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

electrical resistivity imaging of the architecture of substream sediments 1 the modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments there are few methods for noninvasive characterization of streambeds invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments and we have applied the use of one of those techniques to streambeds we demonstrate through two examples how electrical resistivity imaging can be utilized for characterization of subchannel architecture in the first example electrodes installed in riparian boreholes and on the streambed are used for imaging under the river bed the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk in the second example electrical resistivity images determined from data collected using electrodes installed on the river bed provide a constrained estimate of the sediment volume behind a log jam vital to modeling biogeochemical exchange which had eluded measurement using conventional drilling methods owing to the boulder content of the stream the two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels

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 comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

high archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3 5 ga swaziland supergroup south africa new and compiled oxygen isotope data combined with the results of geological and sedimentological studies demonstrate that enclaves of synsedimentary to very early diagenetic cherts are widely preserved in the 3 5 3 2 ga swaziland supergroup barberton greenstone belt south africa the low 1 8 o values of these cherts indicate extremely high ocean temperatures of 55 85 c previously the large depletion in 1 8 o shown by all barberton cherts relative to their phanerozoic counterparts has been attributed to low 1 8 o in archean oceans chert formation during late diagenesis wholesale loss of 1 8 o during alteration and or regional silicification of sediments around hot springs these alternative explanations are not compatible with the new results cherts in the onverwacht group display an isotopic stratigraphy that is inversely repeated in conglomerates in the overlying fig tree and moodies groups demonstrating that the chert 8 0 o values were fixed prior to archean uplift and erosion which started at 3 26 ga the maximum 1 8 o value in barberton cherts 22 is lower than the minimum values 23 in phanerozoic bedded cherts precluding late diagenesis as the explanation of the overall low 1 8 o values regional metamorphic hydrothermal or long term resetting of original 1 8 o values is also precluded by preservation of 1 8 o values across different metamorphic grades and by systematic 1 8 o differences among interbedded chert types stratigraphic units and conglomerate clasts the 7 1 8 o variation of these archean cherts is similar to that of phanerozoic deep sea cherts formed when opal converted to microquartz during burial but the actual archean values are 10 lower marine opal was apparently converted to microquartz during burial to depths of 1 km cherts with 1 8 o 15 reflect conversion during deepest burial or in local areas of enhanced geothermal gradient and or hydrothermal activity cherts with higher 1 8 o values formed during early diagenesis and indicate an extremely hot archean ocean and surface environment

simple data processing of tripotential apparent resistivity measurements as an aid to the interpretation of subsurface structure the advantages of the wenner tripotential method carpenter 1955 for apparent resistivity profiling are described and two new data processing techniques introduced as an aid to the interpretation of apparent resistivity sections pseudo sections these techniques were developed from model data computed using a two dimensional finite difference method oscillatory components present in anomalies on tripotential profiles and related to electrode spacing are shown to be effectively removed by linear filtering that also simplifies their form and aids recognition furthermore it is shown that the ratio of the beta and gamma apparent resistivities is a good indicator of resistivity variation and is particularly sensitive to lateral change model data indicates that over a wide range of conditions enough subsurface information can be obtained by inspection of tripotential resistivity and ratio profiles and from space sections to make possible a useful and sometimes semi quantitative interpretation a rationale for the general interpretation of tripotential data is developed field data are described from an area of weathered granite basement in nigeria a model of the subsurface is developed using parameters derived from the processed observations the observed and calculated apparent resistivity space sections are very similar

resistivity of rock salt in asse germany and petrophysical aspects1 this paper reports that in the asses salt mine germany where extensive research is carried out on various aspects of nuclear waste disposal in rock salt formations the resistivity of a future construction site for a test seal at a depth of 945 m has been investigated measurements have been conducted using various types of the four point electrode configuration on a network of 180 electrodes permanently installed in boreholes a fully computer controlled measurement system has been built consisting of a resistivity meter a switchbox for electrodes and a computer with special control software the system has interactive and programmable automatic working modes with an extensive capability for documentation and processing including the immediate evaluation of apparent resistivities and is suitable for long term continuous observations the average resistivity at the site which consists of almost homogeneous stassfurt rock salt is approximately 0 6 times 10 sup 6 omega m with little variation there is a small anomaly due to a conductive inclusion probably a local anhydrite band there is not indication of anisotropy so far and no significant change with time the specific amount of water in the effective pores and its change can be estimated from the observed resistivities using the extended form of archie smore equation with pore saturation included in this case data for the specific internal surface from samples are available and the order of permeability may be estimated using the formation factor derived from resistivities less

palaeoclimatology evidence for hot early oceans reply robert chaussidon the possibility of a change in 18o values of the oceans has been discussed for the past 30 years1 and the comment by shields and kasting2 does not really bring any new insight into this issue the carbonate 18o curve3 is indistinguishable from that of cherts and shows a huge scatter caused by local geological processes this scatter in 18o up to 20 at a given age far exceeds the sensitivity of the isotope thermometer about 2 per 10 c it therefore prevents any precise additional test of the model and no consensus was ever reached in the literature on this debate from oxygen isotope data alone our approach4 by contrast was to try to find another isotopic proxy 30si that could bring new and independent constraints to test the hypothesis of hot oceans in the early precambrian our interpretation of the 30si values in terms of temperature is fully coherent not only with the 18o of cherts but also with that of marine carbonates and certainly does not overlook these data in addition we indicated4 that our sample set has not the time resolution that would be necessary to look for an effect on silicon isotopes of precambrian global glaciations no chert samples from such periods were analysed

