Bjørn Gjevik

• Bondevik, Stein; Gjevik, Bjørn & Sørensen, Mathilde B. (2013). Norwegian seiches from the giant 2011 Tohoku earthquake. Geophysical Research Letters.  ISSN 0094-8276.  40(13), s 3374- 3378 . doi: 10.1002/grl.50639
• Lynge, Birgit Kjoss; Hjelmervik, Karina Bakkeløkken & Gjevik, Bjørn (2013). Storm surge and tidal interaction in the Tjeldsund channel, northern Norway. Ocean Dynamics.  ISSN 1616-7341.  63(7), s 723- 739 . doi: 10.1007/s10236-013-0625-1 Vis sammendrag

  The aim of this study is to investigate tide–surge interaction in narrow channels with complex and relatively shallow topography. A high-resolution depth-integrated tidal and storm surge model has been implemented for the Tjeldsund channel which is an important sailing lane in northern Norway. A horizontal grid resolution down to 50 m is applied in order to represent the complex bottom topography and the formation of jets and small-scale eddies. Two typically storm surge events in December 2004 have been examined in detail. The tide–surge interaction is found to influence the generation of higher harmonics and the formation of eddies in the current field. In some cases, the magnitude of storm surge currents may reach the same magnitude as the tidal currents enhancing the formation of jets and eddies.

• Teigen, Sigurd Henrik; Nilsen, Frank; Skogseth, Ragnheid; Gjevik, Bjørn & Beszczynska-Möller, A. (2011). Baroclinic instability in the West Spitsbergen Current. Journal of Geophysical Research (JGR): Oceans.  ISSN 2169-9275.  116 . doi: 10.1029/2011JC006974
• Lynge, Birgit Kjoss; Berntsen, J & Gjevik, Bjørn (2010). Numerical studies of dispersion due to tidal flow through Moskstraumen, northern Norway. Ocean Dynamics.  ISSN 1616-7341.  60(4), s 907- 920 . doi: 10.1007/s10236-010-0309-z
• Teigen, Sigurd Henrik; Nilsen, Frank & Gjevik, Bjørn (2010). Barotropic instability in the West Spitsbergen Current. Journal of Geophysical Research (JGR): Oceans.  ISSN 2169-9275.  115 . doi: 10.1029/2009JC005996
• Christensen, Ole; Kostylev, Vladimir; Longva, Oddvar; Thorsnes, Terje; Courtney, Robert C. & Gjevik, Bjørn (2009). Correlations of geological and biological elements in marine habitat mapping in glaciated areas; field tests from the coast of More and Romsdal County, western Norway. Norsk Geologisk Tidsskrift.  ISSN 0029-196X.  89(3), s 229- 246
• Pankratz, Normann; Natvig, Jostein Roald; Gjevik, Bjørn & Noelle, Sebastian (2007). High-order well-balanced finite-volume schemes for barotropic flows: Development and numerical comparisons. Ocean Modelling.  ISSN 1463-5003.  18, s 53- 79 . doi: 10.1016/j.ocemod.2007.03.005
• Gjevik, Bjørn; Hareide, D.; Lynge, B.K.; Ommundsen, A; Skailand, J.H. & Urheim, H.B. (2006). Implementation of High Resolution Tidal Current Fields in Electronic Navigational Chart Systems. Marine Geodesy.  ISSN 0149-0419.  29, s 1- 17
• Gjevik, Bjørn (2006). Flo og fjære langs kysten av Norge, I: Kaare Aksnes (red.),  Almanakk for Norge for året etter Kristi fødsel 2007.  Gyldendal Norsk Forlag A/S.  ISBN 8205354944.  Flo og fjære.  s 48 - 51
• Nilsen, F; Gjevik, Bjørn & Schauer, U (2006). Cooling of the West Spitsbergen Current: Isopycnal diffusion by topographic vorticity waves. Journal of Geophysical Research (JGR).  ISSN 0148-0227.  111
• Orre, Steinar; Gjevik, Bjørn & LaCasce, Joseph H. (2006). Characterizing chaotic dispersion in a coastal tidal model. Continental Shelf Research.  ISSN 0278-4343.  26, s 1360- 1374 . doi: 10.1016/j.csr.2005.11.015
• Thiem, Øyvind; Thiem, O; Berntsen, Jarle & Gjevik, Bjørn (2006). Development of eddies in an idealised shelf slope area due to an along slope barotropic jet. Continental Shelf Research.  ISSN 0278-4343.  26, s 1481- 1495
• Gjevik, Bjørn; Flather, R.A. & Hareide, D. (2004). Sea level oscillahions with 6-h period in the North Sea 29-31 October 2000. An analysis of data from stations in the northen North Sea and along the western coast of Norway. Ocean Dynamics.  ISSN 1616-7341.  54, s 477- 488 . doi: 10.1007/S10236-004-0093-8
• Davies, Alan M.; Xing, Jiuxing & Gjevik, Bjørn (2003). Barotropic eddy generation by flow instability at the shelf edge: Sensitvity to open boundary conditions, inflow and diffusion. Journal of Geophysical Research (JGR).  ISSN 0148-0227.  108(C2), s 17-1- 17-15
• Moe, Halvard; Gjevik, Bjørn & Ommundsen, Atle (2003). A high resolution tidal model for the coast of Møre and Trøndelag, Mid-Norway. Norsk Geografisk Tidsskrift.  ISSN 0029-1951.  57, s 65- 82
• Gjevik, Bjørn; Moe, Halvard & Ommundsen, Atle (2002). Idealized Model Simulations of Barotopic Flow on the Catalan Shelf. Continental Shelf Research.  ISSN 0278-4343.
• Gjevik, Bjørn; Moe, Halvard & Ommundsen, Atle (2002). Idealized model simulations of barotropic flow on the Catalan shelf. Continental Shelf Research.  ISSN 0278-4343.  22, s 173- 198 Vis sammendrag

