Proceedings with Extended Abstracts (single PDF file) - Radio ...

In Fig. 2 a sketch of a mountain lee wave is shown. Here we have to consider three properties,which can yield erroneous velocity estimates: (a) The radar beams point into different phasesof the wave, which means that the generally applied assumption of a homogeneous wind fieldis not applicable; (b) the radial velocity is a composite of the mean horizontal wind velocityand the wave induced fluid velocity, which differs at the three beam directions (c) the reflectivitysurfaces (sheets and laminae) are inclined at different angles due to the mountain wave,which results in differences of the effective pointing angle (aspect sensitivity).Vert.NESWFig. 3 Height-time-velocity plots measured with vertical beam (left)and with the composition of co-planar NE and SW beam direction (right).The measurements were done over 24 hours with the SOUSY Svalbard Radar14 Nov., 07:28, to 15 Nov. 1999, 07:33 UT, during strong mountain wave activity.Fig. 3 shows that these effects have certainly to be taken into account. Whereas in the firsthalf of the observing period the two velocity estimates are about equal, they differ considerablyin the second part of this period. At certain times the velocities even have opposite direction.We clearly attribute this discrepancy in velocity estimates due to the effect of mountainwaves, resulting from properties (a) and (b). Unless one knows more about the waveparameters, the disentangling of horizontal and vertical velocities will be quite uncertain. Thatthere is also an effect of the inclination of reflectivity surfaces (c) was found by Röttger et al.(1990). As shown in Fig. 4, the radial velocity is correlated with the inclination angle.Fig. 4 Radial velocity W measured in the vertical beam and simultaneousestimates of the incidence (inclination) angle δ measured with the Chung-Li VHF Radar307