steep beach morphology changes due to energetic wave forcing abstract the three dimensional variability of the sub aerial beach is examined for waimea bay hawaii a steep slope pocket beach subject to energetic winter swell events the beach is mapped using 32 real time kinematic global positioning system rtk gps surveys collected from march 1996 to july 1997 the survey method provides 4 m horizontal spacing and 2 3 cm vertical accuracy the primary morphology change is the episodic removal and re establishment of a foreshore dune during the winter swell season the average sand volume flux between surveys reaches 8 and 4 m 2 day during peak erosion and accretion periods the sand volume of the sub aerial beach is found to be highly correlated 0 96 with the position of the shoreline longshore variations in morphology include beach cusps with typical peak to trough amplitudes of 0 5 1 5 m and longshore wavelengths of 30 70 m the relationships between the energetic swell forcing and the volume and flux of sand on the sub aerial beach are examined the highest correlation 0 88 is found between the total sand volume and the wave energy flux after the latter is filtered following wright et al wright l d short a d green m o 1985 short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model mar geol 62 339 364 the filter is effective at capturing slow accretion phases following energetic erosion events

chemical composition and tectonic setting of chromian spinels from the ediacaran early paleozoic nama group namibia abstract petrographic and chemical characterization of chromian spinels from the lower and upper schwarzrand subgroup and the upper fish river subgroup of the latest ediacaran to early paleozoic nama foreland basin in namibia is used to infer the tectonic setting of source rocks and evaluate the geotectonic evolution of the damara orogen electron microprobe analysis of detrital chromian spinels from the nama group show three groups of chromian spinels i a group with a cr documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape ma

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

an optical technique for the measurement of longshore currents 1 we present an optical method optical current meter to measure the longshore component of nearshore surface currents by measuring the alongshore drift of persistent sea foam in the surf zone the method uses short time series of video data collected from an alongshore array of pixels these space time data are first fourier transformed to a frequency wave number spectrum and finally to a velocity spectrum a model of the velocity spectrum is fit to the observed spectrum to estimate the foam drift velocity confidence intervals and other measures of the input and output data quality are calculated field test comparisons were made against an in situ bidirectional electromagnetic current meter on the basis of 1 month of video data from the 1997 sandy duck field experiment the root mean square error between the two approaches was 0 10 m s linear regression analysis showed the gain between the two instruments to not be statistically different from one differences between the surface and interior measurements were compared to forcing mechanisms that may cause surface velocity shear velocity offsets and alongshore wind stress were well correlated for cases when waves and wind were not aligned to within 45 when wind and wave forced currents are reasonably separable calculated wind dependent surface current shear modeled as a surface boundary layer correlated well with the observed velocity offsets for observations of nonalignment between wind and waves this technique can be applied to study large scale coastal behavior

a climatology of midlatitude mesoscale convective vortices in the rapid update cycle abstract climatological characteristics of mesoscale convective vortices mcvs occurring in the state of oklahoma during the late spring and summer of four years are investigated the mcv cases are selected based on vortex detection by an objective algorithm operating on analyses from the rapid update cycle ruc model consistent with a previous study true mcvs represent only about 20 of the mesoscale relative vorticity maxima detected by the algorithm the mcvs have a broad range of radii and intensities and their longevities range between 1 and 54 h their median radius is about 200 km and their median midlevel relative vorticity is 1 2 10 4 s 1 there appears to be no significant relationship between mcv longevity and intensity similar to past estimates approximately 40 of the mcvs generate secondary convection within their circulations the mean synoptic scale mcv environment is determined by the use of a ruc based composite analysis at four different stages in the mcv life cycle defined b

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

structural characteristics of deep convective systems over tropical africa and the atlantic ocean abstract the structural properties of convective cloud clusters of tropical africa and the atlantic ocean are studied using six summers of meteosat satellite data in the atmospheric infrared window a cluster at a given brightness temperature threshold is defined as the area covered by adjacent cloud cells with brightness temperature lower than the threshold the clusters are classified according to the area they cover and the position of their center of mass results show that the convective cluster number can be approximated by a power law of the radius with an exponent around 2 this gives a nearly equal contribution of each cluster size to the mean high cloud cover for a given brightness temperature threshold using the visible channel 0 4 1 1 m of meteosat we show that the part of the clusters with reflectance larger than 0 7 also follows a power law the cluster size distributions remain similar for different subregions and seasons even if they are subject to large variations in the mean cloud

convection over tropical africa and the east atlantic during the west african monsoon regional and diurnal variability abstractthe geographic and diurnal variability of moist convection over tropical africa and the east atlantic is examined using the tropical rainfall measuring mission trmm satellite and related to the variability of the convective environment the stratiform rain fraction is highest within oceanic and continental regions just north of the equator both regions have high column relative humidity crh in both monsoon and semiarid continental regions stratiform rain fractions are significantly higher on days when the crh is high which suggests a relationship between these quantities large convective systems with high echo tops dominate the rainfall over the sahel the importance of cape and shear to the development of these types of systems is suggested by the fact these systems are especially common on days when the cape and shear are unusually high both deep convective and stratiform conditional rain rates increase with the size and echo top height of convective systems according to the trmm preci

the response of simulated nocturnal convective systems to a developing low level jet some recent numerical experiments have examined the dynamics of initially surface based squall lines that encounter an increasingly stable boundary layer akin to what occurs with the onset of nocturnal cooling the present study builds on that work by investigating the added effect of a developing nocturnal low level jet llj on the convective scale dynamics of a simulated squall line the characteristics of the simulated llj atop a simulated stable boundary layer are based on past climatological studies of the llj in the central united states a variety of jet orientations are tested and sensitivities to jet height and the presence of lowlevel cooling are explored the primary impacts of adding the llj are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm relative inflow in the jet layer the changes to wind shear have an attendant impact on low level lifting in keeping with current theories for gust front lifting in squall lines the changes to the system relative inflow in turn impact total upward mass flux and precipitation output both are sensitive to the squall line relative orientation of the llj the variations in updraft intensity and system relative inflow are modulated by the progression of the lowlevel cooling which mimics the development of a nocturnal boundary layer while the system remains surfacebased the below jet shear has the largest impact on lifting whereas the above jet shear begins to play a larger role as the system becomes elevated similarly as the system becomes elevated larger changes to systemrelative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the llj

remote sensing of nearshore wave interference wave focusing of energetic swell fields can result in small scale variations associated with coherent interference that can be important for nearshore circulation and beach dynamics however coherent interference is difficult to measure with conventional in situ instruments and is not accounted for in operational wave models as a result such effects are generally ignored in this work we analyze x band radar observations collected at ocean beach san francisco using a wigner ville or coupled mode spectrum to show how long dwell remote sensing technology allows us to identify coherent wave interference our analysis demonstrates that during energetic swell events the nearshore wave field consists of two noncollinear but coherent swell patterns that originate from the same offshore source but are directionally separated due to refraction over the san francisco bar the length scale of the associated alongshore wave height variability 200 m is consistent with the wavenumber separation obtained from the coupled mode analysis this confirms that the small scale variability is primarily due to coherent interference in addition our analysis shows that the shoreline exhibits a strong localized response near the radar site on the 200 m scale which suggests that coherent interference effects can affect wave driven nearshore transport processes and localized erosion

orogenic convection in subtropical south america as seen by the trmm satellite abstractextreme orogenic convective storms in southeastern south america are divided into three categories storms with deep convective cores storms with wide convective cores and storms containing broad stratiform regions data from the tropical rainfall measuring mission satellite s precipitation radar show that storms with wide convective cores are the most frequent tending to originate near the sierra de cordoba range downslope flow at upper levels caps a nocturnally enhanced low level jet thus preventing convection from breaking out until the jet hits a steep slope of terrain such as the sierra de cordoba mountains or andean foothills so that the moist low level air is lifted enough to release the instability and overcome the cap this capping and triggering is similar to the way intense convection is released near the northwestern himalayas however the intense storms with wide convective cores over southeastern south america are unlike their himalayan counterparts in that they exhibit leadi

