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G. J. Mayr L. Armi S. Arnold R. M. Banta L. S. Darby D. D. Durran C. Flamant S. Gaberšek A. Gohm R. Mayr S. Mobbs L. B. Nance I. Vergeiner J. Vergeiner C. D. Whiteman 《Meteorology and Atmospheric Physics》2004,86(1-2):99-119
Summary The lowest pass through the Alpine crest, the Brenner Pass, was heavily instrumented with ground-based and air-borne in-situ and remote sensors during the Special Observation Period (SOP) of the Mesoscale Alpine Programme (MAP) in the fall of 1999 to study gap flow. The main objectives were to study the combined effects of changes of terrain height and changes of width in altering the flow characteristics, to investigate the coupling of the gap flow to the flow aloft, and to provide high-density measurements in the along- and cross-gap directions.Gap flows occurred during one third of the 70-day SOP, a frequency above the long term average. Gap flows took place with and without accompanying cross-barrier flow and with and without a capping inversion. A case study demonstrates the hydraulic jump-like features that occurred in gap flow on 30 October 1999 and illustrates the types of data available for further analyses. 相似文献
2.
Air Pollution Transport in an Alpine Valley: Results From Airborne and Ground-Based Observations 总被引：2，自引：2，他引：0
A. Gohm F. Harnisch J. Vergeiner F. Obleitner R. Schnitzhofer A. Hansel A. Fix B. Neininger S. Emeis K. Schäfer 《Boundary-Layer Meteorology》2009,131(3):441-463
An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms
of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current,
back-and-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference
along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection
of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to
ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type,
upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers. 相似文献
3.
Summary. ?The airflow over an idealized orography with two mountain peaks and a valley between is investigated using a non-linear numerical
model. The flow is assumed to be two-dimensional and nonrotational. Surface friction is neglected. This setup is a first step
in studying the modifications a finely structured “real” topography introduces to the well-studied flow over one isolated
obstacle. The sensitivity of the flow behavior to the valley width is examined for the case of specified mountain volume as
well as constant non-dimensional mountain height. Flow patterns for linear, weakly nonlinear, wave breaking and upstream blocking
cases are examined. Whereas the nondimensional mountain height is still the main measure of the nonlinearity of the flow,
the differing steepness of upslope and downslope caused by the separating valley, strengthens nonlinear effects. It also modifies
wave breaking and upstream blocking. For wide enough valleys wave breaking regions can form above both peaks.
Received January 20, 1999/Revised June 28, 1999 相似文献
4.
Numerical simulations of tracer transport in an idealised, east-west aligned valley are performed with the Regional Atmospheric
Modeling System (RAMS), both two-dimensional and three-dimensional. The results are qualitatively consistent with wintertime
observations in the Austrian Inn Valley. The simulations show an asymmetry in wind circulation and tracer distribution between
the valley sidewalls according to the orientation of the slope with respect to the sun. Two-dimensional sensitivity experiments
are run to investigate the influence of vertical inhomogeneities in thermal stratification and vegetation coverage on the
slope-wind circulation and therewith the tracer transport. It is shown that a transition to a layer of higher stability or
to a region with higher surface albedo causes a reduction of the mass flux in the upslope-wind layer and due to mass continuity
a quasi-horizontal transport out of the slope-wind layer. 相似文献
5.
Summary Numerical simulations of the 24 October 1999 south foehn (MAP-IOP 10) are performed with the Penn State/NCAR mesoscale model MM5 for the Wipp Valley and the adjacent parts of the Inn Valley. The model is run in a multiple-nest configuration, the area of interest being resolved at a mesh size of 800m in most experiments. The study serves to complement an earlier work in which typical flow features of the foehn in the Wipp Valley region were investigated by means of idealized simulations, assessing whether it is possible to reproduce the temporal evolution and the spatial structure of a particular foehn case. A further objective of the paper is to examine the dependence of the model performance on the horizontal resolution, giving some information which resolution will probably be needed for future high-resolution forecasts.An encouragingly large part of the observed flow features could be well reproduced in the simulations. Except for a small region to the east of Innsbruck, the foehn breakthrough is predicted correctly to within an hour. The spatial structure of the so-called pre-foehn, an enhanced westerly wind occurring at Innsbruck prior to the breakthrough of the foehn, also agrees very well with the observations. Moreover, the maximum extent of the foehn in the Inn Valley, the structure of the gravity wave field above the Wipp Valley and the upvalley progression of a shallow cold front in the evening are consistent with the observations. Except for a few places where the airmass boundary between the warm foehn air and the adjacent colder air is not captured correctly throughout the time, the simulated surface temperatures range within 2K of the observed values. Discrepancies between the model results and the observations are found in the vicinity of Innsbruck where a flow-splitting phenomenon induces a very complex flow pattern at low levels. Another source of problems is the surface potential temperature along the Wipp Valley. The observed potential-temperature increase between the Brenner Pass and Innsbruck, which appears to be related to turbulent vertical mixing of stably stratified air, is underestimated by the model. Reducing the horizontal resolution from 800m to 1.4km deteriorates the model performance in marginally resolved side valleys, but the results obtained for the Wipp Valley and the Inn Valley are still of high quality. 相似文献
6.
