westward propagation of latitudinal asymmetry in a coupled ocean atmosphere model abstract hemispheric asymmetries of continental geometry have long been speculated to be the cause of the northern hemisphere position of the intertropical convergence zone over the central and eastern pacific it is unknown however how the effects of continental asymmetries are transmitted to and felt by the central pacific thousands of kilometers away this paper proposes a transmitter mechanism by investigating the response of a coupled ocean atmospheric model to a symmetry breaking force by the american continents the model treats land forcing implicitly as an eastern boundary condition in the absence of oceanic feedback the model response to the eastern boundary forcing is tightly trapped and confined to a small longitudinal extent off the coast whereas the climate over the interior ocean is symmetric about the equator ocean atmosphere coupling greatly enhances the transmissibility of the effects of the land forcing establishing large latitudinal asymmetry over a great zonal extent a westwar

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

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

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

parameterization of the vertical transport of momentum by cumulus clouds part i theory abstract a scheme is developed to parameterize the vertical transport of momentum by cumulus clouds in which the effect of a cloud induced pressure field is included in addition a new form for momentum exchange between clouds and their environment is used the scheme incorporates a simple cloud model which includes both updraft and downdraft and specifies the cloud dynamic fields to enable us to determine the mean pressure gradient force across the clouds it is shown that in a typical environment with vertical wind shear the pressure gradient force is along the direction of the wind shear the equation governing cloud mean momentum together with the diagnostic equation for cloud induced pressure field is solved by iteration to evaluate quantitatively the horizontal pressure gradient force across the cloud and determine the cloud mean momentum application of the parameterization scheme to gate convective events will be presented in part ii of this paper

late pennsylvanian glaciation evidence of icehouse conditions from canyon and cisco units midland basin texas abstract the late paleozoic has long been recognized a time of significant continental glaciation associated with high frequency high amplitude glacioeustasy although precise assessment of glacioeustatic amplitudes are difficult to extract from the stratigraphic record best approximations may be possible by analyzing spatial and temporal distributions of depositional facies utilizing several wells across the study area we used detailed sedimentologic description and depositional facies analysis from 12 wells and applied rigorous cycle stacking pattern analysis exposure surfaces recognition and wireline logs to correlate timelines across the wells on the basis of the high resolution sequence stratigraphic framework built for the scurry area canyon reef operators sacroc field a highly resolved glacioeustatic curve was generated for latest desmoinesian to the latest virgilian our eustatic curve suggests that the missourian and virgilian stages of the late pennsylvanian are characterized by high frequency high amplitude eustatic fluctuations the missourian stage was a period dominated grainstone capped cycles that are isopachous and conformable these cycles reflect a eustatic amplitude of at least 37 m with an average duration of 100 ka suggesting the dominance of short term eccentricity signal the virgilian stage is far more complicated and is characterized by highly shingled cycles compared to the missourian stage deeper water phylloid boundstone and calichified shoal complex grainstones are juxtaposed next to each other which suggests a stronger eustatic amplitude 40 m compared to the missourian stage although the eustatic amplitude of the virgilian cycles is similar to those of the missourian cycles they have a longer frequency 343 ka representative of long term eccentricity we conclude that the late pennsylvanian stratigraphy of the sacroc field in the midland basin records extensive continental glaciation during the missourian stage and increased and reached an acme during the virgilian stage

