on estimating the surface wind stress over the sea abstractour study analyzes measurements primarily from two floating instrument platform flip field programs and from the air sea interaction tower asit site to examine the relationship between

on the height of the warm core in tropical cyclones abstractthe warm core structure of tropical cyclones is examined in idealized simulations using the weather research and forecasting wrf model the maximum perturbation temperature in a control simulation occurs in the midtroposphere 5 6 km in contrast to the upper tropospheric 10 km warm core that is widely believed to be typical this conventional view is reassessed and found to be largely based on three case studies and it is argued that the typical warm core structure is actually not well known in the control simulation the height of the warm core is nearly constant over a wide range of intensities from additional simulations in which either the size of the initial vortex or the microphysics parameterization is varied it is shown that the warm core is generally found at 4 8 km a secondary maximum often develops near 13 14 km but is almost always weaker than the primary warm core it is demonstrated that microwave remote sensing instruments are of insufficient resolution to detect this

measurements of the angle between the wind vector and wind stress vector in the surface layer over the north sea measurements of surface layer turbulence in addition to full meteorological and oceanography quantities over the north sea indicated that the stress vector on long time scales is often aligned with a direction slightly different from the mean wind flow when stratifications were near neutral the angle difference between the stress and wind exhibited a dependence on the heat and momentum fluxes in general the stress vector was observed to be to the left of the flow during stable stratifications while for unstable stratifications it was to the right this finding was consistent using two independent sets of wind stress data i e from marsen 1979 and the north sea platform winter exercise 1985

wind wave nonlinearity observed at the sea floor part ii wavenumbers and third order statistics abstract this is part 2 of a study of nonlinear effects on natural wind generated surface gravity waves in 13 m depth 30 km offshore of virginia at the sea floor in this depth free surface gravity waves are only weakly attenuated at sea and swell frequencies 0 05 0 30 hz but are very strongly attenuated at frequencies higher than about 0 35 hz hence above 0 35 hz relatively long wavelength forced waves excited by nonlinear interactions between directionally opposing free wind waves are exposed at the sea floor an array of pressure transducers at middepth was used to estimate the frequency directional spectrum of free primary sea and swell waves and the associated forced secondary pressure fluctuations were measured with an array on the sea floor in part 1 it was shown that forced wave energy levels at the sea floor increase sharply in response to directionally opposing wind waves in agreement with weakly nonlinear theory in part 2 wavelengths propagation directions and non gaussian

distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

the evolution of dropsonde derived kinematic and thermodynamic structures in developing and nondeveloping atlantic tropical convective systems abstractthe processes by which tropical cyclones evolve from loosely organized convective clusters are still poorly understood because of the data sparse regions in which tropical cyclones form observational studies of tropical cyclogenesis are often more difficult than studies of land based convective phenomena as a result many studies of tropical cyclogenesis are limited to either a few case studies or rely on simulations the 2010 predict and grip field experiments have provided a new opportunity to gain insight into these processes using unusually dense observations in both time and space the present study aims at using these recent datasets to perform a detailed analysis of the three dimensional evolution of both kinematic and thermodynamic fields in both developing and nondeveloping tropical convective systems in the western atlantic five tropical convective systems are analyzed in this study two nondeveloping two developing and one dissipating system although the analysis necessarily inclu

sedimentary flattening and multi extensional deformation along the west african margin abstract the structural world is usually divided into compressional and extensional zones and this tectonic style is representative of the regional deformation which leads to shortening or extension along the west african margin there is no evidence of crustal extension since 100 my ago but the post salt series are intensely deformed by gravity and sedimentary loading normal faults as well as reverse faults are present the modes of deformation of such an area are described using large 3d seismic data sets analogue models and cross section and map restorations results show that 1 surface rotations are large at a regional scale 2 plane deformation is not a valid hypothesis across the margin the amount of extension parallel to the coast being on the same order of magnitude as the extension perpendicular to the margin 3 the surface area of the beds are not preserved the data indicate that the deformation of the shale in such a context is a ductile flow due to body forces and sedimentary loading here called sedimentary flattening competent layers sand prone such as sheet sand lobes or channels constitute passive markers which follow the ductile flow in a brittle mode resulting in boudinage

coupled dynamic thermodynamic forcings during tropical cyclogenesis part i diagnostic framework abstracta diagnostic framework to investigate the role of processes around and during tropical cyclogenesis is presented the key framework metric is the ratio of bulk differences of moist entropy over differences of angular momentum between an inner and outer region of a tropical disturbance or cyclone this ratio is hypothesized to decrease and become negative as both the high entropy core and low level vortex in the inner region amplify during tropical cyclogenesis the time tendency of this ratio can be split into two forcings a moist entropy forcing and an angular momentum forcing each forcing can be further divided into components comprising differences in net advective fluxes and nonadvective boundary fluxes of moist entropy or angular momentum between each region the framework provides a comprehensive way to compare the relative importance of processes leading to tropical cyclogenesis in a tractable consistent manner suggestions on how to apply the framework to numerical model output are given

