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A performance measure for a DART® tsunami buoy network has been developed. DART® buoys are used to detect tsunamis, but the full potential of the data they collect is realized through accurate forecasts of inundations caused by the tsunamis. The performance measure assesses how well the network achieves its full potential through a statistical analysis of simulated forecasts of wave amplitudes outside an impact site and a consideration of how much the forecasts are degraded in accuracy when one or more buoys are inoperative. The analysis uses simulated tsunami amplitude time series collected at each buoy from selected source segments in the Short-term Inundation Forecast for Tsunamis database and involves a set for 1000 forecasts for each buoy/segment pair at sites just offshore of selected impact communities. Random error-producing scatter in the time series is induced by uncertainties in the source location, addition of real oceanic noise, and imperfect tidal removal. Comparison with an error-free standard leads to root-mean-square errors (RMSEs) for DART® buoys located near a subduction zone. The RMSEs indicate which buoy provides the best forecast (lowest RMSE) for sections of the zone, under a warning-time constraint for the forecasts of 3 h. The analysis also shows how the forecasts are degraded (larger minimum RMSE among the remaining buoys) when one or more buoys become inoperative. The RMSEs provide a way to assess array augmentation or redesign such as moving buoys to more optimal locations. Examples are shown for buoys off the Aleutian Islands and off the West Coast of South America for impact sites at Hilo HI and along the US West Coast (Crescent City CA and Port San Luis CA, USA). A simple measure (coded green, yellow or red) of the current status of the network’s ability to deliver accurate forecasts is proposed to flag the urgency of buoy repair.

U.S. Tsunami Warning Centers use real-time bottom pressure (BP) data transmitted from a network of buoys deployed in the Pacific and Atlantic Oceans to tune source coefficients of tsunami forecast models. For accurate coefficients and therefore forecasts, tides at the buoys must be accounted for. In this study, five methods for coefficient estimation are compared, each of which accounts for tides differently. The first three subtract off a tidal prediction based on (1) a localized harmonic analysis involving 29 days of data immediately preceding the tsunami event, (2) 68 pre-existing harmonic constituents specific to each buoy, and (3) an empirical orthogonal function fit to the previous 25 hrs of data. Method (4) is a Kalman smoother that uses method (1) as its input. These four methods estimate source coefficients after detiding. Method (5) estimates the coefficients simultaneously with a two-component harmonic model that accounts for the tides. The five methods are evaluated using archived data from eleven DART buoys, to which selected artificial tsunami signals are superimposed. These buoys represent a full range of observed tidal conditions and background BP noise in the Pacific and Atlantic, and the artificial signals have a variety of patterns and induce varying signal-to-noise ratios. The root-mean-square errors (RMSEs) of least squares estimates of sources coefficients using varying amounts of data are used to compare the five detiding methods. The RMSE varies over two orders of magnitude between detiding methods, generally decreasing in the order listed, with method (5) yielding the most accurate estimate of source coefficient. The RMSE is substantially reduced by waiting for the first full wave of the tsunami signal to arrive. As a case study, the five method are compared using data recorded from the devastating 2011 Japan tsunami., 20 pages; 3 tables; 15 figures

In response to hazards posed by earthquake-induced tsunamis, the National Oceanographic and Atmospheric Administration developed a system for issuing timely warnings to coastal communities. This system, in part, involves matching data collected in real time from deep-ocean buoys to a database of precomputed geophysical models, each associated with a geographical location. Currently, trained operators must handpick models from the database using the epicenter of the earthquake as guidance, which can delay issuing of warnings. In this article, we introduce an automatic procedure to select models to improve the timing and accuracy of these warnings. This procedure uses an elastic-net-based penalized and constrained linear least-squares estimator in conjunction with a sweeping window. This window ensures that selected models are close spatially, which is desirable from geophysical considerations. We use the Akaike information criterion to settle on a particular window and to set the tuning parameters associat...

This study describes winter climate during the last 500 yr for the greater Baltic Sea region through an examination of well-documented time series of ice cover, sea level pressure, and winter surface air temperatures. These time series have been the focus of previous studies, but here their covariation over different time scales is analyzed based on two modern descriptive statistical techniques, matching pursuit and wavelet analysis. Independently, 15 time periods were found during the last 500 yr with different climatic signatures with respect to winter severity, circulation patterns, and interannual variability. The onsets of these periods are presumably caused largely by perturbations within the system, although correspondences with solar and volcanic activity can be identified for certain of the periods. The Baltic region climate has changes on both centennial and decadal time scales, often with rapid transitions. Major warmer periods were the first half of the eighteenth century and the twentieth century. A common feature for warm (cold) periods is low (high) variability on shorter time scales. Century-scale variability and the modulation of interannual and decadal signals are quite diverse in the temporal records and do not suggest strong periodicities. An “event” type conceptual model therefore appears adequate for characterizing Baltic climate variability.