  The effect of along shelf variation in shelf width on barotropic shelf edge flows and topographic shelf waves are investigated with a numerical model. The model topography represents a gradual transition from a narrow straight to a broader straight shelf region. It is designed primary to model the Catalan shelf on the northeastern Mediterranean coast of Spain, but the results obtained here are of general validity and will also apply to shelf flow under similar conditions elsewhere. The numerical experiments are carried out with flow imposed, both steady and oscillatory, at the upstream end of the narrow shelf region. With a prescribed shelf edge flow there is a strong tendency for topographic steering in the transition zone. The adjustment is found to take place on a short time scale of 2-5 days set by propagating wave modes rather than by advection. Bottom friction effects do not lead to significant on-shelf leakage of the flow. Flow instability and eddy formation are found to occur, even in cases where the potential vorticity for the imposed flow does not have a local maximum on the shelf slope. The instability leads to development of anticyclonic eddies on the narrow shelf which undergo strong non-linear adjustment at the transition zone from a narrow to a broader shelf. On the broad section of the shelf near the transition zone there is a tendency for formation of a large anticyclonic eddy. Bottom friction is found to influence the flow instability and the formation of eddies in cases where the flow is marginal for instability and growth of eddies. Particle tracking has been performed in order to study cross shelf mixing and transport. Finally we have studied the current response due to a concentrated wind stress jet acting perpendicular to the coast line in the transition zone between the narrow and the broad shelf regions. A dipolar eddy structure is found to develop with the axis of the dipole tilting about 30 degrees with the axis of the wind jet and with strong current shear in the zone near the dipole axis.

• Moe, Halvard; Ommundsen, Atle & Gjevik, Bjørn (2002). A high resolution tidal model for the area around The Lofoten Islands, Northern Norway. Continental Shelf Research.  ISSN 0278-4343.  22, s 485- 504 Vis sammendrag

  A depth-integrated numerical model with grid resolution 500 m has been used to simulate tides around The Lofoten Islands in northern Norway. The model spans more than 3 deg latitude and covers a sea area of approximately 1.2*10^5 km^2. The fine spatial resolution resolves the important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a large scale tidal model covering the Nordic Seas and implemented with the flow relaxation scheme (FRS). The semi-diurnal components M2, S2 and N2 and the diurnal component K1 are simulated. Harmonic constants for sea level are compared with observations from 21 stations. The best fit is found for the M2 component with a standard deviation between the observed and modelled amplitude and phase of 2.3 cm and 2.5 degrees, respectively. The standard deviation for the other smaller components ranges between 1.5 to 2.8 cm and 5.3 to 16.7 degrees. Current fields from the model are compared with observations in four locations; the Moskenes sound, the Gimsøy channel, the Tjeldsund channel and the Sortland channel. In the Sortland channel the model predicts a dominant diurnal K1 current in agreement with observations.

