coastal seismic wipe outs distribution controlled by pore water salinity abstract the relationship between seismic wipe outs methane accumulation and pore water salinity was investigated using high resolution seismic profiles pore water geochemical measurements and sediment property data from the white oak river estuary north carolina the estuary is a broad shallow drowned river valley filled with organic rich sediment where the salinity changes from fresh to sea water within 10 km uniboom seismic reflection profiles indicate a distinct pattern in the distribution of seismic wipe outs wipe outs dominate the upper estuary but are not observed in the lower estuary sediment pore water chlorinities decrease upstream but the sharpest gradients occur with depth at 50 cm depths in the upper half of the estuary pore waters typically have less than 100 mmol l 1 chloride even though overlying estuarine waters have 300 400 mmol l 1 chloride concave chloride profiles demonstrate that sediments in the upper estuary are actively flushed with fresh water moving upward through the sediments from underlying aquifers the associated decrease in interstitial sulfate concentrations combined with high organic carbon content provides favorable conditions for methane production and accumulation seismic wipe outs are correlated with areas of high methane concentrations and with sediments containing low pore water salinities

on the factors controlling the development of shallow convection in eddy diffusivity mass flux models abstractthis study addresses key aspects of shallow moist convection as simulated by a multiplume eddy diffusivity mass flux edmf model two factors suggested in the literature to be essential f

the atmospheric boundary layer and the gray zone of turbulence a critical review recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters comparable to the dominant turbulence length scales in the atmospheric boundary layer as a result models are starting to partially resolve the coherent overturning structures in the boundary layer in this resolution regime the so called boundary layer gray zone neither the techniques of high resolution atmospheric modeling a few tens of meters resolution nor those of traditional meteorological models a few kilometers resolution are appropriate because fundamental assumptions behind the parameterizations are violated nonetheless model simulations in this regime may remain highly useful in this paper a newly formed gray zone boundary layer community lays the basis for parameterizing gray zone turbulence identifies the challenges in high resolution atmospheric modeling and presents different gray zone boundary layer models we discuss both the successful applications and the limitations of current parameterization approaches and consider various issues in extending promising research approaches into use for numerical weather prediction the ultimate goal of the research is the development of unified boundary layer parameterizations valid across all scales

performance of an eddy diffusivity mass flux scheme for shallow cumulus boundary layers comparisons between single column scm simulations with the total energy mass flux boundary layer scheme temf and large eddy simulations les are shown for four cases from the gulf of mexico atmospheric composition and climate study gomaccs 2006 field experiment in the vicinity of houston texas the scm simulations were run with initial soundings and surface forcing identical to those in the les providing a clean comparison with the boundary layer scheme isolated from any other influences good agreement is found in the simulated vertical transport and resulting moisture profiles notable differences are seen in the cloud base and in the distribution of moisture between the lower and upper cloud layer by the end of the simulations temf has dried the subcloud layer and moistened the lower cloud layer more than les temf gives more realistic profiles for shallow cumulus conditions than traditional boundary layer schemes which have no transport above the dry convective boundary layer changes to the formulation and its parameters from previous publications are discussed

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

large eddy simulation of shallow cumulus over land a composite case based on arm long term observations at its southern great plains site abstractbased on long term observations by the atmospheric radiation measurement program at its southern great plains site a new composite case of continental shallow cumulus shcu convection is constructed for large eddy simulations les and single column models the case represents a typical daytime nonprecipitating shcu whose formation and dissipation are driven by the local atmospheric conditions and land surface forcing and are not influenced by synoptic weather events the case includes early morning initial profiles of temperature and moisture with a residual layer diurnally varying sensible and latent heat fluxes which represent a domain average over different land surface types simplified large scale horizontal advective tendencies and subsidence and horizontal winds with prevailing direction and average speed observed composite cloud statistics are provided for model evaluation the observed diurnal cycle is well reproduced by les however the cloud amount liquid water path and shortw