A theoretical study was carried out to understand how the probability distribution for maximum wave heights (ηm) during tsunamis depends on the initial tsunami amplitude (A) and the tides. It was assumed that the total wave height is the linear sum of the tides and tsunami time series in which the latter is decaying exponentially in amplitude with an e-folding time of 2.0 days, based on the behavior of observed Pacific-wide tsunamis. Direct computations were made to determine the statistics of maximum height for a suite of different arrival times and initial tsunami amplitudes. Using predicted tides for 1992 when the lunar nodal f factors were near unity during the present National Tidal Datum Epoch 1983–2001, the results show that when A is small compared with the tidal range the probability density function (PDF) of the difference ηm − A is closely confined in height near mean higher high water (MHHW). The ηm − A PDF spreads in height and its mean height ηo − A decreases, approaching the PDF of the tides and MSL, respectively, when A becomes large compared with the tidal range. A Gaussian form is found to be a close approximation to the ηm − A PDF over much of the amplitude range; associated parameters for 30 coastal stations along the U.S. West Coast, Alaska, and Hawaii are given in the paper. The formula should prove useful in probabilistic mapping of coastal tsunami flooding.

This study develops a method for estimating the number of casualties that may occur while people evacuate from an inundation zone when a tsunami has inundated an area. The method is based on a simple model of hydrodynamic forces as they affect the human body. The method uses a Tsunami casualty index (TCI) computed at each grid point of a numerical tsunami model to determine locations and times within the tsunami inundation zone where evacuation during the tsunami inundation is not possible and therefore where casualties are likely to occur. The locations and times can be combined with information about population density to compute the potential number of casualties. This information is useful in developing tsunami evacuation routes that avoid such locations. To illustrate the method, it is applied to the Seattle waterfront in Washington State, USA, that is under the threat of possible tsunami disasters due to Seattle Fault earthquakes. Preliminary results suggest that the tsunami casualties may occur within the Seattle waterfront for 15 min, during the time interval from 3 to 18 min after a large Seattle Fault tsunami is generated when the background tide level is mean high water.

Summarization: Tsunamis are an ever-present threat to lives and property along the coasts of most of the world's oceans. As the Sumatra tsunami of 26 December 2004 reminded the world, we must be more proactive in developing ways to reduce their impact on our global society. This article provides an overview of the state of knowledge of tsunamis, presents some challenges confronting advances in the field and identifies some promising frontiers leading to a global warning system. This overview is then used to develop guidelines for advancing the science of forecasting, hazard mitigation programmes and the development of public policy to realize a global system. Much of the information on mitigation and forecasting draws upon the development and accomplishments of a joint state/federal partnership that was forged to reduce tsunami hazards along US coastlines-the National Tsunami Hazard Mitigation Programme. By integrating hazard assessment, warning guidance and mitigation activities, the programme has created a roadmap and a set of tools to make communities more resilient to local and distant tsunamis. Among the tools are forecasting, educational programmes, early warning systems and design guidance for tsunami-resilient communities. Information on international cooperation is drawn from the Global Earth Observing System of Systems (GEOSS). GEOSS provides an international framework to assure international compatibility and interoperability for rapid exchange of data and information. Παρουσιάστηκε στο: Philosophical Transactions

