Papers by Josef Cherniawsky
Birkhäuser Basel eBooks, Dec 10, 2007
The 1700 great Cascadia earthquake (M = 9) generated widespread tsunami waves that affected the e... more The 1700 great Cascadia earthquake (M = 9) generated widespread tsunami waves that affected the entire Pacific Ocean and caused damage as distant as Japan. Similar catastrophic waves may be generated by a future Cascadia megathrust earthquake. We use three rupture scenarios for this earthquake in numerical experiments to study propagation of tsunami waves off the west coast of North America and to predict tsunami heights and currents in several bays and harbours on southern Vancouver Island, British Columbia, including Ucluelet, located on the west coast of the island, and Victoria and Esquimalt harbours inside Juan de Fuca Strait. The earthquake scenarios are: an 1100-km long rupture over the entire length of the subduction zone and separate ruptures of its northern or southern segments. As expected, the southern earthquake scenario has a limited effect over most of the Vancouver Island coast, with waves in the harbours not exceeding 1 m. The other two scenarios produce large tsunami waves, higher than 16 m at one location near Ucluelet and over 4 m inside Esquimalt and Victoria harbours, and very strong currents that reach 17 m/s in narrow channels and near headlands. Because the assumed rupture scenarios are based on a previous earthquake, direct use of the model results to estimate the effect of a future earthquake requires appropriate qualification.
In presenting the current status, future prospects and recommended developmental activities with ... more In presenting the current status, future prospects and recommended developmental activities with respect to physically-based, three-dimensional, time-dependent climate modelling, it is helpful to consider first modelling the individual atmosphere, ocean and sea ice components of the climate system. While satisfactory performance of the individual component models in isolation does not guarantee proper performance in the fully coupled model, it is a necessary condition.
Geophysical Research Letters, Oct 10, 2012
The present study describes a model simulation, where ocean tide dynamics are simulated simultane... more The present study describes a model simulation, where ocean tide dynamics are simulated simultaneously with the ocean circulation. The model is forced by a lunisolar tidal forcing described by ephemerides and by daily climatological wind stress, heat, and fresh water fluxes. The horizontal resolution is about 0.1 and thus, the model implicitly resolves meso-scale eddies and internal waves. In this model simulation the global M 2 barotropic to baroclinic tidal energy conversion amounts to 1.2 TW. We show global maps of the surface signature of the M 2 baroclinic tide and compare it with an estimate obtained from 19 years of satellite altimeter data. Further, the simulated seasonality in the low mode internal tide field is presented and, as an example, the physical mechanisms causing the non-stationarity of the internal tide generated in Luzon Strait are discussed. In general, this study reveals the impact of inter-annual changes of the solar radiative forcing and wind forced ocean circulation on the generation and propagation of the low mode internal tides. The model is able to simulate non-stationary signals in the internal tide field on global scales which have important implications for future satellite altimeter missions.
Journal of Physical Oceanography, May 1, 2000
Internal M 2 tides near Hawaii are investigated with a two-dimensional, two-layer numerical model... more Internal M 2 tides near Hawaii are investigated with a two-dimensional, two-layer numerical model. It is seen that along the Hawaiian Ridge barotropic tidal energy is transformed into baroclinic internal tides that propagate in both northeast and southwest directions, as previously hypothesized. The internal tide for a certain beam is seen to propagate well over 1000 km. with an approximate decay scale of 1000 km. An asymmetric pattern in the baroclinic energy flux is observed to the north and south of the Hawaiian Ridge due to the spatially inhomogeneous baroclinic energy sources. The surface manifestation of the M 2 internal tide in the model is compared with analysis results from TOPEX/ Poseidon satellite altimetry. The baroclinic shortwave variation of a few centimeters amplitude, superposed on the barotropic surface amplitude, agrees well with the altimeter analyses. This, together with snapshots of the interfacial disturbance, allows the authors to sketch the propagation pattern of internal waves emanating northward and southward from the Hawaiian Ridge. Tidal current ellipses in the upper layer are dominated by the baroclinic internal tide with large spatial variability in their magnitude compared to the barotropic tidal ellipses. The M 2 baroclinic energy flux is over 10 kW m Ϫ1 for the strongest energy beam propagating toward the northeast. Along the western Hawaiian Ridge about 3.8 GW of tidal power is converted from barotropic to baroclinic motion. The average northward or southward flux density for the first baroclinic mode is about 1.35 kW m Ϫ1 in the western Hawaiian Ridge. Also, if 2.7 kW m Ϫ1 (1.35 kW m Ϫ1 to each direction) is assumed for the whole 2000-km-long Hawaiian Ridge, a total of 5.4 GW is obtained. This value indicates that there is still a large uncertainty in the rate of barotropic to radiating baroclinic energy conversion along the Hawaiian Ridge.
