airborne synthetic aperture radar tracking of internal waves in the strait of gibraltar abstract as part of the international gibraltar experiment we realized on june 22 and 24 1986 two surveys of the strait of gibraltar on board an aircraft equipped with a synthetic aperture radar our objective was to observe at spring tides and during two twelve hour tidal cycles at 24 h interval the generation of internal wave trains linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current and their eastward propagation in the strait the speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on june 22 the tidal coefficient being equal to 92 with a speed relative to the ground of 2 1 to 2 6 m s 1 24 h later during the second survey on june 24 tidal coefficient 90 we observed the propagation of a train of non linear waves the speed of the leading wave of which being about 1 9 ms 1 our data show that other waves pass over the camarinal sill after the release of the bore and secondary internal wave trains are shown to propagate eastwards from there although our sar data show the appearance of waves west of the northern sill at about 4 h after high water hw the mechanism leading to their generation is not clear these waves could propagate eastwards all along the strait and or northwestwards along the western spanish coast they could be responsible for the solitary type events observed at the eastern entrance of the strait at about 7 h after hw by ziegenbein 1969 1970 these events are noticeable in the hydrological parameters time series of armi and farmer 1988 and in the high rate current data 2 min apart from their april 1986 cruise besides these alongstrait waves our sar data show the existence of cross strait waves and give an idea of their wavelength and speed of propagation their presence leads to perturbations in the current revealed by simultaneous current data at the camarinal sill and north of cape cires

advanced remote sensing of internal waves by spaceborne along track insar a demonstration with terrasar x since the seasat mission in 1978 satellite based synthetic aperture radar sar images have been used to study oceanic internal waves internal waves become visible in sar images because their orbital currents modulate the surface roughness while this leads to an accurate spatial representation of internal wave patterns the complexity of the imaging mechanism makes it difficult to derive actual currents and internal wave amplitudes from sar signatures we demonstrate in this paper how a more robust parameter retrieval is possible with along track interferometric sar insar data that resolve amplitudes and temporal phase changes of the backscattered signal together the latter of which are directly related to the scatterers line of sight velocities our example data set which was acquired by terrasar x in dual receive antenna mode at dongsha south china sea exhibits strong signatures of internal waves in the interferogram amplitude and phase we use a simple internal soliton parameterization and a numerical radar imaging model to find a plausible combination of internal wave parameters which leads to good agreement between simulated and observed signatures testing the sensitivity of radar amplitude and phase signatures to various parameters we show that along track insar data should generally permit more accurate and less ambiguous internal wave parameter retrievals than conventional sar images

coastal lee waves on ers 1 sar images alternative dark bright patterns on ers 1 synthetic aperture radar sar images of the west side of the taiwan strait taken on december 8 1994 were recognized to be the sea surface signature of a coastal lee wave such waves are called coastal lee waves because they occur along the lee side of the coast the coastal lee waves appeared in the form of a wave packet distributed within an offshore band 20 40 km wide the first packet which occurred in the northern portion of the observed area contained six waves with variable wavelengths defined as the spatial separation between two waves from 1 7 to 2 7 km the second packet in the middle contained 10 waves with a relatively uniform wavelength of 4 2 km the third packet in the southern portion contained 17 waves with an average wavelength of 2 0 km the crest lengths were from 20 to 80 km local meteorologic parameters observed simultaneously at fuzhou china close to the imaged area showed an offshore wind of 1 5 3 5 m s and a land surface air temperature of 19 c which was 4 c lower than the sea surface temperature sst thus the lower atmospheric boundary conditions at imaging time were very favorable both for generating the land breeze circulation and small wind waves on the sea surface which are in the bragg scattering wavelength band of the c band ers 1 sar a physical model of a three layer atmosphere was developed in order to explain how the land breeze circulation can generate the coastal lee waves the results showed that the vertical velocity disturbance caused by the wind convergence at the land breeze frontal zone is of vital importance for the generation of coastal lee waves and the model gave very good estimates of the processes observed the sar imaging mechanisms of the waves were analyzed in detail the differences between coastal lee waves and ocean internal waves which appear as similar alternative dark bright patterns on sar images were also discussed

