Temperature formulas (Heat Overlay)

Two temperature formulas are used in the calculation of the PET value:

• The atmospheric temperature T_a
• The wet-bulb temperatur T_w

Atmospheric Temperature formula

$T_{a,t}=T_{station,t}+UH{I}_{max,t}\cdot f_{sun,t}$

where

• $T_{a,t}$ is the calculated atmospheric temperature at time t;
• $T_{station,t}$ is the temperature measured at a weather station at time t;
• $UH{I}_{max,t}$ is the calculated Urban Heat Island effect at time t;
• $f_{sun,t}$ is the sun daily motion factor at time t;

Wet-bulb Temperature formula

$T_{w,t}=T_{a,t}\cdot \arctan (0.151977\cdot \sqrt{\varphi +8.313659})+\arctan (T_a+\varphi )-\arctan (\varphi -1.676331)+0.00391838\cdot {\varphi }^{\frac{3}{2}}\arctan (0.023101\cdot \varphi )-4.686935$

where:

• $T_{w,t}$ is the calculated wet-bulb temperature;
• $T_{a,t}$ is the calculated atmospheric temperature;
• $\varphi$ is the sun altitude angle;

See also

• Wet-bulb temperature

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