climatological features of the weakly and very stably stratified nocturnal boundary layers part iii the structure of meteorological state variables in persistent regime nights and across regime transitions abstractthe evolution of profiles of meteorological state variables during nights with and without transitions in the nocturnal stably stratified boundary layer sbl between weakly stable wsbl a

natural free convection in porous media first field documentation in groundwater 1 natural free convection is a process of great importance in disciplines from hydrology to meteorology oceanography planetary sciences and economic geology and for applications in carbon sequestration and nuclear waste disposal it has been studied for over a century but almost exclusively in theoretical and laboratory settings despite its importance conclusive primary evidence of free convection in porous media does not currently exist in a natural field setting here we present recent electrical resistivity measurements from a sabkha aquifer near abu dhabi united arab emirates where large density inversions exist the geophysical images from this site provide for the first time compelling field evidence of fingering associated with natural free convection in groundwater

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

improved characterization of heterogeneous permeability in saline aquifers from transient pressure data during freshwater injection managing recharge of freshwater into saline aquifers requires accurate estimation of the heterogeneous permeability field for maximizing injection and recovery efficiency here we present a methodology for subsurface characterization in saline aquifers that takes advantage of the density difference between the injected freshwater and the ambient saline groundwater we combine high resolution forward modeling of density driven flow with an efficient bayesian geostatistical inversion algorithm in the presence of a density difference between the injected and ambient fluids due to differences in salinity the pressure field is coupled to the spatial distribution of salinity this coupling renders the pressure field transient the time evolution of the salinity distribution controls the density distribution which then leads to a time evolving pressure distribution we exploit this coupling between pressure and salinity to obtain an improved characterization of the permeability field without multiple pumping tests or additional salinity measurements we show that the inversion performance improves with an increase in the mixed convection ratio the relative importance between viscous forces from injection and buoyancy forces from density difference our work shows that measuring transient pressure data at multiple sampling points during freshwater injection into saline aquifers can be an effective strategy for aquifer characterization key to the successful management of aquifer recharge

sequential approach to joint flow seismic inversion for improved characterization of fractured media seismic interpretation of subsurface structures is traditionally performed without any account of flow behavior here we present a methodology for characterizing fractured geologic reservoirs by integrating flow and seismic data the key element of the proposed approach is the identification within the inversion of the intimate relation between fracture compliance and fracture transmissivity which determine the acoustic and flow responses of a fractured reservoir respectively owing to the strong but highly uncertain dependence of fracture transmissivity on fracture compliance the modeled flow response in a fractured reservoir is highly sensitive to the geophysical interpretation by means of synthetic models we show that by incorporating flow data well pressures and tracer breakthrough curves into the inversion workflow we can simultaneously reduce the error in the seismic interpretation and improve predictions of the reservoir flow dynamics while the inversion results are robust with respect to noise in the data for this synthetic example the applicability of the methodology remains to be tested for more complex synthetic models and field cases

turbulence regimes and the validity of similarity theory in the stable boundary layer over complex terrain of the loess plateau china to gain an insight into the characteristics of turbulence in a stable boundary layer over the complex terrain of the loess plateau data from the semi arid climate and environment observatory of lanzhou university are analyzed we propose a method to identify and efficiently isolate nonstationary motions from turbulence series and then we examine the characteristics of nonstationary motions nonstationary motions refer to gusty events on a greater scale than local shear generated turbulence the occurrence frequency of nonstationary motions is found to depend on the mean flow being more frequent in weak wind conditions and vanishing when the wind speed u is greater than 3 0 ms 1 when u exceeds the threshold value of 1 0 ms 1 for the gradient richardson number ri 0 3 local shear generated turbulence on timescales of less than 4min depends systematically on u with an average rate of 0 05 u however for the weak wind condition neither the mean wind speed nor the stability is an important factor for local turbulence then turbulence is categorized into three regimes based on the behaviors of nonstationary motions and local turbulence regime 1 considers stationary turbulence with a wind speed greater than 3 0 ms 1 and the monin obukhov similarity theory most can be used to calculate the turbulence momentum flux regime 2 examines intermittent turbulence where the most is competent to evaluate the local turbulence momentum flux but not nonstationary motions regime 3 involves wind speed that is less than the threshold value where nonstationary motions are dominant local turbulence is independent of the mean flow and where the most may well be invalid

