Abstract
Previous studies have revealed the relationship between the Madden–Julian oscillation (MJO) and the Arctic Oscillation (AO). The MJO phase 2/3 is followed by the positive AO phase, and the MJO phase 6/7 is followed by the negative AO phase. This study reveals that the MJO phase 6/7–AO connection is modulated by the Quasi-Biennial Oscillation (QBO) through both tropospheric and stratospheric pathways during boreal winter. The MJO 2/3 phase and AO relationship is favored in both QBO easterly (QBOE) and westerly (QBOW) years because of the MJO-triggered tropospheric Rossby wave train from the tropics toward the polar region. The AO following the MJO 6/7 phase shifts to negative in QBOW years, but the MJO–AO connection diminishes in QBOE years. In QBOW years, the Asian-Pacific jet is enhanced, leading to more evident poleward propagation of tropospheric Rossby wave train, which contributes to the tropospheric pathway of the AO–MJO 6/7 connection. Besides, the enhanced Asian-Pacific jet in QBOW years is favorable for vertical propagation of planetary waves into the stratosphere in MJO phase 6/7, leading to negative AO, which indicates the stratospheric pathway of the AO–MJO 6/7 connection.
Highlights
The Madden–Julian Oscillation (MJO) [1,2], which manifests as eastward propagation of tropical convection and precipitation perturbations from the Indian Ocean to the central Pacific on the time scale of 20–60 days, is the dominant intraseasonal variability over the tropics [3]
Previous study has indicated that the Madden–Julian oscillation (MJO)–Arctic Oscillation (AO) connection can be modulated by the mean state
To examine if the MJO–AO connection varies with the phase of the Quasi-Biennial Oscillation (QBO), the probability is illustrated by the quasi-geostrophic Eliassen-Palm flux (EP flux) [48,49]
Summary
The Madden–Julian Oscillation (MJO) [1,2], which manifests as eastward propagation of tropical convection and precipitation perturbations from the Indian Ocean to the central Pacific on the time scale of 20–60 days, is the dominant intraseasonal variability over the tropics [3]. The anomalous signal of the stratospheric polar vortex propagates downward and influences the tropospheric AO [24] Both the MJO and the AO are associated with the Quasi-Biennial Oscillation (QBO), which manifests as alternating easterly and westerly zonal winds over the stratospheric tropics on the time scale of 2.5 years [25,26,27]. The jet stream over the North Pacific is stronger and shifts southward during QBOW years, which is favorable for the meridional propagation of the MJO triggered tropospheric Rossby wave train [11], and contributes to the building of a stronger relationship between the MJO and the NAO.
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