projections of the tropical atlantic vertical wind shear and its relationship with enso in sp ccsm4 abstractthe vertical wind shear over the tropical atlantic ocean and its relationship with enso are analyzed in the superparameterized community climate system model version 4 sp ccsm4 and in the conventional ccsm4 the climatology of vertical wind shear over the tropical atlantic and the enso shear relationship are well simulated in the control runs of sp ccsm4 and ccsm4 however because of different representations of cloud processes in a warmer climate such as the representative concentration pathway 8 5 rcp8 5 scenario sp ccsm4 projects increased mean westerlies at 200 hpa during july through october jaso whereas ccsm4 projects decreased mean westerlies at 200 hpa over the equatorial atlantic the different changes in the upper level wind further contribute to different projection of jaso mean vertical wind shear over the equatorial atlantic in the rcp8 5 scenario when excluding the linear trend projection of the enso shear relationships by sp ccsm4 retains similar features as in the obs

the pacific meridional mode and the occurrence of tropical cyclones in the western north pacific abstractthis study investigates the association between the pacific meridional mode pmm and tropical cyclone tc activity in the western north pacific wnp it is found that the positive pmm phase favors the occurrence of tcs in the wnp while the negative pmm phase inhibits the occurrence of tcs there observed relationships are consistent with those from a long term preindustrial control experiment 1000 yr of a high resolution tc resolving geophysical fluid dynamics laboratory gfdl forecast oriented low ocean resolution flor coupled climate model the diagnostic relationship between the pmm and tcs in observations and the model is further supported by sensitivity experiments with flor the modulation of tc genesis by the pmm is primarily through the anomalous zonal vertical wind shear zvws changes in the wnp especially in the southeastern wnp the anomalous zvws can be attributed to the responses of the atmosphere to the anomalous warming in the northwestern part of the pmm pattern during th

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

three dimensional to two dimensional cross strata transition in the lower pleistocene catanzaro tidal strait transgressive succession southern italy sandstone tidal cross strata are the predominant sedimentary feature of strait fill stratigraphic successions however although widely described in numerous studies tidal strait fill two dimensional and three dimensional cross strata have rarely been reported to occur in discrete intervals which are laterally adjacent or vertically stacked and the meaning of this stratigraphic architecture has not yet been fully investigated understanding of the processes responsible for changes in the internal features of modern and ancient tidal bedforms is essential in order to predict lateral and vertical heterogeneities in analogous reservoir strata this facies based study aims to interpret the three dimensional to two dimensional cross strata transition observed in the lower pleistocene mixed siliciclastic bioclastic sandstone filling the catanzaro strait in southern italy during a continuous phase of tectonically driven marine transgression tidal cross strata disappear in the uppermost interval of the studied succession where mudstone strata prevail this stratigraphic trend is interpreted as the evidence of an important change in the tidal strait hydrodynamics due to a phase of relative sea level rise at the beginning of the transgression three dimensional tidal dunes migrated throughout the ca 3 to 4 km wide and ca 30 km long wnw ese oriented catanzaro strait due to strong tidal currents amplified through the seaway and flowing in semi diurnal phase opposition as the intermediate phase of transgression enlarged the seaway width the tidal current strength decreased as tidal water exchange occurred over a larger cross sectional area the progressive reduction of the bed shear stress modified three dimensional tidal dunes into an extensive two dimensional bedform field at the end of the transgression the further widening of the catanzaro strait into a ca 10 to 12 km wide marine passageway changed the tidally dominated strait into a non tidal open shelf the results of this research suggest the presence of a critical cross sectional area in the narrowest strait centre zone which controls the activation and deactivation of tidal current amplification along a marine seaway