aquifer heterogeneity characterization with oscillatory pumping sensitivity analysis and imaging potential 1 periodic pumping tests in which a fluid is extracted during half a period then reinjected have been used historically to estimate effective aquifer properties in this work we suggest a modified approach to periodic pumping test analysis in which one uses several periodic pumping signals of different frequencies as stimulation and responses are analyzed through inverse modeling using a steady periodic model formulation we refer to this strategy as multifrequency oscillatory hydraulic imaging oscillating pumping tests have several advantages that have been noted including no net water extraction during testing and robust signal measurement through signal processing through numerical experiments we demonstrate additional distinct advantages that multifrequency stimulations have including 1 drastically reduced computational cost through use of a steady periodic numerical model and 2 full utilization of the aquifer heterogeneity information provided by responses at different frequencies we first perform fully transient numerical modeling for heterogeneous aquifers and show that equivalent results are obtained using a faster steady periodic heterogeneous numerical model of the wave phasor the sensitivities of observed signal response to aquifer heterogeneities are derived using an adjoint state based approach which shows that different frequency stimulations provide complementary information finally we present an example 2 d application in which sinusoidal signals at multiple frequencies are used as a data source and are inverted to obtain estimates of aquifer heterogeneity these analyses show the different heterogeneity information that can be obtained from different stimulation frequencies and that data from several sinusoidal pumping tests can be rapidly inverted using the steady periodic framework

analysis of ducted motions in the stable nocturnal boundary layer during cases 99 abstract data obtained with multiple instruments at the main site of the 1999 cooperative atmosphere surface exchange study cases 99 are employed to examine the character and variability of wave motions occurring in the stable nocturnal boundary layer during the night of 14 october 1999 the predominant motions are surprisingly similar in character throughout the night exhibiting largely westward propagation horizontal wavelengths of 1 to 10 km phase speeds slightly greater than the mean wind in the direction of propagation and highly coherent vertical motions with no apparent phase progression with altitude additionally vertical and horizontal velocities are in approximate quadrature and the largest amplitudes occur at elevated altitudes of maximum stratification these motions are interpreted as ducted gravity waves that propagate along maxima of stratification and mean wind and that are evanescent above and occasionally below the altitudes at which they are ducted modal structures for ducte

a comparison of deterministic and stochastic approaches for regional scale inverse modeling on the mar del plata aquifer summary inversion of the spatial variability of transmissivity t in groundwater models can be handled using either stochastic or deterministic i e geology based zonation approaches while stochastic methods predominate in scientific literature they have never been formally compared to deterministic approaches preferred by practitioners for regional aquifer models we use both approaches to model groundwater flow and solute transport in the mar del plata aquifer where seawater intrusion is a major threat to freshwater resources the relative performance of the two approaches is evaluated in terms of i model fits to head and concentration data available for nearly a century ii geological plausibility of the estimated t fields and iii their ability to predict transport we also address the impact of conditioning the estimated fields on t data coming from either pumping tests interpreted with the theis method or specific capacity values from step drawdown tests we find that stochastic models based upon conditional estimation and simulation techniques identify some of the geological features river deposit channels and low transmissivity regions associated to quartzite outcrops and yield better fits to calibration data than the much simpler geology based deterministic model which cannot properly address model structure uncertainty however the latter demonstrates much greater robustness for predicting sea water intrusion and for incorporating concentrations as calibration data we attribute the poor performance and underestimated uncertainty of the stochastic simulations to estimation bias introduced by model errors qualitative geological information is extremely rich in identifying large scale variability patterns which are identified by stochastic models only in data rich areas and should be explicitly included in the calibration process

