Upper atmosphere potassium layer and its seasonal variations at 54 degreesN

We conducted measurements of the upper atmosphere potassium layer and its s easonal variations during 110 nights between June 1996 and June 1997 at Kuh lungsborn, Germany (54 degrees N, 12 degrees E). The observations were perf ormed by a ground-based metal resonance lidar. We measured the following av erage properties of the nightly mean K layer: column density of 4.4 x 10(7) cm(-2); peak density of 47 cm(-3); layer centroid height of 90.5 km and RM S layer width of 4.0 km. The nightly mean column and peak densities exhibit dominantly semiannual variations with maxima in summer and winter. The cen troid height varies semiannually too, attaining highest altitudes during th e equinoxes. The RMS layer width shows a strong annual variation, though, w ith a maximum width in winter. For the first time the seasonal variations o f the K layer can be compared in detail with the variations observed previo usly in the Na and Fe layers. For all three metal layers their centroid hei ghts are dominated by annual variations with quite similar phases. The colu mn densities are dominated by a semiannual variation in the case of the K l ayer but are dominated by an annual variation for the Fe and Na layers. The layer RMS widths are dominated by annual variations in the case of the K a nd Fe layers. That is quite different to semiannual variations in the case of the Na layer.