Airmar PB200 - Manual (Page 63)

PB200 WeatherStation User Manual revision 1.000
Proprietary and Confidential
57
The wind chill temperature is the perceived temperature on a person’s face at the current wind speed. The calculation assumes that the wind speed measured by the sensor is the
same as the wind speed at the face of an observer. The “relative” wind chill uses the measured apparent wind speed for this calculation, and the “theoretical” wind chill uses the
calculated true wind speed. The wind chill temperature is only defined when the air temperature is below 50°F (10°C) and the wind speed is above 3 mph.
The
heat index is the apparent temperature felt by a person's skin when exposed to air with a high moisture content. Dry air allows evaporative cooling of the skin's surface. The
higher the humidity, the less the skin can cool itself with evaporative cooling. The heat index is only defined when air temperature is above 80°F (27°C) and relative humidity is
above 40%.
The
dew point is the temperature at which the water vapor in the air begins to condense into a liquid. If the air were gradually cooled while maintaining constant moisture content,
the relative humidity would rise until it reaches 100%. The air temperature at this point of saturation is called the dew point. If the air is dry enough, it is possible to have a dew
point that is below freezing. The dew point is then sometimes referred to as the frost point. The PB200 calculates dew point from the measured air temperature and relative
humidity sensor readings.