shear flow instability in the stable nocturnal boundary layer as observed by doppler lidar during cases 99 abstract this study investigates a shear flow instability observed in the stably stratified nighttime boundary layer on 6 october 1999 during the cooperative atmosphere surface exchange study cases 99 in south central kansas a scanning doppler lidar captured the spatial structure and evolution of the instability and high rate in situ sensors mounted on a nearby 60 m tower provided stability and turbulence data with excellent vertical resolution data from these instruments are analyzed and linear stability analysis lsa is employed to carefully characterize the wave field its interaction with the mean flow and its role in turbulence generation the event persisted for about 30 min and was confined within the shear zone between the surface and a low level jet llj maximum eigenvalues corresponding to the fastest growing mode of the lsa showed good agreement with the basic wave parameters determined from the lidar data good qualitative agreement was also obtained between the eigenfunction of the f

how multiple partially penetrating wells improve the freshwater recovery of coastal aquifer storage and recovery asr systems a field and modeling study aquifer storage and recovery asr of freshwater in brackish or saline aquifers can be an efficient technique to bridge freshwater shortages in coastal areas however buoyancy effects may cause salinization at the bottom of the asr well during recovery making a part of the freshwater irrecoverable this study shows how such freshwater losses can be reduced applying deep injection and shallow recovery by independently operated multiple partially penetrating wells mppw in a single borehole a small scale asr system with such an mppw was installed in january 2012 and its operation was extensively monitored until october 2012 a seawat model was built and calibrated on the field measurements of this first asr cycle the model was used to compare the mppw with a conventional fully and partially penetrating well the freshwater recovery of those wells was 15 and 30 of the injected water respectively which is significantly less than the 40 recovered by the mppw in subsequent cycles no more than 60 could be recovered by the mppw as mixing in the lower half of the aquifer remained a source of freshwater losses however this recovery is significantly higher than the recovery of the conventional well types this study therefore shows that for less ideal asr conditions a viable system can still be realized using mppw

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

aquifer storage recovery asr of chlorinated municipal drinking water in a confined aquifer abstract about 1 02 10 6 m 3 of chlorinated municipal drinking water was injected into a confined aquifer 94 137 m below roseville california between december 2005 and april 2006 the water was stored in the aquifer for 438 days and 2 64 10 6 m 3 of water were extracted between july 2007 and february 2008 on the basis of cl data 35 of the injected water was recovered and 65 of the injected water and associated disinfection by products dbps remained in the aquifer at the end of extraction about 46 3 kg of total trihalomethanes tthm entered the aquifer with the injected water and 37 6 kg of tthm were extracted as much as 44 kg of tthms remained in the aquifer at the end of extraction because of incomplete recovery of injected water and formation of thms within the aquifer by reactions with free chlorine in the injected water well bore velocity log data collected from the aquifer storage recovery asr well show as much as 60 of the injected water entered the aquifer through a 9 m thick high permeability layer within the confined aquifer near the top of the screened interval model simulations of ground water flow near the asr well indicate that 1 aquifer heterogeneity allowed injected water to move rapidly through the aquifer to nearby monitoring wells 2 aquifer heterogeneity caused injected water to move further than expected assuming uniform aquifer properties and 3 physical clogging of high permeability layers is the probable cause for the observed change in the distribution of borehole flow aquifer heterogeneity also enhanced mixing of native anoxic ground water with oxic injected water promoting removal of thms primarily through sorption a 3 to 4 fold reduction in tthm concentrations was observed in the furthest monitoring well 427 m downgradient from the asr well and similar magnitude reductions were observed in depth dependent water samples collected from the upper part of the screened interval in the asr well near the end of the extraction phase haloacetic acids haas were completely sorbed or degraded within 10 months of injection