• Gjevik, Bjørn; Moe, Halvard & Ommundsen, Atle (1997). Sources of the Maelstrom. Nature.  ISSN 0028-0836.  388, s 837- 838
• Gjevik, Bjørn; Pedersen, Geir Kleivstul; Dybesland, Elen; Harbitz, Carl Bonnevie; Miranda, P.M.A.; Baptista, M.A.; Mendes-Victor, L.; Heinrich, P.; Roche, R. & Guesmia, M. (1997). Modeling tsunamis from earthquake sources near Gorringe Bank southwest of Portugal. Journal of Geophysical Research (JGR): Oceans.  ISSN 2169-9275.  102(C13), s 931- 949 . doi: 10.1029/97JC02179 Vis sammendrag

  The Azores-Gibraltar fracture zone with the huge bathymetric reliefs in the area southwest of Portugal is believed to have been the source of large historic tsunami events. This report describes simulations of tsunami generation and propagation from sources near the Gorringe Bank. The well-documented 1969 tsunami event is examined both with a ray-tracing technique and with finite difference models based on various shallow water equations. Both methods show that the most likely source location is southeast of the Gorringe Bank near the epicenter location determined from seismic data. The tsunami source is calculated by formulas given by Okada [1985] for surface deformation of an elastic half-space caused by faulting. Observed wave amplitude and travel time and values computed from an initial wave field according to Okada [1985] formulas show acceptable agreement for most stations along the coast of Portugal and Spain. However, in order to explain a large primary wave with downward displacement observed on the coast of Morocco, an alternative source model with a larger area of downward displacement has been introduced. This also leads to a better overall fit with observed travel time. Implications for disastrous events, as the one in 1755, are also discussed. Linear hydrostatic shallow water models are used for most of the simulations, but the importance of nonlinearity and dispersion is examined with the Boussinesq equations. The sensitivity of the solution to changes in the location and the strength of the source is discussed, and a series of grid refinement studies are performed in order to assess the accuracy of the simulations.

• Hackett, Bruce; Røed, Lars Petter; Gjevik, Bjørn; Martinsen, Eivind A. & Eide, Lars Ingolf (1995). A review of the Metocean Modeling Project (MOMOP) Part 2: Model validation study, In Daniel R. Lynch & Alan M. Davies (ed.),  Quantitative Skill Assessment for Coastal Ocean Models.  American Geophysical Union (AGU).  ISBN 0-87590-261-8.  14.  s 307 - 327 Vis sammendrag

  Two fully three-dimensional, primitive equation, baroclinic level models are applied to the mid-Norwegian shelf, and their simulations for a period in March 1988 are validated against observations from the NORCSEX'88 field experiment. The main concern is currents, but salinity and temperature fields are also compared. This validation study has elements not only for a model-data comparison, but also a model-model comparison. Thus, a model-model comparison verification study, using two idealized test cases appropriate for the Norwegian Shelf, is performed as a forerunner to the validation proper. A third, layered, model is also included in the verification study for comparison. The idealized test cases consider 1) the baroclinic response to the storm passage across a shelf and 2) flow over a sea mountain. The main difference between the model responses in these test cases lies in the spatial structure of the currents over long time scales, and is attributed to differences in the parameterizations of the horizontal and vertical eddy viscosities and bottom friction. The validation against data uses a hierarchical procedure, in which the overall features of the fields are compared first, followed by comparisons of more detailed features. Three specific comparison products are used here: transports through vertical sections, horizontal distributions and vertical distributions. It is concluded that both models are able to qualitatively generate many of the observed features of the flow, but neither is able to quantitatively reproduce the detailed currents. The model's successes are attributable to their inclusion of required mechanisms for generating and maintaining the currents on the shelf: the barotropic mode, baroclinic modes and nonlinearity. Their shortcomings are inaccurate placement and timing of the mesoscale features and overly weak gradients, especially in the vertical. These are mainly attributable to inadequate parameterizations of subgrid-scale turbulent mixing, to lack of horizontal resolution and to imperfect initial and boundary conditions.

