Circulation calendar

German Bight: Statistical Analyses

Method description

The near-surface circulation patterns in the German Bight are permanently changing due to strong tidal currents and the variability of the local wind field. The net transport of the water mass is defined by the so-called residual currents, i.e., the influence of the tidal currents is eliminated by suitable averaging. The circulation calendars document the direction of the daily residual currents and reveal the high directional variability in the German Bight. Longer periods of constant circulation pattern are caused by persistent wind fields. Generally, the circulation pattern are characterised by a great seasonal and inter-annual variability.

Daily averaged residual currents of the upper model layer (0 – 5 m depth) of the BSH’s operational circulation model BSHcmod version 4 are used to classify the circulation pattern in the German Bight between 53° 15’ – 55° 30’ N and 6° 30’ – 9° E. The data are daily averages which correspond to about 2 tidal periods. The small averaging error is negligible concerning the distribution of the circulation pattern. The most frequent pattern are the cyclonic circulation (C, ~45%) with a pronounced inflow at the south-western border and outflow at the northern border, the opposite directed anticyclonic circulation (A, ~ 13%), and a variable current pattern (V, ~24%). The six directional types with currents towards the E, W, N, S, NW, and SE play only a minor role. For seasonal statistics these patterns are combined in the directional type (DIR = E+W+N+S+NW+SE). Due to the topographical forcing SW and NE pattern are not observed.