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Parameter Calculation

Meteorological variables are being measured every 5 seconds and averaged over a 15 minute period. Hourly and daily values are also being calculated for select variables.

Humidex
Humidex is a dimensionless number that indicates an approximate temperature in degrees Celsius. The Humidex combines the air temperature and humidity into one number that reflects the perceived temperature. It gives a measure of the amount of discomfort felt by the combined effect of the air temperature and humidity.

  • Less than 29: No discomfort
  • 30 to 39:        Some discomfort
  • 40 to 45:        Great discomfort; avoid exertion
  • Above 45:      Dangerous to human health

Following formula was used to calculate Humidex:

image1
image2

Where:

Humidex is perceived temperature in degrees Celsius.
Ta is air temperature in degrees Celsius
Td is dew point in degree Kelvin


Windchill
If low air temperature is accompanied by high winds, a person’s body may loose heat much more rapidly, compared to low wind situations. Therefore, a windy day may feel colder than a calm day. As a result,  temperature is often reported as actual air temperature and how cold that temperature someone perceives, which is called wind-chill temperature index or simply wind-chill temperature . The following formula was used to calculate wind-chill temperature:

Twc = 13.12 + Ta x 0.6215 - 11.37 x Ws0.16 + 0.3965 x Ta x Ws0.16

Where:

Twc = Wind-chill temperature index in degrees Celsius
Ws = Wind speed in kilometres per hour
Ta = Air Temperature in degrees Celsius

Dew point Temperature
The dew point temperature, or simply dew point, represents the temperature to which air must be cooled (without changes in its pressure and moisture content) to reach saturation - when condensation occurs. The dew point is a good indicator of the amount of water vapor present in the air. High dew point values indicate high air water vapor content. When temperature and dew point are the same, the relative humidity is 100% and air is saturated with water vapor.

The dew point temperature is calculated using Tetens' equation solved for dew point with coefficients optimized for the temperature range of -35 to +50 degrees C, using a programming function developed by Campbell Scientific, Ltd for its dataloggers:

image3

where:

Td is dew point temperature in degree Celsius
Vp is saturation vapor pressure in kPa
A1 = 0.61078
A2 = 17.558
A3 = 241.88

Winter precipitation
In winter, precipitation (in mm) represents snow water equivalent, which is about 10 times the amount of snow. For example 1 mm of snow water equivalent would represent approximately 10 mm or 1 cm of snowfall. A heated rain gauge is being used to measure winter precipitation.