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

propagation regimes and populations of internal waves in the mediterranean sea basin abstract the geographical and seasonal distributions of kinematic and nonlinear parameters of long internal waves are derived from the generalized digital environmental model gdem climatology for the mediterranean sea region including the black sea the considered parameters are phase speed of long internal waves and the coefficients at the dispersion quadratic and cubic terms of the weakly nonlinear korteweg de vries type models in particular the gardner model these parameters govern the possible polarities and shapes of solitary internal waves their limiting amplitudes and propagation speeds the key outcome is an express estimate of the expected parameters of internal waves for different regions of the mediterranean basin

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

internal waves in the strait of messina studied by a numerical model and synthetic aperture radar images from the ers 1 2 satellites a new numerical two layer model is presented which describes the generation of internal tidal bores and their disintegration into internal solitary waves in the strait of messina this model is used to explain observations made by the synthetic aperture radar sar from the european remote sensing satellites ers 1 and ers 2 the analysis of available ers 1 2 sar data of the strait of messina and adjacent sea areas show that 1 northward as well as southward propagating internal waves are generated in the strait of messina 2 southward propagating internal waves are observed more frequently than northward propagating internal waves 3 sea surface manifestations of southward as well as northward propagating internal waves are stronger during periods where a strong seasonal thermocline is known to be present 4 southward propagating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow and 5 the spatial separation between the first two internal solitary waves of southward propagating wave trains is smaller in the period from july to september than in the period from october to june the numerical two layer model is a composite of two models consisting of 1 a hydrostatic generation model which describes the dynamics of the water masses in the region close to the strait s sill where internal bores are generated and 2 a weakly nonhydrostatic propagation model which describes the dynamics of the water masses outside of the sill region where internal bores may disintegrate into internal solitary waves due to a technique for movable lateral boundaries the generation model is capable of simulating the dynamics of a lower layer that may intersect the bottom topography the proposed generation propagation model depends on one space variable only but it retains several features of a fully three dimensional model by including a realistic channel depth and a realistic channel width it is driven by semidiurnal tidal oscillations of the sea level at the two open boundaries of the model domain numerical simulations elucidate several observed characteristics of the internal wave field in the strait of messina such as north south asymmetry times of release of the internal bores from the strait s sill propagation speeds and spatial separations between the first two solitary waves of internal wave trains

oceanic internal waves in the sulu celebes sea under sunglint and moonglint moonglint and sunglint satellite imagery acquired from moderate resolution imaging spectroradiometer modis and visible infrared imaging radiometer suite viirs satellite sensors were used to study the characteristics of internal waves iws and their relationship to tides and stratification in the sulu celebes sea tidally generated iws propagate northwestward and southeastward into the sulu and celebes seas showing a spring neap tidal cycle behavior with larger smaller iws occurring under spring neap tides respectively the length of iw crests their wavelength and phase speed derived from the sunglint moonglint image pairs were observed to decrease from spring to neap tides iws in the sulu celebes sea which are correlated with oceanic stratification display seasonal and regional fluctuations in the celebes sea iws were less frequently observed but propagated with faster phase speeds and larger scales compared to those in the sulu sea comparisons of stratification and barotropic tidal transport among the iws generation sites indicate that the shallowing maximum brunt vaisala frequency and strongest tidal transport around pearl bank are major factors contributing to greater iw activity compared to other generation sites iws generated near pangutaran island and pearl bank further merge into one dynamical system creating longer wave crests of 200 km that travel at faster phase speed sim 2 5 text m cdot text s 1 in the sulu sea this paper demonstrates a new application using a combination of sunglint moonglint imagery in tracking an important oceanic phenomenon

