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Christian Kühnlein, Andreas Dörnbrack, and Martin Weissmann

strong and possibly severe turbulence. However, as already pictured by Förchgott (1949) and impressively shown by Hertenstein and Kuettner (2005) using numerical simulations, a variation of the upstream shear at mountaintop level results in a totally different downslope flow and rotor types. Moreover, observations of downslope flows and rotors revealing the spatial structure in the boundary layer and the temporal evolution were missing. Some ground-based coherent Doppler lidar observations were

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Stephan F. J. De Wekker and Shane D. Mayor

proven very useful in the understanding of atmospheric dynamics and structure. Shortly after the development of the first pulsed lasers, the applicability of lidar to the study of mountain-wave-related phenomena was recognized. Collis et al. (1968) were the first to document aerosol lidar observations in the Sierra Nevada in February and March 1967, followed by more comprehensive observations by Viezee et al. (1973) in March and April 1969 and 1970. These studies provided evidence that pulsed

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Michael Hill, Ron Calhoun, H. J. S. Fernando, Andreas Wieser, Andreas Dörnbrack, Martin Weissmann, Georg Mayr, and Robert Newsom

larger-scale flows in the lee of mountains ( Doyle and Durran 2007 ). These simulations are helping to illuminate the importance of surface friction in rotor development by showing, for example, that rotors can fail to develop, even in instances of high shear, if the atmospheric state is unfavorable for lee wave formation. In this paper, we show that two coherent Doppler lidar scanning the same vertical–horizontal plane can provide direct observational evidence showing the spatial extent, strength

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Martin Weissmann, Andreas Dörnbrack, and James D. Doyle

line that is generated by boundary layer separation resulting from strong downslope winds and lifted aloft by the lee wave circulation ( Doyle et al. 2009 ). Some of the major challenges for T-REX are to observe these subrotor vortices, to estimate the strength of the horizontal vorticity, and to investigate their characteristics. In this study, high-resolution scanning Doppler lidar observations taken during T-REX are analyzed, and a method for deriving tangential velocity V ϕ and vorticity

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Susanne Drechsel, Georg J. Mayr, Michel Chong, Martin Weissmann, Andreas Dörnbrack, and Ronald Calhoun

coherent Doppler lidars were operated by the Arizona State University (ASU) and by the Institute of Atmospheric Physics of the German Aerospace Center (DLR), Oberpfaffenhofen, respectively. A proven algorithm for the 3D wind retrieval from multiple Doppler radars was applied to the dual-lidar observations. We chose the Multiple Doppler Synthesis and Continuity Adjustment Technique (MUSCAT) since it provides stable solutions and can be used over complex terrain. A brief description of MUSCAT will be

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Željko Večenaj, Stephan F. J. De Wekker, and Vanda Grubišić

turbulence parameterization in these situations is highly needed. The data and results from our case study can be used to develop and evaluate turbulence parameterizations for complex terrain. Among the many observations made during T-REX IOP 1, scanning aerosol lidar data proved to be particularly helpful in interpreting the results of the TKE budget analysis and in providing a more complete understanding of temporal and spatial variability of turbulence in mountainous terrain. Acknowledgments This work

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Lukas Strauss, Stefano Serafin, and Vanda Grubišić

at elevation angles ranging from 3° to 60° (PPI-03–PPI-60). Lidar-measured fields included the aerosol backscatter intensity, radial Doppler velocity, and Doppler spectral width. In addition to the observational datasets, 700-hPa analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) are used here to provide the context of the large-scale synoptic flow. 3. Observations The main objective of this work is to reexamine the conceptual model of a

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James D. Doyle, Vanda Grubišić, William O. J. Brown, Stephan F. J. De Wekker, Andreas Dörnbrack, Qingfang Jiang, Shane D. Mayor, and Martin Weissmann

Jet Stream Project, both of which took place in the early 1950s ( Holmboe and Klieforth 1957 ; Grubišić and Lewis 2004 ), were the first coordinated research efforts focused on observing topographically forced phenomena and documented several research aircraft penetrations of rotors and associated turbulence ( Holmboe and Klieforth 1957 ). The relatively rare in situ research aircraft encounters with rotors ( Lester and Fingerhut 1974 ), along with occasional lidar observations of downslope

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Bowen Zhou and Fotini Katopodes Chow

flow, which is in the northwest direction ~300°. This synoptic flow is responsible for the daytime down-valley flow because of the channeling effect of the valley ( WHP09 ). The source of the easterly flow is unclear because of the limited horizontal scan range of the lidar. Radiosondes could have captured this flow, but none were launched that night. The 3D simulations, on the other hand, have the advantage of complete spatial and temporal coverage. Once validated against observations, we can use

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Stephen A. Cohn, Vanda Grubiššićć, and William O. J. Brown

. Episodic observations were made with three instrumented aircraft, two of which released dropsondes, as well as two Doppler lidars and one backscatter lidar, two sodars, rawinsondes launched both within and upwind of the valley, a dense network of surface stations in the valley, several in situ flux towers, and other supporting instruments ( Grubiššićć et al. 2008 ). In addition to its phenomenological value, the full T-REX dataset is also being used to evaluate and improve numerical simulations of

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