preferential flow in a sandy vadose zone 2 mechanism and implications abstract field experiments conducted at the hancock agricultural research station during the 1987 growing season showed that preferential flow paths were the dominant flow pattern in the central sand area of wisconsin csaw the observed preferential flow was different from other preferential flow patterns mentioned in the literature e g short circuiting flow and fingering flow this paper presents a detailed discussion of the mechanism of this preferential flow and its influence on groundwater contamination soil solution sampling and solute transport modeling four factors that will determine the occurrence of a funneled flow are a conductivity of the upper finer layer k b slope of the inclined layer sin c retention potential of the upper finer layer 2 r and d ponding potential g l

intensification variability of tropical cyclones in directional shear flows vortex tilt convection coupling abstractthe coupling of vortex tilt and convection and their effects on the intensification variability of tropical cyclones tcs in directional shear flows is investigated in this study the he

simulation of preferential flow in three dimensional heterogeneous conductivity fields with realistic internal architecture subsurface flow is primarily controlled by the distribution of hydrogeological properties spatially correlated random fields currently the primary means of describing heterogeneity in these properties underutilizes the existing knowledge of geological systems a new computer code the braided channel simulator bcs 3d is used to geometrically simulate the spatial heterogeneity of hydrogeological properties using representations of surface topography to estimate the three dimensional arrangement of subsurface units four methods of assigning conductivity were used to generate conductivity fields as a basis for saturated flow simulation variograms measured for each of the conductivity fields give no indication of underlying discrete structure however particle tracking simulations showed that flow occurred along paths of preferentially high hydraulic conductivity results indicate that in systems where the contrast in conductivity is sufficiently great the location and magnitude of flow is constrained by discrete internal structure additionally geometrical simulation techniques such as bcs 3d can be used to produce property fields that embody these discrete geological structures

distribution of groundwater seepage to large surface water bodies the effect of hydraulic heterogeneities abstract at 26 sites on the upper great lakes and their connecting channels where groundwater seepage measurements have been made seepages decrease continually offshore at only seven 26 instead 17 63 of the sites have offshore seepages which substantially exceed those at some locations closer to shore the distributions fall into two consistent patterns one where a nearshore decrease in seepage with increasing distance is succeeded offshore by an increase and a second where nearshore seepages are relatively constant and then increase farther offshore the patterns have been observed in two independent studies using two totally different seepage meter designs and emplacement methods and are attributed to hydrogeologic heterogeneities beneath the surface water body detailed marine geophysical measurements at seven sites on green bay show that the anomalously high offshore seepages there are associated with local thinning of the relatively low hydraulic conductivity glacial sediments separating the bay from the underlying aquifer a fractured dolomite at these locations heterogeneity in sediment thickness is a stronger factor in causing seepage anomalies than is heterogeneity of either sediment or bedrock hydraulic conductivity insufficient information exists to confirm a parallel cause effect relation at the other sites but evidence points in that direction similar seepage anomalies have been observed at other smaller lakes by other researchers but never with this frequency it is argued that the cause of the difference is the size of the great lakes seepage occurs and measurements have been made over much greater offshore distances than in smaller lakes and the likelihood that heterogeneities will occur within the zone of measurement is thus also much greater

the evolution of vortex tilt and vertical motion of tropical cyclones in directional shear flows abstractrecent studies have demonstrated the importance of moist dynamics on the intensification variability of tropical cyclones tcs in directional shear flows here we propose that dry dynamic

spatial distribution and budget for submarine groundwater discharge in eckernforde bay western baltic sea submarine groundwater discharge sgd from subseafloor aquifers through muddy sediments was studied in eckernforde bay western baltic sea the fluid discharge was clearly traced by 222 rn enrichment in the water column and by the chloride profiles in pore water at several sites a considerable decrease in chloride to levels less than 10 of bottom water concentrations was observed within the upper few centimeters of sediment studies at 196 sites revealed that 22 of the seafloor of the bay area was affected by freshwater admixture and active fluid venting a maximal discharge rate of 9lm 22 d 21 was computed by modeling pore water profiles based on pore water data the freshwater flow from subseafloor aquifers to eckernforde bay was estimated to range from 4 3 10 6 to 57 3 10 6 m 3 yr 21 therefore 0 3 4 1 of the water volume of the bay is replaced each year owing to negligible surface runoff by rivers sgd is a significant pathway within the hydrological cycle of this coastal zone high resolution bathymetric data and side scan sonar surveys of pockmarks depressions up to 300 m long were obtained by using an autonomous underwater vehicle steep edges with depths increasing by more than 2 m within 8 10 m in lateral directions equivalent to slopes with an angle of as much as 118 were observed the formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread but easily overlooked pathway affecting the cycle of methane and dissolved constituents to coastal waters of the baltic sea

