Droughts and floods are not only related to abnormal rainfall frequency or intensity,but also associated with the duration of rainfall on multiple timescales.Based on daily rainfall data collected at 249 stations in eastern China and the ERA-interim reanalysis,the long term changes in rainfall duration over the middle and lower reaches of the Yangtze River (hereafter MLRYR) and associated large scale circulation patterns and Rossby wave energy dispersion have been investigated.In the recent 35 years,the average duration of summertime wet spells decreases while that of dry spells increases,indicating a decreasing (negative) trend of rainfall duration over the MLRYR.Further analysis shows that this trend is related to inter-decadal changes in the frequency of persistent rainfall extremes,which is obviously higher in the 1980s and 1990s and lower in the 2000s.The anomalous circulation patterns that describe the inter-decadal and inter-annual changes in rainfall duration over the MLRYR look similar in some regions including Southeast China and the South China Sea,but different between mid-to high-latitudes and lower-latitudes.On both inter-decadal and inter-annual timescales,southeastern China is under control of a notable anticyclonic circulation anomaly in the middle and upper troposphere.The airflow converges into the MLRYR in the middle and lower troposphere and diverges in the upper troposphere with air flowing away from the MLRYR to the ocean.However,associated with inter-decadal changes,an anomalous anticyclonic circulation is located to the east of the Urals while an anomalous cyclonic circulation is found over Mongolia in the lower and upper troposphere.Meanwhile,an anomalous cyclonic circulation can be found over the equatorial Indian Ocean in the middle and lower troposphere.In contrast,on the inter-annual timescale,anomalous anticyclonic circulation can be found on both the east and west sides of Lake Baikal in the lower and upper troposphere.Divergence occurs in the lower troposphere over northeastern Maritime Continent with the air moving towards the MLYRV,whereas convergence develops in the upper troposphere and the air flows away from the MLRYR to lower latitudes.Characteristic Rossby wave propagation and energy dispersion demonstrate significant differences between inter-decadal and inter-annual timescales.On the inter-decadal timescale,a Rossby wave train with alternatively positive-negative-positive-negative geopotential height anomaly can be found in the mid-latitude from the Atlantic to Mongolia.The eastward propagation of waver energy affects the MLRYR.In the mid-and lower troposphere,however,the wave energy dispersion from lower latitudes to MLRYR is relatively weak.On the inter-annual timescale,the Rossby wave activity flux demonstrates more distinct local features.In the lower troposphere,strong wave energy propagates from South China Sea in the lower latitudes to the MLRYR.In the upper troposphere,wave energy dispersion from regions to the west of Lake Baikal to MLRYR is more obvious.These results are helpful for our better understanding of the mechanism for the persistent rainfall anomaly and related droughts/floods over the MLRYR.