Regimes and regime shifts are important concepts for understanding decadal variability in the physical system of the North Pacific because of the potential for an ecosystem to reorganize itself in response to such shifts. There are two prevalent senses in which these concepts are taken in the literature. The first is a formal definition and posits multiple stable states and rapid transitions between these states. The second is more data-oriented and identifies local regimes based on differing average climatic levels over a multi-annual duration , i.e. simply interdecadal fluctuations. This second definition is consistent with realizations from stochastic red noise processes to a degree that depends upon the particular model. Even in 100 year long records for the North Pacific a definition of regimes based solely on distinct multiple stable states is difficult to prove or disprove, while on interdecadal scales there are apparent local step-like features and multi-year intervals where the state remains consistently above or below the long-term mean. The terminologies climatic regime shift, statistical regime shift or climatic event are useful for distinguishing this second definition from the first. To illustrate the difficulty of advocating one definition over the other based upon a relatively short time series, we compare three simple models for the Pacific Decadal Oscillation (PDO). The 104-year PDO record is insufficient to statistically distinguish a single preference between a square wave oscillator consistent with the formal definition for regime shifts, and two red noise models that are compatible with climatic regime shifts . Because of the inability to distinguish between underlying processes based upon data, it is necessary to entertain multiple models and to consider how each model would impact resource management. In particular the persistence in the fitted models implies that certain probabilistic statements can be made regarding climatic regime shifts , but we caution against extrapolation to future states based on curve fitting techniques.

Surface air temperatures (SAT) from three Alaskan weather stations in a north–south section (Barrow, Nome, and St. Paul) show that on a decadal scale, the correlation among the stations changed during the past century. Before the 1960s, Barrow and Nome were dominated by Arctic air masses and St. Paul was dominated by North Pacific maritime air masses. After the 1960s, the SAT correlation in winter between Barrow and St. Paul increased from 0.2 to 0.7 and between Nome and St. Paul from 0.4 to 0.8, implying greater north–south penetration of both air masses. The correlation change in the winter of the Barrow–St. Paul pair is significant at a 95% confidence level. The Nome–St. Paul pair in spring also shows some of this characteristic change in correlation. Relatively stable, high correlations are found among the stations in the fall; correlations are low in the summer. Our study shows a change in the climatological structure of the Bering Sea in the late twentieth century, at present of unknown origin and occurring earlier than the well-known 1976/1977 shift. These climatological results further support the concept that the southeast Bering Sea ecosystem may have been dominated by Arctic species for most of the century, with a gradual replacement by sub-Arctic species in the last 30 years. Copyright © 2005 Royal Meteorological Society.

A new method for real-time tsunami forecasting will provide NOAA’s Tsunami Warning Centers with forecast guidance tools during an actual tsunami event. PMEL has developed the methodology of combining real-time data from tsunameters with numerical model estimates to provide site- and event-specific forecasts for tsunamis in real time. An overview of the technique and testing of this methodology is presented.

Instrumental surface air temperature (SAT) records beginning in the late 1800s from 59 Arctic stations north of 64°N show monthly mean anomalies of several degrees and large spatial teleconnectivity, yet there are systematic seasonal and regional differences. Analyses are based on time–longitude plots of SAT anomalies and principal component analysis (PCA). Using monthly station data rather than gridded fields for this analysis highlights the importance of considering record length in calculating reliable Arctic change estimates; for example, the contrast of PCA performed on 11 stations beginning in 1886, 20 stations beginning in 1912, and 45 stations beginning in 1936 is illustrated. While often there is a well-known interdecadal negative covariability in winter between northern Europe and Baffin Bay, long-term changes in the remainder of the Arctic are most evident in spring, with cool temperature anomalies before 1920 and Arctic-wide warm temperatures in the 1990s. Summer anomalies are general...

Introduction Tectonic processes in the deep ocean occur over an immerse range of temporal and spatial scales. The shortest in time are from seconds to minutes during which earthquakes and landslides occur. The recurrence interval between earthquakes, submarine landslides, and volcanic eruptions may be tens, hundreds, or thousands of years. At the far end of the range are the tens of millions of years over which oceanic plates form at the spreading centers and drift, sometimes thousands of kilometers with speeds of a few centimeters per year, to the subduction zones. It is also over these long time scales that chains of volcanic islands and seamounts form and over even longer time scales that major asteroids may impact the Earth. These processes create a host of smaller-scale geological features, including rift valleys, earthquake fault scarps, submarine landslide deposits, and abyssal hills, which cover vast areas of the ocean floor. Using a wide variety of methods, scientists are developing a better understanding of these geological features and the processes that create them.

The harmonic constant datum (HCD) method is a computationally efficient way of estimating tidal datums relative to mean sea level, without the need to compute long time series. However, datum discontinuities can occur between mixed and diurnal tidal regimes using this method. Solutions to this problem are investigated, with a hypothetical strait that contains a semidiurnal node, using three different procedures: algorithms specifically designed for diurnal tides (DTA), mixed tidal algorithms (MTA) throughout, and cubic polynomial interpolation (CPI) across the diurnal region. DTA creates small discontinuities (≤11% for the strait) in mean higher high water and mean lower low water but does not provide estimates of mean high water or mean low water. MTA gives continuous datums but creates artificial structures in the middle of the diurnal region. CPI provides smooth, continuous datums but does not use the tidal information within the diurnal regions. Which procedure works best depends on the size ...