mesoscale convective complexes and persistent elongated convective systems over the united states during 1992 and 1993 abstract large long lived convective systems over the united states in 1992 and 1993 have been classified according to physical characteristics observed in satellite imagery as quasi circular mesoscale convective complex mcc or elongated persistent elongated convective system pecs and cataloged the catalog includes the time of initiation maximum extent termination duration area of the 52 c cloud shield at the time of maximum extent significant weather associated with each occurrence and tracks of the 52 c cloud shield centroid both mcc and pecs favored nocturnal development and on average lasted about 12 h in both 1992 and 1993 pecs produced 52 c cloud shield areas of greater extent and occurred more frequently compared with mccs the mean position of initiation for pecs in 1992 and 1993 followed a seasonal shift similar to the climatological seasonal shift for mcc occurrences but was displaced eastward of the mean position of mcc initiation in 1992 and 1993 the spatial distribution

influence of the frontal systems on the day to day convection variability over south america abstract cold cloud top fractions derived from international satellite cloud climatology project images and latitude time diagrams are used to study the interaction of frontal systems with tropical convection over south america sa an 11 yr climatology for three frequent types of frontal system tropical convection interaction is built and the associated day to day convection variability is described using satellite images complex principal components and wavelet transforms type 1 is frequent throughout the year especially in austral summer and is characterized by the penetration of a cold front in subtropical sa that interacts with tropical convection and moves with it into lower tropical latitudes type 2 is also more frequent in austral summer and is characterized by amazon convection and enhancement of a quasi stationary northwest southeast oriented band of convection extending from the amazon basin to subtropical sa along the passage of a cold front in the subtropics when the type 2 pattern

interactions between a developing mesoscale convective system and its environment part i observational analysis this paper is the first in a two part series in which the interactions between a growing mesoscale convective system mcs and its surrounding environment are investigated the system studied here developed in northeastern colorado on 19 july 1993 and propagated into kansas as a long lived nocturnal mcs high resolution dual doppler and surface mesonet data collected from this system are discussed in part i while the results of a numerical simulation are discussed in part ii the observations show that organized mesoscale surface pressure and flow features appeared very early in the lifetime of this system long before the development of any trailing stratiform precipitation most of the stratiform anvil advected ahead of the convective line in the strong upper tropospheric westerlies in accordance with this most of the mid and upper tropospheric storm relative flow behind the line remained westerly or rear to front despite the westerlies the strongest flow perturbations with respect to the ambient winds developed to the rear of the line the structure of these perturbations was similar to the upper tropospheric front to rear and midtropospheric rear to front flows typically found in more mature leading line trailing stratiform systems the presence of these perturbations on the upwind side of the convective line indicates that gravity wave propagation was primarily responsible for their development

potassic and sodic metasomatism in the southern province of the canadian shield evidence from the paleoproterozoic serpent formation huronian supergroup canada abstract major element geochemistry petrographic observations and microprobe analyses of the paleoproterozoic serpent formation huronian supergroup canada suggest that these strata experienced both potassium and sodium metasomatism major element data plotted in al2o3 cao na2o k2o compositional space form an array nearly identical to data from sub huronian paleosols reported elsewhere suggesting that serpent fluvial systems captured materials from entire weathering profiles potassium metasomatism was concentrated in shales and represents the illitization of kaolinite which is a residual product of plagioclase weathering sodium metasomatism principally affected silt and sand sized particles microprobe analyses of plagioclase grains indicate that they are nearly pure albite ab96 corresponding whole rock major element data plot in bulk albite space on an al2o3 k2o cao na2o ternary diagram whereas basement rocks plot in bulk andesine and oligoclase space end member compositions and the absence of luminescence when bombarded with an electron beam indicate that the albites are of secondary origin extremely pure albite cements ab99 commonly fringe detrital grains there has been little replacement of detrital k feldspars despite the complete albitization of plagioclase grains the timing of metasomatism at least the last stage is constrained to the period between 1700 and 1750 ma based on geochronologic data reported elsewhere when the southern province of the canadian shield experienced considerable felsic plutonism possibly related to arc collision this plutonism may have resulted in the heating of deep basinal brines stresses associated with orogenic build up or gravity driven groundwater circulation working in concert with the plutonism expelled these brines through the serpent formation and the entire huronian supergroup thoroughly metasomatizing the region such processes associated with collisional tectonics are akin to the development of mississippi valley type pb zn mineralization in the mid continent of the united states

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

observations of elevated convection initiation leading to a surface based squall line during 13 june ihop_2002 abstract the evolution of a mesoscale convective system mcs observed during the international h2o project that took place on the great plains of the united states is described the mcs formed at night in a frontal zone with four initiation episodes occurring between approximately 0000 and 0400 local time radar radiosonde and surface data together show that at least three of the initiation episodes were elevated occurring from moist conditionally unstable layers located above the boundary layer which had been stabilized by previous mcss initiation occurred in northwest southeast oriented lines where a southerly nocturnal low level jet terminated generating elevated convergence one initiation episode was observed using the s band dual polarization doppler radar s pol and occurred at the intersection of this convergence zone with a propagating wave calculations of the scorer parameter were consistent with wave trapping downdrafts from the developing convection generated both waves and bores w

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

mesoscale convective complexes over the united states during 1983 abstract enhanced infrared satellite imagery is used to document the occurrence of mesoscale convective complexes over the united states during 1983 thirty large convective systems are identified that display satellite observable characteristics which satisfy the mcc criteria described by maddox details of the life cycles of these 30 systems are given and four examples are discussed in the context of large scale midtropospheric features this is the third in a series of annual summaries assembled as a documentation for those interested in investigating the mesoscale convective weather systems that occur over the united states

the influence of shelf indenting canyons and infralittoral prograding wedges on coastal morphology the carchuna system in southern spain abstract submarine canyons and progradational sedimentary bodies are common features of continental margins worldwide few studies have analyzed the relationship between the coastal morphology and the morphology and sedimentary characteristics of the adjacent shelf in wave dominated coasts or the potential role played by shelf indenting canyons as inducers of sediment deposition in shallow waters this work presents a study that correlates the coastal morphology with the characteristics of the adjacent offshore shallow shelf in an area with a complex inner bathymetry the carchuna system spain the study area is characterized by large scale non rhythmic cuspate features in the coastline whereas the inner bathymetry exhibits a shallow water infralittoral prograding wedge ipw and a shelf indenting canyon that has tributaries located a short distance from the coastline using detailed bathymetric measurements observational data and wave propagation modeling the influence of the different bathymetric elements was quantified and a mechanism proposed for the generation of the carchuna ipw the wave propagation results show that the canyon is the main source of the alongshore modulation of nearshore waves and that it plays a major role in the generation of the large scale cuspate features in the shoreline additionally these results suggest that the long term coastal erosion associated with extreme storms yielded sufficient sediment which when subsequently transported eastward the dominant littoral drift direction formed the ipw once formed the ipw modified the wave propagation patterns and contributed to the development and reinforcement of the shoreline features

modeled alongshore circulation and force balances onshore of a submarine canyon alongshore force balances including the role of nonlinear advection in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system delft3d swan the model is calibrated with waves and alongshore flows recorded over a period of 1 5 months at 26 sites along the 1 0 2 5 and 5 0 m depth contours spanning about 2 km of coast field observation based estimates of the alongshore pressure and radiation stress gradients are reproduced well by the model model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation stress gradients and the sum of the nonlinear advective terms and bottom stress with the remaining terms e g wind stress and turbulent mixing being negligible the simulations also indicate that unexplained residuals in previous field based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms which are similar in magnitude to the sum of the forcing pressure and radiations stress gradients and to the bottom stress

organization of tropical convection in low vertical wind shears the role of water vapor abstract a modeling study is conducted to gain insight into the factors that control the intensity and organization of tropical convection and in particular to examine if organization occurs in the absence of factors such as vertical wind shear or underlying sea surface temperature sst gradient the control experiment integrates a cloud resolving model for 15 days using a 3d domain exceeding 1000 km in length with no imposed winds and horizontally uniform sst and forcing for convection after 2 days of random activity the convection organizes into clusters with dimensions of approximately 200 km convective systems propagate through the clusters at speeds of 2 3 m s 1 while the clusters themselves propagate at minimal speeds of around 0 5 m s 1 examining the thermodynamic structure of the model domain it is found that the convective free bands separating the clusters are very dry throughout the troposphere and due to virtual temperature effects are correspondingly warmer in the lower tropospher

