an order of magnitude larger than expected. Much of the Iberian shelf edge thus appears to have a larger than expected internaltide. The apparently ubiquitous presence of the large 0.5 h period sinusoidal internal waves is a surprise—it is more usual to observe packets of high frequency waves of depression at a shelf edge. SAR images (e.g. Fig. 8) suggest that the internal wave regime off Galicia is more chaotic than that observed at 41°N, or in other parts of the world. It is possible that internaltidegeneration is complicated by a response involving the Galicia Bank and three-dimensional features along the shelf edge. Since the dissipation measurements at the fixed station were conducted during spring tides the observed values prob- ably represent an upper bound for this part of the shelf. However, this cannot be certain given the rather unusual nature of the internal wave regime.
The internaltide manifests itself as a beam, propa- gating away from the shelf break (Fig. 2a). The beam has a slope that corresponds to the analytical expression for internal-wave characteristics, here in hydrostatic form: s = (ω 2 − f 2 ) 1/2 /N . We compare the outcome of our modal model with that of a fully numerical internal-tidegeneration model, described by Gerkema et al. (2004), which too is lin- ear and hydrostatic; the result from this model, for the same parameter values, is shown in Fig. 2b. We see that the an- gle of propagation as well as the intensity of the cross slope baroclinic current are in good agreement. This means that the modal model performs well even if the topographic scale is fairly short, since here it is even shorter than the internal-tide wavelength (the wavelength of the first mode being equal to the distance between two consecutive surface reflections of the beam). This confirms the expectation expressed in the In- troduction, that the WKB-type derivation in practice remains valid well beyond its formal range of validity.
three-dimensional complexity of the internaltidegeneration can be resolved by numerical models, including global realistic models such as the Hybrid Coordinate Ocean Model (HYCOM, Bleck 2002; Chassignet et al. 2003; Halliwell 2004), and regional models such as the MIT Ocean General Circulation Model (MITgcm, Marshal et al. 1997) and the Regional Ocean Modeling System (ROMS, Song and Haidvogel 1994; Song and Wright 1998; Shchepetkin and McWilliams 2003, 2005). Depending on the internal wave modes, semidiurnal internal tides on continental shelves can have a wave length ranging from O(10) km to O(100) km, which is much larger than the scale of water depth. Because of this, the fluid acceleration is much more pronounced in the horizontal direction, resulting from the wave amplitude. The vertical acceleration from nonhydrostatic pressure is comparatively small. The nonhydrostatic pressure becomes important only when the internal wave length becomes comparable to the water depth. Thus, most internaltide models are hydrostatic models, such as the Regional Ocean Modeling System (ROMS, e.g. Moore et al. 2004; Di Lorenzo et al. 2006; Buijsman et al 2011; Osborne et al. 2011) used in this study.
Internal revenue generation has over the year remained the main focus of all local government in Nigeria, indeed the entire administration of local government are informed by the important role play by internal revenue generation in their society. This is due to the issue of finance that has been the major problem which local government in Nigeria is grappling with in recent times, however, many of them have made attempt to exploit economics potentials of their area which are in abundance, to finance their activities and enhance their development. Thus, however, the effort made some problems still impede effective and efficient revenue generation in local government setting.
The generation of vertical fine structure by inertia-gravity internal waves in a two-dimensional stratified shear flow is investigated. In the linear approxi- mation, the boundary value problem for the amplitude of the vertical velocity of internal waves has complex coefficients, the imaginary part of which is small. The wave frequency and the eigenfunction of the boundary problem for the internal waves are complex (and we show that a weak damping of the wave occurs). The phase shift between the fluctuations of density and vertical velocity differs from π/2; therefore, the wave-induced vertical mass flux is non-zero. It is shown that dispersion curves are cut off in the low-frequency domain due to the influence of critical layers, where the frequency of the wave with the Doppler shift is equal to the inertial one. The Stokes drift ve- locity is determined in the weakly nonlinear approximation, on the second order in the amplitude of the wave. The vertical component of the Stokes drift velocity is also non-zero and contributes to wave transfer. The summary wave mass flux exceeds the turbulent one and leads to irreversible deformation of the average density profile which can be interpreted like a fine structure gen- erated by the wave. On the shelf, this deformation is more than in deep-water part of the Black Sea at the same amplitude of а wave. The vertical scale of the fine structure of Brunt-Väisälä frequency, generated by a wave, corresponds to really observed value.