isolation and physiology of a manganese reducing bacillus polymyxa from an oligocene silver bearing ore and sediment with reference to precambrian biogeochemistry abstract samples from an oligocene silver bearing manganese ore mining site in saguochi country colorado were screened for bacteria which solubilize manganese in the refractory ore thus making the silver more amenable to standard extraction techniques over 300 bacterial isolates were tested manganese reduction was detected by growing the organisms in a mineral salts medium supplemented with the insoluble mno2 pyrolusite reduction of the black mno2 resulted in the formation of colorless solubilized mn2 one of the most efficient manganese reducers was a bacillus polymyxa strain d1 this bacterium was isolated from the ore heap and from a zone 5 cm below the sediment surface of the inlet which drained ore heap leachate into a holding pond isolate d1 has a unique mode of manganese reduction as shown by the following combination of characteristics 1 anaerobiosis is absolutely necessary 2 direct surface contact with the mineral particle is required 3 facultative fermentation occurs concomitantly with manganese reduction and 4 mn4 does not substitute for o2 at the end of the respiratory electron transport chain although the ore deposit is approximately 35 30 ma old d1 probably have first appeared at the site contemporaneous with mining activities as evidenced by its resistance to exogenous zinc used in the silver extractive process if organisms such as d1 were present 600 ma ago they could have played a role in the precambrian manganese cycle as they do in the holocene encrustations of mno2 have been found in precambrian sediments which are thought to be biogenic in origin solubilized reduced mn2 must also have been present to serve as a substrate anaerobic conditions alone are insufficient for the reduction of manganese dioxide therefore it is likely that manganese reduction was due in part to microbial activity solubilization of manganese occurs via microbial dissimilatory reduction as seen with isolate d1 precipitation results from oxidation of manganese coupled to atp synthesis as described by ehrlich 1976 1983

coherent structures in the boundary and cloud layers role of updrafts subsiding shells and environmental subsidence coherent structures such as updrafts downdrafts shells and environmental subsidence in the boundary and cloud layers of shallow convection are investigated using a new classification method using large eddy simulation data the new method first filters out background turbulence and small scale gravity waves from the coherent part of the flow composed of turbulent coherent structures and large scale transporting gravity waves then the algorithm divides this coherent flow into updrafts downdrafts shells subsidence ascendance and four other flow structures using an octant analysis the novel method can systematically track structures from the cloud free boundary layer to the cloud layer thus allowing systematic analysis of the fate of updrafts and downdrafts the frequency and contribution of the coherent structures to the vertical mass flux and transport of heat and moisture can then be investigated for the first time updrafts subsidence and downdrafts subsiding shells to a lesser extent are shown to be the most frequent and dominant contributors to the vertical transport of heat and moisture in the boundary layer contrary to previous perspective environmental subsidence transport is shown to be weak in the cloud layer instead downdrafts shells are the main downward transport contributors especially in the trade inversion layer the newly developed method in this study can be used to better evaluate the entrainment and detrainment of individual or an ensemble of coherent structures from the unsaturated boundary layer to the cloud layer

potential environmental control of free shallow gas in the seafloor of eckernforde bay germany abstract the depth of the free methane gas horizon in eckernforde bay western baltic sea was monitored over 4 months in 1 h intervals with an echo sounder mounted on a tower at the seafloor the depth to the top of the free gas varied between 50 cm and 100 cm below seafloor short term fluctuations of free gas depth are related for the most part to changes of total pressure air pressure and water level the observation period was too short to demonstrate the effect of the annual temperature cycle the correlation of gas depth changes and total pressure agrees well with theory which predicts a linear influence of pressure fluctuations on gas solubility since the methane content in the pore water of eckernforde bay is at the saturation limit environmental changes pressure and temperature variations cannot be buffered and have an instant impact on free gas presence the implications of this observation are manifold geo technically the bearing strength of the seafloor is altered by the presence of gas bubbles similarly sonar systems are influenced by the presence of gas bubbles which alter the acoustic seafloor properties of ecological interest is that pressure drops can trigger a sudden ebullition of the greenhouse gas methane from the seafloor into the atmosphere