What factors modify M2 on seasonal or longer time scales? Gravity, ~1% of M2, through the influen... more What factors modify M2 on seasonal or longer time scales? Gravity, ~1% of M2, through the influence of solar parallax on the Moon's orbit (Cartwright, 1968). Seasonal changes in depth from storm surges (Huess and Andersen 2001). Changes in bottom friction, or vertical viscosity, from changes in stratification. This effect varies significantly in time and place, acting on all time scales, up to the lunar nodal period of 18.6 years (e.g. Foreman et al. 2006) and extending well beyond its source regions. For example, Foreman et al. (1995) found that M2 in Victoria, BC, varies seasonally by about 6%, possibly due to enhanced estuarine stratification and reduced friction from large annual Fraser River runoff. Or any combination of the above.
Pure and Applied Geophysics, 2014
This book presents a new numerical method of conformal mapping (the RT-algorithm) based on the R ... more This book presents a new numerical method of conformal mapping (the RT-algorithm) based on the R and T procedures. Solutions are given for arbitrary simply connected and doubly connected domains with piecewise - smooth contours. The continuum mechanics, including hydrodynamics, electrodynamics and elasticity theory. The bool encompasses a wide range of numerical methods and computer techniques, including computer graphics. Problems analyzed are at the forefront of applied problems in modern technology. Solutions to boundary-value problems on the unit circle and circular annulus are obtaines by systematic use of Taylor an Laurent series, the Ritz method, finite elements, and the conjugate-vortex method. Analytical solutions and experimental data are to verfy results of the numerical computations obtained by the RT-algorithm.
The analysis of seasonal sea level variation in surrounding seas to Korean peninsula revealed tha... more The analysis of seasonal sea level variation in surrounding seas to Korean peninsula revealed that there exist some systematic pattern for the Sa amplitude varying from 20 to 10cm, depending upon the regions such as the Yellow Sea, South Sea and East/Japan Sea (EJS). Results from the analysis of coastal tidal data are presented as well as the analysis result from the satellite altimetry data of Topex/Poseidon, which shows that Sa amplitude from the adjusted sea level are about 7 or so in the Yellow Sea, while its magnitude in the East/Japan Sea is about 3cm. The physical factors, such as atmospheric force and thermosteric force, to influence the seasonal variation of sea level are examined in order to understand the mechanism of spatially systematic variation of the seasonal sea level variation component Sa. The spatial distribution of Sa amplitude by inverse barometric effect varies 10cm to 8cm from the Yellow Sea, through South Sea, to the EJS, respectively. This inverse barometri...
The 1700 great Cascadia earthquake (M=9) generated widespread tsunami waves that affected the ent... more The 1700 great Cascadia earthquake (M=9) generated widespread tsunami waves that affected the entire Pacific Ocean and caused damage as far as Japan. Similar waves may be generated by a future Cascadia earthquake. We use several plausible rupture scenarios in numerical ocean model experiments to predict tsunami heights and currents in Vancouver Island harbours caused by such an earthquake. These scenarios include the rupture of the entire 1100-km length of the Subduction Zone and separate rupture of smaller northern and southern segments. We present the tsunami model results for several harbours including Victoria and Esquimalt harbours for these three scenarios. As expected, the more remote (southern) earthquake has a limited effect in the harbours. However, the other two scenarios produce very significant waves (up to 4.5 m) and strong currents (exceeding 10 knots) in Victoria and Esquimalt harbours that are located inside the Juan de Fuca Strait. The same models indicate that tsu...
Spill Science & Technology Bulletin, 1996
Barocfinic currents for flow along the North Coast of British Columbia were modelled using a fini... more Barocfinic currents for flow along the North Coast of British Columbia were modelled using a finite element approach. Observational data from Loran-C drifters were used to get surface truth data. Least squares fit was appfied to both the wind-driven current and baroclinic current compared with the drifter velocities in Dixon Entrance and Hecate Straits. The current data achieved was found to be useful for oil spill modelling.
