Relationship Between Asian Summer Monsoon Rainfall And ENSO Over The Past 500 Years

The Asian summer monsoon,including two sub-systems in South Asia and East Asia,is closely related to land precipitation,and has a huge impact on local industrial and agricultural production and people's life,thus getting better forecast of the interannual variation of Indian summer monsoon precipitation under the climate warming background,the reconstruction of the ten sets of ENSO indices and the precipitation data of East Asia were provided to investigate the relationship between ENSO and the India summer monsoon rainfall in the past 500 years,the reason behind it and how to understand this phenomenon.Among them,the impact of ENSO on Indian summer monsoon is what we mainly focus on.Finally,the model data of the Community Earth System Model version 1(CESM1)is used to compare the results of the model and the reconstruction data,and the leading factor affecting the precipitation is diagnosed and analyzed.The main conclusions are as follows:The relationship between ENSO and India summer monsoon precipitation for the past 500 years(1470?1999)is not a constant,generally showed a negative correlation,negative correlation degree was weak in the little ice age(LIA),while it has been strengthened in the current warm period(CWP),but after 1980s it began to weaken again.At the same time,the relationship between the middle and lower reaches of the Yangtze River rainfall and ENSO in the past 500 years is obviously smaller than the former.The positive correlation of the two is weak in LIA,and obviously strengthened in CWP,and it is strengthened again after 1980s.The relationship between Asian summer monsoon rainfall anomaly and ENSO over the past 500 years has been determined,not randomly generated.The amplitude and cycle of abnormal Indian summer monsoon precipitation and the middle and lower reaches of the Yangtze River are very different between LIA and CWP,as well as Nino indices.the latter is significantly larger.But the average states of the two periods are almost same.That is to say,relative to the LIA,the ENSO amplitude increases,period becomes larger during the CWP,which lead to a stronger negative correlation between the Indian summer monsoon and ENSO.Whether the precipitation field,the vertical velocity field of 500hPa,the specific wet field,or the 850hPa wind field and the sea surface temperature field,the average state of them are not very different in summer(MJJAS)between LIA and CWP in the CESM model.The position of rainfall and the wind field anomalies are somewhat different beteem the rebuilt data and model data in the Indian region of ENSO developing years and the middle and lower reaches of the Yangtze River of ENSO decaying years.showing an obvious southwest shift tendency.Meanwhile,the East Pacific sea surface temperature anomaly field is obviously larger in El Nino and La Nina developing years in CWP,which is consistent with the reconstructed data.Using small perturbation method,we know that ?'· q is dominant among the factors affecting the precipitation anomaly.That is,compared with LIA,the 500hPa vertical velocity of CWP is greater in the ENSO years,resulting in the abnormally large magnitude of rainfall in the India region in ENSO developing years,as well as in the middle and lower reaches of the Yangtze River but for ENSO decaying years.The magnitude of the ?· q' is small and can be ignored.