air sea interactions over terra nova bay during winter simulation with a coupled atmosphere polynya model a preliminary simulation of the terra nova bay polynya has been performed with a coupled atmosphere polynya model the atmospheric model is a hydrostatic primitive equations model that has been validated previously by a simulation of the strong katabatic winds observed in that area the polynya model includes a representation of the free drift of frazil ice and simple sea ice dynamics and thermodynamics two and three dimensional experiments have been performed under polar night conditions two dimensional experiments show that an open warm water area influences significantly the atmospheric circulation in the antarctic coastal zone an additional ice breeze effect is simulated and is responsible for the strenghthening of the katabatic winds near the coast because of the important temperature difference between the continental air and the ice free ocean up to 40 c strong surface heat fluxes are simulated over the polynya finally a three dimensional experiment has been performed the integration domain includes terra nova bay the polynya observed in that region is well simulated it is found that heat losses from the polynya surface are stronger than previously thought but are probably constrained by the idealized representation of frazil ice which is assumed to be uniform in each grid box this stresses the need for having a better knowledge of frazil ice evolution in large polynyas

radar echoes from lightning and their microphysical environment 1 a uhf profiler radar has detected lightning echoes which occurred preferentially in a balance layer the stratum of mean zero doppler velocity with rising small ice particles and falling graupel and hail thus providing the conditions for collisional charging and lightning the results support prior findings of the role of the balance layer in lightning generation the 32 8 cm profiler radar is particularly well suited for these observations because the lightning echoes are not masked by the precipitation echoes thus allowing simultaneous measurement of the microphysical and kinematic properties

seasonal contrasts in snow cover characteristics on ross sea ice floes snow cover characteristics on ice floes in the ross sea antarctica were examined during cruises in autumn 1998 and summer 1999 the autumn snow cover was shallower colder and had higher and more variable salinity and smaller single and composite grain sizes than the summer snow cover the autumn snow cover was dominated by rounded particles in chains of grains and clusters while the summer snow cover was composed primarily of melt clusters there was extensive flooding of the summer snow cover at the snow ice interface the summer snow cover was nearly isothermal and close to the melting point it exhibited obvious signs of melting and refreezing in the form of ice lenses pipes and superimposed ice although no melt ponds were evident many of the ice lenses were located directly above the saline standing water found on most of the summer ice floes

cation exchange and caco3 dissolution during artificial recharge of effluent to a calcareous sandstone aquifer summary this research describes a field study and laboratory simulations of the geochemical evolution of groundwater following a recharge of effluent into aquifers the study was conducted in the soil aquifer treatment sat system of the shafdan sewage reclamation plant israel the sat system recharges secondary effluent into the calcareous sandstone sediments of the israeli coastal aquifer as a tertiary treatment the reclaimed effluent is recovered ca 500 m off the recharge basin and is used for unlimited irrigation the laboratory simulations in which effluent was pumped through experimental columns packed with pristine shafdan sediment showed that the chemical composition of the outflowing water was controlled mainly by cation exchange and caco 3 dissolution na k and mg 2 were adsorbed and ca 2 was desorbed during the initial stage of recharge the equilibrium distribution of the adsorbed cations was ca 2 60 mg 2 20 and na and k 10 each the ca 2 in the shafdan production wells and in the experimental columns outflow 5 meq l 1 was always higher than the ca 2 in the recharged effluent 3 5 meq l 1 indicating continuous caco 3 dissolution this study demonstrates that besides mixing a suite of geochemical processes should be considered when assessing groundwater quality following artificial recharge of aquifers

initiation locations of lightning flashes relative to radar reflectivity in four small florida thunderstorms this study examines initiation locations of intracloud ic and cloud to ground cg lightning near kennedy space center florida on one day one unicellular and two multicellular thunderstorms occurred over land and one multicellular storm was 30 km offshore the storm over ocean was visible on radar 47 51 minutes before its first flash of 17 total first echoes in the storms over land were 23 12 and 16 minutes prior to the first flashes of 34 16 and 9 total initiation points of 66 flashes were identified using the first initial breakdown ib pulse location from electric field change measurements or a vhf source coincident with the first ib pulse ten ics occurred without enough data to similarly locate the initiation all but 2 of 35 flashes that initiated as negative cgs began below 6 8 km altitude two higher cg initiations 7 1 7 5 km were the first cgs in two storms initiations of 21 normal ics occurred above 7 9 km 6 late stage ics initiated at 5 5 7 5 km and 4 hybrid ic cg flashes initiated as ics at 6 6 8 1 km initiation locations were tightly clustered in small regions of each cell over land early and mature stage flashes initiated within 2 x 2 km in each cell or about 10 25 of the mid level reflectivity coverage one cell over ocean had initiations within 6 x 5 km less than 30 of its reflectivity area the ic initiations generally occurred above reflectivity cores in 15 35 dbz and cg initiations were in 30 45 dbz beside or atop cores

