How well can the Mann model describe typhoon turbulence?

Abstract. More and more wind farms are planned and built in regions prone to tropical cyclones. However, the current International Electrotechnical Commission (IEC) standard provides no clear guidelines on how to account for turbulence occurring during tropical cyclones. This study investigates how well the Mann uniform shear model, a model referenced by the IEC, can model turbulence during tropical cyclone conditions. We analyzed sonic anemometer measurements at 60 m from four typhoon cases in the South China Sea. The Mann model was fit to the one-point spectra in different locations in the typhoon structure. We found that the Mann model can fit the observed spectra outside the typhoon eye and the rainbands to a certain extent. However, several deficiencies are identified. (1) In the outer-cyclone region, spectral energy at wavenumbers smaller than 3×10-3 m−1 is generally larger than predicted by the Mann model, likely reflecting the presence of mesoscale wind fluctuations. (2) Consistent with previous studies, excess spectral energy is observed at wavenumbers larger than 10−1 m−1 in the inner-cyclone and eyewall regions of one typhoon; however, it cannot be ruled out that this excess energy may be related to measurement quality. (3) In the inner-cyclone region, the peak wavenumbers of the alongwind and crosswind spectra are often closer together than predicted by the Mann model. In these cases, the crosswind component exhibits larger-than-predicted spectral energy within the energy-containing subrange. This study can serve as a baseline for further research addressing turbulence in tropical cyclones in the context of structural engineering.