resistivity imaging reveals complex pattern of saltwater intrusion along monterey coast abstract electrical resistivity tomography data were acquired along 40 km of the monterey bay coast in central california these data resulted in electrical resistivity images to depths of approximately 280 m b s l which were used to understand the distribution of freshwater and saltwater in the subsurface and factors controlling this distribution the resulting resistivity sections were interpreted in conjunction with existing data sets including well logs seismic reflection data geologic reports hydrologic reports and land use maps from the region interpretation of these data shows a complex pattern of saltwater intrusion resulting from geology pumping and recharge the resistivity profiles were used to identify geological flow conduits and barriers such as palaeo channels and faults localized saltwater intrusion from individual pumping wells infiltration zones of surface fresh and brackish water and regions showing improvements in water quality due to management actions the use of ert data for characterizing the subsurface in this region has led to an understanding of the spatial distribution of freshwater and saltwater at a level of detail unattainable with the previously deployed traditional well based salinity mapping and monitoring techniques alone significant spatial variability in the extent and geometry of intrusion observed in the acquired data highlights the importance of adopting continuous subsurface characterization methods such as this one

eastern pacific hurricanes jimena of 1991 and olivia of 1994 the effect of vertical shear on structure and intensity abstract shear is a key inhibitor of tropical cyclone intensification although its signature is readily recognized in satellite imagery and theoretical or modeling studies provide some insight detailed observations have been limited airborne radar and in situ observations in hurricanes jimena of 1991 and olivia of 1994 are a step toward better understanding each storm was observed on two consecutive days initially both had small eyes 16 18 km radius and maximum winds of 57 m s 1 over sea surface temperatures sst 28 c in easterly environmental shear jimena maintained constant intensity or weakened gradually for 2 days in 13 20 m s 1 easterly shear olivia intensified in 8 m s 1 shear on the first day overnight the shear diminished to reverse and became westerly on the second day olivia weakened as the shear increased to 15 m s 1 from the west the storm moved over cooler sst and became surrounded by dryer air as convection weakened and the outer rainbands ceased to be effective barriers

multiscale structure and evolution of hurricane earl 2010 during rapid intensification abstractthe structure and evolution of hurricane earl 2010 during its rapid intensification as sampled by aircraft is studied here rapid intensification occurs in two stages during the early stage covering 24 h earl was a tropical storm experiencing moderate northeasterly shear with an asymmetric distribution of convection and the symmetric structure was shallow broad and diffuse the upper level circulation center was significantly displaced from the lower level circulation at the beginning of this stage deep vigorous convection termed convective bursts was located on the east side of the storm and appeared to play a role in positioning the upper level cyclonic circulation center above the low level center by the end of this stage the vortex was aligned and extended over a deep layer and rapid intensification began during the late stage rapid intensification continued as earl intensified 20 m s 1 during the next 24 h the vortex remained aligned in the presence of weaker vertical shear

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

the roles of asymmetric inflow forcing induced by outer rainbands in tropical cyclone secondary eyewall formation abstractthis study analyzes the secondary eyewall formation sef process in an idealized cloud resolving simulation of a tropical cyclone in particular the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands orbs is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of sef the enhancement of convection in the sef region follows the formation and inward contraction of an orb the azimuthal distribution of the enhanced convection is highly asymmetric but regular generally along a half circle starting from the downwind portion of the orb it turns out that the descending radial inflow in the middle and downwind portions of the orb initiates maintains a strong inflow in the boundary layer the latter is able to penetrate into the inner core region sharpens the gradient of radial velocity and reinforces convergence consequently warm and moist air is continuously lifted up at the lead

geologic influence on groundwater salinity drives large seawater circulation through the continental shelf observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources ecosystem function and the composition of the ocean but they cannot be explained by basic theory we show that these independent observations are linked and result from processes that drive variable density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations we use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore even at steady state the associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models results suggest that these phenomena may be common along continental shelves potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations

dynamics of the stratiform sector of a tropical cyclone rainband abstractairborne doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of hurricane rita the stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow beneath downward transport is organized into descending radial inflow in response to two regions of latent cooling in the outer upper regions of the rainband sublimational cooling introduces horizontal buoyancy gradients which produce horizontal vorticity and descending inflow similar to that of the trailing stratiform region of a mesoscale convective system within the zone of heavier stratiform precipitation melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband the organi

aerial infrared imaging reveals large nutrient rich groundwater inputs to the ocean 1 regional high resolution 0 1 c 0 5 m low altitude thermal infrared imagery tir reveals the exact input locations and fine scale mixing structure of massive cool groundwaters that discharge into the coastal zone as both diffuse flows and as 30 large point sourced nutrient rich plumes along the dry western half of the large volcanic island of hawaii these inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting water column profiling and nutrient sampling show that the plumes are cold buoyant nutrient rich brackish mixtures of groundwater and seawater by way of example we illustrate in detail one of the larger plumes which discharges ca 12 000 m3 d 1 ca 8 600 m3 d 1 freshwater rates comparable in volume to high flux groundwater outputs in better known tropical karst terrains we further show how nutrient mixing trends may be integrated into tir sea surface temperatures to produce surface water nutrient maps of regional extent

