A tidally driven fjord-like strait close to an amphidromic region

Abstract. The strait studied in this paper, “Sundalagið Norður”, is the northern part of a narrow body of seawater separating the two largest islands in the Faroe Islands (Faroes). It has shallow sills in both ends and considerably deeper waters in between. South of the southern end of the strait there is an amphidromic region for the semidiurnal tides so that the tidal range is much lower south of the strait than north of it. The resulting tidal forcing generates periodically varying inflow of seawater across the northern sill, but only a part of that manages to cross the narrow and shallow southern sill. Combined with a large input of freshwater, this gives the strait a fjord-like character. To investigate how this fjord-like character affects the circulation within the strait and its exchanges with outside waters, a pilot project was initiated to simulate the dynamics of the strait with a high-resolution ocean model for a month. The model simulations show clearly the dominance of tidal forcing over freshwater (estuarine) and wind on timescales up to a day. On longer timescales, the simulations indicate systematic variations in the net flows (averaged over a diurnal tidal period) through both the upper and deeper layers. These long-period variations of net flow in the model simulations are forced by sea level differences between both ends of the strait generated by the dominant fortnightly and monthly tidal constituents (Mf, MSf, Mm, MSm). Harmonic analysis of sea level records from two tide gauges located off each end of the strait demonstrates that this behaviour is not a model artefact and it has pronounced effects on the strait. Not only does it induce long-period (mainly fortnightly) variations in the net flow through the strait, but it also generates variations in the estuarine characteristics. According to the model simulations, periods with net southward flow, typically lasting a week, have a strait-like character with net southward flow almost everywhere. Periods with net northward flow, in contrast, have a more fjord-like character with stronger salinity stratification and a southward counter-flow in the deep layer. This also induces a large difference in renewal rate of the deep water between the two periods, which is important to consider for human utilization of the strait, especially the local aquaculture plant. The combination of topographic, freshwater, and tidal characteristics creating these long-period variations is rather unusual, and it is not known whether similar systems exist elsewhere, but the long-period variations tend to be masked by the stronger semidiurnal and diurnal variations and may easily be overlooked.

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Annual and interannual sea level variations in the Indian Ocean from TOPEX/Poseidon observations and ocean model simulations

Journal of Geophysical Research Atmospheres ◽

10.1029/1999jc900231 ◽

2000 ◽

Vol 105 (C1) ◽

pp. 975-994 ◽

Cited By ~ 23

Author(s):

Sujit Basu ◽

Steven D. Meyers ◽

James J. O'Brien

Keyword(s):

Indian Ocean ◽

Sea Level ◽

Ocean Model ◽

Model Simulations ◽

The Indian Ocean ◽

Sea Level Variations

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LONG-PERIOD VARIATIONS IN SEASONAL SEA-LEVEL PRESSURE OVER THE NORTHERN HEMISPHERE1

Monthly Weather Review ◽

10.1175/1520-0493(1971)099<0049:lvissp>2.3.co;2 ◽

1971 ◽

Vol 99 (1) ◽

pp. 49-66 ◽

Cited By ~ 18

Author(s):

A. JAMES WAGNER

Keyword(s):

Sea Level ◽

Sea Level Pressure ◽

Level Pressure ◽

Long Period ◽

Period Variations

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Small-Amplitude, Short-Period Variations in the Speed of a Tide-Water Glacier in South-Central Alaska, U.S.A.

Annals of Glaciology ◽

10.1017/s0260305500007175 ◽

1989 ◽

Vol 12 ◽

pp. 187-191 ◽

Cited By ~ 13

Author(s):

Roy A. WaIters

Keyword(s):

Sea Level ◽

Water Pressure ◽

Perturbation Expansion ◽

Field Work ◽

Data Set ◽

Tidal Period ◽

South Central ◽

Short Period ◽

Period Variations ◽

Melt Water

An analysis of field data for the lower reach of Columbia Glacier, Alaska, U.S.A., indicates that, during the time of the field work, glacier-speed variations in the tidal frequency range are dependent on tidal period variations in sea-level at the terminus, and diurnal period variations in melt-water input at the surface. A simple model based on a perturbation expansion of the flow equation provides a suitable framework in which to understand the observations. Variations in sea- level cause variations in the normal stress at the terminus and are transmitted up the glacier by way of the longitudinal stress. The variations in melt-water input affect glacier speed, presumably through changes in basal water pressure. The data set does not allow a detailed analysis of the relation between melt-water input, basal water pressure, and speed.

