Flexural–Gravity Waves on Floating Stratified Ice

AbstractFlexural–gravity waves in the 3 ms to 50 ms period range were recorded on floating layers of ice ranging from 6 cm to 52 cm in thickness. These inversely dispersive waves are analogous to Rayleigh waves propagating on a multi-layered structure. Therefore, flexural–gravity wave dispersion curves can be calculated by the well-known Haskell–Thompson method. This approach allows the effects of snow layers and stratification of the ice to be evaluated. In earlier methods of calculating flexural–gravity wave dispersion. the structure was restricted to a single homogeneous solid layer over a homogeneous fluid. The effect of a low-velocity snow layer is to reduce the short-period phase velocity, and to increase the velocity at long periods. Dispersion curves for ice layers with and without a snow cover cross at an intermediate period that increases as ice thickness increases. These effects are measurable in seismic experiments on frozen ponds and lakes.

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Short-period Rayleigh-wave dispersion across the Tibetan Plateau

Bulletin of the Seismological Society of America ◽

10.1785/bssa0650051051 ◽

1975 ◽

Vol 65 (5) ◽

pp. 1051-1057 ◽

Cited By ~ 1

Author(s):

W. P. Chen ◽

P. Molnar

Keyword(s):

Tibetan Plateau ◽

Simple Wave ◽

Wave Dispersion ◽

New Delhi ◽

The Tibetan Plateau ◽

Period Range ◽

Short Period ◽

Wave Forms ◽

Wave Trains ◽

Rayleigh Wave Dispersion

Abstract Well-dispersed Rayleigh waves within the period range of 4 to 11 sec are observed at New Delhi (NDI) and Shillong (SHL), India, for seven earthquakes near and in the Tibetan Plateau from 1963 to 1971. The dispersion curves and the simply dispersed wave forms suggest a prominent overlying wave guide, probably sediments, in the Tibetan area. The thickness of such sediments is most likely between 2.5 and 7.0 km. The simple wave trains, without much distortion due to multipathing, are consistent with a relatively inert, recent tectonism in Tibet.

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Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

Annales Geophysicae ◽

10.5194/angeo-23-3237-2005 ◽

2005 ◽

Vol 23 (10) ◽

pp. 3237-3260 ◽

Cited By ~ 3

Author(s):

I. V. Subba Reddy ◽

D. Narayana Rao ◽

A. Narendra Babu ◽

M. Venkat Ratnam ◽

P. Kishore ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Lower Stratosphere ◽

Wave Length ◽

Wave Activity ◽

Lower Atmosphere ◽

Wind Fields ◽

Atmospheric Gravity Wave ◽

Short Period ◽

Atmospheric Gravity

Abstract. MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.

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Diurnal variation of short-period (20–120 min) gravity waves in the equatorial Mesosphere and Lower Thermosphere and its relation to deep tropical convection

Annales Geophysicae ◽

10.5194/angeo-29-623-2011 ◽

2011 ◽

Vol 29 (4) ◽

pp. 623-629 ◽

Cited By ~ 5

Author(s):

N. Venkateswara Rao ◽

Y. Shibagaki ◽

T. Tsuda

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Theoretical Calculations ◽

Lower Thermosphere ◽

Tropical Convection ◽

Peak Activity ◽

Medium Frequency ◽

Short Period ◽

Mesosphere And Lower Thermosphere ◽

Mf Radar

Abstract. We study short period gravity waves (20–120 min) in the equatorial Mesosphere and Lower Thermosphere (MLT) using a Medium Frequency (MF) radar at Pameungpeuk (7.4° S, 107.4° E), Indonesia. In particular, we study local time and seasonal variation of the gravity wave variance and its relation to tropical convection. The gravity wave variance at 88 km enhances between 20:00 LT and 07:00 LT, with a peak at 02:00–03:00 LT. The enhancement is mainly observed during February–April and September–October and shows inter-annual variability. Convective activity over the same location persists from 16:00–21:00 LT with a peak activity ~18:00 LT and enhances between November–April. Time delay between the peak of convection and that of gravity wave activity ranges 1–15 h, which is consistent with theoretical calculations and previous reports based on reverse ray tracing analysis.

