On the afternoon of 24 November a ZD1839 concentration swell was measured, where the significant wave height was between 0.4 and 0.5 m and the associated peak wave period was over 7 s. The speed of the wind, blowing from the SW, measured at the Kessulaid weather station was < 5 m s−1. The wave spectrum during this time was shifted towards lower frequencies compared to the spectra from stormy conditions (Figure 6). At first glance, we could explain this swell as a consequence of the strong, 23 m

s−1, NNW wind on 23 November. But the wind dropped some 12 h (Figure 2) before the first signs of swell. Therefore, it is rather unlikely that long swells could flow into the Suur Strait from the rather shallow Väinameri area. Examining the HIRLAM wind field for this period (24 November), one could see a SW storm in the Gulf of Riga with wind speeds of up to 18 m s−1 (Figure 7). The wind speed decreased significantly towards 17-AAG in vitro the Väinameri and matched the measured value at Kessulaid. Thus, the swell at the measurement site can be explained as having been generated by the SW storm in the open Gulf of Riga. The wave field is described by the long fetch (the S wind), the short fetch (the NNW wind) and the swell spectrum during the observation period (Figure 6). As one can see, the southerly wind on 14 November generated a rather broad spectrum, which had its maximum at

0.16 Hz and a secondary, lower peak at 0.3 Hz. The NNW wind on 23 November, 23 m s−1, on the other hand, generated a spectrum where the peak frequency was 0.27 Hz. This was because the NNW winds had a shorter fetch than the southerly winds, so that its spectrum was shifted towards higher frequencies. For the swell coming

from the south, U0126 the spectrum peak was located at 0.13 Hz and the tail of the spectrum contained less energy. The wave-induced and current-induced shear velocities were calculated from the measured time series of waves and currents (Figure 8). The critical shear velocity for the resuspension of grains 0.25 mm in size, which corresponds to the fine sand common to the Väinameri, is 1.4 cm s−1 (Kuhrts et al. 2004). All wave events when the wind was blowing from the south induced sediment resuspension, and the highest shear velocities were obtained during the strong (15 m s−1) southerly wind event on 18 November. Note that the extreme northerly wind event on 23 November did not induce shear velocities larger than the critical value, but it is possible that the swell the next day led to resuspension. For the current-induced shear velocity, the critical value for resuspension was slightly exceeded only on 24 November, when current speeds of up to 0.4 m s−1 generated shear velocities of up to 1.5 cm s−1 in the bottom boundary layer. The root mean square difference between the wave- and current-induced shear velocities was 1.05 cm s−1. The triple-nested wave model with the same bathymetry and forcing as the circulation model was used.