Bow echoes, identifiable by their bow-like shape on radar, are often associated with specific convective processes. The T-initiation Mesoscale Convective System (MCS) exemplifies this phenomenon, appearing as a quasi-linear bow echo with downstream nascent leading convection (LC), forming a 'T' shape on radar. The LC presents challenges for operational forecasts and can lead to severe weather conditions when they merge with parent bow echoes. Focusing on a T-initiation MCS over the Bohai Sea in China, this study investigates the physical mechanisms governing LC initiation. Utilizing the WRF-ARW model, backward trajectory tracking within a Lagrangian framework and vertical momentum budget analysis are employed to explore the dynamic factors driving the uplift of air parcels within the LC cells. Results reveal that a mid-level mesoscale anticyclonic vortex associated with the bow echo’s upper-level outflow modulated the wind field, resulting in stronger vertical wind shear between 2.5–5 km AGL downstream of the bow-echo. Interactions between this enhanced shear and pre-existing vertical motion led to low perturbation pressures at midlevels, which resulted in a nonhydrostatic vertical perturbation pressure gradient force that aided parcel ascent, contributing to the initiation of new LC cells. Thus, this study helps elucidate the self-organizing and sustaining processes of bow echoes by potentially identifying a novel initiation mechanism for LC cells in a T-initiation MCS.

Convective Initiation,T-initiation Mesoscale Convective System