the acoustic turbid layer in muddy sediments of eckernfoerde bay western baltic methane concentration saturation and bubble characteristics in eckernfoerde bay in the western baltic an enclosed basin with organic rich mud acoustic turbidity has been observed since 1952 to investigate the relationships between acoustic properties and free gas we developed a method for rapid sub sampling of gravity cores to determine the total methane content from temperature measurements determinations of the salinity of the pore water and data from the literature saturation limits were calculated for each core it is demonstrated that there is a certain amount of free gas in the mud of eckernfoerde bay but subbottom depths of the oversaturation and of the acoustic turbidity do not correspond the existence of free gas implies the existence of bubbles in the sediment which are regarded to be responsible for the acoustic turbidity bubble sizes observed by x ray computed tomography while still under in situ pressure and temperature vary between 1 and 10 mm equivalent diameter the distribution of bubbles is discontinuous occurring in depth zones from 2 to 20 cm thickness

buoyancy flux modeling for cloudy boundary layers the modeling of the buoyancy flux in a partly cloudy atmospheric boundary layer is complicated by its dependence on the correlation between clouds and vertical velocity elements which can vary significantly with the underlying layer dynamics e g stratocumulus versus shallow cumulus the buoyancy flux is sometimes modeled in terms of higher order statistics such as vertical velocity skewness or saturation variance to try to capture some of these dynamical effects in this work an approximate expression for the buoyancy flux is formulated solely in terms of the liquid potential temperature and total water profiles and their respective flux profiles the predictions compare favorably with the results of an extensive set of large eddy simulations les including simulations of stratocumulus shallow cumulus and transitional behavior in between this formulation is combined with previous results on the relation between cloud top entrainment rate and circulation structure to predict the behavior of quasi steady cumulus coupled boundary layers as a function of a basic set of physical input parameters these predictions also compare favorably with les results

multiple scale simulations of stratocumulus clouds 1 this study introduces a flexible multiple nested modeling framework developed from the weather research and forecasting wrf model for boundary layer cloud research it features a nested large eddy simulation in a hindcasting mode that allows a direct comparison between simulations and observations using this approach we simulated two stratocumulus cases observed at the southern great plains observing site the simulation observation comparisons demonstrate that the multiple nested wrf well reproduces the cloud properties and vertical velocity fields detected by cloud radar and other remote sensing instruments the simulations show that 1 the cloud fields can be strongly modulated by mesoscale organizations 2 the vertical velocity variance and skewness in the boundary layer have well defined diurnal variations and are strongly dependent on external forcings but the in cloud turbulent statistics appears to be more controlled by the internal turbulent processes 3 the organized structures of stratocumulus are only slightly skewed which is consistent with the cloud radar observations that the updraft fraction is close to 50 and 4 the vertical distribution of cloud water and the associated high order moments of continental stratocumulus can be substantially different from its marine counterpart due to different ambient thermodynamic structures this study suggests that the multiple scale wrf modeling system provides a great numerical framework that can be used to address various issues regarding the parameterization of boundary layer clouds

process related classification of acoustic data from the hudson river estuary acoustic surveying provides valuable information on the distribution of sedimentary environments in subaqueous settings frequently differences in acoustic backscatter strength are used to distinguish sedimentary environments on the basis of their grain size composition here we are presenting acoustic backscatter data from the haverstraw bay section of the hudson river estuary that has been mapped using sidescan sub bottom profiling and multibeam bathymetry as part of the benthic mapping project of the hudson river estuary program funded by new york state in addition hundreds of gravity cores and grab samples provide ground truth for a classification of the river bottom into discrete substrate types analyses of sedimentary environments reveal patterns in backscatter strength beyond those that can be related to the sediment grain size distribution alone an integrated interpretation of sidescan sub bottom profiling and high resolution bathymetry data indicates that the backscatter pattern can be attributed to spatial variations in the modern depositional environments which cause differences in bottom roughness and sediment compaction based on an integrated interpretation of the acoustic and sample data sets we distinguished eight different sedimentary classes many of the classes can be linked to dynamic processes including contemporary deposition erosion and sediment migration in sand waves the results provide a better understanding of the dynamic processes of the hudson river estuary and improve the interpretation of the acoustic backscatter data from fine grained sedimentary environments

a buoyancy based mixing length proposal for cloudy boundary layers the parametrization of boundary layer clouds is approached here using a turbulence kinetic energy closure in conservative variables for non precipitating processes and through a new proposal for the turbulence mixing length a subgrid condensation scheme able to treat partially saturated conditions in a model grid cell is also necessary an extension of the buoyancy based bougeault lacarrere mixing length is proposed to take into account moist processes and specifically the effects of phase changes the asymmetry between upward and downward mixing processes is also considered for partial cloudiness conditions the new proposal is tested for stratocumulus capped marine boundary layers and for shallow cumulus convection both over land and sea the validation ismade against large eddy simulation results obtained from model intercomparison cases for stationary regimes as a first step and then for the diurnal evolution of marine stratocumulus and shallow convection over land copyright 2004 royal meteorological society