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

seismic evidence for a moho offset and south directed thrust at the easternmost qaidam kunlun boundary in the northeast tibetan plateau abstract during 2006 to 2007 a small array of broadband seismic stations was deployed across the eastern qaidam kunlun border receiver functions derived from this data set show a coherent p to s converted phase from the moho at 65 km to 58 km below sea level b s l from south to north beneath the kunlun mountains the moho is observed at 45 km b s l beneath the qaidam basin a sharp offset of 15 km in the moho depth is observed just beneath the qaidam kunlun border the close correlation between the surface topography and the sharp moho offset substantiates the view that the kunlun crust is weaker than that of the qaidam basin and thickens vertically in response to compression between india through the tibetan plateau and the qaidam basin furthermore a strong steeply north dipping converted phase can be seen from 5 to 15 km b s l north of the north kunlun fault which is likely a major south directed thrust fault partially responsible for the thickening of the kunlun crust

how ubiquitous is the dipole relationship in tropical atlantic sea surface temperatures several kinds of analysis are applied to sea surface temperature anomalies ssta 1856 1991 to determine the degree to which ssta of opposite sign in the tropical north and south atlantic occur antisymmetric dipole configurations of ssta on basin scales are not ubiquitous in the tropical atlantic unless the data are stratified by both season and frequency inherent dipole behavior cannot be demonstrated upon removing the global el nino southern oscillation signal in ssta which is symmetric between the north and south atlantic from the data the regions north or south of the intertropical convergence zone have qualitatively different temporal variabilities and are poorly correlated dipole configurations do occur infrequently 12 15 of the time but no more so than expected by chance for stochastically independent variables nondipole configurations that imply significant meridional ssta gradients occur much more frequently nearly half of the time cross spectral analysis of seasonally averaged ssta indices for the north and south atlantic show marginally significant coherence with antisymmetric phase in two period bands 8 12 years for the boreal winter spring and 2 3 years for the boreal summer fall antisymmetric coherence is optimal for a small subregion west of angola in the south atlantic with respect to ssta of basin scale in the tropical north atlantic dipole variability even where optimal explains only a small fraction of the total variance in tropical atlantic ssta 7

crustal and upper mantle structure of northern tibet imaged with magnetotelluric data 1 magnetotelluric mt data were collected in northern tibet along the amdo to golmud highway during the 1995 and 1999 project indepth international deep profiling of tibet and the himalaya surveys broadband and long period mt data were collected and the te mode tm mode and vertical magnetic field data were inverted to yield a minimum structure two dimensional resistivity model the model obtained from inverting all responses simultaneously shows that a pervasive midcrustal conductor extends from the kunlun shan to the bangong nuijiang suture the vertically integrated conductivity conductance of this crustal layer is greatest in the northern qiangtang terrane at latitude 34 n the electrical resistivity of the upper mantle is constrained by the mt data to be in the range of 10 30 m across the songpan ganze and qiangtang terranes this is lower than would be expected if asian lithosphere underthrusts northern tibet as far as the qiangtang terrane the mt responses are more consistent with a model in which asian lithosphere extends as far south as the kunlun shan and the upper mantle beneath the songpan ganze and qiangtang terranes is sufficiently hot to contain a small fraction of interconnected partial melt

tidal modeling of an ancient tide dominated seaway part 2 the aptian lower greensand seaway of northwest europe abstract the cretaceous lower greensand deposits of southeastern england and northern france contain abundant evidence of diurnal once daily paleotides with tidal influence increasing into the late aptian the imperial college ocean model icom is used herein to determine the amplitude origin astronomical or co oscillating and characteristics diurnal or semidiurnal of the tides in the shallow marine lower greensand seaway where these sediments were deposited a global ocean paleotidal model of the aptian predicts very low tidal ranges microtidal in the proto central atlantic ocean and boreal ocean with higher tidal amplitudes especially of the diurnal constituents predicted in the northwestern neotethys ocean this suggests that the neotethys ocean was the only significant source of oceanic tides to the lower greensand seaway herein the results of the global ocean paleotidal model are used to supply boundary conditions to a higher resolution regional paleotidal model of the lower greensand seaway the regional paleotidal model shows that the tidal range of the lower greensand seaway is largely controlled by the width of the connections to the open ocean as sea levels rose during the aptian the oceanic connections widened resulting in reduced frictional damping of the oceanic tidal wave coupled with funneling shoaling and coriolis effects this led to tidal amplification sensitivity tests using a variety of paleogeography and paleobathymetry scenarios suggest that the model predictions are robust the global to regional scale paleotidal modeling presented here strongly suggests that there was a connection through france in the aube region of the paris basin from the neotethys ocean to southeastern england however there are no time equivalent deposits in this region to validate this suggestion it is herein argued that that this is due either to postdepositional erosion or to low sediment supply coupled with strong tidal currents sweeping the seafloor to exposed bedrock

