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

over Owens Valley. Although there is an evolution of upwind conditions, we cannot confidently relate changes of the wave position in the valley to this variation in forcing. Fig . 6. (a) Wind speed, (b) wind direction, and (c) potential temperature from T-REX soundings taken approximately 140 km west-southwest (upwind) of Owens Valley. Migration of a wave crest directly over a wind profiler, as happened over the center profiler between 1600 and 1845 UTC, is extremely fortuitous. Rotor flow is

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

. , 1959 : The rotor in the lee of mountains. Geophysics Research Directorate Note 6, AD-208862, Air Force Cambridge Research Laboratories, 20 pp . Lhermitte , R. , and L. Miller , 1970 : Doppler radar methodology for the observation of convective storms. Preprints, 14th Radar Meteorology Conf., Tucson, AZ, Amer. Meteor. Soc., 133–138 . Lugt , H. , 1979 : The dilemma of defining a vortex. Recent Developments in Theoretical and Experimental Fluid Mechanics, U. Müller, K. G. Roesner

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Yanping Li, Ronald B. Smith, and Vanda Grubišić

at 1500 LST). This 3-h time lag between the pressure minimum and temperature maximum is an indication of the valley heat transport mechanism. 5. Numerical simulations a. The setup of idealized 2D simulations To explain the unique phases of the surface pressure observations from the valley stations, the WRF, version 2.1.2, is employed to simulate an idealized diurnal valley circulation and the characteristics of the valley thermal forcing. The model setup is similar to Rampanelli et al. (2004

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Ronald B. Smith, Bryan K. Woods, Jorgen Jensen, William A. Cooper, James D. Doyle, Qingfang Jiang, and Vanda Grubišić

difficulty maintaining an accurate pressure altitude. In Fig. 7 , we compare the observed wind speed, averaged for the two legs, with the geostrophic speed for all the racetracks in the six flights. For slower winds, the flow is slightly supergeostrophic, while for fast winds aloft, the flow is significantly subgeostrophic. We suggest that the strong subgeostrophy aloft is caused by streamline curvature and southward centripetal force in the upper-level troughs above the Sierras. To evaluate this

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Bryan K. Woods and Ronald B. Smith

both convective and shear instabilities ( Liu et al. 1999 ; Satomura and Sato 1999 ). Even in cases for which we believe the aircraft sampled in situ wave breaking, the horizontal transects do not provide any vertical information of either the buoyancy or shear forcing terms to support either mechanism. More work will be required to reveal the generation mechanism for our T-REX short waves. Acknowledgments Wavelet software was provided by C. Torrence and G. P. Compo and is available online ( http

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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

in two spatial dimensions. J. Atmos. Sci. , 42 , 1321 – 1339 . Klemp , J. , and R. Wilhelmson , 1978 : The simulation of three-dimensional convective storm dynamics. J. Atmos. Sci. , 35 , 1070 – 1096 . Klemp , J. , and D. R. Durran , 1983 : An upper boundary condition permitting internal gravity wave radiation in numerical mesoscale models. Mon. Wea. Rev. , 111 , 430 – 444 . Kuettner , J. , 1959 : The rotor flow in the lee of mountains. GRD Research Note 6, Air Force

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Vanda Grubišić and Brian J. Billings

during this time are highly unsteady, showing a transition between wave regimes. At 1200 UTC (cf. Fig. 19e ) 26 March, the wave over Owens Valley weakens as the westerly flow enters the valley, forcing a stronger wave response over and to the lee of the Inyo range. This strong westerly jet appears to detach from the ground at the foot of the Sierra lee slope and extend across the valley. An incipient rotor with surface flow deceleration underneath the lee-wave crest is seen over the valley center

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