analysis of the scale of errors in nearshore bathymetric data most studies of nearshore hydrodynamics sediment transport and morphology focus on bathymetric variability within a narrow band of spatial and temporal scales typically these studies rely on bathymetry estimates derived from field observations consisting of discrete samples in space and time with varying degrees of measurement error sampling limitations which result in aliasing and measurement errors can significantly contaminate variability at resolved scales and may lead to large errors in the representation of the scales of interest using a spectral analysis interpolation errors were analyzed for three different nearshore bathymetric data sets each of which targeted a different range of spatial scales bathymetric features that were unresolved or poorly resolved e g beach cusps introduced the potential for contamination in two of the data sets this contamination was significantly reduced using an appropriate scale controlled interpolation method leading to more accurate representations of the actual bathymetry an additional benefit of using scale controlled interpolation is that interpolation errors may be estimated independently of actual observations which allows one to design bathymetric sampling strategies that ensure that dominant scales are either resolved or largely removed finally interpolation errors corresponding to a particular sample design can be used to determine which interpolated values contribute usefully to a band limited analysis of bathymetric variability

simulations of an observed elevated mesoscale convective system over southern england during csip iop 3 simulations of an elevated mesoscale convective system mcs observed over southern england during the convective storm initiation project csip provide the first detailed modelling study of a case of elevated convection occurring in the uk the study shows that many factors can influence the maintenance of elevated deep convection from large scale flow through to surface heating processes and diabatic cooling within the convective system it is also shown that interactions and feedback mechanisms between a stable layer and the storm can act to maintain deep convection the simulation successfully reproduced an elevated mcs above a low level stable undercurrent with a wave in the undercurrent linked to a rear inflow jet rij convection was fed from an elevated 840 hpa source layer with cape of about 350 j kg 1 the undercurrent in the simulation was approximately 1 km deep about half that observed unlike the observed mcs a transition from elevated to surface based convection occurred in the simulation due to the combined effects of a pre existing large scale e gradient advection and surface heating causing the system to encounter increasingly unstable low level air and a shallower stable layer that was more susceptible to penetration by downdraughts the transition to surface based convection was accompanied by the development of cold pool outflow and an increase in system velocity from about 6 to 10 m s 1 diabatic cooling from microphysical processes in the simulation enhanced the undercurrent and strengthened the rij this strengthened the wave in the undercurrent and led to more extensive convection the existence of a positive feedback process between the convection rij and stable layer is discussed uncertainty in the synoptic scale generating errors in the undercurrent is shown to be a major source of error for convective scale forecasts

geochronological constraints on the evolution of the southern dom feliciano belt uruguay abstract new u pb sensitive high resolution ion microprobe k ar and ar ar data from the southernmost dom feliciano belt allow the identification of four major events orthogneisses from the punta del este terrane indicate a magmatic episode at c 770 ma and high grade metamorphism at 641 17 ma granitoid emplacement at 627 23 ma was roughly coeval with peak metamorphism volcaniclastic rocks of the las ventanas formation dated at 573 11 ma can be correlated with the peripheral foreland basin 571 8 ma transpression and coeval high k calc alkaline magmatism is recorded in the maldonado granite dated at 564 7 ma the following events are postulated 1 magmatism at 850 750 ma related to rifting 2 metamorphism and granite emplacement at 650 600 ma 3 molasse sequences and foreland basins at c 573 ma 4 late magmatism at 580 560 ma associated with transpression the data indicate that 1 the punta del este terrane could be a portion of the coastal terrane of the kaoko belt 2 granitoid emplacement at 650 600 ma in the punta del este and nico perez terranes favours westward subduction and 3 widespread post collisional synkinematic magmatism occurred in the dom feliciano and kaoko belts between 580 and 550 ma supplementary material analytical methods and data are available at http www geolsoc org uk sup18369

un predictability in rip channel systems 1 predicting the development of rip channel systems on beaches is relevant for beach safety nearshore mixing and dispersion and has been puzzling researchers for decades field observations and computer simulations have focused on predicting the spacing and growth time of rip channels as a function of wave characteristics a satisfactory predictor of rip channel spacing and growth time has not yet been proposed here we show that the lack of predictability of rip channels is an inherent property of the system related to the high sensitivity to the bathymetry prior to pattern development sensitivity to the initial cross shore profile appears to be as important as sensitivity to wave height although we might be able to predict rip channel characteristics the information required by such predictors will need to account for the underlying bathymetry implications arising from this study are that other geomorphic patterns could display similar sensitivity

a long lived mesoscale convective complex part ii evolution and structure of the mature complex abstract an eight day episode in august 1977 is described wherein 14 mesoscale convective complexes mccs developed in the central united states including one to the immediate ice of the rocky mountains on each day of the episode in part i of this article the daytime genesis of one of these systems was traced from its pre convective roots in the mountains of central colorado to its incipient mcc stage on the plains of eastern colorado in this paper its continued nocturnal development into a large mcc over kansas is followed satellite imagery shows that this system remained coherent for at least three days as it passed off the east coast and across the western atlantic ocean analysis is focused on the mature stage of this and a second mcc in the episode in order to compare their major dynamic features to those of similar midlatitude systems reported in the literature and also to previous studies of tropical mesoscale convective systems many of the important characteristics of midlatitude mccs fo

rip current types circulation and hazard abstract rip currents are narrow and concentrated seaward directed flows that extend from close to the shoreline through the surf zone and varying distances beyond rip currents are ubiquitous on wave exposed coasts each year they cause hundreds of drowning deaths and tens of thousands of rescues on beaches worldwide and are therefore the leading deadly hazard to recreational beach users the broad definition above masks considerable natural variability in terms of rip current occurrence in time and space flow characteristics and behaviour in particular surf zone rip currents have long been perceived as narrow flows extending well beyond the breakers flushing out the surf zone at a high rate exit flow circulation regime while more recent studies have shown that rip flow patterns can consist of quasi steady semi enclosed vortices retaining most of the floating material within the surf zone circulatory flow circulation regime building upon a growing body of rip current literature involving numerical modelling and theory together with emergence of dense lagrangian field measurements we develop a robust rip current type classification that provides a relevant framework to understand the primary morphological and hydrodynamic parameters controlling surf zone rip current occurrence and dynamics three broad categories of rip current types are described based on the dominant controlling forcing mechanism each category is further divided into two types owing to different physical driving mechanisms for a total of six fundamentally different rip current types hydrodynamically controlled 1 shear instability rips and 2 flash rips which are transient in both time and space and occur on alongshore uniform beaches bathymetrically controlled 3 channel rips and 4 focused rips which occur at relatively fixed locations and are driven by hydrodynamic processes forced by natural alongshore variability of the morphology in both the surf zone and inner shelf zone and boundary controlled 5 deflection rips and 6 shadow rips which flow against rigid lateral boundaries such as natural headlands or anthropogenic structures for each rip current type flow response to changes in hydrodynamic and morphologic forcing magnitude is examined in regard to velocity modulation and changes in circulation regime providing key force response relationships of rip currents we also demonstrate that in the real world rip currents form through a mixture of driving mechanisms and the discrete rip types defined in fact form key elements in a wide and complex spectrum of rip currents on natural beaches it is anticipated that this rip current type classification will serve as a resource for coastal scientists and non specialists with an interest in the rip current hazard and as a platform for future rip current studies finally we suggest some important future research directions highlighting the need for coastal and beach safety communities to collaborate in order to improve rip current education and awareness

diurnal patterns of rainfall in northwestern south america part i observations and context one of the rainiest areas on earth the panama bight and pacific western littoral of colombia is the focal point for a regional modeling study utilizing the fifth generation pennsylvania state university ncar mesoscale model mm5 with nested grids in this first of three parts the observed climatology of the region is presented the seasonal march of rainfall has a northwest southeast axis with western colombia near the center receiving rain throughout the year this study focuses on the august september season the diurnal cycle of rainfall over land exhibits an afternoon maximum over most of south and central america typically composed of relatively small convective cloud systems over some large valleys in the andes and over lake maracaibo a nocturnal maximum of rainfall is observed a strong night morning maximum of rainfall prevails over the coastal ocean propagating offshore and westward with time this offshore convection often takes the form of mesoscale convective systems with sizes comparable to the region s coastal concavities and other geographical features the 10 day period of these model studies 28 august 7 september 1998 is shown to be a period of unusually active weather but with a time mean rainfall pattern similar to longer term climatology it is concluded that the rain producing processes during this time period are likely to be typical of those that shape the seasonal climatology