water chemistry and caco3 dissolution in the saline part of an open flow mixing zone coastal yucatan peninsula mexico along the caribbean coast of the yucatan peninsula brackish ground water mixed fresh water and sea water is channeled through upper pleistocene limestone via fracture controlled caverns in caves cenotes and caletas at xcaret yalku and tancah this open flow coastal mixing zone comprises three major layers 1 an upper dilute zone of gradually increasing salinity with depth slow mixing 2 a thin intermediate zone of rapidly increasing salinity with depth rapid mixing and 3 a lower saline zone of gradually increasing salinity with depth the intermediate layer occurs at different absolute salinities at different localities and it generally corresponds to the level of a notch apparently related to dissolution in the wall rock of the caverns chemical composition of the mixed ground water is consistent with that predicted from theoretical conservative mixing of fresh water and sea water end members sampled in the yucatan coastal region inorganic c alkalinity mg ca and sr ca and 18o and 13c of the mixed water give no indication of dissolution or precipitation of cac03 as the ground water flows rapidly seaward field and petrographic observations however show that aragonite is preferentially dissolving throughout the modern mixing zone and in particular in the saline portion comparison of saturation indices to calculated mixing curves shows that the coastal mixing zone of the eastern yucatan peninsula is undersaturated with respect to cac03 over a wide range of salinity including mixtures of as much as 95 sea water for aragonite and 90 sea water for calcite supersaturation with respect to stoichiometric dolomite is maintained over the whole range of salinities but super saturation with respect to calcian dolomite ca57mg43 can be confined to high salinity mixtures depending on the thermodynamic data base used in calculations these data suggest that 1 dissolution of coastal limestone can take place in the sea water dominated portion of the mixing zone and 2 the mixing zone model for dolomitization can be extended to much higher salinities than is indicated by the widely accepted dorag model

implementation of a non hydrostatic adaptive grid dynamics core in cam3 part ii dynamical influences on itcz behavior and tropical precipitation previous aqua planet simulations reported in the literature have shown the existence of both single and double inter tropical convergence zones itczs in this study horizontal grid resolution strongly affects itcz morphology as well as the amount of tropical precipitation through its influence on resolved dynamics the grid adaptation capability of our global model enables simulations that separate the influence of tropical and extra tropical dynamics on both the itcz and tropical precipitation the presence of single versus double itczs in our aqua planet simulations depends on the resolution of convectively coupled equatorial waves when the tropical resolution is sufficiently high to resolve prominent equatorial waves a double itcz occurs otherwise a single itcz occurs in contrast tropical resolution does not affect the magnitude of tropical precipitation in our aqua planet simulations instead the magnitude is sensitive to extra tropical resolution through its influence on the strength of baroclinic eddies and their forcing of the hadley circulation

impact of a modified convective scheme on the madden julian oscillation and el nino southern oscillation in a coupled climate model 1 the connection between the intraseasonal madden julian oscillation mjo and interannual el nino southern oscillation enso has been proposed and investigated for the last two decades however many fully coupled atmosphere ocean general circulation models gcms are still unable to simulate many important characteristics of these two phenomena partly due to the great uncertainty in the representation of subgrid scale cloud systems we report herein the simulation of an el nino in a fully coupled gcm with a modified convection scheme which captures many of the observed features of the 1997 1998 el nino event the representation of convection in the coupled model plays a major role in modeling both interannual enso and intraseasonal mjo variability in closer accord with observations and in reproducing the evolution of 1997 1998 el nino type events

isotopic fingerprints of milankovitch cycles in pennsylvanian carbonate platform top deposits the valdorria record northern spain sedimentary cyclic sequences deposited during the late palaeozoic ice age are widespread glacio eustatic control of the cyclic patterns is commonly accepted and the durations of the cyclothems generally match the short and long eccentricity milankovitch orbital parameters nevertheless geochemical fingerprints of orbital parameters are poorly documented in deep time sedimentary records here we report on well exposed bashkirian cyclothems of c 123 ka and c 400 ka durations from the valdorria platform the shorter term cyclothems can be grouped into longer term composite sequences that are consistent with generally accepted durations of c 125 ka and c 400 ka for milankovitch eccentricity cycles the stratigraphic pattern is mirrored by the isotope geochemical signals which show distinct recurring trends these trends are confirmed by statistical tests whereas intrinsic factors and or subaerial exposure related to sea level lowstands might have truncated cycle patterns in tectonically stable basins rapid subsidence of the valdorria platform s foreland basin appears to have contributed to a faithful recording of cyclothems of different orders the patterns and biostratigraphic constraint revealed in this study demonstrate the power of orbital forcing in imprinting sedimentary and geochemical signals in the rock record

