PET formulas (Heat Overlay)
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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:
$ PET_{sun}=-13.26+1.25\cdot T_{a,t}+0.011\cdot Q_{gl,t}-3.37\cdot ln(u_{t})+0.078\cdot T_{w,t}+0.0055\cdot Q_{gl,t}\cdot ln(u)+5.56\cdot sin(\phi _{t})-0.0103\cdot Q_{gl,t}\cdot ln(u_{t})\cdot sin(\phi _{t})+0.546\cdot B_{b,t}+1.94\cdot S_{vf} $
where,
- $ T_{a,t} $ is the calculated atmospheric temperature at time t;
- $ Q_{gl,t} $ is the hourly radiation at time t;
- $ u_{t} $ is the calculated wind speed at 1.2 meters above ground time t;
- $ T_{w,t} $ is the calculated wet-bulb temperature at time t;
- $ \phi _{t} $ is the sun altitude at time t;
- $ B_{b,t} $ is the bowen ratio at time t;
- $ S_{vf} $ is the calculated sky view factor.
- Constant values are sourced from the DPRA Heat stress report;
PET Shade and Night formula
The PET shade and night formula is as followed:
$ PET_{shade,night}=-12.14+1.25\cdot T_{a,t}-1.47\cdot ln(u_{t})+0.060\cdot T_{w,t}+0.015\cdot S_{vf}\cdot Q_{d,t}+0.0060\cdot (1-S_{vf})\cdot \sigma \cdot (T_{a,t}+273.15)^{4} $
where,
- $ T_{a,t} $ is the calculated atmospheric temperature at time t;
- $ u_{t} $ is the calculated wind speed at 1.2 meters above ground time t;
- $ T_{w,t} $ is the calculated wet-bulb temperature at time t;
- $ S_{v,f} $ is the calculated sky view factor;
- $ Q_{d,t} $ is the calculated diffusive radiation at time t;
- $ \sigma $ is the Stefan Boltzmann constant, which is $ 5.670374419...\times 10^{-8}W\cdot m^{-2}\cdot K^{-4} $.
- Constant values are sourced from the DPRA Heat stress report;
