Mechanisms Driving the Formation of a Warm-Sector Bow Echo by a Boundary Layer Jet Originating from the Beibu Gulf

Bow echoes are linearly organized convective systems capable of producing severe surface winds. In mid-latitude regions, their formation is often associated with strong vertical wind shear, intense rear-inflow jet (RIJ), and low-level book-end vortex. However, in the low-latitude warm sector, bow echoes can develop in the absence of these characteristics, implying distinct formation mechanisms. This study combines multi-source observations and numerical simulations to investigate a northeastward-propagating warm-sector bow echo over the continental area north of the Beibu Gulf. Results reveal that this bow echo evolved within a regime of a weak cold pool, weak vertical wind shear, a weak mid-level rear inflow (RI), and indistinct book-end vortex. The primary forcing mechanism is identified as the impingement of a boundary layer jet (BLJ). Spatial heterogeneities in wind speed at the leading edge of the BLJ caused the linear convection to bend. Moreover, the RI in this case was unusually shallow and low-level, and its early development was closely associated with, and likely enhanced by, the BLJ-related low-level high-momentum flow rather than by classical midlevel downdraft forcing. This study proposes a conceptual model for bow echo development dominated by BLJ forcing, revealing a non-classical mechanism for bow echo formation under weak synoptic-scale backgrounds.