Recent surveys in Ise Bay, which is a major gulf-type region of freshwater influence in Japan, reveal that a cold dome is often observed in the stratified season. To elucidate the formation mechanism of the cold dome, detailed hydrographic and ADCP surveys were conducted in August 1995. The results show that a cold (T<20°C) water mass existed under the thermocline in the western basin of the bay. By contrast, in the middle layer of the eastern basin, there was mixed water, which exhibited characteristics equivalent to the water in the Irago Strait. A prominent bottom front separated these two different water masses. The ADCP results show a strong inflow in the form of a geostrophic current flowing above the bottom front, while the flow speed was weak in the cold water mass. The inflow area corresponded with the mixed water area, suggesting that the strait water would intrude into the bay along the eastern coast. In the western half of the basin, on the other hand, relict spring water is excluded from the exchange circulation and was trapped beneath the thermocline, where it formed the cold dome. The formation of the cold dome by this process is investigated using a three-dimensional model with two different density structures; a stratified and mixed region. The model results strongly support the formation mechanism of the cold dome, as the observed density and flow fields are successfully demonstrated. The key point to control the mechanism is the coexistence of the stratified and the mixed region. (C) 2002 Elsevier Science Ltd. All rights reserved.