Pure and Applied Geophysics, 2012
We use a numerical tsunami model to describe wave energy decay and transformation in the Pacific ... more We use a numerical tsunami model to describe wave energy decay and transformation in the Pacific Ocean during the 2011 Tohoku tsunami. The numerical model was initialised with the results from a seismological finite fault model and validated using deep-ocean bottom pressure records from DARTs, from the NEPTUNE-Canada cabled observatory, as well as data from four satellite altimetry passes. We used statistical analysis of the available observations collected during the Japan 2011 tsunami and of the corresponding numerical model to demonstrate that the temporal evolution of tsunami wave energy in the Pacific Ocean leads to the wave energy equipartition law. Similar equipartition laws are well known for wave multi-scattering processes in seismology, electromagnetism and acoustics. We also show that the long-term near-equilibrium state is governed by this law: after the passage of the tsunami front, the tsunami wave energy density tends to be inversely proportional to the water depth. This fact leads to a definition of tsunami wave intensity that is simply energy density times the depth. This wave intensity fills the Pacific Ocean basin uniformly, except for the areas of energy sinks in the Southern Ocean and Bering Sea.
Ocean Dynamics, 2014
ABSTRACT The seasonal cycle of the main lunar tidal constituent M2 is studied globally by an anal... more ABSTRACT The seasonal cycle of the main lunar tidal constituent M2 is studied globally by an analysis of a high resolution ocean circulation and tide model (STORMTIDE) simulation, of 19 years of satellite altimeter data, and of multiyear tide-gauge records. The barotropic seasonal tidal variability is dominant in coastal and polar regions with relative changes of the tidal amplitude of 5–10 %. A comparison with the observations shows that the ocean circulation and tide model captures the seasonal pattern of the M2 tide reasonably well. There are two main processes leading to the seasonal variability in the barotropic tide: First, seasonal changes in stratification on the continental shelf affect the vertical profile of eddy viscosity and, in turn, the vertical current profile. Second, the frictional effect between sea-ice and the surface ocean layer leads to seasonally varying tidal transport. We estimate from the model simulation that the M2 tidal energy dissipation at the sea surface varies seasonally in the Arctic (ocean regions north of 60◦N) between 2 and 34 GW, whereas in the Southern Ocean, it varies between 0.5 and 2 GW. The M2 internal tide is mainly affected by stratification, and the induced modified phase speed of the internal waves leads to amplitude differences in the surface tide signal of 0.005–0.0150 m. The seasonal signals of the M2 surface tide are large compared to the accuracy demands of satellite altimetry and gravity observations and emphasize the importance to consider seasonal tidal variability in the correction processes of satellite data.
Journal of Physical Oceanography, 2000
Internal M 2 tides near Hawaii are investigated with a two-dimensional, two-layer numerical model... more Internal M 2 tides near Hawaii are investigated with a two-dimensional, two-layer numerical model. It is seen that along the Hawaiian Ridge barotropic tidal energy is transformed into baroclinic internal tides that propagate in both northeast and southwest directions, as previously hypothesized. The internal tide for a certain beam is seen to propagate well over 1000 km. with an approximate decay scale of 1000 km. An asymmetric pattern in the baroclinic energy flux is observed to the north and south of the Hawaiian Ridge due to the spatially inhomogeneous baroclinic energy sources. The surface manifestation of the M 2 internal tide in the model is compared with analysis results from TOPEX/ Poseidon satellite altimetry. The baroclinic shortwave variation of a few centimeters amplitude, superposed on the barotropic surface amplitude, agrees well with the altimeter analyses. This, together with snapshots of the interfacial disturbance, allows the authors to sketch the propagation pattern of internal waves emanating northward and southward from the Hawaiian Ridge. Tidal current ellipses in the upper layer are dominated by the baroclinic internal tide with large spatial variability in their magnitude compared to the barotropic tidal ellipses. The M 2 baroclinic energy flux is over 10 kW m Ϫ1 for the strongest energy beam propagating toward the northeast. Along the western Hawaiian Ridge about 3.8 GW of tidal power is converted from barotropic to baroclinic motion. The average northward or southward flux density for the first baroclinic mode is about 1.35 kW m Ϫ1 in the western Hawaiian Ridge. Also, if 2.7 kW m Ϫ1 (1.35 kW m Ϫ1 to each direction) is assumed for the whole 2000-km-long Hawaiian Ridge, a total of 5.4 GW is obtained. This value indicates that there is still a large uncertainty in the rate of barotropic to radiating baroclinic energy conversion along the Hawaiian Ridge.
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Papers by Josef Cherniawsky