An Objective Method for Identifying Post-Landfall Tropical Cyclone Remnant Vortices over China and Their Climatological Characteristics

Tropical cyclones (TCs) typically weaken rapidly after landfall and often evolve into remnant vortices (RVs), which can interact with the ambient environment to produce prolonged heavy rainfall and severe secondary hazards. However, the absence of a unified objective definition and incomplete records of RV evolution in the TC best track dataset have hindered systematic and climatological studies. In this study, an automated method is developed to objectively identify and track TC RVs over land. The method dynamically adjusts the search radius according to post-landfall TC displacement and determines the RV center at 850 hPa by jointly considering the geopotential height minimum, relative vorticity maximum, and cyclonic circulation center. Case evaluations indicate that this method reliably captures RV locations across diverse environmental conditions and complex terrain. Based on the identified RVs, a climatological analysis of TC RVs over the Chinese mainland during 1980–2024 is conducted. Results show that TC RVs generally evolve from deep, symmetric warm-core structures to shallow disturbances with only weak low-level vorticity remaining. Remnant activity is primarily concentrated in July–September, with most lifetimes shorter than 48 h, although a small fraction persists beyond 96 h. Their tracks can be classified into northward- and westward-moving types. Northward-moving RVs exhibit longer mean lifetimes, whereas westward-moving RVs, despite shorter average lifetimes, are more prone to extremely long-lasting events. Although westward-moving RVs benefit from more favorable thermodynamic conditions, terrain plays a dominant role in limiting their lifetime. This study provides a methodological basis for objective identification and climatological analysis of TC RVs.