Interaction between an Inland Urban Heat Island and a Sea-Breeze Flow: A Laboratory Study

Abstract

Using laboratory experimental data taken from a temperature-controlled water tank, the basic features of the circulation associated with an inland urban heat island (UHI) of diameter D and surface heating rate H0 and its interaction with a sea-breeze current were investigated. When the environment was stably stratified with a buoyancy frequency N (nocturnal UHIs) and the sea breeze was absent, the UHI circulation was mainly governed by the Froude number [Fr = U/(ND)], in agreement with theoretical predictions found in literature (U was the horizontal velocity scale of the flow based on H0 and D). Furthermore, the results were in agreement with other laboratory studies and with nighttime field observations conducted in large cities. It was found that U, when calculated with H0 + HL (where HL was the surface heat flux associated with the land temperature growth occurring after sunrise), could also be employed as the velocity scale for UHI circulations that develop in statically unstable environments (daytime UHIs). Analysis of the interaction between an inland daytime UHI and a sea-breeze flow with maximum velocity UB showed that the resulting circulation was strongly dependent on the ratio UB/U and that substantial differences from cases in which urban complexes are located along the shore were present. Comparison with numerical experiments also supports these results.