rip current circulation and surf zone retention on a double barred beach abstract rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants between the surf zone and inner shelf concurrent in situ eulerian and lagrangian gps drifter data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy double barred beach the data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current and the exchange process on both days there was a prominent clockwise eddy in the surf zone for which the seaward heading portion formed a rip current in a well defined channel rip incised into the inner bar exit rate measured with drifters from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar from 71 exits to 6 over the two days exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone under higher wave conditions there were stronger pulsations in surf zone currents and more surf zone exits however higher wave conditions caused wave breaking over the outer bar this breaking increases vorticity around the outside of the surf zone eddy which increases surf zone retention this is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies under such conditions drifter exits were rare and occurred due to vortex shedding during lower incident wave conditions eddy vorticity was lower and drifters could relatively freely exit the surf zone this is one of the few studies that investigate surf zone circulation on a high energy double barred beach

rip currents under obliquely incident wind waves and tidal longshore currents abstract a field experiment on the nature of rip currents was conducted on the dutch coast which differs from previous rip current study sites because it is a wind sea dominated environment with mostly obliquely incident waves and tidally driven longshore currents during the experiment three distinct flow patterns obtained with gps tracked drifter instruments were observed 1 a locally governed circulation cell 2 an offshore current that is deflected shore parallel outside the surf zone and 3 a meandering longshore current the transition from rip currents flow patterns 1 and 2 to meandering longshore currents flow pattern 3 occurred gradually within the tidal cycle with longshore currents prevalent at mid to high tide rip currents at this site appeared at depressions in the surf zone bar and typically occurred when the water level fell below nap equivalent to msl even in the presence of obliquely incident waves and tidally driven longshore currents hindcast simulations of the drifter experiments were performed with the numerical model xbeach and showed good agreement with field observations the model was subsequently used to investigate the influence of tidal water level fluctuations longshore currents and obliquely incident waves on rip currents rip currents were initiated when the water level dropped below a specific threshold with the magnitude of the rip current associated with the water level the strength of the tidal current and its orientation with respect to the incident waves governed the offshore extent and orientation of the rip current in contrast to other studies that suggest that rip currents solely occur under shore normal or slightly oblique waves in this study both observations and numerical model simulations indicate that rip currents can exist under large angles of wave incidence when the rip channel is sufficiently wide and the wave height is small

quantification of sand bar morphology a video technique based on wave dissipation a technique is presented to remotely measure the scales and morphology of natural sand bars based on the preferential dissipation of wind waves and swell over the crests of the bar photographic or video images are recorded and statistical uncertainties associated with incident wave height modulations removed by averaging time exposures ground truth testing of the technique was carried out as part of the superduck experiment in october 1986 the time exposures generally provided a good mapping of underlying morphology allowing detection of the bar and determination of cross shore and longshore length scales however during high waves persistent surface foam obscures the relationship of image intensity to local dissipation modeled theoretically by dissipation of a random wave field and an enhancement technique of image differencing must be done to remove the bias errors in the estimate of bar crest distance from the shoreline are generally less than 35 but this value depends on the geometry of the particular bar logistic simplicity and quantitative capabilities make this technique very attractive

on the impact of an offshore bathymetric anomaly on surf zone rip channels 1 we use a nonlinear morphodynamic model to demonstrate that the presence of a single persistent offshore bathymetric anomaly strongly affects the formation nonlinear evolution and saturation of surf zone rip channels in the case of an offshore bump or trough and waves with oblique incidence a rip channel shoreward of the anomaly is enforced by the more seaward alongshore variability in depth the degree of rip channel enforcement is controlled by the strength of the rotational nature of surf zone rip current circulations which is in turn driven by differential broken wave energy dissipation induced by wave refraction across the offshore bathymetric anomaly the alongshore location of this forced rip channel is more stable with increasing offshore anomaly amplitude decreasing offshore wave obliquity and decreasing bathymetric anomaly distance to the shore simulations show that rip channel behavior downdrift and updrift of the offshore perturbation are different in our numerical experiments downdrift rip channels have systematically larger alongshore scales smaller alongshore migration rates and more erosive megacusps than those updrift rip channels therefore self organize into patterns of different alongshore scales and migration rates as a result of an alongshore perturbation in the wave forcing enforced by wave refraction across an offshore bathymetric anomaly these simulations are qualitatively corroborated by video observations of sandbar behavior during a down state sequence at a site with a persistent offshore trough

provenance of the arroyo del soldado group ediacaran to cambrian uruguay implications for the paleogeographic evolution of southwestern gondwana abstract the ediacaran to lower cambrian arroyo del soldado group represents a thick marine sequence cropping out in the eastern border of the rio de la plata craton in central uruguay this work addresses the provenance of different siliciclastic units in the arroyo del soldado group in terms of petrography geochemistry nd isotope and detrital zircon geochronologic data the lower part of the arroyo del soldado group the yerbal formation and the overlying carbonates of the polanco formation are related to an open shelf which formed after rifting along eastern border of the rio de la plata craton u pb zircon dating of reworked detrital material of the yerbal formation shows a provenance with mainly palaeoproterozoic ages 2 0 2 2 ga the yerbal formation shows t dm model ages of 2 1 ga and nd t of 15 the middle part of the arroyo del soldado group is characterized by deposition of coarse sediments barriga negra formation that could be related to a sea level fall during non global glaciation the zircon ages reflect a major contribution from the palaeoproterozoic and secondly from neoproterozoic basement rocks and constrain the maximum age of deposition to 566 ma t dm model ages reflect archaean 2 7 ga and palaeo mesoproterozoic 1 6 1 9 ga mantle extraction ages for the sources the archaean component shows geochemical similarities with a mafic source characterized by high concentration of cr 350 ppm and low th sc 0 7 up section during a sea level rise the deposition of bif shale and chert of the cerro espuelitas formation occurred t dm ages of 2 1 ga suggest a provenance mainly derived from the rio de la plata craton u pb zircon dating of the cerros san francisco formation representing the upper part of the arroyo del soldado group shows a provenance mainly from palaeoproterozoic 2 0 2 1 ga and archaean 2 5 2 9 3 5 ga rocks the scarcity of neoproterozoic zircons along with t dm ages of 2 2 2 9 ga and the extreme recycling that affected the cerros san francisco formation as indicated by petrography and geochemistry do not fit with the hypothesis that the arroyo del soldado group was deposited close to a syntectonic magmatic arc a tectonic scenario in which the arroyo del soldado group was deposited on a passive margin before strike slip collision with the cuchilla dionisio pelotas terrane at ca 530 ma is supported

isotope geochemistry and geochronology of the nico perez terrane rio de la plata craton uruguay u pb shrimp zircon geochronology bulk rock geochemistry and sr nd isotopic data are herein presented in order to better constrain the tectonic evolution of the nico perez terrane npt uruguay the studies are focused on two key geological units located in the southern part of the npt namely carape complex cc and lavalleja metamorphic complex lmc the carape complex previously interpreted as part of a remnant magmatic arc formed at 1 75 ga mainly by partial melting of archean crust t dm model ages between 2 8 and 3 0 ga with strong negative e nd t values the lavalleja metamorphic complex previously interpreted as a back arc basin has volcanic units formed at 0 59 ga during the brasiliano cycle but may also contain older paleoproterozoic units the geochemistry of the lmc meta igneous rocks indicates a complex scenario two distinct signatures have been recognized one similar to morbs and the other similar oibs sm nd t dm model ages of basic rocks present a bimodal paleoproterozoic and archean distribution which is also recognized in several other units of the npt in the light of new results we conclude that the npt represents a cratonic margin setting characterized by the stacking of lithotectonic assemblages with archean paleoproterozoic and neoproterozoic age at the margin of the rio de la plata craton

