A multi-scale simulation of an extreme downslope windstorm over complex topography |
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Authors: | J D Doyle M A Shapiro |
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Institution: | (1) Naval Research Laboratory, Monterey, CA, USA, US;(2) National Center for Atmospheric Research/NOAA/ERL Environmental Technology Laboratory, Boulder, CO, USA, US |
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Abstract: | Summary A severe localized windstorm, with near-surface winds > 60 ms−1, occurred in an isolated valley within the Alpine mountains (> 1800 m) of central Norway on 31 January 1995. A multi-scale
numerical simulation of the event was performed with the Naval Research Laboratory (NRL)’s Coupled Ocean/Atmosphere Mesoscale
Prediction System (COAMPS), configured with four nested grids telescoping down to 1-km horizontal resolution. The windstorm
occurred in response to topographic blocking and deformation of a lower-tropospheric warm front and attendant jet (> 35 ms−1 at 2 km). The key findings are: i) mountain wave resonance and amplification arising from the interaction of the surface-based
front and jet with complex orography, ii) sensitivity of the wave response to differential diabatic heating (vertical) gradients
above the front, and iii) trapped response within the layer of large frontal stratification in the lower troposphere and subsequent
amplification consistent with the theoretically-established two-layer windstorm analogue of Durran (1986).
Received September 29, 1999 Revised December 30, 1999 |
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