the effect of relative flow on the asymmetric structure in the interior of hurricanes abstract asymmetric structure of tropical cyclones simulated by the geophysical fluid dynamics laboratory high resolution triply nested movable mesh hurricane model was analyzed emphasis was placed on the quasi steady component of the asymmetric structure in the region of the eyewall it was found that the asymmetry was primarily caused by the relative wind that is the flow entering and leaving the storm region relative to the moving storm a set of idealized numerical experiments was first performed both with a constant and a variable coriolis parameter f and the addition of basic flows that were either constant or sheared with height analysis was then made for one case of hurricane gilbert 1988 to demonstrate that the quasi steady asymmetric structure analyzed in the idealized studies could be identified in this real data case vorticity analysis in the variable f experiment indicated that quasi steady asymmetries resulted in the eyewall region through the effect of vorticity advection due to

the influence of connected heterogeneity on groundwater flow and salinity distributions in coastal volcanic aquifers abstract geological heterogeneity is a key factor affecting rates and patterns of groundwater flow and the evolution of salinity distributions in coastal aquifers the hydrogeologic systems of volcanic aquifers are characterized by lava flows that can form connected geologic structures in the subsurface surface based geostatistical techniques were adopted to generate geologically realistic statistically equivalent model realizations of a hydrogeologic system based on that of the big island of hawaii conduit models the density dependent groundwater flow and solute transport code seawat was used to perform 3d simulations to investigate subsurface flow and salt transport through these random realizations statistically equivalent geological systems generated with sequential indicator simulation sis and equivalent homogeneous systems were also simulated for comparison simulation results show that conduit realizations tend to have more complex salinity distributions with larger mixing zones for which the center of mass is farther offshore compared to homogeneous and sis realizations the zone of groundwater discharge is also farther offshore than for homogeneous and sis models with higher point fluxes of both fresh and saline water and greater spatial variability this highlights the importance of the geometry of geologic features in coastal groundwater flow and solute transport processes in highly heterogeneous aquifers it also points to the importance of preferential flow with implications for both coastal groundwater resource management and solute fluxes to the ocean

on the characteristic height scales of the hurricane boundary layer in this study data from 794 gps dropsondes deployed by research aircraft in 13 hurricanes are analyzed to studythecharacteristicheightscalesofthehurricaneboundarylayer theheightscalesaredefinedinavariety of ways the height of the maximum total wind speed the inflow layer depth and the mixed layer depth the height of the maximumwind speed and the inflow layerdepth are referred to asthe dynamical boundarylayer heights while the mixed layer depth is referred to as the thermodynamical boundary layer height the data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights consistent with previous studies on the boundary layer structure in individual storms the dynamical boundary layer height is found to decrease with decreasing radius to the storm center the thermodynamic boundary layer height which is much shallower than the dynamical boundary layer height is also found to decrease with decreasing radius to the storm center the results also suggest that using the traditional critical richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer these different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations

asymmetric hurricane boundary layer structure from dropsonde composites in relation to the environmental vertical wind shear this study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmentalverticalwind shearin theinner core region data from1878 gps dropsondesdeployed by research aircraft in 19 hurricanes are analyzed in a composite framework kinematic structure analyses based on doppler radar data from 75 flights are compared with the dropsonde composites shear relative quadrantmeancomposite analysesshow that boththekinematicandthermodynamic boundarylayerheight scalestend to decrease with decreasing radius consistent with previous axisymmetric analyses there is still a clear separation between the kinematic and thermodynamic boundary layer heights both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer the inflow layer depth is found to be deeper in quadrants downshear with the downshear right dr quadrant being the deepest the mixed layer depth and height of maximum tangential wind speed are alike at the eyewall but are deeper outside in quadrants left of the shear the results also suggest that air parcels acquire equivalent potential temperature ue from surface fluxes as they rotate through the upshear right ur quadrant from the upshear left ul quadrant convection is triggered in the dr quadrant in the presence of asymmetric mesoscale lifting coincident with a maximum in ue energy is then released by latent heating in the downshear left dl quadrant convective downdrafts bring down cool and dry air to the surface and lower ue again in the dl and ul quadrants this cycling process may be directly tied to shear induced asymmetry of convection in hurricanes

the relationship between storm motion vertical wind shear and convective asymmetries in tropical cyclones abstract the influence of the direction of storm motion on the azimuthal distribution of electrified convection in 35 atlantic basin tropical cyclones from 1985 to 1999 was examined using data from the national lightning detection network in the inner 100 km flashes most often occurred in the front half of storms with a preference for the right front quadrant in the outer rainbands r 100 300 km flashes occurred predominantly to the right of motion although the maximum remained in the right front quadrant the results are shown to be consistent with previous studies of asymmetries in rainfall radar reflectivity and vertical motion with respect to tropical cyclone motion the motion effect has been attributed to the influence of asymmetric friction in the tropical cyclone boundary layer the authors previously found a strong signature in the azimuthal distribution of lightning with respect to vertical wind shear because both effects show clearly vertical wind shear and storm motion must themse