gravity driven thin skinned extension above zechstein group evaporites in the western central north sea an application of computer aided section restoration techniques normal faulting and halokinesis have been important controls on the deposition and subsequent deformation of mesozoic and tertiary strata in the north sea in addition to the previously documented mechanisms of salt withdrawal dissolution and differential sedimentary loading it is recognized that gravity driven thin skinned extension above inclined salt layers has played an important part in north sea basin development commercial section restoration software has been used to facilitate depth conversion restoration and decompaction of seismic sections selected from an interpreted regional database in the western central north sea allowing validation of the interpretations and a graphical and highly quantitative description of salt assisted extension results of this work show that zechstein group evaporites were deposited in shallow sag basins during the permian triassic sedimentary pods were generated by localized deposition in synclinal basins and grabens above the evaporites bedded salt became folded while mobile salt flowed to fill anticline cores since the early jurassic regional tectonic tilting related to post rift subsidence and increasing sedimentary overburden have caused allochthonous mesozoic and tertiary strata to extend by gravity spreading above the mobile salt layer which detaches the allochthon from the underlying autochthonous late palaeozoic rocks concave up listric normal faults sole out in the salt layer propagate into the overlying cover sewuence and have been active at different geological times causing stratal thickening and folding within the allochthon antithetic and synthetic normal faults have developed producing complex upward branching fault systems in map view the listric faults form curvilinear en echelon arrays the faults linked by relay ramps fault blocks are typically 3 7 km wide 2 3 km thick and 7 10 km long salt movement during the jurassic tertiary has been driven by active extension of the cover causing salt to fill potential voids created by fault block rotation thus salt highs occur beneath sites of extension the listric faults generally dip in the same direction as the sub salt surface although there are also some major counter regional faults during extension regional dips have increased up to about 5 which is sufficient for gravity driven extension above a salt layer a total extension of about 6 has occurred the gravity driven thin skinned extension documented in the western central north sea is a phenomenon which can be recognized elsewhere in the north sea basin and can be readily compared with similar phenomena already documented in offshore angola brazil nova scotia and the gulf of mexico

a unified view of tropical cyclogenesis and intensification idealized high resolution numerical simulations of tropical cyclogenesis are presented in a model that represents deep convection by a warm rain process only starting with an initially weak cloud free axisymmetric warm cored vortex maximum wind speed 5 m s 1 at a radius of 100 km rapid vortex intensification begins after a gestation period on the order of 2 days from a three dimensional perspective the genesis process is similar to that in the rotating convection paradigm for vortex intensification starting with a much stronger initial vortex vmax 15 m s 1 the patterns of deep convection and convectively amplified cyclonic relative vorticity are far from axisymmetric during the genesis period moreover the organization of the cyclonic relative vorticity into a monopole structure occurs at relatively low wind speeds before the maximum local wind speed has increased appreciably barotropic processes are shown to play an important role in helping to consolidate a single signed vorticity monopole within a few hours near the intensification begin time the rotating convection paradigm appears adequate to explain the basic genesis process within the weak initial vortex providing strong support for a hypothesis of montgomery and smith that the genesis process is not fundamentally different from that of vortex intensification in particular genesis does not require a trigger and does not depend on the prior existence of a mid level vortex

a modification of the response method of tidal analysis an easily implemented extension of the standard response method of tidal analysis is outlined the modification improves the extraction of both the steady and the tidal components from problematic time series by calculating tidal response weights uncontaminated by missing or anomalous data examples of time series containing data gaps and anomalous events are analyzed to demonstrate the applicability and advantage of the proposed method

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

genesis of hurricane julia 2010 within an african easterly wave developing and nondeveloping members from wrf letkf ensemble forecasts abstractin this study the predictability of and parametric differences in the genesis of hurricane julia 2010 are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km results show that the genesis of julia is highly predictable with all but two members undergoing genesis despite the high predictability substantial parametric differences exist between the stronger and weaker members notably the strongest developing member exhibits large upper tropospheric warming within a storm scale outflow during genesis in contrast the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm scale outflow a reduction in the rossby radius of deformation in the strongest member aids in the accumulation of the warmth while little contraction takes place in the nondeveloping member the warming in the upper troposphere is responsible for the development of meso scale surface pressure falls and a meso surface low i

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

airborne scatterometer detection of winds and sea surface roughness changes across the gulf stream front abstract this article investigates the scatterometer radar cross section distributions and wind stress spatial variability across a sea surface temperature sst front under different wind directions and synoptic scale atmospheric forcings shipboard meteorological measurements in concert with airborne k u band 14 0 ghz rotating scatterometer data show evidence of mesoscale circulation near the front during low ambient winds 4 m s blowing from the cold side of the sst front to the warm side the mesoscale signature is characterized by a 25 35 counterclockwise shift in the wind direction and a maximum of 4 9 db increase in the backscattering cross section across the front the mesoscale circulation is reduced when the wind direction reverses and the ambient wind flow increases to 13 6 m s the maximum cross section change across the front is reduced to 3 6 db the azimuthal characteristics of the scatterometer data are compared with the predictions of two scatterometer model functions according to the models the anisotropy of the short waves is inversely related to the wind speed such that the short wave directional spreads tend to broaden as the wind speed increases the scatterometer data however show greater short wave anisotropy at the higher wind speeds this measured difference could be caused by current velocity changes or by longwave directional changes across the front

dual aircraft investigation of the inner core of hurricane norbert part i kinematic structure abstract on 24 25 september 1984 air motions and physical processes in the eyewall region of hurricane norbert were investigated with two national oceanic and atmospheric administration noaa aircraft operations center aoc wp 3d research aircraft one aircraft equipped with the airborne doppler radar flew repeated radial penetrations of the eyewall mapping the three dimensional wind field throughout a 40 km radius of the storm center these data provide the first complete documentation of the three dimensional wind field of the inner core of a hurricane on spatial scales of 10 25 km in the horizontal and 1 km in the vertical and temporal scales of 1 2 h the wind field was asymmetric and the asymmetry varied with altitude as altitude increased the location of the maximum tangential wind sloped upwind from left of the storm track at 1 km altitude to right of the storm track above 3 km the radial wind at 1 km altitude was inward in front of the storm and outward behind this pattern in the radial

