a technique for deducing wind direction from satellite microwave measurements of wind speed abstract a technique is presented to deduce wind direction from satellite microwave measurements of wind speed information the technique based on simple ekman boundary layer dynamics makes use of surface pressure fields routinely analyzed at the national meteorological center to demonstrate its application a three day sample of altimeter and scatterometer wind speed data taken from the seasat satellite was used to deduce wind directions the deduced wind vectors are presented and compared with the nmc 1000 mb wind analyses and with the subjectively edited vector winds it is suggested that the technique proposed in this study could be applied to the ocean surface wind speed measurements derived from a satellite altimetric mission to produce a more useful parameter namely the ocean surface wind vector this technique can also be used to objectively resolve potential ambiguities in scatterometer wind directions

model based estimation of wind fields over the ocean from wind scatterometer measurements i development of the wind field model for pt ii see ibid vol 28 no 3 p 361 373 1990 a parametric model for near surface mesoscale wind fields suitable for use in a model based approach to estimate the wind field over a large region of the scatterometer measurement swath from measurements of the radar backscatter of the ocean s surface is discussed the assumptions made in developing the model are described and the accuracy of the resulting model is evaluated the model is based only on scatterometer data and is computationally tractable consisting of a linear equation relating the near surface wind field to a vector of model parameters which is estimated from the scatterometer measurements tradeoffs in the accuracy of the model and the number of unknown parameters are considered

fast rift propagation along the east pacific rise near easter island during a 1983 seabeam cruise we surveyed the easter nazca spreading center which forms the eastern boundary of the easter microplate we have analyzed all available bathymetry and magnetic anomaly data to determine the present fine scale tectonic configuration and recent tectonic evolution of this spreading center the narrowing of the axial brunhes anomaly is best explained by a young propagating rift growing northward at an average rate of 150 mm yr assuming an average spreading rate of 120 mm yr there are indications of a short episode of faster propagation 350 mm yr prior to 0 4 ma these are the fastest rates of rift propagation yet documented the tip of the propagating rift is at about 25 s 112 25 w 180 km south of the previously hypothesized position the recent spreading direction is n85 w a large well defined sheared zone to the west of the western pseudofault bounding the crust formed by the propagating rift suggests that the easter pacific spreading center 360 km to the west is being replaced by the fast propagator

migration of mid ocean ridge volcanic segments the propagation of small offset volcanic spreading centre segments along mid ocean ridge crests may reflect absolute motion of the plate boundary relative to the underlying mesospheric frame such a relationship could be caused by a purely vertical flow of the mantle under spreading centres and would have value in constraining past plate motions from non transform trends generated during along ridge propagation and in linking the major element variability of oceanic crust and upper mantle to the bulk composition and temperatures of mantle ascending under mid ocean ridges

vector empirical orthogonal function modes of the ocean surface wind variability derived from satellite scatterometer data ocean surface winds derived from nscat quikscat and ers 1 2 scatterometer observations during a period from january 1992 to april 2000 were analyzed using the vector empirical orthogonal function veof method with the boreal winter and summer oscillation the first veof is dominated by the indian and east asian monsoons and also shows an annual cycle of the trade winds the second veof represents the boreal autumn and spring oscillation and reveals a transition state between winter and summer the third veof indicates the wind variability associated with el nino southern oscillation enso events because the temporal mode has a high correlation coefficient of 0 8 with the southern oscillation index soi furthermore the third mode reveals the teleconnection of the indian monsoon and wind variability over high latitude oceans such as the aleutian low system with enso events

global systematics of unaveraged mid ocean ridge basalt compositions comment on global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness by e m klein and c h langmuir

volcanic activity and crust mantle exposure in the ultrafast garrett transform fault near 13 28 s in the pacific the 130 km long garrett transform fault which offsets two ultrafast 14 5 cm yr epr spreading segments is the site of volcanic and tectonic activity evidence for recent volcanic events was observed during several dives on oblique ridges 3100 3500 m high trending 040 alpha beta and gamma and on small constructional mounds located in the central transform basin and eastern valley at a depth of 3500 5000 m the constructional features show a fissured terrain suggesting a component of lithospheric opening the strike slip motion of the transform is inferred at several locations between the two epr transform intersection zones from the presence of abundant sediment free talus with crushed rock debris fresh scarps and well developed striations on outcrops of serpentinized peridotites and metamorphosed volcanic breccia the width of the active tectonic zone varies between 200 and 3000 m in the explored area near the eastern and western epr transform intersection zones along the e w trending median ridge walls in the eastern and western transform troughs of the central basin and at several sites on the south facing wall of the transform domain first escarpment the presence of recent volcanic activity implies that the garrett transform behaves as a leaky transform fault the most common volcanics consisting of plagioclase and olivine phyric lava erupted in the transform are compositionally more depleted k ti 0 08 and less evolved mg 60 70 than the basalts encountered on the southern epr segments mg 40 66 and k ti 0 05 0 25 this suggests that different magmatic conditions are operating in the transform domain the transform strike slip motion is responsible for the emplacement of a sliver of serpentinized peridotite located in an area about 2 km wide and 10 km long along the median ridge at the contact with outcrops of metamorphosed basaltic breccia the ultramafics consist of residual harzburgites often impregnated with irregular lenses and dykes of basaltic liquids plagioclase wehrlite and gabbro and are found associated with troctolites dunite and gabbros the emplacement of the ultramafics and their gabbroic inclusions has resulted in the presence of metamorphosed tectonic breccia forming part of the median ridge in the central transform basin