stable boundary layer regimes at dome c antarctica observation and analysis investigation of meteorological measurements along a 45 m tower at dome c on the high east antarctic plateau revealed two distinct stable boundary layer sbl regimes at this location the first regime is characterized by strong winds and continuous turbulence it results in full vertical coupling of temperature wind magnitude and wind direction in the sbl the second regime is characterized by weak winds associated with weak turbulent activity and very strong temperature inversions reaching up to 25 k in the lowest 10 m vertical temperature profiles are generally exponentially shaped convex in the first regime and convex concave convex in the second the transition between the two regimes is particularly abrupt when looking at the near surface temperature inversion and it can be identified by a 10 m wind speed threshold with winds under this threshold the turbulent heat supply toward the surface becomes significantly lower than the net surface radiative cooling the threshold value including its range of uncertainty appears to agree with recent theoretical predictions from the so called minimum wind speed for sustainable turbulence mwst theory for the quasi steady clear sky winter cases the relation between the near surface inversion amplitude and the wind speed takes a characteristic s shape closer analysis suggests that this relation corresponds to a critical transition between a steady turbulent and a steady radiative regime with a dynamically unstable branch in the transition zone these fascinating characteristics of the antarctic boundary layer challenge present and future numerical models to represent this region in a physically correct manner

injection of fresh river water into a saline floodplain aquifer in an attempt to improve the condition of river red gum eucalyptus camaldulensis dehnh the delivery of environmental flows to riverine floodplains is often constrained by water scarcity and infrastructure this means that areas of floodplain are unable to receive environmental water through mechanisms like dam release weir pool surcharge and artificial flooding of low lying areas this study trials aquifer injection as a method of providing environmental flows to areas of stressed river red gum eucalyptus camaldulensis on the floodplain of the lower river murray the objective was to inject fresh river water at the top of the saline alluvial aquifer to reduce root zone salinity and improve the condition of e camaldulensis localized radial freshening of 10 m was observed at each of the five injection wells when 4 9 ml megalitres of river water was injected into the aquifer over 45 days injection was abandoned after 45 days due to aquifer and well clogging and increases in groundwater head which caused four of the five wells to breach the confining clay layer the trial resulted in localized and short lived freshening of the groundwater which reduced salinity in the associated capillary fringe this did not result in an improvement in the tree condition as they lay beyond the lateral extent of the freshening and were unable to access the water solutions to technical issues such as aquifer clogging and well breaching as well as a need to increase the lateral extent of freshening are required before shallow aquifer injection can be recommended as a method of delivering environmental flows copyright 2009 john wiley sons ltd

tracer tests in a fractured dolomite 2 analysis of mass transfer in single well injection withdrawal tests we investigated multiple rate diffusion as a possible explanation for observed behavior in a suite of single well injection withdrawal swiw tests conducted in a fractured dolomite we first investigated the ability of a conventional double porosity model and a multirate diffusion model to explain the data this revealed that the multirate diffusion hypothesis model is consistent with available data and is capable of matching all of the recovery curves second we studied the sensitivity of the swiw recovery curves to the distribution of diffusion rate coefficients and other parameters we concluded that the swiw test is very sensitive to the distribution of rate coefficients but is relatively insensitive to other flow and transport parameters such as advective porosity and dispersivity third we examined the significance of the constant double log late time slopes 2 1 to 2 8 which are present in several data sets the observed late time slopes are significantly different than would be predicted by either conventional double porosity or single porosity models and are believed to be a distinctive feature of multirate diffusion fourth we found that the estimated distributions of diffusion rate coefficients are very broad with the distributions spanning a range of up to 3 6 orders of magnitude fifth when both heterogeneity and solute drift are present late time behavior similar to multirate mass transfer can occur although it is clear that multirate diffusion occurs in the culebra the number of orders of magnitude of variability may be overestimated because of the combined effects of drift and heterogeneity

neutrally buoyant tracers in hydrogeophysics field demonstration in fractured rock electrical and electromagnetic methods are extensively used to map electrically conductive tracers within hydrogeologic systems often the tracers used consist of dissolved salt in water leading to a denser mixture than the ambient formation water density effects are often ignored and rarely modeled but can dramatically affect transport behavior and introduce dynamics that are unrepresentative of the response obtained with classical tracers e g uranine we introduce a neutrally buoyant tracer consisting of a mixture of salt water and ethanol and monitor its movement during push pull experiments in a fractured rock aquifer using ground penetrating radar our results indicate a largely reversible transport process and agree with uranine based push pull experiments at the site which is in contrast to results obtained using dense saline tracers we argue that a shift toward neutrally buoyant tracers in both porous and fractured media would advance hydrogeophysical research and enhance its utility in hydrogeology