role of cumulus congestus in tropical cyclone formation in a high resolution numerical model simulation abstractthe role of cumulus congestus shallow and congestus convection in tropical cyclone tc formation is examined in a high resolution simulation of tropical cyclone fay 2008 it is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near surface circulation prior to genesis while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer the transition from the tropical wave stage to the tc stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region this study suggests that tc formation can be regarded as a two stage process the first stage is a gradual process of moisture preconditioning and low level spinup in which cumulus congestus plays a dominant role the second stage commences with the rapid development of deep convection in the inner pouch region after the air colum

mesoscale interactions in tropical cyclone genesis with the multitude of cloud clusters over tropical oceans it has been perplexing that so few develop into tropical cyclones the authors postulate that a major obstacle has been the complexity of scale interactions particularly those on the mesoscale which have only recently been observable while there are well known climatological requirements these are by no means sufficient a major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development observations exist for only a few forming cases in these the moist convection in the preformation environment is organized into mesoscale convective systems each of which have associated mesoscale potential vortices in the midlevels interactions between these systems may lead to merger growth to the surface and development of both the nascent eye and inner rainbands of a tropical cyclone the process is essentially stochastic but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences for example a monsoon trough provides a region of reduced deformation radius which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices further a strong monsoon trough provides a vertical wind shear that enables long lived midlevel mesoscale vortices that are able to maintain or even redevelop the associated convective system the authors develop this hypothesis by use of a detailed case study of the formation of tropical cyclone oliver observed during toga coare 1993 in this case two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband the eye developed on the edge of the major convective system and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere the importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western north pacific

cross section restoration of salt related deformation best practices and potential pitfalls abstract cross section restoration typically assumes plane strain deformation and area conservation constraints that are usually invalid for salt because of its characteristic three dimensional flow and possible dissolution thus restoration of salt related deformation provides added challenges and uncertainty in this review paper we summarize the historical development of ideas methods and applications of restoration in salt basins while most published restorations do not maintain salt area constraints on its variation range from arbitrary assumptions to quantitatively incorporating isostatic calculations we illustrate several scenarios in which the presence of salt adds ambiguity to restoration primarily because it can hide deformation diapirs can widen during extension and narrow during shortening translating overburden can move into salt and drive allochthonous advance secondary minibasin subsidence can be accommodated at both shallow and deep salt levels and allochthonous salt can record evacuation of deeper salt although we caution against using restoration to test and validate small scale details of interpretations we emphasize that sequential restoration remains an essential tool in structural and basin analyses however because of the uncertainties a regional three dimensional approach and sound geological reasoning are critical for deriving meaningful and useful results from cross section restoration of salt structures

momentum transfer over the coastal zone spatial variations of surface stress over the coastal shoaling zone are studied offshore of duck north carolina by the longez research aircraft equipped to measure both atmospheric turbulence and oceanic waves we find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow than with onshore flow in general the mean square slope of the short waves wavelength shorter than 2 m decreases with offshore distance while the mean square slope of the long waves wavelength longer than 2 m increases with offshore distance with onshore flow the friction velocity is strongly correlated with surface waves in addition the variation of the neutral drag coefficient is well correlated with the atmospheric bulk richardson number with offshore flow the observed momentum flux significantly decreases with offshore distance within the first few kilometer offshore the relationship between the friction velocity and the mean square slope of the short waves and the relationship between the neutral drag coefficient and the atmospheric bulk richardson number are obscured by the direct influence of the upstream land surface on the measured turbulence these relationships for offshore flow agree well with those for onshore flow if the fetch is beyond the immediate influence of the land surface the results in this study suggests that the effects of the strong turbulence advected from over the nearby land surface in offshore flow may lead to ambiguous physical interpretation of the correlation between the momentum flux and the wave state

directional attributes of the ocean surface wind stress vector in a recent paper by geernaert 1988 it was suggested that the stress and wind vectors are rarely aligned and that the deviation of the stress vector direction from the wind vector is related to the surface heat flux it was argued that since cold air advection over the open ocean generally corresponds to upward heat flux the consequent rotation of the winds to the right with height during cold air advection could be responsible for observations of the stress vector to be to the right of the wind flow for unstable stratifications conversely observations of the stress vector to the left of the flow for stable stratifications were suggested to be associated with the turning of the wind vector to the left of the flow for warm air advection or downward heat flux in that study only 30 of the statistical variance of the angle between the wind and wind stress vectors could be explained by air sea heat flux and it was suggested that the orbital velocity spectrum of surface waves i e data unavailable in that study could be important for explaining at least part of the remaining variance in this study we report on measurements of the wind stress vector and wave directional spectrum collected during the synthetic aperture radar x band ocean nonlinearities experiment conducted on the chesapeake light tower during 1988 the experiment yielded data reported herein that provide convincing evidence that the stress vector direction during light winds and near zero air sea heat flux is governed in large part by the direction of long waves on the ocean surface further the measurements suggest that the stress vector has a direction which is a blend between the wind direction and the swell direction