variability of the atlantic meridional mode during the atlantic hurricane season abstract an observational and modeling study is conducted to investigate the structure of the atlantic meridional mode amm during the atlantic hurricane season and the relationship between amm related sst anomalies and environmental conditions that influence seasonal tropical cyclone activity the observational analysis shows that during the atlantic hurricane season the amm exhibits a similar sst and low level wind structure as during boreal spring when the amm is most active observed amm sst variations are accompanied by air temperature and moisture anomalies that are limited to the boundary layer and an anomalous baroclinic circulation structure in the northern subtropical atlantic with an anomalous lower level cyclonic circulation residing under an anomalous upper level anticyclone during a warm phase this baroclinic structure contributes to a reduction in vertical wind shear over the tropical atlantic that is dominated by changes in the upper level flow two sets of model experiments were cond

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

forcing of anomalous sea surface temperature evolution in the tropical atlantic during pacific warm events the seasonal evolution of anomalous interhemispheric sea surface temperature sst gradients in the tropical atlantic from january to april is studied by composites of the 10 warmest warm and 10 coldest cold januaries during 1948 1993 in the equatorial pacific using comprehensive ocean atmosphere data set ship observations in the warm as compared with the cold years an anomalous weakening of the northward sst gradient develops mainly due to anomalous warming in the tropical north atlantic this stems from the combination of three forcings all related to the weakened north atlantic trade winds during pacific warm events most important are the reduced latent heat flux in much of the tropical north atlantic and anomalous downwelling equatorward of 20 n with a further contribution from increased net radiation resulting from the reduced cloudiness due to the diminished convergence in the downstream portion of the north atlantic trades in response to the development of warm anomalies in the tropical north atlantic during january march the cross equatorial northward winds accelerate to april and this leads south of the equator not only to ekman downwelling enhanced divergence reduced cloudiness and increased net radiation but also to enhanced wind speed and evaporation the result is a modest anomalous warming in the western tropical south atlantic increased air temperature over the entire basin presumably due to atmospheric advection from the pacific has little effect on the atlantic sst pattern the anomalous interhemispheric sst gradient controlled primarily by the warm anomaly in the north atlantic has a pivotal role to play in steering the late boreal winter atmospheric circulation in the tropical atlantic sector and thus regional climate anomalies

impact of the atlantic warm pool on the summer climate of the western hemisphere abstract the atlantic warm pool awp is a large body of warm water that comprises the gulf of mexico the caribbean sea and the western tropical north atlantic located to its northeastern side is the north atlantic subtropical high nash which produces the tropical easterly trade winds the easterly trade winds carry moisture from the tropical north atlantic into the caribbean sea where the flow intensifies forming the caribbean low level jet cllj the cllj then splits into two branches one turning northward and connecting with the great plains low level jet gpllj and the other continuing westward across central america into the eastern north pacific the easterly cllj and its westward moisture transport are maximized in the summer and winter whereas they are minimized in the fall and spring this semiannual feature results from the semiannual variation of sea level pressure in the caribbean region owing to the westward extension and eastward retreat of the nash the ncar community atmospher

