a numerical modelling study of the geostrophic adjustment process following deep convection a high resolution numerical model based on the anelastic equations of motion is used to simulate the geostrophic adjustment process that follows the growth of a single deep convective plume interest focuses on the form of the balanced state and the proportions of energy which go into gravity waves dissipation and balanced flow three simulations are described a non rotating case an intermediate rotation case f 10 3s 1 and a high rotation case f 2 10 3s 1 the use of these artificially high rotation rates in the context of the terrestial atmosphere is regarded as a device for shortening the adjustment time thereby rendering the objective of the study computationally feasible the model simulations are two dimensional and use an idealized specification of the moist process in which precipitation is instantaneous and no cloud is permitted the initial state of the model atmosphere is calm and horizontally stratified except for a warm moist bubble near the surface integrations are carried out for 50000 s by which time quasi steady flow states are achieved in the rotating cases the final quasi balanced state takes the form of a well defined lens shaped region of uniform absolute momentum at the neutral buoyancy level and an intense vertical shear line front extending upwards from the surface the response is characterized by two length scales the rossby radius of deformation based on the depth of the convection and a mesoscale cloud scale related to the amount of mass which convects and the rotation rate amongst other factors it is found that 30 of the kinetic energy released in convection is captured in balanced flow considerably larger than indicated in earlier studies and not dependent on the high rotation rates used here simple scaling arguments are used to account for the efficiency of balanced energy retention as a function of the amount of mass that convects and to define an upper bound on the amount of mass that can be convected through a single plume in a rotating environment this is tentatively identified with a maximum possible scale for mesoscale convective systems an analytic model for the balanced state is presented and shown to fit the simulated flow very well the success of this model underlines the secondary role played by mixing in the numerical model

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

a numerical study of the stratiform region of a fast moving squall line part i general description and water and heat budgets abstract a two dimensional nonhydrostatic cloud model is applied to the simulation of a tropical squall line that occurred on 23 june during the copt 81 experiment owing to the use of an ice parameterization scheme the simulation reproduces many interesting features of the stratiform part observed with doppler radars in particular this includes the dynamical thermodynamical and microphysical structures of the stratiform part different parts are clearly identified from the simulation and observations a leading convective zone 40 km wide with large precipitation a developed stratiform zone stretching over 150 km with moderate precipitation between these two regions a transition zone 20 km wide giving only light precipitation and a forward anvil near 12 km the mean horizontal circulation is characterized by two mean flows the front to rear flow that represents upward and rearward injection of boundary layer air and the underlying rear to front flow the simulated vertical velocity except in th

sediment dispersal in the argentine basin evidence from visible light spectra abstract visible light reflectance spectra were determined for each of 236 core top samples from the argentine basin and surrounding areas the spectra were analyzed by taking the first derivative of the raw spectral curves and factor analyzing the first derivative values using wavelengths as variables we used a four factor solution that explains about 90 of the cumulative variance factors were evaluated by comparing factor loadings to first derivative curves from known minerals and mineral combinations by the mapped distributions of the factor scores and by comparison to factors from other areas the four factors represent in order of decreasing variance goethite terrigenous vs pelagic sedimentation organic matter and chlorite the goethite and chlorite factors are useful for interpreting sediment influx and dispersal goethitecomes from the falkland plateau and the argentine continental margin once introduce to the deep ocean goethite appears to be transported primarily by isobath parallel currents chlorite on the other hand is transported into the argentine basin by antarctic bottom water aabw and from the falkland plateau however along the falkland plateau chlorite is transported normal to the slope probably by gravitational processes

a tropical squall line observed during the copt 81 experiment in west africa part 1 kinematic structure inferred from dual doppler radar data abstract this paper deals with the analysis of a tropical squall line observed on 22 june 1981 during the copt 81 convection profonde tropicale experiment the present part i is restricted to the study of the kinematic structure of the system which moved in a moderately unstable atmosphere faster than the environmental air at all levels at the observation time the squall line was in a mature stage the explicit description of the airflow within the system was inferred from dual and single doppler radar data the general characteristics of the squall line are found to be very similar to those of tropical squall lines observed during previous experiments such as vhimex or gate a large cloud system composed of an organized convective line ahead of an extensive trailing anvil cloud stratiform rain fast motion and long lasting structure and a well marked gust front signature at ground level the overall airflow presents a three dimensional structure at the leading edge convective scale updrafts a

a numerical study of the stratiform region of a fast moving squall line part ii relationship between mass pressure and momentum fields abstract in a companion paper a two dimensional simulation of a fast moving tropical squall line was successfully compared to observations performed during the copt81 experiment over west africa the full ice phase parameterization is shown to be crucial in the simulation of trailing anvil precipitation different diagnostic tools are applied to the simulated fields to further our understanding of the scale interactions within a squall line type mesoscale convective system the pressure organization is characterized by two marked features important for explaining the inner circulation first a front to rear midlevel pressure gradient and second the surface pressure mesohigh extending from the gust front to the rear of the most active part of the trailing stratiform region based on the hydrostatic approximation an original method of decomposition of the pressure field is proposed whereby dynamical and buoyant contributions depend only on the horizontal and vertical respectively the mean pressure i

the effects of water content on diffuse reflectance spectrophotometry studies of deep sea sediment cores abstract sediment cores recovered during odp drilling operations are commonly scanned using a minolta cm 2002 spectrophotometer to obtain spectral data core processing procedures aboard the joides resolution require that these spectral data be measured on wet cores however the effects of changing water content on the spectra of marine sediments is unknown we examined the effects of changing water content on visible light vis diffuse reflectance spectra for core samples composed of clay to foraminiferal ooze the spectra of dry powdered samples were measured then the samples were completely saturated 35 water content and spectra were measured at set time intervals as the samples progressively dried the fully saturated samples were appreciably darker than the initial dry samples the samples continued to darken during the initial phases of drying until the water content had decreased from 35 to 20 as the water content continued to decrease below 20 the samples became progressively lighter and attained spectral values similar to the fully saturated samples at water contents of 17 samples continued to lighten until they were totally dry however values never became as light as those of the dry samples prior to initial wetting changes in reflectance with decreasing water content are not uniform across the vis if the water content is greater than 5 the reflectance decrease relative to a dry sample is greater at the red end of the spectrum however at water contents of less than 5 the spectral curves of the wet and dry sediments are similar in shape but the wet sediments are still darker comparison of these data with data obtained from similar saturation experiments using a coarse grained beach sand suggest that the initial darkening of the saturated carbonate sediments apparently results from changing of the physical properties of the sediment decreasing the water content apparently rearranges the grains these studies suggest that maximum information will be obtained when spectral measurements are taken on samples that are allowed to dry as much as possible

relating magnetic susceptibility ms to the simulated thematic mapper tm bands of the chinese loess application of tm image for soil ms mapping on loess plateau 1 magnetic susceptibility ms is a very important physical attribute of the earth s soils and surficial sediments soil containing deposits in the loess plateau of central china offer a unique opportunity to study the relationship between soil reflectance and ms in this paper data on ms and diffuse reflectance spectra obtained from seven loess plateau sections were used to establish quantitative relationships between ms and spectral parameters related to remote sensing by integrating the diffuse reflectance values corresponding to thematic mapper tm channels five tm bands were simulated and served as independent variables for a multiple linear regression relating the bands to ms the resulting calibration equation provides good estimates of ms values and has excellent correlation coefficients 0 90 for all the test samples the application of the regression equation for mapping soil ms was performed using the enhanced tm image from northwest part of loess plateau the ms values obtained from tm data are convincing and compare well with the limited field test data the spatial ms variations on the tm image clearly show a decrease toward the northwest and are in a good agreement with the monsoon directions results of this study demonstrate that the surface ms signal in soil can be mapped with data from satellite based remote sensors operating in the visible and near infrared bands the future possibilities of this method in other soil types and climates need to be explored