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

radar frequency dielectric dispersion in sandstone implications for determination of moisture and clay content 1 the relationship between dielectric permittivity water saturation and clay content for the sherwood sandstone from ne england was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer dielectric permittivity was measured over the full range of saturation levels for various lithologies ranging from clean medium grained sandstone to fine grained sandstone containing up to 5 clay using a specially constructed dielectric cell dielectric constant kr is largely independent of frequency between 350 mhz and 1000 mhz below 350 mhz kr of fine grained clay rich sandstone shows frequency dispersion tests on physical models of the sandstone consisting of a fine fraction of ottawa sand and montmorillonite clay indicate that the clay minerals within the sandstone are responsible for its frequency dispersive behavior these tests also show that increasing pore fluid salinity increases dielectric dispersion at the lower end of the frequency range which indicates that this arises from the interfacial maxwell wagner mechanism associated with platy clay particles water saturated sand clay mixtures show very low dielectric constants at high frequencies over 650 mhz this effect is independent of salinity and probably results from the layered geometric arrangement of solids bound and free water within the swelling clay the complex refractive index method crim with a mineral dielectric constant of about 5 provides a good match to the water saturation versus dielectric constant data for all sherwood sandstone lithologies at frequencies between 350 and 1000 mhz and for clay poor sandstone at lower frequencies below 350 mhz the presence of a few percent of clay in some sherwood sandstone lithologies raises their crim best fit mineral dielectric constant substantially

resistivity and percolation study of preferential flow in vadose zone at bokhorst germany traditional nondestructive resistivity techniques have been applied in combination with tracer displacement and conventional soil moisture recording methods i e buried tensiometer and time domain reflectometry tdr for studying flow processes at an arable site in bokhorst germany three water infiltration experiments were carried out using tap water spiked with a nonreactive tracer at different concentrations the study aimed at exploring the capabilities of these combined techniques for tracing the preferential movement of water in the uppermost 1 5 m of the highly heterogeneous vadose zone the results illustrate that the applied tensiometer and tdr techniques can detect the relatively fast flow process at their position points and thus only tentatively trace the preferential flow the additional application of the resistivity method can trace the preferential flow paths continuously along the plane of measurements the results of the individual applied methods complement and confirm each other

neoarchean deep marine paleotemperature evidence from turbidite successions abstract numerous studies using various proxies have been conducted to ascertain the temperature of the archean ocean if as some of these investigations indicate the archean ocean was relatively hot with a cooling trend through time to the phanerozoic this would have had consequences for sediment erosion transport and deposition substantially higher surface temperatures would cause the viscosity of water an important variable in defining flow hydrodynamics to be lowered in particular less viscous water would have affected the development of current ripples these are dependent on the existence of the laminar sublayer as the sweeps of turbulent eddies impinging on this layer build small mounds that evolve into ripples the laminar sublayer thins at higher temperatures allowing sand grains of smaller sizes to destroy it at modern surface temperatures current ripples cannot form in coarse grained sands and if a hotter ocean existed in the archean it would have inhibited current ripple formation in medium grained sands and possibly even fine grained sands examination of numerous neoarchean deep water turbiditic successions in western superior province led to the realization that ripple cross lamination is rare in all these units as the formation of current ripples is dependent on the flow depositing sediment of the proper grainsize velocities in the appropriate range and existence of a viscous sublayer and the first two prerequisites were met during deposition from these decelerating turbidity currents the existence of the viscous sublayer during the majority of flows must be questioned the occurrence of current ripple cross lamination in well exposed turbidites of the neoarchean mckellar harbour formation was quantified and found to be substantially less than the abundance of ripple cross lamination present in phanerozoic turbidites indicating that the neoarchean deep ocean may have been considerably warmer than the deep ocean of today

palaeoclimatology evidence for hot early oceans arising from f robert m chaussidon 969 972 2006 10 1038 nature05239 robert chaussidon reply the oxygen isotopes in sedimentary cherts siliceous sediments have been used to argue that the precambrian oceans were hot with temperatures of up to 70 c at 3 3 gyr before present1 robert and chaussidon2 measure silicon isotopes in cherts and arrive at a similar conclusion we suggest here that both isotope trends may be caused by variations in seawater isotope composition rather than in ocean temperatures if so then the climate of the early earth may have been temperate as it is today and therefore more consistent with evidence for precambrian glaciations and with constraints inferred from biological evolution

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

shallow to deep transition of continental moist convection cold pools surface fluxes and mesoscale organization abstractlarge eddy simulation is used to investigate the effects of cold pools driven by rain evaporation on the shallow to deep convection transition over land the physically consistent methodolo

control of deep convection by sub cloud lifting processes the alp closure in the lmdz5b general circulation model recently a new conceptual framework for deep convection scheme triggering and closure has been developed and implemented in the lmdz5b general circulation model based on the idea that deep convection is controlled by sub cloud lifting processes such processes include boundary layer thermals and evaporatively driven cold pools wakes which provide an available lifting energy that is compared to the convective inhibition to trigger deep convection and an available lifting power alp at cloud base which is used to compute the convective mass flux assuming the updraft vertical velocity at the level of free convection while the alp closure was shown to delay the local hour of maximum precipitation over land in better agreement with observations it results in an underestimation of the convection intensity over the tropical ocean both in the 1d and 3d configurations of the model the specification of the updraft vertical velocity at the level of free convection appears to be a key aspect of the closure formulation as it is weaker over tropical ocean than over land and weaker in moist mid latitudes than semi arid regions we propose a formulation making this velocity increase with the level of free convection so that the alp closure is adapted to various environments cloud resolving model simulations of observed oceanic and continental case studies are used to evaluate the representation of lifting processes and test the assumptions at the basis of the alp closure formulation results favor closures based on the lifting power of sub grid sub cloud processes rather than those involving quasi equilibrium with the large scale environment the new version of the model including boundary layer thermals and cold pools coupled together with the deep convection scheme via the alp closure significantly improves the representation of various observed case studies in 1d mode it also substantially modifies precipitation patterns in the full 3d version of the model including seasonal means diurnal cycle and intraseasonal variability