• Røed, Lars Petter; Hackett, Bruce; Gjevik, Bjørn & Eide, Lars Ingolf (1995). A review of the Metocean Modeling Project (MOMOP) Part 1: Model comparison study, In Daniel R. Lynch & Alan M. Davies (ed.),  Quantitative Skill Assessment for Coastal Ocean Models.  American Geophysical Union (AGU).  ISBN 0-87590-261-8.  13.  s 285 - 305 Vis sammendrag

  Considered are the results of a model comparison study performed as part of the Metocean Modeling Project (MOMOP). The study involves the design of five test cases, relevant to the Norwegian Shelf, by which three-dimensional, baroclinic numerical ocean models can be verified. The first two of these are two-dimensional, in which processes connected to the geostrophic adjustment problem and wind-driven upwelling in a stratified ocean are considered. The remaining cases are three-dimensional and reveal the model's response to flow over a sea mountain (Case 3) and wind-driven flow in the presence of a shelf topography including a steep shelf slope (Cases 4 and 5). Six models participated, including level models, layered models and spectral (in the vertical) models. Two of the models are in sigma-coordinates. The remaining models are straightforward Cartesian coordinate models. The comparison exercise turned out to be as important for the development and design of appropriate test cases as for studying and comparing model results. It was concluded that only the upwelling case was appropriatly designed for the the desired physical processes, while the remaining test cases needed some modification. In retrospect, it would have been useful to test the design a priori using a proven model. Nevertheless, it was found that a model comparison study is a powerful verification tool, in particular for complex, nonlinear, baroclinic ocean models. Concerning the models themselves, it was felt that, given enough time and resources, most, if not all, of the models could have produced acceptable results.

• Harbitz, Carl Bonnevie; Pedersen, Geir Kleivstul & Gjevik, Bjørn (1993). Numerical Simulations of Large Water Waves due to Landslides. Journal of Hydraulic Engineering.  ISSN 0733-9429.  1119(12) . doi: 10.1061/(ASCE)0733-9429(1993)119:12(1325) Vis sammendrag

  A mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of slide generated waves in fjords. The equations are solved numerically by a finite difference technique. To examine the performance of the numerical model we have simulated the slide catastrophe in Tafjord, western Norway, 1934. The predicted runup heights are in good agreement with measured runup heights. The effects of wave amplification are estimated in runup zones with gentle beach slopes. The model results reveal wave energy trapping due to the fjord geometry. This causes standing wave oscillations in accordance with the observations.

• Martinsen, Eivind A.; Gjevik, Bjørn & Røed, Lars Petter (1979). A numerical model for long barotropic waves and storm surges along the western coast of Norway. Journal of Physical Oceanography.  ISSN 0022-3670.  9, s 1126- 1138
• Gjevik, Bjørn & Røed, Lars Petter (1976). Storm surges along the western coast of Norway. Tellus. Series A, Dynamic meteorology and oceanography.  ISSN 0280-6495.  28(2), s 166- 182 Vis sammendrag

  Storm surge situations along the western coast of Norway between 62oN and 68oN are examined. The observations show that large storm surges are caused by strong south westerly winds acting along a large section of the coast. This situation occurs when an intense low pressure center moves relatively close to the coast and in a direction nearly parallel to it. A model of surge generation by propagating wind fields acting along a straight coast is studied. Analytical solutions for the surge amplitude along the coast are obtained and discussed. The theory is applied to storm surge situations along the western coast of Norway, and it shows that the wind stress in the direction along the coast and the Coriolis force are important forces for the generation of large surges. The wind stress component normal to the coast (i.e., north westerly winds) and the changes in the atmospheric pressure contribute less to the surge.

Se alle arbeider i Cristin

• Gjevik, Bjørn (2009). Flo og fjære langs kysten av Norge og Svalbard. Farleia Forlag.  ISBN 978-82-998031-0-6.  351 s.
• Grue, John; Gjevik, Bjørn & Weber, Jan Erik (ed.) (1996). Waves and Nonlinear Processes in Hydrodynamics. Kluwer Academic Publishers.  ISBN 0-7923-4031-0.  402 s.