transient groundwater dynamics in a coastal aquifer the effects of tides the lunar cycle and the beach profile 1 detailed field measurements are combined with a numerical modeling to characterize the groundwater dynamics beneath the discharge zone at waquoit bay massachusetts groundwater salinity values revealed a saline circulation cell that overlaid the discharging freshwater and grew and disappeared with the lunar cycle the cell was initiated by a greater bay water infiltration during the new moon when high tides overtopped the mean high tide mark flooding the flatter beach berm and inundating a larger area of the beach the dynamics of this cell were further characterized by a tracer test and by constructing a density dependent flow model constrained to salinity and head data the numerical model captured the growing and diminishing behavior of the circulation cell and provided the estimates of freshwater and saline water fluxes and travel times furthermore the model enabled quantification of the relationship between the characteristics of the observed tidal cycle maximum minimum and mean tidal elevations and the different components of the groundwater circulation freshwater discharge intertidal saline cycling and deep saline cycling we found that 1 recharge to the intertidal saline cell is largely controlled by the high tide elevation 2 freshwater discharge is positively correlated to the low tide elevation whereas deep saline discharge from below the discharging freshwater is negatively correlated to the low tide elevation so when the low tide elevation is relatively high more freshwater discharges and less deep saltwater discharges in contrast when low tides are very low less freshwater discharges and more deep salt water discharges 3 offshore inflow of saline water is largely insensitive to tides and the lunar cycle

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

comment on mixed convection processes below a saline disposal basin by simmons c t narayan k a 1997 journal of hydrology 194 263 285

retrieval of microscale flow structures from high resolution doppler lidar data using an adjoint model radial velocity data measured by high resolution doppler lidar hrdl are assimilated with a four dimensional variational data assimilation 4dvar method to retrieve microscale flow structures in an atmospheric boundary layer the control variables of 4dvar consist of initial three dimensional velocity and temperature fields as well as profiles of eddy viscosity and thermal diffusivity the effects of lateral boundary conditions and buffer zones on the retrieval quality are evaluated using identical twin experiments with synthetic observational data prior to hrdl data retrieval it is found that use of inflow outflow boundary conditions in conjunction with buffer zones yields good results hrdl field observations are then assimilated with 4dvar together with the above treatment of boundaries to recover microscale flow structures in a convective boundary layer the uncertainty of the retrieved data is assessed by conducting a grid sensitivity test a large scale flow structure resembling a dry microburst is observed in the retrieved wind field characteristics of this structure are discussed and compared with those of a typical microburst

effects of tidal fluctuations and spatial heterogeneity on mixing and spreading in spatially heterogeneous coastal aquifers we study the combined effect of heterogeneity in the hydraulic conductivity field and tidal oscillations on the three dimensional dynamics of seawater intrusion in coastal aquifers we focus on the quantification of its impact on solute mixing and spreading of the freshwater seawater interface three dimensional monte carlo realizations of log normally distributed permeability fields were performed and for each realization numerical variable density flow and solute transport simulations were conducted mixing is characterized by the spatial moments of concentration the enhanced solute mixing is quantified by an effective dispersion coefficient the simulations show that heterogeneity produces an inland movement of the toe location along with a significant widening of the transition zone which is linearly proportional to the product of the arithmetic mean of the correlation lengths in the three spatial dimensions a and the permeability field variance lnk2 we find that once tidal oscillations are included as the degree of heterogeneity increases the combined effect of heterogeneity and tidal oscillations on mixing and spreading of the interface reduces this is explained by the fact that an increase in the log permeability variance induces an increase in both the effective permeability and the spatial connectivity which implies a more uniform hydraulic response to tidal forcing and as a result the degree of mixing decreases this study also identifies that the mixing behavior induced by tidal oscillations in heterogeneous coastal aquifers is controlled by the effective tidal mixing number ntme which depends on the amplitude the period the storativity and the effective horizontal permeability