structural characteristics of convective systems over south america related to cold frontal incursions abstract international satellite cloud climatology project isccp dx and microwave sensor data collected by the tropical rainfall measuring mission trmm are used to identify and describe structural characteristics of convective systems css over continental south america sa related to cold frontal incursions in a 3 yr period an austral wet season climatology for cs events of the three most important types of front tropical convection interaction is built by applying latitude time diagrams and a cloud tracking method to dx data type 1 is characterized by the penetration of a cold front over subtropical sa that interacts with convection and moves with it into lower tropical latitudes type 2 refers to amazon convection and its enhancement in a quasi stationary northwest southeast oriented band extending from the amazon to subtropical sa along with the passage of a cold front in the subtropics and characterizes the synoptic formation of the south atlantic convergence zone a quasi stationary cold fro

satellite and radar survey of mesoscale convective system development abstract an investigation of several hundred mesoscale convective systems mcss during the warm seasons april august of 1996 98 is presented circular and elongated mcss on both the large and small scales were classified and analyzed in this study using satellite and radar data the satellite classification scheme used for this study includes two previously defined categories and two new categories mesoscale convective complexes mccs persistent elongated convective systems pecss meso circular convective systems m ccss and meso elongated convective systems m ecss around two thirds of the mcss in the study fell into the larger satellite defined categories mccs and pecss these larger systems produced more severe weather generated much more precipitation and reached a peak frequency earlier in the convective season than the smaller meso systems overall pecss were found to be the dominant satellite defined mcs as they were the largest most common most severe and most prolific

pressure gradient driven nearshore circulation on a beach influenced by a large inlet tidal shoal system 1 the nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal using a coupled wave and wave averaged nearshore circulation model it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal the model is used to predict waves and currents during field experiments conducted near the mouth of san francisco bay and nearby ocean beach the field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along ocean beach and across the ebb tidal shoal numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at ocean beach due to the resulting spatial variation in nearshore wave height wave induced setup exhibits a strong alongshore nonuniformity resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing the analysis of momentum balances inside the surf zone shows that under wave conditions with intensive wave focusing the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation inducing heterogeneous alongshore currents pressure gradient forced alongshore currents can exhibit flow reversals and flow convergence or divergence in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves

evaluation of the model representation of the evolution of convective systems using satellite observations of outgoing longwave radiation 1 we introduce a technique for assessing the diurnal development of convective storm systems based on outgoing longwave radiation fields using the size distribution of the storms measured from a series of images we generate an array in the length scale time domain based on the standard score statistic it demonstrates succinctly the size evolution of storms as well as the dissipation kinematics it also provides evidence related to the temperature evolution of the cloud tops we apply this approach to a test case comparing observations made by the geostationary earth radiation budget instrument to output from the met office unified model run at two resolutions the 12 km resolution model produces peak convective activity on all length scales significantly earlier in the day than shown by the observations and no evidence for storms growing in size the 4 km resolution model shows realistic timing and growth evolution although the dissipation mechanism still differs from the observed data citation pearson k j r j hogan r p allan g m s lister and c e holloway 2010 evaluation of the model representation of the evolution of convective systems using satellite observations of outgoing longwave radiation j geophys res 115 d20206 doi 10 1029 2010jd014265

seven doppler radar and in situ analysis of the 25 26 june 2015 kansas mcs during pecan abstractthis case study analyzes a nocturnal mesoscale convective system mcs that was observed on 25 26 june 2015 in northeastern kansas during the plains elevated convection at night pecan pro

reply to the comment on provenance of the arroyo del soldado group ediacaran to cambrian uruguay implications for the paleogeographic evolution of southwestern gondwana precambrian res 171 2009 57 73 by zimmermann

elevated mixed layers and associated severe thunderstorm environments in south and north america abstractthis study presents a climatological and composite analysis of elevated mixed layers emls in south and north america derived from the ncep climate forecast system reanalysis the emls are identified based on objective criteria applied to the reanalysis data composite analyses of synoptic scale conditions and severe weather parameters associated with spring eml cases are presented emls are more frequent immediately to the east of the andes and the rockies the north american emls form by surface heating over the higher terrain of the rockies with peak frequency occurring in spring and summer emls in south america are generated by differential temperature advection due to ageostrophic circulations east of the andes as indicated by the temperature lapse rate tendency equation which relates to the higher frequency of emls during the cold season in south america emls over north america are about 100 hpa lower than over south america due to the lower height of the rockies in comparison to the a

a case study of terrain influences on upscale convective growth of a supercell abstractsatellite and ground based radar observations have shown that the northern half of argentina south america is a region susceptible to rapid upscale growth of deep moist convection into l

the cuchilla dionisio terrane uruguay an allochthonous block accreted in the cambrian to sw gondwana abstract the cuchilla dionisio terrane cdt of uruguay is a tectonostratigraphic unit defined as the block to the east of the sierra ballena shear zone sbsz it is composed of a palaeo to mesoproterozoic metamorphic basement cerro olivo and chafalote complexes intensely reworked and intruded by syncollisional to late orogenic granites between 680 and 550 ma dacitic and rhyolitic volcanism is recorded around 570 575 ma cerros de aguirre and sierra de rios formations the cdt is correlated with the pelotas terrane of southern brazil the western boundary of the block in brazil is defined by the cangucu and major gercino shear zones which are the northward extension of the sbsz the present position of the cdt is not a consequence of orthogonal collision after completion of a wilson cycle but of lateral sinistral accretion along the above mentioned megashear zones the allochthonous nature of the cdt is postulated on the grounds that a magmatism in the cdt is ca 120 ma younger than metamorphism of neighbouring volcanosedimentary successions e g porongos group in brazil and b while intense volcanism occurred in the cdt in the late vendian represented by the cerros aguirre and sierra de rios formations a passive continental margin deepening to the e existed on the eastern edge of the rio de la plata craton represented by the arroyo del soldado group therefore the cdt and rio del la plata craton were separated hundreds or thousands of kilometers by late vendian times accretion of the cdt took place at 530 ma by tangential collision and was one of the last events in the complicated amalgamation of w gondwana in uruguay the cdt collided with the nico perez terrane generating the sbsz and sinistrally reactivating the sarandi del yi piriapolis shear zone in brazil the cdt pelotas terrane collided with the parana block and a series of parautochthonous terranes curitiba apiai characterized by a transamazonian basement strongly reworked in the neoproterozoic the provenance of the cdt is still uncertain considering that both transamazonian and namaqua natal kibaran ages have been reported from its basement previously reported nd model ages tdm strongly suggest an african affinity the dom feliciano belt is thus a collage of diachronous units formed in different geotectonic settings and not the product of a single orogenic cycle terrane docking at different stages mainly by lateral accretion was the dominant process therefore usage of the name dom feliciano belt should be restricted only to descriptive purposes

response of simulated squall lines to low level cooling abstract organized convection has long been recognized to have a nocturnal maximum over the central united states the present study uses idealized numerical simulations to investigate the mechanisms for the maintenance propagation and evolution of nocturnal like convective systems as a litmus test for the basic governing dynamics the experiments use horizontally homogeneous initial conditions i e they include neither fronts nor low level jet streams the simulated storms are allowed to mature as surface based convective systems before the boundary layer is cooled in this case it is then surprisingly difficult to cut the mature convective systems off from their source of near surface inflow parcels even when 10 k of the low level cooling has been applied the preexisting system cold pool is sufficient to lift boundary layer parcels to their levels of free convection the present results suggest that many of the nocturnal convective systems that were previously thought to be elevated may actually

offshore controls on nearshore rip currents 1 the rip current field resulting from the transformation of surface gravity waves over offshore submarine canyons is studied employing a wave transformation model and a wave induced circulation model over observed bathymetry we find that wave height variations associated with undulations in the canyon contours cause rip current circulation cells with alongshore spacing of o 100m even though the nearshore bathymetry displays no variations at these length scales further the predicted rips correspond to observed rip currents during the nearshore canyon experiment ncex motivated by these results we study the relationship between o 100 m scale variations in offshore bathymetric contours and the resulting rip current field in the nearshore to isolate the roles of possible bathymetric features we construct a series of idealized case studies that include site characteristics found at ncex that are conducive of rip current development such as a curved shoreline an offshore submarine canyon and undulations in the canyon contours our results show that the first two components are unable to produce the observed short scale circulation systems while wave refraction over undulations in the canyon walls at length scales of o 100 m provides a sufficient disturbance to generate alongshore wave height variations that drive multiple rip currents for a variety of incident wave conditions rips are not generated when the wave period is short or when the angle of incidence is large analysis of the alongshore momentum balances further demonstrates that the rip current locations are also strongly influenced by inertial effects hence nonlinear processes are important within the rip current circulation cell and we find that nonlinear advective acceleration terms balance a large portion of the driving alongshore gradient in the mean water surface elevation in the vicinity of the rip currents with bottom friction accounting for the remainder away from the rips the balance is between the wave forcing and the pressure gradient outside the surf zone and wave forcing and bottom friction inside the surf zone as expected

mesoscale convective vortices observed during bamex part ii influences on secondary deep convection abstract observations from the bow echo and mesoscale convective vortex mcv experiment are used to examine the role of the five mesoscale convective vortices described in part i on heavy precipitation during the daytime heating cycle persistent widespread stratiform rain without deep convection occurs for two strong mcvs in conditionally stable environments with strong vertical shear two other mcvs in moderate to strong vertical shear have localized redevelopment of deep convection termed secondary convection on their downshear side where conditional instability exists the strongest of the five mcvs occurs in weak vertical shear and has widespread secondary convection which is most intense on its conditionally unstable southeast periphery the two mcvs with only localized secondary convection have well defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer pbl although the amplitude is significantly greater the kinematically der

