evidence of surface wave enhancement in the southwest indian ocean from satellite altimetry wave height data from geosat over the period november 1986 to february 1989 were used to survey the occurrence of wave amplification attenuation in the southwest indian ocean more than half of the wave profiles that were inspected revealed some enhancement in the agulhas current with 17 of the profiles showing fractional amplification of more than 40 relative to the background wave height other aspects that were considered included attenuation of wave height in the shelf region and the characterization of the agulhas return current by wave height variations

shuttle imaging radar experiment the shuttle imaging radar sir a acquired images of a variety of the earth s geologic areas covering about 10 million square kilometers structural and geomorphic features such as faults folds outcrops and dunes are clearly visible in both tropical and arid regions the combination of sir a and seasat images provides additional information about the surface physical properties topography and roughness ocean features were also observed including large internal waves in the andaman sea

investigation of ocean surface wave refraction using terrasar x data as a scientific and technological continuation of the x band synthetic aperture radar x sar and shuttle radar topography mission srtm missions the new x sar namely terrasar x tsx was launched on june 15 2007 since then it has provided numerous high quality data over land and ocean operationally in this paper surface wave refraction and diffraction are investigated using tsx imagery acquired over the coast of terceira island situated in the north atlantic peak wavelength and wave direction are determined by sar 2 d image spectra they are compared to measurements of x band marine radar and results of the wave prediction model wam significant wave height in the near shore shallow water region is estimated from tsx spotlight mode data following the wave refraction laws and using the developed xwave empirical algorithm image spectra of the tsx subscenes in the full coverage region are given to investigate significant changes of wave direction and length by analyzing another tsx image acquired in stripmap mode a shadow zone in the lee side of terceira island is identified it is influenced jointly by wave refraction and diffraction furthermore a cross sea pattern revealed in the image spectra is investigated the cross sea is generated by the diffracted wave rays from the northern and southern coasts of the island less wave directional spreading for the cross sea situation is observed as well when compared to the image spectra at the origin of diffraction

a comparison of sir b directional ocean wave spectra with aircraft scanning radar spectra directional ocean wave spectra derived from shuttle imaging radar b sir b l band imagery collected off the coast of southern chile on 11 and 12 october 1984 were compared with independent spectral estimates from two airborne scanning radars in sea states with significant wave heights ranging from 3 to 5 meters the sir b derived spectra at 18 and 25 off nadir yielded reasonable estimates of wavelengths directions and spectral shapes for all wave systems encountered including a purely azimuth traveling system a sir b image intensity variance spectrum containing predominantly range traveling waves closely resembles an independent aircraft estimate of the slope variance spectrum the prediction of a u s navy global spectral ocean wave model on 11 october 1984 exhibited no significant bias in dominant wave number but contained a directional bias of about 30 espect to the mean of the aircraft and spacecraft estimates

observations of wind waves in the gulf stream frontal zone experimental results of a study of wind waves in the gulf stream frontal zone are presented measurements of two dimensional radar spectra of surface waves and surface current were performed during ship crossings of the gulf stream under different wind conditions waves reflected from the gulf stream were observed on the windward side for an along current wind these effects resulted in a widening of the spectrum angular distribution and a deviation of the mean wave direction from that of the wind trapped waves were observed under against current winds depending on wave age the trapped waves were either locally generated developing waves or entered into the jet downstream nearly fully developed waves trapped waves significantly increased the wave energy locally the experimental data are interpreted in terms of wave kinematics and the equation of spectrum evolution in the relaxation approximation

insights into orogenic processes from drab schists and minor intrusions southern sao francisco craton brazil abstract minor altered intrusions and drab retrogressed schists can easily be overlooked in geological studies but this contribution explores these rocks within the archaean and palaeoproterozoic southern sao francisco craton ssfc brazil using geological relationships and accessory mineral in situ analyses in the context of cratonic assembly three magmatic pulses are documented i archaean and ii palaeoproterozoic felsic intrusions both hosted by archaean protoliths and iii palaeoproterozoic felsic intrusions in palaeoproterozoic supracrustal sequences archaean felsic intrusions confirm the palaeoarchaean age of the mafic ultramafic sequence of the rio das velhas greenstone belt and rhyacian intrusions mark the collisional stage of the mineiro belt with the sfc at c 2130 ma greenstone belt schists show a wide distribution of rounded soccer ball archaean detrital and metamorphic zircon grains ranging in age from 3200 to 2750 ma with an interpreted overprinting high grade metamorphic event at c 2700 to 2680 ma most high grade metamorphic rims have th u 0 1 negative ehf t values and ree pattern consistent with eclogite granulite metamorphic facies reinforcing the hypothesis of a dehydrated refractory crust formed during the stabilization of the ssfc even though no such protoliths are preserved this event links crustal thickening and partial melting of archaean lower crust archaean rutile crystals from the greenstone belt schist were reset during the palaeoproterozoic event but still preserve the early archaean high grade metamorphic signature the presence of unstable ilmenite replaced by rutile in the schist associated to felsic intrusions with the same age at c 2130 ma suggest high pressure low temperature prograde metamorphism during the collisional stage of the palaeoproterozoic orogen elongate and prismatic zircon grains from the rhyacian intrusions have low ehf t signature and crystallised from partial melting of sedimentary protoliths accretionary events produced thicker and more differentiated crust by the end of rhyacian time easily overlooked rocks in this study when studied have revealed a rich multi event history of cratonic evolution