electric study of fracture anisotropy at falkenberg germany electric and electromagnetic methods have been applied for mapping subsurface fractures and the directional dependence of in situ electric parameters at the hot dry rock site at falkenberg germany this study includes the determination of several anisotropy parameters like the mean longitudinal and transverse resistivity components m x1d4c1 and t respectively the anisotropy coefficient and the strike angle terrain conductivity measurements using the technique of frequency domain electromagnetic induction reveal a dominant anomaly strike of east south east west north west nearly parallel to the fracturing strike of n110 with increasing distance from the central borehole the mise a la masse potential differences exhibit a transition from a direct to a paradoxical relationship to the resistivity anisotropy induced by the fracturing these observations are explained using a model for an ellipsoidal fracture the qualitative interpretation of the sounding data of schlumberger and crossed square

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

borehole time domain reflectometry in layered sandstone impact of measurement technique on vadose zone process identification the hydraulic behaviour of the vadose zone of a layered sandstone aquifer has been investigated using borehole based time domain reflectometry tdr both a commercially available portable packer tdr system trime b3l borehole packer probe and specially designed borehole emplaced tdr probes were used to monitor seasonal fluctuations in water content in the vadose zone of a layered sandstone over 1 year under natural rainfall loading the data show that the vadose zone contains seasonal perched water tables that form when downward percolating water reaches layers of fine grained sandstone and siltstone and causes local saturation the formation of perched water tables is likely to lead to lateral flow bypassing the less permeable finer layers this contrasts with behaviour inferred from previous studies of the same aquifer that used borehole radar and resistivity which suggested its vadose zone behaviour was characterized by uniform downwards migration of wetting fronts to investigate the impact of measurement technique on observed response the tdr data reported here were used to produce simulated zero offset profile zop borehole radar responses this simulation confirmed the limited ability of zop borehole radar to detect key vadose zone processes because the phenomenon of critical refraction minimizes the sensitivity of the results to high water content layers the ability of the resistivity method to detect perched water table responses is also limited because of the relatively large sampling volume of the technique the study illustrates that inappropriate technique selection results in hydrological process mis identification with serious consequences for the usefulness of data in hydrological modeling

shifting the diurnal cycle of parameterized deep convection over land 1 in most atmospheric circulation models used for climate projections cloud and convective processes are not explicitly resolved but parameterized such models are known to produce a diurnal cycle of continental thunderstorms in phase with insolation while observed precipitation peaks in late afternoon we propose a new approach which corrects this long standing bias of parameterized convection in this approach deep convection triggering and intensity are controlled by sub cloud processes here boundary layer thermals and gust fronts and potentially orography or surface heterogeneities the representation of the diurnal cycle of deep convection is greatly improved in 1d mode with rainfall maximum delayed from midday to late afternoon provided parameterizations account for the key role played by shallow cumulus in preconditioning deep convection and by gust fronts in the self sustaining of thunderstorms in the afternoon

a numerical investigation of squall lines part ii the mechanics of evolution abstract the physical processes involved in the evolution of the model squall line presented in part i of this study are examined it is found that both the thermal and dynamic effects are important in the development of the midlevel meso scale low pressure zone located just to the rear of the convective core based on this observation a positive feedback mechanism is proposed to explain the abrupt transformation of the more or less upright convection line into a quasi steady meso scale convective system possessing an extensive trailing stratiform region in order to set the stage for this transformation to take place the convective updraft is required to possess an initial upshear tilt qualitative arguments are given to show that this initial tilt might be the result of a moderate wind shear at low levels and none or reverse shear in the middle to high levels results from model sensitivity experiments are presented to support the theory in addition to the dynamic effects of the low level wind sh

microscale oxygen isotope variations in 1 9 ga gunflint cherts assessments of diagenesis effects and implications for oceanic paleotemperature reconstructions abstract variations in the oxygen isotope composition 18 o of five cherts from the 1 9 ga gunflint iron formation canada were studied at the micrometer scale by ion microprobe to try to better understand the processes that control 18 o values in cherts and to improve seawater paleotemperature reconstructions gunflint cherts show clearly different 18 o values for different types of silica with for instance a difference of 15 between detrital quartz and microquartz microquartz in the five samples is characterized by large intra sample variations in 18 o values 18 o of quartz varies from 4 6 to 6 6 at the 20 m scale and from 12 to 14 at 2 m scale isotopic profiles in microquartz adjacent to hydrothermal quartz veins demonstrate that microquartz more than 200 m away from the veins has preserved its original 18 o value at the micrometer spatial resolution of the ion probe data reveal that microquartz has preserved a considerable 18 o heterogeneity that must be regarded as a signature inherited from its diagenetic history modelling of the 18 o variations produced during the diagenetic transformation of sedimentary amorphous silica precursors into microquartz allows us to calculate seawater temperature t sw at which the amorphous silica precipitated and diagenesis temperature t diagenesis at which microquartz formed that reproduce the 18 o distributions mean range and shape measured at micrometer scale in microquartz the two critical parameters in this modelling are the 18 o value and the mass fraction of the diagenetic fluid under these assumptions the most likely ranges for t sw and t diagenesis are from 37 to 52 c and from 130 to 170 c respectively

