Gill GMX100 User Manual page 137

Gill Instruments Ltd
_____________________________________________________________________________________________________________
Heat Index
HEATIDX -
What the temperature feels like to the human body when relative humidity is combined with the air
temperature (also known as apparent temperature).
Simple Heat Index is defined as:
HI s = 0.5 * {T + 61.0 + [(T-68.0)*1.2] + (RH*0.094)}
where: HI s = Simple Heat Index expressed as an apparent temperature in degrees F.
T = MaxiMet Temperature in degrees F.
RH = MaxiMet Relative Humidity in percent.
Rothfusz Heat Index is defined as:
HI r = -42.379 + 2.04901523*T + 10.14333127*RH - 0.22475541*T*RH - 0.00683783*T*T -
0.05481717*RH*RH + 0.00122874*T*T*RH + 0.00085282*T*RH*RH -
0.00000199*T*T*RH*RH
See http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml
where: HI r = Rothfusz Heat Index expressed as an apparent temperature in degrees F.
T = MaxiMet Temperature in degrees F.
RH = MaxiMet Relative Humidity in percent.
Rothfusz Adjustment is defined as follows:
If the Relative Humidity is less than 13% and the Temperature is above 80 and below 112 degrees
F (above 26.66 and below 44.44 °C):
R Adj = -[(13-RH)/4]*SQRT{[17-ABS(T-95.)]/17}
where: R Adj = Rothfusz Adjustment,
T = MaxiMet Temperature in degrees F,
RH = MaxiMet Relative Humidity in percent,
ABS and SQRT are the absolute value and square root functions, respectively.
If the Relative Humidity is greater than 85% and the Temperature is above 80 and below 87 degrees F
(above 26.66 and below 30.55 °C).
R Adj = [(RH-85)/10] * [(87-T)/5]
where: R Adj = Rothfusz Adjustment.
T = MaxiMet Temperature in degrees F.
RH = MaxiMet Relative Humidity in percent.
If Relative Humidity and Temperature conditions are outside the two bands defined above:
R Adj = 0
where: R Adj = Rothfusz Adjustment
When HI s ≥ (HI r + R Adj), MaxiMet Heat Index shall be: HI = HI s
where: HI = MaxiMet Heat Index expressed as an apparent temperature in degrees F,
HI s = Simple Heat Index expressed as an apparent temperature in degrees F
When HI s < (HI r + R Adj), MaxiMet Heat Index shall be: HI = HI r + R Adj
where: HI = MaxiMet Heat Index expressed as an apparent temperature in degrees F,
HI r = Rothfusz Heat Index expressed as an apparent temperature in degrees F,
R Adj = Rothfusz Adjustment.
Result e.g. +028 (°C default).
Note: Heat Index is only reported when the temperature is above 75°F (approximately 23.88°C) and
both Relative Humidity and Temperature are functioning.
__________________________________________________________________________________________________
MaxiMet
Doc. No. 1957-PS-021
Page 137 Issue 3
May 2018