The Nor'west arch is a weather pattern peculiar to the east coast of New Zealand's South Island. For this reason, it is also often referred to as the Canterbury arch, although it is visible in both Otago and Marlborough as well as in the Canterbury Region. It is shown in an apparent arch of high white cloud in an otherwise clear blue sky over the Southern Alps, and is accompanied by a strong hot northwesterly or northerly wind simply known as The Nor'wester.
The Nor'west arch, as visible from Christchurch, shows a blue belt of clear sky to the west from which high white cloud streams.
Closer to the Canterbury coast, some distance from the mountains of the Southern Alps, it appears as a clear area of blue above the mountains, with white cloud streaming to the east from it. The phenomenon is similar to the Chinook arch seen in the Pacific regions of the United States and Canada.
The Nor'wester is a föhn wind - moist air is driven over the Southern Alps, falling as condensation on the western side, leaving the eastern plains in the rain shadow.Typical shot of a Canterbury, New Zealand nor'west arch during sunset
The Nor'west arch is a föhn cloud. The northwesterly wind drives warm moist air from over the Tasman Sea, and it is pushed up by the presence of the Southern Alps, causing it to cool rapidly. The area to the east of the divide is in the rain shadow of the Alps; much of the moisture is dumped on the West Coast, and is responsible for the temperate rainforests found there. As the air passes over the alps, the water vapour remaining becomes visible in a band of cloud over the mountains at the top of each wave of air. From the perspective of a viewer on the eastern side, this appears as an 'arch' of cloud. The standing wave or arch is caused by the moisture condensing and becoming visible towards the top of the wave and then evaporating again as the air descends to the trough of the wave.
Nor'westers caused by cold fronts will often change within a day or two to a cool southerly wind accompanied by rain showers, as the front passes through. In mid-winter, a Nor'wester is often followed by a brief but intense cold snap, frequently bringing thunder, hail, or rain and sometimes snow which may settle to sea level.
OccurrenceEdit
The Nor'west arch can be seen as far north as Amberley and as far south as Central Otago, but it is at its most prominent on the Canterbury Plains, due to the flat and low-lying nature of the land to the east of the mountains.
The Nor'wester can blow at any time of year, but is less common in winter. Many of the strongest northerly and northwesterly winds blow ahead of cold fronts. A front lying across the South Island will often extend from northwest to southeast, reaching northern parts of the West Coast before it reaches corresponding areas on the east coast. The steep air pressure gradient ahead of the cyclonic system associated with a front gives these nor'westers their strength; they will commonly reach gale force and cause isolated damage to trees and buildings.[1] Once every few years, a nor'wester will approach hurricane strength and cause widespread damage.
EffectsEdit
The heat and lack of moisture characteristic of nor'westers play a major role in the intermittent droughts experienced by Canterbury and other regions on New Zealand's eastern coasts.[citation needed] The Nor'wester has a deep psychological effect on many people subjected to its hot, dry nature. It has been statistically linked to increases in suicide and domestic violence.[2]
About 10 percent of people affected by the nor’wester feel elated and wonderful. But the rest feel depressed, irritable, and lacking energy. People feel they can’t cope with everyday things. ... There is irrational anxiety and a sense of foreboding.
^"Dunedin homes without water as wind topples trees". Radio New Zealand. 21 December 2010. Retrieved 1 November 2011.
^Erick Brenstrum, Canterbury's damaging nor'wester, New Zealand Geographic. Reprinted from New Zealand Geographic No.1 (Jan-Mar 1989). Accessed 2007-06-17.
^Chinooks, Plains Folk, Prairie Public Broadcasting. Accessed 2007-06-17.
Wikimedia Commons has media related to Nor'west arch.