convection in gate the difficult problem of parameterizing tropical convection in large scale models of the atmosphere led to the global atmospheric research program s atlantic tropical experiment gate whose goal was to improve basic understanding of tropical convection and its role in the global atmospheric circulation a dense network of instrumented ships equipped with upper air sounding equipment and quantitative weather radars were located over the atlantic ocean in the intertropical convergence zone itcz just west of equatorial africa the ship network was supplemented by a fleet of research aircraft and a geosynchronous meteorological satellite the data obtained show that the deep convection in the itcz was concentrated in two types of cloud clusters rapidly moving squall clusters and slowly moving nonsquail clusters the clusters were characterized by large mid to upper level cloud shields or anvil clouds that emanated from penetrative cumulonimbus convection accompanying the deep cumulonimbus in each cluster was a log normal spectrum of smaller convective features ranging from moderate cumulonimbus down to tiny nonprecipitating cumulus the large cumulonimbus were typically grouped within a cluster into one or more mesoscale precipitation features or mpf s which were apparently triggered in mesoscale regions of intensified low level convergence as an mpf matured it developed a region of stratiform precipitation adjacent to its active deep convective cells the stratiform precipitation fell from the anvil cloud associated with the stratiform precipitation were a mesoscale downdraft below the anvil cloud and an apparent mesoscale updraft within the anvil cloud itself above the mesoscale downdraft these mesoscale drafts were distinct from the convective scale updrafts and downdrafts of the cumulus and cumulonimbus cells of the cluster downdrafts both convective scale and mesoscale filled the planetary boundary layer in the vicinity of cumulonimbus with stable air of low moist static energy these wakes of downdraft air exerted a strong control on where future convection broke out the results of gate show that to simulate the effects of tropical convection in large scale numerical models of the atmosphere a variety of phenomena must be accounted for including not only convective scale updrafts and downdrafts but anvil clouds with mesoscale updrafts and downdrafts downdraft induced boundary layer transformations and mesoscale convergence patterns experimentation with ways of including some of these features of tropical convection in large scale diagnostic and prognostic studies is under way but much work remains to be done

a salt tracer test monitored with surface ert to detect preferential flow and transport paths in fractured karstified limestones in hard rock aquifers fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths one critical issue in hydrogeological research is to identify characterize and monitor such fractured zones at a representative scale a tracer test monitored with surface electrical resistivity tomography ert could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer however multiple challenges exist including the lower resolution of surface ert compared with crosshole ert the finite time that is needed to complete an entire data acquisition and the strong dilution effects we conducted a natural gradient salt tracer test in fractured limestones to account for the high transport velocity we injected the salt tracer continuously for four hours at a depth of 18 m we monitored its propagation with two parallel ert profiles perpendicular to the groundwater flow direction concerning the data acquisition we always focused

quantitative imaging of solute transport in an unsaturated and undisturbed soil monolith with 3 d ert and tdr electrical resistivity tomography ert has proved to be a valuable tool for imaging solute transport processes in the subsurface however a quantitative interpretation of corresponding ert results is constrained by a number of factors one such factor is the nonuniqueness of the ert inverse problem if no additional constraints are imposed in the vadose zone further problems arise from the general ambiguity of the imaged bulk electrical conductivity in terms of water content and solute concentration in this study we address these issues in detail for a solute tracer experiment conducted in an undisturbed unsaturated soil monolith where the tracer transport was monitored by means of 3 d smoothness constrained ert and time domain reflectometry tdr measurements the experimental design allowed the determination of solute tracer concentrations directly from imaged bulk electrical conductivity independent tdr data and effluent tracer concentrations provided a ground truth for the ert derived apparent convection dispersion equation transport parameters the apparent transport velocity calculated from the ert results was consistent with that based on tdr data and the sampled effluent independent of the degree of smoothness imposed in the ert inversion on the other hand the apparent dispersivity calculated from the ert results was larger than that estimated from tdr data but smaller than that estimated from the sampled effluent with the magnitude of deviations dependent on the degree of smoothing importantly no mass balance problems were observed in the ert results we believe that this is largely a consequence of the uniform application of the tracer as a front and of the configuration of the electrode array with respect to the main transport direction in conclusion the study demonstrates that ert can yield unprecedented quantitative information about local and column scale solute transport characteristics in natural soils

a dual mass flux framework for boundary layer convection part ii clouds this paper presents the extension of the eddy diffusivity mass flux edmf framework for turbulent transport into the statistical modeling of boundary layer clouds the advection diffusion decomposition that defines edmf is projected onto the turbulent distribution as used in the statistical cloud model each edmf component is thus assigned its own independent probability density function pdf resulting in an updraft pdf and a diffusive pdf this double pdf system is configured and integrated in conserved variable space with the position and orientation of each pdf determined by its unique nature the parameterization of the associated updraft diffusion decomposition of variance introduces close ties to the transport scheme whereas the grid box mean variance is reconstructed using a prognostic variance budget the variance of the updraft component is parameterized as a function of the spread among various resolved model updrafts individual model components and the scheme as a whole are evaluated in detail against large eddy simulations of a number of prototype subtropical trade wind cases the results show that various structures in cloud fraction condensate and variance are reproduced the diffusive pdf acts to represent stratiform clouds the advective pdf represents cumuliform clouds in conditionally unstable layers this allows representation of complex scenarios in which both cloud forms occur such as the transitional trade wind regime featuring cumulus rising into stratocumulus