on the dynamics of internal waves in a nonlinear weakly nonhydrostatic three layer ocean aspects of the dynamics of internal solitary waves evolving in a three layer ocean are investigated using a new numerical multilayer model that solves the nonlinear weakly nonhydrostatic boussinesq equations and uses high resolution in situ data the model applications refer to two different phenomena frequently observed in the real ocean which can be described using a three layer model rather than a two layer model in the first application the influence of the strength of a shallow seasonal thermocline superimposed on a two layer permanent stratification on the structure of internal solitary waves is studied it is found that while for small to medium wave amplitudes a decrease in the strength of the thermocline yields an increase in the simulated wavelengths for large wave amplitudes this dependence is no longer monotonic in particular in the limiting case of a vanishing thermocline first mode internal solitary wave solutions of the three layer numerical model tend to the analytical internal solitary wave solutions of the miyata equations a two layer model in which the full nonlinearity of the shallow water theory up to first order phase dispersion is retained in the second application that refers particularly to high resolution observations made north and south of the strait of messina in the eurafrican mediterranean basin the generation of internal solitary waves by the evolution of surface and subsurface water jets is investigated the analysis of the in situ data shows in fact that from very energetic surface and subsurface jet like disturbances subject to strong turbulent mixing internal solitary waves emerge as robust quasi nondissipative oceanic features idealized flow conditions aimed at approximating possible initial stages of the observed water jets are imposed to force our numerical model in general good agreement is found between characteristics of observed and simulated wave fields our investigation identifies the observed water jets as peculiar features of the complex ocean dynamics and suggests that layered numerical models can represent helpful tools in understanding fundamental processes inherent in their intricate dynamics

generation mechanism of internal waves by a vertically sheared tidal flow over a sill the internal response over a sill to strong tidal flow superimposed on a vertically sheared steady flow is examined with a simple two layer analytical model as in the case where the vertical shear is absent the upstream propagating internal wave is gradually formed through interference of infinitesimal amplitude internal waves elementary waves emanating from the sill at each instant of time hibiya 1986 with the composite internal froude number exceeding falling below unity in the accelerating decelerating stage of the two layer flow the upstream propagating elementary waves come close together over the sill in this case however the amplitude of the elementary wave is increased when the lower layer velocity is larger than the upper layer velocity whereas it is reduced when the upper layer velocity is larger than the lower layer velocity as a result the internal wave field over the sill differs markedly between the ebb and flood tidal phases it follows from this analytical result that in the strait of gibraltar the internal wave propagating mediterraneanward is significantly amplified during the ebb westward phase of the tidal flow whereas such amplification does not take place throughout the tidal cycle for the internal wave propagating atlanticward this is consistent with the result from satellite observation that the sea surface signatures caused by underlying large amplitude internal wave trains appear only on the mediterranean side and not on the atlantic side

observation of a nonlinear wave disturbance in the marine atmosphere by the synthetic aperture radar aboard the ers 1 satellite a nonlinear wave disturbance in the marine atmosphere associated with an atmospheric cold front has been identified on a spaceborne radar image of the north sea by its imprint on the sea surface this nonlinear wave disturbance is either a solitary wave disturbance or an undular bore propagating in the lower marine atmosphere the radar image showing sea surface manifestations of this atmospheric wave disturbance was acquired over the north sea by the synthetic aperture radar sar aboard the first european remote sensing satellite ers 1 on march 8 1992 atmospheric waves become visible on radar images of the sea surface because they are associated with a varying wind field at the sea surface which modulates the sea surface roughness and thus the backscattered radar power the identification of the wave pattern visible on the ers 1 sar image as a sea surface manifestation of an atmospheric nonlinear wave disturbance has been possible because this disturbance was also captured by meteorological sensors mounted on an 80 m high meteorological mast located on the island of heligoland geophysical parameters characterizing the atmospheric wave disturbance are derived from the ers 1 sar image and from the in situ meteorological data the wave period in the reference frame moving with the average wind is 9 5 min the average wavelength is 2300 m and the propagation velocity is 4 5 4 9 m s 1 estimates of the amplitude of the wind speed fluctuations in the wave propagation direction derived from the meteorological measurements at heligoland and from the gray level variations in the sar image yield values between 1 3 and 3 0 m s 1 the experimental data are interpreted in terms of theories of atmospheric nonlinear gravity waves

on the discrimination of radar signatures of atmospheric gravity waves and oceanic internal waves on synthetic aperture radar images of the sea surface synthetic aperture radar sar images acquired over the ocean frequently show sea wave like patterns that have wavelengths well above those of ocean surface waves and that are sea surface signatures of oceanic internal waves oiws or of atmospheric gravity waves agws however it is often difficult to decide whether they result from the first or the second kind of waves which has led many investigators to misinterpret sar images of the sea surface based on solitary wave and radar imaging theories of agws and oiws we present criteria that help distinguish between them however there are cases where these criteria which are based solely on the shape and structure of the features visible on the sar images yield ambiguous results in these cases one must resort to additional information on the generation of agws and oiws which are listed in this paper