pito and orongo fracture zones the northern and southern boundaries of the easter microplate southeast pacific abstract the easter rapanui microplate is a case example of a large dual spreading center system in a region where the fastest seafloor spreading on earth is occurring today recent theoretical models of the tectonic evolution of dual spreading center systems have explored the effects of shear and rigid rotation on the boundaries and internal structure of microplates but the models must be critically constrained by improved relative motion and structural fabric data sets during the january 1987 rapanui expedition on the n o jean charcot we conducted a sea beam magnetics gravity survey of a portion of the microplate boundaries the method that was used was to fully map selected portions of the boundaries in order to establish precise structural relationships the northern terminus of the east rift or eastern boundary of the microplate is expressed as a series of parallel nw se trending valleys including what appears to be with 5890 m depth the deepest active rift axis mapped in the pacific today pito rift the northern end of the pito rift merges with an e w to 083 narrow band of linear faults interpreted to be a transform fault between the nazca and easter rapanui plates the northern triple junction between the easter rapanui nazca and pacific plates is a rff type with the two transform faults colinear along an approximately e w direction the southwestern boundary of the easter rapanui microplate is marked by a series of en echelon offsets outlined by depressions which merge into an approximately e w zone where shear must be predominant the southern triple junction is a rrf junction with an overlapping ridge system the structural data acquired during the survey provide strong constraints for kinematic models of the microplate the structural data need to be combined with crustal age determinations in order to derive a model for the evolution of the microplate

the seasat a satellite scatterometer the geophysical evaluation of remotely sensed wind vectors over the ocean on the seasat a satellite a microwave scatterometer was used to determine the vector wind over the world s oceans the technique is based on the sensitivity of microwave radar backscatter to the centimeter length ocean waves created by the action of the surface wind this paper describes the algorithm used to convert the scatterometer s measurements of ocean normalized radar cross section to the neutral stability vector wind at 19 5 m height and the comparison of these winds with high quality surface observations the wind vector algorithm used an empirical model function to describe the dependence of the ocean 0 on the 19 5 m neutral stability wind vector two model functions developed from a limited base of aircraft and satellite measurements were evaluated by using an independent set of in situ surface wind observations from the joint air sea interaction experiment jasin although these model functions were found to have some weaknesses the results of these comparisons produced better results than the seasat specifications of wind speed accuracy of 2 m s and wind direction accuracy of 20 over the 0 16 m s range of winds observed during jasin an improved model function was later developed by tuning to these jasin data so that the remaining biases between the observed surface winds and the scatterometer derived winds were minimized results are presented for this model function compared against other surface wind observations from the gulf of alaska seasat experiment and the seasat storms hurricane experiment

wind direction alias removal studies of seasat scatterometer derived wind fields owing to the antenna configuration and the biharmonic nature of the anisotropic return of the probing radar the seasat scatterometer wind reports consist of as many as four wind directions at each point of observation a systematic methodology is proposed for selection of the true direction from among these in the absence of any in situ observations the techniques employed are those familiar to meteorological analysts they were subjected to rigorous testing for the jasin workshop with two teams performing independent analyses the agreement of the two analyses was striking comparison with wind directions from the jasin data set and those estimated from the analyzed pressure field show agreement largely within the seasat specifications it is concluded that the methodology employed is suitable for seasat scatterometer data users

on the evolution of the qe ii storm i synoptic aspects abstract the hurricane force winds and heavy seas which battered the liner queen elizabeth ii on 10 and 11 september 1978 were associated with an extreme example of a meteorological bomb as defined by sanders and gyakum despite the existence of surface buoys and the relatively high density of mobile ships in the north atlantic real time weather analyses subjective forecasts and numerical prognoses all erred in the intensity and track of this storm in this study deficiencies in the real time surface analysis were compensated for by the addition of seasat a surface wind fields and previously discarded conventional ship reports this paper examines the synoptic aspects of this case with emphasis on physical mechanisms most likely responsible for the development the cyclone originated as a shallow barocline disturbance west of atlantic city new jersey and explosive deepening 60 mb 24 h commenced once the storm moved offshore and in association with cumulus convection adjacent to the storm cent

modeling the geostrophic drag coefficient for aidjex a model of the planetary boundary layer flow over the arctic pack ice was found to relate geostrophic flow determined from a large scale pressure field to the surface stress vector a summary of the model and some data comparison is presented

evolution of microstructure in compacted london clay during wetting and loading the influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils these are based on assumptions regarding the interaction b