concentric eyewall asymmetries in hurricane gonzalo 2014 observed by airborne radar abstracttwo eyewall replacement cycles were observed in hurricane gonzalo by the noaa p3 tail ta radar and the recently developed nasa high altitude imaging wind and rain airborne profiler hiwrap radar these observations captured detailed precipitation and kinematic features of gonzalo s concentric eyewalls both before and after the outer eyewall s winds became the vortex maximum winds the data were analyzed relative to the deep layer environmental wind shear vector during the beginning eyewall replacement cycle stages the inner and outer eyewalls exhibited different asymmetries the inner eyewall asymmetry exhibited significant low level inflow updrafts and positive tangential acceleration in the downshear quadrants consistent with observational and theoretical studies the outer eyewall asymmetry exhibited these features in the left of shear quadrants further downwind from those of the inner eyewall it is suggested that the low level inflow occurring at the outer but not at the inner eyewal

vortex rossby waves in a numerically simulated tropical cyclone part i overall structure potential vorticity and kinetic energy budgets abstract the asymmetric structure in the inner core of a numerically simulated tropical cyclone is analyzed in this study the simulated tropical cyclone is found to be highly asymmetric in the inner core in the mid lower troposphere the asymmetry in the core is dominated by azimuthal wavenumber 1 and wavenumber 2 vortex rossby waves these waves propagate azimuthally upwind against the azimuthal mean cyclonic tangential flow around the eyewall and thus have a much longer cyclonic rotation period by a factor of 2 than the period of a parcel moving with the cyclonic mean tangential flow around the circumference they also propagate outward against the boundary layer inflow of the azimuthal mean cyclone the waves are only visible within a radius of about 60 km from the cyclone center beyond this distance the radial gradient of potential vorticity pv of the azimuthal mean cyclone is too weak to support the vortex rossby waves although the divergent motion remains strong the geopotential height an

a numerical study of convective scale structures in the outer cores of sheared tropical cyclones 1 updraft traits in different vertical wind shear magnitudes

quadrant distribution of tropical cyclone inner core kinematics in relation to environmental shear abstractairborne doppler radar data collected in tropical cyclones by national oceanic and atmospheric administration wp 3d aircraft over an 8 yr period 2003 10 are used to statistically analyze the vertical structure of tropical cyclone eyewalls with reference to the deep layer shear convective evolution within the inner core conforms to patterns shown by previous studies convection initiates downshear right intensifies downshear left and weakens upshear analysis of the vertical distribution of radar reflectivity and vertical air motion indicates the development of upper level downdrafts in conjunction with strong convection downshear left and a maximum in frequency upshear left intense updrafts and downdrafts both conform to the shear asymmetry pattern while strong updrafts occur in the eyewall intense downdrafts show far more radial variability particularly in the upshear left quadrant though they concentrate along the eyewall edges strong updrafts are collocated with low level inflow and

submarine lava tubes and channels high resolution side looking sonar surveys of the east pacific rise and seamounts in the eastern pacific have revealed the common presence of lava tubes and channels in seafloor volcanic terrains tube and channel systems commonly issue from small volcanic cones or domes are continuous for distances of 1 3 km and are considered to be important in distributing lavas around seafloor extrusive sites and creating characteristic morphology eruption rate and volume are probably the most important controlling factors in determining whether tubes or channels will form volatile content and state slope angle and preeruption surface morphology are secondary factors that influence the ease with which a tube or channel may form and its direction and shape seafloor tubes and channels may also have a profound influence on the structure and evolution of the upper oceanic crust tubes and channels are likely to form intracrustal horizontal pathways for circulating hydrothermal fluids flow differentiation processes acting within tubes and channels may affect the chemical composition of lavas and could be partially responsible for the chemical diversity of rocks along accretionary boundaries seafloor tubes and channels that are either partially water filled or contain volcaniclastics which are then buried within the volcanic pile can lower the compressional velocity and seismic response of the upper oceanic crustal layer along spreading axes

hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer a case study in jeju volcanic island korea abstract in order to identify the origin of saline groundwater in the eastern part of jeju volcanic island korea a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions the total dissolved solid contents of groundwaters are highly variable 77 21 782 mg l oxygen hydrogen sulfur and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater strontium isotopic compositions and br cl and i cl ratios strongly suggest that the source of salinity is modern seawater intrusion hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation exchange reactions the highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions these properties enhance the salinization of groundwater observed in the study area based on the cl br and 18 o data seawater was determined to have intruded inland some 2 5 km from the coastline considering the poor correlation of sampling depth and cl concentrations observed the position of seawater freshwater interface is not uniformly distributed in the study area due to heterogeneities of the basaltic aquifers

satellite derived rain rates in vertically sheared tropical cyclones 1 when tropical cyclones interact with environmental vertical wind shear they often take on an asymmetric structure prior observational and modeling studies have identified a preference for rainfall enhancement in the directions that are down shear and also to the left of the shear vector in the northern hemisphere this study composites hundreds of snapshots of the rain fields for atlantic tropical cyclones between 1988 2004 taken from satellite borne passive microwave radiometer estimates quadrant mean rain rates are fairly symmetrical in weakly sheared hurricanes for cases with shear greater than 10 m s 1 the favored downshear and left of shear quadrants have a factor of two greater rain rates in the inner core than the non favored quadrants beyond 100 km from the center this asymmetry increases to a factor of four or more the magnitude of the asymmetry is greater for tropical storms although the mean rain rates are less