effects of the gulf stream on ocean waves in the present study a third generation numerical wave model is used to study effects of a straight gulf stream and a gulf stream ring on ocean waves in swell and storm conditions the model accounts for all relevant processes of propagation generation and dissipation of the waves including current effects without imposing a priori restraints on the spectral development of the waves the dominating mechanism affecting the waves appears to be current induced refraction even though the short crestedness of the incoming waves tends to mask its effects also in swell conditions depending on wind and wave conditions refraction may trap locally generated waves in the straight gulf stream or it may reflect wave energy back to the open ocean in the gulf stream ring refraction induces a considerable variation in significant wave height and short crestedness but it hardly affects the mean wave direction in storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following current situations

storm waves focusing and steepening in the agulhas current satellite observations and modeling strong ocean currents can modify the height and shape of ocean waves possibly causing extreme sea states in particular conditions the risk of extreme waves is a known hazard in the shipping routes crossing some of the main current systems modeling surface current interactions in standard wave numerical models is an active area of research that benefits from the increased availability and accuracy of satellite observations we report a typical case of a swell system propagating in the agulhas current using wind and sea state measurements from several satellites jointly with state of the art analytical and numerical modeling of wave current interactions in particular synthetic aperture radar and altimeter measurements are used to show the evolution of the swell train and resulting local extreme waves a ray tracing analysis shows that the significant wave height variability at scales 100 km is well associated with the current vorticity patterns predictions of the wavewatch iii numerical model in a version that accounts for wave current interactions are consistent with observations although their effects are still under predicted in the present configuration from altimeter measurements very large significant wave height gradients are shown to be well captured and also associated with the current vorticity patterns at global scale

spatial variations of ocean wave directional spectra from the seasat synthetic aperture radar seasat synthetic aperture radar ocean wave spectra for a 900 km pass are analyzed and interpreted in the context of both their probable generation sources and their surface current and bathymetric modifiers systematic vector wavenumber variations of several times the standard error of determination 1 5 in magnitude and 0 9 in direction occur along the entire 900 km pass the large scale spatial variation of a 200 m swell system can be accurately accounted for as a result of dispersion from a distant storm the more local variations are qualitatively well correlated in position with known currents and bathymetry but show systematic biases that appear partly due to an environmentally dependent instrument transfer function in the regions of high current and highest sea state there is also substantial evidence that a large angular deviation in the center of the pass is the result of a mesoscale eddy just to the east

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

ocean wave directional spectra and wave current interaction in the agulhas from the shuttle imaging radar b synthetic aperture radar sir b synthetic aperture radar ocean wave spectra for a 200 km pass crossing the agulhas current off the coast of africa are analyzed a significant enhancement of one spectral peak along the northern edge of the current is attributed both to amplification of the waves by refraction dominated wave current interaction and to transient specular backscatter contributions spatially correlated to the waves

wave current interaction near the gulf stream during the surface wave dynamics experiment this paper presents a case study on the wave current interaction near the local curvature of a gulf stream meander the wave data were obtained from in situ measurements by a pitch roll discus buoy during the surface wave dynamics experiment swade conducted off wallops island virginia from october 1990 to march 1991 owing to the advection of the gulf stream by the semidiurnal tide the discus buoy was alternately located outside and inside the gulf stream the directional wave measurements from the buoy show the changes in wave direction wave energy and directional spreading when waves encountered the current in the gulf stream meanders a wave refraction model using the ray tracing method with an estimated gulf stream velocity field and meandering condition was used to simulate wave refraction patterns and to estimate wave parameters at relative locations corresponding to buoy measurements the numerical simulation shows that a focusing zone of wave rays was formed near the boundary and behind the crest of a simulated gulf stream meander the focusing of wave rays causes changes in wave direction increases in wave energy and decreases in wave directional spreading which are in good agreement with the results from the buoy measurements

