Mesoscale studies using clear-air Doppler radar

The use of clear-air Doppler radar in the study of mesoscale phenomena is explored by performing several case studies using observations from four field experiments that included the radar and a variety of other instruments. The radar operated at 45 or 50 MHz, providing high temporal resolution vertical profiles of the vertical and horizontal wind components through most of the troposphere in both clear and cloudy conditions.;The radar observations are shown to provide a consistent picture of the passage of fronts associated with a strong extratropical cyclone. Observational evidence of the temporal evolution of one jetstreak and of superposition effects associated with the interaction between two jetstreaks are presented. In a second study, the episodic enhancement of vertical and horizontal velocity variability at a site near mountains is found to be due to lee waves. Two-dimensional linear perturbation theory and three-dimensional numerical simulations are used as guides to check against the radar-observed vertical structure in both trapped and vertically propagating lee waves. The passage of a baroclinic system is found to have produced a transition in the wave type. The temporal variability observed by the radar on time scales less than an hour in a trapped lee wave is shown to result from small directional changes in the upstream winds. In a third study, vertical velocity measurements from the radar and from sodars give unique information about the behavior of gravity waves associated with a gravity current. Ambient stratification features are shown to have strongly influenced the type and vertical extent of the waves. Both Kelvin-Helmholtz waves generated in the regions of high wind shear and lee-type waves forced by the gravity current acting as an obstacle are identified. In another study, the vertical structure of a ducted mesoscale gravity wave and its relationship to surface perturbations are established. The observed structure was that of a standing internal gravity wave with one half of a vertical wavelength between the ground and the critical level. The environment is shown to have been conducive to wave ducting.;Overall, a promising consistency is found between radar-observed vertical motions and those expected within the various mesoscale phenomena studied.