Numerical studies of heat island circulations

Abstract

A two dimensional model has been set up to investigate the circulation induced by an urban heat island in the absence of synoptic winds. The boundary conditions need to be formulated carefully and due to difficulties arising here, we restrict our attention to cases of initially stable thermal stratification. Heat island circulations are allowed to develop from rest and prior to the appearance of the final symmetric double cell pattern, a transitional multi-cell pattern is observed in some cases. The influence on the steady state circulation of various parameters is studied, among which are eddy transfer coefficients, the heat island intensity, the initial temperature stratification and the heat island size. Some results are presented for a case in which differential surface cooling beneath an initially stable atmosphere produces a circulation and an unstable layer capped by an elevated inversion over the city. It is hoped that this case is vaguely representative of the night-time heat island with no geostrophic wind.

Enhancement and Initiation of a Cumulus by a Heat Island

“…air concentrates near the boundary of the heat island because *T *r is largest there. The zone where air concentrates moves gradually toward the center of the heat island in the same manner as studied by Delage and Taylor (1970). The motion of the circulation affects the location where the cumulus is initially formed and its development.…”

“…(4) Comparison of results of cases 6 and 10 The vertical grid interval is 200m hitherto in this paper, while *z= 100m is usually used when circulation induced by the heat island and others concerning the heat island are numerically studied (e.g., Delage and Taylor, 1970;Sawai, 1978). The effect of the vertical grid interval on the simulation is examined in this section.…”

“…It will be shown, however, that the heated area at the surface generates a vertical temperature field which possesses characteristics of those observed in urban areas, as is known from numerical studies already done on heat islands (e.g., Delage and Taylor, 1970).…”

A Preliminary Report on the Experiment of Thermal Convective Circulation under the Inversion Layer in the Stratified Wind Tunnel

“…An urban heat island is one of the so-called man-made climates, and the existence of a characteristic heat island circulation was numerically and observationally studied by several researchers recently (DELAGE and TAYLOR, 1970 ;FINDLAY and HERT, 1969). Figure 4 is an example of numerical simulation by DELAGE and TAYLOR (1970) under an elevated thermal inversion.…”

Current research and future challenges in urban mesoscale modelling

“…Owing to the complexity of the problem, it is only with the advent of computers that studies of mesoscale circulations received a strong boost. In terms of urban mesoscale modelling, Delage and Taylor (1970) and Bornstein (1975) were one of the first to investigate the impacts of the urban heat island on wind fields and boundary layer structure. Such studies were motivated by the need for a better understanding of the dynamics and thermodynamics of the urban PBL, with particular interest in pollutant dispersion, but were still very idealized and simple (two dimensional).…”