A major difficulty in investigating the nature of interdecadal variability of climatic time series is their shortness. An approach to this problem is through comparison of models. In this paper a first-order autoregressive [AR(1)] model is contrasted with a fractionally differenced (FD) model as applied to the winter-averaged sea level pressure time series for the Aleutian low [the North Pacific (NP) index] and the Sitka winter air temperature record. Both models fit the same number of parameters. The AR(1) model is a “short-memory” model in that it has a rapidly decaying autocovariance sequence, whereas an FD model exhibits “long memory” because its autocovariance sequence decays more slowly. Statistical tests cannot distinguish the superiority of one model over the other when fit with 100 NP or 146 Sitka data points. The FD model does equally well for short-term prediction and has potentially important implications for long-term behavior. In particular, the zero crossings of the FD model tend t...

The small amount of North Pacific SST variance explained by the first two organized modes, as well as the irregular nature of the decadal-interdecadal variability of SSTs and spatial atmospheric forcing, suggest that a low order, nonlinear, chaotic system of atmospheric/oceanic variability may be acting in the North Pacific. Systems, which visit many states yet tend to return to the vicinity of previously observed patterns, have properties similar to mathematical chaos. Wavelet analyses of the wintertime Pacific Decadal Oscillation, Aleutian Low intensity from 1900, and Sitka air temperatures from 1832 suggest broad-banded time series with irregular oscillatory behavior. The different frequency bands do not appear to be independent; their alignment has resulted in major shifts around 1847, 1880?, 1925, 1945, 1977, and minor shifts in 1958 and 1989. Although the observational time series are too short to prove that the coupled atmosphere and ocean in the North Pacific is chaotic, the notion that it is stable for decadal periods and then exhibits rapid transitions is the basis for our conceptual model. This model suggests that the North Pacific system is less sensitive to external forcing when it is near one of its stable states. At other times the system is more responsive to short-term extreme events such as ENSO, Siberian snow cover, hemispheric atmospheric modes, or local SST anomalies. Increased interannual variability is expected around the times of interdecadal shifts. Recent persistence of La Nina as well as enhanced interannual variability in several other time series, are consistent with a possible shift of the PDO in 1999.

A method is derived to forecast theextreme heights of later waves in Pacific-widetsunamis, for locations in the vicinity of real-timereporting tide gages. The forecast for wave peaks hasthe form ηF(t) = ηB(t) + ηe(t),where ηe = Aσ exp [- (t - to)/τ ]. Here, the forecast begins attime t = to, which is 4 h after tsunamidetection at a tide gage, σ is the standarddeviation of tsunami-band fluctuations observed in the2-h time interval before the forecast begins,ηB is a background water level predictionthat includes the tides and lower frequencyoscillations, τ = 48 h is an e-folding decayconstant, and A = 3.0 is a constant coefficient.Placing a minus sign in front of ηe providesa forecast for wave troughs. This form for theforecast, and the values of the parameters, arejustified using probability theory and Monte Carlosimulations based on 3000 synthetic tsunami timeseries. The method is then tested successfully (i.e.,agreement within 0.5 m) against six past Pacific-widetsunamis, as observed at U.S. tide gages. These casestudies include the five major tsunamis to produceloss of life and/or substantial damage to U.S. coastalcommunities during the Twentieth Century. The sixthstudy is the 1994 Shikotan tsunami, which is thelatest Pacific-wide tsunami to trigger tsunamiwarnings for U.S. regions. Algorithms for detectinglocal tsunami onset and generating forecasts are givenin an appendix, together with a description of thewavelet method used to generate the synthetic tsunamiseries.

Low, neap tides occurred along the West Coast of the United States and Canada around 0500 UT January 27, 1700, a time for the last major Cascadia earthquake/tsunami based on teletsunami arrival times in Japan [Satake et al., 1996]. However, high-range perigean spring tides occurred only a week later, illustrating how accurately occurrence times must be known to constrain the region's background water levels during such events. The ranges of background water levels increase northward from 3 m at Monterey to 8.5 m at Queen Charlotte, as estimated from the amplitudes of perigean spring tides and subtidal winter fluctuations.