sea ice ridging in the ross sea antarctica as compared with sites in the arctic at the end of the 1980 austral winter surface roughness measurements were made by laser profilometer during a series of flights over the ross sea pack ice the total track length was 2696 km and 4365 ridges were counted the frequency distribution of individual ridge heights was found to be well described by a negative exponential distribution no clear cut regional variation was noted in ridge heights the distribution of ridge frequencies per kilometer showed a strong positive skew with a modal value of 1 88 the most frequent ridging occurred off the east coast of victoria land comparisons with similar data sets from the arctic indicate that large ridges are significantly more likely in the arctic ocean than in the ross sea utilizing a reasonable model for the geometry of ridges estimates are made of the average thickness of a hypothetical continuous layer composed only of the deformed ice from ridges the noncoastal ross sea value of 0 09 m is less than half of the lowest comparable value from the arctic 0 20 m central beaufort sea where values in excess of 1 0 m have been observed in the shear zones north of greenland

winter snow cover on sea ice in the weddell sea measurements of snow thickness temperature salinity density and stratigraphy acquired during the 1992 winter weddell gyre study are presented results indicate that the winter snow cover on sea ice in the weddell sea is extremely variable extreme fluctuations in antarctic synoptic conditions air temperature precipitation humidity and wind speed occur during the austral winter they result in unique modifications and additions to the snow layer during the aging process and act to stabilize an otherwise easily wind redistributed shallow snow cover and develop well packed drift features the latter occur even over relatively undeformed areas of sea ice and have a significant localized effect on the snow thickness distribution significant variability in snow grain size mean 2 73 3 12 mm and density 0 32 0 09 g cm 3 is observed as a result of cyclical switches between high and low temperature gradient metamorphism multiple icy layers indicate multiple thaw freeze events one such event occurred during a 3 day station during which the air temperature rose by 22 c in 12 hours to approximately 0 c this paper also examines mechanisms for flooding of the snow ice interface including snow loading even where the latter is not a factor the layer of snow immediately above the snow ice interface is commonly damp and saline 10 limitations in the data set are discussed and comparisons are drawn with other experiments

precipitation development in a new mexico thunderstorm observations were made of a thunderstorm over langmuir laboratory for atmospheric research on 2 august 1984 four doppler radars were closely spaced allowing observations to be taken at high elevation angles as a result the vertical component of the precipitation particle velocity was accurately measured in conjunction with the vertical air velocity obtained by integration of the continuity equation the particle terminal velocity field was computed backward integration of particle trajectories showed that most precipitation embryos originated near the tops of thunderstorm precursor clouds when these cloud tops were 7 8 km above sea level early and mature phase precipitation grew by accretion at levels below 7 km and resulted in relatively high density graupel or hail late phase precipitation underwent growth mainly above 8 km and was sufficiently small in diameter and low in density to undergo rapid melting at the freezing level

