Vapor Isotope Probing of Typhoons Invading the Taiwan Region in 2016

Every year, several typhoons originating from the West Pacific come close to Taiwan, modulating the regional weather through intense rainfall and enhanced humidity. The isotopic ratios (delta O-18 and delta D) in the typhoon vapor evolve along its track due to rainout, recycling, and replenishment. In 2016, this signature was recorded in Taipei as typhoon vapors invaded the local atmosphere. After typhoon disintegration, the isotope ratios of the local atmosphere slowly return to the background value. The fall and rise in the ratios give rise to a V-shaped variation. The processes controlling the fall (like moisture turnover, typhoon speed, wind speed, and direction) are fast (1-2 days). In contrast, the recovery is slow (several days) depending on the replacement rate of the local atmospheric moisture by incoming oceanic vapor. An isotope evolution model based on Rayleigh condensation and a box model of moisture mixing in the recovery phase are proposed and employed to explain the V-shape. The combination of these two models for four major typhoons (Nepartak, Megi, Meranti, and Malakas) shows close agreement with observations. The evolution model suggests that the precipitation efficiency, PE (rainfall/overhead moisture), and typhoon size are two important parameters controlling the decrease in ratio. The characteristic turnover time of typhoon moisture (inverse of PE, obtained from European Centre for Medium-Range Weather Forecasts fifth Re-Analysis data) is estimated to be similar to 2 days for a Pacific typhoon of 500 km radius. Our isotope study provides important constraints on the moisture budget of Pacific typhoons.

Automated summary

This study analyzes the impact of isotopic ratios evolution in typhoon vapor on regional weather, and proposes an evolution model based on Rayleigh condensation and moisture mixing to explain this variation. The results show that typhoon size and precipitation efficiency are two important parameters causing a decrease in ratio.