Subtidal coastal sea level fluctuations affect coastal ecosystems and the consequences of destructive events such as tsunamis. We analyze a time series of subtidal fluctuations at Crescent City, California, during 1980–1991 using the maximal overlap discrete wavelet transform (MODWT). Our analysis shows that the variability in these fluctuations depends on the season for scales of 32 days and less. We show how the MODWT characterizes nonstationary behavior succinctly and how this characterization can be used to improve forecasts of inundation during tsunamis and storm surges. We provide pseudocode and enough details so that data analysts in other disciplines can readily apply MODWT analysis to other nonstationary time series.

[1] We have developed a method to compute the total energy transmitted by tsunami waves, to the case where the earthquake source is unknown, by using deep-ocean pressure measurements and numerical models (tsunami source functions). Based on the first wave recorded at the two closest tsunameters (Deep-Ocean Assessment and Reporting of Tsunamis (DART)), our analysis suggests that the March 11, 2011 Tohoku-Oki tsunami generated off Japan originated from a 300–400 km long and 100 km wide area, and the total propagated energy is 3 × 1015J (with 6% uncertainty). Measurements from 30 tsunameters and 32 coastal tide stations show excellent agreement with the forecasts obtained in real time. Our study indicates that the propagated energy and the source location are the most important source characteristics for predicting tsunami impacts. Interactions of tsunami waves with seafloor topography delay and redirect the energy flux, posing hazards from delayed and amplified waves with long duration. Seafloor topography also gives its spectral imprint to tsunami waves. Travel time forecast errors are path-specific and correlated to the major wave scatterers in the Pacific. Numerical dissipation in the propagation modeling highlights the need of high-resolution inundation models for accurate coastal predictions. On the other hand, it also can be used to account for physical dissipation to achieve efficiency. Our results provide guidelines for the earliest reliable tsunami forecast, warnings of long duration tsunami waves signals and enhancement of the experimental tsunami forecast system. We apply the method to quantify the energy of 15 past tsunamis, independently from earthquake magnitudes. The small tsunami to seismic radiation energy ratios, and their variability (0.01–0.8%), reinforce the importance of using deep-ocean tsunami data, the direct measures of tsunamis, for estimates of tsunami energy and accurate forecasting.

We use a scattering index to identify the regions in the Pacific Ocean where topographic features scatter significant tsunami energy. Based on linear wave theory, the index is computed from the Smith/Sandwell topography. Consistent with numerical simulations, it shows that there is a narrow band of strong scatterers running across the ocean from the northwest (Emperor Seamount Chain) to the southeast (Easter Island Fracture Zone). The eastern Pacific is nearly devoid of scatterers, except for this band and isolated features along the eastern margin. To the west of the band lies a region with moderate scattering; the strongest scattering occurs in the southwestern Pacific. The Pacific is rimmed by island arcs and shallow continental shelves that also trap and scatter tsunamis. These results show that numerical models of trans-Pacific tsunamis must resolve the effects of the small-scale topography in order to accurately simulate their wave patterns and amplitudes.

Numerical model simulations, combined with tide-gauge and satellite altimetry data, reveal that wave amplitudes, directionality, and global propagation patterns of the 26 December 2004 Sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid-ocean ridge topographic waveguides.

The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers.

A tsunameter (soo-NAHM-etter) network has been established in the Pacific by the National Oceanic and Atmospheric Administration. Named by analogy with seismometers, the NOAA tsunameters provide early detection and real-time measurements of deep-ocean tsunamis as they propagate toward coastal communities, enabling the rapid assessment of their destructive potential. Development and maintenance of this network supports a State-driven, high-priority goal of the U.S. National Tsunami Hazard Mitigation Program to improve the speed and reliability of tsunami warnings. The network is now operational, with excellent reliability and data quality, and has proven its worth to warning center decision-makers during potentially tsunamigenic earthquake events; the data have helped avoid issuance of a tsunami warning or have led to cancellation of a tsunami warning, thus averting potentially costly and hazardous evacuations. Optimizing the operational value of the network requires implementation of real-time tsunami forecasting capabilities that integrate tsunameter data with numerical modeling technology. Expansion to a global tsunameter network is needed to accelerate advances in tsunami research and hazard mitigation, and will require a cooperative and coordinated international effort.

