© Janey Thomas
Woolshed Hill (1 429 m), Arthur’s Pass National Park, New Zealand
Latitude: 42° 57' 57'' S
Longitude: 171° 46' 35'' E
13 January 2014 1420 (Local Time)
Camera direction: towards NNW
Image P/S code: P.25.5
Image I.D.: 6078
The foehn wall is a cloud formation which, during an episode of foehn winds, lies over and along a mountain ridge and which appears to an observer downwind from the ridge as a wall or bank of cloud.
This picture shows an example of the foehn wall over the Southern Alps of New Zealand. The Southern Alps is a mountain range that extends for approximately 500 km, south-west to north-east, along much of the length of New Zealand's South Island. With several peaks at heights of over 3 000 m above sea level, it forms a major barrier roughly perpendicular to the prevailing westerly airflow. Air rising over the mountains cools, forming cloud and precipitation on the western side, whilst air descending on the lee side gives a warm, dry foehn wind. The foehn wall marks the eastern limit of the cloud that exists over the windward, western side of the mountain range.
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This picture was taken from a location in Argentina to the east of the Andes mountain range during a foehn wind event. There are two main features in the image:
1) The large band of cloud over the mountains is known as a foehn wall. The foehn wall is a cloud formation which, during an episode of foehn winds, lies over and along a mountain ridge and which appears to an observer downwind from the mountains as a wall or bank of cloud. The foehn wall marks the eastern limit of the cloud that exists over the windward side of the mountain range.
2) The warm, dry downslope foehn wind (known locally in Argentina as the Zonda wind) is strong enough here to raise dust to a small height above the ground. This is known as drifting dust.
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