The Formation Patterns of Tropical Cyclones in the Northwest Pacific and the Modulation Mechanisms of Their Environmental Fields

Abstract

Tropical cyclone genesis (TCG) in the Northwest Pacific is strongly influenced by the interaction of large-scale oceanic and atmospheric environmental fields. This study investigates the spatiotemporal characteristics of TCG from 1991 to 2020 and examines the modulation mechanisms of major environmental factors. Tropical cyclone records from the China Meteorological Administration best-track dataset are combined with NOAA ERSST.v5 sea-surface temperature data and ERA5 atmospheric reanalysis fields. The analysis focuses on the effects of the El Niño–Southern Oscillation (ENSO) and tropospheric vertical wind shear (VWS), while relative humidity, low-level vorticity, low-level convergence, and upper-level divergence are included as supporting diagnostic variables. Environmental conditions are extracted within a 5° × 5° region around each genesis location during the 48–24 h period before genesis. Sen's slope estimation, the Mann–Kendall trend test, composite analysis, partial correlation, and bootstrap methods are employed to examine long-term variability, spatial migration, and statistical relationships. The study aims to clarify how ENSO-related sea-surface temperature anomalies and VWS jointly modulate the frequency and spatial distribution of TCG. The proposed framework provides a basis for improving environmental diagnosis, short-term climate prediction, and tropical cyclone risk assessment.