The North Pacific (NP) index is a time series related to atmospheric pressure variations at sea level and is an important indicator of the NP climate. We consider three statistical models for the NP index, namely, a Gaussian stationary autoregressive process, a Gaussian stationary fractionally differenced (FD) process, and a ‘signal plus noise’ process consisting of a square wave oscillation with a pentadecadal period embedded in Gaussian white noise. Each model depends upon three parameters, so all three models are equally simple. Statistically each model fits the NP index equally well. The fact that this index consists of just a hundred observations makes it unrealistic to expect to be able to clearly prefer one model over the other. Although the models fit equally well, their implications for the long term behavior of the NP index can be quite different in terms of, e.g., generating regimes of characteristic lengths (i.e., stretches of years over which the NP index is predominantly either above or below its long term average value). Because we cannot determine a preferred model statistically, we are faced with either entertaining multiple models when considering what the long term behavior of the NP index is likely to be or using physical arguments to select one model. The latter approach would arguably favor the FD process because it has an interpretation as the synthesis of first order differential equations involving many different damping constants.

This paper describes a Research and Development activity to develop tsunami forecasting tools for the Pacific Disaster Center (PDC). The activity included analytical and numerical sensitivity studies of tsunami wave characteristics offshore of Hawaii, for ranges of earthquake source parameters in the Alaska-Aleutian Subduction Zone (AASZ). This region is a major source of destructive tsunamis that strike Hawaii. A set of tsunami numerical simulation scenarios was designed to be the basis for the sensitivity analysis. The simulation results have been stored as an online database with a World-Wide Web interface. A database user can very quickly obtain a model prediction of the tsunami offshore wave heights at chosen locations for a wide variety of AASZ earthquake scenarios. This database provides a comprehensive offshore tsunami forecasting tool for hazard mitigation managers.

It is found empirically that, at tide gauges in the eastern North Pacific, later waves in a teletsunami are bounded in amplitude by envelopes that can be determined from observations of earlier waves at the same site. This is illustrated using the teletsunami generated by the 4 October 1994 Shikotan earthquake. The envelopes have the form η(t)=AσT in which t is the time since the local onset of the tsunami and σT is the standard deviation of the tsunami-band fluctuations that are observed in a time interval T immediately preceding t. For t ≤ 10 hr, T = t+2 hr and T = 12 hr thereafter. Values for the multiplicative factor A = 3.0 and the temporal parameters for T were determined by tuning the envelope to several teletsunamis. In principle, such envelopes can be extrapolated forward in time and added to predictions of background water levels to forecast the maximum elevations of tsunami waves that might occur during the next few hours. However, several issues need to be addressed before such a scheme can be used operationally These include the choice of inundation thresholds that are appropriate for tsunamis and the spatial distribution of gauges needed to adequately monitor tsunami waves in a region.

The 25 April 1992 Cape Mendocino earthquake generated a tsunami characterized by both coastal trapped edge wave and non-trapped tsunami modes that propagated north and south along the U.S. West Coast. Both observed and synthetic time series at Crescent City and North Spit are consistent with the zero-order edge wave mode solution for a semi-infinite sloping beach depth profile. Wave amplitudes at Crescent City were about twice that observed at North Spit, in spite of the fact that the source region was three times farther from Crescent City than North Spit. The largest observed amplitude was due to an edge wave which arrived almost three hours after the initial onset of the tsunami; since such waves are highly localized nearshore, this suggests that the enhanced responsiveness at Crescent City is at least partly due to local dynamic processes. Furthermore, the substantially delayed arrival of this wave, which was generated at the southern end of the Cascadia Subduction Zone, has significant implications for hazard mitigation efforts along the entire U.S. West Coast. Specifically, this study demonstrates that slow-moving but very energetic edge wave modes could be generated by future large tsunamigenic earthquakes in the CSZ, and that these might arrive unexpectedly at coastal communities several hours after the initial tsunami waves have subsided.

[1] Recent paleoseismic and geologic studies indicate that a tsunami occurred 1100 years ago in Puget Sound. This study aims to reproduce and validate the model tsunami, using a finite difference model based on nonlinear shallow water theory and abathymetry/topography computational grid that takes into account the 1-meter rise in sea level that has occurred in the region during the past 1100 years. Estimates of tsunami height, the extent of inundation, and the current velocity pattern are provided at the northern head of Cultus Bay, Whidbey Island, where paleotsunami sand deposits have been found. The model demonstrates that a tsunami generated when the background water level was at mean high water or above could have surged across the then-existing coastal marsh, penetrated the full length of the shallow bay, and deposited the observed sand layers.

