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Storm track activity over the North Pacific associated with the Madden‐Julian Oscillation under ENSO conditions during boreal winter
Author(s) -
Takahashi Chiharu,
Shirooka Ryuichi
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd021973
Subject(s) - climatology , storm track , storm , madden–julian oscillation , boreal , el niño southern oscillation , environmental science , winter storm , track (disk drive) , meteorology , oceanography , geography , geology , engineering , convection , mechanical engineering , archaeology
The present study investigates modulation by the Madden‐Julian Oscillation (MJO) of storm track activity (STA) over the North Pacific (NP) during boreal winter for El Niño and La Niña periods. STA defined by vertically averaged synoptic eddy kinetic energy (EKE) greatly intensifies over the western North Pacific (WNP) and central eastern North Pacific during La Niña and El Niño years, respectively, when the MJO convection is located over the central Indian Ocean (IO)‐Maritime Continent. When the MJO moves into the western central Pacific, the STA in La Niña years is suppressed (enhanced) at higher (lower) latitudes than in El Niño years. Diagnoses of EKE and eddy available potential energy budgets indicate that the difference in STA over the WNP for the MJO phases between El Niño–Southern Oscillation (ENSO) years is mainly contributed by baroclinic energy conversion and potential energy conversion between background and eddy (BC PE ). We reveal that BC PE is mainly attributed to intraseasonal baroclinicity and eddy heat flux (EHF) anomalies and their interactions with strong winter mean baroclinic fields in the WNP. Through the EHF, synoptic eddies act to counterbalance an intraseasonal temperature that is primarily caused by the anomalous horizontal advection of mean temperature by MJO‐related flow. The intraseasonal circulation and associated temperature and EHF anomalies dominate in northwest (southeast) portion of the NP during La Niña (El Niño), leading to BC PE difference. Changes in the spatial pattern and strength of the NP circulation and STA are caused by dominance of strong MJO amplification over the IO (central Pacific) during La Niña (El Niño).