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Small-Amplitude, Short-Period Variations in the Speed of a Tide-Water Glacier in South-Central Alaska, U.S.A.

Annals of Glaciology ◽

10.3189/s0260305500007175 ◽

1989 ◽

Vol 12 ◽

pp. 187-191 ◽

Cited By ~ 4

Author(s):

Roy A. WaIters

Keyword(s):

Sea Level ◽

Water Pressure ◽

Perturbation Expansion ◽

Field Work ◽

Data Set ◽

Tidal Period ◽

South Central ◽

Short Period ◽

Period Variations ◽

Melt Water

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Long-period variations of sea-level in Australasia

Geophysical Journal International ◽

10.1111/j.1365-246x.1986.tb04545.x ◽

1986 ◽

Vol 87 (1) ◽

pp. 43-54 ◽

Cited By ~ 54

Author(s):

J. I. Pariwono ◽

J. A. T. Bye ◽

G. W. Lennon

Keyword(s):

Sea Level ◽

Long Period ◽

Period Variations

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Turning the tide: comparison of tidal flow by periodic sea level fluctuation and by periodic bed tilting in scaled landscape experiments of estuaries

Earth Surface Dynamics ◽

10.5194/esurf-5-731-2017 ◽

2017 ◽

Vol 5 (4) ◽

pp. 731-756 ◽

Cited By ~ 3

Author(s):

Maarten G. Kleinhans ◽

Maarten van der Vegt ◽

Jasper Leuven ◽

Lisanne Braat ◽

Henk Markies ◽

...

Keyword(s):

Sea Level ◽

Tidal Currents ◽

Surface Flow ◽

Water Levels ◽

Tidal Range ◽

Level Fluctuation ◽

Tidal Period ◽

Sea Level Fluctuations ◽

Sediment Mobility ◽

Sea Level Fluctuation

Abstract. Analogue models or scale experiments of estuaries and short tidal basins are notoriously difficult to create in the laboratory because of the difficulty to obtain currents strong enough to transport sand. Our recently discovered method to drive tidal currents by periodically tilting the entire flume leads to intense sediment transport in both the ebb and flood phase, causing dynamic channel and shoal patterns. However, it remains unclear whether tilting produces periodic flows with characteristic tidal properties that are sufficiently similar to those in nature for the purpose of landscape experiments. Moreover, it is not well understood why the flows driven by periodic sea level fluctuation, as in nature, are not sufficient for morphodynamic experiments. Here we compare for the first time the tidal currents driven by sea level fluctuations and by tilting. Experiments were run in a 20  ×  3 m straight flume, the Metronome, for a range of tilting periods and with one or two boundaries open at constant head with free inflow and outflow. Also, experiments were run with flow driven by periodic sea level fluctuations. We recorded surface flow velocity along the flume with particle imaging velocimetry and measured water levels along the flume. We compared the results to a one-dimensional model with shallow flow equations for a rough bed, which was tested on the experiments and applied to a range of length scales bridging small experiments and large estuaries. We found that the Reynolds method results in negligible flows along the flume except for the first few metres, whereas flume tilting results in nearly uniform reversing flow velocities along the entire flume that are strong enough to move sand. Furthermore, tidal excursion length relative to basin length and the dominance of friction over inertia is similar in tidal experiments and reality. The sediment mobility converges between the Reynolds method and tilting for flumes hundreds of metres long, which is impractical. Smaller flumes of a few metres in length, on the other hand, are much more dominated by friction than natural systems, meaning that sediment suspension would be impossible in the resulting laminar flow on tidal flats. Where the Reynolds method is limited by small sediment mobility and high tidal range relative to water depth, the tilting method allows for independent control over the variables flow depth, velocity, sediment mobility, tidal period and excursion length, and tidal asymmetry. A periodically tilting flume thus opens up the possibility of systematic biogeomorphological experimentation with self-formed estuaries.