autumn sea ice thickness ridging and heat flux variability in and adjacent to terra nova bay ross sea antarctica the variability of sea ice thickness and snow depth observed from the r v nathaniel b palmer in late may 1998 in and adjacent to terra nova bay tnb ross sea antarctica is described conductive heat fluxes are estimated on the basis of the observed snow and ice thicknesses there was only 6 areal coverage of open water in tnb and 87 of the areal coverage of unridged ice was 0 3 m thick between the western and eastern margins of tnb there were increases in the area weighted unridged ice thickness 0 05 0 25 m and the areal extent of ridging 2 5 18 5 ridged ice accounted for 44 66 of the total ice mass in tnb and was as vital to thickening the ice cover as it was outside the bay where 30 60 of the total ice mass was contained within the 5 35 of ice that was ridged satellite passive microwave special sensor microwave imager ssm i data show that the extensive ice cover in tnb was normal for this time of year probably because of the blocking effect of thick ridged 100 concentration pack ice outside the bay despite the extensive ice cover in tnb there was an order of magnitude difference in area weighted mean heat flux between the bay and the pack ice for example depending on the choice of bulk snow thermal conductivity value ks 0 14 or 0 31 w m 1 k 1 the heat flux values for unridged ice were 199 or 216 w m 2 in tnb versus 35 or 49 w m 2 on the inbound pack ice leg and 20 or 39 w m 2 on the outbound pack ice leg factoring in the contribution of ridges to the ice thickness distribution decreased the heat flux in the bay and the pack ice by 25 or 36 depending on ks the greatest proportion of the heat flux in tnb occurred through the ice no more than 30 of the heat loss was from open water since the ice conditions observed in tnb were apparently normal for the time of year the heat fluxes also must have been quite normal

lightning charge analyses in small convection and precipitation electrification cape experiment storms a least squares method for analyzing multiple ground based measurements of electric field changes produced by lightning has been applied to seven small thunderstorms that occurred on july 19 and august 9 1991 during the convection and precipitation electrification cape experiment two of the storms produced little or no cloud to ground cg lightning and a third produced cg lightning only during its early stages a total of 79 flashes were analyzed on july 19 and 315 on august 9 about 58 of these discharges could be fitted to either a point charge q or a point dipole p model and in this sample the spatial pattern of the q and p solutions was consistent with a tripole or double dipole charge pattern in the cloud in cases where there was little or no cg lightning the inferred region of upper positive charge was quite close to the inferred negative region comparisons of the locations of upper p solutions with measurements of radar reflectivity at s band show that the p solutions tended to cluster at altitudes where the reflectivity was between 25 and 35 dbz comparisons of q and p model solutions with the locations of cg flash strike points determined using a network of wideband direction finders showed an average horizontal displacement of 3 9 km with a standard deviation of 3 3 km this displacement is consistent with the expected random development of a stepped leader channel from the altitude of the negative q region to the ground

regions where lightning flashes began regions where 773 flashes began during 13 thunderstorms were located by calculating centroids of the sources of the first six or 10 vhf pulses that were emitted by each flash sources were located by measuring differences in the times at which their pulses arrived at five widely spaced receivers stationed on the ground we found that the distribution of origin heights was bimodal with peaks at 5 3 and 9 2 km above mean sea level amsl standard errors in the coordinates of flash origins were estimated to be 20 80 m in x and y and 160 240 m in the height coordinate z there were 431 flashes in the lower group and 342 in the higher flashes in the lower group were more numerous in 10 storms in three storms high flashes were in the majority there was evidence to suggest that this condition depended partly on the phase of the host thunderstorm recorded e field changes produced by 165 flashes whose paths we had mapped convinced us that the vast majority of the 773 flashes including the 342 high flashes had also been negative flash origins tended to cluster in regions that were a few kilometers or less in horizontal diameter densities of flash origins in these regions ranged from 1 25 to 25 km 3 the origins of 658 flashes were mapped onto radar precipitation patterns of their host storms we found that 66 of the flashes began within one picture element approximately 270 m of the contours for 20 dbz 27 began inside these contours and most of these began at edges of high reflectivity cores the remaining 7 began outside the 20 dbz contours similar results 73 19 8 were obtained for 276 high flashes that began at heights above 7 4 km amsl but 195 ground flashes scored 54 36 9 and showed a greater tendency to begin inside the 20 dbz contours the distribution of distances between origins and their nearest 20 dbz contours showed a marked peak near zero we concluded that charge density in thunderclouds was affected by the presence of heavy precipitation and that 20 dbz surfaces enclosed regions that carried excess negative charge