Se alle arbeider i Cristin

• Gjevik, Bjørn (2016). Ulykken på Ona i 1670 - Kan noe liknende skje i dag?, I: Jarle Sanden (red.),  Årbok 2016 Romsdalsmuseet- Naturkatastrofer.  Romsdalsmuseet.  ISBN 978-82-90251-94-4.  kapittel 3.  s 35 - 48
• Gjevik, Bjørn & Nilsen, Steinar (2014). Beretninger om linefiske på bankene utenfor Midt-NorgeBeretninger om linefiske på bankene utenfor Midt-Norge, I: Kolbjørn Aune & Eilert Bjørkvik (red.),  Årbok for Fosen 2014.  Fosen Historielag.  ISBN 978-82-90341-44-7.  Kapittel.  s 115 - 140
• Hjelmervik, Karina Bakkeløkken; Lynge, Birgit Kjoss & Gjevik, Bjørn (2013). Modelling of tides and storm surges in Theldsund channel.
• Bondevik, Stein; Sørensen, Mathilde B. & Gjevik, Bjørn (2012). Norwegian fjords sang along – observations of seiches following the 2011 Tohoku, Japan, earthquake.
• Sørensen, Mathilde B.; Bondevik, Stein & Gjevik, Bjørn (2012). Norwegian fjords sang along – observations of seiches following the 2011 Tohoku, Japan, earthquake.
• Gjevik, Bjørn (2011). Månen nær jorda 19.mars. Forskning.no : nettavis med nyheter fra norsk og internasjonal forskning.
• Gjevik, Bjørn (2011). Vær, vind og sjø - fra Petter Dass til moderne forskning, I: Knut Skorpen & Anne Severinsen (red.),  Årbok for Helgeland 2011.  Helgeland Historielag.  ISBN 978-82-90148-41-1.  kapittel 2.  s 10 - 18
• Gjevik, Bjørn (2010). Flo og fjære langs kysten av Norge. Almanakk for Norge.  ISSN 0806-5632.  s 48- 51
• Gjevik, Bjørn (2010). Flo og fjære langs norskekysten. Kysten.  ISSN 0332-9550.  (3), s 16- 20
• Gjevik, Bjørn (2010). Tidevannet - Et mangfoldig og komplekst fenomen. Fra Fysikkens Verden.  ISSN 0015-9247.  (1)
• Hjelmervik, Karina Bakkeløkken; Lynge, Birgit Kjoss; Ommundsen, Atle & Gjevik, Bjørn (2009). Modelling of tides and storm surges in the Tjeldsund channel in northern Norway.
• Weber, Jan Erik H. & Gjevik, Bjørn (2008). Havnivået langs Norskekysten. Forskning.no : nettavis med nyheter fra norsk og internasjonal forskning.
• Hjelmervik, Karina Bakkeløkken; Ommundsen, Atle & Gjevik, Bjørn (2007). Model simulations of tidal currents in Tjeldsundet and Ramsundet, northern Norway.
• Hjelmervik, Karina Bakkeløkken; Ommundsen, Atle & Gjevik, Bjørn (2006). Modellsimuleringer av tidevannstrømmen i Tjeldsundet og Ramsundet. Preprint series (Universitetet i Oslo. Matematisk institutt), Mechanic. 2006:1.
• Gjevik, Bjørn (2005). Flodbølge-faren i Norge. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Gjevik, Bjørn & Pedersen, Geir Kleivstul (2005). Flodbølger fra skred og jordskjelv. Fra Fysikkens Verden.  ISSN 0015-9247.  (1), s 4- 10
• Gjevik, Bjørn; Pedersen, Geir Kleivstul & Harbitz, Carl Bonnevie (2005). Flodbølger – kan de varsles?. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Hjelmervik, Karina Bakkeløkken; Ommundsen, Atle & Gjevik, Bjørn (2005). Implementation of non-linear advection terms in a high resolution tidal model. Preprint series (Universitetet i Oslo. Matematisk institutt), Mechanic. 2005:1.
• Ommundsen, Atle; Hjelmervik, Karina Bakkeløkken & Gjevik, Bjørn (2005). Tidevannstrømmen i Tjeldsund-Ramsund, 1.-3. november 2005. FFI-notat. 2005/03188.
• Gjevik, Bjørn & Fagerland, Morten Wang (2003). Felteori og vektoranalyse. Forelesninger og oppgaver i MEK1100.
• Gjevik, Bjørn (2000). Hva vet vi om Golfstrømmen utenfor norskekysten ?.
• Gjevik, Bjørn (2000). Modeller for tidevann og tidevannstrømmer langs norskekysten. Vis sammendrag

  Tidevann og tidevannsstrømmer kan beregnes ved hjelp av matematiske modeller og datamaskiner. I foredraget forklares det hvordan slike beregninger blir gjennomført. Resultatene sammenlignes med målinger langs norskekysten og visualiseres ved videoanimasjoner. Beregnet strømfelt vil i fremtiden inngå i den nye generasjon av elekroniske sjøkart og strømfelter vil kunne sees på kartmonitoren når man seiler i strømsterke farvann.

