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The influence of Typhoon Kalmaegi on internal waves near the Dongsha Islands in the northeastern South China Sea was investigated using mooring observation data. We observed, for the first time, that the phenomenon of regular variation characteristics of the 14-d spring-neap cycle of diurnal internal tides (ITs) can be regulated by typhoons. The diurnal ITs lost the regular variation characteristics of the 14-d spring-neap cycle during the typhoon period owing to the weakening of diurnal coherent ITs, represented by O1 and K1, and the strengthening of diurnal incoherent ITs. Results of quantitative analysis showed that during the pre-typhoon period, time-averaged modal kinetic energy (sum of Modes 1–5) of near-inertial internal waves (NIWs) and diurnal and semidiurnal ITs were 0.62 kJ/m2, 5.66 kJ/m2, and 1.48 kJ/m2, respectively. However, during the typhoon period, the modal kinetic energy of NIWs increased 5.11 times, mainly due to the increase in high-mode kinetic energy. At the same time, the modal kinetic energy of diurnal and semidiurnal ITs was reduced by 68.9% and 20%, respectively, mainly due to the decrease in low-mode kinetic energy. The significantly reduced diurnal ITs during the typhoon period could be due to: (1) strong nonlinear interaction between diurnal ITs and NIWs, and (2) a higher proportion of high-mode diurnal ITs during the typhoon period, leading to more energy dissipation. [ABSTRACT FROM AUTHOR]

Abstract Strong tidal currents in and around the narrow straits of the Lesser Sunda Islands, Indonesia, affect ocean sea surface temperatures (SST) via non-linear tide-induced mixing. A fortnightly spring–neap cycle in tidal currents can induce a similar cycle in SST, which has been observed to occur in and south of Lombok Strait. Here we report on an atmospheric response to the fortnightly SST cycle which is detected in relative humidity and air temperature measurements at Bali. The fortnightly cycles in both the ocean SST and the Bali atmospheric data have a strong seasonal cycle, with peak signals occurring during boreal summer.

25-hour time series measurements of vertical salinity profiles and currents in Zuari estuary were done during both spring and neap tidal cycles of pre-monsoon (April-May), south-west monsoon (June-September) and post-monsoon (October-December) seasons during 2011 at four different stations along the estuary. Measurements were done at locations, near the mouth (called the bay station), lower middle estuary, upper middle estuary and upstream. Based on these observations, variations in stratification at different time scales (daily, spring-neap cycle and seasonal) are described. In the mixed tidal regime with semi-diurnal dominance, stratification at higher low water succeeding lower high water is more intense than that at lower low water succeeding higher high water over a tidal cycle. During pre-monsoon, when river discharge is negligible, the spring-neap cycle hardly causes any change in peak stratification factor (stratification factor, Δ S, is difference between the bottom and surface salinity), attained within a tidal cycle at the bay and upstream stations. However, during spring, the peak stratification factor (Δ S) of lower and upper mid-estuarine stations decreases by about two and one, respectively. During monsoon at the lower middle estuary station, salinity value peaks only at high water which is similar to the pre-monsoonal conditions at the upstream station. High stratification observed during high waters at the lower middle estuary during monsoon weakens marginally at the peak of the high waters, during both spring and neap phases. Due to the incursion of high-saline downstream water along the bottom, the bottom water gets saturated slightly before the peak of high water. Because of this, the salinity of bottom layer remains constant for about 2-3 h, while the surface salinity still continues to increase up to the peak of high water, resulting in the weakening of stratification. Moreover, during monsoon, the magnitude of the flood flow progressively reduced from mouth to upstream and no flood flow was observed at the upstream station. Variation of computed potential energy anomaly is found to match with that of stratification factor (Δ S) closely. [ABSTRACT FROM AUTHOR]

Tidal fronts are associated with the transition between homogeneous and vertically stratified water and are characterized by the simultaneous availability of light and nutrients that enhance the growth of marine productivity. We study the variability in the position of two tidal fronts located in Patagonia Argentina: the San Matías and Valdés fronts. The rate of tidal dissipation in these regions is among the highest of the world oceans. The study is based on the analysis of over 1200 satellite derived sea surface temperature images. The results indicate that the mean monthly position of both fronts is strongly linked to the characteristics of the bottom topography. In response to increasing surface heat flux the fronts displace toward shallower areas. Similarly, a slight displacement towards deeper waters is observed when the heat flux decreases. High frequency variability is revealed by the standard deviation around monthly averages. At the mouth of the San Matías gulf, the front location variability in the spring–neap cycle is around 10 km, while east of the Valdés Peninsula the fortnightly cycle is masked by high frequency fluctuations (~30 km) governed by meanders and meso-scale filaments. A simple conceptual model is proposed which suggests that the mean frontal position is determined by the bottom topography while its seasonal variability is driven by the surface heat flux, and the front intensity is modulated by the spring–neap transition. [ABSTRACT FROM AUTHOR]