why the oxygen isotopic composition of sea water changes with time the oxygen isotopic composition of oxygen in minerals and oxygen in water this sea water is determined by interactions with equilibrium fractionation is a strong function of fresh silicate rocks interactions at high temperature varying for many minerals from about

gpr study of pore water content and salinity in sand high resolution studies of hydrological problems of the near surface zone can be better accomplished by applying ground probing radar gpr and geoelectrical techniques the authors report on gpr measurements 500 and 900 mhz antennae which were carried out on a sorted clean sand both in the laboratory and at outdoor experimental sites the outdoor sites include a full scale model measuring 5 x 3 x 2 4 m sup 3 with three buried sand bodies saturated with water of various salinities studies investigate the capability of gpr to determine the pore water content and to estimate the salinity these parameters are important for quantifying and evaluating the water quality of vadose zones and aquifers the radar technique is increasingly applied in quantifying soil moisture but is still rarely used in studying the problems of water salinity and quality the reflection coefficient at interfaces is obtained from the amplitude spectrum in the frequency and time domains and is confirmed by 1d wavelet modelling in addition the gpr velocity to a target at a known depth is determined using techniques of two way traveltime cmp semblance analysis and fitting an asymptotic diffraction curve the results demonstrate that the reflection coefficient increases with increasing salinity of the moisture thesemore results may open up a new approach for applications in environmental problems and groundwater prospecting e g mapping and monitoring of contamination and evaluation of aquifer salinity especially in coastal areas with a time varying fresh water lens less

representing equilibrium and nonequilibrium convection in large scale models a new diagnostic convective closure which is dependent on convective available potential energy cape is derived under the quasi equilibrium assumption for the free troposphere subject to boundary layer forcing the closure involves a convective adjustment time scale for the free troposphere and a coupling coefficient between the free troposphere and the boundary layer based on different time scales over land and ocean earlier studies with the ecmwf integrated forecasting system ifs have already demonstrated the model s ability to realistically represent tropical convectively coupled waves and synoptic variability with use of the standard cape closure given realistic entrainment rates a comparison of low resolution seasonal integrations and high resolution short range forecasts against complementary satellite and radar data shows that with the extended cape closure it is also possible independent of model resolution and time step to realistically represent nonequilibrium convection such as the diurnal cycle of convection and the convection tied to advective boundary layers although representing the late night convection over land remains a challenge a more in depth regional analysis of the diurnal cycle and the closure is provided for the continental united states and particularly africa including comparison with data from satellites and a cloud resolving model crm consequences for global numerical weather prediction nwp are not only a better phase representation of convection but also better forecasts of its spatial distribution and local intensity

possible evidence for episodic epeiric marine and fluvial sedimentation and implications for palaeoclimatic conditions c 2 3 1 8 ga kaapvaal craton south africa abstract the debate on palaeoproterozoic atmospheric composition climate and the timing and nature of the postulated great oxidation event possibly at c 2 3 ga remain matters of debate within precambrian geology this paper contributes to the debate through examination of physical sedimentary structures preserved within two separate groups of sedimentary deposits from the central and northern portions of the kaapvaal craton south africa within the c 2 3 2 1 ga pretoria group study of epeiric marine sandstones and mudrocks magaliesberg and silverton formations c 2 1 ga suggests that fluvial input was predominant over low energy reworking by waves winds and tides this together with extensive evidence for microbial mat growth within the littoral sandstones of the magaliesberg formation points to strongly episodic sedimentation by both marine and fluvial processes within two younger basins belonging to the c 2 05 1 8 ga waterberg group anomalously high palaeoslopes calculated according to standard palaeohydrological methods combined with direct field evidence for sediment gravity flows and sheetflood deposition within an overall braided fluvial setting again suggest episodic sedimentation strongly episodic sedimentation can most easily be reconciled with a greenhouse palaeoclimate at least for that part of kaapvaal at that time taken together these data sets point to the postulate that the generally accepted change from a palaeoproterozoic greenhouse through a great oxidation event c 2 3 ga to less extreme climatic conditions may have been gradational and even diachronous across the earth s cratons at that time

origin and mechanisms of k si metasomatism of ca 3 4 3 3ga volcaniclastic deposits and implications for archean seawater evolution examples from cherts of kittys gap pilbara craton australia and msauli barberton greenstone belt south africa abstract the effects of k si metasomatism during the formation of early archean replacement cherts have been quantified in this study by the investigation of two well known stratigraphic sections the msauli chert mc barberton greenstone belt south africa and the kittys gap chert kgc pilbara craton western australia the kgcs have a dacitic precursor similar to duffer formation dacites pilbara craton while the mcs are derived from al depleted komatiites similar to those from the weltevreden formation barberton greenstone belt mass balance calculations reveal that the volcaniclastic deposits had initial porosities of up to 85 vol for the kgc and of 65 vol for the mc secondary porosities 27 vol mc 8 vol kgc produced during k metasomatism are proportional to the dissolution of fe ca mg rich glass and precursor minerals komatiites have a higher chemical exchange potential than dacites each gram releasing 1 2 mmol fe2 2 8 mmol mg2 1 4 mmol ca2 and 1 1 mmol na to seawater together with 4 4 mmol o2 k metasomatism of 1 g of komatiite further implies an uptake of 0 67 mmol of k and 2 7 mmol of h the highest silica uptake is achieved for the kgc 82 mmol g of precursor this silica enrichment most likely operated in the water column and at the sediment water interface by sorption mechanisms on the surface of detrital particles and particulate organic matter as a result of seawater silica saturation acidic conditions ph 5 5 6 5 and hot temperatures 70 c favored the formation of k rich phyllosilicates by interaction with seawater during the early diagenetic alteration of the volcaniclastic particles the widespread occurrence of k si metasomatism in volcanic and sedimentary rocks can be regarded as a general alteration process of the early archean seafloor with a major influence on seawater composition the highly k selective metasomatism confirms previous studies suggesting that the archean ocean was acidic and probably in equilibrium with a co2 rich atmosphere