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

long term observations of the convective boundary layer using insect radar returns at the sgp arm climate research facility abstract a long term study of the turbulent structure of the convective boundary layer cbl at the u s department of energy atmospheric radiation measurement program arm southern great plains sgp climate research facility is presented doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the cbl the observations cover four summer periods 2004 08 and are classified into cloudy and clear boundary layer conditions profiles of vertical velocity variance skewness and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions a conditional sampling method is applied to the original doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport overall the derived turbulent statistics are consistent with previous aircraft and lidar observations the obs

parameterization of continental boundary layer clouds 1 large eddy simulations less of continental boundary layer clouds blcs observed at the southern great plains sgp are used to study issues associated with the parameterization of sub grid blcs in large scale models it is found that liquid water potential temperature l and total specific humidity qt which are often used as parameterization predictors in statistical cloud schemes do not share the same probability distribution in the cloud layer with l skewed to the left negatively skewed and qt skewed to the right positively skewed the skewness and kurtosis change substantially in time and space when the development of continental blcs undergoes a distinct diurnal variation the wide range of skewness and kurtosis of l and qt can hardly be described by a single probability distribution function to extend the application of the statistical cloud parameterization approach this paper proposes an innovative cloud parameterization scheme that uses the boundary layer height and the lifting condensation level as the primary parameterization predictors the les results indicate that the probability distribution of these two quantities is relatively stable compared with that of l and qt during the diurnal variation and nearly follows a gaussian function verifications using les output and the observations collected at the atmospheric radiation measurement arm climate research facility arcf sgp site indicate that the proposed scheme works well to represent continental blcs

theoretical understanding of the linear relationship between convective updrafts and cloud base height for shallow cumulus clouds part ii continental conditions abstractzheng and rosenfeld found linear relationships between the convective updrafts and cloud base height zb using ground based observations over both land and ocean the empirical relationships

vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds 1 continental boundary layer bl stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the bl vertical velocity structure of these clouds is studied using data from the atmospheric radiation measurement program s southern great plains observing facility located near lamont oklahoma data from vertically pointing cloud radar from eleven cases of nonprecipitating bl stratocumulus clouds are used to obtain half hourly values of in cloud vertical velocity variance skewness updraft fraction downdraft fraction and mass flux the variance showed a general decrease with height while the skewness was weakly positive in the cloud layer and negative near cloud top on half hourly time scales vertically coherent structures spanning through the entire cloud layer were responsible for 40 of the observed vertical velocity variance while horizontally temporally coherent structures lasting at least 20 s were responsible for 77 of the vertical velocity variance the half hour periods were then classified on the basis of the surface buoyancy flux b as small b periods b 60wm 2 small b periods exhibited lower variance near cloud base compared to large b periods with the differences being reversed near cloud top the skewness was positive in the cloud layer during large b periods and negative during small b periods while the skewness was negative near cloud top in both scenarios the small b periods had about ten times more updrafts greater than 1 m s 1 near cloud top compared to large b periods

seismic reflectivity effects from seasonal seafloor temperature variation the effects of seasonal temperature variation on sound speed contrasts at the seafloor are usually considered negligible in the analysis of seismic data but may be significant at large incidence angles offsets important for inversion of sediment elastic properties or long range acoustic transmission in coastal areas the maximum annual seafloor temperature variation can be several degrees celsius or more corresponding to a sound speed variation of 30 m s or more thermal pulses propagate via conduction several meters into the seafloor resulting in a damped quasi sinusoidal temperature profile with predictable wave number characteristics the oscillating seasonal and spatial character of this signal creates a time and frequency dependent effect on the elastic seafloor reflectivity results of numerical simulations show that the expected temperature profile for most sediment types and porosities will have the strongest affect on frequencies between about 60 and 600 hz at incidence angles greater than about 50