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

nighttime turbulent events in a steep valley a nested large eddy simulation study this numerical study investigates the nighttime flow dynamics in owens valley california nested highresolution large eddy simulation les is used to resolve stable boundary layer flows within the valley on 17 april during the 2006 terrain induced rotor experiment the valley atmosphere experiences weak synoptic forcings and is largely dominated by buoyancy driven downslope and down valley flows tower instruments on the valley floor record a continuous decrease in temperature after sunset except for a brief warming episode this transient warming event is modeled with good magnitude and temporal precision with les analysis of the les flow field confirms the event to be the result of a slope to valley flow transition as previously suggested by researchers based on field observations on the same night a northerly cold airflow from the great basin is channeled through a pass on the eastern valley sidewall the current plunges into the stable valley atmosphere overshooting the altitude of its neutral buoyancy and generating a large scale oscillatory motion the resulting cross valley flow creates strong vertical shear with the down valley flow in the lower layers of the atmosphere a portion of the cross valley flow is captured by a scanning lidar the nested les is in good agreement with the lidar recorded radial velocity furthermore the les is able to resolve kelvin helmholtz waves and ejection and sweep events at the two layer interface which lead to topdown vertical mixing

first observations of elevated ducts associated with intermittent turbulence in the stable boundary layer over bosten lake china nocturnal radiative cooling is a main driver for atmospheric duct formation within this atmospheric process the impacts of intermittent turbulence on ducting have seldom been studied in this paper we reported two confusing ducting events observed in the early morning in august 2014 over bosten lake china when a stable boundary layer sbl still survived by using tethered high resolution gps radiosondes elevated ducts with strong humidity inversions were observed during the balloon ascents but were absent during observations made upon the balloon descent several minutes later this phenomenon was initially hypothesized to be attributable to turbulence motions in the sbl and the connection between the turbulence event and the radar duct was examined by the statistical thorpe method turbulence patches were detected from the ascent profiles but not from the descent profiles the possible reasons for the duct formation and elimination were discussed in detail the turbulent transport of moisture in the sbl and the advection due to airflows coming from the lake are the most probable reasons for duct formation in one case the downward transport of moisture by turbulence mixing within a kelvin helmholtz billow at the top of the low level jet resulted in duct elimination in another case the passage of density currents originating from the lake may have caused the elimination of the duct few studies have attempted to associate intermittent turbulence with radar ducts thus this work represents a pioneering study into the connection between turbulent events and atmospheric ducts in a sbl

turbulent erosion of persistent cold air pools numerical simulations abstracthigh resolution idealized numerical simulations are used to examine the turbulent removal of cold air pools commonly observed in mountain valleys and basins a control simulation with winds aloft increasing from 0 5 to 20 m s 1 over 20 h combined with typical cold air pool stratification illustrates the interplay over time of lowering of the top of the cold air pool spillover downstream of the valley from the upper reaches of the cold air pool wavelike undulations affecting the cold air pool s depth and stratification across the valley and smaller temporal and spatial scale kelvin helmholtz waves within the uppermost layers of the cold air pool the heat budget within the cold air pool demonstrates the nearly compensating effects of vertical and horizontal advection combined with turbulent heating of the upper portion of the cold air pool and cooling in the layers immediately above the cold air pool sensitivities of turbulent mixing in cold air pools to stratification and upstream terrain are

