Resonance of long waves generated by storms obliquely crossing shelf topography in a rotating ocean

2011 ◽  
Vol 682 ◽  
pp. 261-288 ◽  
Author(s):  
S. THIEBAUT ◽  
R. VENNELL
Keyword(s):  
Continental Shelf ◽  
Time Scale ◽  
Incident Angle ◽  
Storm Surges ◽  
Wave Mode ◽  
Kelvin Wave ◽  
Translation Speed ◽  
Proudman Resonance ◽  
Forced Waves ◽  
Storm Characteristics

The oceanic forced wave beneath a moving atmospheric disturbance is amplified by Proudman resonance. When modified by the Earth's rotation this classical resonance only occurs if the disturbance time scale is smaller than the inertial period. With or without Coriolis effects, free transients generated by storm forced waves obliquely crossing step changes in water depth at particular angles are shown to resonate by exciting a range of long barotropic free waves. Rotationally influenced slow atmospherically forced waves crossing a vertical coast at a critical angle lead to a form of subcritical resonance, which occurs only when the component of the disturbances' phase velocities along the coast matches that of a free Kelvin wave (KW). In a rotating ocean, transients generated by disturbances crossing a step at a particular angle are shown to excite a free double Kelvin wave (DKW). This new type of resonance only occurs for sufficiently large steps and disturbances with time scale greater than the inertial period. A storm crossing a step shelf can result in the excitation of an infinite set of edge waves, a single KW, a unique DKW and a first-mode continental shelf wave, depending on the topography and the disturbance time scale, translation speed and incident angle. The study of resonances and wave mode excitations generated by storms crossing a coast or a continental shelf may contribute to understanding how a particular combination of the storm characteristics can result in destructive coastal events with time scales encompassing the typical meteotsunami period band (tens of minutes) and storm surges with periods of several hours or days.

scholarly journals Projected Climate Change Impacts on Hurricane Storm Surge Inundation in the Coastal United States

2020 ◽  
Vol 6 ◽  
Author(s):  
Jeane Camelo ◽  
Talea L. Mayo ◽  
Ethan D. Gutmann
Keyword(s):  
Climate Change ◽  
Storm Surge ◽  
Climate Change Impacts ◽  
Storm Surges ◽  
Translation Speed ◽  
Climate Change Research ◽  
Average Change ◽  
Projected Changes ◽  
Storm Characteristics ◽  
The Impact

The properties of hurricanes directly influence storm surges; however, the implications of projected changes to the climate are unclear. Here, we simulate the storm surges of historical storms under present day and end of century climate scenarios to assess the impact of climate change on storm surge inundation. We simulate 21 storms that impacted the Gulf of Mexico and Atlantic Coasts of the continental U.S. from 2000 to 2013. We find that the volume of inundation increases for 14 storms and the average change for all storms is +36%. The extent of inundation increases for 13 storms, and the average change for all storms is +25%. Notable increases in inundation occur near Texas, Louisiana, Mississippi, the west coast of Florida, the Carolinas, and New Jersey. Our calculations of inundation volume and extent suggest that at the end of the century, we can expect hurricanes to produce larger storm surge magnitudes in concentrated areas, as opposed to surges with lower magnitudes that are widespread. We examine changes in maximum wind speed, minimum central pressure, translation speed, and radius of the 33 ms−1 wind to assess the impacts of individual storm characteristics on storm surge. We find that there is no single storm characteristic that directly relates to storm surge inundation or its climate induced changes. Even when all the characteristics are considered together, the resulting influences are difficult to anticipate. This is likely due to the complexity of the hydrodynamics and interactions with local geography. This illustrates that even as climate change research advances and more is known about projected impacts to hurricanes, implications for storm surge will be difficult to predict without explicit numerical simulation.

scholarly journals AMO- and ENSO-Driven Summertime Circulation and Precipitation Variations in North America

