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Patrick A. Reinecke and Dale R. Durran

propagation of uncertainties in the specification of initial conditions, the predictability of forecasts for mesoscale motions with spatial scales on the order of 10 km would be limited to time scales on the order of 1 h. This discouraging prospect has largely been supplanted by a more optimistic view based on experiences with high-resolution NWP models demonstrating that realistic mesoscale circulations can be generated during the forecast without having to specify mesoscale precursors to these

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Junhong Wang, Jianchun Bian, William O. Brown, Harold Cole, Vanda Grubišić, and Kate Young

importance of vertical motion in the atmosphere, it is crucial to measure the VV on all temporal and spatial scales. However, the VV is difficult to measure mainly because of its small magnitude (an order of a few centimeters per second; Holton 1992 ). In the past, the VV was not measured directly; instead it was derived from horizontal winds using the continuity equation. Over the past few decades, various techniques have been developed to directly measure the VV, including sonic anemometry on flux

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

, and (iii) evaluate the ability of high-resolution models to forecast the wave characteristics including three dimensionality. The paper that addresses these points is organized as follows. A description of the numerical model is contained in section 2 . The observational analysis is presented in section 3 . Numerical simulations results are discussed in section 4 and the summary and conclusions appear in section 5 . 2. Numerical model description The numerical simulations of

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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

including sensitivity of mountain-wave predictions to the model formulation. During the Terrain-Induced Rotor Experiment (T-REX; Grubišić et al. 2008 ), high-resolution forecasts were routinely conducted to assist in mission planning using a number of different three-dimensional nonhydrostatic numerical models such as the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS 1 ; Hodur 1997 ), two dynamical cores of the Weather Research and Forecasting model (WRF), namely the Advanced Research

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Peter Sheridan and Simon Vosper

1. Introduction The Sierra Nevada range is a well-known source of strong mountain waves, downslope windstorms, and turbulence associated with lee-wave rotors, which represent hazards to aviation, residents, and property and are difficult for forecasters to predict ( Holmboe and Klieforth 1957 ; Grubisic and Lewis 2004 ). Continued increase in the resolution of operational numerical weather prediction (NWP) models is expected to improve forecasts as the phenomena become more explicitly resolved

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Laurence Armi and Georg J. Mayr

combination of changes on the large scale and the local scale made it possible for foehn to penetrate nearly 3 km down the Sierra Nevada slopes to the floor of Owens Valley. Figure 4 tracks the large-scale evolution at approximate crest height of the model Sierra Nevada in the European Centre for Medium-Range Weather Forecasts (ECMWF) global analyses in 6-hourly intervals from 1800 UTC through 1200 UTC (1000–0400 LST). Throughout this 18-h period, the large-scale flow upstream and across the sierras

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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

. The horizontal advection and horizontal smoothing terms are represented by fourth-order accurate differencing, and second-order differencing is used to represent the vertical advection, pressure gradient, and divergence terms. A Robert time filter is applied to all predicted variables. A time splitting technique with a semi-implicit formulation for the vertical acoustic modes is used to efficiently integrate the compressible equations ( Klemp and Wilhelmson 1978 ). The model formulation and

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Juerg Schmidli, Brian Billings, Fotini K. Chow, Stephan F. J. de Wekker, James Doyle, Vanda Grubišić, Teddy Holt, Qiangfang Jiang, Katherine A. Lundquist, Peter Sheridan, Simon Vosper, C. David Whiteman, Andrzej A. Wyszogrodzki, and Günther Zängl

1. Introduction Over mountain areas the evolution of the boundary layer is particularly complex as a result of the interaction between boundary layer turbulence and thermally induced mesoscale wind systems, such as the slope and valley winds (e.g., Rotach et al. 2008 ). As the horizontal resolution of operational forecasts progresses to finer resolution, a larger spectrum of thermally induced wind systems can be explicitly resolved. It is therefore useful to document the current state

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

waves and rotors as well as simulations of valley flows under more quiescent conditions. This includes the performance of forecast and research models under such conditions and simulation of small-scale features of rotors ( Doyle et al. 2009 , 2011 ; Schmidli et al. 2011 ). In turn, interpretation of the observations benefits from insights gained from the model simulations. Prior to T-REX and SRP, the majority of observations of rotors and the conditions surrounding them were made in the four

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

mesoscale models that parameterize the effects of turbulence use a local closure technique (e.g., Stensrud 2007 ). If a prognostic equation for TKE is included, a parameterization for ε is required (e.g., Mellor and Yamada 1974 ): where is the mean value of TKE and Λ is an empirical length-scale parameter. There is unfortunately no unique rule as to how to determine this parameter. It is often chosen by nudging the simulated flow to the observed flow (e.g., Stull 1988 ). Using the data obtained

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