Distinct impacts of the MJO and the NAO on cold wave amplitude in China

Abstract

Previous observations suggested a connection between the Madden–Julian Oscillation (MJO) and the North Atlantic Oscillation (NAO), yet few of them contrasted the influences between the MJO and the NAO on extreme weather and climate events. In this study, it is found that the impacts of the MJO and the NAO on winter cold wave amplitude (CWA) over China can be distinctive. Time‐lagged correlation analysis indicates that the response of the CWA to the MJO is characterized by a significant anomalous centre over the Tibetan Plateau and its adjacent region, whereas that to the NAO is mainly over western and northeastern China. The ECMWF model from the Sub‐seasonal to Seasonal (S2S) project can approximately reproduce the relationship between CWA and these indices at intraseasonal time‐scale. The MJO‐associated convective activities along the Equator can modulate the local Hadley circulation. When the convection centre of the MJO is located over the Maritime Continent, it can trigger subsidence over the Tibetan Plateau and its adjacent region, warm the surface and consequently decrease the CWA. When descending flows associated with the MJO prevail over the Maritime Continent due to the eastward propagation of the MJO, the situations tend to be opposite. The intraseasonal variations of the NAO will induce eastward‐propagating Rossby wave trains, which usually favour the significantly positive (negative) pressure, temperature and consequently negative (positive) CWA anomalies over western and northeastern China. Thus, the MJO and the NAO might provide two critical predictability sources for sub‐seasonal forecasts of the extreme temperature events.