precise major component determinations in deep sea sediments using fourier transform infrared spectroscopy abstract experiments using fourier transform infrared spectroscopy ftir on a set of powdered deep sea sediment samples show that it is an efficient method of quantifying the relative abundances of quartz clay and calcite ratios of absorption bands characteristic of different minerals are precise and reproducible to a relative error of about 1 provided that samples are ground to

interception of atmospheric fluxes by arctic sea ice evidence from cosmogenic 7be 1 the natural cosmogenic radionuclide 7be t1 2 53 4 d is supplied to the surface ocean from the atmosphere and in the arctic ocean can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species analyses of 7be in samples of surface water surface sea ice water beneath the ice sea ice sediments and precipitation from the eurasian basin of the arctic ocean show that the fraction of sea ice coverage determines the amount of 7be in the surface water when sea ice coverage is 80 the water column inventory drops to 58 20 bq m 2 the 7be inventory in sea ice is 39 23 bq m 2 and mass balance calculations show that sea ice can intercept 30 18 of the atmospheric flux of 7be during the studied period we suggest that other atmospherically transported contaminants should be similarly intercepted 7be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the fram strait is 500 g m 2 a value comparable to previously measured fluxes in sediment traps deployed in the area

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

properties of tropical convection observed by millimeter wave radar systems abstract this paper describes the results of analysis of over 825 000 profiles of millimeter wave radar mwr reflectivities primarily collected by zenith pointing surface radars observing tropical convection associated with various phases of activity of the large scale tropical circulation the data principally analyzed in this paper come from surface observations obtained at the atmospheric radiation measurement manus site during active and break episodes of the madden julian oscillation mjo and from observations collected from a shipborne radar during an active phase of the monsoon over the indian ocean during the joint air sea monsoon interaction experiment it was shown for example in a histogram regime analysis that the mwr data produce statistics on convection regimes similar in most respects to the analogous regime analysis of the tropical rainfall measuring mission radar radiometer observations attenuation of the surface mwrs by heavy precipitation however incorrectly shifts a small fracti

a three dimensional simulation of a tropical squall line convective organization and thermodynamic vertical transport abstract three dimensional convective scale simulations of an african squall line observed during the french copt 81 experiment are presented three simulations with different representations of large scale forcing are performed on a domain of 50 km along the line by 80 km across the line they exhibit a similar circulation pattern characteristic of a squall line but differ in intensity the first simulation supposes an unperturbed environment and produces a slow moving squall line 7 m s 1 with weaker total precipitation rate then observed 25 the second one includes a representation of observed thermodynamic and dynamic environment modifications and produces a fast moving squall line 10 m s 1 still weaker than observations 50 or the rain rate the third simulation takes into account the forcing induced by the rear inflow jet as depicted by smull and houze and observed on that day it allows the system to reach an intensity in agreement with observations the convective region 30 km wid

neogene changes in southern ocean sedimentation based on mass accumulation rates at four continental margins 1 high resolution mass accumulation rates mar were determined from lithologic logs based on downhole log and continuous core data for six sites at four continental margins around the southern ocean total mar was calculated at ocean drilling program odp site 1095 on the margin of the antarctic peninsula and odp site 1165 on the margin of prydz bay antarctica carbonate and noncarbonate terrigenous mar were calculated for odp sites 1123 and 1124 east of new zealand and sites 1168 and 1172 west and southeast of tasmania shifts in carbonate mar are seen around tasmania and new zealand at 23 and 14 ma suggesting changes in deep water circulation and surface carbonate productivity at these times carbonate mar dropped at sites 1124 and 1168 at 23 ma and increased at 14 ma at sites 1123 1168 and 1172 the overall character of total mar at antarctic sites 1095 and 1165 is a continual and relatively constant decrease in total mar during the neogene with periods of stepwise decrease one such decrease is seen at 14 ma at site 1165 coincident with increased carbonate mar in new zealand and tasmania sites 1123 1124 1168 and 1172 and likely related to mid miocene expansion of the east antarctic ice sheet another step drop in total mar is seen at 9 ma at site 1165 possibly reflecting diversion of sediment to a newly formed prydz channel fan

multicomponent analysis of ftir spectra quantification of amorphous and crystallized mineral phases in synthetic and natural sediments abstract the study of weathering and erosion processes requires the establishment of a mass balance of minerals from the soils towards the sedimentation area this calls for the development of quantitative tools that can be applied to mixtures of finely divided and sometimes poorly crystallized minerals found in soils and sediments we present here the use of fourier transform infrared ftir absorbance spectroscopy in the mid infrared as a method to calculate mineral modes for such materials samples were prepared using the kbr disc method this ensures that lambert beer s law is valid a quantitative determination of the mineral content from various blends was performed by making a multicomponent analysis of the experimental spectrum using the spectra of each component in the mixture to check the validity of the procedure the multicomponent analysis was performed on spectra from synthetic mixtures of standard minerals quartz kaolinite gibbsite amorphous silica good agreement between actual and computed wt was obtained in the range 1315 315 cm 1 this application of ftir spectroscopy was used to quantify the mineral components of a lacustrine sediment cored at salitre minas gerais brazil the major phases are organic matter kaolinite gibbsite quartz anatase and amorphous silica phytoliths and sponge spicules fifty three samples were analyzed quantitative results from ftir spectroscopy were compared to chemical analyses to assess the validity of the method for the natural sediments phases with no sharp diagnostic spectral features such as anatase or amorphous silica were quantified using the multicomponent analysis the variations of the main mineral phases along the core reflect the mechanisms of transfer from the surrounding soils to the sediment area and the role of the vegetal cover over the drainage area

late quaternary sedimentation in the western north atlantic stratigraphy and paleoceanography abstract a detailed analysis of stratigraphic indices was undertaken to study paleoclimatic change in the western north atlantic three stratigraphic indicators carbonate content globorotalia menardii and uvigerina peregrina were tested in ten radiocarbon dated cores from the north american continental margin of these carbonate content appears to be most accurate carbonate content exhibits two major increases from late glacial time to the present estimated ages of the average of the mid point of these increase are 13 200 b p and 8600 b p an absolute chronology was established down fifteen cores using these stratigraphic indicators and the radiocarbon dates sea surface temperature sst estimates derived from planktonic foraminifera were mapped at 2000 yr intervals from 2000 b p to 14 000 b p sst warms rapidly from 12 000 to 8000 b p reaches a maximum between 8000 and 6000 b p and gradually cools after 6000 b p bottom waters were monitored with uvigerina peregrina and dissolution indices the disappearance of uvigerina suggests that the water type it lives in low o 2 started to thin from both the top and bottom by 13 000 b p and by 7300 b p had disappeared fragmentation of planktonic foraminifera was used as an index of dissolution in most cores dissolution was intense during late glacial time lessened during early postglacial time and resumed in the late postglacial

