Urban climate related aspects of the force-restore method

Simple formulations are developed for the force-restore model for predicting homogeneous- and layered-soil surface temperature variations. Equivalent electrical circuits are used to describe the nocturnal cooling of typical urban ground surfaces under calm, cloudless conditions. The surface cooling of homogeneous soils at night is characterized by a time constant referred to as the cluster thermal time constant (CTTC). This parameter is constant for all soil types irrespective of the substrate thermal properties and equals the reciprocal of the angular frequency of the heating cycle (e.g. diurnal, annual). The cooling of two-layered soil surfaces is also characterized by two time constants the sum of which equals CTTC. Ground surface temperature predictions obtained by the force-restore model compare satisfactorily with numerical simulations carried out for the same substrate and radiative forcing. Also, model predictions are shown to be in general agreement with a field ground surface temperature data set.