comparison of shuttle imaging radar b ocean wave image spectra with linear model predictions based on aircraft measurements during october 1984 coincident shuttle imaging radar b synthetic aperture radar sar imagery and wave measurements from airborne instrumentation were acquired the two dimensional wave spectrum was measured by both a radar ocean wave spectrometer and a surface contour radar aboard the aircraft in this paper we compare two dimensional sar image intensity variance spectra with these independent measures of ocean wave spectra to verify previously proposed models of the relationship between such sar image spectra and ocean wave spectra the results illustrate both the functional relationship between sar image spectra and ocean wave spectra and the limitations imposed on the imaging of short wavelength azimuth traveling waves

wave current interaction study in the gulf of alaska for detection of eddies by synthetic aperture radar high resolution ers i synthetic aperture radar sar images are used to detect a mesoscale eddy such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the gulf of alaska during high sea states and high winds the direct surface signature of the eddy was not clearly visible but the wave refraction in the eddy area was observed the rays of the wave field are traced out directly from the sar image the ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction these observations are simulated by a ray tracing model which incorporates a surface current field associated with the eddy the numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing the model data comparison for each ray shows the model predictions are in good agreement with the sar data

on the estimation of wave slope and height varnance spectra from sar imagery a procedure is described for using synthetic aperture radar sar imagery to estimate two dimensional ocean wave slope and height variance spectra the logic underpinning the procedure is based both on the results of the numerical simulation of sar wave imagery and analytic descriptions of the sar imaging process the procedure when applied to sar imagery of waves acquired during the recent shuttle imaging radar mission sir b is shown to produce spectra that agree with independent measures of both the two dimensional slope and height variance spectra the implications of these results for future sar missions aimed at measuring ocean waves are considered

the tectonic evolution of the quadrilatero ferrifero minas gerais brazil abstract the structural framework of the quadrilatero ferrifero is the result of two main deformational events the first is an extensional event of palaeoproterozoic age between 2 100 and 1700 ma the transamazonian event which resulted in the formation of archaean granite gneiss domes and the nucleation of regional synclines in the overlying rio das velhas and minas supergroups strata such regional synclines are continuous with each other and are bordered by structural granite gneiss highs at the contact between these units ductile brittle to ductile extensional shear zones are developed representing the dislocation surfaces of archaean blocks this tectonism is probably related to the evolution of a metamorphic core complex formed in the hinterland to the west of a transamazonian collision zone which structured the paramirim craton the second event is compressive and associated with the closure of the pan african brasiliano proto ocean 650 500 ma situated to the east of quadrilatero ferrffero qf during this event a west verging fold and thrust belt ftb developed causing inversion amplification translation and rotation of the basinal synclines the ftb affected mainly the eastern portion of qf and obliterated many of the tectonic features of the extensional event

estimating aircraft sar response characteristics and ocean wave spectra in the labrador sea extreme waves experiment the labrador extreme waves experiment lewex was an international effort to assess methods of measuring and modeling the directional aspects of wind generated ocean waves especially their evolution in the presence of rapidly turning winds the author describes data processing methods that have been developed to derive estimates of two dimensional wave height variance spectra from the ocean imagery obtained in lewex by a c band synthetic aperture radar sar system aboard a canadian cv 580 aircraft sar spectra at altitudes of 20000 and 12000 ft are compared for both large approximately 50 degrees and small approximately 25 degrees radar look angles independence spectral estimates from both a surface contour radar and a radar ocean wave spectrometer aboard a nasa aircraft are used to verify the surface wave spectrum

sun glitter imagery of surface waves part 2 waves transformation on ocean currents under favorable imaging conditions the sentinel 2 multi spectral instrument msi can provide spectacular and novel quantitative ocean surface wave directional measurements in satellite sun glitter imagery ssgi owing to a relatively large swath with high spatial resolution 10 m ocean surface roughness mapping capabilities changes in ocean wave energy and propagation direction can be precisely quantified at very high resolution across spatial distances of 10 km and more this provides unique opportunities to study ocean wave refraction induced by spatial varying surface currents as expected and demonstrated over the grand agulhas current area the mesoscale variability of near surface currents documented and reconstructed from satellite altimetry can significantly deflect in coming south western swell systems based on ray tracing calculations and unambiguously revealed from the analysis of sentinel 2 msi ssgi measurements the variability of the near surface current explains significant wave current refraction leading to wavetrapping phenomenon and strong local enhancement of the total wave energy in addition to its importance for wave modeling and hazard prediction these results open new possibilities to combine different satellite measurements and greatly improve the determination of the upper ocean mesoscale vorticity motions