effect of large eddies on atmospheric surface layer turbulence and the underlying wave field to improve existing models for air sea interaction a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air sea interface is needed recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples this was done using synthetic aperture radar sar imagery of ocean surface and almost simultaneous advanced very high resolution radiometer avhrr imagery of cloud streets at a cold air outbreak the intent of our study is to further validate this hypothesis in a general case of coastal circulation for this purpose we analyze a suite of collocated simultaneous records of airflow radar return and surface elevations from a coastal platform we investigate the influence of large eddies 20 60 min on the turbulent properties of the airflow in the first 2 m above the ocean surface the analysis shows very prominent peaks in the magnitude of 12 to 16 min fluctuations which are further modulated in 20 to 40 min intervals these scales and modulations are characteristic for all variables of interest here the detected scales and their modulation suggest significant interaction of surface layer within the first 1 2 m with large eddies of scales of o 1 and o 10 km the intermittent structure of turbulence responds by alternating contributions from bursts and sweeps the frequency of occurrence of bursts and sweeps also reveals the influence of large structures the instantaneous cross correlation between the shorter scales of momentum flux and radar return corresponding to the individual burst events can be 4 times as strong as the overall cross correlation

on wind wave current interactions during the shoaling waves experiment 1 this paper presents a case study of wind wave current interaction during the shoaling waves experiment showex surface current fields off duck north carolina were measured by a high frequency ocean surface current radar oscr wind wind stress and directional wave data were obtained from several air sea interaction spar asis buoys moored in the oscr scanning domain at several times during the experiment significant coastal currents entered the experimental area high horizontal shears at the current edge resulted in the waves at the peak of wind sea spectra but not those in the higher frequency equilibrium range being shifted away from the mean wind direction this led to a significant turning of the wind stress vector away from the mean wind direction the interactions presented here have important applications in radar remote sensing and are discussed in the context of recent radar imaging models of the ocean surface

the engines of gravity driven movement on passive margins quantifying the relative contribution of spreading vs gravity sliding mechanisms movement of gravity driven systems on passive margins is fuelled by the loss of gravitational potential energy two end member modes gravity spreading and gravity gliding are defined by whether the potential energy loss is due to deformation and movement towards the base of the system spreading or by movement parallel to the base of the system gliding most natural systems consist of a mixture of the two processes hitherto use of these concepts has been limited or equivocal due to lack of a quantitative measure in some cases characterisation of gliding vs spreading systems based on secondary attributes has resulted in controversy because there is a lack of consensus as to which of these are truly diagnostic this paper presents a new simple quantitative method based on vector analysis providing a numerical measure of the relative contribution of spreading vs gliding the method is applied to synthetic examples where deformation can be tracked and to natural examples where a valid palinspastic reconstruction is available the results confirm that most natural examples exhibit mixed mode behaviour and that some have been mischaracterized much of the angola margin is dominated by spreading the method can also provide an estimate of the absolute amount of gravitational potential energy released in the movement and the energy contribution made by gliding vs spreading determining the dominant process has implications for predicting the development of seafloor topography and stratal architecture

a vortex based perspective of eastern pacific tropical cyclone formation tropical cyclone formation over the eastern pacific during 2005 and 2006 was examined using primarily global operational analyses from the national centers for environmental prediction this paper represents a vortex view of genesis adding to previous work on tropical cyclone formation associated with tropical waves between 1 july and 30 september during 2005 and 2006 vortices at 900 hpa were tracked and vortex following diagnostic quantities were computed vortices were more abundant during periods of an enhanced hadley circulation with monsoon westerlies around 10 n in the lower troposphere this zonally confined hadley circulation was significantly stronger during the genesis of developing vortices developing vortices were stronger at the outset with a deeper potential vorticity maximum compared to nondeveloping vortices this implies that developing disturbances were selected early on by favorable synoptic scale features the characteristic time mean reversal of the meridional gradient of absolute vorticity in the lower troposphere was found to nearly vanish when the aggregate contribution of strong vortices was removed from the time mean vorticity this finding implies that it is difficult to unambiguously attribute development to a preexisting enhancement of vorticity on the synoptic scale the time mean enhancement of cyclonic vorticity primarily results from the accumulated effect of vortices it is suggested that horizontal deformation in the background state helps distinguish developing vortices from nondevelopers and also biases the latitude of development poleward of the climatological itcz axis

appraisal of recent theories to understand cyclogenesis pathways of tropical cyclone madi 2013 the present study aims to examine the new understanding of cyclogenesis by analyzing the genesis sequence of formation of a very severe cyclonic storm madi 6 13 december 2013 that occurred over the bay of bengal we have generated a high resolution 18 km 6 km and 2 km analysis using three dimensional variational data assimilation technique and weather research and forecasting model the genesis sequence of madi cyclone is analyzed using the concepts in the marsupial theory and other theories of tropical cyclone formation major results are as follows the developed analysis is found useful for tracking the movement of westward moving parent disturbance from 15 days prior to the genesis identifying developed pouch region in the lagrangian frame of reference understanding the evolution of the pouch and convection within the pouch region and for the study of intensification inside the pouch region also large scale priming of environment concurs with the hypotheses of the marsupial theory of tropical cyclogenesis the analysis of dynamical and thermodynamical processes within the pouch region showed gradual moistening uplifting of moisture diabatic heating causing buoyant convection in the vorticity rich environment followed by vortex tube stretching development of convection heavy precipitation strengthening of lower level convergence and hence spin up during a day or two preceding the genesis of madi cyclone in general it is concluded that intensification within pouch region during the cyclogenesis phase followed the marsupial paradigm and bottom up mechanism

