Abstract:Regions Of Freshwater Influence (ROFI) existing between oceans and estuaries often yield significant fishery resources. To inform fishermen of the real-time ocean state, an operational prediction system focusing on a specific coastal region would normally require accurate and timely runoff data for all rivers. In this paper, hydrometeorological procedures providing the required runoff data on a daily basis were coupled with an Ocean General Circulation Model (OGCM) to evaluate the impacts of runoff processes on ocean simulations within a ROFI. The procedures we adopted employ a distributed tank model based on water mass and heat budgets derived from predicted meteorological datasets. An exponential relationship between runoff rates and watershed areas was used to determine model parameters in order to estimate the runoff from many other small rivers. The coupled model reproduced a surface salinity field in the bay that was in good agreement with observations, and simulated the expected clockwise circulation generated by the high net total discharge associated with snowmelt. Our results underline the fact that implementation of hydrological processes into ocean simulations is essential for a better understanding of water circulation driven by runoff into semi-enclosed bays over interannual timescales.

Abstract:A numerical simulation and stationary geophysical survey at Omaehama, Japan, described the hydrogeology in a tidal flat and adjacent sea water column. The simulation of a tidally influenced aquifer with inland fresh groundwater discharges showed three circulations in the subterranean tidal flat estuary: a small, tide-induced recirculation (TIR) near the sloping beach, a deeper circulation (DC) across the interface between saltwater and freshwater, and a large, tidal flat-induced circulation (TFIC) in the offshore subterranean tidal flat and slope. The horizontal distribution of the simulated submarine groundwater discharge (SGD) showed two peaks, depending on the distance from the coast along the transect line of tidal flat; the offshore peak was quantitatively consistent with the previously observed peak based on automated seepage measurements. Time-series of the observed resistivity profiles using a marine cable (140 m) showed the structure of the fresh water/salt water interface, and indicated a salt wedge intruding from the bottom aquifer and infiltration at the surface in the beach and nearshore tidal flat. The qualitative structure of the resistivity hardly changed at each tidal stage. These results qualitatively validated the circulation patterns shown by the numerical simulation. The source of this discharging groundwater in the tidal flat is a complex mixture of fresh groundwater derived from the landward aquifer, as well as locally recycled seawater, which can contribute to the purification of the nearshore seawater.

No abstract

[1] Heat and water mass transports tagged by water type in a bay were investigated using daily outputs from a high-resolution land-sea coupled model. The modeled circulation and water property distribution were similar to those reported by observations. In this paper, the heat angle is introduced to accurately define the roles of the lateral heat flux (LF) into the bay and the net surface heat flux on temperature changes in the bay water. As a result, ocean phenomena in the bay can be categorized by using the heat angle in an intensive LF regime on short-period timescales and a gradual LF regime on intraseasonal timescales. Our close examination revealed that the velocity fields can be classified into three flow patterns: a twin vortex accompanied by positive LF, a clockwise flow with negative LF, and an anticlockwise flow with both LFs. These patterns occur in both intensive and gradual LF regimes. Intensive wind-driven LF forced by atmospheric disturbances was often observed from summer to autumn in 2008, accompanying the intrusion of southern subtropical Tsugaru warm water that was colder than the deep bay water (LF < 0) and subarctic Oyashio water that was warmer than the surface bay water (LF > 0), but both were hardly found in 2009. This thermal contrast affects the interannual difference in the stratification inherent in the bay. Our integrated analysis method is useful for prompt and robust understanding of the thermal and dynamic states in a bay based on ocean simulation data.