Decadal change of extreme consecutive dry days in spring over the middle and lower reaches of the Yangtze River around the early 2000s: The synergistic effect of mega-El Niño/Southern Oscillation, Atlantic Multidecadal Oscillation, and Arctic sea ice

Abstract

Base on daily station precipitation data from 1960 to 2019, the variability of extreme consecutive dry days (extreme-CDDs) over the middle and lower reaches of the Yangtze River (MLRYR) during spring sowing time (March–April) is investigated. It is found that the extreme-CDDs over MLRYR experienced a significant decadal increase around the early 2000s. Associated with this decadal change, the Mongolian high and western North Pacific anticyclone (WNPA) are significantly intensified and weakened, respectively. The intensified Mongolian high and weakened WNPA lead to anomalous northerlies and water vapor divergence over MLRYR, providing favorable atmospheric conditions for more extreme-CDDs over the region. Further mechanism analyses suggest that the transition of mega-El Niño/Southern Oscillation (mega-ENSO) from negative-phase to positive-phase contributes to the decadal weakening of WNPA. And the phase transition of Atlantic Multidecadal Oscillation (AMO) and decadal decrease of sea ice over the Barents Sea lead to intensified Mongolian high through exciting atmospheric wave train. Multiple linear regression shows that there could be a synergistic role of mega-ENSO, AMO, and sea ice over the Barents Sea in the decadal change in extreme-CDDs over MLRYR around the early 2000s. Analysis on the simulation of 14 models in the Atmospheric Model Intercomparison Project (AMIP) experiment from phase 6 of the Coupled Model Intercomparison Project (CMIP6) shows that the models can reproduce the observed decadal intensification of the Mongolian high and weakening of WNPA around the early 2000s, which indicates the contribution of mega-ENSO, AMO, and sea ice over the Barents Sea to the decadal changes in Mongolian high, WNPA and extreme-CDDs over MLRYR.