sedimentation and shale tectonics of the northwestern niger delta front abstract the modern day slope and outer shelf of the niger delta are characterized by fault bounded sedimentary depocentres and intervening shale structures some of which are diapiric using two dimensional seismic reflection data and stratigraphic information from five wells the neogene history of a 70 30 km portion of the northwestern niger delta shelf and slope has been examined the shale structures were established by late miocene time probably in response to lateral shale withdrawal from beneath the advancing deltaic load combined with compressional uplift and folding of pro delta strata during pliocene and pleistocene time these structures were buried by the prograding delta and extensional growth faulting commenced stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period throughout the pliocene extension and subsidence were concentrated in a graben like depocentre bounded by both regional and counter regional growth faults during the early pleistocene subsidence on the regional growth fault ceased and growth was transferred to the counter regional growth fault set the geometry and history of the depocentre is analogous to salt related depocentres typical of the northern gulf of mexico and atlantic margins of brazil and angola to explain the history of the niger delta study area a model is proposed in which the miocene pleistocene sedimentary package has slid basinward breaking up during extension thereby creating seaward stepping depocentres examples from analogue modelling studies are used to suggest possible origins for the large counter regional growth faults

ers 1 scatterometer measurements i the relationship between radar cross section and buoy wind in two oceanic regions extensive european remote sensing satellite ers 1 spacecraft scatterometer measurements were collocated within spl plusmn 25 km of buoy measurements at midlatitudes and in the equatorial pacific during 1992 1994 two different directional functional forms for the geophysical model were fit to these measurements described by cross section maxima aligned and offset with respect to the mean wind direction the two models exhibit fits with similar residuals for each of three years in the equatorial region thus neither of these two model functions can convincingly be identified as more accurate than the other unless additional factors are considered nevertheless the offset model results in an average directional offset near 10 spl deg for each season during the three year period whereas no such offset was inferred at midlatitudes the cross section dependence on wind direction also exhibits another unexpected average property a larger downwind compared to upwind cross section a sub 10 spl ap 0 25 db in the equatorial pacific this characteristic could be caused by a concentration of the short bragg waves on the backside of the long wave crests both of these unexpected characteristics are likely related to a dominant systematic swell traveling nearly perpendicular to the prevailing easterly winds across the equatorial pacific ocean the possible cross section dependence on wind stress and wind speed is due to long waves when adjusting the buoy measurements to a common height are discussed

influence of detachment layer thickness on style of thin skinned shortening abstract there are several parameters which may determine whether detachment folds or thrust faults develop in thin skinned compressional systems a fundamental but little publicised parameter is apparent from consideration of detachment fold growth as a detachment fold amplifies its core must be filled by redistribution of ductile material if the mobile material were insufficient to supply the volume required by the fold core through redistribution fold growth would be inhibited and eventually faulting would occur the volume of a detachment fold core is compared here with the volume of available underlying mobile material for various amounts of shortening and sizes of fold the occurrence of detachment folds versus thrusts in several compressional belts is successfully predicted by this relationship

the formation of moist vortices and tropical cyclones in idealized simulations abstractthe upscale aggregation of convection is used to understand the emergence of rotating coherent midtropospheric structures and the subsequent process of tropical cyclone formation the cloud model version 1 cm1 is integrated on an f plane with uniform sea surface temperature sst and prescribed uniform background flow deep convection is maintained by surface fluxes from an ocean with uniform surface temperature convection begins to organize simultaneously into moist and dry midtropospheric patches after 10 days after 20 days the patches begin to rotate on relatively small scales moist cyclonic vortices merge eventually forming a single dominant vortex that subsequently forms a tropical cyclone on a realistic time scale of about 5 days radiation that interacts with clouds and water vapor aids in forming coherent rotating structures using the path to genesis provided by the aggregated solution the relationship between thermodynamic changes within the vortex and changes in the character

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

restoration of cross sections to constrain deformation processes of extensional terranes abstract restoring balanced cross sections constrains the possible deformation processes affecting extensional terranes with a ductile substratum such as salt and syndeformational sedimentation cross sections are divided into fault blocks and shear domains each of which can be undeformed with a different set of parameters the success of restorations is judged by compatibility between the blocks and the reasonableness of the restored structures fault blocks in physical models restore with simple shear at about 60 dipping in the direction which removes extension corresponding to an antithetic orientation in the hangingwalls of normal growth faults and subparallel to the fault in the footwall other components of the deformation are rigid rotation translation and decompaction shear angles inferred from natural examples are more varied ranging from vertical to moderately inclined nearly always dipping in a direction that removes extension

development and nondevelopment of binary mesoscale vortices into tropical cyclones in idealized numerical experiments abstractthe evolution of two symmetric midlevel mesoscale vortices situated above a warm ocean is examined with a basic cloud resolving model idealized numerical experiments provide insight into how the evolution may vary with the initial vortex separation distance d and other parameters that influence the time scale for an isolated vortex to begin rapid intensification the latter parameters include the ambient middle tropospheric relative humidity rh and the initial midlevel wind speed of each vortex at relatively low rh there exists an interval of d where binary midlevel vortex interaction prevents tropical cyclone formation while tropical cyclones generally develop at high rh similar values of d can delay the process if the vortices are initially weak prevention or inhibition of tropical cyclone formation occurs in association with the outward expulsion of lower tropospheric potential vorticity anomalies as the two vortices merge in the middle troposphere it is proposed that the primary mecha

incorporation of stratification effects on the oceanic roughness length in the derivation of the neutral drag coefficient abstract based on the assumption that over the sea the roughness length of the wind profile scales with the wind stress a new formulation that describes the drag coefficient as a function of the given neutral drag coefficient and stability is derived the new formulation is compared to an earlier formulation where roughness changes with stability were ignored the two are then illustrated with data collected from both the marine remote sensing project 1979 and the tower ocean wave and radar dependence experiment 1984 it was found that when the surface roughness was allowed to depend on wind stress and therefore stability the stratification correction to the neutral drag coefficient was larger than for the case when the roughness length was not allowed to vary