ancient channels of the susquehanna river beneath chesapeake bay and the delmarva peninsula three generations of the ancestral susquehanna river system have been mapped beneath chesapeake bay and the southern delmarva peninsula closely spaced seismic reflection profiles in the bay and boreholes in the bay and on the southern delmarva peninsula allow detailed reconstruction of each paleochannel system the channel systems were formed during glacial low sea level stands and each contains a channel fill sequence that records the subsequent transgression the trunk channels of each system are 2 to 4 km wide and are incised 30 to 50 m into underlying strata they have irregular longitudinal profiles and very low gradients within the chesapeake bay area the three main stem channels diverge from the head of the bay toward the southeast the channels are rarely coincident although they commonly intersect all three main channels pass beneath the southern delmarva peninsula forming an age progression from north oldest to south youngest beneath the peninsula and from east oldest to west youngest beneath chesapeake bay southward progradation of the tip of the delmarva peninsula during interglacial high sea level stands caused southward migration of the mouth of the bay so that the next generation of channels were incised progressively further towards the southwest the youngest paleochannel is clearly of late wisconsinan age about 18 ka and the intermediate one appears to be late illinoian in age or about 150 ka the age of the oldest paleochannel is not well constrained but it is in the range of about 200 to 400 ka the three paleochannel systems imply a dynamic coastal plain environment and at least two previous generations of the chesapeake bay both the chesapeake bay and the southern delmarva peninsula have changed considerably in the past half million years

large eddy simulation of the diurnal cycle of shallow cumulus convection over land summary large eddy simulations of the development of shallow cumulus convection over land are presented many characteristics of the cumulus layer previously found in simulations of quasi steady convection over the sea are found to be reproduced in this more strongly forced unsteady case furthermore the results are shown to be encouragingly robust with similar results obtained with eight independent models and also across a range of numerical resolutions the datasets produced are already being used in the development and evaluation of parametrizations used in numerical weather prediction and climate models

variability of acoustic turbidity in eckernforde bay southwest baltic sea related to the annual temperature cycle abstract the sediments of eckernforde bay southwest baltic sea are known for their high contents of gas it causes acoustic turbidity i e the masking of sedimentary horizons by absorption and scattering of seismic energy due to free gas bubbles also known as basin effect repeated surveys with side scan sonar and subbottom profiler along coincident profiles gave new insight into the variability of the acoustic turbidity for the first time it is evidenced that its depth varies by several decimeters with an annual cycle we explain this by the temperature dependent solubility of methane the depth of the acoustic turbidity however does not vary in phase with the annual surface temperature cycle the delay is an effect of the poor heat conductivity of the overlying water and sediment

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

the holocene gas system of the ria de vigo nw spain factors controlling the location of gas accumulations seeps and pockmarks abstract high resolution seismic profiles cored sediment gravity cores and vibro cores and radiocarbon data from suitable shell material were used to establish the stratigraphic context of gassy sediments in the ria de vigo mapping of seeps and pockmarks were compared with the stratigraphy of gassy sediment to ascertain the relationships in the ria de vigo three holocene seismic units were identified the first two uh 1 and uh 2 correspond to the transgressive systems tract tst and the third uh 3 corresponds to the highstand systems tract hst the presence of acoustic turbidity within the three seismic units indicates that generation of gas took place during the relative sea level rise that occurred after the younger dryas event i e during the tst and mainly during the hst the relative sea level variations are shown to be a major factor controlling the type fine vs coarse grained and distribution of facies lateral and vertical that generate and or allow gas accumulation or escape acoustic turbidity due to presence of free gas was recognized in the three holocene units with a total of 12 acoustic turbidity fields mapped in the ria de vigo no significant variations in the spatial distribution or extent of the gas fields or in their vertical location below the present sea bed have been observed during the seismic surveys carried out in the ria during the last decade furthermore gas escape from the sediment and active pockmark has been observed therefore we conclude that gas escape seeps pockmark generation and maintenance and methane formation are in equilibrium the combined analysis of high resolution seismic profiles sediment temperature pore water salinity and hydrostatic pressure revealed 1 a direct relationship between depth of free gas and hydrostatic pressure and 2 a direct link between sediment temperature and number of acoustic plumes from seabed to water column more acoustic plumes were detected in summer when the temperature of the sediment was higher than in winter indicating a seasonal variation of seeps within the ria salinity showed no significant differences between sea bottom water and sediment pore water and was therefore not a major factor controlling gas front variations

