Comparison of current simulations by the state-of-the-art operational models in the Gulf of Finland with ADCP measurements

Current modeling results from two operational models (Baltic-wide HIROMB-BS01 with 1 nautical mile resolution and subregional HIROMB-EST with 0.5 mile resolution) were compared with ADCP measurements at four sites of different topographic and hydrographic background in the Gulf of Finland. Both models predict a reasonable match with the observed subsurface currents in most of the cases, although there are no data to carry out the assimilation of mesoscale oceanographic features. The correlations of the modeled currents with the observed counterparts yield quite often the values above 0.5, both in the low-frequency and high-frequency range. In general, the models tend to generate less current variability (smaller standard deviations) than observed. There is also some site-specific bias of mean currents. Near-bottom and coastal currents are highly constrained by the topography. High current speeds (above 20 cm/s) were measured in the deep layers of the rough-bottom area around a small island. Such currents were in general well simulated by the 0.5 nm model, only slightly biased by the dominating direction. The modeled near-bottom currents are simply transformable into more realistic results if the correct topography is taken into account. Both the observations and the subregional model results revealed similar halocline-intensified EOF modes of vertical current structure, the amplitudes of which were correlated quite well.