effect of three dimensional structure on the stormwide horizontal accelerations and momentum budget of a simulated squall line abstract past studies of the effects of mesoscale convective systems mcss on the environmental flow have been limited by data coverage and resolution in the current study the mcs scale stormwide horizontal accelerations and momentum budget associated with an oceanic mcs are analyzed using output from a high resolution three dimensional numerical model integrated over a large domain the simulation is based on an observed mcs that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment an important aspect of both the observed and simulated mcs is its evolution from a quasi two dimensional to an asymmetric three dimensional morphology which was demonstrated in companion studies to result from the finite length of the mcs interacting with environmental vertical shear that varies in direction with height herein the authors focus on the effects of the three dimensional structure on mcs scale horizontal accelerations the horizontal accelera

sediment colour analysis from digital images and correlation with sediment composition sediment colour records can be extracted from digital images of sediment core surfaces which provide the spatial resolution needed to measure colour in laminated sediments digital cameras sample colour in three broad wavelengths red green and blue which are subsequently translated into the cie l a b colour space methods to extract calibrated colour values are discussed in this paper l a and b values are correlated with geochemical analyses of cm scale bulk sediment samples the sediments are from a suite of laminated and homogenous sections containing organic matter carbonate biogenic opal and lithogenic material in variable proportions total organic carbon toc content has the dominant effect on sediment colour results show that there is a strong correlation with lightness l for toc values between 0 5 and 10 but that sediment lightness becomes saturated at higher toc concentrations biogenic opal content cannot be resolved using the l a b colour space biogenic opal in itself has a light colour but it tends to occur in darker coloured sediments because of a positive correlation between opal and toc content carbonate content in the measured sections is generally less than 25 at which values its effect on colour is obscured by the other sediment components the geological society of london 2006

comparison between a three dimensional simulation and doppler radar data of a tropical squall line transports of mass momentum heat and moisture abstract results from a detailed three dimensional cloud model are extensively compared with doppler radar data in the case of a fast moving tropical squall line observed during the copt81 experiment the comparisons use a two dimensional statistical analysis in which we consider each four dimensional field as the sum of a two dimensional averaged vertical field and a four dimensional residual field representative of along line and temporal fluctuations these fluctuations are analyzed by computing the time average of spatial variances and the temporal variance of spatial averages the results indicate good agreement in both quality and quantity particularly for the vertical velocity and line normal wind the consequences of this agreement are two fold first a physical and comprehensive model of the convective part of a tropical squall line emerges that is coherent with both observations and simulations this conceptual model emphasizes the importance of along line fluctuations second it is possib

organic carbon distribution in the north atlantic ocean during the last glacial maximum abstract the organic carbon content of eighty two last glacial maximum lgm sediment samples from the north atlantic ocean was determined with a coulometer organic carbon in these sediments averaged about 0 5 by weight slightly higher than in modern sediments factors that control organic carbon distribution were examined in two ways by mapping the spatial distribution of organic carbon during the lgm and by comparing organic carbon content to sediment characteristics in general sediment organic content increases with increasing sedimentation rate increasing clay content and decreasing carbonate content the spatial distribution of lgm organic content is similar in most respects to the mapped modern distribution the primary exception being areas of high organic content one area of high organic content off nortwest africa is situated in the same area geographically but is larger than its modern counterpart perhaps indicating that wind driven upwelling was more intense and or widespread during the lgm the two other areas of high organic carbon content the north american margin and west of the mid atlantic ridge mar at about 40 n have no modern counterpart on the north american margin south of cape cod organic carbon content is generally 0 6 and in several samples is 0 9 the increased organic carbon content of sediment in this area appears to be related to an increase in sedimentation rate and the concomitant increase in inorganic nutrients the area west of the mar is more perplexing and appears to be related to changes in lgm surface circulation

numerical simulation of a midlatitude squall line in two dimensions abstract a two dimensional anelastic cloud model was used in attempts to numerically replicate the observed structure of a midlatitude squall line initial conditions were adapted from observations of the 22 may 1976 oklahoma line model simulations were made with and without considering the ice phase of water these model storms have within the constraints of the model s geometry replicated the basic multicellular character and general line normal airflow typical of these lines in addition the structure and intensity of the subcloud cold air pool and the propagation speeds developed by the storms appear to be reasonable further it was found that the initial conditions chosen resulted in model storms which were not only long lasting but also essentially repetitive indicating that a state of quasi equilibrium had been attained the storms did not decay because the environmental conditions ahead of the storms were favorable and essentially unchanged during the course of the simulations the inclusio

cloud microphysics radiation and vertical velocities in two and three dimensional simulations of deep convection this study investigates the importance of dimensionality for the characteristics of simulations performed with cloud system resolving models csrms in addition to intrinsic questions related to dimensionality in csrms the issue has gained added interest since csrms can be utilized instead of conventional cloud parametrizations to represent deep convection within global climate models such csrms may be either two or three dimensional csrm simulations of five observed cases of deep convection are performed in both two and three dimensions 2d and 3d with the aim of elucidating the impact of dimensionality on overall cloud statistics observed profiles of the large scale average of advection of temperature and humidity are applied to initiate and maintain the convection two of the cases are from tropical oceanic regions the other three cases are continental the average ascent rate in deep convective cloudy updraughts is about 20 50 higher at mid levels of the troposphere in 3d than in 2d for all cases this corresponds to an increase by a similar percentage in the vertical mass flux of deep updraughts in the oceanic cases furthermore the weak ascent 0 1 w 1 m s 1 outside the deep convective updraughts is much less prevalent in 3d than in 2d with vertical velocities being about 20 lower for a given cumulative frequency and a lower vertical mass flux downdraughts are weaker in 3d for most cases there is a substantial sensitivity of the vertical profiles of cloud liquid and cloud ice and of other microphysical species to dimensionality this is consistent with the sensitivity of the dynamics of convection corresponding changes in radiative transfer especially in the short wave band result from the cloud radiative interactions in particular the peak in domain averaged cloud liquid content in the melting layer is about 50 higher in most of the 2d simulations the land cases display more sensitivity of the short wave radiative flux to the choice of orientation of the vertical plane of 2d simulations less

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

sediment mineralogy based on visible and near infrared reflectance spectroscopy visible and near infrared spectroscopy vnis can be used to measure reflectance spectra wavelength 350 2500 nm for sediment cores and samples a local ground truth cali bration of spectral features to mineral percentages is calculated by measuring reflectance spectra for a suite of samples of known mineralogy this approach has been tested on powders core plugs and split cores and we conclude that it works well on all three unless pore water is present initial vnis studies have concentrated on determination of relative proportions of carbonate opal smectite and illite in equatorial pacific sediments shipboard vnis based determination of these four components was demonstrated on ocean drilling program leg 199 rock colour is one of our oldest clues to com position and spectroscopy instruments now surpass the eye in providing quantitative compo sitional information the experimental technique is straightforward and non intrusive simply illu minate a rock surface record the spectrum of reflected light and extract any spectral responses that are sensitive to mineralogy reflectance spectroscopy can be used on powders core plugs and split cores and measurements take only seconds these advantages make the tech nique particularly attractive for depleted inter vals of core e g many basalts and for climate proxies requiring thousands of high resolution measurements

