively,with the hightest in 2013 and the lowest in 2015.