Atmospheric Intraseasonal Oscillation On The Qinghai-Tibet Plateau And Its Impact On Persistent Abnormal Precipitation In The Middle And Lower Reaches Of The Yangtze River

Base on the FNL(Final)daily reanalysis data of four time a day,horizontal resolution of 1.0 ° × 1.0 °,daily precipitation data of meteorological stations in China,spanning from 2001 to 2015,using the power spectrum analysis,Lanczos band-pass filtering,correlation analysis and other methods to study the Tibetan Plateau atmospheric characteristics of intraseasonal oscillation and its possible relationship with the persistent anomalous precipitation in the middle and lower reaches of the Yangtze River.The conclusions are as follows:(1)Through the power spectrum analysis,it was found that the zonal wind,meridional wind,and geopotential height elements at 200 hPa and 500 hPa were ubiquitous in the 10-20 days,20-30 days,30-60 days,and 60-90 days.(2)The analysis of meteorological elements after 10-30 filtering shows that the horizontal structure is mainly manifested as the alternation of the Intraseasonal Oscillation cyclone system and the anti-cyclone system.The vertical structure shows baroclinism in the low latitudes of 10°N and 90°E To 32°N and 90°E.The plateau was mainly positive pressure in the first half of June and early August,and the baroclinic pressure at other times.The positive pressure of 50 ° N and 90 ° E was observed in the high latitudes.It shows that baroclinism is strong in low latitudes and strong in high latitudes.In terms of propagation,the characteristics of the Tibetan Plateau are quite different in all years and time periods.In some cases,they are the sinks of the low-frequency oscillations of the 10-30 day periods and some of the sources of the low-frequency oscillations.(3)During the period from 2001 to 2015,the precipitation in the middle and lower reaches of the Yangtze River in June-August generally showed a clear upward trend.,the precipitation was less before 2008,and then the precipitation increased significantly.According to the definition of persistent anomalous precipitation,17 consecutive anomalous precipitation occurred during the statistical period,with precipitation mainly occurring in June and July.The longest duration of abnormal precipitation in the middle and lower reaches of the Yangtze River is 11 days from July 5th to 15 th,2010.The average total rainfall area in the precipitation process is 2438mm;the shortest is 7 days,and the continuous abnormal precipitation is at least 819 mm.In 2010,the abnormal precipitation began to cover the entire middle and lower reaches of the Yangtze River,with a central value of 158 mm.(4)The fluctuation of the intraseasonal oscillation in the Tibetan Plateau has agood correlation with the daily precipitation in the middle and lower reaches of the Yangtze River.During the period of persistently abnormal precipitation,the low-frequency oscillations of the Tibetan Plateau are active for 10-30 days,showing a peak period.When the precipitation gradually decreases,there is a brief interval,and the low-frequency oscillations are in the trough stage.(5)The main reason for the continuous abnormal precipitation in the middle and lower reaches of the Yangtze River in 2010 was due to the convergence of cold and warm air,which was conducive to the generation of precipitation and the low-frequency precipitation oscillation in the middle and lower reaches of the Yangtze River lags behind the low-frequency oscillation of the Tibetan Plateau.When the low frequency oscillation of the Tibetan Plateau is at the crest(trough),the precipitation intensity in the middle and lower reaches of the Yangtze River is still increasing(decreasing).From the aspect of phase angle,it is considered that the low frequency oscillation of the precipitation in the middle and lower reaches of the Yangtze River lags one phase of the low frequency oscillation of the Tibetan Plateau.