The Effects of a Foehn Wind on Human Thermal Exchange: The Canterbury Nor'wester
Authors: TULLER STANTON E. 
Published: May 2008

The nor'wester and other foehn winds are noted for their warmth. The Romans considered the most important characteristic of a foehn to be the warmth of the wind and not its direction (Brinkmann, 1971). The patterns of equilibrium skin temperature presented here illustrate the warmth of the human environment with the nor'wester as compared with other common weather types at Christchurch.

The most significant effect of a nor'wester which produced its warmth in this study was the relatively high air temperature. The magnitude of human convective heat flux density was reduced despite the high wind speed. Evaporative heat flux density was higher especially during summer when the difference in vapour pressure be tween the nor'wester and other weather types was most pronounced, and the warmer environment stimulated a higher skin wetness with the nor'wester. Solar radiation and net long wave radiation exchange both increased with clearer skies and had a less consistent pattern because of variations in cloud cover. On average, however, both tended to be greater under a nor'wester than under other weather types. Quantitively, the convective and evaporative heat flux densities accounted for the greatest absolute differences in the human energy budget between the nor'wester and other weather types, followed by solar radiation and long wave radiation.

Evaporative heat flux density was the largest single term in the human energy budget (with the exception of metabolic heat production) during hot, summer nor'westers. Convective heat flux density was dominant during other daytime nor'westers and all other weather types. Net long wave radiation was the most important term for the clear night case.

The warmth of the nor'wester can be considered to be favourable during most situations. Equilibrium skin temperature for a standing person was consistently closer to the optimum value under the nor'wester than with other weather types. The benefits were especially noticeable in winter. Heat strain becomes a possibility in the warmer part of the year, however, especially for people who are exercising and those in the urban environment.

Many people complain about the effect of foehn winds and the nor'wester is no exception. Many things are involved in creating the overall sensation of pleasantness or unpleasantness in a particular environment. Such things as changes in the electrical field or in the ion state of the atmosphere have been suggested as possible contributions to foehn effects. Some people do not like very dry winds regardless of their overall thermal effects. Strong and gusrty winds themselves may cause unpleasantness by disrupting clothing and hair, making walking difficult or carrying grit and other objects into the air (Arens and Ballanti, 1977). Wind speeds encountered with a nor'wester are frequently near or above the upper limit which most people would find agreeable. Thermal exchange is only part of the total effect of a weather type on human beings. It is one factor, however, on which the nor'wester under most circumstances can be considered to have a favourable influence.