direct correlation of the marine oxygen isotope record with the chinese loess plateau iron oxide and magnetic susceptibility records abstract monsoons are a major feature of global atmospheric circulation and derive heat and moisture from the oceans and transports much of that heat and moisture to nearby continents the east asian monsoon derives its heat and moisture from the eastern equatorial pacific and transfers it to southeast asia and the loess plateau of central china in order to examine the phasing of marine and terrestrial climatic events associated with this monsoon we have analyzed a core from the western pacific v21 146 downwind from the loess plateau iron oxides and magnetic susceptibility were analyzed because they have been used as loess plateau paleoclimate proxies comparison of temporal changes in both iron oxide and susceptibility signals in v21 146 to the well known luochuan loess section reveals an excellent correlation both in the timing and direction of the variations comparison of our loess plateau paleoclimatic proxies in v21 146 to previously published oxygen isotope data from this core suggests that through marine isotope stage mis 9 coincident with loess plateau interglacial soil level 3 s3 ocean temperature increases and the onset of monsoonal conditions on the loess plateau were synchronous however for mis 11 12 interglacial glacial s4 l5 changes in the ocean appear to significantly lead those on land and there is a lack of correlation between mis 13 and s5 these out of phase events may be a response to a reorganization of the ocean atmosphere system as indicated by changes in the 13c record it has previously been suggested that changes in eolian flux record eolian transport from the loess plateau but we find little correlation between eolian flux and our loess plateau proxies suggesting that some of the eolian sediments were derived from outside the loess plateau

what controls the transition from shallow to deep convection abstract in this study a 2d cloud system resolving model csrm is used to assess the control mechanism for the transition from shallow to deep convection in the diurnal cycle over land by comparing with a 3d csrm under conditions taken from the large scale biosphere atmosphere field study in the amazon the authors show that the 2d csrm reproduces the main features evident in previous 3d simulations reasonably well to extract the essence of the transition from shallow to deep convection the observed case is idealized to isolate two control parameters the free troposphere stability and the relative humidity the emergence of a distinct transition between shallow and deep convection shows that the convective transition is an intrinsic property of the system a transition time is defined to evaluate the key mechanism of the transition the authors show that the transition coincides with the time when the lapse rate of the virtual potential temperature of the clouds becomes larger than that of the env

evaluating color reflectance spectral methods for estimating biogenic contents of south china sea sediments abstract the biogenic contents of marine sediment cores are useful proxies for revealing past oceanic and climatic variability color reflectance spectral methods provide a rapid and non destructive avenue for acquiring high resolution biogenic content data from the split surfaces of marine sediment cores this study presents new results on the applications of color reflectance methods for determining the biogenic contents of sediment cores retrieved from the south china sea scs a dynamic setting that receives biogenic components such as carbonate total organic carbon toc and opal from the sea and terrestrial sediments transported by the pearl river and kao ping river from the north and the sunda shelf from the south our study found that the color reflectance methods that are based on a regionally limited calibration provide more optimal estimates of the biogenic content of marine cores from the scs than do basin scale calibration methods though the regional calibrations appear to be successful our analyses indicate the complexity of applying color reflectance methods in marine sediment core studies we also performed a controlled experiment that was designed to quantitatively test how the carbonate content increased the influence of color reflectance changes using outcropped pleistocene aged sediment samples taken from the moon world mw in southwestern taiwan as control data the results of this experiment suggest that the regression equations for estimating caco 3 content based on core data are not solely driven by input variables responding directly to caco 3 content changes and that the composition of terrestrial sediment inputs into the scs are complicated both spatially and temporally our studies also suggest that a better understanding of the compositional changes of terrestrial sediment inputs into the scs will be required to minimize the uncertainties of biogenic content estimations by color reflectance methods

7be in sargasso sea and long island sound waters 7be was measured in surface waters of the western sargasso sea and long island sound the calculated standing crop in the sargasso sea is equal to that predicted from precipitation collectors long island sound is deficient in 7be virtually none exists in the water column and less than half of the expected standing crop has been reported for the sediments a possible sink for the missing 7be may be the salt marshes or tidal mud flats ringing long island sound

the oklahoma kansas mesoscale convective system of 10 11 june 1985 precipitation structure and single doppler radar analysis abstract the 10 11 june mesoscale convective system observed in kansas during pre storm is studied using a variety of observations including conventional radar satellite and single doppler radar this storm at maturity consisted of a strong line of convection trailed by a broad region of stratiform rain the pre storm doppler radar observations show that the general airflow pattern is similar to that seen in previously analyzed cases however since the doppler observations were quite extensive in time and space they permit several details of the airflow to be revealed for the first time a rear inflow jet front to rear flow aloft and a mesoscale updraft and downdraft were all present the mesoscale downdraft commenced at the top of the slanted rear inflow jet sublimation and evaporation of hydrometeors in this flow apparently generated the necessary cooling to drive the mesoscale downdraft circulation the intensity and slope of the rear inflow jet varied with location in the storm which apparen

evaluating optical lightness as a proxy for carbonate content in marine sediment cores abstract optical lightness is increasingly being used as a proxy for the carbonate content of marine sediment we compared three measurements of optical lightness gray scale brightness and l to carbonate content to test the reliability of these measurements as carbonate content proxies in five piston cores from isotope stages 1 though 6 0 130 ka all measures of optical lightness are reasonable proxies of relative but not absolute changes in carbonate content in contrast in the upper sediments of odp hole 997a which are holocene to pliocene in age lightness values in only the top 10 m of the 180 m analyzed exhibit a strong correlation to carbonate content to better understand which factors control the optical lightness of sediments we analyzed samples in which carbonate content remained constant while the composition of three common clay minerals chlorite illite and kaolinite was varied kaolinite even at a concentration of 20 did not significantly change optical lightness however 20 illite reduced optical lightness by 30 and 20 chlorite reduced lightness by 20 we conclude that regional and temporal changes in the composition of the non carbonate sediment fraction may significantly alter the relationship between lightness and carbonate content we recommend that care must be taken when applying these measures to sediment sequences which span long time intervals or to sediment samples taken over a broad geographical areas

dynamical influence of microphysics in tropical squall lines a numerical study abstract based on environmental conditions of the 22 and 23 june squall lines during the convection profonde tropicale in 1981 copt81 experiment in west africa a series of numerical simulations are performed with a two dimensional nonhydrostatic cloud model to examine the dynamical effect of microphysics in tropical squall lines the role of ice phase microphysics strongly depends on ambient conditions for the environment of strong convective instability the ice phase is important regarding the system scale structure but is not important to the convective scale dynamics on the other hand the ice influence is crucial to the squall line convective system if the environment has a weak convective instability and is almost saturated at low levels

transport of carbonate sediment in the western north atlantic evidence from oxygen and carbon isotopes abstract in most deep ocean environments the carbonate component is usually considered to be of pelagic origin deposited on the sea bed without extensive transport even when evidence exists that carbonate fractions have been transported the transport is usually viewed as being intrabasinal stable isotope analyses 18 o and 13 c of the carbonate contained in the fine fraction m of eight cores from the north american continental margin and the west flank of the mid atlantic ridge mar suggest that carbonate sedimentation patterns may be influenced by transport to a greater extent than previously recognized in holocene sections of all the cores the fine fraction and foraminiferal isotopic signals are comparable in cores from the flanks of the mar the fine fraction and foraminiferal isotopic signals remain comparable during the entire glacial interglacial cycle on the north american margin however the pattern is strikingly different starting about 10 ka and extending back into glacial times the fine fraction isotopic signal in margin cores becomes increasingly depleted reaching a value of 8 pdb the foraminiferal signal from these same cores follows the typical glacial interglacial pattern and gets heavier during glacial time the holocene correspondence of foraminiferal and fine fraction isotope curves throughout the north american basin suggests that both have the same intrabasinal pelagic source however in late glacial age sediments from the north american margin the divergence of foraminiferal and fine fraction isotope signals indicates different sources for each component based on the isotopic signals and the timing of changes in the signal a substantial proportion of the fine fraction carbonate on the north american margin appears to be derived from diagenetically altered carbonate rock this fine carbonate sediment probably resulted from physical erosion of carbonate rock by glacial processes and deposition in the north american basin by the retreating wisconsin glacier