Extensive observations performed in the last decade have provided much information on the properties of internal solitary waves in the South China Sea. In mooring observations, waves are generated in the Luzon Strait and propagate westward across the deep basin of the northern South China Sea in clusters (Ramp et al., 2004; Duda and Rainville, 2008). Waves last for 7-8 days in each cluster, and no waves are observed for 5 days between clusters. Two types of waves are observed at a particular mooring each day: type-A waves arrive at the same time each day and type-B waves arrive one hour later. Ramp et al. (2004) found that waves are generated around the time of the spring tides. Later with 10 moorings spanning from the Luzon Strait to the upper continental slope, Alford et al. (2010) further studied the arrival time, speed, width, energy, amplitude, and number of trailing waves. They confirmed the findings of Ramp et al. (2004) that waves occur twice daily in a particular pattern of narrower type-A waves alternating with wider, smaller type-B waves. Waves begin as broad internal tides close to the ridges in the Luzon Strait, steepening to 3– 10 km wide in the deep basin and 200–300 m on the upper slope. In the deep basin, type-A waves propagate faster than type-B waves and speeds of both types of waves are higher than the phase speed of linear waves. However, type-B waves propagate faster than type-A waves on the continental slope.
Abstract. The tides for the Mediterranean Sea are described through a high resolution model (MEDI10) developed by as- similation of tide-gauge data and T/P data into a barotropic ocean tide model. Tidal parameters from 56 coastal tide- gauge stations around the Mediterranean for eight principal constituents: M2, S2, N2, K2, K1, O1, P1 and Q1 and from 20 stations for M2, S2, K1, O1 are included in the model. TOPEX/Poseidon data with all corrections applied except for the ocean tides and bathymetry from TOPO 13.1 were used for development of the model. Numerical experiments were carried out for the estimation of the friction velocity and of the decorrelation length scale. The experiments related to the friction velocity showed that the use of spatially varying fric- tion velocity, estimated as a function of position in the model domain, gives better results than a constant value. The exper- iments related to the estimation of the decorrelation length suggest that the results are not sensitive for lengths close to ten times the length of the grid cell. The assessment of the model is based on ten tide-gauge observations that are not used for the assimilation. Comparisons were carried out with contemporary published global or regional models. The final solution is computed using 76 selected coastal tide-gauge sta- tions. The comparison between the observed and the model constituents results in a Root Sum of Squares (RSS) equal to 1.3 cm.
In this paper, after reviewing the two most commonly used classical methods of elliptic grid generation, a new elliptic grid generation method was proposed. In this method the general idea was similar to the previous methods; solving a multi- dimensional interpolation problem, but the interpolants were different parameters. In the simple differential method presented, an initial grid was deformed to conform to the given physical boundaries and the differences between coordinates of boundary nodes of an initial grid and the final grid are used as interpolants. Two poison equations are introduced as grid generation equations and the boundary conditions are the interpolants discussed. FDM scheme in one step and FVM scheme in both one step and multi steps have been used to solve the equations and the skewness diagram is presented to study the smoothness of final grids better. FVM solver generates smoother grids with better quality especially in complex geometries and with a partially adapted grid as an initial grid. As a result, it can be mentioned that the proposed
the background of oceanic internal wave spectra, over which intense processes of internal wave generation occur leading to the appearance of large-amplitude (up to extreme values of 500 m) internal waves (Alford et al., 2015). Data of the large- amplitude internal waves in various areas of the World Ocean are collected in numerous papers (Apel et al., 1985; Salusti et al., 1989; Holloway et al., 1999; Morozov, 1995, 2018; Ramp et al., 2004; Sabinin and Serebryany, 2007; Shroyer et al., 2011; Xu and Yin, 2012; Kozlov et al., 2014; Xu et al., 2016). For example, extreme waves of high amplitudes in the Strait of Gibraltar and Kara Gates Strait were analyzed in Morozov et al. (2002, 2003, 2008). Large-amplitude internal waves are of interest to researchers due to their dangerous im- pact on offshore platforms (Fraser, 1999; Song et al., 2011), their influence on safety of submarines and underwater vehi- cles (Osborn, 2010), and the fact that they also cause phase fluctuations of acoustic signals over large distances (Warn- Varnas et al., 2003; Rutenko, 2010; Si et al., 2012). Special warning systems are developed now in regions of high risk of a pipe and platform damage by intense internal waves (Stöber and Moum, 2011).
