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Parameter |
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Symbol |
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Unit |
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D e s c r i p t i o n |
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measured
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Temperature |
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T |
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°C |
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Air
Temperature
[inside the radiation shield - for minimize the solar radiation
(direct
&
reflected)
temperature error]. |
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Relative Humidity |
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H |
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% |
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Air relative
Humidity refers to the amount of water vapor in the air. |
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Wind Speed |
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W |
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m/s2 |
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Wind Speed |
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Wind Direction |
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° |
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Wind Direction |
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Barometric
Pressure |
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P |
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mb |
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The weight of the air that
makes up our atmosphere exerts a pressure on the surface of the earth.
This pressure is known as atmospheric pressure. Generally, the more air
above an area, the higher the atmospheric pressure. This, in turn, means
that atmospheric pressure changes with altitude. For example, atmospheric
pressure is greater at sea-level than on a mountaintop. To compensate for
this difference in pressure at different elevations, and to facilitate
comparison between locations with different altitudes, meteorologists
adjust atmospheric pressure so that it reflects what the pressure would be
if measured at sea-level. This adjusted pressure is known as barometric
pressure. |
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Solar Radiation |
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R |
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W/m2 |
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Global Solar
Radiation, a measure of the intensity of the sun’s radiation reaching a
horizontal surface. This irradiance includes both the direct component
from the sun and the reflected component from the rest of the sky |
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Rainfall |
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mm |
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The amount of precipitation that falls in a
specific horizontal surface. |
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calculated |
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Dewpoint |
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D |
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°C |
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Dew-point is the temperature
to which air must be cooled for saturation (100% relative humidity) to
occur, providing there is no change in water content |
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Heat Index |
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TH |
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°C |
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The Heat Index uses the
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
saturated with water vapor) the apparent temperature "feels" higher than
the actual air temperature, because perspiration evaporates more slowly. |
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Wind Chill |
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TW |
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°C |
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The
Wind Chill
takes into account how the speed of the wind affects our perception of the
air temperature. The faster the wind blows, the faster heat is carried
away. |
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Temperature Humidity Wind Index
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THW |
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°C |
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The THW Index uses humidity, temperature and
the cooling
effects of wind, to
calculate an apparent temperature. |
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Temperature Humidity Sun Wind Index
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THSW |
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°C |
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The THWS Index uses humidity, temperature, the cooling
effects of wind and the heating effects of direct solar radiation to
calculate an apparent temperature. |
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Evapotranspiration |
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ET |
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mm |
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Evapotranspiration is a
measurement of the amount of water vapor retuned to the air in a given
area. ET is the opposite of rainfall. For ET estimation required:
air temperature, relative humidity, average wind speed and solar
radiation. |
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Solar Energy |
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E |
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1Ly |
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The amount of accumulated solar radiation
energy over a period of time is measured in Langleys.
1 Langley = 11.622 Watt-hours
per square meter
= 3.687 BTUs per square foot
= 41.84 kilojoules per
square meter |
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Wind Run |
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km |
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Wind run is
measurement of the "amount" of wind passing the station during a given
period of time |
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Air Density |
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Kg/m3 |
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Air Density = 1.2929 X
273.13
X
( AP - (
SVP x RH ))
( T +
273.13) 760
Where:
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T = Temperature in
Celsius |
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AP = Absolute Pressure (mm of
Hg) |
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SVP = Saturation Vapor Pressure
of air over water at temp T (see Table 1 below) |
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RH = Relative Humidity
(decimal) |
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Heating / Cooling
degree-days |
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Although
degree-days are most commonly used in agriculture, they are also useful in
building design and construction, and in fuel use evaluation. The
construction industry uses heating degree-days to calculate the amount of
heat necessary to keep a building, be it a house or a skyscraper,
comfortable for occupation. Likewise, cooling degree-days are used to
estimate the amount of heat that must be removed (through
air-conditioning) to keep a structure comfortable. Heating and cooling
degree-days are based on departures from a base temperature
(18.3°C). |
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