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

introduction studies of ocean wave spectra from the shuttle imaging radar b experiment imagery of ocean surface waves obtained from synthetic aperture radar sar provides a unique two dimensional fine resolution view of the ocean wave field which has been long thought to be of considerable value for studying air sea inter action wave generation and propagation and wave current refraction wave spectra from sar have also been thought to be extremely useful for updating and verifying global wave forecast models such promise prompted a sar to be placed on seasat an oceanographic satellite which operated in a rather glorious mode for only a little over 3 months in 1978 this imagery has been well studied and indeed has demonstrated the feasibility of acquiring useful directional wave spectra from space e g vesecky and stewart 1982

a stable mid late holocene monsoon climate of the central tibetan plateau indicated by a pollen record abstract a 9500 year holocene pollen record from a river valley wetland of the central tibetan plateau reveals the history of climate fluctuations at the beginning of the holocene the catchment area of the study site was covered by sparse drought tolerant herbaceous vegetation suggesting a climate cooler and drier than today this period was characterised by a high rate of soil erosion as indicated by the deposition of siliciclastic sediment at the site the environment became wetter during the early mid holocene around 8060 7120 cal bp and during which a wetland habitat dominated by sedges was developed at the site throughout the mid holocene the wetland remained stable with steady accumulation of organic material a change to a slightly drier condition took place in the late holocene and after about 1000 cal bp a marked increase in drought tolerant herbs occurred although no trees lived around the site the record shows low but steady increasing tree pollen frequencies throughout the mid late holocene this result confirms a stable largely monsoonal climate in central tibet over the middle to late holocene it also suggests that the optimum period of monsoonal precipitation in central tibet occurred later and lasted longer than that in the east asian monsoon region

lithofacies associations and structural evolution of the archean rio das velhas greenstone belt quadrilatero ferrifero brazil a review of the setting of gold deposits abstract the rio das velhas greenstone belt is located in the quadrilatero ferrifero region in the southern extremity of the sao francisco craton central southern part of the state of minas gerais se brazil the metavolcano sedimentary rocks of the rio das velhas supergroup in this region are subdivided into the nova lima and maquine groups the former occurs at the base of the sequence and contains the major au deposits of the region new geochronological data along with a review of geochemical data for volcanic and sedimentary rocks suggest at least two generations of greenstone belts dated at 2900 and 2780 ma seven lithofacies associations are identified from bottom to top encompassing 1 mafic ultramafic volcanic 2 volcano chemical sedimentary 3 clastic chemical sedimentary 4 volcaniclastic association with four lithofacies monomictic and polymictic breccias conglomerate graywacke graywacke sandstone graywacke argillite 5 resedimented association including three sequences of graywacke argillite in the north and eastern at greenschist facies and in the south at amphibolite metamorphic facies 6 coastal association with four lithofacies sandstone with medium to large scale cross bedding sandstone with ripple marks sandstone with herringbone cross bedding sandstone siltstone 7 non marine association with the lithofacies conglomerate sandstone coarse grained sandstone fine to medium grained sandstone four generations of structures are recognized the first and second are archean and compressional driven from nne to ssw the third is extensional and attributed to the paleoproterozoic transamazonian orogenic cycle and the fourth is compressional driven from e to w is related to the neoproterozoic brasiliano orogenic cycle gold deposits in the rio das velhas greenstone belt are structurally controlled and occur associated with hydrothermal alterations along archean thrust shear zones of the second generation of structures sedimentation occurred during four episodes cycle 1 is interpreted to have occurred between 2800 and 2780 ma based on the ages of the mafic and felsic volcanism and comprises predominantly chemical sedimentary rocks intercalated with mafic ultramafic volcanic flows it includes the volcano chemical sedimentary lithofacies association and part of the mafic ultramafic volcanic association the cycle is related to the initial extensional stage of the greenstone belt formation with the deposition of sediments contemporaneous with volcanic flows that formed the submarine mafic plains cycle 2 encompasses the clastic chemical sedimentary association and distal turbidites of the resedimented association in the eastern sector of the quadrilatero ferrifero it was deposited in the initial stages of the felsic volcanism cycle 2 includes the coastal and resedimented associations in the southern sector in advanced stages of subduction in this southern sedimentary cycle it is also possible to recognize a stable shelf environment following the felsic volcanism cycle 3 comprises sedimentary rocks of the volcaniclastic and resedimented lithofacies associations largely in the northern sector of the area the characteristics of both associations indicate a submarine fan environment transitional to non marine successions related to felsic volcanic edifices and related to the formation of island arcs cycle 4 is made up of clastic sedimentary rocks belonging to the non marine lithofacies association they are interpreted as braided plain and alluvial fan deposits in a retroarc foreland basin with the supply of debris from the previous cycles

