Abstract
Abstract. The impacts of environmental moisture on the intensification of a tropical cyclone (TC) are investigated in the Weather Research and Forecasting (WRF) model, with a focus on the azimuthal asymmetry of the moisture impacts relative to the storm path. A series of sensitivity experiments with varying moisture perturbations in the environment are conducted and the Marsupial Paradigm framework is employed to understand the different moisture impacts. We find that modification of environmental moisture has insignificant impacts on the storm in this case unless it leads to convective activity that deforms the quasi-Lagrangian boundary of the storm and changes the moisture transport into the storm. By facilitating convection and precipitation outside the storm, enhanced environmental moisture ahead of the northwestward-moving storm induces a dry air intrusion to the inner core and limits TC intensification. In contrast, increased moisture in the rear quadrants favors intensification by providing more moisture to the inner core and promoting storm symmetry, with primary contributions coming from moisture increase in the boundary layer. The different impacts of environmental moisture on TC intensification are governed by the relative locations of moisture perturbations and their interactions with the storm Lagrangian structure.
Highlights
While the forecast of tropical cyclone (TC) tracks has been significantly improved in the past several decades, the TC intensity forecast is still a great challenge for most operational numerical weather prediction centers (DeMaria et al, 2007).Environmental moisture has been considered as one of the important factors for TC intensity forecasting
We investigate the impacts of environmental moisture on TC intensity and structure using the Weather Research and Forecasting (WRF) model with artificially modified environmental moisture surrounding a storm vortex
The dry rear (DR) simulation (Fig. 1e) is similar to the moist rear (MR) simulation but the magnitude of the relative humidity (RH) perturbation is reduced to 30 % of the maximum RH at each level, which is drier than the CTRL
Summary
While the forecast of tropical cyclone (TC) tracks has been significantly improved in the past several decades, the TC intensity forecast is still a great challenge for most operational numerical weather prediction centers (DeMaria et al, 2007). Braun et al (2012) showed that dry air located 270 km away from the storm center had little impact on hurricane intensity with no mean flow. L. Wu et al.: Impact of environmental moisture on tropical cyclone intensification impact on hurricane intensity, the storm size was reduced. In a sensitivity study of Typhoon Talim (2005), Ying and Zhang (2012) showed that enhanced moisture promoted convection in outer rainbands and resulted in the weakening of the storm while dry air inhibited outer rainbands and contributed to a stronger storm with smaller size. Most previous modeling studies prescribed moisture perturbations without considering their relative location to a storm vortex (e.g., in the environment, outer rainband or inner core, front or rear quadrants), which may cause different impacts on the storm structure and intensity.
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