Buoyancy and tide-driven exchange between river and coastal ocean

日期：2011/10/11　14：00

地點：科一館 S-325

演講者：陳世楠　助理教授
             Assistant Prof. Shih-Nan Chen

現職：台灣大學海洋研究所
          Institute of Oceanography, NTU

講題：Buoyancy and tide-driven exchange between river and coastal ocean

摘要：

We use the isohaline coordinate method to compare the exchange flow in two contrasting estuaries, the long (with respect to tidal excursion) Hudson and short Merrimack River, using validated numerical models. The isohaline method averages fluxes in salinity space rather than in physical space, yielding the isohaline exchange flow that incorporates both subtidal and tidal fluxes and precisely satisfies the Knudsen relation. The isohaline method can be consistently applied to both subtidally and tidally dominated estuaries. In the Hudson, the isohaline exchange flow is similar to results from the Eulerian analysis, and the conventional estuarine theory can be used to quantify the salt transport based on scaling with the baroclinic pressure gradient. In the Merrimack, the isohaline exchange flow is much larger than the Eulerian quantity, indicating the dominance of tidal salt flux. The exchange flow does not scale with the baroclinic pressure gradient but rather with tidal volume flux. This tidal exchange is driven by tidal pumping due to the jet-sink flow at the mouth constriction (Stommel and Farmer 1952), leading to a linear dependence of exchange flow on tidal volume flux. Finally, to characterize the exchange processes among different systems, we propose a tidal conversion parameter Q_in/Q_prism that measures the fraction of tidal inflow (Q_prism) that is converted into net exchange (Q_in). We also demonstrate that the length scale ratio between tidal excursion and salinity intrusion provides a characteristic to distinguish estuarine regimes.