skeletal aragonite neomorphism in plio pleistocene sandy limestones and sandstones hollywood florida usa abstract the basic mechanics of the neomorphism of aragonitic shells to calcite are generally understood but fundamental questions remain concerning the details of the process completely and partially neomorphosed aragonitic skeletal fragments recovered in cores of plio pleistocene limestones and sandstones from hollywood florida provide some insights into the process skeletal aragonite neomorphism occurred in a volume for volume manner across solution films which resulted in the preservation of ghosts of fine scale microstructures neomorphic calcite crystals that replaced skeletal aragonite in at least some instances inherited their crystallographic orientation from adjoining calcite cement crystals rather than from the host shell microstructure some neomorphic calcite crystals inherited the optical orientation of nearby echinoderm ossicles however host shell microstructure commonly controlled the direction of migration of the neomorphic replacement front anisotropies in shell solubility influenced the directional rates of growth of neomorphic calcite crystals as evidenced by the strong tendency for the boundaries between neomorphic calcite and aragonite to parallel or coinicide with shell microstructural features no examples were observed where neomorphic calcite replaced aragonite along euhedral crystal faces such as commonly occurs during dolomitization and the replacement of limestone by megaquartz

observations of kelvin helmholtz instability at a cloud base with the middle and upper atmosphere mu and weather radars 1 using the very high frequency 46 5 mhz middle and upper atmosphere radar mur ka band 35 ghz and x band 9 8 ghz weather radars a kelvin helmholtz kh instability occurring at a cloud base and its impact on modulating cloud bottom altitudes are described by a case study on 8 october 2008 at the shigaraki mu observatory japan 34 85 n 136 10 e kh braids were monitored by the mur along the slope of a cloud base gradually rising with time around an altitude of 5 0 km the kh braids had a horizontal wavelength of about 3 6 km and maximum crest to trough amplitude of about 1 6 km nearly monochromatic and out of phase vertical air motion oscillations exceeding 3 m s 1 with a period of 3 min 20 s were measured by the mur above and below the cloud base the axes of the billows were at right angles of the wind and wind shear both oriented east north east at their altitude the isotropy of the radar echoes and the large variance of doppler velocity in the kh billows including the braids indicate the presence of strong turbulence at the bragg 3 2 m scale after the passage of the cloud system the kh waves rapidly damped and the vertical scale of the kh braids progressively decreased down to about 100 m before their disappearance the radar observations suggest that the interface between clear air and cloud was conducive to the presence of the dynamical shear instability by reducing static stability and then the richardson number near the cloud base downward cloudy protuberances detected by the ka band radar had vertical and horizontal scales of about 0 6 1 1 and 3 2 km respectively and were clearly associated with the downward air motions observed oscillations of the reflectivity weighted doppler velocity measured by the x band radar indicate that falling ice particles underwent the vertical wind motions generated by the kh instability to form the protuberances the protuberances at the cloud base might be either kh billow clouds or perhaps some sort of mamma reflectivity weighted particle fall velocity computed from doppler velocities measured by the x band radar and the mur showed an average value of 1 3 ms 1 within the cloud and in the protuberance environment

the convective boundary layer in the terra incognita numerical simulations of a convective boundary layer cbl are performed to investigate model behavior in the terra incognita also known as the gray zone the terra incognita of the cbl refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies which are on the order of the boundary layer depth using the rayleigh benard thermal instability as reference a set of idealized simulationsisused toshow that grayzone modelingisnot onlya numericalchallenge but also poses dynamical difficulties when the grid spacing falls within the cbl gray zone grid dependent convection can occur the size of the initial instability structures is set by the grid spacing rather than the natural state of the flow this changes higher order flow statistics and poses fundamental difficulties for gray zone modeling applications

