The impact of waves and sea spray on modelling storm track and development

Lichuan Wu,Anna Rutgersson,Erik Sahlée,Xiaoli Guo Larsén

doi:10.3402/tellusa.v67.27967

Lichuan Wu, Anna Rutgersson + Show 2 more

Open Access

https://doi.org/10.3402/tellusa.v67.27967

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Abstract

In high wind speed conditions, sea spray generated by intensely breaking waves greatly influences the wind stress and heat fluxes. Measurements indicate that the drag coefficient decreases at high wind speeds. The sea spray generation function (SSGF), an important term of wind stress parameterisation at high wind speeds, is usually treated as a function of wind speed/friction velocity. In this study, we introduce a wave-state-dependent SSGF and wave-age-dependent Charnock number into a high wind speed–wind stress parameterisation. The newly proposed wind stress parameterisation and sea spray heat flux parameterisation were applied to an atmosphere–wave coupled model to study the mid-latitude storm development of six storm cases. Compared with measurements from the FINO1 platform in the North Sea, the new wind stress parameterisation can reduce wind speed simulation errors in the high wind speed range. Considering only sea spray impact on wind stress (and not on heat fluxes) will intensify the storms (in terms of minimum sea level pressure and maximum wind speed), but has little effect on the storm tracks. Considering the impact of sea spray on heat fluxes only (not on wind stress) can improve the model performance regarding air temperature, but it has little effect on the storm intensity and storm track performance. If the impact of sea spray on both the wind stress and heat fluxes is taken into account, the model performs best in all experiments for minimum sea level pressure, maximum wind speed and air temperature.

Highlights

Severe storm systems threaten offshore activities as well as coastal and inland areas
We introduce a wave-state-dependent sea spray generation function (SSGF) and wave-age-dependent Charnock coefficient into a wind stress parameterisation (Kudryavtsev et al, 2012) and apply heat fluxes incorporating the contribution of spray-related processes in an atmosphereÁwave coupled model to investigate their impact on the midlatitude storm development
To verify the model performance when introducing the parameterisations into the coupled model system, the results from the nearest grid point in the model are compared with FINO1 hourly data

Summary

Introduction

Severe storm systems threaten offshore activities as well as coastal and inland areas. Appropriate descriptions of processes such as airÁsea interaction can play a role in better forecasts and better climate descriptions of these systems. AirÁsea interaction processes are responsible for transporting energy, heat and matter between the ocean and the atmosphere. Momentum and heat fluxes are essential factors affecting storm intensity, storm tracks and precipitation. Appropriate momentum and heat flux parameterisations in numerical models can play an essential role in weather forecasting and climate studies. Momentum and heat flux parameterisations have been studied for decades, there is no general agreement on their formulation, especially in extreme wind conditions Takagaki et al, 2012) Momentum and heat flux parameterisations have been studied for decades, there is no general agreement on their formulation, especially in extreme wind conditions (e.g. Takagaki et al, 2012)

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