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Yanping Li, Ronald B. Smith, and Vanda Grubišić

turbulent interaction between the valley air and the overlying atmosphere ( Figs. 13b , 14 ). The daily maximum mixed-layer depth was calculated according to (5) for the three WRF simulations ( Figs. 11 , 14 ). This gives H ∼ 1600 m and H ∼ 1400 m for the weak and moderate westerly cases as compared with H ∼ 1800 m (with mixed-layer top at 2800 m) for the quiescent case. This agrees with the observational results shown in Fig. 8 . 6. The valley depth and seasonal effects To extend our results

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Shiyuan Zhong, Ju Li, C. David Whiteman, Xindi Bian, and Wenqing Yao

of the wind direction during the transition periods reflects the fact that the time of wind reversal from up to down valley or vice versa changes with season because of the seasonal variations of the sunrise/sunset times and the effects on local sunrise and sunset times of shadowing from the ridgeline and local topography. The lower constancy in daytime wind direction is another indication of the role of daytime turbulent mixing in coupling the surface winds with winds aloft, allowing the wind

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Stefano Serafin, Lukas Strauss, and Vanda Grubišić

, as described in the text. The data shown in (c) and (d) correspond to 1-h intervals in which the hourly average winds speed > 7 m s −1 in at least one of the group 3 stations. As in Figs. 3 and 4 , the relative frequencies sum up to 100%. This pattern of diurnal and seasonal variability is not specific to westerly winds. Figure 9b shows that, at stations 1, 2, and 7, winds with U > 7 m s −1 from all other directions also have relatively high frequency in the afternoon hours and in the

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

(e.g., Salathé and Smith 1992 ). The displacement estimates provide one method for testing the linearity of the waves. We define the nondimensional nonlinearity parameter A = Nη M / U . A typical low stratosphere value is A = (0.02 s −1 )(1000 m)/ (35 m s −1 ) ≈ 0.6, so that nonlinear effects are important but not dominant at the observed altitudes. Further aloft, as the wind speed decreases, A exceeds unity and the wave will become more nonlinear. 4. Conserved variable diagrams If the

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

radiosonde and dropsonde data, between sounding (both radiosonde and dropsonde) and aircraft, and between radiosonde and MAPR data to qualitatively assess the strength and limitation of the method. Based on the discussions in section 2a , the method of estimating the VV from dropsonde data is superior to the one used for radiosondes because of the uncertainty in the balloon volume and drag coefficient for the radiosonde and no pendulum effects and self-induced motions for the dropsonde. The dropsonde

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