high resolution numerical studies of stable boundary layer flows in a closed basin evolution of steady and oscillatory flows in an axisymmetric arizona meteor crater 1 we describe high resolution numerical simulations of flow within and over an axisymmetric approximation of the arizona meteor crater under stable boundary layer conditions motivations included guidance of and comparisons with observations during the meteor crater experiment metcrax performed in october 2006 modeling objectives were to assess the dynamical processes accounting for cold pool breakup various initial stable boundary layer sbl flows were considered on the basis of observed sbl flows and responses forcing conditions include impulsive sbl startups constant sbl accelerations and oscillatory sbl flows dominant responses include kelvin helmholtz shear instability at the top of the crater cold pool gravity waves arising from the crater geometry and seiches within the crater cold pool shear instability at the cold pool top exhibits a range of behaviors in response to different initial conditions including vortex shedding from the inflow crater lip vortex pairing strong mixing and erosion of the cold pool stratification and secondary vortex formation at the top of the mixing layer gravity wave responses depend on the flow speed are strongly three dimensional and time dependent and impact flow structure within and above the crater seiches arise from transient or oscillatory forcing and exhibit complex responses and spatial structures including upward phase progression multiple periods and vertical structures and sloshing that ejects cold pool air into the external sbl we conclude that both sloshing of cold pool air and mixing accompanying shear instability represent efficient dynamical mechanisms by which cold pool stratification can be eroded in response to external sbl motions

nested large eddy simulations of the intermittently turbulent stable atmospheric boundary layer over real terrain the nighttime stable atmospheric boundary layer over real terrain is modeled with nested high resolution large eddy simulations less the field site is located near leon kansas where the 1999 cooperative atmosphere surface exchange study took place the terrain is mostly flat with an average slope of 0 58 the main topographic feature is a shallow valley oriented in the east west direction the night of 5 october is selected to study intermittent turbulence under prevailing quiescent conditions brief turbulent periods triggeredby shear instability waves are modeled with good magnitude andtemporalprecision with a dynamic reconstruction turbulence closure in comparison conventional closures fail to excite turbulent motions and predict a false laminar flow a plausible new intermittency mechanism previously unknown owing to limited spatial coverage of field instruments at this site is unveiled with the less turbulence can be generated through gravity wave breaking over a stagnant cold air bubble in the valley upwind of the main tower the bubble is preceded by the formation of a valley cold air pool due to down valley drainage flows during the evening transition the bubble grows in depth by entraining cold down valley and downslope flows from belowandiserodedbyshear inducedwavebreakingonthetop thecyclicprocessofformationanderosionis repeated during the night leading to sporadic turbulent bursting

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

a grid refinement based approach for modeling the convective boundary layer in the gray zone a pilot study abstractthe model gray zone refers to the range of grid spacings comparable to the dominant length scale of the flow in the gray zone the flow is partially resolved and partially subgrid scale sgs neither ensemble averaging based parameterizations nor turbulence closures are appropriate for parameterizing the effects of sgs motions on the resolved flow the gray zone of the convective boundary layer cbl is in the range of cbl depth typically o 1 km a new approach that seeks explicit resolution of the unstable surface layer through a nest layer of fine grid spacing is proposed to improve cbl parameterization in the gray zone to provide the theoretical basis for the approach a linear analytic model is presented and one way nested simulations are performed to investigate the dynamical coupling between the surface layer and the mixed layer the analytic model shows that at the onset of thermal instability the vertical and horizontal structures of the mixed layer are set by surface layer forcings

obtaining parsimonious hydraulic conductivity fields using head and transport observations a bayesian geostatistical parameter estimation approach 1 flow path delineation is a valuable tool for interpreting the subsurface hydrogeochemical environment different types of data such as groundwater flow and transport inform different aspects of hydrogeologic parameter values hydraulic conductivity in this case which in turn determine flow paths this work combines flow and transport information to estimate a unified set of hydrogeologic parameters using the bayesian geostatistical inverse approach parameter flexibility is allowed by using a highly parameterized approach with the level of complexity informed by the data despite the effort to adhere to the ideal of minimal a priori structure imposed on the problem extreme contrasts in parameters can result in the need to censor correlation across hydrostratigraphic bounding surfaces these partitions segregate parameters into facies associations with an iterative approach in which partitions are based on inspection of initial estimates flow path interpretation is progressively refined through the inclusion of more types of data head observations stable oxygen isotopes 18o 16o ratios and tritium are all used to progressively refine flow path delineation on an isthmus between two lakes in the trout lake watershed northern wisconsin united states despite allowing significant parameter freedom by estimating many distributed parameter values a smooth field is obtained