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

predominance of high th u magmatic zircon in brazilian shield sandstones the strong predominance of magmatic th u 0 2 zircon grains in quartz sandstones from 10 locations in the brazilian shield as measured by sensitive high resolution ion microprobe shrimp introduces a strong bias in the tectonic interpretation of source terrains because the metamorphic sources remain undetected in the detrital population zircon grains from many mature and some immature sedimentary terrains show th u ratios 0 2 ratios commonly considered magmatic complemented by the near absence of metamorphic th u ratios 0 1 metamorphic rims on magmatic zircon grains from the brazilian shield are nearly absent from quartz sandstones only being present in shielded young cores of a few crystals high u metamorphic portions of zircon grains are more defective and liable to undergo comminution by abrasion during weathering and transport and they do not remain in the sand fraction ages obtained from detrital zircon in mature sandstones reflect magmatic sources not the full spectrum of orogenic events only less mature sedimentary rocks preserve a full record of orogenic rocks in the source mostly magmatic events were characterized in previous zircon provenance studies brazilian shield detrital zircon may be a proxy for equivalent investigations in other provinces of the world

experimental study of nearshore dynamics on a barred beach with rip channels 1 wave and current measurements are presented from a set of laboratory experiments performed on a fixed barred beach with periodically spaced rip channels using a range of incident wave conditions the data demonstrate that the presence of gaps in otherwise longshore uniform bars dominates the nearshore circulation system for the incident wave conditions considered for example nonzero cross shore flow and the presence of longshore pressure gradients both resulting from the presence of rip channels are not restricted to the immediate vicinity of the channels but instead are found to span almost the entire length of the longshore bars in addition the combination of breaker type and location is the dominant driving mechanism of the nearshore flow and both are found to be strongly influenced by the variable bathymetry and the presence of a strong rip current the depth averaged currents are calculated from the measured velocities assuming conservation of mass across the measurement grid the terms in both the cross shore and longshore momentum balances are calculated and their relative magnitudes are quantified the cross shore balance is shown to be dominated by the cross shore pressure and radiation stress gradients in general agreement with previous results however the rip current is shown to influence the wave breaking and the wave induced setup in the rip channel analysis of the longshore balance shows that the overall strength of the longshore feeder currents is governed by a balance between longshore pressure gradient forcing and an opposing radiation stress gradient in addition the longshore feeder currents show maxima in the bar trough region providing experimental evidence that longshore pressure gradients can shift longshore current maxima shoreward from the bar crest finally since the longshore radiation stress gradient in the surf zone is governed by the amount of wave dissipation on the rip current there exists a positive feedback mechanism whereby a strong rip current can weaken the radiation stress gradient opposing the feeder currents and lead to even stronger feeder currents and rips

serial upstream propagating mesoscale convective system events over southeastern south america abstract serial mesoscale convective system mcs events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern south america from infrared satellite imagery during the spring and summer these events begin over the southern la plata river basin with individual convective systems generally moving eastward with the cloud layer mean wind however an important and common subset of these serial mcs events shows individual mcss moving to the east or southeast yet the region of convective development as a whole shifts upstream to the north or northwest analyses of the composite mean environments from 10 of these upstream propagating serial mcs events using ncep ncar reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the united states the serial mcs events form within an environment of strong low level warm advection and strong moisture advection between the surface and 700 hpa from the amazon

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

acritarchs of las ventanas formation ediacaran uruguay implications for the timing of coeval rifting and glacial events in western gondwana abstract acritarchs and other organic walled microfossils occurring in siltstones of the las ventanas formation quebrada de viera and el perdido members are systematically described and illustrated the assemblage includes the following species leiosphaeridia tenuissima leiosphaeridia minutissima lophosphaeridium sp soldadophycus bossii soldadophycus major soldadophycus sp and vendotaenia antiqua the microflora is characterized by low diversity six species dominance of l tenuissima absence of acanthomorphic acritarchs and relatively large size of sphaeromorphs reaching 400 m in diameter a number of species are shared with acritarch assemblages preserved in the overlying arroyo del soldado group differences between assemblages include the occurrence of abundant bavlinella faveolata and small size of spheroids in the arroyo del soldado group the assemblage occurring in las ventanas formation is assigned to the ediacaran leiosphere palynoflora which spans the interval between the base of the ediacaran end of the marinoan glaciation 635 ma and the termination of the gaskiers glaciation 582 ma an early ediacaran age between 615 and 579 ma is also supported by available radiometric ages an extensional setting for las ventanas basin is suggested on the basis of the bimodal synsedimentary volcanism strong palaeorelief great thickness of alluvial fan conglomerates and the evolution from continental to open marine environments diamictites occurring in the quebrada de viera member are described for the first time including associated dropstones which suggest a glacial origin if confirmed this would be one more example of the association between rifting and glaciation in the neoproterozoic coeval with a low diversity high abundance acritarch microflora a causal relationship between these tectonic climatic and biologic events is discussed

mesoscale circulation growth under conditions of weak inertial instability abstract the hypothesis that inertial instability plays a role in the upscale development of mesoscale convective systems mcss is explored by sampling environments that supported the growth of mcss in the preliminary regional experiment for storm stormscale operational and research meteorology pre storm network with high quality special soundings secondary circulations that occurred in the presence of inertial instabilities were analyzed and documented using rawinsonde data with high spatial and temporal resolution from the pre storm field program additional examples of mcs environments were examined using data from the mesoscale analysis and prediction system results show strong divergence and cross stream accelerations occurred at upper tropospheric levels where inertial instabilities were present these accelerations were not uniform over the domain but were focused in the regions of instability also the analyses of these data showed that regions of inertial instability may be more commonpla

rip currents and alongshore flows in single channels dredged in the surf zone to investigate the dynamics of flows near nonuniform bathymetry single channels on average 30 m wide and 1 5 m deep were dredged across the surf zone at five different times and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions in addition circulation was simulated with the numerical modeling system coawst initialized with the observed incident waves and channel bathymetry and with an extended set of wave conditions and channel geometries the simulated flows are consistent with alongshore flows and rip current circulation patterns observed in the surf zone near the offshore directed flows that develop in the channel the dominant terms in modeled momentum balances are wave breaking accelerations pressure gradients advection and the vortex force the balances vary spatially and are sensitive to wave conditions and the channel geometry the observed and modeled maximum offshore directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking wave driven setup across the nonuniform bathymetry a function of wave height and angle water depths in the channel and on the sandbar and a breaking threshold and the breaking wave driven alongshore flow speed the offshore directed flow speed increases with dissipation on the bar and reaches a maximum when the surf zone is saturated set by the vertical scale of the bathymetric variability

the structure evolution and dynamics of a nocturnal convective system simulated using the wrf arw model abstractprevious studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central united states forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate this study utilized the wrf arw model to simulate a nocturnal mesoscale convective system that occurred over the southern great plains on 3 4 june 2013 a low level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer the storm was elevated and associated with bores that assisted in the maintenance of the system three dimensional variations in the system s structure were found along the cold pool which were examined using convective system dynamics and wave theory shallow lifting occurred on the southern flank of the storm conversely the southeastern flank had deep lifting with favorable integrated vertical shear ov

