Impact of El Niño−Southern Oscillation on Quasi-Biweekly Oscillation Over the Western North Pacific in Boreal Winter

Impacts of El Niño−Southern Oscillation (ENSO) on the quasi-biweekly oscillation over the western North Pacific (WNP-QBWO) in boreal winter are investigated in the study. The WNP-QBWO in boreal winter primarily propagates westward from the tropical western Pacific to WNP. During the La Niña winter, the QBWO over the WNP has stronger intensity and propagates westward at a faster speed, while it is weaker and propagates more slowly during the El Niño winter. The possible mechanisms may involve the ENSO-related background moisture and zonal wind vertical shear changes that can significantly modulate the WNP-QBWO's behaviours in boreal winter. A 2.5-layer atmospheric model is applied in the study and confirms the results. It is further revealed that the moisture change is dominant in modulating the WNP-QBWO's intensity, while both the moisture and vertical shear changes may together contribute to the zonally propagating speed of the WNP-QBWO in boreal winter. These results can deepen our understanding of dynamic processes associated with the WNP-QBWO in boreal winter and are conducive to the predictability study.