New Wind Chill Temperature (NWCT) - marharyta/apparent-temperature GitHub Wiki

The standard way to measure Wind Chill Index had various shortcomings, which ultimately led to revisiting the theory and researching more how wind affected the perception of temperature. The New Wind Chill temperature is based on a  model of the heat exchanges between the human head and the environment.

The original index, which gives unreal high values, especially on low air temperatures and high wind speeds. Bluestein & Zecher verify that Siple & Passel did not take into account the physic model resistance in their experiments, overestimating heat transfer. (Monteiro, L. M. 2005)

As result of an Internet conference on wind chill, hosted by the Canadian Weather Service in 2000 (Maarouf and Bitzos 2000), Environment Canada (EC) and the U.S. National Weather Service (NWS) convened a group of interested parties and researchers to evaluate the state of the art in WCT determination and to recommend a better approach. (Osceski, R. & Bluestein,  M. 2005)

In research The New Wind Chill Equivalent Temperature Chart by Randall Osevski and Maurice Bluestein they decided to concentrate on areas of exposed skin. In winter, the face is the most exposed area.

The new index is based on a numerical model of the heat exchanges between the human head and the environment. Osczevski (2000a, 2000b) presents two indexes: one combining air temperature and speed considering a correction factor to solar radiation and others to determine the risk of frostbite.

The author developed a computer controlled thermal head mannequin and also did experiments with volunteers in acclimatized chambers. Bluestein & Osczevski (2002) propose the NWCT. They describe the physical modeling of a face exposed to the wind: the front half of a vertical thermal cylinder of 180mm external diameter, with 25 concentric layers, simulating heat exchanges. Individual speed was set to 4,8 km/h, obtained from researches with pedestrians in crossing corns, to which the wind speed is added. To radiation exchanges, it assumes to be a clear sky night. So, the NWCT is calculated to a relative air movement of 4,8 km/h, representing a situation in which the heat loss and skin temperature are equivalent to the real one. The initial constraints provided by theoretical research information include the temperature range of -50 Celsius to 10 Celsius  and the wind speed from 10 to 80 km/h. Within those ranges the NWCT formulas give the most accurate predictions. They should not be used at very low wind speeds, that is, less than 3 mph or 5 km/h .

After creating tests the current indices from the formula give the correct corresponding values, described in the table. It is safe to assume the formulas have accurate indices and represent the model correctly.

The New Wind Chill Temperature formula is provided as (for Celsius):

Figure 23. (Osevski, R. & Bluesteinn. 2005)

And for Fahrenheit values:

Figure 24. (Osevski, R. & Bluesteinn. 2005)

Module for calculations: https://github.com/marharyta/apprent-temperature/blob/master/src/apparentTemperature/newWindChill.js

Tests: https://github.com/marharyta/apprent-temperature/blob/master/test/newWindChill.test.js