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico ii structure the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope

observations of summer turbulent surface fluxes in a high arctic fjord the summer atmospheric boundary layer over a fjord in the high arctic has been investigated during three consecutive years 2008 2010 measurements of turbulent surface layer fluxes of momentum and sensible heat using a sonic anemometer and slow response instruments were taken from a tower on the coast of isfjorden svalbard and analysed for seasonal variability and differing fetch conditions the results resembled the atmospheric boundary layer characteristics previously found for ice free winter conditions the momentum flux was usually directed downwards but for low wind speeds there was a possible contribution of swell giving an upward directed momentum flux the cross wind component of the momentum flux sometimes contributed significantly to the total flux the sensible heat flux was very dependent on the origin of air whether it had a long over water fetch or originated from land areas with or without glaciers in addition to non stationarity of the flow due to the influence of the fjord s shape and its surrounding topography low wind speeds questioned the validity of the monin obukhov similarity theory whereas the over water fetch and off wind angle were of minor importance moreover some results especially the off wind angle were very sensitive to how the raw data were treated in particular which coordinate rotation method was employed the double rotation or the planar fit method

an investigation of composite dropsonde profiles for developing and nondeveloping tropical waves during the 2010 predict field campaign abstractcomposite dropsonde profiles are analyzed for developing and nondeveloping tropical waves in an attempt to improve the understanding of tropical cyclogenesis these tropical waves were sampled by 25 reconnaissance missions during the 2010 pre depression investigation of cloud systems in the tropics predict field campaign comparisons are made between mean profiles of temperature mixing ratio relative humidity radial and tangential winds relative vorticity and virtual convective available potential energy cape for genesis and nongenesis cases genesis soundings are further analyzed in temporal progression to investigate whether significant changes in the thermodynamic or wind fields occur during the transition from tropical wave to tropical cyclone significant results include the development of positive temperature anomalies from 500 to 200 hpa 2 days prior to genesis in developing waves this is not observed in the nongenesis mean progressive mesoscale moistening of the column is observe

cross section restoration and balancing as aid to seismic interpretation in extensional terranes structural cross sections in extensional terranes can be improved significantly by restoration and balancing principles originally developed for fold and thrust belts in rift basins and passive continental margins use of restoration techniques in analysis of growth faults elongate salt swells and other extensional structures results in geologically valid seismic interpretations sections must be in depth as opposed to two way time and oriented in the direction of material transport and decompaction must accompany restoration hanging wall deformation is characterized by different processes depending on the mechanical properties of the rocks being extended and can be approximated by various geometric and kinematic models antithetic faulting is analogous to antithetic shear combined antithetic and synthetic faulting is approximated by vertical shear domino style extension corresponds to rigid body rotation and flexural slip flow is modeled by bed length balance methods selection of the appropriate algorithm is crucial for proper restoration and balancing applications of these techniques illustrated here using seismic data from the gulf coast and north sea include 1 evaluating and adjusting seismic interpretations 2 projecting listric fault trajectories to depth 3 delineating more accurately the geometry and extent of hydrocarbon reservoirs 4 identifying new exploration leads 5 determining the deformation history of an area and 6 constraining the timing and direction of hydrocarbon migration and entrapment

estimation of wind friction velocity and direction at the ocean surface from physical models and space borne radar scatterometer measurements this paper presents a new technique for estimating the wind friction velocity at the ocean surface from c band radar scatterometer measurements this technique uses physical models of ocean surface waves and electromagnetic backscattering from a rough surface at intermediate angles of incidence to generate predictions of the normalized radar cross section nrcs or 0 of the ocean surface for a given wind friction velocity and observational geometry the ocean spectral model used in this technique has been developed specifically for this application it combines in situ wave measurements at low wave numbers with the phillips 1985 equilibrium spectral model this choice of ocean wave model is supported by a set of open ocean wave measurements summarized in this paper a suite of models derived from both in situ and remote measurements of the sea surface is used to characterize the directional spreading of ocean waves relative to the wind direction the resulting two dimensional ocean wave spectra are used with a composite surface model to predict radar backscattering from the ocean surface at c band these radar cross section predictions are combined with ers 1 scatterometer measurements in a cost function minimization scheme to yield estimates of the friction velocity vector at the ocean surface we present examples of this technique and compare friction velocity retrievals obtained via this scheme with buoy based measurements under a variety of wind and wave conditions on the basis of the analysis of a limited number of cases this technique yielded friction velocity estimates for which the magnitude was within 22 and the direction was within 25 given that scientific applications require magnitude estimates within 10 15 and directional estimates within 20 of in situ measurements these preliminary results suggest that this is a promising approach to wind retrieval

