Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New...
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![Page 1: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/1.jpg)
Observations of foehn interaction with lake breeze and valley wind
circulations, Lake Tekapo, New Zealand
Hamish McGowan
School of Geography, Planning and Architecture, University of Queensland, Brisbane,
Australia
![Page 2: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/2.jpg)
Research collaborators• Prof. Andy Sturman
Centre for Atmospheric Research, University of Canterbury, Christchurch, NZ
• Dr. Meinolf KossmannGerman Meteorological Service (DWD), Offenbach a. M., Germany
• Dr. Peyman Zawar-RezaCentre for Atmospheric Research, University of Canterbury, Christchurch, NZ
![Page 3: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/3.jpg)
Aim Of The Research• To develop a clearer understanding of the
interaction of thermal and dynamic forcing of airflow in complex terrain.
• Improve knowledge of the way in which various atmospheric processes interact in particularly complex environments to develop equally complex local wind regimes.
![Page 4: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/4.jpg)
Background• 6 years of complex terrain windfield research –
foehn triggered dust storms.
• Frequent observation of foehn events that were not forecast (potential wind hazard).
• Increased development of New Zealand’s alpine region (tourism, agriculture) requiring improved local and meso-scale forecasting capabilities
![Page 5: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/5.jpg)
South Islandof
New Zealand
Source NASA
![Page 6: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/6.jpg)
Lake Tekapostudy area
(April 1998)
Source NASA
![Page 7: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/7.jpg)
Looking north over Lake Tekapo
![Page 8: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/8.jpg)
View south over Lake Tekapo
![Page 9: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/9.jpg)
Godley Valley
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The upper Godley Valley and Main Divide
![Page 11: Observations of foehn interaction with lake breeze and valley wind circulations, Lake Tekapo, New Zealand Hamish McGowan School of Geography, Planning.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649ea85503460f94bab9bf/html5/thumbnails/11.jpg)
MeteorologicalMonitoring Network
1997 - 1999
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‘Typical’ foehn
• Moderate to strong foehn nor’wester dominates regional windfield
• Wind speeds in alpine valleys may > 40 ms-1
• Significant orographic rainfall and spillover precipitation• Barrier jet formation upwind of barrier with well developed lee
trough formation downwind
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14 February 1999• Alpine foehn not forecast!
• Rawinsonde soundings identified ridge-top (2500 m agl.) light W/NW gradient flow at 5ms-1
• Thermally driven circulations recorded at most coastal and lowland locations
• Foehn onset recoded in the Godley Valley at 1000NZST – linked to local surface heating
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Foehn advance and retreat, 14 Feb 1999
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Vertical wind speed and direction profiles – Godley Valley
1600
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Foehn – Lake Breeze Interaction• Typical light foehn – lake breeze interaction (a). Cold air
ramping (an important mechanism for pollution dispersion).
• 14 February 1999 situation (b). May result in fumigation over lake and associated shoreline
Foehn Foehn
Valley wind
(a) (b)
Valley wind
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Conclusions • The wind field at Lake Tekapo represents a complex superposition of multi-
scale wind systems: lake/land breezes, up-/down-slope winds, mountain/valley winds, plain-
to-basin circulation and foehn
• Foehn onset ‘initially’ governed by airflow at 500hPa, surface sensible heat flux, thermally induced local and regional scale circulations.
• During light/moderate foehn conditions the topographically channelled foehn regularly decouples from the surface and flows over the lake breeze (cold air ramping).
• The foehn may ground over the downwind shoreline in response to increased surface mixing (fumigation possible)
• A climatology of alpine foehn events is to be developed (ie to improve forecasting of alpine foehn, role of foehn in mean annual temps)