shallow cumulus representation and its interaction with radiation and surface at the convection gray zone abstractthis study presents a systematic analysis of convective parameterizations performance with interactive radiation microphysics and surface on an idealized day with shallow convection to t

the contributions of shear and turbulence to cloud overlap for cumulus clouds vertical cloud overlap the ratio of cloud fraction by area and by volume for cumulus clouds are studied using large eddy simulations les due to the inefficient wide range values of cloud overl

the impact of horizontal resolution on the simulations of convective development over land summary cloud resolving models crms can be used to provide subgrid information for use in improving the representation of the development of convection in large scale models however for the crm to be of value it must itself give an accurate representation of the processes involved in the work presented here we focus on the development of convection in simulations of both shallow and deep convection over land and consider sensitivity to the horizontal resolution in a crm in both shallow and deep cases it is found to be necessary to provide adequate resolution of the sub cloud layer in order to obtain a satisfactory representation of the transport of moisture from the sub cloud layer into the free troposphere typically this requires the horizontal grid spacings to be no coarser than around one quarter of the sub cloud layer depth poorer resolution with the present model leads to signie cant delays in the development of convection while a more sophisticated subgrid scheme could reduce the sensitivity to resolution the work here has shown the resolution required to explicitly resolve the key processes using this improved resolution may be one technique for reducing the discrepancies between some model results and observations reported in earlier studies

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

a new bulk shallow cumulus model and implications for penetrative entrainment feedback on updraft buoyancy abstract a new refinement of albrecht et al s bulk model for shallow cumulus convection is presented it is used to illuminate fundamental aspects of oceanic shallow cumulus boundary layer structure including updraft buoyancy and vertical velocity scales cumulus mass flux temperature and humidity profiles and trade inversion height the new model like albrecht et al s includes a subcloud mixed layer and a cumulus layer with linear gradients of conserved thermodynamic variables topped by a sharp capping inversion albrecht et al s model was not mathematically well posed leading to an inconsistency between its heat and moisture balances at the inversion base the new bulk model resolves this problem by diagnosing rather than prognosing the cumulus layer gradients and introducing a penetrative entrainment closure to determine the growth of the cumulus layer into the overlying free troposphere it uses more realistic assumptions about lateral cumulus entrainment and detrainment and a simplified s

gas charged sediments in the ria de arousa short to long term fluctuations repeated surveys at control sites in the gas accumulation fields from the ria de arousa galicia nw spain have shown that the top of the acoustic turbidity fluctuates vertically the vertical movement of gas fronts is more apparent in the gas fields located in the outer ria where fluctuations of up to 1 5 ms 1 1 m have been detected at the inner ria the depth to the top of the gas horizons varied between 0 5 and 1 ms 40 to 80 cm short term diurnal fluctuations associated with the hydrostatic pressure variations of the water column during a tidal cycle have been identified as the most likely factors to explain fluctuations of gas fields in the outer ria at the inner ria gas fields are affected by these short term pressure changes superimposed on long term temperature and salinity variations of bottom water masses this combination produces a different pattern of variation in gas fields from the inner and the outer ria prominent pockmarks and acoustic plumes have also been monitored throughout the three seismic surveys many of these pockmarks exhibit active characteristics including the observance of plumes of escaping fluids and sediment

