Effects of roughness length on the FSU one-dimensional atmospheric boundary layer model forecasts

A. BIROL KARA, AHSHA TRIBBLE, PAUL H. RUSCHER

Abstract

This paper is concerned with the sensitivity of the forecasts obtained from the "Florida State University Atmospheric Boundary Layer (FSU1DPBL) Model" when solely considering a variation in the roughness length parameter. The model is mainly used to evaluate the sensitivity of the roughness length of momentum on the model forecasts. The roughness length calculations are perfomed using both wind speed components and wind direction. Based on these calculations, the commonly used values of roughness length of momentum indicated in the literature is compared to that for Tallahassee (TLH) calculated from observations. In addition, model forecasts obtained using the calculated roughness length are compared with those using the classical value of the roughness length. The focus on these comparisons is mainly on the variations, if any, in the forecasts for the atmospheric boundary layer (ABL) height, sensible heat flux, soil heat flux, latent heat flux, and 10-meter wind speed. Results show that the fluxes do not have much variation when using both classical roughness length and the calculated roughness length. However, the 10-meter wind speed appears to be overestimated using the classical roughness length value in comparison to the calculated value.

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