Tides are very often neglected or taken for granted, “they are just the sea advancing and retreating once or twice a day.” The Ancient Greeks and Romans weren’t particularly concerned with the tides at all, since in the Mediterranean they are almost imperceptible. It was this ignorance of tides that led to the loss of Caesar’s war galleys on the English shores, he failed to pull them up high enough to avoid the returning tide.
exerts the greater pull on Earth. The most extreme tides, called spring tides, occur during full and new moons when Earth, moon, and sun are in a line. During quarter and three quarter moons, the moon, Earth and sun form a right angle and the tidal range (the difference between high and low tides) is the smallest. These tides are called neap tides. Most areas have two low and two high waters per day with one set of high and low more extreme than the others. This is called a mixed semidiurnal tide (mixed because the two tide cycles are uneven and semidiurnal because there are two sets per day). The two high and low water levels occur over approximately 24 hours with each high and low approximately six hours apart. Tide cycles actually occur over a lunar day, which is 24 hours and 50 minutes long. The two low tides in a day occur on average every 12 hours 25 minutes. The time of the first low tide each day occurs on average approximately 50 minutes later than the day before. Local topographic features may cause these times to vary.
2013; Johnston and Rudnick, 2015; Boettger et al., 2015; Hall et al., 2017a), including the calculation of energy fluxes using current velocity measurements from gliders equipped with ADCPs (Johnston et al., 2013, 2015). However, ADCPs are not routinely integrated with commercially available glider platforms (Seaglider, Slocum, and SeaExplorer), in part due to their higher power requirement. Synergy with moored ADCP data allows accurate calculation of internaltide energetics without the endurance limitations and data analysis complexities of an ADCP-equipped glider (e.g., Todd et al., 2017).
The separation of spatial and temporal variability is a com- mon problem when interpreting glider data due to their slow speed (Rudnick and Cole, 2011) and imperfect positioning. In this context, the inability of the glider to perfectly hold sta- tion by the ADCP mooring leads to error in the calculation of internaltide energy flux (Sect. 3) due to mis-sampling of the spatially and temporally varying density field. An under- standing of this error is important for both mission planning and interpretation of results. Other missions along the Eu- ropean continental slope (e.g. Hall et al., 2017a) have shown that a glider operating as a virtual mooring by repeatedly div- ing to 1000 m around a fixed station can maintain a “watch circle” with a diameter of approximately 5 km, i.e. all dives
Abstract. In this paper we present a novel method to deter- mine the time of occurrence of tidal slack with a GPS re- ceiver mounted on an anchored buoy commonly used to de- lineate shipping lanes in estuaries and tidal channels. Slack tide occurs when the tide changes direction from ebb to flood flow or from flood to ebb. The determination of this point in time is not only useful for shipping and salvaging, it is also important information for calibrating tidal models, for deter- mining the maximum salt intrusion and for the further refine- ment of the theory on tidal propagation. The accuracy of the timing is well within 10 min and the method – able to oper- ate in real time – is relatively cheap and easy to implement on a permanent basis or in short field campaigns.
Abstract. Due to the space-borne missions CoRoT and Kepler, noteworthy breakthroughs have been made in our understanding of stellar evolution, and in particular about the angular momentum redistribution in stellar interiors. Indeed, the high-precision seismic data provide with the measurement of the mean core rotation rate for thousands of low-mass stars from the subgiant branch to the red giant branch. All these observations exhibit much lower core rotation rates than expected by current stellar evolution codes and they emphasize the need for an additional transport process. In this framework, internal gravity waves (herefater, IGW) could play a signifivative role since they are known to be able to transport angular momentum. In this work, we estimate the efficiency of the transport by the IGW that are generated by penetrative convection at the interface between the convective and the radiative regions. As a first step, this study is based on the comparison between the timescale for the waves to modify a given rotation profile and the contraction/expansion timescale throughout the radiative zone of 1.3M stellar models. We show that IGW, on their own, are inefficient to slow down the
Abstract - The present scenario of the automotive and agricultural sectors is fairly scared with the depletion of fossil fuel. The researchers are working towards to find out the best replacement for the fossil fuel; if not at least to offset the total fuel demand. In regards to emission, the fuel in the form of gaseous state is much than liquid fuel. By considering the various aspects of fuel, hydrogen is expected as a best option when consider as a gaseous state fuel. It is identified as a best alternate fuel for internal combustion engines as well as power generation application, which can be produced easily by means of various processes. The hydrogen in the form of gas can be used in the both spark ignition and compression ignition engines for propelling the vehicles. The selected fuel is much cleaner and fuel efficient than conventional fuel. The present study focusing the various aspects and usage of hydrogen fuel in S.I engine and C.I engine.