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    South Foehn in the Wipp Valley on 24 October 1999 (MAP IOP 10): Verification of High-Resolution Numerical Simulations with Observations

    Source: Monthly Weather Review:;2004:;volume( 132 ):;issue: 001::page 78
    Author:
    Gohm, Alexander
    ,
    Zängl, Günther
    ,
    Mayr, Georg J.
    DOI: 10.1175/1520-0493(2004)132<0078:SFITWV>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: A case study of a south foehn windstorm observed across the Brenner Pass in the Wipp Valley near the Austrian?Italian border is presented based on a detailed comparison and verification of high-resolution numerical simulations with observations. The event of 24 through 25 October 1999 was part of the Intensive Observing Period 10 of the Mesoscale Alpine Programme (MAP). The simulations were performed with the fifth-generation Pennsylvania State University?NCAR Mesoscale Model (MM5). The observations were collected with a ground-based scanning Doppler lidar, an airborne aerosol backscatter lidar, a Doppler sodar, several weather stations, and two radiosounding systems. The study provides a synoptic-scale and mesoscale overview of the event and focuses on a comparison of simulated and observed fields for a 9-h period on 24 October 1999. The quantitative agreement between the numerical results and the observations is discussed in terms of root-mean-square error (rmse) and mean error (ME). Rmse values are high during the early stage of the event (?7 m s?1), have a transient peak for about 1 h at 1400 UTC, and are minimal at the fully developed foehn stage near 1500 UTC (?5 m s?1). The discrepancies at the beginning are likely to be related to deficiencies in the model profile on the upstream side of the pass, exhibiting a too low inversion and a too shallow southerly flow. The transient error peak at 1400 UTC is related to a mismatch in the timing of the enhancement of the upper-level winds. Moreover, evidence is found for an overestimation of the mass flux through the lower Brenner gap, which is the narrowest and deepest part of the incision in the main Alpine crest, and a subsequent underestimation of the flow descent into the Wipp Valley on the leeward side of the Brenner Pass. Considering mass continuity, the latter effect is probably a result of the former. Nevertheless, the model captures most of the striking foehn features: Simulated isentropes and aerosol backscatter measurements consistently indicate regions of flow descent, across-valley asymmetries, and hydraulic jump?like features. The across-valley asymmetry of the foehn strength near the Wipp Valley exit is particularly well reproduced by the model. The primary reason for the stronger winds on the eastern sidewall is the asymmetry in the position of the mountain ridges protruding into the valley together with the westward bending of the valley axis.
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      South Foehn in the Wipp Valley on 24 October 1999 (MAP IOP 10): Verification of High-Resolution Numerical Simulations with Observations

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4205293
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    contributor authorGohm, Alexander
    contributor authorZängl, Günther
    contributor authorMayr, Georg J.
    date accessioned2017-06-09T16:15:12Z
    date available2017-06-09T16:15:12Z
    date copyright2004/01/01
    date issued2004
    identifier issn0027-0644
    identifier otherams-64204.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4205293
    description abstractA case study of a south foehn windstorm observed across the Brenner Pass in the Wipp Valley near the Austrian?Italian border is presented based on a detailed comparison and verification of high-resolution numerical simulations with observations. The event of 24 through 25 October 1999 was part of the Intensive Observing Period 10 of the Mesoscale Alpine Programme (MAP). The simulations were performed with the fifth-generation Pennsylvania State University?NCAR Mesoscale Model (MM5). The observations were collected with a ground-based scanning Doppler lidar, an airborne aerosol backscatter lidar, a Doppler sodar, several weather stations, and two radiosounding systems. The study provides a synoptic-scale and mesoscale overview of the event and focuses on a comparison of simulated and observed fields for a 9-h period on 24 October 1999. The quantitative agreement between the numerical results and the observations is discussed in terms of root-mean-square error (rmse) and mean error (ME). Rmse values are high during the early stage of the event (?7 m s?1), have a transient peak for about 1 h at 1400 UTC, and are minimal at the fully developed foehn stage near 1500 UTC (?5 m s?1). The discrepancies at the beginning are likely to be related to deficiencies in the model profile on the upstream side of the pass, exhibiting a too low inversion and a too shallow southerly flow. The transient error peak at 1400 UTC is related to a mismatch in the timing of the enhancement of the upper-level winds. Moreover, evidence is found for an overestimation of the mass flux through the lower Brenner gap, which is the narrowest and deepest part of the incision in the main Alpine crest, and a subsequent underestimation of the flow descent into the Wipp Valley on the leeward side of the Brenner Pass. Considering mass continuity, the latter effect is probably a result of the former. Nevertheless, the model captures most of the striking foehn features: Simulated isentropes and aerosol backscatter measurements consistently indicate regions of flow descent, across-valley asymmetries, and hydraulic jump?like features. The across-valley asymmetry of the foehn strength near the Wipp Valley exit is particularly well reproduced by the model. The primary reason for the stronger winds on the eastern sidewall is the asymmetry in the position of the mountain ridges protruding into the valley together with the westward bending of the valley axis.
    publisherAmerican Meteorological Society
    titleSouth Foehn in the Wipp Valley on 24 October 1999 (MAP IOP 10): Verification of High-Resolution Numerical Simulations with Observations
    typeJournal Paper
    journal volume132
    journal issue1
    journal titleMonthly Weather Review
    identifier doi10.1175/1520-0493(2004)132<0078:SFITWV>2.0.CO;2
    journal fristpage78
    journal lastpage102
    treeMonthly Weather Review:;2004:;volume( 132 ):;issue: 001
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
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