multiscale interactions in an idealized walker cell analysis with isentropic streamfunctions abstracta new approach for analyzing multiscale properties of the atmospheric flow is proposed in this study for that the recently introduced isentropic streamfunctions are employed here for scale decomposition with haar wavelets this method is applied subsequently to a cloud resolving simulation of a planetary walker cell characterized by pronounced multiscale flow the resulting set of isentropic streamfunctions obtained at the convective meso synoptic and planetary scales capture many important features of the across scale interactions within an idealized walker circulation the convective scale is associated with the shallow congestus and deep clouds which jointly dominate the upward mass flux in the lower troposphere the synoptic and planetary scales play important roles in extending mass transport to the upper troposphere where the corresponding streamfunctions mainly capture the first baroclinic mode associated with large scale overturning circulation the intermediate scale features of

using dc resistivity tomography to detect and characterize mountain permafrost direct current dc resistivity tomography has been applied to different mountain permafrost regions despite problems with the very high resistivities of the frozen material plausible results were obtained inversions with synthetic data revealed that an appropriate choice of regularization constraints was important and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features the theoretical results were verified with three field experiments conducted in the swiss and the italian alps at the first site near zermatt switzerland the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated on the murtel rock glacier eastern swiss alps a steeply dipping boundary at its frontal part was observed and extremely high resistivities of several m indicated a high ice content the base of the rock glacier remained unresolved by the dc resistivity measurements but it could be constrained with transient em soundings on another rock glacier near the stelvio pass eastern italian alps dc resistivity tomography allowed delineation of the rock glacier base and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the murtel rock glacier

simulations of nocturnal drainage flows by a q2l turbulence closure model abstract nocturnal drainage flows observed over a nearly two dimensional ridge called rattlesnake hills near richland washington are simulated by using a simplified turbulence closure model in which only turbulence kinetic energy and turbulence length scale equations are solved prognostically the present model is slightly simpler than a level 2 5 model which has been extensively used in previous simulations of various atmospheric boundary layer phenomena wind and temperature profiles computed by the present model are generally in excellent agreement with observations made by towers erected on the slope of rattlesnake hills strong coupling between the mean and turbulence variables is also demonstrated

a multiple mass flux parameterization for the surface generated convection part i dry plumes abstract the present study introduces a parameterization for the mixing in the surface generated free convection regime including dry and moist convection cases the parameterization explicitly represents the plumes that drive the convective turbulence ascending parcels that have similar properties in the surface layer are grouped into updrafts with a determined fractional area the updrafts ascend according to an entraining plume model and may eventually overturn the plume model can either use a time or a length scale for the lateral entrainment closure the plumes environment is assumed to be horizontally uniform a one dimensional framework is used to evaluate the parameterization in the case of a dry convective boundary layer cbl the predicted variances are underestimated presumably due to the uniform environment assumption the contrast between the strong upward motions and the compensating subsidence is simulated and the skewness of w increases realistically with height the plumes dyn

a model for late archean chemical weathering and world average river water abstract interpretations of the geologic record of late archean near surface environments depend very strongly on an understanding of weathering and resultant riverine transport to the oceans the late archean atmosphere is widely recognized to be anoxic p o 2 g 10 5 to 10 13 bars p h 2 g 10 3 to 10 5 bars detrital siderite feco3 pyrite fes2 and uraninite uo2 in late archean sedimentary rocks also suggest anoxic conditions however whether the observed detrital minerals could have been thermodynamically stable during weathering and riverine transport under such an atmosphere remains untested similarly interpretations of fluctuations recorded by trace metals and isotopes are hampered by a lack of knowledge of the chemical linkages between the atmosphere weathering riverine transport and the mineralogical record in this study we used theoretical reaction path models to simulate the chemistry involved in rainwater and weathering processes under present day and hypothetical archean atmospheric boundary conditions we included new estimates of the thermodynamic properties of fe ii smectites as well as smectite and calcite solid solutions simulation of present day weathering of basalt calcite by world average rainwater produced hematite kaolinite na mg saponite and chalcedony after 10 4 moles of reactant minerals kg 1 h2o were destroyed combination of the resultant water chemistry with results for granitic weathering produced a water composition comparable to present day world average river water warw in contrast under late archean atmospheric conditions p co 2 g 10 1 5 and p h 2 g 10 5 0 bars weathering of olivine basalt calcite to the same degree of reaction produced kaolinite chalcedony and na fe ii rich saponite late archean weathering of tonalite trondhjemite granodiorite ttg formed fe ii rich beidellite and chalcedony combining the waters from olivine basalt and ttg weathering resulted in a model for late archean warw with the composition na ca2 fe2 mg2 cl hco 3 sio2 aq the ph of the water was 6 3 and it is much richer in hco 3 and in mg fe relative to ca na compared to present day warw at higher ph2 g e g 10 4 0 bars organic acid anions could be metastable our results are consistent with the thermodynamic stability of fe ii clays pyrite uraninite and under some conditions siderite during weathering and riverine transport overall our results provide a basis for assessing the formation of organic hazes and the mobility of trace elements and nutrients due to fluctuations of the late archean atmosphere