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The Tampa Bay Coastal Ocean Model Performance for Hurricane Irma

Marine Technology Society Journal ◽

10.4031/mtsj.52.3.6 ◽

2018 ◽

Vol 52 (3) ◽

pp. 33-42 ◽

Cited By ~ 4

Author(s):

Jing Chen ◽

Robert H. Weisberg ◽

Yonggang Liu ◽

Lianyuan Zheng

Keyword(s):

Continental Shelf ◽

Sea Level ◽

Coastal Ocean ◽

Ocean Model ◽

Tampa Bay ◽

Water Levels ◽

Model Simulations ◽

Coastal Ocean Model ◽

Hurricane Irma

AbstractThe Tampa Bay response to Hurricane Irma in September 2017 is analyzed using a combination of in situ observations and numerical model simulations. The observations include winds and water levels from in situ recording stations. The model simulations are by the Tampa Bay Coastal Ocean Model (TBCOM), which downscales from the continental shelf to the estuary by nesting the unstructured grid, Finite-Volume, primitive equation Community Ocean Model (FVCOM) in the West Florida Coastal Ocean Model, which in turn downscales from the deep ocean across the continental shelf by nesting FVCOM in the Gulf of Mexico Hybrid Coordinate Ocean Model. Both the observations and the model simulations show a rapid negative storm surge (a setdown of sea level) followed by a positive surge associated with the change of wind direction. The initial forecast underestimates the magnitude of the negative surge. After adjusting for the difference between the winds actually observed compared with the original forecast winds, the hindcast sea level simulation very closely matches the observations. These findings imply that a massive exchange of water occurred between Tampa Bay and the adjacent continental shelf as the hurricane passed by the region. A large portion of the bay water was flushed out to the south, to be replaced by new waters advected in from the along the coast to the north.

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On nearly-commensurable periods in the restricted problem of three bodies, with calculations of the long-period variations in the interior 2:1 case

Symposium - International Astronomical Union ◽

10.1017/s0074180900105480 ◽

1966 ◽

Vol 25 ◽

pp. 197-222 ◽

Cited By ~ 4

Author(s):

P. J. Message

Keyword(s):

Periodic Solution ◽

Periodic Solutions ◽

Large Amplitude ◽

Restricted Problem ◽

Small Amplitude ◽

Minor Planets ◽

Long Period ◽

Numerical Integrations ◽

Period Variations ◽

The Mean

An analytical discussion of that case of motion in the restricted problem, in which the mean motions of the infinitesimal, and smaller-massed, bodies about the larger one are nearly in the ratio of two small integers displays the existence of a series of periodic solutions which, for commensurabilities of the typep+ 1:p, includes solutions of Poincaré'sdeuxième sortewhen the commensurability is very close, and of thepremière sortewhen it is less close. A linear treatment of the long-period variations of the elements, valid for motions in which the elements remain close to a particular periodic solution of this type, shows the continuity of near-commensurable motion with other motion, and some of the properties of long-period librations of small amplitude.To extend the investigation to other types of motion near commensurability, numerical integrations of the equations for the long-period variations of the elements were carried out for the 2:1 interior case (of which the planet 108 “Hecuba” is an example) to survey those motions in which the eccentricity takes values less than 0·1. An investigation of the effect of the large amplitude perturbations near commensurability on a distribution of minor planets, which is originally uniform over mean motion, shows a “draining off” effect from the vicinity of exact commensurability of a magnitude large enough to account for the observed gap in the distribution at the 2:1 commensurability.

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