Haid Maren Gohm Alexander Umek Lukas Ward Helen C. Rotach Mathias W. 《Boundary-Layer Meteorology》2022,182(3):335-362
Boundary-Layer Meteorology - We present a comprehensive analysis of four south föhn events observed during the Penetration and Interruption of Alpine Foehn (PIANO) field campaign in the Inn... 相似文献
7.
The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn 总被引：1，自引：0，他引：1
Summary This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution
of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn
1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer
settings, which mainly differ in the height above ground of the lowest model level (z
1). Specifically, z
1 takes values of about 7 m, 22 m and 36 m, and the experiments with z
1 = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results
are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the
dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z
1 is examined for several different regions.
Our validation results show that at least over the Wipp Valley, the dependence of the model skill on z
1 tends to be larger and more systematic than the impact of the PBL scheme. The agreement of the simulated wind field with
observations tends to benefit from moving the lowest model layer closer to the ground, which appears to be related to the
dependence of lee-side flow separation on z
1. However, the simulated 2 m-temperatures are closest to observations for the intermediate z
1 of 22 m. This is mainly related to the fact that the simulated low-level temperatures decrease systematically with decreasing
z
1 for all PBL schemes, turning a positive bias at z
1 = 36 m into a negative bias at z
1 = 7 m. The systematic z
1-dependence is also observed for the temperatures at a fixed height of 36 m, indicating a deficiency in the self-consistency
of the model results that is not related to a specific PBL formulation. Possible reasons for this deficiency are discussed
in the paper. On the other hand, a systematic z
1-dependence of the 36-m wind speed is encountered only for one out of the five PBL schemes. This turns out to be related to
an unrealistic profile of the vertical mixing coefficient.
Correspondence: Günther Z?ngl, Meteorologisches Institut der Universitat München, 80333 München, Germany 相似文献
8.
Summary In this paper, very-high-resolution numerical simulations are presented to analyze the small-scale dynamics of the foehn in
the lower Wipp Valley and the adjacent parts of the Inn Valley. This region was one of the target areas for foehn observations
during the Mesoscale Alpine Programme (MAP). Our simulations consider two MAP cases that markedly differed in the depth of
the foehn flow. To isolate the dynamical effect of the key orographic features in the Wipp Valley region, we performed sensitivity
experiments with different topography modifications. These involve lowering or even removing the Nordkette range, which constitutes
the northern side wall of the east–west-oriented Inn Valley, and closing the Stubai Valley, which is the northernmost and
largest tributary of the Wipp Valley. A comparison with surface and lidar observations indicates that our present model resolution
of 467 m significantly improves the realism of the simulations compared to a resolution of 800 m, as used in a previous study.
The Nordkette is found to have a twofold impact on the dynamics of foehn breakthrough into the Inn Valley. In reality, this
mountain chain deflects part of the southerly foehn current coming from the Wipp Valley into the perpendicularly oriented
Inn Valley. Our sensitivity tests indicate that this flow deflection tends to accelerate the foehn breakthrough into the Inn
Valley, while upstream blocking effects induced by the Nordkette act to slow down the process of foehn breakthrough. The flow
pattern in the Wipp Valley reveals that the upstream effects of the Nordkette are not quite far-reaching. The amplitude of
the gravity waves over the lower Wipp Valley gets somewhat reduced by these upstream effects, but the overall flow pattern
remains largely unaffected. Closing the Stubai Valley also has a minor effect of the wave structure and tends to reduce the
cross-valley variability of the foehn flow in the lower Wipp Valley. 相似文献
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