seasonal changes of sea ice characteristics off east antarctica data on antarctic sea ice characteristics and their spatial and temporal variability are presented from cruises between 1986 and 1993 for the region spanning 60 150 e between october and may in spring the sea ice zone is a variable mixture of different thicknesses of ice plus open water and in some regions only 30 40 of the area is covered with ice 0 3 m thick the thin ice and open water areas are important for air sea heat exchange crystallographic analyses of ice cores supported by salinity and stable isotope measurements show that approximately 50 of the ice mass is composed of small frazil crystals these are formed by rapid ice growth in leads and polynyas and indicate the presence of open water throughout the growth season the area averaged thickness of undeformed ice west of 120 e is typically less than 0 3 m and tends to increase with distance south of the ice edge ice growth by congelation freezing rarely exceeds 0 4 m with increases in ice thickness beyond this mostly attributable to rafting and ridging while most of the total area is thin ice or open water in the central pack much of the total ice mass is contained in ridges taking account of the extent of ridging the total area averaged ice thickness is estimated to be about 1m for the region 60 90 e and 2 m for the region 120 150 e by december new ice formation has ceased in all areas of the pack and only floes 0 3 m remain in most regions these melt completely over the summer and the new season s ice formation starts in late february by march the thin ice has reached a thickness of 0 15 0 30 m with nilas formation being an important mechanism for ice growth within the ice edge

the relationship between lightning type and convective state of thunderclouds thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud ic and cloud to ground cg lightning a consistent temporal evolution starting with peak ic activity changing to predominant cg activity and concluding with strong outflow microburst suggests that ice is responsible for both the electrical i e lightning and dynamical i e microburst phenomena the ic activity is attributed to the updraft driven accumulation of graupel particles in the central dipole region and the subsequent cg activity to the descent of ice particles beneath the height of the main negative charge the subsequent descent and melting of ice particles beneath the height of the 0 c isotherm are associated with the acceleration of the downdraft and outflow the ic lightning precursor can provide a valuable short term 5 10 min warning for microburst hazard at ground level

on the sea ice regime of the ross sea antarctica variations spatiotemporelles de la glace de mer determinees a partir de donnees microondes passives et meteorologiques hydrologiques

the vertical structure of toga coare convection part ii modulating influences and implications for diabatic heating abstract the temporal variability of western pacific warm pool convection especially its vertical structure is examined in this study distributions of convective echo top heights and 30 dbz contour heights have been produced from shipboard radar data collected during tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare elevation and suppression of convective heights was primarily influenced by the phase of the intraseasonal oscillation iso with heights being suppressed during convectively inactive and westerly wind burst wwb phases of the iso echo top heights were greatest during the convective phases and post wwb phases of the iso however at least some very deep convection was always present within the area observed by radar indicating that local conditions were favorable for deep convection even when the large scale environment was not capable of supporting widespread deep convection in addition to the iso echo top and 30 dbz contour heights were als

investigation of groundwater residence times during bank filtration in berlin a multi tracer approach berlin relies on induced bank filtration from a broad scale lake type surface water system because the surface water contains treated sewage wastewater residues are present in surface water and groundwater multiple environmental tracers including tritium and helium isotopes 3h 3he 4he stable isotopes 18o and 2h and a number of persistent sewage indicators such as chloride boron and a selection of pharmaceutical residues phenazone type analgesics and their metabolites carbamazepine and anthropogenic gadolinium gdexcess were used to estimate travel times from the surface water to individual production and observation wells at two sites the study revealed a strong vertical age stratification throughout the upper aquifer with travel times varying from a few months to several decades in greater depth whereas the shallow bank filtrate is characterized by the reflection of the time variant tracer input concentrations and young 3h 3he ages the deeper older bank filtrate displays no tracer seasonality 3h 3he ages of a few years to decades and strongly deviating concentrations of several pharmaceutical residues reflecting concentrations of the source surface water over time the phenazone type pharmaceuticals persist in the aquatic environments for decades bank filtration in berlin is only possible at the sandy lakeshores in greater water depth impermeable lacustrine sapropels inhibit infiltration the young bank filtrate originates from the nearest shore whereas the older bank filtrate infiltrates at more distant shores this paper illustrates the importance of using multiple tracer methods capable of resolving a broad range of residence times to gain a comprehensive understanding of time scales and infiltration characteristics in a bank filtration system copyright 2007 john wiley sons ltd

