Minimum Wind Stress for the Occurrence of Blue Tide on the Southeast Shore of Tokyo Bay

2014

AMM

Self Cite

An analytical model based on some solutions in the context of a two-layered fluid was developed to estimate the occurrence of northeasterly wind-driven coastal upwelling associated with “Aoshio” on the northeast shore of Tokyo Bay, and its validity was verified by comparing with observation data [1]. In this study, influences of all of the factors incorporated into this analytical model (including densities and thicknesses of the upper and lower layers, the parameter expressing the influences of interfacial friction and bottom friction) on the model are analyzed. The analytical model is found to express the competition between the wind-shear effect and the stratification effect: when the former dominates over the latter, Aoshio will occur on the northeast shore of the bay. The parameter that can be used to characterize the stratification effect can be simply expressed in terms of the product of density contrast and the square of thickness of the upper layer. Using different values of this parameter corresponding to different months in the model can simply estimate in which months it is easy for Aoshio phenomenon to happen on the northeast shore of the bay, and the result is roughly consistent with an observation phenomenon that Aoshio was frequently observed on the northeast shore of the bay in September and May and relatively less observed in June and July during 1978-2010.

Section: Introductionmentioning

confidence: 99%

Qualitative Discussion of Influences of some Factors on the Occurrence of Wind-Driven Coastal Upwelling Associated with “Aoshio” on the Northeast Shore of Tokyo Bay Using the Developed Analytical Model

2014

AMM

Self Cite

“…Plenty of studies regarding "Aoshio" phenomenon in Tokyo Bay have been carried out [1,2,3,4]. Specially, Zhu and Isobe [2] used a two-layered model to analyze the occurrence of northeasterly wind-driven coastal upwelling associated with "Aoshio" on the northeast and southeast shores of the bay, and this motivates us to explore whether a optimal wind direction for coastal upwelling in the bay exists or not.…”

Section: Introductionmentioning

confidence: 99%

The Optimal Wind Direction for the Occurrence of Wind-Driven Coastal Upwelling Associated with “Aoshio” on the Southeast Shore of Tokyo Bay

2014

AMM

Self Cite

Whether the optimal wind direction for the occurrence of wind-driven coastal upwelling associated with "Aoshio" on the southeast shore of Tokyo Bay exists was not clear. In this study, Tokyo Bay was assumed to be a narrow, infinitely long channel with only the southeast shore and the northwest shore being its two boundaries, and the optimal wind direction for coastal upwelling associated with "Aoshio" on the southeast shore of this idealized channel was discussed. It is found that the optimal wind direction varies with wind duration. If wind duration is very short, the optimal wind direction is almost across the channel while, with the increasing wind duration, the optimal wind direction approaches gradually to be along-channel. This transition is attributed to the increasingly important role that played by the Coriolis force in the motion of the two-layered fluid with the increasing wind duration.

“…During this process, a large concentration of dissolved oxygen at the bottom is consumed, and the bottom water consequently becomes oxygen-depleted and even anoxic. On the other hand, along the seasonal temperature stratifications, fresh water inflows around the bay and intermittent precipitation result in a high-temperature, low-salinity upper water layer and a low-temperature, high-salinity lower water layer [6][7][8][9]. As a result, a stable density stratification forms in which the lighter upper water overlies the heavier lower water, hindering the vertical circulation that brings dissolved oxygen from the surface to the bottom and thus enhances the oxygen-depleted state of the lower water [5,8].…”

Section: Introductionmentioning

confidence: 99%

Applying a Simple Analytical Solution to Modelling Wind-Driven Coastal Upwelling of Two-Layered Fluid at the Head of Tokyo Bay, Japan

Bai

Dou

et al. 2017

Water

Abstract:Blue tides at the head of Tokyo Bay are a hydro-environmental phenomenon where seawater appears to be milky blue because of the reflection of the sunlight off surface water containing large amounts of sulphur particles. Its appearance is due to the coastal upwelling of bottom oxygen-depleted water induced by northeasterly wind-driven circulation. Blue tides cause the death of many shellfish and other aquatic animals across the head of Tokyo Bay and consequently result in substantial economic losses to coastal fisheries. This paper examines the occurrence of wind-driven blue tides in Tokyo Bay, based on a simplified hydrodynamic model and observational analysis. The model assumed a two-layer structure with a wind-driven upper layer and an oxygen-depleted lower layer. In this study, we derived a simple analytical solution to determine a critical wind condition for which the lower layer outcrops at the surface if the wind forcing is sufficiently strong, resulting in the mixing of the two layers and giving rise to blue tide. The results of sensitivity analyses of the analytical solution to all incorporated factors were found to be in accordance with a qualitative understanding of the blue tide phenomenon. More importantly, comparisons of observational data with real cases of blue tide during 1978-2016 and without blue tide during [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016] suggested that this analytical solution was mostly valid. This study would be helpful for gaining a better understanding of the hydro-dynamical mechanism of blue tide.