Interactions of an urban heat island and sea-breeze circulations during winter over the metropolitan area of São Paulo, Brazil

Abstract

The Town Energy Budget (TEB) model, a detailed urban parameterisa- tion using a generalised canyon geometry, coupled with the Regional Atmospheric Modelling System (RAMS) is used to simulate the wintertime local circulation in the megacityenvironmentofthemetropolitanareaofSaoPaulo(MASP)inBrazil.Model simulations are performed using actual topography and land-use fields. Comparison with a simple urban parameterisation based on the LEAF-2 scheme is also shown. Validation is based on comparison between model simulations and observations. Sen- sitivity tests with TEB reveal an important interaction between the sea breeze and the MASP heat island circulation. Even though topography is known to play an impor- tant role in the MASP region's weather, in these tests the simulations were performed without topography in order to unambiguously identify the interaction between the two local circulations. The urban heat island (UHI) forms a strong convergence zone in the centre of the city and thereby accelerates the sea-breeze front toward the centre of the city. The presence of the urban region increases the sea-breeze front propa- gation mean speed by about 0.32ms −1 when compared with the situation of no city. After its arrival in the urban region, the sea-breeze front stalls over the centre of the city for about 2h. Subsequently, the sea breeze progresses beyond the city when the heat island dissipates. Thereafter, the sea breeze propagates beyond the urban area at a decelerated rate compared to a simulation without an UHI.