a multiple mass flux parameterization for the surface generated convection part ii cloudy cores abstract the multiple mass flux approach introduced in a companion paper aims at parameterizing the surface generated convection in the atmosphere the original aspects of this model are as follows a number of convective updrafts are released in the surface layer they initially have distinct fractional area and thermodynamic properties determined through surface layer similarity that is by assuming that the thermodynamic fluxes are constant throughout the surface layer each updraft ascent is diagnosed using an entraining plume model in the case of cumulus convection this comprehensive formulation provides consistent representations of the subcloud mixing the cloud mixing and the associated cloudiness in the present paper this model is evaluated in two shallow moist convection cases using the one dimensional modeling framework in the continental convection case the diurnal cloud growth and the related subcloud layer ventilation agree with large eddy simulations in the oceanic convection cas

mesoscale downdraft influences on vertical vorticity in a mature mesoscale convective system abstract the vorticity dynamics of a lower tropospheric mesovortex within a mature mesoscale convective system mcs is investigated with observations from a special sounding network and with dual doppler radar measurements the data show that the vorticity distribution and tendency were dictated by the mesoscale downdraft which formed within the storm s trailing stratiform region and not by the mesoscale updraft at midlevels preexisting vertical vorticity was amplified by convergence as environmental air overtook the storm from the rear and funneled into the evaporatively cooled mesoscale downdraft vertical vorticity within the stratiform region also increased by the twisting of horizontal vorticity associated with a backing wind the horizontal vorticity vector pointed opposite the velocity vector and tipped into positive vertical vorticity when the row encountered the mesoscale downdraft at lower middle storm levels the twisted vorticity was subsequently amplified by convergence along with preexi

alternating si and fe deposition caused by temperature fluctuations in precambrian oceans precambrian banded iron formations contain thin alternating layers of iron and silica rich minerals microbial culture experiments show that these alternations could be caused by changes in the relative dominance of microbial iron oxidation and abiotic silica precipitation driven by fluctuating ocean temperature

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

a combined eddy diffusivity mass flux approach for the convective boundary layer a better conceptual understanding and more realistic parameterizations of convective boundary layers in climate and weather prediction models have been major challenges in meteorological research in particular parameterizations of the dry convective boundary layer in spite of the absence of water phase changes and its consequent simplicity as compared to moist convection typically suffer from problems in attempting to represent realistically the boundary layer growth and what is often referred to as countergradient fluxes the eddy diffusivity ed approach has been relatively successful in representing some characteristics of neutral boundary layers and surface layers in general the mass flux mf approach on the other hand has been used for the parameterization of shallow and deep moist convection in this paper a new approach that relies on a combination of the ed and mf parameterizations edmf is proposed for the dry convective boundary layer it is shown that the edmf approach follows naturally from a decomposition of the turbulent fluxes into 1 a part that includes strong organized updrafts and 2 a remaining turbulent field at the basis of the edmf approach is the concept that nonlocal subgrid transport due to the strong updrafts is taken into account by the mf approach while the remaining transport is taken into account by an ed closure large eddy simulation les results of the dry convective boundary layer are used to support the theoretical framework of this new approach and to determine the parameters of the edmf model the performance of the new formulation is evaluated against les results and it is shown that the edmf closure is able to reproduce the main properties of dry convective boundary layers in a realistic manner furthermore it will be shown that this approach has strong advantages over the more traditional countergradient approach especially in the entrainment layer as a result this edmf approach opens the way to parameterize the clear and cumulus topped boundary layer in a simple and unified way

the effect of horizontal resolution on indian monsoon depressions in the met office nwp model monsoon depressions are synoptic scale features that are responsible for a significant fraction of the rain over northern india during the summer monsoon season and as such it is important to quantify their structure and behaviour in numerical weather prediction models it is known that increasing model resolution is strongly correlated with improved forecasts in the short term and global circulation in the longer term as well as better representation of tropical cyclones here we explore the sensitivity of depressions to changes in resolution using the met office unified model seven nwp case studies of depressions from 2013 15 were run at eight resolutions corresponding to equatorial grid spacing of between 16 and 208 km and compared with data for the same events from trmm and era interim reanalysis we found that at the low resolution end of the spectrum increases in resolution led to improvements in the composite structure but with diminishing returns the model also persistently overestimated the depression intensity in particular the wind speed and the warm core aloft with the source appearing to originate in the mid troposphere the sensitivity of the diurnal cycle to resolution was also explored the stratiform component was found to be very well represented by the model whereas the convective component was described quite poorly improvement in most components of structure with increasing model resolution were marginal beyond n320 63 km and n512 39 km for dynamic and thermodynamic fields respectively