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

notes and correspondence convective eddy momentum tendencies in long cloud resolving model simulations abstract domain average momentum budgets are examined in several multiday cloud resolving model simulations of deep tropical convection in realistic shears the convective eddy momentum tendency f neglected in many global circulation models looks broadly similar in two and three dimensional simulations it has a large component in quadrature with the mean wind profile tending to cause momentum profile features to descend this component opposes and exceeds in magnitude the corresponding large scale vertical advective tendency which would tend to make features ascend in convecting regions the portion of f in phase with the mean wind is isolated by vertically integrating f u yielding a kinetic energy tendency that is overwhelmingly negative the variation of this energy damping with shear flow kinetic energy and convection intensity measured by rain rate gives a cumulus friction coefficient around 40 to 80 per centimeter of rain in 3d runs large scatter reflects the effects of varying co

physical and chemical stratigraphy suggest small or absent glacioeustatic variation during formation of the paradox basin cyclothems the paradox basin cyclothems previously have been interpreted as milankovitch style glacial interglacial cycles from the late paleozoic ice age but an unambiguous test for a glacioeustatic origin has not been conducted a high resolution coupled chemical and physical stratigraphic analysis of two outcrop sections and three core segments provides new evidence that supports either minor sea level change of several meters or an autocyclic mechanism for parasequence formation high amplitude sea level change is ruled out by the scale of thin top negative isotopic meteoric diagenesis trends associated with parasequence tops and subaerial exposure fabrics isotopic gradients from shelf light to basin heavy indicate that parasequences are deposited diachronously with isotopes of more distal sections recording increased basin restriction these results support the idea that the late pennsylvanian was a prolonged period of relatively static eustasy agreeing with recent studies in the western usa the methods provide a new set of tools and context for extracting environmental information from cyclic upward shallowing carbonate parasequences

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

glacioeustasy meteoric diagenesis and the carbon cycle during the middle carboniferous middle carboniferous carbonates in the western u s have undergone pleistocene bahamas style meteoric diagenesis that may be associated with expanding late paleozoic ice sheets fourteen stratigraphic sections from carbonate platforms illustrate the regional distribution and variable intensity of physical and chemical diagenesis just below the middle carboniferous unconformity these sections contain top negative carbon isotope excursions that terminate in regional exposure surfaces that are associated with some combination of karst towers desiccation cracks fabric destructive recrystallization or extensive root systems the timing of the diagenesis is synchronous with similarly scaled top negative carbon isotope excursions observed by others in england kazakhstan and china the mass flux of negative carbon required to generate similar isotopic profiles across the areal extent of middle carboniferous platform carbonates is a significant component of the global carbon cycle we present a simple carbon box model to illustrate that the 13c of dissolved inorganic carbon in the ocean could be elevated by 1 4 as isotopically light carbon from the weathering of terrestrial organic matter reacts with exposed platforms before reaching the ocean and atmosphere these results represent an improvement on global biogeochemical models that have struggled to provide a congruent solution to the high 13c of the late paleozoic icehouse

effects of vertical wind shear on the cumulus transport of momentum observations and parameterization abstract dynamical effects of organized cumulus convection on its environment with vertical wind shear are studied analyses of the wind field and momentum budget residual for mesoscale convective systems observed during sesame and pre storm reveal systematic differences in the vertical transport of horizontal momentum between mesoscale convective complex mcc and squall line cases in the mcc a distinct minimum in wind speed appears over the area of intense convection and the momentum budget residual acts to decelerate the environmental wind and to reduce the upper level vertical shear therefore the inferred vertical transport of momentum in the mcc is downgradient in the upper layer on the other hand in the squall line there is no wind speed minimum and the upper level vertical shear of the line normall component of the environmental wind increases as convection develops thus the vertical transport of momentum normal to the squall line is upgradient in the upper layer although the transport of

