As the formation and separation of eddies in the wake of large islands depends on the Froude number of the flow, it was determined by applying the concept of the dividing streamline using profile data. The calculation of characteristic properties like the distances between cyclonic and anti-cyclonic vortices, the propagation speed of the eddies or the shedding period of a vortex pair, requires the automatic identification and tracking of the eddies. Hence, appropriate analysis techniques had to be developed. They are based on horizontal cross-sections which are coarsened and smoothed at first because the eddies are superimposed by the small scale, turbulent signal in the data. It is known from satellite observations that the vortices span the whole depth of the boundary layer. The high areal resolution of the simulations permits to take a step further and to examine especially the vertical structure of single eddies. Thus, the spatially averaged structure of single eddies in a mature state is presented here for the first time.
The simulation results show that the properties of the vortex streets are almost constant with height and that the eddies extend throughout the whole depth of the boundary layer. The eddies are further characterised by vertical axes, warm cores and pressure minima independent of their sense of rotation. There is a continuous updraft in the order of 10 cm/s in the centre of the vortex. This causes a divergent outflow at the vortex' top where a maximum of potential temperature is located which originates from the lowering of the capping inversion due to the flow divergence. This may be responsible for the cloud-free centres of many observed vortices in satellite pictures. The influence of the turbulence on the vortex streets is small. Merely the mean radius of the eddies descends with increasing turbulence indicating a faster decay of the eddies. This can be ascribed to higher mixing which is associated with higher turbulence. Variations of the wind speed in the simulations affects the Froude number of the flow and therewith its character. In addition to a vortex street, a wavy wake could be simulated due to the exceeding of the critical Froude number of the flow.