PET formulas (Heat Stress Overlay)
The physiological equivalent temperature PET is calculated for two possible options based on the situation:
- A cell is in the shade or it is night at time t: PETshade, night;
- A cell is in the sun during the day: PETsun;
PET Sun formula
The PET sun formula is as followed:
where,
- Ta,t is the calculated atmospheric temperature at time t;
- Qgl,t is the hourly radiation at time t;
- ut is the calculated wind speed at 1.2m above ground time t;
- Tw,t is the calculated wet-bulb temperature at time t;
- ϕt is the sun altitude at time t;
- Bb,t is the bowen ratio at time t;
- Svf is the calculated sky view factor.
PET Shade and Night formula
The PET shade and night formula is as followed:
PETshade,night,t = -12.14 + 1.25 · Ta,t - 1.47 · ln(ut) + 0.060 · Tw,t + 0.015 · SvfQd,t + 0.0060 · (1-Svf) · σ · (Ta,t+273.15)4
where,
- Ta,t is the calculated atmospheric temperature at time t;
- ut is the calculated wind speed at 1.2m above ground time t;
- Tw,t is the calculated wet-bulb temperature at time t;
- Svf is the calculated sky view factor;
- Qd,t is the calculated diffusive radiation at time t;
- σ is the Stefan Boltzmann constant, which is 5.670374419...×10-8 W⋅m-2⋅K-4.