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

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

a mass flux scheme view of a high resolution simulation of a transition from shallow to deep cumulus convection in this paper an idealized high resolution simulation of a gradually forced transition from shallow nonprecipitating to deep precipitating cumulus convection is described how the cloud and transport statistics evolve as the convection deepens is explored and the collected statistics are used to evaluate assumptions in current cumulus schemes the statistical analysis methodologies that are used do not require tracing the history of individual clouds or air parcels instead they rely on probing the ensemble characteristics of cumulus convection in the large model dataset they appear to be an attractive way for analyzing outputs from cloud resolving numerical experiments throughout the simulation it is found that 1 the initial thermodynamic properties of the updrafts at the cloud base have rather tight distributions 2 contrary to the assumption made in many cumulus schemes nearly undiluted air parcels are too infrequent to be relevant to any stage of the simulated convection and 3 a simple model with a spectrum of entraining plumes appears to reproduce most features of the cloudy updrafts but significantly overpredicts the mass flux as the updrafts approach their levels of zero buoyancy a buoyancy sorting model was suggested as a potential remedy the organized circulations of cold pools seem to create clouds with larger sized bases and may correspondingly contribute to their smaller lateral entrainment rates our results do not support a mass flux closure based solely on convective available potential energy cape and are in general agreement with a convective inhibition cin based closure the general similarity in the ensemble characteristics of shallow and deep convection and the continuous evolution of the thermodynamic structure during the transition provide justification for developing a single unified cumulus parameterization that encompasses both shallow and deep convection

a density current parameterization coupled with emanuel s convection scheme part i the models abstract the aim of the present series of papers is to develop a density current parameterization for global circulation models this first paper is devoted to the presentation of this new wake parameterization coupled with emanuel s convective scheme the model represents a population of identical circular cold pools the wakes with vertical frontiers the wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts the budget equations for mass energy and water yield evolution equations for the prognostic variables the vertical profiles of the temperature and humidity differences between the wakes and their exterior they also provide additional terms for the equations of the mean variables the driving terms of the wake equations are the differential heating and drying due to convective drafts the action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precip

departures from convective equilibrium with a rapidly varying surface forcing convective equilibrium is a long standing and useful concept for understanding many aspects of the behaviour of deep moist convection for example it is often invoked in developing parametrizations for large scale models however the equilibrium assumption may begin to break down as models are increasingly used with shorter time steps and finer resolutions here we perform idealized cloud system resolving model simulations of deep convection with imposed time variations in the surface forcing a range of rapid forcing time scales from 1 to 36 h are used in order to induce systematic departures from equilibrium for the longer forcing time scales the equilibrium assumption remains valid in at least the limited sense that cycle integrated measures of convective activity are very similar from cycle to cycle for shorter forcing time scales cycle integrated convection becomes more variable with enhanced activity on one cycle being correlated with reduced activity on the next suggesting a role for convective memory further investigation shows that the memory does not appear to be carried by the domain mean thermodynamic fields but rather by structures on horizontal scales of 5 20 km such structures are produced by the convective clouds and can persist beyond the lifetime of the cloud even through to the next forcing cycle

roles of deep and shallow convection and microphysics in the mjo simulated by the model for prediction across scales the november event of the madden julian oscillation mjo during the dynamo field campaign was simulated using the global compressible nonhydrostatic model for prediction across scales mpas with global coarse 60 and 15 km and regional the indian ocean cloud permitting 3 km meshes the purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in mjo simulations two cumulus schemes were used tiedtke and grell freitas the deep and shallow components of tiedtke scheme can be turned on and off individually the results reveal that microphysics alone without cumulus parameterization is able to produce strong signals of the mjo in precipitation with 3 km mesh and weak mjo signals with 15 km mesh a shallow scheme tiedtke along with microphysics strengthens the mjo signals but makes them less well organized on large scales a deep cumulus scheme can either improve the large scale organization of mjo precipitation produced by microphysics and shallow convection tiedtke or impair them grell freitas the deep scheme of tiedtke cannot reproduce the mjo well without its shallow counterpart the main role of shallow convection in the model is to transport moisture upward to the lower mid troposphere by doing so it removes dry biases in the lower mid troposphere a distinct feature in simulations with weak or no mjo signals and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the mjo all roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving mjo simulations in other words a holistic approach should be taken that consider parameterization of shallow cumulus microphysics boundary layer as well as deep cumulus as a whole for model improvement

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

a thermal plume model for the convective boundary layer representation of cumulus clouds abstract the thermal plume model a mass flux scheme combined with a classical diffusive approach originally developed to represent turbulent transport in the dry convective boundary layer is extended here to the representation of cloud processes the modified parameterization is validated in a 1d configuration against results of large eddy simulations les as well as in a 3d configuration against in situ measurements for a series of cases of dry and cloudy convective boundary layers accounting for coherent structures of the mixed layer with the mass flux scheme improves the representation of the diurnal cycle of the boundary layer particularly its progressive deepening during the day and the associated near surface drying results also underline the role of the prescription of the mixing of air between the plume and its environment and of submean plume fluctuations

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

large eddy simulation of the convective atmospheric boundary layer abstract large eddy simulations of a free convective atmospheric boundary layer with an overlying capping inversion are considered attention is given to the dependence of the results upon the various factors influencing the simulation the subgrid model the domain size and the mesh resolution by providing artificial constraints upon the convection the results also provide extra insight into the underlying dynamics the gross features of the boundary layer such as the overall energy budget are not sensitive to the details of the simulations but a number of important factors are revealed it has been found that near the surface the subgrid diffusivity must be larger than is usually supposed in order for the vertical velocity skewness to have the correct sign this region of the flow has a significant subgrid scale heat flux and it seems that the subgrid model requires improvement in such cases a revised model which under statically unstable conditions allows the mixing length of the subgrid scale tu

a unified eddy diffusivity mass flux approach for modeling atmospheric convection abstracta fully unified parameterization of boundary layer and moist convection shallow and deep is presented the new parameterization is based on the stochastic multiplume eddy diffusivity mass