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Juerg Schmidli, Gregory S. Poulos, Megan H. Daniels, and Fotini K. Chow

were observed in California’s Owens Valley during the Terrain-Induced Rotor Experiment (T-REX). In one case the flow in the north–south-oriented valley was characterized by a three-layer structure with a midlevel (2–2.5 km MSL) upvalley flow after midnight local time, sandwiched between a low-level northerly downvalley flow and an above-ridge-top northwesterly flow. The second case was characterized by a strong and deep downvalley jet, with average wind speeds exceeding 15 m s −1 for several

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James D. Doyle, Qingfang Jiang, Ronald B. Smith, and Vanda Grubišić

(1999) showed that for stratified flow impinging on a topographic ridge, low-level jets occur along the northern and southern portions of the ridge flanks, which they refer to as tip jets. In the Northern Hemisphere, westerly flow is deflected primarily leftward around the obstacle, which results in strong jets and downslope flows along the northern flank. Doyle and Shapiro found that jets along the southern ridge flanks can be prominent as well, and consistent with the principal of conservation of

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Qingfang Jiang and James D. Doyle

-valley soundings are similar to their upstream counterparts except that the 0000 UTC 14 April sounding reveals an approximately 1.5-km-deep westerly jet above the surface. 3) Surface observations The 16 automatic weather stations, each of which consists of a standard 10-m meteorological tower and sensors for wind, temperature, relative humidity, and pressure measurements, were deployed near Independence approximately along three linear segments across the valley floor ( Fig. 1c ). For the convenience of

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

1. Introduction The sharp boundary between the troposphere and stratosphere has been largely explained as the result of convective cloud-top entrainment (e.g., Staley 1960 ; Reid and Gage 1981 ; Held 1982 ; Sherwood and Dessler 2003 ). The tropopause is defined not only by the jump in temperature lapse rate but also by strong gradients in water vapor and ozone concentrations. In midlatitudes, the jet stream often has its maximum speed at the tropopause level. It is suspected that these

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Vanda Grubišić and Brian J. Billings

be associated with 1) an upper-level pressure trough along the Pacific coast with strong westerly flow across the Sierra, and 2) a cold or occluded front approaching California from the northwest, placing Owens Valley in the prefrontal environment. In addition, the jet stream typically was found to cross Oregon or northern California during strong wave events, though some events did occur with a westerly jet stream crossing the Sierra. It was also observed that cold air damming occurred to some

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Patrick A. Reinecke and Dale R. Durran

( Fig. 3a ), a relatively sharp, negatively tilted trough is situated directly over the northern California coastline. A 45 m s −1 jet maximum is located at the base of the trough with strong southwesterly flow extending northeastwards to the northern Sierra Nevada. Six hours later, at 0000 UTC 26 March 2006 ( Fig. 3b ), the trough has progressed eastward such that the strongest winds are directly upstream of the Owens Valley and oriented nearly perpendicular to the barrier. The spatial extent of

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Patrick A. Reinecke and Dale Durran

9-km domains are identical. d. Model simulations The 0000 UTC ensemble mean analysis and 0600 UTC ensemble mean forecast of the 500-hPa geopotential height field and wind speeds on the 27-km domain are plotted in Fig. 13 . At the analysis time ( Fig. 13a ) a low pressure trough is located just offshore of the western United States. Associated with the low pressure trough is a jet extending around the base of the trough and into the central portion of California. The wind speeds within the jet

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Thomas Raab and Georg Mayr

. This special case is termed “single-layer hydraulics.” Further assumptions are for the flow to be hydrostatic and incompressible in the integrated layer. Analytical solutions also exist for a continuously stratified upstream flow under the assumption of neutrally stratified fluid above the flow. Long’s (1955) seminal laboratory and analytical studies found an accelerated flow passing over the crest of an obstacle and descending as a jet beneath a slow recirculation zone. Smith (1985) developed

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James D. Doyle, Saša Gaberšek, Qingfang Jiang, Ligia Bernardet, John M. Brown, Andreas Dörnbrack, Elmar Filaus, Vanda Grubišić, Daniel J. Kirshbaum, Oswald Knoth, Steven Koch, Juerg Schmidli, Ivana Stiperski, Simon Vosper, and Shiyuan Zhong

extends from above the mountain to the upstream lateral boundary at an approximate altitude of 5 km. The jet results from an in situ increase in momentum at the upstream boundary that subsequently self-advects toward the ridge. The jet has a minimal impact on the solution by 4 h. Fig . 7. Horizontal perturbation wind component (color, interval 2.5 m s −1 ) and potential temperature (black contours, interval 10 K) for Ex2500_ns ( h m = 2500 m, no slip) at the final time (4 h) for all models and

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Laurence Armi and Georg J. Mayr

. Grubišić , 2008 : Mountain waves entering the stratosphere . J. Atmos. Sci. , 65 , 2543 – 2562 , doi: 10.1175/2007JAS2598.1 . Vosper , S. , 2004 : Inversion effects on mountain lee waves . Quart. J. Roy. Meteor. Soc. , 130 , 1723 – 1748 , doi: 10.1256/qj.03.63 . Winters , K. B. , and L. Armi , 2014 : Topographic control of stratified flows: upstream jets, blocking and isolating layers . J. Fluid Mech. , 753 , 80 – 103 , doi: 10.1017/jfm.2014.363 . 1 Lilly (1978) did not have

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