A cross-spectral analysis is made of subtidal (0.01-0.5 cpd) sea level (SSL), atmospheric pressure and wind fluctuations observed during 1966-1988 in the southern reaches of the fjord system formed by the Straits of Juan de Fuca/Georgia and Puget Sound. It shows that observed SSL can be largely explained by quasi-steady inverse barometer compensation to atmospheric pressure and the propagation of adjusted sea level fluctuations from the nearby continental shelf, with some local weather forcing in summer. Variations in coherence, amplitudes and relative phase between seasons, locations and frequencies support previous work that both barotropic and baroclinic processes have important influences in SSL within the fjord system.

The concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed. Observational definitions of incipient motion are many and not entirely compatible. Some laboratory flume observations of sediment movement suggest that no true threshold exists. Current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time‐mean velocities. A combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept.

Pressure fluctuations on the deep seafloor at frequencies below inertial and tidal have been measured. Between 0.1 and 1 cycle per day the variance is about 2 mb2, spectra diminish with increasing frequency as ω−n, n=1.5 to 2, and a signal-to-instrument noise ratio of 10 dB is achieved. Fluctuations are in phase and highly coherent within the MODE area (>0.95 at 200 km) and even with inferred (atmosphere plus sea level) Bermuda subsurface pressures (0.8 at 700 km). Station differences (to which MODE-sized eddies would make the principal contribution) are relatively small. The large horizontal scale of the recorded bottom pressure fluctuations resembles that of atmospheric pressure, yet the coherence locally between atmospheric and bottom pressure is slight; the recorded fluctuations may be related to a barotropic ocean response to a variable wind stress on the subtropical gyre. Bottom temperature records show “sudden” (1 day) changes of order 30 millidegrees Celcius separated by long intervals (2...

During 1971 to 1974, offshore pressure gages were developed in the Gulf of Mexico and the Caribbean Sea to measure tides and bottom pressure continuum. The observations indicate that the Gulf of Mexico has a Helmholtz resonance with a period of 1.56d. While the lack of confidence limits on theoretical cotidal charts hinders the comparison between theory and observation, the latter tend to support a model with direct astronomical forcing. The observations in the Caribbean Sea verify the general features of theoretical cotidal charts. At a six-month long station in the Eastern Caribbean, bottom pressure fluctuations with 4 to 5-d period are coherent and in phasewith atmospheric waves in the Easterlies. The inverse barometer compensation appeared to be less complete in this semi-enclosed sea, spanned by weather systems, than in the open ocean. An appendix gives corrections to the response method of tidal analysis, the procedure for converting the results to harmonic constants with error estimates, and tables of analytic l results.

An analytic theory is presented for free, barotropic Kelvin waves subject to constant, vertical eddy viscosity on a semi-infinite, f-plane shelf of constant depth bordering a straight, vertical coast. A coastal boundary condition closes the solutions of Sverdrup (1927) and Fjeldstad (1929) by requiring that the component of vertically integrated, volume transport normal to the coast be zero just seaward of coastal boundary layers. This condition on offshore transport is then found to hold everywhere seaward of the coastal layers. One condition on the complex wavenumber components is the dispersion relation in which frictional bottom stress appears in an equivalent depth. The coastal boundary condition then fixes the wavenumber components. The effects of vertical viscosity are found to depend on the frequency ω′ relative to the inertial frequency and on the Ekman number E or, more conveniently, the vertical scale E½ of steady, bottom Ekman layers. Below a frequency dependent on E½, low-frequency K...

We study theoretically the effects of linear (Rayleigh) friction on free internal waves in the equatorial wayeguide. The waves may be vertically propagating or in standing vertical modes. Analytic solutions on a beta-plane show that the meridional scale of the wayeguide becomes significantly larger than the inviscid value only when the frequency is much less than the friction coefficient. In the limit of zero frequency, the meridional scale grows without bound. The amount of zonal damping depends on the wave type. Kelvin, high-frequency Yanai (mixed Rossby-gravity), inertial-gravity and low-wavenumber (non-dispersive) Rossby waves decay relatively slowly while low-frequency Yanai and high-wavenumber (short) Rossby waves are much more strongly attenuated. With friction, transitions to evanescence are spread over frequency bands; waves that had zero group velocity without friction are zonally evanescent with friction. Off the equator, friction changes amplitude nodes into non-zero minima and smooth...