• Gjevik, Bjørn (2000). Summary and assessment of the NDP MetOcean project.
• Gjevik, Bjørn (2000). Summary and assessment of the NDP MetOcean project.
• Gjevik, Bjørn & Hareide, Daniel (2000). Ekstrem vannstandsendring og strøm i Oslofjorden. Natten mellom 3. og 4. desember 1999. Naturen.  ISSN 0028-0887.  (5), s 258- 263 Vis sammendrag

  I Oslofjorden er tidevannet, altså de regelmessige skiftningene i vannstand som følge av månen og solas virkning, mindre enn 36 cm. Atmosfærisk pådrag som lufttrykkendringer og sterk vind kan enkelte ganger føre til mye større utslag enn dette. Når vannstanden endrer seg mye over forholdsvis kort tid må storevannmasser transporteres gjennom Drøbaksundet og det vil medføre meget sterk strøm i det trange sundet. Manuskript finnes på: http://www.math.uio.no/~bjorng/oslofjord/manus.pdf

• Gjevik, Bjørn; Moe, Halvard & Ommundsen, Atle (2000, 16. oktober). Venturing into the vortex. [Radio].  Channel Four, Equinox Lethal Seas : Northlight Productions. Vis sammendrag

  The whirlpool occupies a mythical place in our consciousness. It is an oceanic phenomenon which inspires worldwide awe and terror. Every culture which witnesses this rare spectacle has its legends of monsters of the deep, seizing seafarers and dragging them to their doom. But what are the scientific facts behind the legend? Equinox ventures into the eye of the Maelstrom to capture unique footage of the world's most lethal seas, showing the whirlpool in all its mighty grandeur.

• Moe, Halvard; Gjevik, Bjørn & Ommundsen, Atle (2000). A high resolution tidal model for the coast of Møre and Trøndelag, Mid Norway. Vis sammendrag

  A numerical model with grid resolution 500 m has been used to simulate tides on a section of the shelf off the coast of Møre and Trøndelag in western Norway. The model spans about 3 degrees latitude and covers a sea area of approximately 8x10^4 km^2. The fine spatial resolution resolves the important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a larger scale tidal model covering the Nordic Seas. The semi-diurnal components M_2, S_2 and N_2 and the diurnal component K_1 are simulated. Harmonic constants for sea level are compared with observations from 28 stations. The standard deviations between the observed and modelled amplitudes and phases for the dominant semi-diurnal component, M_2, are 1.7 cm and 5.1 degrees respectively. Current fields from the model are compared with observations from stations along the pipeline from Tjeldbergodden on the coast to the oil and gas fields on the northern rim of Haltenbanken.

• Moe, Halvard; Ommundsen, Atle & Gjevik, Bjørn (2000). A high resolution tidal model for the area around The Lofoten Islands, Northern Norway. Vis sammendrag

  A numerical model with grid resolution 500 m has been used to simulate tides around The Lofoten Islands in northern Norway. The model spans more than 3 degrees latitude and covers a sea area of approximately 1.2x10^5 km^2. The fine spatial resolution resolves the important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a large scale tidal model covering the Nordic Seas. The semi-diurnal components M_2, S_2 and N_2 and the diurnal component K_1 are simulated. Harmonic constants for sea level are compared with observations from 21 stations. The best fit is found for the M_2 component with a standard deviation between the observed and modelled amplitude and phase of respectively 2.3 cm and 2.5 degrees. The standard deviation for the other smaller components ranges 1.5-2.8 cm and 5.3-16.7 degrees. Current fields from the model are compared with observations in four locations; the Moskenes sound, the Gimsøy channel, the Tjeldsund channel and the Sortland channel. Current speed is found to be in good agreement with observations. In the Sortland channel the model predicts a dominant diurnal K_1 current in agreement with observations.

