Modulation of the QBO on the MJO-related surface air temperature anomalies over Eurasia during boreal winter

Abstract

Previous studies have indicated the modulation of the Madden–Julian oscillation (MJO) by the Quasi-Biennial Oscillation (QBO) and the influence of the MJO on surface temperature over Eurasia during boreal winter. The present study reveals that the MJO-related circulation anomalies are different in easterly and westerly QBO years, leading to distinct surface temperature anomaly patterns over Eurasia. During the easterly QBO years, the surface air temperature anomalies over Eurasia display a meridional dipole pattern in MJO phase 2 associated with the mid-latitude surface anticyclonic anomalies. The development of surface anomalous anticyclone is attributed to a combined effect of negative North Atlantic Oscillation (NAO)-related mid-latitude wave train and stronger MJO convection triggered poleward propagation of Rossby wave train. The negative NAO is related to the easterly QBO through the Holton–Tan relationship. The anomalous overturning circulation excited by the stronger MJO convection in easterly QBO years also contributes to the development and eastward extension of anomalous anticyclone. The anticyclonic anomalies induce the meridional temperature anomaly pattern by horizontal advection. During the westerly QBO years, the surface air temperature anomalies over Eurasia show a zonal alternating pattern in MJO phase 3, which corresponds to the development of mid-latitude Rossby wave train associated with positive NAO with a stronger MJO–NAO connection in westerly QBO years. The MJO convection induces upper-level divergent wind anomalies, contributing partially to the development of the Rossby wave source and helping the building of the mid-latitude wave train. The zonal temperature anomalies over Eurasia are also contributed by the horizontal advection associated with surface cyclonic anomalies.