quasi three dimensional modeling of rip current systems 1 the focus of the paper is the analysis of the flow in rip current systems generated by channels in longshore bars on a beach the horizontal variations of rip current systems are described through the use of the quasi three dimensional nearshore circulation model shorecirc model predictions are compared to laboratory measurements of waves and current velocities throughout the entire rip current system and show reasonable agreement the rips in the two channels are found to behave differently because of the depth variation across the basin it is found that higher bottom stress leads to more stable flow where the rip current meanders less and fewer eddies are generated the wave current interaction creates forcing which reduces the distance rip currents flow offshore and can lead to a slow pulsation of the rip current this pulsation is in addition to the instabilities of a jet which can also be present in rip currents the three dimensionality of the rip current system is found to have a significant effect on the overall circulation patterns index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes keywords rip currents nearshore circulation numerical modeling waves

a double moment multiple phase four class bulk ice scheme part ii simulations of convective storms in different large scale environments and comparisons with other bulk parameterizations abstract part i of this study described a detailed four class bulk ice scheme 4ice developed to simulate the hydro meteor profiles of convective and stratiform precipitation associated with mesoscale convective systems in part ii the 4ice scheme is incorporated into the goddard cumulus ensemble gce model and applied without any tuning to two squall lines occurring in widely different environments namely one over the pica ocean in the global atmospheric research program s garp atlantic tropical experiment gate and the other over a midlatitude continent in the cooperative huntsville meteorological experiment cohmex comparisons were made both with earlier three class ice formulations and with observations in both cases the 4ice scheme interacted with the dynamics so as to resemble the observations much more closely than did the model runs with either of the three class ice parameterizations the following features were well simulated in the cohmex case a lack of stratiform rain at the s

swan predictions of waves observed in shallow water onshore of complex bathymetry abstract swan model predictions initialized with directional wave buoy observations in 550 m water depth offshore of a steep submarine canyon are compared with wave observations in 5 0 2 5 and 1 0 m water depths although the model assumptions include small bottom slopes the alongshore variations of the nearshore wave field caused by refraction over the steep canyon are predicted well over the 50 days of observations for example in 2 5 m water depth the observed and predicted wave heights vary by up to a factor of 4 over about 1000 m alongshore and wave directions vary by up to about 10 sometimes changing from south to north of shore normal root mean square errors of the predicted wave heights mean directions periods and radiation stresses less than 0 13 m 5 1 s and 0 05 m 3 s 2 respectively are similar near and far from the canyon squared correlations between the observed and predicted wave heights usually are greater than 0 8 in all water depths however the correlations for mean directions and radiation stresses decrease with decreasing water depth as waves refract and become normally incident although mean wave properties observed in shallow water are predicted accurately nonlinear energy transfers from near resonant triads are not modeled well and the observed and predicted wave energy spectra can differ significantly at frequencies greater than the spectral peak especially for narrow band swell

mesoscale convective systems over southeastern south america and their relationship with the south american low level jet abstract prior studies have shown that the low level jet is a recurrent characteristic of the environment during the initiation and mature stages of mesoscale convective systems mcss over the great plains of the united states the south american low level jet sallj over southeastern south america sesa has an analogous role advecting heat and moisture from the amazon basin southward into the central plains of southeastern south america generating ideal environmental conditions for convection initiation and growth into mcss this research has two purposes one is to describe the characteristics of a 3 yr mcs sample in south america south of the equator and its related geographical distribution of convection frequency the other is to advance the knowledge of the evolution of favorable environmental conditions for the development of large mcss specifically those that mature under sallj conditions high horizontal and temporal resolution satellite images are used to detect mcss in the area for the

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

extreme summer convection in south america abstract tropical rainfall measuring mission trmm precipitation radar pr and national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data are used to indicate mechanisms responsible for extreme summer convection over south america the three dimensional reflectivity field is analyzed to define three types of extreme echo deep convective cores wide convective cores and broad stratiform regions the location and timing of these echoes are sensitive to midlatitude synoptic disturbances crossing the andes at the leading edges of these disturbances the nocturnal south american low level jet sallj transports moisture along the eastern edge of the andes from the tropical to the subtropical part of the continent where the sallj rises over lower but steep mountains on the east side of the southern central andes deep and wide convective cores are triggered in the evening when the sallj withdraws to the north as the disturbance passes nocturnal trig

life cycle variations of mesoscale convective systems over the americas abstract using goes 7 isccp b3 satellite data for 1987 88 the authors studied the evolution of the morphological and radiative properties of clouds over the life cycles of deep convective systems cs over the americas at both tropical and middle latitudes a deep convective cloud system is identified by adjacent satellite image pixels with infrared brightness temperatures tir 245 k 28 c that at some time contain embedded convective clusters that are defined by pixel values of tir 218 k 55 c the first part of the analysis computes parameters for each convective system that describe the system areal size number of convective clusters fractional convective area average and maximum size of the convective clusters shape eccentricity and orientation mean tir variance of tir tir gradient and the mean variance and gradient of collocated visible reflectances when available the second part of the analysis searches a 5 5 region centered on each convective system but in the subsequent

alongshore momentum transfer to the nearshore zone from energetic ocean waves generated by passing hurricanes wave and current measurements from a cross shore array of nearshore sensors in duck nc are used to elucidate the balance of alongshore momentum under energetic wave conditions with wide surf zones generated by passing hurricanes that are close to and far from to the coast the observations indicate that a distant storm hurricane bill 2009 with large waves has low variability in directional wave characteristics resulting in alongshore currents that are driven mainly by the changes in wave energy a storm close to the coast hurricane earl 2010 with strong local wind stress and combined sea and swell components in wave energy spectra has high variability in wave direction and wave period that influence wave breaking and nearshore circulation as the storm passes during both large wave events the horizontal current shear is strong and radiation stress gradients bottom stress wind stress horizontal mixing and cross shore advection contribute to alongshore momentum at different spatial locations across the nearshore region horizontal mixing during hurricane earl estimated from rotational velocities was particularly strong suggesting that intense eddies were generated by the high horizontal shear from opposing wind driven and wave driven currents the results provide insight into the cross shore distribution of the alongshore current and the connection between flows inside and outside the surf zone during major storms indicating that the current shear and mixing at the interface between the surf zone and shallow inner shelf is strongly dependent on the distance from the storm center to the coast

mesoscale convective systems in weakly forced large scale environments part i observations abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment analyses indicate that the large scale flow created a broad region of potential buoyant energy but owing to a restraining inversion and weak large scale upward motion convection was initiated only where lifting associated with mesoscale features was able to eliminate the inversion the series of mcss developed sequentially and moved eastward across the moist axis two of these systems had a large component of motion against the mean tropospheric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances each system produced an outflow of cold downdraft air that spread progressively farther south than that from the preceding system this description of the development and evolution of convection is very different from traditional ones wherein convection develops and moves more or less in pha

physical linkages between an offshore canyon and surf zone morphologic change the causes of surf zone morphologic changes observed along a sandy beach onshore of a submarine canyon were investigated using field observations and a numerical model delft3d swan numerically simulated morphologic changes using four different sediment transport formulae reproduce the temporal and spatial patterns of net cross shore integrated between 0 and 6 5 m water depths accretion and erosion observed in a 300 m alongshore region a few hundred meters from the canyon head the observations and simulations indicate that the accretion or erosion results from converging or diverging alongshore currents driven primarily by breaking waves and alongshore pressure gradients the location of convergence or divergence depends on the direction of the offshore waves that refract over the canyon suggesting that bathymetric features on the inner shelf can have first order effects on short term nearshore morphologic change this article is protected by copyright all rights reserved

wave driven setup and alongshore flows observed onshore of a submarine canyon 1 the effect of alongshore variations in the incident wavefield on wave driven setup and on alongshore flows in the surfzone is investigated using observations collected onshore of a submarine canyon wave heights and radiation stresses at the outer edge of the surfzone water depth 2 5 m varied by up to a factor of 4 and 16 respectively over a 450 m alongshore distance resulting in setup variations as large as 0 1 m along the shoreline water depth 0 3 m even with this strong alongshore variability wave driven setup was dominated by the cross shore gradient of the wave radiation stress and setup observed in the surfzone is predicted well by a one dimensional cross shore momentum balance both cross shore radiation stress gradients and alongshore setup gradients contributed to the alongshore flows observed in the inner surfzone when alongshore gradients in offshore wave heights were large and a simplified alongshore momentum balance suggests that the large o 1 kg s2 m observed setup induced pressure gradients can drive strong o 1 m s alongshore currents