structural pattern of the galapagos microplate and evolution of the galapagos triple junctions a 13 000 km2 microplate intervenes to prevent the junction of the nazca cocos and pacific plates in the eastern equatorial pacific ocean west of the galapagos islands the microplate is rotating clockwise at 6 m y about an absolute pole 400 km southeast of its center so that although its northern margin has a similar motion to adjacent parts of the cocos plate its southern margin is 50 slower the perimeter of the galapagos microplate is best defined by bathymetry and has been surveyed with sea beam and examined by deep tow two of the three triple junctions on its margins are ridge ridge ridge rrr junctions 160 km apart on the crest of the east pacific rise epr the most like a classic rrr junction is the pacific nazca galapagos intersection at 1 10 n where the epr axis is joined by a narrow volcanic ridge 70 km long and 1 km high the cocos nazca galapagos junction at the west end of the cocos nazca spreading center is inferred to be of the rff type but the transform fault branches are represented by large nontransform offsets lack of stable transform faults is related to rapid westward migration of the junction caused by lengthening of the cocos nazca axis at 60 70 mm yr this rate which was once required to maintain a stable nazca cocos pacific rrr junction has persisted even after birth of the microplate about 1 ma continuing propagation of the cocos nazca axis has opened up the hess deep rift basin in the eastern epr flank in advance of the eruptive propagator tip this rift valley has a relief of more than 3 km from its uplifted rims to the floor where severe attenuation exposes basal layers of the epr crust the similar dietz deep rift basin at the southeastern margin of the microplate 70 km from hess deep was formed when a lengthening galapagos nazca spreading axis rifted through another part of the epr flank

chemistry of deep 3500 5600 m pacific morb why is the pacific anomalous in contrast with the atlantic and indian oceans the pacific shows the global correlations of axial depth and basalt chemistry only weakly or not at all for unaveraged data in the past this observation has been partly explained by the limited depth window of available pacific samples we report on new very young basalt samples collected by submersible from pacific ridges at 3500 5600 m nearly doubling the depth interval of pacific samples these samples from the pito deep hess deep and the garrett transform do not conform to the global correlation of depth vs chemistry and show the local trend of chemical variation the pacific as a whole is thus unusual compared to the atlantic and indian oceans we propose that the anomalous behavior of the pacific is due mostly to its relatively rapid spreading rate and tectonic shifts leading to an absence of a dynamic equilibrium between mantle temperature and seafloor depth observed elsewhere

seasat scatterometer detection of gale force winds near tropical cyclones hurricane center advisories specifying the radius of gale force winds gfw in tropical cyclones are severely limited by inadequate data their accuracy is especially vulnerable in the data void tropical ocean regions the seasat a satellite scatterometer sass sensed surface winds associated with numerous tropical cyclones although instrument design ruled out retrieval of winds within the inner core of the storm surface truth studies indicate sass can detect the threshold of gale force winds 17 18 1 with an accuracy comparable to the original seasat specifications 2 ms 1 or 10 and 20 accurate and abundant sass observations were thus used as verification for advisories specifying the radius of gale force winds for tropical cyclones in the pacific and atlantic ocean basins advisories were found to consistently overestimate the radius of gfw often by a factor of two in the central pacific large asymmetries in the gfw distribution measured by sass were often in considerable disagreement with symmetric circular and semicircular advisory values however advisories that had access to low level aircraft data closely matched sass measured gfw values

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

the relationship between wind vector and normalized radar cross section used to derive seasat a satellite scatterometer winds the dependence of ocean normalized radar cross section nrcs or 0 on the 19 5 m neutral stability wind vector for the seasat a satellite scatterometer sass is described for the sass wind vector algorithm this dependence is specified in the form nrcs u where is the radar incidence angle is the angle between wind direction and radar azimuth and u is the neutral stability wind speed in meters per second at a height of 19 5 m the development of models to express this relationship and to provide the basis for inversion of nrcs to sass winds is traced from its initial form based on aircraft scatterometer measurements through the seasat field validation experiments goasex storms and jasin to its final form comparison of the model nrcs versus surface wind speed with sass data from these experiments are made

wind field model based estimation of seasat scatterometer winds a model based approach to estimating near surface wind fields over the ocean from seasat scatterometer sass measurements is presented the approach is a direct assimilation technique in which wind field model parameters are estimated directly from the scatterometer measurements of the radar backscatter of the ocean s surface using maximum likelihood principles the wind field estimate is then computed from the estimated model parameters the wind field model used in this approach is based on geostrophic approximation and on simplistic assumptions about the wind field vorticity and divergence but includes ageostrophic winds nine days of sass data were processed to obtain unique wind estimates comparisons in performance to the traditional two step point wise wind retrieval followed by ambiguity removal wind estimate method and the model based method are provided using both simulated radar backscatter measurements and actual sass measurements in the latter case the results are compared to wind fields determined using subjective ambiguity removal while the traditional approach results in missing measurements and reduced effective swath width due to fore aft beam cell coregistration problems the model based approach uses all available measurements to increase the effective swath width and to reduce data gaps the results reveal that the model based wind estimates have accuracy comparable to traditionally estimated winds with less noise in the directional estimates particularly at low wind speeds in addition wind fields generated using the model based procedure can be used to detect and correct ambiguity removal errors in ambiguity removed point wise wind fields a separate procedure based only on the wind field model can also be used as a data quality check to detect errors in point wise ambiguity removal