observed directional characteristics of the wind wind stress and surface waves on the open ocean sonic anemometer data were taken during the surface waves processes program swapp in march 1990 in the north pacific measurements of the wind stress vector span several strong wind events significant angles between the wind stress vector and the mean wind vector are seen simultaneous measurements of the directional wave field were made with a surface scanning doppler sonar the data suggest that the wind stress direction is influenced by the direction of the surface waves especially for stronger winds overall the stress vector lies between the mean wind and the mean wave directions at the higher wind speeds over 8 6 m s there is a nonzero correlation between the variations in wave directions and stress directions as well finally the stress and wave component directions have similar frequency dependence over the frequency band where wave energy is nonnegligible suggesting a dynamic link

surface wave effects on the translation of wind stress across the air sea interface in a fetch limited coastal embayment abstractthe role of surface gravity waves in structuring the air sea momentum flux is examined in the middle reaches of chesapeake bay observed wave spectra showed that wave direction in chesapeake bay is strongly correlated with basin geometry waves preferentially developed in the direction of maximum fetch suggesting that dominant wave frequencies may be commonly and persistently misaligned with local wind forcing direct observations from an ultrasonic anemometer and vertical array of advs show that the magnitude and direction of stress changed across the air sea interface suggesting that a stress divergence occurred at or near the water surface using a numerical wave model in combination with direct flux measurements the air sea momentum flux was partitioned between the surface wave field and the mean flow results indicate that the surface wave field can store or release a significant fraction of the total momentum flux depending on the direction of the wind when wind blew across dominant fetc

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

the influence of oblique waves on the azimuthal response of a ku band scatterometer a laboratory study the authors conducted experiments in the large wind wave tank at irphe to examine the influence of longer waves propagating at oblique angles to the wind direction on microwave backscattering measurements were made of wind wave directional spectra and cross sections from a 13 5 ghz scatterometer at 30 spl deg from nadir incidence angle the authors characterize the scatterometric azimuthal scans with respect to the magnitude and the direction of the maximum backscattered power scans of solely wind waves are used to assess the effects of oblique waves for which the scans yield trends that are related to the oblique wave direction relative to the wind and the oblique wave steepness in particular cross section maxima are enhanced by oblique waves and the direction of maxima rotates from the wind axis toward the oblique wave direction these scatterometer data in addition to other oblique wave studies led the authors to conclude that wind vectors produced from standard retrieval algorithms for scatterometers should be used with prudence in regions with significant veering winds such as near meteorological fronts

development of north atlantic tropical disturbances near upper level potential vorticity streamers abstracttropical cyclone tc development near upper level potential vorticity pv streamers in the north atlantic is studied from synoptic climatology composite and case study perspectives midlatitude anticyclonic wave breaking is instrumental in driving pv streamers into subtropical and tropical latitudes in particular near the time mean midocean trough identified previously as the tropical upper tropospheric trough twelve tcs developed within one rossby radius of pv streamers in the north atlantic from june through november 2004 08 this study uses composite analysis in the disturbance relative framework to compare the structural and thermodynamic evolution for developing and nondeveloping cases the results show that incipient tropical disturbances are embedded in an environment characterized by 850 200 hpa westerly vertical wind shear and mid and upper level quasigeostrophic ascent associated with the pv streamer with minor differences between developing and nondeveloping cases the key differ

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

simulation and interpretation of the genesis of tropical storm gert 2005 as part of the nasa tropical cloud systems and processes experiment abstract several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones this paper examines high resolution simulations of tropical storm gert 2005 which formed in the gulf of mexico during nasa s tropical cloud systems and processes experiment to investigate the development of low level circulation and its relationship to the precipitation evolution two simulations are examined one that better matches available observations but underpredicts the storm s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm the roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed gert are discussed during 21 25 july two episodes of convective system development occurred in each precipitation system evolution was characterized by i

diabatic divergence profiles in western pacific mesoscale convective systems abstract heating in the atmosphere can be expressed as diabatic divergence d which is nearly equal to the actual horizontal divergence in tropical convection high quality profile measurements from airborne doppler radar purls in ten mesoscale convective systems mcs observed during toga coare are examined and the mean profile is compared with rawinsonde array measurements young convective features have strong near surface convergence while older cells with better developed downdrafts and stratiform precipitation areas have their peak convergence aloft in the mean then surface flow is only weakly convergent or oven divergent so that the main convergence into mcss is deep and peaked aloft with a sharp melting convergence at 0 c divergence prevails above 10 km altitude but was undersampled by the radar unusual but well sampled observations in the purl dataset include a persistent widespread profile feature in one well sampled mcs a cyclone rainband oscillatory reverberations c

wind stress and surface waves observed on lake washington abstract new results from turbulent flux measurements made over lake washington include the following 1 the only direct measure of the vertical transport of the horizontal momentum heat and matter in the surface boundary layer is the so called eddy correlation method however even if the measurement errors are negligible the results obtained from point observations may show large scatter due to lack of stationarity and horizontal homogeneity in the turbulent field and to the sampling variability scatter may be greatly reduced by spatial averaging in this study such an effect is achieved by determining the surface roughness length hence the neutral drag coefficient from the measured wave height spectrum which reflects the atmospheric input integrated over the fetch applicability and usefulness of the approach for general field measurements and remote sensing is discussed 2 the evolution of the wave field observed on lake washington agrees in peak frequency and the slope of the equilibrium ra