atlantic sediments glacial interglacial comparisons to assess the regional effects of glaciation on sedimentation in the atlantic ocean we compare sediment types distributions and rates between recent core top and last glacial maximum lgm 18 000 years b p stratigraphic levels based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than recent during both the recent and lgm carbonate content shows an east west asymmetry with western basins exhibiting lower carbonate values input of ice rafted detritus into the north atlantic during lgm time interrupts this topographic control on carbonate distribution considerably farther south than at present in the south atlantic this effect is minor comparison of lgm and recent sediment distributions indicates that the lgm seafloor was dominated by biogenic oozes calcareous clays and clays while the recent is dominated by biogenic oozes and marls coarse grained detritus is much more prevalent in lgm sediments derived not only from glacial input but also from fluvial and aeolian sources sedimentation rates calculated from lgm to recent sediment thickness in cores are 4 cm 1000 yr for most of the ocean higher rates are typical of the continental margin off the amazon river the north american basin and a small region off west equatorial africa

rapid oxygen utilization in the ocean twilight zone assessed with the cosmogenic isotope 7be 1 the rate of oxygen utilization beneath the sunlit surface ocean provides a measure of the export rate of biologically produced carbon to the deep sea and its variation with depth suggests where remineralization of that carbon occurs the latter consideration is relevant to the efficiency of carbon sequestration in deep water however accurate characterization of this process particularly within 200 m of the euphotic zone where carbon utilization is most intense has been difficult owing to limitations of techniques applied to these shallow depths here a novel approach utilizing the cosmogenic isotope 7be indicates that at a site in the subtropical north atlantic 65 of sinking carbon is remineralized within 200 m of the ocean s surface and is thus readily available for return to the atmosphere the corresponding oxygen utilization rates are greater than would be suggested by the attenuation with depth of organic matter measured by shallow sediment traps

pliocene glacial cyclicity in a deep sea sediment drift antarctic peninsula pacific margin abstract giant deep sea sediment drifts are widespread features along the continental rise of the west antarctic peninsula representing the most proximal continuous sedimentary recorders for west antarctic ice events and glacial interglacial cyclicity sediment physical geochemical records and x ray images derived from odp leg 178 site 1095 sediment drift 7 show characteristics in glacial interglacial cyclicity and associated sedimentary processes during early pliocene two boundary types dividing half cycles have been recognized 1 interglacial to glacial transitions that are distinct and characterized by a sharp boundary and abrupt change in lithology 2 glacial to interglacial transitions that are diffuse and characterized by a gradual decline of sediment physical and geochemical values with a marked reduction in sedimentation rates the boundaries defined in conjunction with magneto and biostratigraphic tie points form the framework for the calculation of relative sedimentation and accumulation rates used for reconstructing early pliocene paleoproductivity and terrigenous flux to the drift warm early pliocene climate conditions for west antarctic peninsula region are indicated by open ocean conditions in glacials short residence times of the grounded ice sheet at the shelf edge with sporadic fluctuations as well as periodic collapses of the ice sheet front we propose a 5 phase drift sedimentation model for the early pliocene and postulate a highly dynamic ice sheet likely reduced in thickness resulting in oscillations which lie closer to the shelf edge than was the case during the late quaternary

digital image analysis of outcropping sediments comparison to photospectrometric data from quaternary loess deposits at şanoviţa romania and achenheim france abstract the possibility to use colour data as extracted from two selected loess paleosol sequences is discussed here colour data are a fast and inexpensive method of proxy data generation we compare the outcome from analysing outcrop images taken by digital cameras in the field and spectral colour data as determined under controlled laboratory conditions by nature differences can be expected due to variations in illumination moisture and sample preparation outcrop inclination may be an issue for photographs correction for this is possible when marks can be used for rectification in both cases the data extracted from the images match the visual impression of the photos well and are useful for obtaining a more quantitative measure for field observations smoothness as measured by autocorrelation is high for an image from achenheim france where an image with a width of ca 1 1 m and a depth of 1 6 m was analysed data from a narrower image part from anovi a romania are noisier in both cases a significant correlation between data extracted by digital image analysis and laboratory measurements could be established suggesting that image analysis is a useful tool where outcrop and light conditions allow good photographs with similar illumination especially where high resolution proxy data is required

sensitivity of radiative convective equilibrium simulations to horizontal resolution abstract this paper investigates the impacts of horizontal resolution on the statistical behavior of convection an idealized radiative convective equilibrium is simulated for model resolutions ranging between 2 and 50 km the simulations are compared based upon the analysis of the mean state the energy and water vapor transport and the probability distribution functions for various quantities it is shown that at a coarse resolution the model is unable to capture the mixing associated with shallow clouds this results in a dry bias in the lower troposphere and in an excessive amount of water clouds despite this deficiency the coarse resolution simulations are able to reproduce reasonably well the statistical properties of deep convective towers this is particularly apparent in the cloud ice and vertical velocity distributions that exhibit a very robust behavior a theoretical scaling for the vertical velocity as function of the grid resolution is derived based upon the behavior of an idealized ai

mid to late holocene organic carbon export variability at the southern boundary of the california current an approach based on diffuse spectral reflectance of marine sediment cores here we present the results obtained from diffuse spectral reflectance dsr on the visible wave spectra on a 4 5 m long calypso kasten core md02 2506 c2 collected from the san lazaro basin slb with the aim of reconstructing the mid to late holocene variability in export production in the california current system ccs we applied an r mode maximum likelihood factor analysis on the first derivative of the diffuse spectral reflectance we then compared the factor scores obtained with this method and the organic carbon oc content of the core in order to establish a statistical transfer function between both variables we eliminated high frequency noise with the aid of singular spectral analysis ssa from both records increasing the correlation between both variables r 0 71 p 0 001 these results indicated that dsr can be used as a reliable proxy of the oc content in high resolution slb sediments which we used to reconstruct past ccs organic carbon export variability our findings suggest changes in organic carbon production and export from the mid to late holocene most likely resulting from changing influences on the slb due to the interaction of the pacific decadal oscillation pdo and el nino

spectral reflectance of carbonate minerals in the visible and near infrared 0 35 2 55 microns calcite aragonite and dolomite