a scheme for improving scatterometer surface wind fields a method is presented for improving quikscat surface wind fields the university of washington planetary boundary layer model is used to retrieve a surface pressure field from any swath of quikscat surface wind vectors an alternate set of surface wind vectors is computed from the newly calculated pressure field the latter can be smoothed and the process can be iterated new surface wind vectors can be calculated where ambiguity removal fails and where measurements are missing the present methodology preserves boundary layer dynamics and is an improvement over a statistical filter

on a satellite scatterometer as an anemometer the seasat a satellite scatterometer sass wind algorithm was tested against surface wind fields three classes of surface wind fields were used point measurements an isotach field over an intensively measured triangle with 200 km sides and synoptic scale winds determined from pressure and temperature fields and a planetary boundary layer model these comparisons can verify optimal capabilities of sass at accuracies of 2 m s 1 and 20 sass ability to locate fronts accurately is also established complications in nonsteady highly variable fields indicate problems exist in unqualified application of the sass algorithm to all conditions

ocean surface pressure fields from satellite sensed winds abstract the university of washington s planetary boundary layer model is inverted to use remotely sensed satellite scatterometer derived surface winds as input to calculate maritime surface pressure fields the analysis of three different synoptic storm situations is performed using the model and is then compared to conventional national weather service analyses agreement is good isolation of the pbl secondary flow stratification and thermal wind effects in the model revealed that each may be significant under certain conditions however the model shows sensitivity to the thermodynamic features only in a general sense and even a neutral stratification solution gives a good approximation the high density of the scatterometer data produces mesoscale hundreds of kilometers dynamic details which cannot be confirmed by conventional data at this stage

petrology of the east pacific rise crust and upper mantle exposed in hess deep eastern equatorial pacific the hess deep a rifted oval shaped depression located east of the galapagos triple junction at the tip of the cocos nazca ridge about 101 w 2 n was explored in 1988 during 21 submersible dives a total of 11 dives were devoted to the exploration of the e w trending intrarift ridge 15 km in length 3000 5400 m in depth north of the hess deep depression the intrarift ridge represents an outcrop of recent 1 m y crustal and subcrustal material created at the axis of the east pacific rise epr and emplaced during the lithospheric extention responsible for the westward propagation of the cocos nazca rift francheteau et al 1990 the lithospheric block has undergone cataclastic deformation and was dislocated by tectonic activity as attested to by the mixed and erratic distribution of rock types and by the occurrence of polygenic breccias and gabbroic mylonites the samples are metamorphosed to varying degrees but their protolith textures are generally well preserved their relic mineralogy indicates that they consist of harzburgites dunites gabbroic cumulates gabbronorites and olivine gabbros isotropic gabbros dolerites and basalts some samples of refractory harzburgites and most dunitic cumulates with local accumulation of chromite have been impregnated by wehrlitic and gabbroic primitive melts similar to those described from the mantle crust transition zone of the samail ophiolite complex oman the mineral chemistry indicate that the ultramafics partly reequilibrated with the magmatic impregnations in the liquidus solidus temperature range of 980 1100 c the dolerites and basalts have been derived from mid ocean ridge basalt primary melts presenting a broad range of incompatible element composition which suggests intermittent cycles of magmatic processes involving a progressive melting of a composite source with discontinous extraction of liquids as proposed for the epr volcanics near 13 n hekinian et al 1989 most of the rocks underwent partial retrograde metamorphism and recorded several episodes of recrystallization from the upper greenschist facies ultramafics and gabbros to diagenetic alteration volcanics the cumulate gabbronorites the isotropic gabbros and some dolerites were partially albitized and amphibolitized during the penetration of seawater in the ocean crust prior to serpentinization several samples of unfoliated amphibolites are believed to be completely metamorphosed gabbroic rocks the gabbroic cumulates and the plagioclase rich melt impregnations were variably rodingitized presence of various ca silicates such as epidote prehnite hydrogarnet and zeolite in relation to the serpentinization of the peridotites one dive located on the scarps forming the northern wall of the hess deep to the east of the explored area revealed the presence of in situ outcrops of isotropic gabbros doleritic dikes and extrusives and permitted to observe the contact between the sheeted dike complex and the high level isotropic gabbros

wind and pressure fields near tropical cyclone oliver derived from scatterometer observations the results of this study demonstrate that the surface wind velocity and pressure fields derived from spaceborne scatterometers are useful in monitoring the location and intensity of tropical cyclones satellite borne microwave scatterometers can penetrate the cloudy core regions of tropical cyclones to resolve the circulation in detail over data sparse regions the location of the cyclone observed by the ers 1 scatterometer is very close to that revealed in geostationary meteorological satellite images the surface winds provided by the ers 1 scatterometer are used here with a modified two layer planetary boundary layer model which includes effects of curvature stability and secondary flow to derive surface pressures near tropical cyclone oliver the curvature effect is found to be more significant than stability and secondary flow which are crucial in deriving accurate surface pressure fields in midlatitudes