mesoscale and convective structure of a hurricane rainband abstract the mesoscale thermodynamic kinematic and radar structure of a hurricane floyd rainband observed on 7 september 1981 is presented data are from 26 aircraft passes through the rainband from 150 to 6400 m a composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km in the direction parallel to rainband orientation radar reveals cellular reflectivity structure on the upwind and central portions of the rainband the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall in the radial direction a decrease of 12 k in e is observed across the rainband in the subcloud layer convective scale up and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

hodograph curvature and updraft intensity in numerically modeled supercells abstract a set of numerical simulations of supercell thunderstorms has been carried out with a range of low level curvatures in the environmental hodograph and midlevel shears they cover a range of hodograph shape as measured by the integrated helicity of the lowest 3 km of the hodograph the peak updraft occurs in the first hour of the storms and tends to be greater for larger values of environmental helicity there is also a slight tendency for greater updraft intensity with lesser values of midlevel shear significantly air in the core of the updrafts at midlevels 5 km is not the most unstable air at the level the most buoyant air rises in a region with a downward directed pressure gradient force which slows its ascent conversely pressure gradient forces at lower levels 2 3 km accelerate less buoyant air upward into the core of the midlevel updrafts the pressure gradient force is larger in the cases with more curvature in the environmental wind than the low curvature environments this i

effects of vertical wind shear and storm motion on tropical cyclone rainfall asymmetries deduced from trmm abstract vertical wind shear and storm motion are two of the most important factors contributing to rainfall asymmetries in tropical cyclones tcs global tc rainfall structure in terms of azimuthal distribution and asymmetries relative to storm motion has been previously described using the tropical rainfall measuring mission microwave imager rainfall estimates the mean tc rainfall distribution and the wavenumber 1 asymmetry vary with storm intensity and geographical location among the six oceanic basins this study uses a similar approach to investigate the relationship between the structure of tc rainfall and the environmental flow by computing the rainfall asymmetry relative to the vertical wind shear the environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200 and 850 hpa levels over an outer region extending from the radius of 200 800 km around the storm center the wavenumber 1 maximum rainfall asymmetry is downshear left right in the northern

seven types of subgrain boundaries in octachloropropane abstract subgrain boundaries in thin sheets of octachloropropane deformed at 0 7 0 8 t m on the stage of a microscope are seen to appear in the material in seven different ways type i boundaries show the classical evolution by polygonization of bent crystals type ii are essentially kink boundaries which migrate sideways during deformation to reach their present positions in the crystals type iii develop at the sites of former grain boundaries by reduction of misorientation of adjacent grains type iv and v originate by impingement of migrating grain boundaries or subgrain boundaries respectively type vi propagate in their own planes behind migrating grain boundaries to which they are attached type vii develop statically from optically strain free grains by a process probably otherwise similar to the type i process two thirds of the boundaries are types i or ii in view of the variety of subgrain boundary histories in ocp interpretation of similar features in minerals ought to be undertaken cautiously criteria are needed for telling the different types of subgrain boundaries apart in situations where only a final view of the structure is available as in optical and electron micrographs of rocks

utilizing multichannel electrical resistivity methods to examine the dynamics of the fresh water seawater interface in two hawaiian groundwater systems 1 multichannel electrical resistivity er measurements were conducted at two contrasting coastal sites in hawaii to obtain new information on the spatial scales and dynamics of the fresh water seawater interface and rates of coastal groundwater exchange at kiholo bay located on the dry kona side of the big island and at a site in maunalua bay oahu there is an evidence for abundant submarine groundwater discharge sgd however the hydrologic and geologic controls on coastal groundwater discharge are likely to be different at these two sites while at kiholo bay sgd is predominantly through lava tubes at the maunalua bay site exchange occurs mostly through nearshore submarine springs in order to calculate sgd fluxes it is important to understand the spatial and temporal scales of coastal groundwater exchange from er time series data subsurface salinity distributions were calculated using site specific formation factors a salinity mass balance box model was then used to calculate rates of point source i e spatially discreet and total fresh water discharge from these data mean sgd rates were calculated for kiholo bay 9 200 m3 d and for the maunalua bay site 5 900 m3 d while such results are on the same order of magnitude to geochemical tracer derived sgd rates the er sgd rates provide enhanced details of coastal groundwater exchange that can enable a more cohesive whole watershed perspective

rapid intensification of a sheared fast moving hurricane over the gulf stream abstracthurricane irene 1999 rapidly intensified from 65 to 95 kt 33 4 to 48 9 m s 1 in 18 h during the rapid intensification ri period the northeastward storm motion increased from 10 to 18 m s 1 the ambient southwesterly vertical wind shear increased from 6 7 to 10 13 m s 1 and the downshear tilt of the inner core vortex increased the azimuthal wavenumber 1 asymmetric convection that developed was consistent with a superposition of shear induced and storm motion induced forcing for vertical motion downshear and ahead of the center although the diabatic heating remained strongly asymmetric it was of sufficient intensity to dramatically increase the azimuthally averaged heating this heating occurred almost entirely inside the radius of maximum winds a region known to favor rapid warm core development and spinup of the vortex it is hypothesized that asymmetric forcing from the large vertical wind shear and rapid storm motion were responsible for ri an unanswered question is what determin

