The prediction of impervious ground surface temperature by the surface thermal time constant (STTC) model

Abstract

Temperature patterns of impervious and dry ground surfaces typical of urban and dry rural environments are considered. Ground-surface temperature depends on the thermophysical properties of the ground material between the surface in question and the constant temperature plane at the diurnal “penetration depth” (lower boundary of participating layer), on wind conditions and on solar and long-wave infrared radiation exchange and geometries. The surface thermal time constant (STTC) analytical model introduced here is an effective tool for predicting ground-surface temperature in homogeneous and layered soils. The STTC itself is defined as the energy stored in the ground participating layer per unit change of the absorbed radiation flux density on the ground's surface. An extensive series of field observations were conducted. Surface and ground temperature patterns and meteorological conditions in winter and summer were obtained continuously during a nine-month period of measurements. Calculated values of surface temperature by means of the STTC model showed good agreement with observed values. The STTCs of the impervious concrete and asphalt surfaces — typical of urban environments — were found to be 2.2 hours and 1.8 hours respectively, and that of dry bare soil — typical of rural environments — 1.3 hours. The STTC, here defined as a thermal property of the ground, compares qualitatively with the thermal inertia (admittance) of a homogeneous ground layer represented by (kϱc) 1 2 commonly used in numerical models for predicting surface temperature.