2012 ◽  
Vol 25 (19) ◽  
pp. 6477-6495 ◽  
Author(s):  
Qi Hu ◽  
Song Feng
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
Time Scale ◽  
Southern Oscillation ◽  
Precipitation Anomaly ◽  
Enso Cycle ◽  
Interannual Variations ◽  
Recent Climate ◽  
Precipitation Anomalies ◽  
Forced Waves

Abstract Interannual and multidecadal time-scale anomalies in sea surface temperatures (SST) of the North Atlantic and North Pacific Oceans could result in persistent atmospheric circulation and regional precipitation anomalies for years to decades. Understanding the processes that connect such SST forcings with circulation and precipitation anomalies is thus important for understanding climate variations and for improving predictions at interannual–decadal time scales. This study focuses on the interrelationship between the Atlantic multidecadal oscillation (AMO) and El Niño–Southern Oscillation (ENSO) and their resulting interannual to multidecadal time-scale variations in summertime precipitation in North America. Major results show that the ENSO forcing can strongly modify the atmospheric circulation variations driven by the AMO. Moreover, these modifications differ considerably between the subtropics and the mid- and high-latitude regions. In the subtropics, ENSO-driven variations in precipitation are fairly uniform across longitudes so ENSO effects only add interannual variations to the amplitude of the precipitation anomaly pattern driven by the AMO. In the mid- and high latitudes, ENSO-forced waves in the atmosphere strongly modify the circulation anomalies driven by the AMO, resulting in distinctive interannual variations following the ENSO cycle. The role of the AMO is shown by an asymmetry in precipitation during ENSO between the warm and cold phases of the AMO. These results extend the outcomes of the studies of the recent Climate Variability and Predictability (CLIVAR) Drought Working Group from the AMO and ENSO effects on droughts to understanding of the mechanisms and causal processes connecting the individual and combined SST forcing of the AMO and ENSO with the interannual and multidecadal variations in summertime precipitation and droughts in North America.

Interactions between Moisture and Tropical Convection. Part II: The Convective Coupling of Equatorial Waves

2020 ◽  
Vol 77 (5) ◽  
pp. 1801-1819 ◽  
Author(s):  
Brandon Wolding ◽  
Juliana Dias ◽  
George Kiladis ◽  
Eric Maloney ◽  
Mark Branson
Keyword(s):  
Gravity Wave ◽  
Time Scale ◽  
Empirical Relationship ◽  
Phase Relationship ◽  
Static Stability ◽  
Kelvin Wave ◽  
Easterly Waves ◽  
Temperature Anomalies ◽  
Trmm Precipitation ◽  
Static Energy

Abstract The exponential increase in precipitation with increasing column saturation fraction (CSF) is used to investigate the role of moisture in convective coupling. This simple empirical relationship between precipitation and CSF is shown to capture nearly all MJO-related variability in TRMM precipitation, ~80% of equatorial Rossby wave–related variability, and ~75% of east Pacific easterly wave–related variability. In contrast, this empirical relationship only captures roughly half of TRMM precipitation variability associated with Kelvin waves, African easterly waves, and mixed Rossby–gravity waves, suggesting coupling mechanisms other than moisture are playing leading roles in these phenomena. These latter phenomena have strong adiabatically forced vertical motions that could reduce static stability and convective inhibition while simultaneously moistening, creating a more favorable convective environment. Cross-spectra of precipitation and column-integrated dry static energy show enhanced coherence and an out-of-phase relationship in the Kelvin wave, mixed Rossby–gravity wave, and eastward inertio-gravity wave bands, supporting this narrative. The cooperative modulation of precipitation by moisture and temperature anomalies is shown to shorten the convective adjustment time scale (i.e., time scale by which moisture and precipitation are relaxed toward their “background” state) of these phenomena. Speeding the removal of moisture anomalies relative to that of temperature anomalies may allow the latter to assume a more important role in driving moist static energy fluctuations, helping promote the gravity wave character of these phenomena.