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

strong lg attenuation in the tibetan plateau the widespread existence of strong lg attenuation in the tibetan plateau is further demonstrated by analysis of lg spectra on many paths within the plateau and quantitative estimates of the lg attenuation from low frequency lg signals for new localized path geometries strong path length dependent shifts of the lg spectra to lower corner frequencies with increasing distance are observed across the plateau consistent with a low regional average 1 hz lg attenuation value q 0 of about 125 there are clearly lateral variations within the plateau found in this and other recent studies with localized areas having q 0 values of 60 90 low enough to eliminate high frequency lg energy over path lengths of just several hundred kilometers while some localized areas may have higher q 0 values of up to 147 or higher a q 0 value of 103 is found in south central tibet compatible with recent work by others for higher frequencies on very localized scales and values from 83 to 147 are found in eastern tibet the lowest q 0 estimates found in tibet tend to be in areas for which there is evidence of volcanism and or partial melting within the crust however the strong regional attenuation may have a contribution from scattering by small scale crustal heterogeneity the strong lg attenuation in tibet gives a new constraint for understanding the tectonic development of the plateau and presents challenges to seismic monitoring of the region for possible clandestine nuclear tests

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

the role of the mean state in meridional mode structure and growth abstractthis study uses a simple linear coupled model to investigate the role of the wes feedback and itcz mean states in meridional mode variability optimal structures that maximize transient growth are calculated for mean states characteristic of boreal spring and boreal fall in the tropical atlantic during boreal spring the leading optimal structure is a zonal mode that propagates westward and does not resemble the observed meridional mode in contrast the leading optimal structure during fall is a sea surface temperature sst monopole over the northern hemisphere nh that propagates equatorward and westward and that closely matches meridional mode variability during this season it is found that the boreal fall optimal growth greatly exceeds growth of the corresponding optimal during boreal spring despite the observed boreal spring peak in atlantic meridional mode variance sensitivity studies are used to explore the role of northern or southern hemisphere initial conditions itcz width and itcz

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

extratropical forcing of tropical atlantic variability during boreal summer and fall abstractthe connection between midlatitude atlantic sea surface temperature sst anomalies and tropical sst variations during boreal summer and fall are investigated using a coupled general circulation model gcm this research follows on an observational study that finds that using linear inverse modeling lim predictions of boreal summer tropical atlantic meridional mode amm variations can be made with skill exceeding persistence with lead times of about one year the lim framework identified extratropical atlantic sst anomalies as important precursors to the amm variations the authors have corroborated this finding using a general circulation model coupled to a slab ocean which represents a completely different physical basis from the lim initializing the gcm with the lim derived optimal sst anomaly in november results in a steady equatorward propagation of sst anomalies into the subtropics during the following boreal spring thereafter the gcm suggests that two possible feedbacks propagate

lower cretaceous tides revealed by cross bedding with mud drapes the sand dominated folkestone beds widely exposed around the weald of south east england are of upper aptian to lower albian lower cretaceous age and range in thickness up to 84 m refs 1 3 their content of ammonites bivalves and sponges indicates a marine origin while their relative coarseness and the incorporation of drifted timber point to a shallow water deposition near land one striking sedimentary facies is formed by medium to coarse grained cross bedded sands in which several foreset and or bottomset surfaces support mud drapes although it was suggested4 that this facies may have been formed by the storm induced movement of sand waves i now consider that the facies is best explained by the migration of sand waves under the influence of strongly asymmetrical tides and that the mud drapes are formed at slack water a model of this process has been described elsewhere5 and i now describe measurements of a section which supports my earlier conjecture6that the separation of the mud drapes is systematically related to the phase of the spring neap tidal cycle at the time of deposition although criteria for recognizing tidal deposits have long been available it has not previously been possible to analyse a series of ancient sediments with a view to characterizing the tidal regime

tidal inlet sequence sundance formation upper jurassic north central wyoming the sandstones and coquinas of the upper 20 m of the sundance formation are interpreted as a tidal inlet back barrier shoal and sandy tidal flat sequence deposited at the close of marine jurassic sedimentation in north central wyoming the barrier strandline maintained a generally e w trend as it prograded to the north the lateral migration of inter barrier tidal inlets along the regressive shoreline of the late sundance sea caused the coquinas and sandstones of the uppermost sundance formation to be deposited as tabular laterally extensive units tidal bundles sigmoidal reactivation surfaces herringbone cross lamination and abundant mud drapes within the sandstones are evidence of considerable tidal influence during the deposition of the uppermost sundance formation earlier models which attach an offshore environment of deposition to the sequence do not explain the tabular geometries of the sandstone and coquina units and their conformable stratigraphic relationship with the overlying non marine sediments of the morrison formation

