In the atmospheric boundary layer (ABL), under high pressure conditions and negligible geostrophic winds, problems associated with pollution are the most critical. In this situation, the urban heat island plays a major role in the close-to-the-ground atmospheric dynamics and in dispersion processes at scales in the order of tens of meters (small scales). This article presents water tank laboratory simulations of an urban heat island in a stably stratified ABL, neglecting geostrophic winds and the effects of Coriolis force. The phenomenon is studied in the framework of a similarity theory developed for a nocturnal and low-aspect ratio urban heat island extended to the diurnal case. Image analysis techniques appear suitable to fully describe the phenomenon. The high resolution data provides a detailed fluid dynamic characterization of the urban heat island circulation. Present laboratory results, normalized by similarity theory scaling parameters, compare well with literature data. Graphical Abstract: [Figure not available: see fulltext.] © 2012 The Visualization Society of Japan.

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