Supplement to &amp;ldquo;Numerical Simulation of Lee-Wave Events over the Pyrenees&amp;rdquo;

Satomura, Takehiko

doi:10.2151/jmsj1965.74.1_147

Cited by 5 publications

(8 citation statements)

References 8 publications

(6 reference statements)

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“…may suggest that the former result is a consequence of transient adaptation of the model. Satomura and Bougeault (1994) obtained a momentum flux constant with altitude, which one would indeed expect for the stationary result of a two-dimensional model. The first three-dimensional lee wave simulation of PYREX was performed by Broad (1996).…”

Section: B Nonhydrostatic Modelssupporting

confidence: 56%

“…This study also showed a large variability of the momen-tum flux in the direction parallel to the crest line. Recently, Satomura (1996) showed that the linear result for a 3D, stationary mountain wave over an elliptical mountain exhibits decrease with height of the momentum flux, as measured during PYREX. This strongly suggests that the observations should be considered as influenced by 3D effects (at the scale of the whole range).…”

Section: B Nonhydrostatic Modelsmentioning

confidence: 94%

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PYREX: A Summary of Findings

Bougeault¹,

Bénech²,

Bessemoulin³

et al. 1997

Bull. Amer. Meteor. Soc.

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About six years ago, the planned field experiment Pyrenean Experiment (PYREX) was presented in the Bulletin. After a successful field phase in October and November 1990, and much work to prepare a consistent database, interpret the measurements, and compare model results with observations, it is possible to present today a summary of scientific results. New insight has been obtained in the areas of mountain drag measurement and interpretation, humidity measurement, boundary layer measurement by lidar, the ability of mesoscale models to represent orographic flows, the roughness length of mountains, and parameterization of subgrid-scale gravity waves. The present paper summarizes these results and may be understood as an introduction to this unique dataset on orographic flows. The authors believe that much interesting research can still be achieved with the PYREX data, which are accessible to any interested scientist.

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Section: B Nonhydrostatic Modelssupporting

confidence: 56%

Section: B Nonhydrostatic Modelsmentioning

confidence: 94%

PYREX: A Summary of Findings

Bougeault¹,

Bénech²,

Bessemoulin³

et al. 1997

Bull. Amer. Meteor. Soc.

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“…The mountain gravity wave drag predicts well the drag measured at ground level (Bessemoulin et al 1993) but overstates, by nearly an order of magnitude, the Reynolds stress measured by airplanes aloft. In the mesoscale context (i.e., neglecting the Coriolis force), this discrepancy between the measured mountain drag and the measured stresses has essentially five origins: 1) the wave dissipation in the boundary layer (Georgelin et al 1994) or the breaking of the waves at low level (Miranda and James 1992); 2) the unsteady nature of the waves due to the time variations of the incident flow (Bell 1975;Lott and Teitelbaum 1993); 3) the downstream transfer of momentum by trapped waves (Bretherton 1969;Durran 1995;, or simply the fact that the Reynolds stress is measured over a finite distance so even nontrapped waves can induce nonzero momentum fluxes through the domain downwind lateral boundary (Keller 1994); 4) the momentum flux leakage that occurs through the domain lateral boundary when the waves are threedimensional (Smith 1980); although in the three-dimensional case, Satomura (1996) has shown that the evaluation of the Reynolds stress along a line, rather than over a plane, can explain its variation with altitude in the steady inviscid case; and 5) the fact that for real and high mountains, the lowlevel flow goes around the mountain rather than over it, and a large part of the drag is related to low-level flow deceleration (Schär and Durran 1997) rather than to wave emission.…”

Section: Introductionmentioning

confidence: 99%

On the Transfer of Momentum by Trapped Lee Waves: Case of the IOP 3 of PYREX

Georgelin

Lott

2001

J. Atmos. Sci.

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The airplane data collected between 4 and 12 km above the Pyrénées during the intensive observation period (IOP) 3 of the Pyrénées Experiment (PYREX) are analyzed again. A spectral analysis of the velocity and potential temperature series shows that the mountain waves are dominated by two oscillations with well-defined horizontal wavenumbers. At nearly all altitudes, at least one among these two oscillations can be extracted: the short oscillation dominates the signal below 6 km and the long one above. These two oscillations contribute to the Reynolds stress below 5 km and not above. Linear steady nondissipative simulations show that the short oscillation is a trapped resonant mode and the long one a leaking, or partially leaking, resonant mode of the background flow. Pseudo-momentum flux budgets show that the short resonant mode only contributes to the Reynolds stress at low level (here below 3 to 4 km typically) while the long one contributes to the Reynolds stress at all levels. At low level, (below 4 to 6 km typically), the long mode can induce a decay of the Reynolds stress amplitude, when it partially leaks toward the stratosphere. Various tests, changing the incident flow profiles within limits provided by the different soundings available this day, reveal, on the one hand, that the above findings are quite robust. On the other hand, they reveal that the resonant modes response is very sensitive to the background flow and orography specifications. In some of the steady linear simulations, the long resonant oscillation has a Reynolds stress that is constant with altitude. In all of them the downwind extent of the lee waves is overestimated and the waves amplitude is too large. To explain these mismatches with the observations, we present simulations that last 3 h only, so the resonant modes patterns are everywhere unsteady. They show that during their build-up phase, all the leaking modes can make the Reynolds stress amplitude decays with altitude at low level (here below 4 to 6 km, typically). At this time, the downstream extent of the waves is also correctly predicted. These linear unsteady simulations also give realistic waves amplitude and Reynolds stress profiles if the mountain is cut off to parameterize nonlinear low-level flow splitting. By using a nonlinear model, the simulated waves are matched to that observed through an adjustment of the parameters of the turbulent diffusion parameterization scheme: with enough dissipation, the model response can become quite realistic. In these nonlinear simulations, the background flow is chosen so that there is only one resonant mode and this mode does not contribute much to the Reynolds stress in the inviscid case. When increasing the mountain height and the dissipation, the overall structure of that mode stays unchanged, and it never contributes much to the Reynolds stress. This indicates that the dissipative and nonlinear processes alone are not likely to produce the observed low-level stress variations associated with the resonant modes.

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“…La question de la variation du flux de quantité de mouvement avec l'altitude a été réexaminée très récemment par Satomura (1996). Dans un article très convaincant, il montre que la solution linéaire stationnaire tridimensionnelle correspond à une forte diminution du flux de quantité de mouvement avec l'altitude, même dans la partie centrale, dès que le vent amont n'est plus parallèle à la chaîne de montagnes.…”

Section: Modèles Non Hydrostatiquesunclassified