Investigating the Definition of Rapid Intensification in Typhoons: A Process-based Approach

Rapid intensification (RI) contains complex characteristic, resulting in forecasting challenge. The current RI definition is based on the approximately the 95^th percentile of the overwater intensity changes from National Hurricane Center (NHC) best-track database in Atlantic and eastern North Pacific basins during the 1995-2012 time period at 12-, 24-, 36-, and 48-h lead time. This study attempts to investigate the deterministic differences in TC structure between RI and non-RI based on different RI definitions from 1959 to 2022, using data from International Best Track Archive for Climate Stewardship (IBTrACS) in western North Pacific. Additionally, the results are validated through a large number of Weather Research and Forecasting Model (WRF) simulations. To assess the most suitable RI threshold, the azimuthal average of equivalent potential temperature, potential vorticity, and vertical velocity from ECMWF Reanalysis v5 (ERA5) data was employed in the composite analysis.

Preliminary results indicate that the majority of the parameters exhibit the greatest anomaly differences when the RI threshold is set at 65 kt/24h and 50 kt/24h, particularly during the period from 2013 to 2022 (Fig. 1). For the past decade, the RI threshold that best reflects bimodality has increased to 42.5 kt/24h, as compared to Lee et al. (2016). This implies an increasing trend in tropical cyclone intensity, particularly during instances of RI.

The ongoing work includes the simulation experiments and statistical results of the WRF, which will be presented in the upcoming conference meeting.