origin of the oceanic lithosphere in a global examination of mid ocean ridge basalt morb glass compositions we find that na8 fe8 depth variations do not support modeling of morbs as aggregates of melt compositions generated over a large range of temperature and pressure however the na 8 fe8 variations are consistent with the compositional systematics of solidus melts in the plagioclase spinel lherzolite transition in the cao mgo al2o3 sio2 na2o feo cmasnf system for natural compositions the p trange for melt extraction is estimated to be 1 2 1 5 gpa and 1250 12808c this p trange is a close match with the maximum p t conditions for explosive pressurerelease vaporization of carbonate bearing melts it is proposed that fracturing of the lithosphere induces explosive formation and escape of co2 vapor this provides the vehicle for extraction of morbs at a relatively uniform tand p the upper portion of the co2 bearing and slightly melted seismic low velocity zone flows toward the ridge rises at the ridge axis to lower lithosphere depths melts much more extensively during this rise and releases morb melts to the surface driven by explosively escaping co2 vapor the residue and overlying crust produced by this melting then migrate away from the ridge axis as new oceanic lithosphere the entire process of oceanic lithosphere creation involves only the upper 140 km when lithospheric stresses shift fracture formation to other localities escape of co2 ceases the vehicle for transporting melt to the surface disappears and ridges die inverse correlations of na8 vs fe8 for morb glasses are explained by mantle heterogeneity and positive variations superimposed on the inverse variations are consistent with progressive extraction of melts from short ascending melting columns the uniformly low temperatures of morb extraction are not consistent with the existence of hot plumes on or close to ocean ridges in this modeling the southern atlantic mantle from bouvet to about 268n is relatively homogeneous whereas the atlantic mantle north of about 268 ns hows significant long range heterogeneity the mantle between the charlie gibbs and jan mayen fracture zones is strongly enriched in feo mgo perhaps by a trapped fragment of basaltic crust iceland is explained as the product of this enrichment not a hot plume the east pacific rise galapagos ridge gorda ridge and juan de fuca ridge sample mantle that is heterogeneous over short distances the mantle beneath the red sea is enriched in feo mgo relative to the mantle beneath the northern indian ocean

a method for determining equivalent depths of the atmospheric boundary layer over the oceans the concept of an equivalent depth of the atmospheric boundary layer is discussed in the framework of vertically integrated boundary layer equations a method is presented by which these depths may be computed from sea level pressure analyses and ocean surface wind speed measurements an explicit representation that yields a realistic value for the equivalent depth from the equator to the pole is given in terms of these parameters for this study the equivalent depths were calculated from 3 days of altimeter wind speed data taken from seasat this study shows that over the mid latitude and polar regions and in the range of surface wind speeds between 5 m s and 15 m s the equivalent depths are calculated to be about 700 800 m comparable to the heights of the atmospheric boundary layer in the polar region both scale heights are also quite comparable in values ranging between 200 and 600 m over the tropics however the conventional scale heights as is well known are unreasonably large whereas the calculated equivalent depths are quite realistic and well defined it is therefore concluded that the method presented in this study may be used to infer heights of the atmospheric boundary layer over the global oceans in addition the calculated equivalent depths together with the measured surface wind speeds provide an estimate of the spin up time for the boundary layer flows during the 3 day period the spin up times are found to vary between 4 5 hours in the polar regions to about 39 4 hours in the mid latitudes

causes and rate limiting mechanisms of ridge propagation a fracture mechanics model all known propagating rifts pr s are growing away from shallow ridge axis seafloor we examine a model for rift propagation in which the ridge axis conduit like a crack in the lithosphere propagates in response to a stress concentration at its tip the stress concentration near the tip which causes progressive failure of the lithosphere is primarily due to excess gravity spreading stresses associated with anomalously shallow ridge axis along the growing ridge this stress concentration near the tip is characterized by a stress intensity factor k which must exceed a threshold value to cause failure of the plate a remotely applied tensile stress would make a positive contribution to k but would act equally on both ridge segments and not favor the propagation of either the pressure in the crack may depending on its distribution make either a positive or negative contribution to k for a high enough propagation rate viscous flow induced suction due to the growth of the ridge axis as well as the reduced vertical flow near the pr tip would make k 0 this simple model thus includes a mechanism to control the speed of propagation and is consistent with the axial morphology of the spreading segment associated with the well studied 95 5 w pr of the galapagos spreading center analytical solutions for the contribution to the stress intensity factor of viscous forces resisting ridge axis growth and causing the pr axial topography are consistent with the observed propagation rate for asthenosphere viscosities of about 1019 pa s 1020 p we also examine a more general model of a ridge transform ridge system on the basis of energy conservation in terms of energetics this more general model reduces to that of a single propagating ridge axis crack when both the work done by forces driving propagation and the viscous dissipation due to forces resisting propagation are generated along the growing ridge axis however the more general model also includes mechanisms that may stop ridge propagation propagation will stop either when the energy needed for transform migration is larger than that available for ridge axis growth or when the strain energy absorbed at the dying ridge axis is comparable to that released at the growing ridge axis i e if the stress intensity factors for both ridge axes are similar both of these possibilities may occur when the propagating rift completely propagates through a ridge segment as at 85 w in the galapagos finally in this model the slight systematic differences in ridge axis orientation of the growing and dying ridges are a consequence rather than a cause of ridge propagation