External linksEdit
Meteorological explanations of the Nor'wester
New Zealand Meteorological Service Learning Centre
October 22, 2023
west, arch, weather, pattern, peculiar, east, coast, zealand, south, island, this, reason, also, often, referred, canterbury, arch, although, visible, both, otago, marlborough, well, canterbury, region, shown, apparent, arch, high, white, cloud, otherwise, cle. The Nor west arch is a weather pattern peculiar to the east coast of New Zealand s South Island For this reason it is also often referred to as the Canterbury arch although it is visible in both Otago and Marlborough as well as in the Canterbury Region It is shown in an apparent arch of high white cloud in an otherwise clear blue sky over the Southern Alps and is accompanied by a strong hot northwesterly or northerly wind simply known as The Nor wester The Nor west arch as visible from Christchurch shows a blue belt of clear sky to the west from which high white cloud streams Closer to the Canterbury coast some distance from the mountains of the Southern Alps it appears as a clear area of blue above the mountains with white cloud streaming to the east from it The phenomenon is similar to the Chinook arch seen in the Pacific regions of the United States and Canada Contents 1 Formation 2 Occurrence 3 Effects 4 See also 5 References 6 External linksFormation Edit nbsp The Nor wester is a fohn wind moist air is driven over the Southern Alps falling as condensation on the western side leaving the eastern plains in the rain shadow nbsp Typical shot of a Canterbury New Zealand nor west arch during sunsetThe Nor west arch is a fohn cloud The northwesterly wind drives warm moist air from over the Tasman Sea and it is pushed up by the presence of the Southern Alps causing it to cool rapidly The area to the east of the divide is in the rain shadow of the Alps much of the moisture is dumped on the West Coast and is responsible for the temperate rainforests found there As the air passes over the alps the water vapour remaining becomes visible in a band of cloud over the mountains at the top of each wave of air From the perspective of a viewer on the eastern side this appears as an arch of cloud The standing wave or arch is caused by the moisture condensing and becoming visible towards the top of the wave and then evaporating again as the air descends to the trough of the wave Nor westers caused by cold fronts will often change within a day or two to a cool southerly wind accompanied by rain showers as the front passes through In mid winter a Nor wester is often followed by a brief but intense cold snap frequently bringing thunder hail or rain and sometimes snow which may settle to sea level Occurrence EditThe Nor west arch can be seen as far north as Amberley and as far south as Central Otago but it is at its most prominent on the Canterbury Plains due to the flat and low lying nature of the land to the east of the mountains The Nor wester can blow at any time of year but is less common in winter Many of the strongest northerly and northwesterly winds blow ahead of cold fronts A front lying across the South Island will often extend from northwest to southeast reaching northern parts of the West Coast before it reaches corresponding areas on the east coast The steep air pressure gradient ahead of the cyclonic system associated with a front gives these nor westers their strength they will commonly reach gale force and cause isolated damage to trees and buildings 1 Once every few years a nor wester will approach hurricane strength and cause widespread damage Effects EditThe heat and lack of moisture characteristic of nor westers play a major role in the intermittent droughts experienced by Canterbury and other regions on New Zealand s eastern coasts citation needed The Nor wester has a deep psychological effect on many people subjected to its hot dry nature It has been statistically linked to increases in suicide and domestic violence 2 About 10 percent of people affected by the nor wester feel elated and wonderful But the rest feel depressed irritable and lacking energy People feel they can t cope with everyday things There is irrational anxiety and a sense of foreboding Neil Cherry 3 See also EditChinook arch Lee waves Southeast Australian foehn Roaring fortiesReferences Edit Dunedin homes without water as wind topples trees Radio New Zealand 21 December 2010 Retrieved 1 November 2011 Erick Brenstrum Canterbury s damaging nor wester New Zealand Geographic Reprinted from New Zealand Geographic No 1 Jan Mar 1989 Accessed 2007 06 17 Chinooks Plains Folk Prairie Public Broadcasting Accessed 2007 06 17 nbsp Wikimedia Commons has media related to Nor west arch External links EditMeteorological explanations of the Nor wester New Zealand Meteorological Service Learning Centre Retrieved from https en wikipedia org w index php title Nor 27west arch amp oldid 1180042857, wikipedia, wiki, book, books, library,