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The decay of flexural-gravity waves in long sea ice transects

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2009.0187 ◽

2009 ◽

Vol 465 (2109) ◽

pp. 2785-2812 ◽

Cited By ~ 15

Author(s):

Gareth L. Vaughan ◽

Luke G. Bennetts ◽

Vernon A. Squire

Keyword(s):

Sea Ice ◽

Gravity Waves ◽

Experimental Validation ◽

Ocean Waves ◽

Correct Identification ◽

Period Range ◽

Reflection And Transmission ◽

Transmission Coefficients ◽

Naturally Occurring ◽

Flexural Gravity Waves

Flexural oscillations of floating sea ice sheets induced by ocean waves travelling at the boundary between the ice and the water below can propagate great distances. But, by virtue of scattering, changes of ice thickness and other properties encountered during the journey affect their passage, notwithstanding attenuation arising from several other naturally occurring agencies. We describe here a two-dimensional model that can simulate wave scattering by long (approx. 50 km) stretches of inelastic sea ice, the goal being to replicate heterogeneity accurately while also assimilating supplementary processes that lead to energy loss in sea ice at scales that are amenable to experimental validation. In work concerned with scattering from solitary or juxtaposed stylized features in the sea ice canopy, reflection and transmission coefficients are commonly used to quantify scattering, but on this occasion, we use the attenuation coefficient as we consider that it provides a more helpful description when dealing with long sequences of adjoining scatterers. Results show that scattering and viscosity both induce exponential decay and we observe three distinct regimes: (i) low period, where scattering dominates, (ii) high period, where viscosity dominates, and (iii) a transition regime. Each regime’s period range depends on the sea ice properties including viscosity, which must be included for the correct identification of decay rate.

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Ocean-excited plate waves in the Ross and Pine Island Glacier ice shelves

Journal of Glaciology ◽

10.1017/jog.2018.66 ◽

2018 ◽

Vol 64 (247) ◽

pp. 730-744 ◽

Cited By ~ 5

Author(s):

ZHAO CHEN ◽

PETER D. BROMIRSKI ◽

PETER GERSTOFT ◽

RALPH A. STEPHEN ◽

DOUGLAS A. WIENS ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Lamb Waves ◽

Seismic Array ◽

Flexural Wave ◽

Ice Shelf ◽

Storm Activity ◽

Ice Shelves ◽

Flexural Gravity Waves ◽

Plate Waves

AbstractIce shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of grounded ice loss. Long-period gravity-wave impacts excite vibrations in ice shelves that can expand pre-existing fractures and trigger iceberg calving. To investigate the spatial amplitude variability and propagation characteristics of these vibrations, a 34-station broadband seismic array was deployed on the Ross Ice Shelf (RIS) from November 2014 to November 2016. Two types of ice-shelf plate waves were identified with beamforming: flexural-gravity waves and extensional Lamb waves. Below 20 mHz, flexural-gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow-water gravity-wave speeds (~70 m s−1). In the 20–100 mHz band, extensional Lamb waves dominate and propagate at phase speeds ~3 km s−1. Flexural-gravity and extensional Lamb waves were also observed by a 5-station broadband seismic array deployed on the Pine Island Glacier (PIG) ice shelf from January 2012 to December 2013, with flexural wave energy, also detected at the PIG in the 20–100 mHz band. Considering the ubiquitous presence of storm activity in the Southern Ocean and the similar observations at both the RIS and the PIG ice shelves, it is likely that most, if not all, West Antarctic ice shelves are subjected to similar gravity-wave excitation.

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An error analysis of frequency-time analysis

Bulletin of the Seismological Society of America ◽

10.1785/bssa0730010143 ◽

1983 ◽

Vol 73 (1) ◽

pp. 143-155

Author(s):

Chi-Chin Feng ◽

Ta-liang Teng

Keyword(s):

Surface Wave ◽

Matched Filter ◽

Data Extraction ◽

Wave Dispersion ◽

Dispersion Analysis ◽

Time Analysis ◽

Surface Wave Dispersion ◽

Period Range ◽

Dispersion Measurement ◽

Short Period

abstract The temporal resolution and accuracy of frequency-time analysis (FTAN) as applied to surface-wave dispersion analysis are examined for a period range from 10 to 200 sec. The constant relative bandwidth filter (Dziewonski et al., 1969), optimum bandwidth filter (Inston et al., 1971), and display-equalized filter (Nyman and Landisman, 1977) are carefully examined with respect to their adequacy of application over a broad period range. Among these Gaussian filters, the optimum bandwidth filter gives a better performance for relatively short-period (less than 50 sec) dispersion measurement. To measure surface-wave dispersion for a broad period range, a “matched-filter FTAN” technique is introduced by modifying the “residual dispersion measurement” technique (Dziewonski et al., 1972). A detailed numerical analysis is made on this new technique; the result demonstrates a significant improvement on both the resolution and the accuracy of surface-wave dispersion data extraction over a broad period range up to at least 200 sec.

