the takes the order of . This is the reason why is defined as the thickness of the Ekman layer. A number of important properties of the Ekman spiral will follow from this solution: When , it appears that the flow has a transverse component with respect to the interior flow, which differs 45 degrees to the left on the northern hemisphere, , and 45 degrees to the right on the southern hemisphere, . Note that, in this case, the angle between this flow and the interior flow is at its maximum. It will decrease for increasing . When takes the value of , the resulting flow is in line with the interior flow, but will be increased with , with respect to the interior flow. For higher values of , there will be a minimal transverse component in the other direction as before. The exponential term will go to zero for , resulting in . Because of these properties, the velocity vector of the flow as a function of depth will look like a spiral. Surface Ekman Spiral The solution for the flow forming the bottom Ekman spiral was a result of the shear stress exerted on the flow by the bottom. Logically, wherever shear stress can be exerted on a flow, Ekman spirals will form. This is the case at the air-water interface, because of wind. A situation is considered where a wind stress is exerted along a water-surface with an interior flow beneath. Again, the flow is uniform, has a geostrophic interior and is homogeneous fluid. The equations of motion for a geostrophic flow, which are the same as stated in the bottom spiral section, can be reduced to: The boundary conditions for this case are as follows: Surface : and Towards interior : and With these conditions, the solution can be determined: Some differences with respect to the bottom Ekman spiral emerge. The deviation from the interior flow is exclusively dependent on the wind stress and not on the interior flow. Whereas in the case of the bottom Ekman spiral, the deviation is determined by the interior flow. The wind-driven component of the flow is inversely proportional with respect to the Ekman-layer thickness . So if the layer thickness is small, because of a small viscosity of the fluid for example, this component could be very large. At last, the flow at the surface is 45