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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. 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 wind simply known as The Nor'wester.
The northwesterly wind in the South Island is a foehn wind. Warm moist air from over the Tasman Sea is pushed up by the presence of the Southern Alps, causing it to cool rapidly. Much of the moisture is dumped on the West Coast, and is responsible for the temperate rain forests 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.
| “ | 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. | ” |
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 nor'west 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. Once every few years, a nor'wester will approach hurricane strength and cause widespread damage.
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.
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.
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 Research by the environmental scientist Neil Cherry indicated that the mechanism is a significant buildup of positive ions, strongest somewhat inland from the coast, and electric fields of this strength have been shown to upset the melatonin/seratonin balance in some people.3
See also
References
- ^ Chinooks, Plains Folk, Prairie Public Broadcasting. Accessed 2007-06-17.
- ^ Erick Brenstrum, Canterbury's damaging nor'wester, MetService. Reprinted from New Zealand Geographic No.1 (Jan-Mar 1989). Accessed 2007-06-17.
- ^ Dr Neil Cherry's research. Accessed 2007-06-17. Quote: "The positive ions in the nor'wester are creating a stronger local electric field and those norwest ions travel over the sea breeze creating the electric field down to earth, so both of the [inland and coastal] populations were receiving the changed electric field from the ions. I looked up the literature on melatonin and seratonin and found that electromagnetic fields in many studies of electrical workers show reduced melatonin. That suggested that the nor'westers were altering the seratonin/melatonin ratio through the altered electric fields."
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- This page was last modified on 18 October 2008, at 22:23.
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