tropical cyclone motion and evolution in vertical shear abstract the motion and the evolution of tropical cyclone like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model the study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear the influence of vortex structure and the role of diabatic heating the results show that the initial response of the vortex to the vertical shear is to tilt downshear as soon as the tilt develops the upper level anticyclonic and lower level cyclonic circulations begin to interact with each other as a result of these interactions the tilted axis of the vortex reaches a stable state after an initial adjustment which varies with the structure of the vortex its environmental flow shear and the cumulus convective heating the motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms most of the vortices move with the environmental flow at about 650 hpa or

convective scale variations in the inner core rainbands of a tropical cyclone airborne doppler radar documented a variety of convective scale structures within the inner core rainbands of hurricane rita 2005 as predicted by past studies wind shear determined azimuthal variations in the convection all convective scale circulations had radial inflow at low levels upward motion and outflow in the midtroposphere convective cells at smaller radii contained a low level tangential jet determined largely by tangential acceleration due to angular momentum conservation uy r term while cells at larger radii contained a low level and or midlevel jet determined jointly by the uy r and vertical advection terms the outflow was at a higher lower altitude for the outer inner cells radial variations in the convective cells are attributable to differencesin buoyancy and vertical shear of the radial wind u z more buoyant updrafts at larger radii enhance vertical advection of y creating local tangential jets at midlevels at smaller radii the stronger low level radial inflow contributes to a greater u z confining convectively generated jets to low levels the low level tangential jet and convectively generated pressure gradients produce outward pointing supergradient acceleration that decelerates the boundary layer inflow consequently this supergradient flow will enhance convergence and convection at the radius of inner rainbandcells increasing the likelihoodof secondary eyewall formation it is hypothesized that a critical zone for secondary eyewall formation exists where sufficiently high u z consistently constrains the altitudes of convectively generated supergradient flow so that convection in this radial zone leads to a newly developed eyewall once an incipient secondary eyewall forms at a certain radius subsidence occurring along its inner edge separates it from the primary eyewall

vertical structure of hurricane eyewalls as seen by the trmm precipitation radar abstractstatistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones shown by the tropical rainfall measurement mission trmm precipitation radar pr shows that the eyewall contains high reflectivities and high echo tops with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure the overall echo strength height of echo top and presence of intense echo perturbations all increase with vortex strength intense echo perturbations decrease in frequency with low sea surface temperatures when the pr data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear the nature of convective processes in different parts of the eyewall becomes apparent the normalized statistics of the echo intensity brightband structure and maximum echo top height show that processes generating convective precipitation are generally favored in the dow

on the initial development of asymmetric vertical motion and horizontal relative flow in a mature tropical cyclone embedded in environmental vertical shear in this paper the authors focus on the initial development of asymmetric vertical motion and horizontal relative flow in a mature tropical cyclone tc embedded in an environmental vertical shear the fully compressible nonhydrostatic tc model was used to perform a series of numerical experiments with a mature tc with different intensities embedded in shear with different magnitudes and different vertical profiles results show that the development of both the wavenumber 1 asymmetric vertical motion and horizontal relative flow for a tc embedded in vertical shear is quite sensitive to both the magnitude and the vertical profile of wind shear as well as the intensity of the tc itself diagnostic analysis based on the quasi balanced potential vorticity inversion indicates that the balanced dynamics can only explain a small portion of the asymmetric vertical motion and relative flow the unbalanced processes contribute predominantly to the developmentoftheasymmetricflowinthesimulations itisshownthattheeyewallofamaturetcplaysarole somewhat like a material cylinder embedded in an environmental flow with vertical shear the interaction between the environmental shear and the eyewall produces vertical gradient of convergence divergence of horizontal wind around the lateral edge of the eyewall this forces much stronger asymmetric vertical motion than the balanced processes do and drives significant horizontal relative divergent flow over the storm core which opposes vertical shear and reduces the vertical tilt of the storm axis in addition the budget analysis for the axisymmetric tangential wind demonstrates that the asymmetric flow plays a dominant role in weakening the storm top down

