Investigation of the influence of the height of the convective boundary layer on turbulence structure near the surface over the Baltic Sea has been performed with measurements from the site Östergarnsholm. Especially the normalized wind gradient has been studied.

Östergarnsholm is a small island east of Gotland in the Baltic Sea. On a 30-m high tower turbulence measurements have been performed at three levels and profile measurements at five levels (wind and temperature). Due to the position of the tower and the slop of the sea floor outside the island the site represents undisturbed over water conditions in the sector 100-220 degrees. The height of the boundary layer has been determined from radio soundings performed during two spring periods (1997, 2000) and tree autumn experiments (1996, 1998 and 1999).

In previously experiment performed over land at an agricultural site the normalized wind gradient was found to be largely influenced by the height of the boundary layer. Results from the measurements at Östergarnsholm suggest that the influence of the height of the boundary layer for the normalized wind gradient is even larger then the results from the land study. This result may be caused by the lack of a diurnal variation of the height of the boundary layer that exist over land, i.e. no large abrupt variation of the height of the boundary layer over the Baltic Sea and thus the influence becomes more pronounced. This larger influence may also be coupled to the waves and the presence of swell.

Most likely the height of the boundary layer effects also other turbulence statistics over the Baltic Sea more compared to over land.