On the long-term evolution of an intense localized divergent vortex on the beta-plane

2000 ◽  
Vol 422 ◽  
pp. 249-280 ◽  
Author(s):  
G. M. REZNIK ◽  
R. GRIMSHAW ◽  
E. S. BENILOV
Keyword(s):  
Time Scale ◽  
Near Field ◽  
Relative Vorticity ◽  
Translation Speed ◽  
Ocean Eddies ◽  
Second Stage ◽  
Third Stage ◽  
Typical Time ◽  
Vortex Size ◽  
Time Required

The evolution of an intense barotropic vortex on the β-plane is analysed for the case of finite Rossby deformation radius. The analysis takes into account conservation of vortex energy and enstrophy, as well as some other quantities, and therefore makes it possible to gain insight into the vortex evolution for longer times than was done in previous studies on this subject. Three characteristic scales play an important role in the evolution: the advective time scale Ta (a typical time required for a fluid particle to move a distance of the order of the vortex size), the wave time scale Tw (the typical time it takes for the vortex to move through its own radius), and the distortion time scale Td (a typical time required for the change in relative vorticity of the vortex to become of the order of the relative vorticity itself). For an intense vortex these scales are well separated, Ta [Lt ] Tw [Lt ] Td, and therefore one can consider the vortex evolution as consisting of three different stages. The first one, t [les ] Tw, is dominated by the development of a near-field dipolar circulation (primary β-gyres) accelerating the vortex. During the second stage, Tw [les ] t [les ] Td, the quadrupole and secondary axisymmetric components are intensified; the vortex decelerates. During the last, third, stage the vortex decays and is destroyed. Our main attention is focused on exploration of the second stage, which has been studied much less than the first stage. To describe the second stage we develop an asymptotic theory for an intense vortex with initially piecewise-constant relative vorticity. The theory allows the calculation of the quadrupole and axisymmetric corrections, and the correction to the vortex translation speed. Using the conservation laws we estimate that the vortex lifetime is directly proportional to the vortex streamfunction amplitude and inversely proportional to the squared group velocity of Rossby waves. For open-ocean eddies a typical lifetime is about 130 days, and for oceanic rings up to 650 days. Analysis of the residual produced by the asymptotic solution explains why this solution is a good approximation for times much longer than the expected formal range of applicability. All our analytical results are in a good qualitative agreement with several numerical experiments carried out for various vortices.

scholarly journals Dynamical Origin of Low-Frequency Variability in a Highly Nonlinear Midlatitude Coupled Model

2006 ◽  
Vol 19 (24) ◽  
pp. 6391-6408 ◽  
Author(s):  
S. Kravtsov ◽  
P. Berloff ◽  
W. K. Dewar ◽  
M. Ghil ◽  
J. C. McWilliams
Keyword(s):  
Nonlinear Oscillation ◽  
Time Scale ◽  
Low Frequency ◽  
Coupled Model ◽  
Zonal Flow ◽  
Wave Mode ◽  
Ocean Basin ◽  
Coupled Mode ◽  
Highly Nonlinear ◽  
Channel Configuration

Abstract A novel mechanism of decadal midlatitude coupled variability, which crucially depends on the nonlinear dynamics of both the atmosphere and the ocean, is presented. The coupled model studied involves quasigeostrophic atmospheric and oceanic components, which communicate with each other via a constant-depth oceanic mixed layer. A series of coupled and uncoupled experiments show that the decadal coupled mode is active across parameter ranges that allow the bimodality of the atmospheric zonal flow to coexist with oceanic turbulence. The latter is most intense in the regions of inertial recirculation (IR). Bimodality is associated with the existence of two distinct anomalously persistent zonal-flow modes, which are characterized by different latitudes of the atmospheric jet stream. The IR reorganizations caused by transitions of the atmosphere from its high- to low-latitude state and vice versa create sea surface temperature anomalies that tend to induce transition to the opposite atmospheric state. The decadal–interdecadal time scale of the resulting oscillation is set by the IR adjustment; the latter depends most sensitively on the oceanic bottom drag. The period T of the nonlinear oscillation is 7–25 yr for the range of parameters explored, with the most realistic parameter values yielding T ≈ 20 yr. Aside from this nonlinear oscillation, an interannual Rossby wave mode is present in all coupled experiments. This coupled mode depends neither on atmospheric bimodality, nor on ocean eddy dynamics; it is analogous to the mode found previously in a channel configuration. Its time scale in the model with a closed ocean basin is set by cross-basin wave propagation and equals 3–5 yr for a basin width comparable with the North Atlantic.