implications of melting for stabilisation of the lithosphere and heat loss in the archaean abstract the increased depth and volume of melting induced in a higher temperature archaean mantle controls the stability of the lithosphere heat loss rates and the thickness of the oceanic crust the relationship between density distributions in oceanic lithosphere and the depth of melting at spreading centres is investigated by calculating the mineral proportions and densities of residual mantle depleted by extraction of melt fractions the density changes related to compositional gradients are comparable to those produced by thermal effects for lithosphere formed from a mantle which is 200 c or more hotter than modern upper mantle if archaean continental crust formed initially above oceanic lithosphere the compositional density gradients may be sufficient to preserve a thick archaean continental lithosphere within which the archaean age diamonds are preserved the amount of heat advected by melts at mid ocean ridges today is small but heat advected by melting becomes proportionally more important as higher mantle temperatures lead to a greater volume of melt and as the rate of production of oceanic plates increases archaean tectonics could have been dominated by spreading rates 2 3 times greater than now and with mantle temperatures between ca 1600 c and 1800 c at the depth of the solidus mid ocean ridge melting would produce a relatively thick but light refractory lithosphere on which continents could form protected from copious volcanism and high mantle temperatures

a numerical study of wave refraction in shallow tidal waters wave observations taken at two shallow water sites off the coast of south west wales u k are examined the buoys are located in a region of strong semi diurnal tides and the observations show significant variation at semi diurnal frequencies in period amplitude and direction the interaction between tides and waves is studied using linear theory of wave refraction by slowly varying currents and depths it is shown that quasi steady analytical models fail to reproduce the tidally induced variations in wave parameters a linear ray tracing model including the effects of both spatial and temporal variations in the tidal currents and elevations improves the simulation of the observed modification of the waves short period waves respond to variations in current refraction over a tidal cycle long period waves are more influenced by variations in water depth over a tidal cycle

air sea interaction and feasibility of tsunami detection in the open ocean 1 recent observations of tsunami shadows i e extended darker strips on the ocean surface along a front of a weak tsunami off oahu hawaii suggest that tsunamis in the deep ocean may be remotely detected through changes in ocean surface roughness in this paper physical mechanisms responsible for the formation of tsunami shadows are considered the hypothesis that the change in surface roughness is due to an air sea interaction is examined using an eddy viscosity model for the average reynolds stresses in turbulent flow a theory is developed to model tsunami induced perturbations in the atmospheric boundary layer it is demonstrated that in the lowest tens of centimeters of the atmosphere tsunami induced perturbations of the mean wind velocity are much greater than current velocities in the water and can be comparable to the unperturbed wind velocity enhancement of tsunami induced wind velocity perturbations compared to currents in the tsunami wave occurs because of a generation of a viscous wave in the air by a coherent elevation of large expanses of the ocean surface in the tsunami wave the ratio of the maximum wind velocity perturbation to the amplitude of the current velocity approximately equals d 4 2 ln2 u 2 cz0 where is the von karman constant u is the friction velocity of a background wind z0 is the roughness length of the ocean surface d is ocean depth and and c are the tsunami wavelength and velocity respectively the results are shown to be robust with respect to a choice of a closure model for reynolds stresses dependence of the tsunami induced atmospheric perturbations on background wind velocity and direction tsunami period and amplitude and ocean depth is studied implications of the theoretical predictions on the feasibility of a satellite based system relying on radars and or microwave radiometers for early tsunami warning are discussed

the stratigraphy of the 3 5 3 2 ga barberton greenstone belt revisited a single zircon ion microprobe study abstract recent field and geochemical studies indicate a need to test the stratigraphy of the ca 3 5 ga barberton greenstone belt as it is presently adopted 1 2 this work uses the ion microprobe shrimp to attempt such a test results show that 1 volcaniclastic sediments of the theespruit formation