a multiscale numerical study of hurricane andrew 1992 part ii kinematics and inner core structures despite considerable research understanding of the temporal evolution of the inner core structures of hurricanes is very limited owing to the lack of continuous high resolution observational data of a storm in this study the results of a 72 h explicit simulation of hurricane andrew 1992 with a grid size of 6 km are examined to explore the inner core axisymmetric and asymmetric structures of the storm during its rapid deepening stage based on the simulation a conceptual model of the axisymmetric structures of the storm is proposed most of the proposed structures confirm previous observations the main ingredients include a main inflow outflow in the boundary layer upper troposphere with little radial flow in between a divergent slantwise ascent in the eyewall a penetrative dry downdraft at the inner edge of the eyewall and a general weak subsiding motion in the eye with typical warming drying above an inversion located near an altitude of about 2 3 km the storm deepens as the axes of these features contract it is found that the inversion divides the eye of the hurricane vertically into two parts with a deep layer of warm dry air above and a shallow pool of warm moist air below the air aloft descends at an average rate of 5c m s 21 and has a residency time of several days in contrast the warm moist pool consists of air from the main inflow and penetrative downdrafts offset somewhat by the air streaming in a returning outflow into the eyewall in the lowest 2 km it is subject to the influence of the upward heat and moisture fluxes over the underlying warm ocean the warm moist pool appears to play an important role in supplying high ue air for deep convective development in the eyewall the penetrative downdraft is dry and originates from the return inflow in the upper troposphere and it is driven by sublimative evaporative cooling under the influence of the asymmetric radial inflow of dry cold air in the midtroposphere it penetrates to the bottom of the eye azimuthally downshear with a width often greater than 100 km in a radially narrow zone along the slantwise inner edge of the eyewall it is further shown that all the meteorological fields are highly asymmetric whereas the storm scale flow features a source sink couplet in the boundary layer and dual gyres aloft the inner core structures exhibit alternative radial inflow and outflow and a series of inhomogeneous updrafts and downdrafts all the fields tilt more or less with height radially outward and azimuthally downshear furthermore pronounced fluctuations of air motion are found in both the eye and the eyewall sometimes a deep layer of upward motion appears at the center of the eye all these features contribute to the trochoidal oscillation of the storm track and movement the main steering appears to be located at the midtroposphere 4 5 km and the deep layer mean winds represent well the movement of the hurricane

constraints on the partitioning of kīlauea s lavas between surface and tube flows estimated from infrared satellite data sulfur dioxide emission rates and field observations this paper describes how observations of sulfur dioxide so2 degassing rates obtained in situ thermal emission rates obtained from infrared satellite data and semiquantitative flow field observations can be used to elucidate the partitioning of lava between the surface and tube systems at k lauea volcano hawai i over a decadal timescale for most of our study period 2000 to 2009 we found that the infrared spectral radiance measured by moderate resolution imaging spectroradiometer from the flow field under clear sky conditions is controlled by the lava effusion rate and the amount of flow accommodated by the subsurface tube system at k lauea the degree of tubing is estimated qualitatively using field observations and we show that the satellite data and in situ gas data can be used to estimate the percentage of lava on the surface relative to the total amount erupted this empirical relationship works to describe many cases in the past decade at k lauea but breaks down when there is a lack of concurrent clear sky radiance and so2 data or when magma is being stored and degassed prior to eruption our observations provide a simple way to estimate the partitioning of k lauea s total lava supply between surface and tube fed flows using a long term dataset this is important because the transition between periods when lava is distributed primarily by surface flows to periods where tubes dominate has been suggested to indicate significant changes in the character of decadal scale eruptions at k lauea heliker et al bull volcanol 59 381 393 1998 in addition it is during those times when surface flows predominate that the flow field does most of its lateral expansion and the hazards associated with the lava effusion become more pronounced

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

the role of paleochannels in groundwater seawater exchange relict fluvial channels that are infilled with high permeability sediments act as preferred pathways for groundwater flow and solute transport in coastal regions such paleochannels can provide a hydraulic connection between freshwater aquifers and the sea facilitating saltwater intrusion landward or freshwater discharge offshore although paleochannels have been implicated in several instances of saltwater intrusion there has been little direct study of these channels to confirm their role in this work simulation modeling of a general multi layered coastal plain aquifer setting indicates that when a paleochannel breaches a confining unit offshore submarine groundwater discharge of intermediate salinity occurs this discharge is largely concentrated along the margins of the channel conversely seawater inflow occurs along the channel axis resulting in higher salinity in the middle of the channel relative to the flanks chirp seismic and electromagnetic data collected offshore wrightsville beach nc usa confirm these simulation results and indicate fresher porewater along channel flanks and slightly higher porewater salinity along the channel axis hence paleochannels contribute to the spatial variability in submarine groundwater discharge by serving as conduits of focused fluid exchange simulations also reveal that the freshwater saltwater transition zone is closer to land below paleochannels than in locations with a continuous confining unit this indicates that such channels are likely to be significant modes of saltwater intrusion into confined aquifers when excess freshwater extraction occurs on land

saltwater intrusion in the unconfined coastal aquifer of ravenna italy a numerical model summary the ravenna pine forests represent an historical landmark in the po river plain they have great environmental historical and tourist value the san vitale pine forest is located 10 km north of the town it is surrounded by an urban area the city industrial infrastructure and the waterworks of the agricultural drainage system most land in this area is below mean sea level as a result no natural freshwater hydraulic gradient contrasts the density gradient of saltwater in the last century many events land subsidence land reclamation and drainage urban and industrial development and gas and deep groundwater extractions coastal dune destruction led to the intrusion of large volumes of brackish and saline groundwater today the freshwater in this coastal aquifer consists of low salinity water lenses floating on the saltwater wedge this study is aimed at understanding how past and present human activities have affected the saltwater intrusion process in the phreatic aquifer and how the predicted future sea level rise will affect the salinisation process we used a numerical model to quantify these effects on the density dependent groundwater flow hydraulic head and salinity distribution seepage and salt load fluxes to the surface water system the simulations show that over the last century artificial subsidence and heavy drainage started the salinisation process in the study area and a relative sea level rise will accelerate the increase in salt load in the coming decades affecting the entire aquifer climatic conditions in the area result in limited precipitations throughout the year and preclude efficient aquifer recharge especially in spring and summer when saltwater seepage is extensive the lack of a continuous coastal dune system favors salt wedge intrusion

