Measured and simulated latent and sensible heat fluxes at two marine sitesin the Baltic Sea

In this study, turbulent heat flux data from two sites within the Baltic Se a are compared with estimates from two models. The main focus is on the lat ent heat flux. The measuring sites are located on small islands close to th e islands of Bornholm and Gotland. Both sites have a wide wind direction se ctor with undisturbed over-water fetch. Mean parameters and direct fluxes w ere measured on masts during May to December 1998. The two models used in this study are the regional-scale atmospheric model HIRLAM and the ocean model PROBE-Baltic. It is shown that both models overe stimate the sensible and latent heat fluxes. The overestimation can, to a l arge extent, be explained by errors in the air-water temperature and humidi ty differences. From comparing observed and modelled data, the estimated 8- month mean errors in temperature and humidity are up to 1 degreesC and 1 g kg(-1),respectively. The mean errors in the sensible and latent heat fluxes for the same period are approximately 15 and 30 W m(-2), respectively. Bulk transfer coefficients used for calculating heat and humidity fluxes at the surface were shown to agree rather well with the measurements, at leas t for the unstable data. For stable stratification, the scatter in data is generally large, and it appears that the bulk formulation chosen overestima tes turbulent heat fluxes.