The tropical easterly jet (TEJ) is a crucial upper-tropospheric component of the Asian summer monsoon system, with its core position exhibiting distinct intraseasonal variability during boreal summer. However, the underlying dynamical mechanisms remain inadequately understood. This study identifies a distinct northwest–southeast (NW–SE) oscillation of the TEJ core, closely linked to alternating cyclonic and anticyclonic anomalies over the tropical Indian Ocean (IO). These circulation anomalies modulate the upper-tropospheric wind field, inducing westerly (easterly) anomalies over the southern Indian Peninsula (SIP) and promoting a northwestward (southeastward) displacement of the TEJ core. A vorticity budget analysis reveals that this NW–SE oscillation is primarily governed by three dominant dynamic processes: planetary vorticity advection, horizontal advection of relative vorticity, and the tilting term. While this intraseasonal oscillation of the TEJ core is primarily maintained by upper-tropospheric dynamic processes, its initiation is modulated by the northward propagation of large-scale convective anomalies associated with the boreal summer intraseasonal oscillation (BSISO). During BSISO phases 6–8 (2–4), the northward propagation of suppressed (enhanced) convection induces positive (negative) relative vorticity and associated westerly (easterly) anomalies in the upper troposphere over the northern IO by generating southerly (northerly) wind anomalies over the SIP. These circulation anomalies promote a northwestward (southeastward) displacement of the TEJ core roughly one phase later. Overall, these findings improve our understanding of the spatiotemporal variability of the TEJ core and underscore the combined dynamical and thermodynamical controls governing its intraseasonal fluctuations.
 

Tropical easterly jet (TEJ); Intraseasonal variability; Northwest–southeast oscillation; Vorticity budget; Boreal summer intraseasonal oscillation (BSISO)