PET formulas (Heat 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: PET_{shade, night};
• A cell is in the sun during the day: PET_sun;

PET Sun formula

The PET sun formula is as followed:
PET_sun = -13.26 + 1.25·T_a,t + 0.011·Q_gl,t - 3.37·ln(u_t) + 0.078·T_w,t + 0.0055·Q_gl,t·ln(u) + 5.56·sin(ϕ) - 0.0103·Q_gl,t·ln(u)·sin(ϕ)+0.546·B_b,t + 1.94·S_vf
where,