transgression of an estuarine channel and tidal flat complex the lower triassic of barles alpes de haute provence france the lower triassic succession of barles alpes de haute provence france comprises an unconformable quartz arenite sand body of 90m thickness the succession may be informally divided into i lower channellized cross bedded member overlain by ii an upper fining upward member the lower member comprises vertically stacked subtidal channel units separated into five major sand bodies by thin developments of fine grained channel margin and shoal deposits subtidal channel fill deposits are dominated by varying scales of cross bedding these scales vary systematically from the base to the top of the member with large scale planar sets dominating the lowest channel sand body sand body 1 medium scale planar and trough cross bedding characterizing sand bodies 2 4 the largest scale planar sets in the highest sand body sand body 5 this upward change in cross bedding scale is concomitant with a decrease in both the relief of major channel sand body erosion surfaces and the proportion of preserved interchannel shoal deposits the succeeding fining upward member comprises small scale tidal channel units overlain by channel shoal and tidal flat deposits tidal flat sequences are characterized by parallel laminated wave and current rippled sandstones separated by bioturbated fine grained siltstones and mudstones the vertical variation in facies of the lower triassic succession suggests two main periods of deposition the lower member is considered to preserve successively more seaward components of a transgressive estuarine complex the overlying upper member records the seaward progradation of tidal channel shoal and tidal flat environments the unconformity bounded nature of the lower member combined with its systematic variation in facies suggests it may represent an incised valley estuarine fill developed in response to an early triassic relative sea level fall and subsequent rise succeeding tidal channel and tidal flat deposits forming the upper fining upward member reflect a change in sediment supply and or rate of relative sea level rise comparable with a progradational shoreline it is unclear whether this final depositional episode represents a period of highstand progradation or a later lowstand shoreline system developed following a further period of relative sea level fall and rise

morphodynamic and experimental assessments of wave theories in intermediate water depths although the near bed wave induced currents predicted by the various wave theories are responsible for seabed sediment transport it is presently unclear which theory should be included in coastal geomorphic models the theoretical expressions for near bed shorenormal flows are re examined and the predictions are tested with morphodynamic and laboratory data five wave theories airy stokes cnoidal solitary and gerstner are summarized here and arranged to predict the maximum onshore and offshore near bed flows and the flow asymmetry as functions of the wave period the wave height and the water depth morphodynamic argument suggests that only stokes and cnoidal wave theories predict the asymmetry required to generate prototype seabed profiles in intermediate water depths laboratory measurements of wave induced near bed flows are then reported and analysed the results suggest that stokes wave theory over predicts the observed peak flows a correction is derived which is shown to be analogous to the pressure attenuation corrections which are routinely applied to wave recording seabed mounted transducer measurements

fullerenes found in the permo triassic mass extinction period fullerenes have been identified by high performance liquid chromatography with uv visible spectroscopic analysis of toluene extracts of deep sea claystones from permo triassic p t boundary sections in the inuyama area central japan the analysis reveals the presence of 10 20 parts per trillion of c60 only in the dark colored rock samples suggesting the anoxia at the time of the p t boundary 250 million years ago when the greatest phanerozoic mass extinction occurred the fullerenes were likely synthesized within locally anoxic zone in the extensive wildfires on the supercontinent pangea and deposited on an anoxic deep sea floor of the superocean panthalassa