This work lists important references on the issue of critical stress for incipient motion and erosion, principally for noncohesive, abiotic sediments. It emphasizes publications subsequent to the bibliography compiled in 1966 by the Committee on Sediment Transport Mechanics. These references refer to the paper ``Do Critical Stresses for Incipient Motion and Erosion Really Exist?'' by J. William Lavelle and Harold O. Mofjeld, Journal of Hydraulic Engineering, March, 1987.

On 10 August 1976 Hurricane Belle passed rapidly over the highly stratified shelf of the New York Bight. Records from Aanderaa current-meter moorings show that the response to the hurricane depended strongly on bathymetry. At deeper stations (∼70 m depth), intense, first-mode, internal near-inertial oscillations were generated at frequencies ∼1% less than the local inertial frequency. At shallower stations (∼50 m depth), only weak, heavily damped second-mode oscillations were observed in the current records, with no corresponding inertial signals in temperature. In the Hudson Shelf Valley, inertial motion occurred only near the surface. This was probably due to topographic effects. The divergence and curl of the wind stress contributed equally to the forcing. The response at the deeper stations is consistent with Geisler's (1970) theory for the open ocean in which a hurricane leaves a wake of internal-inertial oscillations if it travels faster than the internal phase speed and if its horizontal s...

Since 1997, PMEL has been involved in the R’D effort to provide tsunami-forecasting capabilities for the Pacific Disaster Center (PDC) in Hawaii. As a part of this effort, modeling tools for the short-term forecasting, and assessing the risk of tsunami inundation have been developed. The Short-term Inundation Forecasting for Tsunamis (SIFT) will involve gathering information from several observation system — seismic network, Deepocean Assessment, and Reporting of Tsunamis (DART), and coastal tide-gages —,“sifting” through the information that will be used for tsunami modeling and, finally, provide inundation forecast for selected communities based on simulation results.

Bottom pressure observations (November 1981 to August 1982) show that the diurnal tides dominate the outer reaches of the northeastern Bering Sea shelf. The diurnal tides decrease inshore from the shelf break (maximum K1 amplitude of 38 cm) and appear to be evanescent Sverdrup (Poincare) waves on the outer shelf. The K1 amplitude (2.3 cm) in the Bering Strait is 6% of that at the shelf break. The diurnal phase lags vary little (322°–359°G for the K1 tide) between the stations. North and eastward from the shelf break, the tides become smaller and more semidiurnal. The semidiurnal amplitudes vary considerably between stations; these observations show the effects of semidiurnal amphidromic systems predicted by numerical models. The M2 amplitude (7.6 cm) in the Bering Strait is about a third of that at the shelf break (M2 amplitude of 23 cm). The semidiurnal phase lags are earliest at the shelf break (87°G for M2) and appear to increase toward St. Lawrence Island (336°G for M2 in Shpanberg Strait) and the Bering Strait (202°G for M2). The tidal harmonic constants fluctuated seasonally, possibly in response to the variations in ice cover. The diurnal amplitudes generally increased during winter, while the semidiurnal amplitudes decreased. At the shelf break the K1 amplitude increased 2.5 cm or 7%, but the O1 and semidiurnal M2 amplitudes (0.4 cm or 2% for M2) showed little variation. In Bering Strait the variations in M2 amplitude (up to 3.0 cm) amounted to 37% of the mean amplitude; the decrease may be due to attenuation of the M2 tide from the Arctic Ocean in addition to damping of the M2 tide on the northeastern Bering Sea shelf. Shorter-term fluctuations were also observed in the tides. The tidal fluctuations may contribute to those observed in the deep sea. Numerical models show a set of amphidromic systems (including a semidiurnal system off Cape Navarin) and rapid phase transitions in the vicinity of some of the stations; these models are in relatively good agreement with the observations.

The past 20 years have seen a major increase in the measurement, analysis, and modeling of sea level phenomena. Whether the topic is the measurement of long-term climatic changes in sea level, mapping the global distribution of tides with satellites, or developing high-resolution storm surge models, there is a large technical literature on these and other sea level topics that is very useful, but often difficult for the nonspecialist or student to understand and apply. While previous texts and references, such as those by Defant [1961], Neumann and Pearson [1966], and Dietrich et al. [1980] provide an introduction to the classic description of tides a n d other sea level phenomena, none of these provides an introduction to the important advances that have occurred during this recent period.