Interannual And Interdecadal Variabilities In The Rainy Season Characteristics Over North China And Their Influence Factors

Using the National Climate Center's monitoring data of the rainy season in North China from 1961 to 2017,atmospheric reanalysis data from the National Center for Environmental Prediction/Atmospheric Research(NCEP/NCAR),NOAA Sea Surface Temperature(SST)data,and 130 climate indices from the National Climate Center,the interannual and interdecadal variabilities in the rainy season characteristics over North China and the influence factors are analyzed from the onset date and the precipitation of the Rainy season in North China.During the period from 1961 to2017,the rainy season in North China began as early as July 6th,and at the latest on August 10 th,the average date is July 18 th.The onset date of the Rainy season in North China(OSDRS_NC)has significant interannual variations,but the long-term trend of the OSDRS_NC is not obvious.According to the OSDRS_NC from1961-2017,the abnormal early years(12 years)and abnormal late years(8 years)were screened,and the synthetic circulation fields of the low,middle and high layers in the early and late years were studied.It is found that the OSDRS_NC is closely related to the activities of the western Pacific subtropical high(WPSH),the East Asian subtropical westerly jet stream(EAWJS),and the East Asian summer monsoon(EASM).When the establishment of the EAWJS,the second northward jump of the WPSH and the northward movement of the EASM are earlier than normal,the OSDRS_NC is earlier than normal,and vice versa.At the same time,using relevant analysis methods,it is found that the relationship between the OSDRS_NC and the SST over the Tropical Indian Ocean and the equatorial central and eastern Pacific is significant and stable in the spring and summer.Furthermore,the regression mechanism is used to analyze the possible influence mechanism.The results show that when the Ni?o3.4 index and the Indian Ocean Basin-wide Warming(IOBW)display positive(negative)anomalies,the WPSH enhances(weakens)and shifts to the south,the Lake Baikal high enhances(weakens)and the EASM weakens(enhance).These anomalies lead to late(early)onset of the rainy season in North China.Based on the monitoring data of the rainy season in North China and the average monthly precipitation data of 160 stations in China,the relationship and the climate characteristics of the precipitation in summer,in rainy season and in July,August was compared.It is found that 60% of the precipitation in July and August in North Chinacomes from precipitation in the rainy season.There is a four-year interannual oscillation period in the precipitation of rainy season.Further,the precipitation in the rainy season in North China was found a reduced mutation in 1996 with a difference of 40 mm by the sliding t-test method.At the same time as the precipitation change in the rainy season in North China,the corresponding impact factors related to precipitation have also changed.By calculating the sliding correlation coefficient between the precipitation in the rainy season in North China and the 130 climate indices from the National Climate Center,it is found that the influence of the previous winter sea surface temperature on the rainy season in North China is very weak,and the relationship between the tropical South Atlantic SST and the rainy season is also gradually weakened after 1975 to pass the significance test;In the spring,the relationship between the Northern Hemisphere Polar Vortex Area Index,the NINO A SSTA Index and the precipitation in North China Rainy Season has increased interdecadal,the relationship between the South Indian Ocean Dipole Index and the precipitation in North China Rainy Season has remained significantly negative correlated since the 1990s;In July and August,the sea surface temperature in NINO 3and NINO 3.4 had a significant negative correlation with the rainy season rainfall,while the relationship between the NINO A SSTA Index had an interdecadal enhancement.In July and August,the Western Pacific Sub Tropical High Westward Ridge Point Index showed a significant negative correlation with the rainy season rainfall in North China after 1976.At the same time,the area and intensity of the West Pacific subtropical high are not the key factors affecting the rainy season in North China.Using SPSS software to establish the regression model of spring northern hemisphere polar vortex area index,summer West Pacific subtropical high west extension ridge point index,summer NINO3.4 sea temperature index,summer NINO3 sea temperature index,NINOA sea temperature index and North China rainy season rainfall.The equation is Y(North China rainy season rainfall)=-490.709-28.763 ×1(NINO 3 area sea temperature index)+9.363 × 2(spring northern hemisphere polar vortex area index).