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

coupled rock eval pyrolysis and spectrophotometry for lacustrine sedimentary dynamics application for west central african rainforests kamalete and nguene lakes gabon in recent years nguene lake and kamalete lake gabon west central africa have been studied repeatedly providing comprehensive reconstructions of environmental changes over the last millennia both lakes are in different geomorphological and environmental settings they are therefore excellent sites to test new methodological approaches indeed the sedimentary cores provide various facies and the previous studies provide references for calibrating the results of new methods in this methodological issue the present study aims to evaluate the potential of spectrophotometric and rock eval coupled analysis to describe the holocene lake and marsh deposits from tropical moist forests this assessment is carried out on samples taken from two well documented reference cores the spectrophotometric analysis provides reproducible colour measurements which inform about the nature of the main colour bearing constituents coupled with rock eval pyrolysis this technique can be used to describe lithological changes and identify the probable source of sedimentary organic matter in the studied cases this approach identified the facies dominated by detrital terrigenous inputs iron bearing signature and high oi values and those associated with a more abundant primary production chlorophyll signature low oi and high hi providing a distinction between palustrine and lacustrine dynamics however although the facies are comparable sedimentary dynamics and sediment sources may vary depending on geomorphological and climatic contexts

numerical simulations of interactions between gravity waves and deep moist convection abstract this study uses a numerical model to simulate deep convection both in the tropics over the ocean and the midlatitudes over land the vertical grid that was used extends into the stratosphere allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates a large number of trajectories are used to evaluate the behavior of tracers in the troposphere and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere in addition fourier analysis is used to characterize the waves in the stratosphere it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers finally this study examines the wave energy flux as a means to provid

modeling study of a tropical squall type convective line abstract a multidimensional and time dependent cloud scale model is used to investigate the dynamic and micro physical processes associated with convective and stratiform regions within a tropical squall type convective line the evolution of the total convective and stratiform portions of rainfall is also estimated by using model output a three dimensional version of the model covers a horizontal domain about 96 96 km2 frequently the horizontal extent of an observed stratiform region is over a few hundred kilometers therefore a two dimensional version of the model with a 512 km horizontal length is also used to incorporate a complete stratiform region two dimensional model result recapture many interesting features as observed in particular the fractional portion of stratiform rain as well as its fractional area coverage are in good agreement with observations a significant amount of ice particles melted to rain near the freezing level in the trailing part of the modeled squall system during i

structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes abstract this study documents the precipitation and kinematic structure of a mature eastward propagating oceanic squall line system observed by instrumented aircraft during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare doppler radar and low level in situ observations are used to show the evolution of the convection from an initially linear nnw sse oriented convective line to a highly bow shaped structure with an embedded low to midlevel counterclockwise rotating vortex on its northern flank in addition to previously documented features of squall lines such as highly upshear tilted convection on its leading edge a channel of strong front to rear flow that ascended with height over a rear inflow that descended toward the convective line and a pronounced low level cold pool apparently fed from convective and mesoscale downdrafts from the convective line rearward the observations of this system showed distinct multiple maxima in updraft strength with

numerical simulation of the diurnal evolution of tropical island convection over the maritime continent abstract numerical simulations of the diurnal evolution of tropical island convection observed during the maritime continent thunderstorm experiment mctex are performed using the meteorological research institute nonhydrostatic model mri nhm the mri nhm is double nested within a form of the australian bureau of meteorology research centre s limited area assimilation and prediction system specially operated for the mctex period excellent agreement is found between the simulation and observed evolution of the convective clouds over the tiwi islands on 27 november 1995 a transition from horizontal convection occurring during the morning to vertical convection in afternoon is evident in the morning the sea breeze appears along the coastlines with a clear contrast evident in structure between the windward and leeward sides at the windward coast the sea breeze intrudes inland more rapidly where the larger surface heat flux modifies the lowest air mass and makes the sea breeze front sbf indistinct

a tropical squall line observed during toga coare extended comparisons between simulations and doppler radar data and the role of midlevel wind shear abstract results from a three dimensional cloud model are extensively compared with airborne doppler radar data in the case of a tropical oceanic squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment the comparison is based on the precipitation patterns the dynamical and thermodynamical distributions and the vertical transport of horizontal momentum the model simulates the evolution of the mesoscale convective system mcs frontal convective line from a quasi linear to a broken pattern the area located south of the break which designates the region where the mcs leading edge reorientates from the n s to the e w direction is composed of a pronounced bow shaped structure with two vortices located on both sides of a strong rear inflow the vertical circulation is characterized by a jump updraft and an overturning downdraft both structures exhibit a vertical intense updraft in the break zone whereas the jump updraft is more sloped and less in

sediment accumulation rates west of the mid atlantic ridge 35 n abstract although carbonate curves have a long history of use for temporal correlation only limited agreement concerning the reasons for down core carbonate variations has been reached in this study these variations are examined by analyzing absolute accumulation rates of both carbonate and terrigenous sediment components carbonate content was determined in nine cores from approximately 3000 5000 m water depth down core variation in carbonate was correlated to an oxygen isotope curve to establish a down core time stratigraphy weight percent carbonate carbonate accumulation rate and terrigenous sediment accumulation rate were plotted as a function of water depth and time 0 130 000 yrs b p the weight percent carbonate plot indicates that carbonate content decreases with increasing water depth however the carbonate accumulation rate data demonstrates that this decrease in weight percent carbonate does not result from a decrease in the carbonate accumulation rate in the deeper cores the accumulation rate of carbonate actually increases in these deep cores the increase in carbonate accumulation rate is offset by a larger increase in the accumulation rate of terrigenous sediment resulting in a decrease in weight percent carbonate high accumulation rates of both carbonate and terrigenous sediment in cores below 4250 m appears to result from transport and redeposition of sediment most of the carbonate sediment deposited in these deep cores appears to be derived from shallow areas of the mid atlantic ridge mar the terrigenous sediment probably results from deposition by deep currents

the subtropical nutrient spiral 1 we present an extended series of observations and more comprehensive analysis of a tracer based measure of new production in the sargasso sea near bermuda using the 3 he flux gauge technique the estimated annually averaged nitrate flux of 0 84 0 26 mol m 2 yr 1 constitutes only that nitrate physically transported to the euphotic zone not nitrogen from biological sources e g nitrogen fixation or zooplankton migration we show that the flux estimate is quantitatively consistent with other observations including decade timescale evolution of the 3 h 3 he inventory in the main thermocline and export production estimates however we argue that the flux cannot be supplied in the long term by local diapycnal or isopycnal processes these considerations lead us to propose a three dimensional pathway whereby nutrients remineralized within the main thermocline are returned to the seasonally accessible layers within the subtropical gyre we describe this mechanism which we call the nutrient spiral as a sequence of steps where 1 nutrient rich thermocline waters are entrained into the gulf stream 2 enhanced diapycnal mixing moves nutrients upward onto lighter densities 3 detrainment and enhanced isopycnal mixing injects these waters into the seasonally accessible layer of the gyre recirculation region and 4 the nutrients become available to biota via eddy heaving and wintertime convection the spiral is closed when nutrients are utilized exported and then remineralized within the thermocline we present evidence regarding the characteristics of the spiral and discuss some implications of its operation within the biogeochemical cycle of the subtropical ocean index terms 4808 oceanography biological and chemical chemical tracers 4845 oceanography biological and chemical nutrients and nutrient cycling 4805 oceanography biological and chemical biogeochemical cycles 1615 4820 oceanography biological and chemical gases keywords nutrients productivity tritium helium 3

effects of under resolved convective dynamics on the evolution of a squall line abstractsimulations of a squall line observed on 20 may 2011 during the midlatitude continental convective clouds experiment mc3e using 750 and 250 m horizontal grid spacing are performed the h

