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Ann. Geophys., 25, 1735-1744, 2007
www.ann-geophys.net/25/1735/2007/
© European Geosciences Union 2007
An observational study of the evolution of the atmospheric boundary-layer over Cabo Frio, Brazil
S. H. Franchito1, V. Brahmananda Rao1, T. O. Oda2, and J. C. Conforte1
1Centro de Previsão de Tempo e Estudos Climáticos, CPTEC/INPE Instituto Nacional de Pesquisas Espaciais, INPE CP 515, 12245-970, São José dos Campos, SP, Brazil
2Instituto de Estudos do Mar Almirante Paulo Moreira Rua Kioto, 253, 28930-000, Arraial do Cabo – RJ – Brazil
Abstract. The effect of coastal upwelling on the evolution of the atmospheric boundary
layer (ABL) in Cabo Frio (Brazil) is investigated. For this purpose,
radiosounding data collected in two experiments made during the austral
summer (upwelling case) and austral winter (no upwelling case) are analysed.
The results show that during the austral summer, cold waters that crop up
near the Cabo Frio coast favour the formation of an atmospheric stable
layer, which persists during the upwelling episode. Due to the low SSTs, the
descending branch of the sea-breeze circulation is located close to the
coast, inhibiting the development of a mixed layer mainly during the day. At
night, with the reduction of the land-sea thermal contrast the descending
motion is weaker, allowing a vertical mixing. The stable ABL favours the
formation of a low level jet, which may also contribute to the development
of a nocturnal atmospheric mixed layer. During the austral winter, due to the
higher SSTs observed near the coast, the ABL is less stable compared with
that in the austral summer. Due to warming, a mixed layer is observed
during the day. The observed vertical profiles of the zonal winds show that the
easterlies at low levels are stronger in the austral summer, indicating that
the upwelling modulates the sea-breeze signal, thus confirming model simulations.
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