Two questions are raised with regard to interpretation of tidal bundles. 1. Does the thick-thin alternation of foreset laminae generally represent semi-diurnal tide? 2. Is it a valid inference that the packages of mud-draped foresets, which occur in alternation with packages of foresets devoid of mud-drapes in a cross-set, denote neap periods? Under certain circumstances (1) thick-thin alternation can develop in a diurnal tidal regime, and (2) packages of mud-draped foresets may form during spring periods. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism thought to be responsible for the observed fortnightly modulation of estuarine circulation in Tokyo Bay was investigated in December 1998 using a two-layer theoretical model, which was verified using a three-dimensional non-hydrostatic model. The influence of the difference in kinetic energy between the upper and lower layers on estuarine circulation was clarified in terms of vorticity, which was defined by the difference in the velocities of the two layers. The ratio of the difference in kinetic energy between the two layers to the baroclinic energy was attributed to the change in strength of estuarine circulation. Thus, the mechanism for fortnightly modulations of estuarine circulation may be due to the suppression of upper-water withdrawal during spring tide, when the ratio is more than 1, and the enhancement of upper-water withdrawal during neap tide, when the ratio is close to 0. [Copyright &y& Elsevier]

The Great Bay Estuarine System, in New Hampshire, USA, has been the focus area for an attempt to develop a robust finite element method model for estuarine hydrodynamics. Past studies used a nonlinear, time stepping, kinematic model with limited success (Ip et al. Advances in fluid mechanics III, WIT, Southampton (2000) 569; Bilgili et al. J. Geophys. Res. – Oceans 107 (2002); Ertu¨rk et al. Estuar. Coast. Shelf Sci. 47 (1998) 119). We add dynamic physics (that is, local accelerations) for deep-water areas and keep kinematic physics (that is, without local and advective accelerations), with the inclusion of a porous medium beneath the open channel, for shallow and dewatering areas. The choice of which physics set to apply is made on an elemental depth dependent basis. The addition of the local acceleration terms for deep-water areas is seen to greatly improve accuracy in matching of tidal phasing over previous studies. Simulations involving M2/M4/M6 tidal constituents result in strong agreement to observed data from the 1975 Great Bay field program (Swift & Brown, Estuar. Coast. Shelf Sci. 17 (1983) 297), in terms of both tidal heights and cross-section averaged velocities. Comparisons with 10 tidal elevation observation stations and four cross-section averaged current transects show good agreement, displaying average normalized root mean square misfit values of 0.08 and 0.25, respectively. Study of the simulated momentum balance shows the size of the contributions from acceleration terms to be on the order of a third the size of the contributions from the pressure gradient and bottom stress terms. Although relatively small, they are observed to peak at the crucial time of tidal reversal. Application of the model for long-term simulation using an M2/N2/S2 forcing shows the ability to realistically capture the spring–neap cycle. The tidally rectified flow is generally described as a constant spatial pattern with overall amplitude modulation following the spring–neap cycle. [Copyright &y& Elsevier]

In order to estimate daily ration of juvenile Pomatoschistus lozanoi and to evaluate the effect of tide and daylight on its feeding activity, two 24-h samplings were performed, one (in 1985) with high water around midnight, the other (in 1986) with low water around midnight. Incidently, the sampling in 1985 was around neap tide and in 1986 it was around spring tide. The fish were observed to feed more intensively during the night. Daily ration in 1985 was estimated to be about 1% of body ash-free dry weight (ADW). For 1986, the estimate is about 5% of body ADW in spite of similar water temperatures at both sampling dates. It is suggested that a semilunar rhythm, either in the fish or in the invertebrate prey, is the basis of the observed difference. This phenomenon may also explain the prominent 14-ring bands observed in the otoliths. Because of the influence of the various rhythms on feeding activity in fishes living in a strongly tidal environment, an accurate estimate of daily ration from production estimates and a P:C ratio established in the laboratory may be logistically less demanding than an estimate from stomach-content data. [ABSTRACT FROM PUBLISHER]

Strong tidal currents in and around the narrow straits of the Lesser Sunda Islands, Indonesia, affect ocean sea surface temperatures (SST) via non-linear tide-induced mixing. A fortnightly spring–neap cycle in tidal currents can induce a similar cycle in SST, which has been observed to occur in and south of Lombok Strait. Here we report on an atmospheric response to the fortnightly SST cycle which is detected in relative humidity and air temperature measurements at Bali. The fortnightly cycles in both the ocean SST and the Bali atmospheric data have a strong seasonal cycle, with peak signals occurring during boreal summer. [ABSTRACT FROM AUTHOR]

Abstract: The present paper comments on a recent publication by Woodworth et al. [Woodworth, P.L., Blackman, D.L., Pugh, D.T., Vassie J.M., 2005. On the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi-diurnal tide. Estuarine, Coastal and Shelf Science 64 (2–3), 235–240.]. It is shown how tidal asymmetries associated with astronomical tides can be accounted for in an extreme sea level analysis, despite the difficulty of deriving probability distribution functions if a large number of tidal constituents are considered. The use of the term spring–neap cycle in a diurnal tidal regime is discussed. [Copyright &y& Elsevier]