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Evaluation of Various Approximations in Atmosphere and Ocean Modeling Based on an Exact Treatment of Gravity Wave Dispersion

Monthly Weather Review ◽

10.1175/mwr-d-13-00148.1 ◽

2013 ◽

Vol 141 (12) ◽

pp. 4487-4506 ◽

Cited By ~ 7

Author(s):

John K. Dukowicz

Keyword(s):

Fluid Dynamics ◽

Gravity Wave ◽

Gravity Waves ◽

Acoustic Waves ◽

Wave Dispersion ◽

Ocean Modeling ◽

Governing Equations ◽

Low Aspect Ratio ◽

Hydrostatic Approximation ◽

Compressible Fluid Dynamics

Abstract Various approximations of the governing equations of compressible fluid dynamics are commonly used in both atmospheric and ocean modeling. Their main purpose is to eliminate the acoustic waves that are potentially responsible for inefficiency in the numerical solution, leaving behind gravity waves. The author carries out a detailed study of gravity wave dispersion for seven such approximations, individually and in combination, to exactly evaluate some of the often subtle errors. The atmospheric and oceanic cases are qualitatively and quantitatively different because, although they solve the same equations, their boundary conditions are entirely different and they operate in distinctly different parameter regimes. The atmospheric case is much more sensitive to approximation. The recent “unified” approximation of Arakawa and Konor is one of the most accurate. Remarkably, a simpler approximation, the combined Boussinesq–dynamically rigid approximation turns out to be exactly equivalent to the unified approximation with respect to gravity waves. The oceanic case is insensitive to the effects of any of the approximations, except for the hydrostatic approximation. The hydrostatic approximation is inaccurate at large wavenumbers in both the atmospheric and oceanic cases because it eliminates the entire buoyancy oscillation flow regime and is therefore to be restricted to low aspect ratio flows. For oceanic applications, certain approximations, such as the unified, dynamically rigid, and dynamically stiff approximations, are particularly interesting because they are accurate and approximately conserve mass, which is important for the treatment of sea level rise.

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Characteristics of mesospheric gravity waves near the magnetic equator, Brazil, during the SpreadFEx campaign

Annales Geophysicae ◽

10.5194/angeo-27-461-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 461-472 ◽

Cited By ~ 48

Author(s):

M. J. Taylor ◽

P.-D. Pautet ◽

A. F. Medeiros ◽

R. Buriti ◽

J. Fechine ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Magnetic Equator ◽

Small Scale ◽

Medium Scale ◽

Source Regions ◽

High Quality Image ◽

Short Period ◽

Spread F ◽

Radio Measurements

Abstract. As part of the SpreadFEx campaign, coordinated optical and radio measurements were made from Brazil to investigate the occurrence and properties of equatorial Spread F, and to characterize the regional mesospheric gravity wave field. All-sky image measurements were made from two sites: Brasilia and Cariri located ~10° S of the magnetic equator and separated by ~1500 km. In particular, the observations from Brasilia provided key data in relatively close proximity to expected convective sources of the gravity waves. High-quality image measurements of the mesospheric OH emission and the thermospheric OI (630 nm) emission were made during two consecutive new moon periods (22 September to 9 November 2005) providing extensive data on the occurrence and properties of F-region depletions and regional measurements of the dominant gravity wave characteristics at each site. A total of 120 wave displays were observed, comprising 94 short-period events and 26 medium-scale gravity waves. The characteristics of the small-scale waves agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions for the Brasilia and Cariri datasets. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short-period events, suggesting they originated from the same source regions. Medium-scale waves are generally less susceptible to wind filtering effects and modeling studies utilizing these data have successfully identified localized regions of strong convection, mainly to the west of Brasilia, as their most likely sources (Vadas et al., 2009).

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Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra

Natural Hazards and Earth System Science ◽

10.5194/nhess-7-625-2007 ◽

2007 ◽

Vol 7 (5) ◽

pp. 625-628 ◽

Cited By ~ 36

Author(s):

A. Rozhnoi ◽

M. Solovieva ◽

O. Molchanov ◽

P.-F. Biagi ◽

M. Hayakawa

Keyword(s):

Gravity Waves ◽

Fresnel Zone ◽

Signal Amplitude ◽

Magnetic Storms ◽

Frequency Range ◽

Atmospheric Gravity Waves ◽

Period Range ◽

Before And After ◽

Atmospheric Gravity ◽

Large Earthquakes

Abstract. We analyze variations of the LF subionospheric signal amplitude and phase from JJY transmitter in Japan (F=40 kHz) received in Petropavlovsk-Kamchatsky station during seismically quiet and active periods including also periods of magnetic storms. After 20 s averaging, the frequency range of the analysis is 0.28–15 mHz that corresponds to the period range from 1 to 60 min. Changes in spectra of the LF signal perturbations are found several days before and after three large earthquakes, which happened in November 2004 (M=7.1), August 2005 (M=7.2) and November 2006 (M=8.2) inside the Fresnel zone of the Japan-Kamchatka wavepath. Comparing the perturbed and background spectra we have found the evident increase in spectral range 10–25 min that is in the compliance with theoretical estimations on lithosphere-ionosphere coupling by the Atmospheric Gravity Waves (T>6 min). Similar changes are not found for the periods of magnetic storms.

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