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

low energy rip currents associated with small bathymetric variations we show for the first time that low energy waves can induce a rip current system over subtle alongshore bathymetric variations comprehensive field measurements across a rip current that morphologically migrated 12 m day through a coherent cross and alongshore array of co located pressure and velocity sensors were obtained the rip current is associated with a small bathymetric surfzone non uniformity 1 in 300 alongshore variation the circulation was kinematically non uniform for 5 of the time over the course of the 20 day experiment and was present at low tides associated with increases in rip current activity the presence of the rip current and mild sloped rip channel induce statistically significant alongshore variations in hrms wave direction directional spreading infragravity waves and very low frequency motions changes in the directional spreading are correlated with the presence of very low frequency motions influenced by the presence of the rip current

simulation of a serial upstream propagating mesoscale convective system event over southeastern south america using composite initial conditions abstract serial upstream propagating mesoscale convective system mcs events over southeastern south america are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation however the mechanisms of upstream propagation for these events have not been explored to remedy this situation a numerical simulation of the composite environmental conditions from 10 observed serial mcs events is conducted results indicate that the 3 day simulation from the composite yields a reasonable evolution of the large scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves however as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation the cold pool and its interaction with the env

reply to the comment by sanchez bettucci et al on provenance of the arroyo del soldado group ediacaran to cambrian uruguay implications for the paleogeographic evolution of southwestern gondwana precambrian res 171 2009 57 73

neoproterozoic to lower palaeozoic successions of the tandilia system in argentina implication for the palaeotectonic framework of southwest gondwana the cryogenian to uppermost ediacaran successions of the tandilia system sierras bayas group and cerro negro formation in central eastern argentina is exceptional because of its unmetamorphosed and nearly undeformed character its sediment provenance trend and the absence of any identified glacial deposit and the deposition of warm water carbonates we decipher a dramatic change in the basin evolution from small scale depositional areas during the neoproterozoic to a larger basin related to an active continental margin throughout the uppermost ediacaran the base of the succession is represented by immature detritus of alkaline composition villa monica formation but towards the top of this formation the material is sorted and reworked nonetheless still reflecting in its detritus the local rocks the clastic deposition is interrupted by diagenetic overprinted dolomites the unconformable overlying quartz arenitic ediacaran cerro largo formation reworked the cryogenian villa monica formation and contains mainly felsic granitic and metamorphic basement material of slightly wider variety while the dominant alkaline geochemical signature in rocks of the villa monica formation disappears based on diagenetic petrographic and sedimentological data we can interpret the unconformity representing a longer time of erosion the cerro largo formation shows a transition to mudstones and the heterolithic facies of the olavarria formation the top of the sierras bayas group is represented by limestones loma negra formation which are discordantly overlain by the uppermost ediacaran cerro negro formation the latter displays detrital material derived from a continental arc mafic and felsic sources several arc related geochemical proxies th sc 20 are recorded in the sediment detritus as are syn depositional pyroclastites the absence of volcanic material in the underlying rocks allows proposing that the cerro negro formation is related to an active continental margin fringing gondwana terra australis orogen as a retro arc or retro arc foreland basin

resetting of neodymium isotopes and redistribution of rees during sedimentary processes the early proterozoic chelmsford formation sudbury basin ontario canada abstract the rees abundances and neodymium isotope compositions of sandstones and siltstones from the early proterozoic chelmsford formation reveal that the rees in some samples were redistributed during the early proterozoic by surficial processes and that prior to redistribution the nd isotope system was partially reset the chelmsford formation is a coarse grained turbidite sequence the youngest of three clastic units that fill the sudbury basin in ontario it is constrained to have been derived from nearby late archean superior province rocks by petrography major and trace element chemistry and pb isotopic compositions of whole rocks and feldspar although ree patterns and nd model ages for samples from around the base of the formation reflect their derivation from undisturbed superior province rocks tdm 2800 ma five samples from higher in the stratigraphic section show evidence that up to 60 of their la has been removed and sm nd has increased by up to 60 these samples also have anomalously high nd model ages tdm 3400 to 4400 ma the presence of pronounced positive ce anomalies in the samples with anomalous tdm indicates the influence of surficial processes on the ree composition the data scatter about a vertical array on a plot of f sm nd vs ndt 1800 nd calculated at 1800 ma approximately the depositional age with values of f sm nd between 0 45 and 0 14 mixing of nd from other sources is difficult to reconcile with the petrography major and trace element geochemistry and nd and pb isotopes removal of an lree enriched phase from the sedimentary system provides a viable mechanism to produce the ree and nd isotopic characteristics of the chelmsford formation samples neodymium isotopes require that this phase was partially isotopically equilibrated with the matrix sediment near the time of sedimentation this study shows the dangers of indiscriminate use of nd model ages in provenance studies and demonstrates that the simultaneous examination of sm nd and nd isotopes on f sm nd vs nd or isochron plots is required for the recognition of sedimentary redistribution of the ree

a connection between the neoproterozoic dom feliciano brazil uruguay and gariep namibia south africa orogenic belts evidence from a reconnaissance provenance study abstract a provenance study of neoproterozoic siliciclastic successions in the stratigraphically and tectonically lowermost and uppermost parts of the pan african gariep belt stinkfontein subgroup and oranjemund group respectively in southwestern africa as well as in the rocha group of the punta del este terrane dom feliciano belt in uruguay revealed that the oranjemund and rocha groups can be correlated and most likely formed in the same basin thus the rocha group is considered to represent the fill of the westernmost part of a re activated ediacaran gariep basin the lower parts of the oranjemund and rocha groups reflect erosion of mafic rocks whereas the upper parts are derived from a predominantly felsic source area first major and trace element geochemical data are consistent with oceanic islands of within plate geochemistry in the immediate vicinity as the most likely source of the mafic input into the lower part of the oranjemund group whereas a combination of continental margin and island arc is indicated as source for the bulk of the younger sediments in the upper oranjemund group age spectra obtained by shrimp u pb analyses of detrital zircon grains from the stinkfontein subgroup port nolloth group the oranjemund group and the rocha group are very similar except for a lack of the youngest age group around 600 ma in the stinkfontein subgroup in all three units zircon grains of 1000 1200 ma dominate with a further peak in the age distribution between 1700 and 2000 ma these ages compare well with the pre gariep basement geology in southwestern africa where the former age range corresponds to magmatic and high grade metamorphic activity in the mesoproterozoic namaqua natal belt and the latter to an extensive palaeoproterozoic andean type volcanic arc richtersveld terrane comparable ages are conspicuously absent in the basement of the rio de la plata craton in south america derivation of the rocha group sediments from a similar source as the contemporaneous oranjemund group sediments is therefore suggested the most likely source of the youngest detrital zircon grains in these two stratigraphic units is the 640 590 ma magmatic arc of the dom feliciano belt this interpretation explains the continental island arc component in the sediment provenance and takes into account the absence of comparable magmatism in the gariep belt two stages of basin evolution are distinguished for the gariep basin an early failed continental rift that subsequently became re activated as back arc basin related to the cryogenian dom feliciano arc consequently the gariep basin does not represent the main suture between the rio de la plata and the kalahari cratons this suture is now suspected to be west of the dom feliciano volcanic arc and might be connected with the sierra ballena major gercino lineament

a case study of a chaco low level jet event abstract this paper concentrates on the analysis of the life cycle of the low level jet llj during a summer chaco jet event this is accomplished through the use of the eta centro de previsao del tempo e estudos climaticos cptec regional model in order to obtain high temporal and spatial detail of the main processes taking place both the low level circulation and the geopotential height evolution at different latitudes are analyzed to provide a more detailed description of the effects of topography and differential warming on the evolution of this current this study shows that the life cycle of the particular event analyzed is not the same at the different latitudes swept by this well organized northerly current expanding from 15 to 32 s during two consecutive days a common feature to all the examined latitudes is the presence of a diurnal cycle linked to local effects which is more evident during the first day and a half of the simulation this cycle was identified not only by a nocturnal maxi