Helicopter Observations of the Sea Breeze over a Coastal Area

Abstract

Thermodynamical observations by a helicopter have been conducted to study the internal structure of the sea breeze blowing inland from Tosa Bay during three periods (September 1993, November 1994 and 1995). Inland-intrusion distances of the midday sea breeze observed at each flight leg were in the 10–25-km range, depending on the intensity of the ambient flow associated with the gradient wind, atmospheric stratification, and the geographical features of the observed area. The sea breeze observed over the sea had well-defined features, in particular a turbulent wake behind the head of the sea-breeze front and a closed sea-breeze circulation cell containing the subsidence of the return flow. In addition, a moist layer distributed around 15–20 km offshore forms because the land breeze moves in this region. Moreover, a calm condition exists from the coast to about 10 km offshore. Both phenomena are found before the onset of the sea breeze in the early morning. Such remarkable characteristics of the sea breeze are found over the sea, with a background of land–sea configuration that consists of a flat plain with small mountains and a bay opened out to sea.