Investigation of short-period gravity waves with the Lindenberg 482 MHz tropospheric wind profiler

During four consecutive days in May 2001, convectively forced short-period (6-45 min) gravity waves were observed with a 482 MHz wind profiler, which is continuously operated by the Deutscher Wetterdienst (German Weather Service) at the Lindenberg observatory, 60 km south-east of Berlin. The objective of this campaign was to investigate onset and development of convectively forced gravity waves in the lower and middle troposphere. The wave character could be unambiguously identified by simultaneous vertical wind and temperature measurements and their respective phase shift of pi/2. In accordance with previous findings, convection waves were found to be generated at the top of the convective boundary layer. They propagate predominantly horizontally with a slow but clearly recognizable vertical increase of wave activity. The layer with significant wave activity reached the upper detection range at 7.0 km within a couple of hours on each of the observational days. Gravity wave activity started to decay after 16 UTC with a slower rate than the simultaneously decaying forcing convection. Some wave activity remained during the night but at low amplitude levels. The vertical wind energy component of the free atmosphere was found to be about 30% of the corresponding convective boundary layer (CBL) energy, which is much more than previously reported values from numerical simulations. The wavelet analysis of highly resolved wind profiler vertical velocity data (Deltat = 16 s. Deltaz = 250 m) in the boundary layer and free troposphere gives new insights into the temporal and vertical development of very-short-period convection waves through the troposphere. At the CBL top, a broad spectrum of wave scales with intrinsic periods between 6 and 45 min is generated. With increasing height, shorter scales (T less than or equal to 13 min) disappear and only longer ones remain. Wave trapping, which is confirmed by vertically orientated phase lines, is an important mechanism here.