• Ommundsen, Atle & Gjevik, Bjørn (2000). Scattering of tidal Kelvin waves along shelves which vary in their lengthwise direction. Vis sammendrag

  The effect of along shelf variation in shelf width on the propagation of Kevin waves with semi-diurnal, M2, or diurnal, K1, period is studied using a numerical model. Two idealized cases are considered characterized by either a transition zone from a broad to a narrow shelf or vice versa. Simulations show that the semi-diurnal Kelvin waves adjust gradually in the transition zone to a transmitted Kelvin wave matching the downstream depth profile. The simulations of a propagating diurnal Kelvin wave show mode conversion and the development of shelf waves. This may lead to regions on the shelf with dominant diurnal currents even in cases where the sea surface amplitude of the diurnal tide is much smaller than the semi-diurnal.

• Gjevik, Bjørn (1999). Effect of along shelf variation in bathymetry on shelf slope currents and tides.
• Gjevik, Bjørn (1999). Moskstraumen; Myter Diktning og Virkelighet.
• Gjevik, Bjørn & Moe, Halvard (1999). Idealized model simulations of barotropic flow on the Catalan shelf. Vis sammendrag

  The effect of a shelf width increase on barotropic shelf edge flows and topographic shelf waves are investigated with a numerical model. The numerical experiments are carried out with flow imposed upstream, both steady and oscillatory, at the narrow shelf. A prescribed shelf edge flow gives a strong tendency for topographic steering in the transition zone. The adjustment is found to take place on a short time scale of 2-5 days set by propagating wave modes rather than by advection. Bottom friction effects do not lead to significant on-shelf leakage of the flow. Flow instability and eddy formation is found to occur, even in cases when the potential vorticity for the imposed flow does not have a local maximum on the shelf slope. The instability lead to development of anticyclonic eddies on the narrow shelf which undergo a strong non-linear adjustment at the transition zone from a narrow to a broader shelf. On the broad section of the shelf near the transition zone there is a tendency for formation of a large anticyclonic eddy. Bottom friction influences the flow instability and eddy formation in cases where the situation is marginal for flow instability and growth of eddies. Finally we have studied the current response due to a consentrated wind stress jet acting perpendicular to the coast line in the zone between the narrow and the broad shelf regions. A dipole eddy structure is found to develop with the axis tilting about 30 degrees with the axis of the wind jet and with strong current shear in the zone near the dipole axis.

• Gjevik, Bjørn; Moe, Halvard & Ommundsen, Atle (1999). Idealized model simulations of barotropic flow on the Catalan shelf. Vis sammendrag

  The effect of longshelf variation in shelf width on barotropic shelf edge flows and topographic shelf waves are investigated with a numerical model. The model topography represents a gradual transition from a narrow straight to a broader straight shelf region. It is designed primary to model the Catalan shelf on the northeastern Mediterranean coast of Spain, but the results obtained here are of general validity and will also apply to shelf flow under similar conditions elsewhere. The numerical experiments are carried out with flow imposed, both steady and oscillatory, at the upstream end of the narrow shelf region. With a prescribed shelf edge flow there is a strong tendency for topographic steering in the transition zone. The adjustment is found to take place on a short time scale of 2-5 days set by propagating wave modes rather than by advection. Bottom friction effects do not lead to significant on-shelf leakage of the flow. Flow instability and eddy formation are found to occur, even in cases where the potential vorticity for the imposed flow does not have a local maximum on the shelf slope. The instability leads to development of anticyclonic eddies on the narrow shelf which undergo strong non-linear adjustment at the transition zone from a narrow to a broader shelf. On the broad section of the shelf near the transition zone there is a tendency for formation of a large anticyclonic eddy. Bottom friction is found to influence the flow instability and the formation of eddies in cases where the flow is marginal for instability and growth of eddies. Particle tracking has been performed in order to study cross shelf mixing and transport. Finally we have studied the current response due to a concentrated wind stress jet acting perpendicular to the coast line in the transition zone between the narrow and the broad shelf regions. A dipolar eddy structure is found to develop with the axis of the dipole tilting about 30 degrees with the axis of the wind jet and with strong current shear in the zone near the dipole axis.

Se alle arbeider i Cristin