AERMOD Tech Guide
3.2 Derived Parameters in the SBL
During stable conditions the energy budget term associated with the ground heating component is highly site-specific. During the day, this component is only about 10% of the total net radiation, while at night, its value is comparable to that of the net radiation (Oke, 1978). Therefore, errors in the ground heating term can generally be tolerated during the daytime, but not at night. To avoid using a nocturnal energy balance approach that relies upon detailed knowledge of the ground heating characteristics, AERMIC has adopted a much simpler semi-empirical approach for computing u* and L in stable conditions.