Characteristics Of The Low-frequency Oscillations Of The Tropical Ocean And The Qinghai-Tibet Plateau Atmosphere In The Summer Of 2016 And Their Impact On Precipitation In China

Based on reanalysis data from NCEP/NCAR,daily outgoing longwave radiation(OLR)data from NOAA and 805 stations daily precipitation data in China,this paper first uses the wavelet analysis method and the Lanczos filter to analysis the characteristics of the low-frequency precipitation in China and low-frequency oscillation in the atmosphere of the tropical ocean and the Tibetan Plateau.Then,a number of diagnostic analysis methods,such as composite analysis,EOF orthogonal decomposition,time lag correlation analysis,SVD and MV-EOF method are used to analyze the effects of the low-frequency oscillation in the tropical oceans and the Tibetan Plateau on precipitation in China in the summer of 2016.The main results are as follows:(1)In the summer of 2016,precipitation in the Yangtze River Basin and Northeast China exhibits a noticeable 30-60-day oscillation feature,and low-frequency precipitation in the two regions presents opposite variation tendency of phase.When the low-frequency precipitation in the Yangtze River Basin shows positive(negative)anomalies,the low-frequency precipitation in the Northeast China displays negative(positive)anomalies.(2)The 500hPa zonal wind over the Tibetan Plateau in summer is controlled by 30-60d intraseasonal oscillation and 10-30d quasi-biweekly oscillation,while the 200hPa zonal wind is mainly controlled by intraseasonal oscillation.There are 3 different patterns of spatial distribution of the first three modes of the low-frequency zonal wind EOF decomposition at two altitude:the south-north pattern,the consistent pattern,and the east-west pattern.The 500hPa low-frequency zonal wind on the Tibetan Plateau is significantly positively correlated with the low-frequency precipitation lag 5-7 day in the Yangtze River Basin and the concurrent precipitation in the Northeast China.Phase 3(7)is the most important period that causes the opposite phase of low-frequency precipitation in the Yangtze River Basin and Northeast China.At this time the Tibetan Plateau is dominated by westerly(easterly),and the low-frequency precipitation in the Yangtze River Basin shows positive(negative)anomalies,the low-frequency precipitation in the Northeast China displays negative(positive)anomalies.(3)The low-frequency oscillation in the tropical oceans is dominated by 30-60d intraseasonal oscillation.The spatial distribution of the first mode of EOF decomposition of the low-frequency OLR in the tropical ocean is consistent with the key region obtained by the first mode of the SVD analysis.The first mode of SVD analysis of low-frequency OLR in tropical oceans and low-frequency precipitation in China shows that:when the convective activities in the tropical oceans north of the equator and Indonesia are weakened(intensified),low-frequency precipitation in Northeast China shows positive(negative)anomalies and low-frequency precipitation in the Yangtze River Basin shows negative(positive)anomalies.The low-frequency OLR in tropical oceans is significantly negatively correlated with the low-frequency precipitation lag 0-13 day in the Yangtze River Basin and positively correlated with the low-frequency precipitation lag 3-16 day in the Northeast China.Compared with the low-frequency oscillation on the Tibetan Plateau,the tropical oceans atmospheric low-frequency oscillation has a better correlation with the low-frequency precipitation in the Yangtze River Basin and Northeast China.Phase 3(7)is the vital period that leads to the low-frequency precipitation in the Yangtze River Basin showing negative(positive)anomalies and also the most important period that causes the opposite phase of low-frequency precipitation in the Yangtze River Basin and Northeast China.(4)The low-frequency OLR in tropical oceans,500hPa low-frequency zonal wind on the Tibetan Plateau and the low-frequency precipitation in China are decomposed by MV-EOF,and the result shows that the combined effect of low-frequency oscillation in tropical oceans and the Tibetan Plateau can affect the low-frequency precipitation in China.The first mode of MV-EOF analysis shows that:When the eastern and western parts of the Tibetan Plateau are westerly and easterly,respectively,the convective activities in East Indian Ocean are intensified and in the Indonesia and its east are weakened,leading to the low-frequency precipitation shows the opposite characteristics of north and south in eastern China.According to the result of the first 3 modes,the low-frequency convective activities in tropical oceans is the main reason for the opposite phase of low-frequency precipitation in the Yangtze River Basin and Northeast China.