seasonal variability of shallow biogenic gas in chesapeake bay abstract methane gas in chesapeake bay sediments occurs in buried paleodrainage channels incised during the last glacial sealevel lowstand repeat acoustic surveys of two chesapeake bay sites during the past year with a 2 15 khz chirp sonar profiler and 100 khz sidescan sonar show that the top of the zone of acoustically opaque gas bubbles in the sediments fluctuates vertically by up to 0 5 m apparently in response to seasonal temperature changes the vertical movement of the gas layer is most apparent in the main channel of the bay where the methane gas is very close to the seafloor in areas where the gas is seen to be very near the seafloor on the chirp profiler records the sidescan sonar data show corresponding high backscatter this does not appear to be the result of differing sediment types it is not likely that the sidescan signal is penetrating the seafloor at the shallow outer grazing angles of the sidescan swath therefore the gas must extend to the water sediment interface the areas of high backscatter caused by the gas are observed to change seasonally expanding during the summer high temperature period and shrinking during the winter low temperature period

a dual mass flux framework for boundary layer convection part i transport abstract this study considers the question of what is the least complex bulk mass flux framework that can still conceptually reproduce the smoothly varying coupling between the shallow convective cloud layer and the subcloud mixed layer to this end the model complexity of the classic single bulk mass flux scheme is enhanced inspired by recent large eddy simulation results the authors argue that two relatively minor but key conceptual modifications are already sufficient to achieve this goal i retaining a dry transporting updraft in the moist limit and ii applying continuous updraft area partitioning to this dual mass flux dualm framework the dry updraft represents all internal mixed layer updrafts that terminate near the mixed layer top whereas the moist updraft represents all updrafts that condense and rise out of the mixed layer as buoyant cumulus clouds the continuous area partitioning between the dry and moist updraft is a function of moist convective inhibition above the mixed layer top

exploration methods for late quaternary shallow biogenic gas reservoirs in the hangzhou bay area eastern china commercial accumulations of shallow biogenic gas have been widely found in the world the successful development and exploitation of shallow gas is dependent on using suitable technology to effectively prospect for this kind of resource shallow biogenic gas reservoirs buried less than 120 m 393 7 ft have been discovered and successfully exploited in the hangzhou bay area northern zhejiang province eastern china in this study we describe the methods used for the exploration of shallow gas including cone penetration test cpt shallow shear wave seismic data soil gas radon analysis microbiological prospecting and electromagnetic surveying the cpt is effective in helping to determine stratigraphic divisions and correlations especially reservoir identification dense cpts are useful for both the preliminary exploration and enlarging a known gas field shallow shear wave seismic profiles identify the top surface of a gas bearing sand bed which shows a strong reflecting boundary the reflection will sharply decline where the gas bearing sand body pinches out thus a gas bearing sand body can be outlined the area of gas reservoirs can further be determined by high soil gas radon content over the boundary of the gas accumulation methane consuming bacteria can act as an indicator for the presence of methane within the gas bearing area electromagnetic methods can aid in determining whether there is gas in the sand bodies and in determining the thickness of the gas layer

shallow gas off the rhone prodelta gulf of lions sediment cores acquired in 2004 off the rhone prodelta show consistent anomalous methane concentrations of up to 87 440 ppm methane compositional and isotopic data support a biogenic origin although there are a few sites that show strongly depleted delta c 13 values 53 o pdb suggesting a mixed source for the gas biogenic and thermogenic anomalous methane concentrations samples with more than 90 ppm are discussed and integrated with organic carbon data sedimentary rates and adcp profiles highest gas concentrations were found directly off the river mouth 20 40 m water depth and where the ifremer models point to the thickest accumulation 2 m in response to the rhone flood event in areas unaffected by the high flux of organic matter and rapid thick flood deposition or in between flood events the conditions for methanogenesis and gas accumulation have not been met in these areas the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub surface we propose that in the rhone prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial c 2006 elsevier b v all rights reserved

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

observations of boundary layer structure made during the 1981 kontur experiment data collected by two aircraft over the german bight during the 1981 kontur experiment are described turbulence data were obtained throughout the depth of the mixed layer in near neutral to slightly convective conditions similarity theory generally orders the data well and shows the effect of stability on turbulence structure under these conditions the humidity flux profile however is found to depend on conditions at the top of the mixed layer spectral analysis is used to investigate the variation of turbulence length scales with height and the mixed layer eddy structure differences in spectra from alongwind and acrosswind sampling directions are found particularly near the surface spectra of the transverse wind component show that two dimensional roll circulations were generally present in the mixed layer and became more pronounced with increasing instability