on bagnold s sediment transport equation in tidal marine environments and the practical definition of bedload bagnold s sediment transport equation has proved to be important in studying tidal marine environments this paper discusses three problems concerning bagnold s transport equation and its practical application 1bagnold s suspended load transport equation and the total load transport equation with are incorrect from the viewpoint of energy conservation in these equations the energy loss due to bedload transport has been counted twice the correct form should be for suspended load transport and for total load transport with 2the commonly used bagnold s transport coefficient k varies as a non linear function of the dimensionless excess shear stress which can be represented best by the power law where the coefficient a and exponent b depend on sediment grain size d the empirical values of a and b for fine to medium grained sands are determined using guy et al s 1966 flume experiment data 3the sediment transport rates predicted from this equation are compared with bedform migration measurements in the flume and the field this comparison shows that the sediment transport rates measured from bedform migrations are higher than the predicted bedload transport rates but comparable to the calculated total load bedload plus intermittent suspended load transport rates this indicates that bedform migration involves both bedload and intermittent suspended load transport as a logical conclusion bedform migration data should be compared with bagnold s total load transport equation rather than with his bedload transport equation in this respect the term bed material might be more appropriate than the term bedload for estimating sediment transport rate from bedform migration data the sediment transport rates predicted from this modified bagnold transport equation are in good agreement with field measurements of bedform migration rates in four individual tidal marine environments which cover a wide range of sediment grain size flow velocity and bedform conditions ranging from small ripples megaripples to sandwaves

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

palaeotidal speeds and ranges estimated from cross bedding sets with mud drapes tidally formed cross bedding sets in which mud drapes are spaced out among sandy foresets occur in cretaceous1 4 eocene5 and holocene6 sands deposited subtidally by strongly asymmetrical sand waves a striking feature of some sets4 6 is that the horizontal drape spacing measured in the direction of sand wave advance varies cyclically on a time scale related to the spring neap tidal cycle as indicated by the numbers of drapes each drape forms part of a distinctive lithological couplet consisting of a group of sandy foresets recording avalanching on the steeper side of the sand wave followed by the drape itself typically divided into upper and lower parts by a centrally placed silt sand parting the drapes have been assigned to slack water but the groups of sandy foresets to episodes of vigorous flow the combination suggesting a quantitative model based on the tide here i show how the peak speeds and ranges of ancient tides can be estimated by combining an empirical bedload transport function with appropriate measurements from such cross bedding sets

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

modulation of western north pacific tropical cyclone activity by the atlantic meridional mode this study examines the year to year modulation of the western north pacific wnp tropical cyclones tc activity by the atlantic meridional mode amm using both observations and the geophysical fluid dynamics laboratory forecast oriented low ocean resolution version of cm2 5 flor global coupled model 1 the positive negative amm phase suppresses enhances wnp tc activity in observations the anomalous occurrence of wnp tcs results mainly from changes in tc genesis in the southeastern part of the wnp 2 the observed responses of wnp tc activity to the amm are connected to the anomalous zonal vertical wind shear zvws caused by amm induced changes to the walker circulation during the positive amm phase the warming in the north atlantic induces strong descending flow in the tropical eastern and central pacific which intensifies the walker cell in the wnp the intensified walker cell is responsible for the suppressed enhanced tc genesis in the eastern western part of the wnp by strengthening weakening zvws 3 the observed wnptc amm linkage is examined by the long term control and idealized perturbations experiment with flor fa a suite of sensitivity experiments strongly corroborate the observed wnptc amm linkage and underlying physical mechanisms

a pan atlantic decadal climate oscillation sea surface temperature sst variabilities on time scales of 10 14 years have been documented in various parts of the atlantic ocean here we present observational evidence that these regional variabilities are part of a coherent pan atlantic decadal oscillation pado characterized by zonal bands of sst and wind anomalies stacked in the meridional direction with alternate polarities from the south atlantic all the way to greenland we propose that the interaction of wind evaporation and sst is key to establishing this interhemispherical pado based on results from a new ocean atmosphere coupling model forced by extratropical wind forcing the model successfully reproduces the observed decadal oscillation in both sst and wind velocity over the tropics this decadal extratropical forcing of the tropics is in sharp contrast to the well known tropics to extratropics teleconnection that operates on interannual time scales in association with el nino southern oscillation enso