physical and logistical considerations of using ultrasonic anemometers in aeolian sediment transport research abstract recently ultrasonic anemometers uas have become available for precise high frequency measurement of three dimensional velocity and turbulence properties except for a few wind tunnel and computational fluid dynamics cfd simulations advances in aeolian sediment transport and bedform research have been limited to field studies using instrumentation that is either incapable of measuring turbulence e g cup anemometers or unable to withstand sediment laden airflow e g hotfilms in contrast extensive progress has occurred in fluvial research where turbulence instrumentation has been available for some time this paper provides a pragmatic discussion on using uas in aeolian research recent advances using this technology are reviewed and key physical and logistical considerations for measuring airflow properties and near surface shear stress using uas over complex terrain are discussed physical considerations include limitations of applying boundary layer theory to flow over natural surfaces such as non logarithmic velocity profiles resulting from roughness and topographically induced effects and the inability of instrumentation to measure within the thin constant stress region these constraints hinder accurate shear velocity u shear stress and sand transport estimation uas allow measurement of turbulent reynolds stress rs that in theory should equal profile derived shear stress discrepancies often exist between these quantities however due to three dimensional spanwise flow components and rapid distortion effects i e unbalanced production and dissipation of turbulence common in flow over complex terrain while the rs approach yields information on turbulent contributions to near surface stress generation little evidence exists showing that rs is a better measure of forces responsible for sediment transport consequently predictive equations for sediment transport using rs do not exist there is also a need to identify the role of micro turbulent events e g burst sweep cycles and macro turbulent structures e g separation cells shear layers in aeolian dynamics in field settings to validate recent wind tunnel and cfd simulations a conundrum exists regarding whether velocity data should be rotated to correct for potential sensor misalignment effects in unsteady non uniform flow over complex terrain streamline angles vary spatially and temporally with height and location thus determination of and correction to true streamline coordinates is difficult caution should be exercised with correction methods that remove implicit vertical velocity trends as this may preclude detection of geomorphically important flow behaviour e g lift at a dune crest and may complicate interpretations of rs instruments should be aligned with the underlying surface and flow visualization should be used to adjust sensor measurement planes as close as possible to local streamlines logistical considerations include sensor design advantages and operational limitations data communication formats and field deployment strategies each can affect measurement accuracy and are easily overlooked sampling range frequency and period are also important as they limit the range of velocities and scales of turbulence that can be characterized ultrasonic anemometers offer a new sampling resolution to measure turbulent airflow properties in field settings with proper considerations of their limitations uas may allow researchers to close the gap between fluvial research and develop more robust models of aeolian processes and morphodynamics

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

computerized balanced cross section locace to reconstruct an allochthonous salt sheet offshore louisiana abstract the evolution of an allochthonous salt sheet underlying the mississippi fan is quantified using the two dimensional locace balanced section program a first set of tests shows that the shape of the principal normal fault associated with the salt sheet is inconsistent with a roll over geometry when using flexural slip or simple 120 linear shear criteria with a fixed footwall geometry the next test with corrected fault geometry allows coherent restoration at the early lower miocene using the flexural slip criterion in two dimensional reconstructions the area of salt cannot be balanced i e the area available for salt is considerably wider than the actual salt area shown on the initial section thus either salt was dissolved or perhaps more likely salt moved outside the plane of section calling for a three dimensional volumetric reconstruction procedure the final interpretation is geometrically consistent and suggests that since early lower miocene time a large amount of salt moved out of the plane of section forming the allochthonous salt masses an attempt to approximately balance salt volumes in three dimensions suggests that the amount of salt escaping the system is at least 18

the fetch experiment an overview the flux etat de la mer et teledetection en conditions de fetch variable fetch was aimed at studying the physical processes associated with air sea exchanges and mesoscale oceanic circulation in a coastal region dominated by frequent strong offshore winds the experiment took place in march april 1998 in the northwestern mediterranean sea gulf of lion observations were collected with the r v l atalante with an air sea interaction spar asis buoy with waverider buoys and with research aircraft equipped for in situ and remote sensing measurements the present paper is an introduction to the following special section which groups 12 papers including this one presenting results on turbulent flux measurements at the ocean surface on the behavior of the marine atmospheric boundary layer on the ocean waves characteristics on the ocean circulation and on remote sensing of surface parameters this overview presents the background and objectives of fetch the experimental setup and operations and the dominant atmospheric and oceanic conditions and introduces the different papers of the special section

variation of the drag coefficient and its dependence on sea state using a gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the pisa mast 28 km offshore in the german bight during autumn and winter 1979 these data were analyzed to identify the relationship between wind stress and surface waves it was found that wind stresses for wind speeds above 15 m s were regularly higher than open ocean wind stresses as reported by smith 1980 and by large and pond 1981 for the same mean wind speed these results when described in terms of the drag coefficient compared closely with the results of sheppard et al 1972 who collected surface layer statistics over lough neagh northern ireland after modeling the surface waves of the north sea as a function of wave saturation or wave age it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum by applying the wave dependent roughness length model described by kitaigorodskii 1973 the north sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea

some evidence of colinear wind stress and wave breaking abstract data collected during the surface waves and processes program are employed to investigate a possible interrelation between wind stress and surface wave breaking from comparison of data from 15 half hour long time segments the directions of the wind stress and the whitecap motion are observed to be generally colinear with both lying between the mean wind and the swell as well a nondimensionalized whitecap speed is found to correlate with the drag coefficient these results suggest that the magnitude and direction of the wind stress might be estimated from wave breaking information