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

combined interpretation of pumping and tracer tests theoretical considerations and illustration with a field test pumping and tracer tests are two well established ground water reservoir tests hydraulic conductivity can be derived from both conductivities are studied in a mainly layered heterogeneous coastal aquifer in belgium with a pumping and tracer test and results of both are compared characteristics and important points in performance and interpretation of the tests are discussed the interpretation method of pumping tests must be chosen very carefully application of interpretation methods based on models underestimating or even neglecting the leakage towards the pumped permeable layer results in an overestimation of the horizontal conductivity of this layer the larger the distance of the used observation well s the larger this overestimation becomes this is illustrated here with the interpretation of the drawdown data obtained during the pumping test using different analytical models and a numerical model with an inverse axi symmetric numerical model incorporating layered heterogeneity results of the pumping test are in good agreement with results from the tracer test many discrepancies between pumping and tracer test data performed in layered heterogeneous media can be explained when realistic pumping test interpretation methods are applied and when leakage is not underestimated

the impact of variably saturated conditions on hydrogeochemical changes during artificial recharge of groundwater artificial recharge of groundwater is often used to either purify partially treated wastewater or to enhance the quality of surface water by percolation through a variably saturated zone in many cases the most substantial purification process within the infiltration water is the redox dependent biodegradation of organic substances the present study was aimed at understanding the spatial and temporal distribution of the redox reactions that develop below an artificial recharge pond near lake tegel germany at this site like at many artificial recharge sites the hydraulic regime immediately below the pond is characterised by cyclic changes between saturated and unsaturated conditions these changes which occur during each operational cycle result from the repeated formation of a clogging layer at the pond bottom regular hydrogeochemical analyses of groundwater and seepage water in combination with continuous hydraulic measurements indicate that no3 and mn reducing conditions dominate beneath the pond as long as water saturated conditions prevail manganese fe and so42 reducing conditions are confined to a narrow zone directly below the clogging layer and in zones of lower hydraulic conductivity the formation of the clogging layer leads to a steady decrease of the infiltration rate which ultimatively causes a shift to unsaturated conditions below the clogging layer atmospheric o2 then starts to penetrate from the pond fringes into this region leading to i the re oxidation of the previously formed sulphide minerals and ii the enhanced mineralisation of sedimentary particulate organic c the mineralisation of sedimentary particulate organic c leads to an increased h2co3 production and subsequent dissolution of calcite

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

winter snow cover variability on east antarctic sea ice copyright 1998 by the american geophysical union analysis of the first detailed data set of snow characteristics collected over east antarctic sea ice in winter confirms that on small scales snow on antarctic sea ice is highly variable in both thickness and properties high amplitude cyclical variability in atmospheric forcing related to the passage of storms is responsible for the high degree of textural heterogeneity observed changes in snow properties were examined over a 3 week period during which a largely icy snow cover formed at near freezing temperatures metamorphosed to snow in which facetted crystals and depth hoar dominated as the air temperature plummeted even on flat ice significant localized thickening of snow occurs in the form of barchan dunes although we observed great variability in snow thickness and properties on local scales overall snow thickness distribution and the complex textural assemblage of snow types are similar from region to region similar observations were made by sturm et al 1998 in west antarctica large scale similarities are also apparent in mean snow density grain size and bulk snow salinity although high variability is again found across individual floes rapid depth hoar formation is a ubiquitous process that greatly affects the density texture grain size and effective thermal conductivity of the snow cover the observed heterogeneity results in varying snow effective thermal conductivities the mean bulk effective thermal conductivity computed from the proportion of observed snow types is 0 164 w m 1 k 1 significantly lower than values typically used in large scale sea ice modeling but similar to that derived by sturm et al 1998 in a near simultaneous experiment in the bellingshausen and ross seas it varies from 0 097 to 0 383 w m 1 k 1 in different snow pits the findings support those of sturm et al 1998 that periodic flooding and subsequent snow ice formation which are also ubiquitous processes effectively diminish the degree to which basal snow processes create inhomogeneities in the snow pack