a physical model based field wise and self contained algorithm for removing directional ambiguities of ocean surface winds retrieved from scatterometer measurements an algorithm is introduced to remove the directional ambiguities in ocean surface winds measured by scatterometers which requires scatterometer data only it is based on two versions of pbl planetary boundary layer models and a low pass filter a pressure field is first derived from the median filtered scatterometer winds is then noise filtered and is finally converted back to the winds respectively by an inverted pbl model a smoothing algorithm and a pbl model the derived wind field is used to remove the directional ambiguities in the scatterometer data this new algorithm is applied to hurricane eugene and produces results comparable to those from the current standard ambiguity removal algorithm for nasa jpl seawinds project which requires external numerical weather forecast analyses data

the spreading rate dependence of three dimensional mid ocean ridge gravity structure we analyze over 1300 km of high resolution along axis gravity profiles at ridges with half spreading rates ranging from 1 2 to 5 5 cm yr the results show consistently higher along axis gradients of mantle bouguer anomaly at the slow spreading mid atlantic ridge mar 0 3 1 2 mgal km than at the intermediate to fast spreading cocos nazca ridge and east pacific rise epr 0 1 0 2 mgal km the regional peak to trough amplitude of mantle bouguer anomaly is also greater along the mar 30 60 mgal than the cocos nazca ridge and the epr 10 20 mgal with increasing spreading rate the regional peak to trough amplitude of axial seafloor depth decreases from 1000 1700 m to 200 700 m 3 d numerical experiments suggest that mantle contributions to the gravity can be significant only near large offset transforms at the more commonly observed non transform offsets gravity anomalies will reflect crustal thickness variations the along axis gravity data thus indicate that the amplitude of along axis crustal thickness variation decreases with increasing spreading rate we propose that this spreading rate dependent crustal accretion style may originate in the mantle finite amplitude mantle upwelling is intrinsically plume like 3 d beneath a slow spreading ridge but more sheet like 2 d beneath a fast spreading ridge such a transition in mantle upwelling may occur if the relative importance of passive upwelling over buoyant upwelling increases with increasing spreading rate small amplitude 3 d upwellings may occur at a fast spreading ridge but their effects on crustal thickness variations will be significantly reduced by along axis melt flows along a persistent low viscosity crustal magma chamber in contrast the large crustal thickness variations due to 3 d mantle upwellings will be maintained at a slow spreading ridge because less along axis melt flows can occur in the colder and more rigid crust there

wettability decay in an oil contaminated waste mineral mixture with dry wet cycles the dependency of soil particle wettability on soil water content implies that soils subjected to drying wetting cycles become wettable with wetting and water repellent with drying while this has been demonstrated widely the results are contradictory when water repellent soils are subjected to a sequence of cycles added to this past wettability measurements were seldom done in batches of samples collected from the field at natural or dry water contents with little appreciation that slight particle size variations different drying wetting histories and fabric as required by different wettability measurement methods may alter the results this note presents soil particle wettability soil water content relations by means of an index test following staged drying and wetting paths over a period of 8 months for an untreated oil contaminated anthropogenic soil a mixture of slag coal particles fly ash and mineral particles from barry docks uk a site formally used for oil storage which is to be remediated and redeveloped for housing the results revealed a decrease in the water repellency and increasing mineralization and bacterial activity with the wetting and drying cycles

on satellite scatterometer model functions satellite scatterometer model functions are the empirical correlations between observed backscatter and geophysical parameters one problem is the choice of surface truth for the latter currently buoy data and general circulation model surface analyses have been used to establish 10 m neutrally stratified wind model functions the correlation between backscatter and surface winds has been the foundation of the scatterometers the backscatter is anisotropic with respect to wind direction allowing wind direction information to be derived from multiple looks at the same patch of ocean here the evolution of a model function for the pressure gradient hence surface geostrophic wind is given the european center for medium range weather forecasts surface pressure analyses are used to establish the pressure based model function there are limitations and advantages to both geophysical data sets

evidence for variable upper mantle temperature and crustal thickness in and near the australian antarctic discordance abstract the southeast indian ridge seir in and near the australian antarctic discordance aad exhibits at a constant spreading rate almost the full range of the many geophysical and geochemical parameters characteristic of the slow mid atlantic ridge and fast east pacific rise we used satellite derived gravity data in combination with seamarc ii bathymetry in and near the aad to examine regional density variations in the upper mantle beneath the aad through three dimensional gravity analysis we found that at least two end member models satisfy the gravity observations regional crustal thickness variations of at least 3 km along the seir near the aad or a temperature anomaly of the order of 150 c in the upper mantle beneath the seir these new observations combined with other geophysical and geochemical characteristics of the australian antarctic discordance provide further evidence that the temperature structure of a mid ocean ridge is a controlling factor in addition to spreading rate in the crustal accretionary process numerical models of mantle flow beneath mid ocean ridges offer one means of investigating the dynamic effect of a variable upper mantle temperature on the accretionary process our results indicate that temperature is important especially at intermediate and slower spreading rates where thermal effects can dominate mantle flow beneath a mid ocean ridge and result in increasing crustal production with decreasing spreading rate at the constant intermediate spreading rate of 37 mm yr characteristic of the seir in and near the aad our numerical models show that significant crustal thinning 2 4 km can occur with relatively small variations in upper mantle temperature all else being equal thus combined with our end member gravity models these observations and results suggest that both anomalously cool upper mantle and thin crust exist beneath the aad