cloud resolving modeling of cloud systems during phase iii of gate part ii effects of resolution and the third spatial dimension abstract two and three dimensional simulations of cloud systems for the period of 1 7 september 1974 in phase iii of the global atmospheric research programme garp atlantic tropical experiment gate are performed using the approach discussed in part i of this paper the aim is to reproduce cloud systems over the gate b scale sounding array comparison is presented between three experiments driven by the same large scale conditions i a fully three dimensional experiment ii a two dimensional experiment that is an east west section of the three dimensional case and iii a high resolution version of the two dimensional experiment differences between two and three dimensional frameworks and those related to spatial resolution are analyzed the three dimensional experiment produced a qualitatively realistic organization of convection nonsquall clusters a squall line and scattered convection and transitions between regimes were simulated the two dimensional experiments produced convective organ

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

predicting the thickness of fresh water lenses in carbonate paleo islands abstract fresh water lenses in carbonate sand and grainstone islands can be modeled using dupuit ghyben herzberg methods the results indicate that the thickness of the lens h in a homogeneous infinite strip island will be a function of the island s width a hydraulic conductivity k and the amount of recharge r the ratio of r k in most modern carbonate islands of holocene sands and pleistocene rocks is in the range of 10 4 to 10 6 this means h should be 1 to 3 the magnitude of a however vertical and lateral variations in k variations in island shape the presence of intra island evaporitic ponds and marshes and the presence of a mixing zone result in actual h a ratios that range from 0 2 to about 2 with 1 being the most representative value the thic ness of a paleo lens in an ancient carbonate shoal or reef complex can therefore be estimated if the width of the interpreted island can be approximated from facies or isopach maps an example from the late jurassic smackover formation in oaks field louisiana indicates that the estimated thickness of paleo lenses is identical to the thickness of the porosity zones in a series of off lapping oolite shoal complexes a second example from the late permian san andres formation in yates field west texas reveals that the estimated thickness of paleo lenses is essentially equivalent to the thickness of a phreatic cave system formed on paleo islands developed along the san andres shelf margin the h a method for estimating the thickness of paleo lenses and the possible extent of island stage fresh water diagenesis in ancient carbonates is more useful than the ghyben herzberg rule h 40 times the elevation of the water table because the gh rule requires estimation of paleo water table and paleo sea level positions to within a couple of centimeters such estimates are typically impossible in ancient rocks

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

quantifying the relationship between water depth and carbonate facies abstract carbonate facies often are used to define meter scale parasequence or cyclic structure in ancient sedimentary basins these parasequences constitute the fundamental stratigraphic unit in many studies of ancient climate and life on earth of interest is the uncertainty associated with the assumptions that underpin the parasequence definition and interpretation this work presents a method that uses modern maps of bathymetry and the geographic distribution of facies atop the great bahama bank to extract a signal of water depth change from facies transitions in vertically stacked carbonate strata this probabilistic approach incorporates the observed complexity in the water depth distribution of immediately adjacent modern carbonate environments and results in an impartial and explicit interpretation of stratigraphic data with quantified uncertainties specifically this analytical tool can distinguish sequences of facies that are likely to record information about changing water depths from sequences of facies that do not additionally the quantitative signal extracted from sequences of discrete or qualitative data can be used for the correlation of stratigraphic sequences by quantifying geologic observations through a lens of modern data the reproducibility and accuracy of sedimentary interpretations can be improved to build a more authentic picture of earth history