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

estimating late winter heat flow to the atmosphere from the lake dominated alaskan north slope the conductive heat flux through the snow cover f a is used as a proxy to examine the hypothesis that there is a significant heat flow from the alaskan north slope to the atmosphere because of the large number of lakes in the region f a is estimated from measurements of snow depth temperature and density on tundra grounded ice and floating ice in mid april 1997 at six lakes near barrow northwestern alaska the mean f a values from tundra grounded ice and floating ice are 1 5 5 4 and 18 6 w m 2 respectively a numerical model of the coupled snow ice water soil system is used to simulate f a and there is good agreement between the simulated and measured fluxes the flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn the flux from the floating ice is high because the ice has a relatively high thermal conductivity and a body of relatively warm water remains below the growing ice at the end of winter the flux from the grounded ice is intermediate between that from the tundra and that from the floating ice and depends on the timing of the contact between the growing ice and the lake sediments and whether or not those sediments freeze completely using the estimated f a values combined with the areal fractions of tundra grounded ice and floating ice derived from synthetic aperture radar images area weighted f a values are calculated for six areas f a values for the ice vary between 9 8 and 13 8 w m 2 and those from the ice plus tundra vary between 3 9 and 5 3 w m 2 the f a values are similar to those observed in the sea ice covered regions of the south and north polar oceans in winter the north slope of alaska may thus make a significant contribution to the regional energy budget in winter

joint assimilation of piezometric heads and groundwater temperatures for improved modeling of river aquifer interactions the ensemble kalman filter enkf is increasingly used to improve the real time prediction of groundwater states and the estimation of uncertain hydraulic subsurface parameters through assimilation of measurement data like groundwater levels and concentration data at the interface between surface water and groundwater measured groundwater temperature data can provide an additional source of information for subsurface characterizations with enkf additionally an improved prediction of the temperature field itself is often desirable for groundwater management in this work we investigate the worth of a joint assimilation of hydraulic and thermal observation data on the state and parameter estimation with enkf for two different model setups i a simple synthetic model of a river aquifer system where the parameters and simulation conditions were perfectly known and ii a model of the limmat aquifer in zurich switzerland where an exhaustive set of real world observations of groundwater levels 87 and temperatures 22 was available for assimilation year 2007 and verification year 2011 results for the synthetic case suggest that a joint assimilation of piezometric heads and groundwater temperatures together with updating of uncertain hydraulic parameters gives the best estimation of states and hydraulic properties of the model for the real world case the prediction of groundwater temperatures could also be improved through data assimilation with enkf for the validation period it was found that parameter fields updated with piezometric heads reduced rmse s of states significantly heads 49 temperature 15 but an additional conditioning of parameters on groundwater temperatures only influenced the characterization of the temperature field

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

thunderstorm electrification a case study the paper presents interpretation of triple doppler radar observations of a thunderstorm that occurred at the kennedy space center florida precipitation particle motions inside the storm as evaluated from the three radial velocity radar data sets are presented in a selected vertical plane throughout the storm development these data are interpreted and compared with observations of vhf radio emission sources and lightning charge centers derived from an earlier analysis krehbiel 1981 the main feature of the particle motion field is the persistence at nearly the same altitude throughout the entire period of analysis of a balance level characterized by a zero value of the precipitation particle mean vertical velocity further analysis based on considerations of radar reflectivity and air velocity suggests the presence at this altitude of relatively large precipitation particles suspended in an updraft the lightning negative charge centers appear to be less than 1 km above the particle balance level

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

heat transport and temperature distribution during managed artificial recharge with surface ponds summary managed aquifer recharge mar is a well established practice for managing groundwater reserves in a sustainable way in this paper we look at the influence of temperature variations of the infiltration water in the recharged aquifer the paper focuses on mar systems consisting of an infiltration pond surrounded by extraction wells a number of different 2d configurations and an operational system in the belgian dune area are investigated using field observations and numerical modelling with seawat seasonally varying temperature in the infiltration water results in a zonation of subsequent lower and higher temperatures in the aquifer the impact of infiltration water temperature in the aquifer is significant but restricted to the area between the pond and extraction wells quickly decreasing farther from the infiltration area colder water during winter results in a decrease of infiltration capacity which can be as high as 1 5 2 times with respect to summer infiltration infiltration water temperature variations equally influence residence times of the infiltrated water in general residence times become smaller for water infiltrated during summer and larger for water infiltrated during winter infiltration and extraction rate their ratios and seasonal variability and location of extraction wells are all contributing factors to the impact of varying temperature of the infiltration water finally it is shown that temperature provides only a rough proxy for residence times of solutes because of the important conduction of heat