interpretation of scatterometer ocean surface wind vector eofs over the northwestern pacific abstract satellite scatterometer winds over the northwestern pacific were analyzed with the vector empirical orthogonal function veof method the hilbert huang transform hht a newly developed non linear and non stationary time series data processing method was also employed in the analysis a combination of european remote sensing satellite ers 1 2 scatterometer nasa scatterometer nscat and nasa s quick scatterometer quikscat winds covering the period from january 1992 to april 2000 and the area of 0 50 n 100 148 e constitutes the baseline for this study the results indicate that annual cycles dominate the two leading veof modes the first veof shows the east asian monsoon features and the second represents a spring autumn oscillation we removed the annual signal from the data set and calculated the interannual veofs the first interannual veof represents the interannual variability existing in the spring autumn oscillation the temporal mode is correlated with the southern oscillation index soi but has a half year lag with respect to the soi the spatial mode of the first interannual veof reflects the response of the tropical and extratropical winds to enso events the second interannual veof is another enso related mode and the temporal veof mode is correlated with the soi with a correlation coefficient of 0 78 revealing the wind variability over mid latitudes which is associated with enso events further analysis indicated that the wind variability over the coast of east asia represents anomalies of a hadley cell the quasi biennial oscillation qbo was found in the temporal mode indicating and verifying that the qbo in the wind fields is related to enso events the third veof shows the interannaul variability in the winter summer mode and displays the interannual variability of the east asian monsoon the three leading interannual veofs are statistically meaningful as confirmed by a significance test

removal of ambiguous wind directions for a ku band wind scatterometer using three different azimuth angles the seasat a satellite scatterometer sass sensor demonstrated very successfully that ku band scatterometers can make accurate synoptic measurements of surface wind speed over the ocean because sass provided normalized radar cross section nrcs measurements from only two azimuths however the harmonic relationship of nrcs with azimuth results in up to four ambiguous wind directions the primary improvement to be incorporated in a next generation scatterometer design such as navy remote ocean sensing system nross is the addition of a third azimuth look at each sampled cell with this and other instrument improvements preliminary studies indicate that wind direction ambiguities aliases could successfully be removed in at least 80 percent of the cases furthermore these studies show that in over 90 percent of the wind solutions the two most probable solutions correctly identify the wind streamlines methods were studied which could examine typical streamline patterns derived from scatterometers using continuity or pattern recognition techniques to determine which of the possible two wind directions was correct in addition unambiguous solutions were sought for cases where streamlines were not correctly defined this paper describes several approaches for such alias removal algorithms these algorithms were developed with the aid of simulated three beam scatterometer ambiguous wind solution data based on noss conditions over a known windfield the resulting algorithms were evaluated using a different set of simulated orbital data but withholding the true winds

wavenumber spectra of pacific winds measured by the seasat scatterometer abstract vector winds measured by the seasat a satellite scatterometer sass are analyzed to determine the spatial structure of oceanic surface winds over wavelengths from 200 to 2200 km the analysis is performed in four latitudinal bands in the pacific ocean sampling characteristics of sass preclude the possibility of determining full two dimensional spectra the analysis is therefore limited to one dimensional along the satellite ground track spectra of vector wind components and kinetic energy the salient features of the results are summarized as follows i for each of the four geographic regions the spectra of meridional and zonal wind components and of kinetic energy are consistent with a power law dependence on wavenumber for midlatitude regions in both the northern and southern hemispheres the wave number dependence of kinetic energy is k 2 2 while for tropical regions in both hemisphere it is k 1 9 ii for each individual region the spectral dependence on wavenumber is nearly the same

satellite based midlatitude cyclone statistics over the southern ocean 1 scatterometer derived pressure fields and storm tracking 1 a wavelet based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the european centre for medium range weather forecasts ecmwf the resulting modified pressure fields are used to identify low pressure centers over the southern ocean and to build statistics of midlatitude cyclones during 7 years of the seawinds on quikscat operational period july 1999 to june 2006 the impact of the scatterometer derived pressure swaths is assessed with a statistical analysis of cyclone characteristics central pressure radius depth performed in parallel on the ecmwf and on the modified pressure fields more low pressure centers 5 10 depending on the season are identified with the modified pressure fields in particular incipient lows captured earlier than ecmwf and more short lived mesoscale cyclones with a life span less than 4 days the cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average a parallel spectral analysis reveals 1 additional energy at scales less than 2000 km in the modified pressure fields

