Benefits of high-resolution downscaling experiments for assessing strong wind hazard at local scales in complex terrain: a case study of Typhoon Songda (2004)

Tetsuya Takemi,Rui Ito

doi:10.1186/s40645-019-0317-7

Tetsuya Takemi, Rui Ito

Open Access

https://doi.org/10.1186/s40645-019-0317-7

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Abstract

This study investigated the representation of surface winds in complex terrain during the passage of Typhoon Sondga (2004) in downscaling simulations with the horizontal grid spacing of 200 m. The mountainous areas in Hokkaido where forest damages occurred in the typhoon event were chosen for the present analysis. The 200 m grid simulations were compared with the simulations with the grid spacing of 1 km. The 200 m grid simulations clearly indicated more enhanced and more frequent extremes both in the stronger and weaker ranges of surface winds than the 1 km grid case. Both in the 200 m grid and 1 km grid cases, the mean and maximum winds in the analysis areas during the simulated time period increase with the increase in the terrain slope angle, but in the 200 m grid case, the relationships of the mean and maximum winds against the terrain slope angle includes wide scatter. In this way, the response of the wind representations to the grid spacing appears differently between the 200 m and 1 km grid cases. A parameter characterized subgrid-scale orography was used to quantify the influences of the terrain complexity on surface winds, demonstrating that the area-maxima and spatial variance of surface winds are more enhanced with the increase in the subgrid-scale orography in the higher-resolution case. It is suggested that the high-resolution simulations at the 200 m grid highlight the fluctuating nature of surface winds in complex terrain, because of the better representation of the model terrain at 200 m. Benefits of the representation of surface winds in simulations at the resolution on the order of 100 m are due to the better representation of complex terrain, which enables to quantitatively assess the impacts of strong winds on forest and natural vegetation in complex terrain.

Highlights

Dynamical downscaling is a useful approach in weather and climate researches in order to assess the impacts of weather disturbances and extreme weather phenomena at mesoscales and local scales
The wind data measured at automated weather stations (AMeDAS) of Japan Meteorological Agency (JMA) were used
We have investigated the representations of typhooninduced surface winds in complex terrain in highresolution simulations of a specific event in Hokkaido, the northern part of Japan, as a case study for Typhoon Songda (2004)

Summary

Introduction

Dynamical downscaling is a useful approach in weather and climate researches in order to assess the impacts of weather disturbances and extreme weather phenomena at mesoscales and local scales. Because deep cumulus convection plays a critical role in spawning severe weather such as heavy rainfalls and strong winds, a horizontal grid spacing that can adequately resolve the activities and effects of deep convection is required to better represent severe weather phenomena in numerical simulations. From a climate research point of view, Kitoh et al (2016) emphasized that the importance of high-resolution downscaling in representing extremes lies in reproducing well-resolved topography in numerical models. Takayabu et al (2016) listed high-resolution topography as one of the factors that add values to dynamical downscaling. This study deals with the issue on the benefits or added values of dynamical downscaling by conducting a higher-resolution grid spacing on the order of 100 m

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