coupled sedimentary and δ13c records of late mississippian platform to slope successions from south china insight into δ13c chemostratigraphy abstract variability in stratigraphic accumulation rates and distribution of stratal hiatuses along with strong endemism of index fossils hinder regional to global stratigraphic correlation of the visean serpukhovian v s boundary interval late mississippian and thus geological inferences regarding the onset of the late paleozoic ice age here we integrate high resolution 13c time series with detailed sedimentary facies analysis of late visean early serpukhovian v s carbonate platform to slope successions from south china to evaluate the influences of local depositional and diagenetic processes on 13ccarb and to address the correlation issue analysis of 11 sedimentary facies from 5 outcrop sections indicates a restricted platform setting yashui section dominated by bioclastic wacke packstone to lime mudstone in which paleokarst developed and contemporaneous carbonate slope settings dominated by thin bedded lime mudstones intercalated with slumps and calciturbidites based on vertical facies assemblages three depositional units are recognized recording a significant sea level drawdown across the v s boundary multiple negative 13c excursions 1 can be correlated across the v s boundary interval in several slope sections naqing luokun and narao sections variability in the v s boundary 13c record in some sections is interpreted to record truncation physically by submarine erosion by slumps or chemically during karstification a long term decrease in 13c values through the serpukhovian of the yashui section likely records local influences on carbon cycling in the restricted platform setting this negative 13c trend and associated depositional facies at the yashui section can be correlated to the arrow canyon section usa which together with other coeval global sedimentary and geochemical records indicate a widespread eustatic drawdown in the late visean with initial buildup of gondwanan ice sheets we conclude that integrated sedimentary facies analysis and 13c chemostratigraphy can be used for stratigraphic correlation when interpreted within a well constrained sedimentary and carbon isotope regional framework

a numerical study of the vertical transport of momentum in a tropical rainband abstract the vertical transport of horizontal momentum in a convective tropical rainband is studied using a two dimensional cloud ensemble model twelve simulations are made under the same large scale conditions the vertical transports of v momentum parallel to the rainband are essentially the same in all of the simulations even though the structure of the clouds is different in each of the runs the magnitude of the v memomentum transport by clouds is fairly large it takes only half of a day to smooth out the tropical low level easterly jet parallel to the rainband if no other processes am operating the vertical transports of u momentum perpendicular to the rainband are quite different in all of the simulations this difference can be explained by the dissimilarities in the distributions of horizontal momentum associated with various cloud configurations the simulated vertical transports of horizontal momentum are compared with those computed with the schneider and lindzen scheme the results su

convective momentum transport and perturbation pressure field from a cloud resolving model simulation this study uses a 2d cloud resolving model to investigate the vertical transport of horizontal momentum and to understand the role of a convection generated perturbation pressure field in the momentum transport by convective systems during part of the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period it shows that convective updrafts transport a significant amount of momentum vertically this transport is downgradient in the easterly wind regime but upgradient during a westerly wind burst the differences in convective momentum transport between easterly and westerly wind regimes are examined the perturbation pressure gradient accounts for an important part of the apparent momentum source in general it is opposite in sign to the product of cloud mass flux and the vertical wind shear with smaller magnitude examination of the dynamic forcing to the pressure field demonstrates that the linear forcing representing the interaction between the convective updrafts and the large scale wind shear is the dominant term while the nonlinear forcing is of secondary importance thus parameterization schemes taking into account the linear interaction between the convective updrafts and the large scale wind shear can capture the essential features of the perturbation pressure field the parameterization scheme for momentum transport by zhang and cho is evaluated using the model simulation data the parameterized pressure gradient force using the scheme is in excellent agreement with the simulated one the parameterized apparent momentum source is also in good agreement with the model simulation other parameterization methods for the pressure gradient are also discussed

