Influence of ENSO on the Stratosphere-Troposphere Coupling during Stratospheric Sudden Warming Events

Abstract

Influence of El Niño/Southern Oscillation (ENSO) on the stratosphere-troposphere dynamical linkage during stratospheric sudden warming (SSW) events is investigated based upon the composite analysis using 44 winter record of NCEP-NCAR reanalysis data. Stratospheric waves with zonal wavenumber 1 (2), which are linked with tropospheric teleconnections over the Pacific-North America-Atlantic sector (the Eurasian sector), are important for the onset of SSWs during the warm (cold) phase of ENSO. During the cold phase, easterly anomalies associated with SSWs penetrate into the troposphere, and annular-mode-like height anomalies appear subsequently in the troposphere. On the other hand, during the warm phase, easterly anomalies are restricted in the stratosphere, and zonally asymmetric height anomalies are observed in the troposphere about 10 days after the warming peak in the stratosphere. Modulation of storm track activities due to lower stratospheric anomalies is found to be important for the downward penetration of zonal wind anomalies into the troposphere.