A comparison between long term measured and modeled sensible heat and momentum fluxes using a High Resolution Limited Area Model (HIRLAM)

The objective of this paper is to study the surface fluxes obtained by a Hi gh Resolution Limited Area Model (HIRLAM), used for weather forecasts. The question arises whether the quality of the fluxes are high enough to make H IRLAM a proper tool for performing calculations of the water and energy bud gets over the Baltic Sea, which is one of the aims of the BALTEX project. T urbulent fluxes modeled by HIRLAM are compared with direct flux measurement s over sea for an extended time period. The model is shown to overestimate both sensible heat and momentum flux for the studied period. The sensible h eat Aux for the studied period is overestimated by 8.1 W/m(2) and the momen tum flux is systematically overestimated by 0.03 kg/ms(2) or 50 %. It is sh own that the values of parameters in the surface parameterization scheme ca n be improved, for example will a lower value of the Charnock's coefficient agree better with the measurements. The sensitivity of the surface scheme to changes in mean parameters is studied. It is also shown that it is of gr eat importance to have correct values of the near surface wind speed and th e temperature difference between air and sea to obtain correct fluxes.