upwelling and primary production during the u s geotraces east pacific zonal transect the 2013 u s geotraces eastern pacific zonal transect epzt traversed the highly productive peruvian coastal upwelling pcu region in this work the flux of nitrate into the euphotic zone is derived for stations within the pcu using a previously developed method whereby dilution of the water column 7be inventory by upwelled 7be free water provides a means to infer upwelling rates furthermore with knowledge of upwelling rates 7be profiles are used to constrain vertical diffusivity within the upper thermocline these transport terms are applied to nitrate profiles to estimate net community production between 79 w and 104 w along the epzt which includes the zone of active upwelling to the edge of the oligotrophic gyre with a simple one dimensional model the calculated upwelling rates were inversely related to mixed layer temperature and ranged from 0 to 3 0 m d results using a depth dependent upwelling rate with a component of horizontal advection are also described vertical diffusivities near the base of the euphotic zone were in the range 1 7 4 5 10 4 m2 s these values are compared to those generated by analysis of temperature profiles net community production averaged 15 mmol c m2 d for stations between 84 w and 104 w and was 134 mmol c m2 d for the furthest inshore station at 79 w which displayed the lowest sst and greatest rate of upwelling

reflectance spectroscopy in the visible and near infrared 0 35 2 55 µm applications in carbonate petrology reflectance spectroscopy in the visible and near infrared 0 35 to 2 55 m offers a rapid inexpensive nondestructive tool for determining the mineralogy and for investigating the minor element chemistry of the hard to discriminate carbonate minerals and can in one step provide information previously obtainable only by the combined application of two or more analytical techniques when light interacts with a mineral certain wavelengths are preferentially absorbed the positions and widths of absorptions due to vibrations of the carbonate radical and the positions and shapes of absorptions due to transition metal cations if present can be used to determine mineralogy relative intensities of absorptions due to transition metal cations can be used to determine concentration of these cations because absorptions due to fe2 and mn2 occur in different regions of the spectrum the presence of one cation does not interfere with analysis for the other detection limits for mn2 are about 0 1 wt mn and for fe2 are about 0 01 wt fe this technique is also very sensitive to the presence of water and indicates that aqueous fluid inclusions are nearly ubiquitous in carbonate minerals and rocks spectra indicate that inclusions are particularly abundant in skeletal carbonates and that the quantity of inclusions in skeletal material varies from one type of organism to another spectra indicate that inclusions are lost during diagenesis of skeletal material providing a new criterion for diagenetic studies

on the dependence of squall line characteristics on surface conditions abstractthe influence of surface conditions in the form of changing surface temperatures on fully developed mesoscale convective systems mcss is investigated using a cloud system resolving setup of the icosahedral nonhydrostatic icon model 1 km grid spacing the simulated mcss take the form of squall lines with trailing stratiform precipitation after the squall lines have reached a quasi steady state secondary convection is triggered ahead of the squall line resulting in an increase of squall line propagation speed also known as discrete propagation the higher propagation speed is then maintained for the remainder of the simulations because secondary convection ahead of the squall line acts to reduce the environmental wind shear over the depth of the squall line s cold pool the surface conditions have only a marginal effect on the squall lines themselves this is so because the surface fluxes cannot significantly affect the cold pool which is continuously replenished by midtropospheric air t

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

quantitative reassessment of brick red lutites evidence from reflectance spectrophotometry abstract brick red lutites are distinctive bright red sediments deposited in the western north atlantic these unique sediments were derived from permo carboniferous outcrops in the canadian maritime provinces transported out the gulf of st lawrence through the cabot straits and redistributed by the western boundary undercurrent along the north american continental margin in this study we used fourteen cores taken off eastern north america to more precisely examine the input and depositional history of brick red lutites our study differs from previous studies in the manner in which the red sediment was identified unlike previous studies which used color charts to assess the presence of brick red lutites we used visible light reflectance spectrophotometry the primary mineral imparting a red color to brick red lutites is hematite experiments with known quantities of hematite in a matrix mineralogically similar to western north atlantic sediment indicate that the presence of hematite can be detected at weight percentages of less than 0 1 using spectral reflectance data we characterized the distribution of brick red lutites for two broadly defined time levels latest glacial and early holocene as expected the maximum input of brick red lutite was during late glacial time and input decreased reaching a minimum during the early holocene since the early holocene there has been little change in the distribution of this unique red sediment on the north american margin however our reflectance spectra indicate renewed accumulation of hematite rich sediment at the present time in the cabot straits

structure and evolution of the 22 february 1993 toga coare squall line numerical simulations abstract in this study a numerical cloud model is used to simulate the three dimensional evolution of an oceanic tropical squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment and investigate the impact of small scale physical processes including surface fluxes and ice microphysics on its structure and evolution the observed squall line was oriented perpendicular to a moderately strong low level jet salient features that are replicated by the model include an upshear tilted leading convective region with multiple updraft maxima during its linear stage and the development of a 30 km scale midlevel vortex and associated transition of the line to a pronounced bow shaped structure in this modeling approach only surface flukes and stresses that differ from those of the undisturbed environment are included this precludes an unrealistically large modification to the idealized quasi steady base state and thus allows us to more easily isolate effects of

spectrophotometer analysis of holocene sediments from an anoxic fjord saanich inlet british columbia canada abstract a borehole core through the holocene sediments of saanich inlet british columbia canada was analyzed using high resolution spectrophotometry to determine whether spectral signal variations can be used as environmental climatic proxies the effects of post drilling oxidation and water loss on the core sample were assessed by comparing spectral measurements taken onboard the research ship immediately after the core was opened with shore based measurements taken one year later for saanich inlet sediments the shore based measurements provided more reliable indications of the degree of basin anoxia our spectral analyses allowed us to identify all the major features of the saanich inlet sediment sequence mazama ash and fraser river drainage stratigraphic markers oxygenation state of the basin by using the first derivative value at 675 nm as a proxy for changes in organic matter content and the colorimetric parameter b as an indicator of diatom content we were able to recognize changes in terrestrially derived organic matter om and diatom concentrations in the sediment we suggest that these variations are due to changes in upwelling intensity and fluctuations in sea level during the holocene our results confirm the potential value of spectrophotometry in identifying sediment composition and in reconstructing paleoenvironments

a comparison of the results of a two dimensional numerical simulation of a tropical squall line with observations abstract a comparison of the results of a two dimensional numerical simulation of a tropical squall line with observations shows good agreement in most respects the two dimensional model should provide a valuable research tool for understanding the physical processes that are taking place and for discovering the effects of different wind and thermodynamic environments on squall line characteristics in the simulation high pressure develops ahead of the system relative to that behind at most levels the momentum flux is mainly confined to below 6 km and in the region of strong convection the squall line is multicellular and significant perturbations are associated with convection embedded in the stratiform region considerable horizontal accelerations occur at large distances from the region of strong convection away from the system aloft and towards it at low levels the effect of excluding the ice phase in the simulation is shown to lead to cloud tops some 3 km lower than when it is incorporated alth