scholarly journals Generation of Rossby waves off the Cape Verde peninsula; role of the coastline

2019 ◽  
Author(s):  
Jérôme Sirven ◽  
Juliette Mignot ◽  
Michel Crépon
Keyword(s):  
Rossby Wave ◽  
Time Scale ◽  
Rossby Waves ◽  
Numerical Study ◽  
Cape Verde ◽  
Water Model ◽  
Kelvin Wave ◽  
Reduced Gravity ◽  
The North

Abstract. In December 2002 and January 2003 satellite observations of Chlorophyll showed a strong coastal signal along the west african coast between 10° and 22° N. In addition, a wavelike pattern with a wavelength of about 750 kms was observed from December 20th 2002 and was detectable for one month in the open sea, south west to the Cape Verde peninsula. Such a pattern suggests the existence of a locally generated Rossby wave which slowly propagated westward during this period. To verify this hypothesis a numerical study based on a reduced gravity shallow water model has been conducted. A wind burst, broadly extending over the region where the offshore oceanic signal is observed, is applied during 5 days. A Kelvin wave quickly develops along the northern edge of the cape, then propagates and leaves the area in a few days. Simultaneoulsly, a Rossby wave whose characterisics seem similar to the observed pattern forms and slowly propagates westward. The existence of the peninsula limits the extent of the wave to the north. The spatial extent of the wind burst determines the extent of the response and correspondingly the time scale of the phenomenon (about 100 days in the present case). When the wind burst has a large zonal and small meridional extent, the behaviour of a wave to the north of the peninsula differs from that to the south. These results are corroborated and completed by an analytical study of a linear reduced gravity model using a non-Cartesian coordinate system. This system is introduced to evaluate the potential impact of the coastline shape. The analytical computations confirm that, considering the value of the wavelength, a time scale around 100 days can be associated with the observed wave. They also show that the role of the coastline remains moderate at such time scales. On the contrary, when the period becomes shorter (smaller than 20–30 days), the behaviour of the waves is modified because of the shape of the coast. South of the peninsula, a narrow band of sea isolated from the rest of the ocean by two critical lines appears. Its meridional extent is about 100 km and Rossby waves could propagate there towards the coast.

scholarly journals Scattering of a Semidiurnal Barotropic Kelvin Wave into Internal Waves over Wide Continental Shelves

2017 ◽  
Vol 47 (10) ◽  
pp. 2545-2562 ◽  
Author(s):  
Alexander E. Yankovsky ◽  
Tianyi Zhang
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Energy Flux ◽  
Wave Structure ◽  
Wave Mode ◽  
Wave Radiation ◽  
Semidiurnal Tide ◽  
Kelvin Wave ◽  
Scattering Parameter ◽  
Continental Shelves

