High frequency variability of the surface layers in the Skagerrak during SKAGEX

This paper presents spatial and temporal distributions of freshwater height and potential energy in the Skagerrak during the period of Skagerrak Experiment (SKAGEX). In SKAGEX extensive quasi-synoptic hydrographic measurements were taken during one month. These fields provide a basis for an examination of the dynamics of the surface layer. Qualitatively they show a time-series of destruction and re-establishment of the cyclonic circulation. The response to changes in the magnitude and direction of the wind is very rapid. It appears to take approximately one week to develop a strong cyclonic circulation from a situation with very weak baroclinic currents. Freshwater inflow from the Kattegat calculated from recording current meters correlates well with the changes of total freshwater volume within the Skagerrak. Inflow of freshwater-influenced water along the Jutland coast was during this particular period of equal importance in re-filling the Skagerrak freshwater pool. By tracking an outbreak of freshwater from the Kattegat along the coasts of Skagerrak, it is qualitatively verified that the freshwater flow within the coastal currents is in geostrophic balance and proportional to the freshwater height squared. Another estimation using the current meter data shows that the inflow of potential energy from the Kattegat may give a substantial contribution to the total potential energy of the Skagerrak, at least during calm weather conditions. The inflow of potential energy along the Jutland coast was also of importance during the SKAGEX period. However, comparing the conditions of the SKAGEX period with a previous calculation of the profile potential energy (Gustafsson and Stigebrandt, 1996. Journal of Sea Research, 35, 39–53), it is concluded that the advection of potential energy through the open boundaries is not strong enough to explain the high profile potential energy content during winter-time. Thus, the inflows seem to be of major importance for the energetics of the Skagerrak during the calm summer period, but of minor importance during the windier winter.