mountain wave like spurious waves associated with simulated cold fronts due to inconsistencies between horizontal and vertical resolutions a newly developed global nonhydrostatic model is used for life cycle experiments lces of baroclinic waves and the resolution dependency of frontal structures is examined lces are integrated for 12 days with horizontal grid intervals ranging from 223 to 3 5 km in a global domain in general fronts become sharper and corresponding vertical flow strengthens as horizontal resolution increases however if the ratio of vertical and horizontal grid intervals is sufficiently small compared to the frontal slope s the overall frontal structure remains unchanged in contrast when the ratio of horizontal and vertical grid intervals exceeds 2s 4s spurious gravity waves are generated at the cold front a linear model for mountain waves quantitatively explains the mechanism of the spurious waves the distribution of the basic wind is the major factor that determines wave amplitude and propagation the spurious waves propagate up to a critical level at which the basic wind speed normal to the front is equal to the propagation speed of the front results from the linear model suggest that an effective way to eliminate spurious waves is to choose a stretched grid with a smaller vertical grid interval in lower layers where strong horizontal winds exist

cloud resolving simulations of deep convection over a heated mountain abstract cloud resolving numerical simulations of airflow over a diurnally heated mountain ridge are conducted to explore the mechanisms and sensitivities of convective initiation under high pressure conditions the simulations are based on a well observed convection event from the convective and orographically induced precipitation study cops during summer 2007 where an isolated afternoon thunderstorm developed over the black forest mountains of central europe but they are idealized to facilitate understanding and reduce computational expense in the conditionally unstable but strongly inhibited flow under consideration sharp horizontal convergence over the mountain acts to locally weaken the inhibition and moisten the dry midtroposphere through shallow cumulus detrainment the onset of deep convection occurs not through the deep ascent of a single updraft but rather through a rapid succession of thermals that are vented through the mountain convergence zone into the deepening cloud mass emerging t

alternative methods for specification of observed forcing in single column models and cloud system models we discuss alternative methods for prescribing advective tendencies in single column models scms and cloud system models these include revealed forcing in which the total advective tendency is prescribed from observations horizontal advective forcing in which the horizontal advective tendencies are prescribed together with the observed vertical motion which is combined with the predicted sounding to determine the tendencies due to vertical advection and relaxation forcing in which the horizontal advective tendencies are computed by relaxing the sounding toward the observed upstream sounding with a relaxation timescale determined by the time required for the wind to carry parcels across the grid column when relaxation forcing is used the horizontal advective tendencies can be diagnosed from the model output and compared with the corresponding observed tendencies we present scm results to illustrate these three forcing methods based on data from several field experiments in both the tropics and the midlatitudes each method is shown to have its strengths and weaknesses overall the results presented here do not show unambiguous differences between revealed forcing and horizontal advective forcing the two methods appear to be generally comparable revealed forcing may therefore be preferred for its simplicity relaxation forcing guarantees realistic soundings of the state variables but can produce large errors in parameterized processes which are driven by rates e g fluxes rather than states in particular relaxation forcing gives large errors in the precipitation rate in this model we demonstrate that relaxation forcing leads to unrealistically high low precipitation in versions of the model which tend to produce unrealistically dry humid soundings the observed horizontal advective tendencies in the tropics are so weak especially for temperature that small absolute errors in the diabatic tendencies diagnosed with relaxation forcing can lead to large relative errors in the diagnosed horizontal advective tendencies

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

a gcss model intercomparison for a tropical squall line observed during toga coare i cloud resolving models results from eight cloud resolving models are compared for the first time for the case of an oceanic tropical squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment there is broad agreement between all the models in describing the overall structure and propagation of the squall line and some quantitative agreement in the evolution of rainfall there is also a more qualitative agreement between the models in describing the vertical structure of the apparent heat and moisture sources the three dimensional 3d experiments with an active ice phase and open lateral boundary conditions along the direction of the system propagation show good agreement for all parameters the comparison of 3d simulated fields with those obtained from two different analyses of airborne doppler radar data indicates that the 3d models are able to simulate the dynamical structure of the squall line including the observed double peaked updraughts however the second updraught peak at around 10 km in height is obtained only when the ice phase is represented the 2d simulations with an ice phase parametrization also exhibit this structure although with a larger temporal variability in the 3d simulations the evolution of the mean wind profile is in the sense of decreasing the shear but the 2d simulations are unable to reproduce this behaviour

a parameterization of mesoscale enhancement of surface fluxes for large scale models abstract the paper investigates the enhancement of surface fluxes by atmospheric mesoscale motions the authors show that horizontal wind variabilities induced by these motions i e gustiness need to be considered in the parameterization of surface fluxes used in general circulation models gcms as they always occur at subgrid scale it is argued that there are two different sources of gustiness deep convection and boundary layer free convection the respective scales time and length and the convective patterns are very different for each of these sources a general parameterization of the gustiness distinguishing these two effects is proposed for boundary layer free convection the gustiness is related to the free convection velocity to establish this relationship both observations and numerical simulations are used revisiting the coupled ocean atmosphere response experiment data the authors propose a new value of the proportionality coefficient that links the free convection velocity and th

on the mass flux representation of vertical transport in moist convection abstractthis study investigates to what extent the convective fluxes formulated within the mass flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large eddy simulations less of six well documented cloud cases including both deep and shallow convection two methods are used to decompose the les resolved vertical fluxes decompositions based on the coherent convective features using the mass flux top hat profile and by two dimensional fast fourier transform 2d fft in terms of wavenumbers the analyses show that the convective fluxes computed using the mass flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction a result consistent with the mass flux dynamic view of moist convection and previous studies however

organic carbon accumulation in baffin bay and paleoenvironment in high northern latitudes during the past 20 m y the results of the investigation of organic carbon deposition in baffin bay provide important information about paleoenvironmental evolution in high northern latitudes during cenozoic time during miocene to quaternary time organic carbon enrichment of up to 3 insediments sampled at ocean drilling program site 645 was controlled mainly by increased supply of terrigenous organic matter two distinct maxima were identified 1 a middle miocene maximum possibly reflecting a dense vegetation cover and fluvial sediment supply from adjacent islands which decreased during late miocene and early pliocene time because of expansion of tundra vegetation due to global climatic deterioration 2 a late pliocene pleistocene maximum probably caused by glacial erosion and meltwater outwash significant amounts of marine organic carbon were deposited in baffin bay during middle miocene time suggesting higher surface water productivity triggered by the inflow of cold and nutrient rich arctic water masses the decrease in average surface water productivity to values similar to those of modern baffin bay occurred during the late miocene and were probably caused by development of a seasonal sea ice cover reaching maximum expansion during the past 3 4 m y

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values

a dual tracer approach to estimate upwelling velocity in coastal southern california abstract the distribution of the cosmogenic radionuclide 7be t 1 2 53 d in the surface ocean has previously been used to estimate upwelling velocity in the open ocean however the loss of 7be to particle export has limited this approach in high particle density environments like the continental margins in this study we combine a mass balance of 7be with a 234th budget in the surface ocean to constrain the loss of 7be to particle sinking at the san pedro ocean time series spot in the inner southern california bight during spring 2013 upwelling velocities all in m d 1 determined from the 7be mass balance were observed to increase from 0 5 0 6 in january to 2 5 1 3 in may then decrease to 1 2 0 5 in june these results agree within uncertainty with upwelling velocities derived from the monthly bakun upwelling index which ranged from 0 1 to 2 8 m d 1 supporting the pressure field based approach evidence from a heat budget and the nutrient distribution over the course of the study supports that the upwelling signal at spot 20 km offshore is not transported from coastal upwelling near shore but instead is dominantly a local signal likely driven by wind stress curl