AbstractIn boundary areas of the World Ocean, a semidiurnal tide propagates in the form of a Kelvin wave mode trapped by the coastline. Over wide continental shelves, the semidiurnal tide is no longer a pure Kelvin wave but attains features of a zero-mode edge wave. As a result, the wave structure and the alongshore energy flux concentrate over the continental shelf and slope topography and become very sensitive to the variations of shelf geometry. When a semidiurnal Kelvin wave encounters alongshore changes of the shelf width, its energy scatters into other wave modes, including internal waves. A particularly strong scattering occurs on wide shelves, where Kelvin wave structure undergoes significant modifications over short alongshore distances. These dynamics are studied using the Regional Ocean Modeling System (ROMS). This study found that when the alongshore energy flux in the Kelvin wave mode converges on the shelf, the offshore wave radiation occurs through barotropic waves, while for the divergent alongshore energy flux, internal waves are generated. Under favorable conditions, more than 10% of the incident barotropic Kelvin wave energy flux can be scattered into internal waves. For the surface-intensified stratification mostly the first internal mode is generated, while for the uniform with depth stratification, multiple internal modes are present in the form of an internal wave beam. A nondimensional internal wave scattering parameter is derived based on the theoretical properties of a Kelvin wave mode, bottom topography, and stratification.

scholarly journals An Object-based Climatology of Precipitation Systems in Sydney, Australia

2021 ◽  
Author(s):  
Hooman Ayat ◽  
Jason P. Evans ◽  
Steven C. Sherwood ◽  
Joshua Soderholm
Keyword(s):  
Cell Tracking ◽  
Clustering Algorithms ◽  
Warm Season ◽  
Radar Data ◽  
Cold Season ◽  
Translation Speed ◽  
Precipitation System ◽  
Different Seasons ◽  
Storm Characteristics ◽  
Sydney Australia

Abstract The climate is warming and this is changing some aspects of storms, but we have relatively little knowledge of storm characteristics beyond intensity, which limits our understanding of storms overall. In this study, we apply a cell-tracking algorithm to 20 years of radar data at a mid-latitude coastal-site (Sydney, Australia), to establish a regional precipitation system climatology. The results show that extreme storms in terms of translation-speed, size and rainfall intensity usually occur in the warm season, and are slower and more intense over land between ~10am and ~8pm (AEST), peaking in the afternoon. Precipitation systems are more frequent in the cold season and often initiate over the ocean and move northward, leading to precipitation mostly over the ocean. Using clustering algorithms, we have found five precipitation system types with distinct properties, occurring throughout the year but peaking in different seasons. While overall rainfall statistics don't show any link to climate modes, links do appear for some system types using a multivariate approach. This climatology for a variety of precipitation system characteristics will allow future study of any changes in these characteristics due to climate change.

Kelvin waves on oceanic boundaries

1972 ◽  
Vol 55 (1) ◽  
pp. 113-127 ◽  
Author(s):  
John W. Miles
Keyword(s):  
Continental Shelf ◽  
Wave Speed ◽  
Vertical Wall ◽  
Kelvin Waves ◽  
Infinite Plane ◽  
Kelvin Wave ◽  
Numerical Examples ◽  
Sustained Change ◽  
Plane Sheet ◽  
Wave Induced

The primitive Kelvin wave (on a rotating, semi-infinite, plane sheet of water of uniform depth bounded by a vertical wall) is corrected for the effects of the Earth's curvature, the reduction in depth over the continental shelf, and bends in the coastline. The results are of interest for coastal propagation of the tides; numerical examples are given for the California coastline. It is found that the Earth's curvature reduces the wave speed south of Cape Mendocmo by 8–10% (the possible range for other coastlines is roughly ± 15%) and that the continental shelf reduces the wave speed by 2−8%. The off-shore mass transport (which vanishes identically for the primitive Kelvin wave) induced by curvature and/or the shelf also is calculated. The analysis of Packham & Williams (1968) for diffraction of a Kelvin wave by a corner is extended to obtain explicit results for the phase of the transmission coefficient. It is found that a sustained change in the direction of the coastline may induce a phase shift of the order of an hour (1·3 hours for the bend at Cape Mendocino), but that small distortions of the coastline without a sustained change in direction have negligible effects on the transmitted Kelvin wave at tidal frequencies.

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