and Canadian weather services use a model accepted by the National Weather Service. Weather services in different countries use standards unique to their country or region for example, the U.S. All the formulas attempt to qualitatively predict the effect of wind on the temperature humans perceive. Many formulas exist for wind chill because, unlike temperature, wind chill has no universally agreed-upon standard definition or measurement. The faster the wind speed, the more readily the surface cools. Moving air disrupts this boundary layer, or epiclimate, allowing for cooler air to replace the warm air against the surface. As convection from a warm surface heats the air around it, an insulating boundary layer of warm air forms against the surface. The rate of convection depends on both the difference in temperature between the surface and the fluid surrounding it and the velocity of that fluid with respect to the surface. When the apparent temperature is higher than the air temperature, the heat index is used instead.Ī surface loses heat through conduction, evaporation, convection, and radiation. Its values are always lower than the air temperature in the range where the formula is valid. Wind chill (popularly wind chill factor) is the sensation of cold produced by the wind for a given ambient air temperature on exposed skin as the air motion accelerates the rate of heat transfer from the body to the surrounding atmosphere. Wind chill index values for a range of temperatures and wind speeds, from the standard wind chill formula for Environment Canada. For other uses, see Wind chill (disambiguation). This article is about the meteorological effect of "wind chill".
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