are coal balls rare a cyclostratigraphic analysis of coal ball occurrence in north america abstract from the perspective of phanerozoic time coal balls are rare apparently limited to a 24 m y interval 323 299 ma in the pennsylvanian and earliest permian yet within this interval coal balls occur in many coals approximately 82 transgressive regressive sedimentary cycles have been described for the midcontinent illinois and appalachian basins of north america during the mid to late pennsylvanian one third 27 82 have coal balls including 57 of major cycles 36 of intermediate cycles and 16 of minor cycles coal ball occurrence in the donets basin is similar over an interval of about 4 m y 315 311 ma latest bashkirian to mid moscovian 39 11 28 of transgressive regressive cycles have coal balls as north american paleoclimate became drier tree ferns replaced lycopsids as the dominant plant in peat swamps at the desmoinesian missourian boundary and coal ball occurrence declined overall 47 of cycles 19 40 with lycopsid or cordaitean dominance have coal balls whereas 19 8 42 of cycles with tree fern dominance have coal balls p this pattern may reflect the relative abundance of coal in the late pennsylvanian with drier paleotropical climates in the missourian virgilian leading to less paleotropical coal fewer mines and a lower probability of discovering missourian and virgilian coal balls however average cycle duration decreased from 150 kyr in the desmoinesian to 100 kyr in the missourian and virgilian and faster rates of relative sea level rise could have affected coal ball abundance particularly if coal balls formed in marine swamps with more rapid transgression leading to thinner coals or to freshwater coals directly overlain by marine sediments rygel et al 2008 suggested that missourian virgilian cycles recorded more erosional relief than desmoinesian cycles consistent with increased amplitude and rates of sea level rise during each glacial eustatic cycle changes in missourian virgilian cycles may have been augmented by stratigraphic attenuation as sediment filled the antecedent topography

seasonal migration of itcz precipitation across the equator why can t gcms simulate it 1 the secondary meridional circulation induced by convective momentum transport cmt within the ascending branch of the hadley circulation is a missing dynamical mechanism that can cause common failure of general circulation models gcms in simulating seasonal migration of the intertropical convergence zone itcz precipitation maximum across the equator this failure is manifested by the model bias that the precipitation peak remains north of the equator during november march the cmt induced secondary circulation characterized by strong downward motion along the equatorial belt and upward motion south and north of the belt tends to modify the meridional distribution of precipitation with the strongest impacts during boreal winter and spring a 20 year gcm simulation with the cmt parameterization successfully reproduces the observed seasonal migration of the itcz precipitation across the equator with the peaks near 8 n during boreal summer and near 8 s during boreal winter

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

the nature of the δ13c of periplatform sediments implications for stratigraphy and the global carbon cycle the carbon isotopic composition y 13 c of bulk carbonates obtained from a transect of sites drilled through platform and periplatform sediments of holocene to early miocene age has been compared to ascertain whether changes in the y 13 c can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the y 13 c of the dissolved inorganic carbon in the oceans over this time period five of the sites were drilled during leg 166 of the ocean drilling project 1003 1007 in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of holocene to oligocene age that are contained in 17 depositional sequences a q two shallow water sites clino and unda were situated on a extension of the same transect on great bahama bank in a water depth of 10 15 m with the exception of unda and clino the y 13 c of the carbonates ranges from 5x in the younger sequences to 1x in the early miocene in each of the sites the y 13 c is strongly positively correlated with the percentage of aragonite as a consequence the y 13 c of sequences a through f is strongly correlated reflecting the decreasing amount of aragonite with increasing depth in the two platform sites the y 13 c is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the pleistocene although the y 13 c of the individual sequences can be correlated in most instances between the odp holes the changes are not related to global changes in the y 13 c of the oceans which in contrast to the y 13 c of the platform sediments become isotopically lower towards the present day instead variations in the y 13 c appear to be related to varying mixtures of y 13 c rich banktop sediments and pelagic material

mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport 1 this study demonstrates that the momentum transport by cumulus convection plays a significant role in the organization and northward propagation of intraseasonal iso convection anomalies over the indian and western pacific regions during boreal summer a version of seoul national university s atmosphere ocean coupled general circulation model simulates northward propagation when convective momentum transport cmt is implemented the northward propagation disappears when cmt is disabled an axially symmetric shallowwatermodel withaparameterized cmtis used to understand the role of cmt in the northward propagation of iso the basic mechanism of northward propagation is the lower level convergence to the north of convection which is induced by the secondary meridional circulation associated with large momentum mixing by convection in the region of large mean vertical shear a large meanverticalshearexistsinsouthasianregionduringboreal summer citation kang i s d kim and j s kug 2010 mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport geophys res lett 37 l24804 doi 10 1029 2010gl045072

parametrization of momentum transport by convection i theory and cloud modelling results summary the theory of the mass flux approach to parametrization of convective momentum transport is presented a cloud resolving model is used to simulate momentum transport by ensembles of deep convective clouds in two very different regimes a mid latitude cold air outbreak and tropical convection forced by convergence idealized unidirectional wind profiles are used to simplify interpretation of the results diagnostics relevant to the parametrization problem are presented and it is shown that for both regimes the approximations inherent in the parametrization equations are reasonable the pressure gradients inside clouds play an important role in determining horizontal velocities in the clouds for the cold air outbreak with linear shear the results suggest that these pressure gradients are proportional to the shear and to the up downdraught mass fluxes sensitivity studies suggest that the results are not very sensitive to resolution or parametrization of subgrid scale processes giving some confidence that the results are reasonably accurate for the tropical case with a low level jet the pressure gradients change sign with the wind shear in part i1 of this paper these results will be used to develop and validate a mass flux parametrization of convective momentum transport which is tested in single column and global versions of the meteorological office unified model

coupling of convective momentum transport with convective heating in global climate simulations abstract the effects of convective momentum transport cmt on global climate simulations are examined in this study comparison between two sets of 20 yr 1979 98 integration using the ncar community climate model version 3 ccm3 illustrates that the inclusion of cmt in the convection scheme systematically modifies the climate mean state over the equatorial region the convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection this reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the hadley circulation the major heating peak during the boreal winter is moved to south of the equator at about 10 s which is closer to the heat budget residuals of the ecmwf reanalysis data the responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone

potential vorticity in models of the ocean circulation existing observations suffice to give a qualitative description of the wind driven and thermohaline components of the ocean circulation but a hierarchy of analytical and numerical models is now needed for in coupled ocean atmosphere models of the earth s climate potentialvorticity is a more appropriate diagnostic field variable than angular momentum for the ocean circulation because of the complicated geometry of basins patterns of potential vorticity onsurfaces of constant density help validate ocean circulation models and give physical insight into how the oceancirculation works high resolution models suggest that the lateral mixing of potential vorticity by mesoscale eddies along isopycnal surfaces is of the same order as large scale advection and that the assumption of inviscid potential vorticity conserving flow in the thermocline is not appropriate for the real ocean a satisfactory test of this conjecture will require the extensive measurements planned for the world ocean circulation experiment models also indicate that the transport of water mass properties by mesoscale eddies is largely a mixing along isopycnal surfaces the wcak temperaturc gradients along isopycnal surfaces in most areas of the ocean limit the effectiveness of the mesoscale eddies in transporting significant amounts of heat across latitude circles

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

the tropospheric response to tropical and subtropical zonally asymmetric torques analytical and idealized numerical model results abstractthe tropospheric response to prescribed tropical and subtropical zonally asymmetric torques which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection is investigated the linear analytical gill model response to westward upper tropospheric torques is compared to the response to a midtropospheric heating which is a familiar point of reference the response to an equatorial torque projects onto a kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels in contrast the torque and heating both produce rossby gyres of the same sign to the west of the forcing and the zonal mean streamfunction responses are identical when the forcings are shifted into the northern hemisphere the streamfunction responses have opposite signs there is upwelling in the southern northern hemisphere in response to the torque heating the nonlinear response to westward torques was explored in idealized