scylla and charybdis observed from space scylla and charybdis are in greek mythology two immortal and irresistible monsters who beset the narrow waters separating the italian peninsula from sicily they give poetic expressions to exceptional oceanographic features encountered in the strait of messina recently the seasat satellite has added new information on the oceanography of this strait for the first time experimental evidence is presented that internal waves are generated in the strait of messina the generation mechanism is linked to tidal currents washing over the shallow sill within the strait the experimental data originate from a synthetic aperture radar sar image obtained from the seasat satellite on sept 15 1978 and from subsequent in situ measurements carried out from the italian research vessel bannock in nov 1980 the circular wave pattern visible on the seasat sar image is interpreted in terms of internal solitons furthermore the seasat sar image also reveals tagli special types of tidal bores encountered in the strait of messina

the motloutse complex and the zimbabwe craton limpopo belt transition in botswana abstract the archaean rocks of northeastern botswana are divided into named lithostratigraphic complexes each a different assemblage of stratiform lithologies granitoids and gneisses and each with differences in metamorphic grade structural style and metallic mineralisation the motloutse complex lies between four other complexes it includes granitoids and orthogneisses typical of the zimbabwe craton to the east detached segments of the quartzite carbonate pelite association of the anomalous matsitama schist belt to the west and migmatites similar to those of the limpopo belt to the south but is itself a distinctive lithological assemblage it shows a higher grade of metamorphism than the adjacent cratonic terranes but lacks the granulites of the limpopo belt it is delineated by relatively abrupt changes in structural style and fabric orientation of which most if not all coincide with shear zones or faults it is partly bounded against the limpopo belt by the magogaphate shear zone but also flanks the western boundary of the limpopo belt central zone west of 27 35 e the motloutse complex was formed in the late archaean between 2 7 ga and 2 5 ga ago in a zone of plutonism which separated a crustal fragment bearing the depositional basin of the matsitama shelf type sequences from the developing greenstone belts to the east during regional deformation elements of the matsitama belt and associated paragneisses were thrust from the southwest over the active magmatic zone and were then infolded with and underplated by migmatites orthogneisses and granitoids of the developing motloutse complex the terranes which were thus accreted to the southwestern margin of the zimbabwe craton during this episode of deformation and crustal thickening d1 d3 were then cut across by dextral movement on the magogaphate shear zone during d4 so juxtaposing the limpopo belt with the motloutse complex the area of the motloutse complex was previously regarded as a transitional boundary between the craton and the mobile belt but is here seen instead as an intracratonic accretionary assemblage on which the ene wsw limpopo trend was partly superimposed during d4 shearing delineation of lithostratigraphic complexes elsewhere in the zimbabwe craton and the limpopo belt may be possible and can be expected to clarify the pattern to which these provinces were assembled during the archaean prior to d4 deformation

estimating ocean coherence time using dual baseline interferometric synthetic aperture radar a new technique for measuring the coherence time of the ocean surface at radar wavelengths has been developed and tested this technique requires an interferometric synthetic aperture radar system with at least two unique baselines along the direction of platform motion the coherence time of the surface may be presented as a high resolution coherence time map this technique was tested using the jpl airsar along track interferometer measurements of the ocean coherence at the l band were made at high spatial resolution under a variety of conditions a new operating technique that results in the required two baselines is described some parametric analysis is performed pertaining to the design of such a system a representative interferometric data set acquired at the strait of messina in 1991 is presented to illustrate the technique the interferometric phase data reveal and measure tidal currents flowing through the strait while the coherence time image shows considerable structure not visible in the backscatter or phase image coherence times in and around the strait were measured to be of the order of 0 1 s at the l band which is in agreement with previous estimates and measurements

analysis of nonlinear internal waves observed by landsat thematic mapper in this work we test the compatibility between the theoretical parameters of a nonlinear wave model and the quantitative information that one can deduce from satellite derive0 data the theoretical parameters are obtained by applying an inverse problem to the solution of the cauchy problem for the korteweg de vries equation our results are applied to the case of internal wave patterns elaborated from two different satellite sensors at the south of messina the thematic mapper and at the north of messina the synthetic aperture radar