relationships among narrow bipolar events total lightning and radar inferred convective strength in great plains thunderstorms 1 narrow bipolar events nbes are a recently discovered distinct class of intracloud lightning discharges whose associated processes produce the most powerful very high frequency vhf radiation observed from lightning nbes are thus the prime candidate for proposed satellite based vhf global lightning mapping and storm tracking missions in this study we offer a detailed evaluation of the great plains los alamos sferic array lasa we then statistically compare nbe rates to non nbe lightning rates measured by both the lasa and the national lightning detection network nldn and to nexrad radar inferred metrics of convective strength for thunderstorms in the great plains from may to july 2005 we find strong correlations between total lightning rate and convective strength especially in terms of the height of 30 dbz radar echo however we find much weaker correlations between nbe rate and non nbe lightning rate and between nbe rate and radar inferred convective strength though nbes occur in the same storms as other lightning they cluster more closely in both space and time and may be indicative of specific types of storms and or specific stages in convective development indeed we find that nbes are more prevalent in and perhaps indicative of the strongest convection however even the strongest convection as inferred by radar does not always produce nbes we compare these results to past studies of nbes which were based in florida we also briefly discuss the implications of these results for satellite based vhf lightning detection

lightning location relative to storm structure in a supercell storm and a multicell storm relationships between lightning location and storm structure are examined for one radar volume scan in each of two mature severe storms one of these storms had characteristics of a supercell storm and the other was a multicell storm data were analyzed from dual doppler radar and dual vhf lightning mapping systems the distributions of vhf impulse sources were compared with radar reflectivity vertical air velocity and their respective gradients in the supercell storm lightning tended to occur along streamlines above and downshear of the updraft and reflectivity cores vhf impulse sources were most concentrated in reflectivities between 30 and 40 dbz and were distributed uniformly with respect to updraft speed in the multicell storm on the other hand lightning tended to coincide with the vertical reflectivity and updraft core and with the diverging streamlines near the top of the storm the results suggest to us that the location of lightning in these severe storms was most directly associated with the wind field structure relative to updraft and reflectivity cores since the magnitude and vertical shear of the environmental wind are fundamental in determining the reflectivity and wind field structure of a storm we suggest that these environmental parameters are also fundamental in determining lightning location

electrification life cycle of incipient thunderstorms this work evaluates how clouds evolve to thunderstorms in terms of microphysical characteristics and produces the first intracloud ic and cloud to ground cg lightning flashes observations of 46 compact isolated thunderstorms during the 2011 2012 spring summer in southeast brazil with the x band polarimetric radar and two and three dimensional lightning location systems demonstrated key parameters in a cloud s vertical structure that produce the initial electrification and lightning activity the majority 98 of the first cg flashes were preceded by approximately 6 min by intracloud ic lightning the most important aspect of the observations going into this paper which came originally from the visual examination of a large number of thunderstorms is that an initial positive differential reflectivity zdr associated with supercooled raindrops evolved to reduced zdr and even negative values in the cloud layer between 0 and to 15 c before and during the time of the initial lightning suggesting evolution from supercooled raindrops to frozen particles promoting the formation of the conical graupel an enhanced negative specific differential phase kdp down to 0 5 km 1 in the glaciated layer above 40 c was predominantly observed at the time of the first cg flash indicating that ice crystals such as plates and columns were being vertically aligned by a strong electric field these results demonstrate that the observations of zdr evolution in the mixed layer and negative kdp in the upper levels of convective cores may provide useful information on thunderstorm vigor and lightning nowcasting

water quality changes in the dunes of the western belgian coastal plain due to artificial recharge of tertiary treated wastewater abstract since july 2002 tertiary treated waste water has been used to artificially recharge the phreatic aquifer of the dunes in the belgian western coastal plain the purpose of this project is to develop a sustainable water source and thereby minimize lowering of the water table while maintaining production capacity the recharged water is extracted via production wells located south and north of two ponds used for the recharge the uniqueness of this system is that the total dissolved solids in this recharge water is low 50 mg l in comparison with natural dune water 550 mg l in this paper water quality of recharge water groundwater between ponds and extraction wells extracted water and dune water is analysed the extraction water quality is determined by mixing of recharged water and dune water mineralisation of the recharge water occurs mainly by carbonate dissolution further o2 consumption no 3 reduction and oxidation of fe sulfide minerals are distinguished at the beginning of 2007 clogging of the ponds began to occur and it was observed that extraction rates and temperature of the recharge water influenced the amount of water which could be recharged using cl data it is confirmed that all the recharged water is recovered by the extraction wells finally it is concluded that the quality of the extracted water does not change significantly as a function of time