Impact of boreal autumn Antarctic oscillation on winter wet-cold weather in the middle-lower reaches of Yangtze River Basin

The Antarctic Oscillation (AAO) is the dominant mode of the southern extratropical atmospheric mass variability which has potential influences on the Northern Hemisphere (NH). This study reveals a significantly negative correlation between the September–October (SO) AAO index (AAOI) and the occurrence rate of following January–February (JF) wet-cold weather (the latter is quantified by a Precipitation-Temperature (PT) Index) in Southern China (SC) especially the Middle and Lower Reaches of Yangtze River Basin (MLRY). JF PT of SC (SCPT) is modulated by both northerly air flow in the lower troposphere and southerly air flow in the middle-lower troposphere. The SO AAO stimulates Southern Ocean Dipole (SOD) pattern-like sea surface temperature anomalies (SST anomalies: SSTA), which induces a Northern Atlantic Oscillation (NAO)-like atmospheric response along with the tropical northern Atlantic (NA) precipitation anomalies in the following JF through ocean-air interaction. As for wet-cold conditions, there exists an eastward propagational wave train from the tropical-subtropical NA to the East Asian atmospheric patterns, in turn influencing the intensity of East Asian Winter Monsoon (EAWM) and Middle East Jet Stream (MEJS), subsequently the penetration of northerly cold flow and southerly wet flow into MLRY. The variation of JF SOD also regulates the local meridional-vertical cells, in turn influencing the intensity of precipitation over the tropical NA and SC, accompanied with the penetration of wet-warm flow into SC and the adjacent regions. In addition to the tropospheric processes, the stratospheric Quasi Biennial Oscillation (QBO) may serve as the stratospheric pathway for the impact of SOD on NH climate, inducing/reducing the JF SCPT response to SOD SST. To summarize, SO AAO affects the JF SCPT by modulating both dry-cold northerly air flow and wet-warm southerly air flow through tropospheric and stratospheric pathway.