Appendix A Weather Data - DAVIS Vantage Pro2 Console Manual

Appendix A
Weather Data
Refer to this appendix to learn more about the weather variables that are mea-
sured, displayed, and logged by your Vantage Pro2 Station. Some weather
variables require optional sensors. See "Optional Sensors" starting on page 2.
Wind
The anemometer measures wind speed and direction, and is part of the Inte-
grated Sensor Suite (ISS). The console calculates a 10-minute average wind
speed and 10-minute dominant wind direction. The 10-minute average wind
speed is displayed in the console ticker whenever wind has been selected on
the console. The last six 10-minute dominant wind directions are included in
the compass rose wind display.
Temperature
The ISS houses the outside temperature sensor in a vented and shielded
enclosure that minimizes the solar radiation induced temperature error. The
console houses the inside temperature sensor. Additional temperature sensors
are available for wireless stations and can measure up to eight locations.
Apparent Temperatures
Vantage Pro2 calculates three apparent temperature readings: Wind Chill,
Heat Index, and the Temperature/Humidity/Sun/Wind (THSW) Index. Appar-
ent temperatures use additional weather data to calculate what a human body
perceives the temperature to be in those conditions.
Wind chill
Wind chill takes into account how the speed of the wind affects our perception
of the air temperature. Our bodies warm the surrounding air molecules by
transferring heat from the skin. If there's no air movement, this insulating
layer of warm air molecules stays next to the body and offers some protection
from cooler air molecules. However, wind sweeps that warm air surrounding
the body away. The faster the wind blows, the faster heat is carried away and
the colder you feel. Wind has a warming effect at higher temperatures.
Note: The Wind chill is not calculated above 92° F (33° C) for consoles with firmware ver-
sion May 2005 (or version 1.6) or later, or above 78° F (26° C) for earlier firmware
versions.
Heat Index
The Heat Index uses temperature and the relative humidity to determine how
hot the air actually "feels." When humidity is low, the apparent temperature
will be lower than the air temperature, since perspiration evaporates rapidly to
cool the body. However, when humidity is high (i.e., the air is more saturated
with water vapor) the apparent temperature "feels" higher than the actual air
temperature, because perspiration evaporates more slowly.
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