high temperature transient creep in olivine rocks abstract the transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 k and a confining pressure of 300 mpa in a high resolution gas medium deformation apparatus the specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation the results confirm the finding of earlier workers that the high temperature transient flow properties of olivine rocks can be effectively modelled in terms of a burgers body rheology observations of time dependent strain recovery after unloading further support this model the viscosity in the transient regime 1 is found to have the same sensitivity to temperature and stress within the errors of each estimate as has been found previously for steady state creep viscosity 2 thus the ratio 2 1 is found to be relatively insensitive to temperature and stress with values between 0 17 and 0 67 these values are higher than the 2 1 0 1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals the ratio of the shear moduli in the transient and steady state regimes 2 1 is found to be weakly sensitive to temperature at 250 mpa stress and 300 mpa confining pressure the value of 2 1 decreases slowly as temperature increases for the present experiments 0 05 2 1 which is comparable to the range of values reported in previous studies

facies analysis in the lower greensand using ground penetrating radar this paper presents the results of a ground penetrating radar survey in the woburn sands formation lower greensand group near leighton buzzard a total of almost 4 km of survey has been acquired to investigate the internal structure of the sands the radar survey achieved a resolution on the order of tens of centimetres with penetration up to 10 m and revealed a variety of horizontal dipping and curved reflectors the reflections are interpreted using seismic interpretation methodology two scales of unconformity defined radar sequences are described first order radar sequence boundaries can be identified at the termination of primary reflectors second order radar sequence boundaries can be identified at the terminations of both primary reflectors and first order surfaces first order radar sequence boundaries are interpreted as reactivation surfaces within bedforms which are produced by changes in bedform geometry in response to a change in hydraulic regime or superimposed bedforms second order surfaces are interpreted as the product of bedform migration reflection character and geometry are described and form the basis of a ground penetrating radar facies analysis nine different radar facies have been identified these are interpreted as large sets of planar cross stratification sets of trough cross stratification cosets of cross stratification tidal bundles clay drapes diagenetic concretions and possibly bioturbated sands a reconstruction of the bedforms suggests that they were formed by very large curved crested dunes these interpretations are checked against outcrop as the sands are excavated in working sand pits

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

sedimentology of the bengal shelf bangladesh comparison of late miocene sediments sitakund anticline with the modern tidally dominated shelf abstract characterisation of latest miocene facies of the bay of bengal reveals a range of tidal and fluvially dominated sediments that represent sedimentation on a broad shallow shelf that was strongly influenced by tidal and seasonal cyclicity these tidally influenced sediments are excellently exposed within growth anticlines of the westward migrating chittagong tripura fold belt ctfb and permit detailed study of the late miocene bengal shelf for comparison with the modern subaqueous deltaic sediments at the outcrop scale facies associations record a subtidal shelf migrating intertidal subtidal bedforms tidal and incised channels the subtidal shelf comprises extensive sand sheets interbedded with thick clay horizons while the migrating intertidal subtidal bedforms exhibit a decrease in bedform size from large dunes to small ripple scale cross stratification that reflect a decrease in current velocity and sand silt grade sediment supply as the bedforms migrated rootlet horizons within these intertidal subtidal bedforms may represent a lower delta plain environment the tidal channel facies consists of metre scale sandstone beds that are rich in locally derived clay clasts with up to 0 5 m of incision into a rhizolith horizon below incised channel facies records a coarse pebbly sandstone with clasts derived from a reworked clastic source with metre scale scour at the base of this facies association into laminated and rhizolith clays a 534 m one and two dimensional section within the sitakund anticline north of chittagong is characterised by 20 100 m thick tidally dominated progradational parasequences mudstones with isolated sand lenses and abundant trace fossils of the cruziana ichnofacies coarsen upwards to fine medium grained sandstones deposited in shallower high energy environments these sands were deposited under both uni directional and bi directional currents resulting in dune scale cross stratification and are overlain by 2 5 cm thick clay drapes considered to be of a thickness greater than that typical of deposition from a single slackwater episode the main controls on sedimentation are the seasonally influenced river and sediment discharge onto the shelf from the himalayan source region combined with the influence of daily spring neap tides channel and bedform migration and minimal wave action over the shallow shelf the modern bay of bengal shelf provides an analogue for interpreting processes recorded within the miocene succession allowing construction of a depositional model for the late miocene shelf of the brahmaputra ganges delta system with sedimentation dominated by tidal and seasonal cyclicity