10:45 〜 11:00
[ACG38-07] Intraseasonal Northwest–Southeast Oscillations of the Tropical Easterly Jet Core: Dynamical Mechanisms and Modulation by the Boreal Summer Intraseasonal Oscillation
キーワード：tropical easterly jet, intraseasonal variability, boreal summer intraseasonal oscillation, monsoon dynamics
The tropical easterly jet (TEJ) is a crucial upper-tropospheric component of the Asian summer monsoon that exhibits pronounced intraseasonal variability in its core position. However, the dynamical mechanisms driving this variability remain poorly understood. This study examines the northwest–southeast (NW–SE) oscillatory pattern of the TEJ core during boreal summer, elucidating its underlying dynamical mechanisms and modulation by the boreal summer intraseasonal oscillation (BSISO). Cyclonic (anticyclonic) anomalies over the tropical Indian Ocean, accompanied by westerly (easterly) wind anomalies to their southern flank, induce non-uniform changes in the TEJ wind speed that drive the northwestward (southeastward) displacement of the TEJ core. A vorticity budget analysis identifies three dominant dynamical processes governing this oscillation: planetary vorticity advection, horizontal advection of relative vorticity, and the tilting term. Furthermore, BSISO events are classified into two distinct types based on upper-tropospheric wind anomalies over the southern Indian Peninsula: BSISO with westerly anomalies (BSISO–WA) during phases 1–3 and BSISO with easterly anomalies (BSISO–EA). BSISO–WA events accelerate the northwestward shift of the TEJ core by one phase, while BSISO–EA events delay this shift and weaken the amplitude of the NW–SE oscillation. These findings not only advance our understanding of the multi-time scale variability of the TEJ core position but also provide critical insights into the role of BSISO in modulating this monsoon component, with potential implications for improving monsoon forecasting and climate model representation.