the impact of seasat a scatterometer data on the numerical prediction of the queen elizabeth ii storm the development of the queen elizabeth ii storm from 1200 ut on september 9 1978 to 0000 ut on september 11 1978 is forecast with a limited area fine resolution 100 km numerical weather prediction model forecasts from initial conditions that include and exclude seasat scatterometer surface winds are performed when the seasat winds are allowed to influence the upper levels of the atmosphere a large positive impact is found

spreading rate dependence of three dimensional structure in oceanic spreading centres segmentation by transform faults and other types of along axis discontinuity1 is a well described but poorly explained characteristic of oceanic spreading centres here we use numerical experiments to explore the dynamics of mantle flow and melting beneath a mid ocean ridge buoyant upwelling driven by compositional density variations resulting from the extraction of the melt that forms the ocean crust exhibits a spreading rate dependent transition between two dimensional and three dimensional upwelling structures for low spreading rates and mantle viscosities an initial two dimensional structure transforms into a three dimensional one at high spreading rates an initially two dimensional structure remains two dimensional these results suggest that the origin of spreading centre segmentation may be different at fast and slow spreading rates

model based estimation of wind fields over the ocean from wind scatterometer measurements ii model parameter estimation for pt i see ibid vol 28 no 3 p 349 360 1990 the feasibility of a model based approach to wind field estimation is discussed in this approach the parametric model for near surface mesoscale wind fields developed in pt i is used the parameters of the model are estimated from the wind scatterometer measurements the wind field estimate is then computed from the estimated model parameters unlike the traditional pointwise approach this approach takes advantage of the inherent correlation in the winds at different sample points to estimate the wind field more accurately and resolve directional ambiguity the accuracies of wind field estimates obtained using the traditional pointwise estimation scheme and the model based approach using simulated scatterometer measurements are compared

mesoscale variability in marine winds at mid latitude wind data were collected by the national oceanic and atmospheric administration wp 3d aircraft on low level 50 and 90 m crosswind and along mean wind tracks of approximately 350 km during the storm transfer and response experiment in november and december 1980 observed mesoscale variations in the marine wind fields are characterized by the velocity correlation tensor for three atmospheric regimes cloud streets open and closed cellular convection and prefrontal warm air advection the dominant scale of mesoscale variation in the offshore wind field normal to the mean wind direction in the case of old continental air flowing over a warmer ocean producing cloud streets was 27 km for this case the standard deviation in momentum transfer which was calculated from 2 km subsets of the flight track by the bulk aerodynamic method assuming a constant drag coefficient was 13 of the synoptic scale 330km mean the dominant scale of mesoscale variation for open cellular convection was 62km and the dominant scale for closed cellular convection was 90 km the standard deviation of mesoscale momentum transfer scales greater than 2 km constant drag coefficient for a 345 km flight track containing both cell types was 26 of the synoptic scale mean the warm air advection case had no measurable mesoscale variability for each regime a model of the horizontal velocity correlation tensor which can be used to estimate a mesoscale variability is fitted to the observed velocity correlation tensor with velocity component and weather regime dependent coefficients this general model is consistent with an interpretation of the mesoscale wind field as an ensemble of coherent structures associated with cloud type in which the spatial variability of the wind field in each weather regime is associated with physically determined dominant length scales i e cells or rolls as contrasted with a continuum interpretation of two dimensional turbulence to accurately describe regional winds and fluxes at the sea surface wind speed and temperature data should be averaged over the dominant mesoscale length scale with either a suitable time average or a spatial average such as can be obtained by scatterometry or an estimate of the mesoscale variability should be explicitly stated it is also suggested that enhanced vertical flux in the oceanic mixed layer occurs at length scales of atmospheric boundary layer structures

a holocene calcrete from north yorkshire england implications for interpreting palaeoclimates using calcretes glacial gravels of late devensian dimlington stadial age 26 000 13 000 years bp at west tanfield north yorkshire england have been cemented by carbonate rich solutions to produce a strongly indurated calcrete horizon the low mg cements occur as drusy spar needle fibres alveolar septal structures micrite and micropinnacles indicative of vadose zone cementation some complex pore partition structures attributed to precipitation along meniscus films also occur these partitions separate air dominated and water dominated microenvironments of the vadose zone the abundance of vadose fabrics shows that the accumulation is not a groundwater calcrete in addition much of the carbonate appears to have been precipitated by biological mediation carbon and oxygen isotopic data suggest that the carbonate did not form as a result of freezing as has been suggested for some arctic soil carbonates the pollen history of the area since the devensian suggests that this calcrete precipitated at low temperatures this contrasts with widely reported occurrences of calcrete in soils of hot arid or semi arid regions and suggests that palaeo calcretes should not be used as absolute palaeoclimatic indicators the unusual occurrence albeit localized of a thick calcrete under a cool and wet climate probably reflects the well drained nature of the gravels the abundance of caco3 as limestone clasts in the gravel and a high degree of biological activity beneath a forest cover which created a local environment favouring carbonate precipitation