analysis of nonlinear internal waves in the new york bight this paper presents the results on internal wave analysis of the current meter mooring data in the new york bight from the sar internal wave signature experiment sarsex selective sets of current and temperature measurements are analyzed for a parametric study of internal wave characteristics and shear effects on wave parameters are studied based on the limited data from moorings the solitary wave theory has been extended for the wave evolution on a continental shelf by including dissipation and shoaling effects a series of numerical simulations are performed to demonstrate the relative importance of dissipation and shoaling effects from an observed initial wave packet at the upstream mooring the numerical evolution simulation compares reasonably well with the measurements at the distant mooring for the leading two large solitons

a new analytical model for internal solitons in the ocean abstract a new model for tidally generated internal solitons in the ocean is advanced based on a little known asymptotic analytical solution to the weakly nonlinear korteweg de vries equation the solution has many of the properties observed in oceanic internal solitary waves solitons it has been adapted to simulate the dynamics of stratified fluid flow driven by tidal forcing at continental shelves and sills and the adaptation describes the canonical behavior of such solitary wave trains it is shown that the solitons are positioned at the leading edge of an internal tidal bore on the shelf and that the distance between successive packets of solitons constitutes the internal tidal wavelength a future paper will apply the model to field observations from four geographical regions

tidal forcing of the water mass interface in the strait of messina the tidal currents of the strait of messina and their effect on the displacement of the water mass interface are discussed utilizing the historical velocity data of francesco vercelli taken from 100 anchor stations during 1922 and 1923 the data show a complex strongly tidal behavior in which speeds of 200 300 cm s are attained over the sill messina is an amphidromic point for the tides of the two main basins of the mediterranean sea and two distinct water masses flow through the strait at different stages of the tide the subsurface levantine intermediate water flowing north alternating with surface tyrrhenian water flowing south the time evolution of the interface between the two marine water layers at the semidiurnal periodicity is computed from the observed distribution of acceleration term for the baroclinic component this interface shows large vertical oscillations with amplitudes of 100 m intersecting both the surface and bottom the results are in reasonable agreement with recent satellite data and other recent field observations and numerical experiments an estimate of the mean position of the interface is made by assuming that the potential energy required to uplift the interface from the equilibrium depth of 150 m to the observed 30 m depth over the sill is derived from the time independent contribution of the nonlinear field acceleration term the results are in reasonable agreement with observations

evidence of short internal waves trailing strong internal solitary waves in the northern south china sea from synthetic aperture radar observations abstract sea surface signatures of short internal waves trailing strong internal solitary waves isws have been detected on several synthetic aperture radar sar images acquired by the advanced synthetic aperture radar asar onboard the european envisat satellite over the northern south china sea scs such configurations were found recently by vlasenko et al 2010 in numerical simulations carried out with the mit general circulation model mitgcm they showed that the short internal waves which have wavelengths of 1 5 km and amplitudes of 20 m ride on second mode isws the existence of these short internal waves which follow a first mode isw can be explained in terms of the taylor goldstein equation that includes a shear in the background current associated with a second mode isw the simulations predict that the short internal waves occur in two distinct areas one close to the luzon strait ls and the other further west in the first area they are generated by the disintegration of a baroclinic bore which is generated by the interaction of the tidal current with the steep two ridged topography in the ls in the second area they are generated when the faster first mode isw overtakes the second mode isw of the previous tidal cycle we have screened the asar archive of the european space agency esa and found many sar images acquired over the northern scs showing sea surface signatures of such short internal waves trailing a much longer first mode strong isw the detailed analysis of six of these sar images shows good correlation between modeled and observed internal wave fields

evidence for the influence of atlantic ionian stream fluctuations on the tidally induced internal dynamics in the strait of messina abstract on 24 and 25 october 1995 high resolution oceanographic measurements were carried out in the strait of messina by using a towed conductivity temperature depth chain and a vessel mounted acoustic doppler current profiler during the period of investigation the surface water of the tyrrhenian sea north of the strait sill was heavier than the surface water of the ionian sea south of the strait sill as a consequence during northward tidal flow surface water of the ionian sea spread as a surface jet into the tyrrhenian sea whereas during southward tidal flow heavier surface water of the tyrrhenian sea spread after having sunk to a depth of about 100 m as a subsurface jet into the ionian sea both jets had the form of an internal bore which finally developed into trains of internal solitary waves whose amplitudes were larger north than south of the strait sill these measurements represent a detailed picture of the tidally induced internal dynamics in the strait of messina during the period of i