Using flushing rate to investigate spring-neap and spatial variations of gravitational circulation and tidal exchanges in an estuary

Spring-neap and spatial variations of gravitational circulation and tidal exchanges in the Sumjin River Estuary (SRE) were investigated using the flushing rate. The flushing rate was calculated between multiple estuarine segments and the adjacent bay to examine the spatial variation of two exchanges. The strength of gravitational circulation and tidal exchanges modulated significantly between spring and neap tides, where stratification alternated between well-mixed and highly-stratified conditions over the spring-neap cycle. Tide-driven dispersive flux of salt dominated over gravitational circulation exchange near the mouth during spring tide due to the larger tidal amplitude that caused well-mixed conditions and rapid exchange. In contrast, the central and inner regimes were found to be partially stratified during spring tide due to the reduction in tidal amplitude where both gravitational circulation and tidal exchanges were important in transporting salt. The combined contributions of two fluxes were also found during neap tide along the SRE due to the significant reduction in vertical mixing that accompanied strong stratification. Gravitational circulation exchange almost entirely dominated in transporting salt at the upstream end during spring and neap tides.

Dispersive Fluxes between the Coastal Ocean and a Semienclosed Estuarine Basin

Scalar exchange between San Francisco Bay and the coastal ocean is examined using shipboard observations made across the Golden Gate Channel. The study consists of experiments during each of the following three “seasons”: winter/spring runoff (March 2002), summer upwelling (July 2003), and autumn relaxation (October 2002). Within each experiment, transects across the channel were repeated approximately every 12 min for 25 h during both spring and neap tides. Velocity was measured from a boat-mounted ADCP. Scalar concentrations were measured at the surface and from a tow-yoed SeaSciences Acrobat. Net salinity exchange rates for each season are quantified with harmonic analysis. Accuracy of the net fluxes is confirmed by comparison with independently measured values. Harmonic results are then decomposed into flux mechanisms using temporal and spatial correlations. In this study, the temporal correlation of cross-sectionally averaged salinity and velocity (tidal pumping flux) is the largest part of the dispersive flux of salinity into the bay. From the tidal pumping flux portion of the dispersive flux, it is shown that there is less exchange than was found in earlier studies. Furthermore, tidal pumping flux scales strongly with freshwater flow resulting from the density-driven movement of a tidally trapped eddy and stratification-induced increases in ebb–flood frictional phasing. Complex bathymetry makes salinity exchange scale differently with flow than would be expected from simple tidal asymmetry and gravitational circulation models.

Evidence for energetic electron and iondispersive microinjections in theEarth's magnetotail as far as 27 <i>R_E</i>

High energy and time resolution measurements of energetic electron and ion fluxes obtained by the DOK-2 experiment on board the Interball-tail satellite provide us the opportunity to study the short-lived (1–3min), localized, and often periodic and dispersive flux increases within the plasma sheet. We have deliberately selected and studied two intervals corresponding to the dawn and dusk magnetotail flanks. Dispersive electron (ion) bursts in the dawn side (dusk side) are observed from L=7 to L=27. These bursts, having an individual entity, are termed microinjections and are observed in radial distances greater than those predicted by the ``injection boundary model." In this paper we suggest that the dispersive fluxes at widely separated radial distances are produced by multiple pulsating isospectrum surfaces ordered in succession. At the inner edge of the plasma sheet, the isospectrum surface is considered by Sarafopoulos (2002) as a meandering injection boundary. Roughly, we estimate that the wavelength for an oscillating isospectrum surface is

A Unified Method of Estimating Longitudinal Dispersion in Estuaries

A procedure was developed to estimate the rate of longitudinal dispersion from the observed data and verified by applying it to both the narrow, partially-stratified estuary and the wide, well-mixed estuary. It was found that the dispersive flux is not proportional to the longitudinal salinity gradient (dS/dx) in estuaries and is most closely related to velocity, the advective flux and (dS/dx)2 rather than dS/dx. The results obtained from the procedure showed that negative longitudinal dispersion can occur especially in flood tide. It was investigated whether the dispersion coefficient estimated from observed salinity data can be applied to the prediction of a water quality, such as dissolved oxygen, BOD, ammonia or temperature. The observed dispersion coefficients were successfully applied in a water quality model.