Impacts of Turbulence Length Scales on Numerical Forecasts of Hurricane Earl (2010)

Recent studies based on numerical simulations of an idealized hurricane have revealed that hurricane intensity and structure are highly sensitive to horizontal turbulence length scale in a turbulence parameterization scheme. In this study, this sensitivity is investigated using real case simulations. Numerical forecasts of Category 4 Hurricane Earl (2010) using Weather Research and Forecasting (WRF) model with varying horizontal resolutions and turbulence length scale were conducted. It is found that the turbulence length scale has much larger impact on the intensity than the model resolution. Choosing a turbulence length scale of about 1000m as suggested by other studies only produces a weak Category 3 storm. Not only the structures of Earl change significantly, but also the large scale environment and the evolutions of the downstream Hurricane Danielle and upstream Tropical Storm Fiona are dramatically different. These results again indicate proper turbulence parameterization scheme is essential for successful hurricane predictions.