Abstract
The effect of wind on summer water temperature trends in a semi-closed bay (Tokyo Bay, Japan) is examined through several numerical experiments using a high-resolution three-dimensional ocean model. The model is executed under no-wind and uniform southerly/northerly wind conditions, and monthly mean currents and temperature distributions and heat transport in Tokyo Bay for July are calculated. The model results show that wind has a significant effect on heat transport and temperature distribution in the bay. (1) When a southerly wind prevails northward cool water transport intensifies while southward warm water transport declines, thus decreasing the water temperature in the central bay area while increasing temperature at the bay head. (2) A northerly wind has an opposing effect and decreases the water temperature in coastal bay head area while increase the temperature along the southwest coast. The results also suggest that the trend of increasing southerly wind amplitude may have affected water temperature trends in Tokyo Bay from 1979 to 1997. The model results demonstrated that the an intensified southerly wind lowers water temperatures in most areas of the bay by enhancing upwelling and open ocean-water intrusion near the bay mouth while increases temperatures in the bottom layer of the bay head by suppressing southward warm water transport.
Highlights
Trends of increasing coastal water temperature with significant impacts on local ecosystems have been recently reported (e.g., Nixon et al 2004; Presten 2004; Shearman and Lentz 2010)
The results suggest that the trend of increasing southerly wind amplitude may have affected water temperature trends in Tokyo Bay from 1979 to 1997
The modeling results demonstrated that the heat transport processes and consequent distribution of water temperature in Tokyo Bay are significantly influenced by wind forcing
Summary
Trends of increasing coastal water temperature with significant impacts on local ecosystems have been recently reported (e.g., Nixon et al 2004; Presten 2004; Shearman and Lentz 2010). Similar trends have been observed in Fukuoka Bay, another semi-closed bay in Japan (Aoki and Isobe 2006) The continuation of this decreasing summer water temperature trend will greatly impact the local environment and ecosystem and the coastal urban climate (Oda and Kanda 2009). The previous studies have suggested that descending summer water temperature trends in these coastal bays are associated with increased cool water intrusion from the open ocean. To further elucidate the mechanisms that control water temperature trends in Tokyo Bay during strong summer stratification periods, the detailed heat transport pathways in the bay and their dominant processes must be identified. Magome et al (2012)’s observation and modeling results demonstrated that southerly winds suppress water exchange processes at the bay mouth and trap bay water in the head region.
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