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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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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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James D. Doyle and Dale R. Durran

the subject of two of the first modern U.S. multiagency field programs in meteorology, the Sierra Wave Project (SWP) and its follow-on, the Jet Stream Project (JSP), both of which took place in the early 1950s ( Holmboe and Klieforth 1957 ; Grubišić and Lewis 2004 ). With the exception of research aircraft observations of several rotor events in the lee of the Rocky Mountains ( Lester and Fingerhut 1974 ) and occasional serendipitous remote sensing lidar measurements of rotors ( Banta et al. 1990

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Vanda Grubišić and Brian J. Billings

of atmospheric rotors was considerably advanced during the 1950s Sierra Wave Project in Owens Valley, California, in the lee of the southern Sierra Nevada ( Holmboe and Klieforth 1957 ). While primarily designed as a study of the mountain lee-wave phenomenon, data on atmospheric rotors were collected as well because the primary instrumentation in both phases of this project were instrumented sailplanes ( Grubišić and Lewis 2004 ). A number of important observations relating to the mountain wave

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