large submarine groundwater discharge sgd from a volcanic island 1 we measured seepage rates of coastal groundwater from a volcanic island standing in the south sea of korea the seepage rates measured along the sandy coast were in the range 50 300 m yr which are much higher than those reported from typical continental coast the 18o tracer in potential seeping waters signifies that they are mixtures of basal groundwater and pristine seawaters on the eastern coast of jeju almost all groundwater discharge is attributed to recirculating seawater while fresh groundwater contributes about 20 of the total submarine groundwater discharge sgd on the western coast of jeju thus sgd appears to be important for the management of water resources in western jeju the measured radionuclides 228ra 226ra and 222rn and nutrients in the groundwater suggest that the discharge of both fresh and recirculated seawater will have a significant influence on the budget of coastal nutrients and other chemical constituents in this region

effect of volcanic dykes on coastal groundwater flow and saltwater intrusion a field scale multiphysics approach and parameter evaluation volcanic dykes are common discrete heterogeneities in aquifers however there is a lack of field examples of and methodologies for comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport we have applied an integrated multi physics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer the approach involved ground geophysical imaging passive magnetics and electrical resistivity tomography well hydraulic testing and tidal propagation analysis which provided constraints on the geometry of the dyke network the subsurface saltwater distribution and the sandstone hydrodynamic properties and connectivity a three dimensional variable density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations a good agreement of model simulations with tide induced head fluctuations geophysically derived pore water salinities and measured apparent resistivities was obtained when dykes hydraulic conductivity storativity and effective porosity are respectively about three one and one orders of magnitude lower than the host aquifer the presence of the dykes results in barrier like alterations of groundwater flow and saltwater intrusion preferential flowpaths occur parallel to observed dyke orientations freshwater inflows from upland recharge areas concentrate on the land facing side of the dykes and saltwater penetration is higher on their sea facing side this has major implications for managing groundwater resources in dyke intruded aquifers including in coastal and island regions but also provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems this article is protected by copyright all rights reserved

the dynamic response of the hurricane wind field to spiral rainband heating abstract the response of the hurricane wind field to spiral rainband heating is examined by using a three dimensional nonhydrostatic linear model of the vortex anelastic equations diabatic heat sources which are designed in accordance with previous observations of spiral rainbands are made to rotate with the flow around the hurricane like wind field of a balanced axisymmetric vortex common kinematic features are recovered such as the overturning secondary circulation descending midlevel radial inflow and cyclonically accelerated tangential flow on the radially outward side of spiral rainbands comparison of the responses to the purely convective and stratiform rainbands indicates that the overturning secondary circulation is mostly due to the convective part of the rainband and is stronger in the upwind region while midlevel radial inflow descending to the surface is due to the stratiform characteristics of the rainband and is stronger in the downwind region the secondary horizontal wind maxim

a numerical study of hurricane erin 2001 part ii shear and the organization of eyewall vertical motion a high resolution numerical simulation of hurricane erin 2001 is used to examine the organization of vertical motion in the eyewall and how that organization responds to a large and rapid increase in the environmental vertical wind shear and subsequent decrease in shear during the early intensification period prior to the onset of significant shear the upward motion in the eyewall was concentrated in small scale convective updrafts that formed in association with regions of concentrated vorticity herein termed mesovortices with no preferred formation region around the eyewall asymmetric flow within the eye was weak as the shear increased an azimuthal wavenumber 1 asymmetry in storm structure developed with updrafts tending to occur on the downshear to downshear left side of the eyewall continued intensification of the shear led to increasing wavenumber 1 asymmetry large vortex tilt and a change in eyewall structure and vertical motion organization during this time the eyewall structure was dominated by a vortex couplet with a cyclonic anticyclonic vortex on the downtilt left downtilt right side of the eyewall and strong asymmetric flow across the eye that led to strong mixing of eyewall vorticity into the eye upward motion was concentrated over an azimuthally broader region on the downtilt side of the eyewall upstream of the cyclonic vortex where low level environmental inflow converged with the asymmetric outflow from the eye as the shear diminished the vortex tilt and wavenumber 1 asymmetry decreased while the organization of updrafts trended back toward that seen during the weak shear period based upon the results for the erin case as well as that for a similar simulation of hurricane bonnie 1998 a conceptual model is developed for the organization of vertical motion in the eyewall as a function of the strength of the vertical wind shear in weak to moderate shear higher wavenumber asymmetries associated with eyewall mesovortices dominate the wavenumber 1 asymmetry associated with the shear so that convective scale updrafts form when the mesovortices move into the downtilt side of the eyewall and dissipate on the uptilt side under strong shear conditions the wavenumber 1 asymmetry characterized by a prominent vortex couplet in the eyewall dominates the vertical motion organization so that mesoscale ascent with embedded convection occurs over an azimuthally broader region on the downtilt side of the eyewall further research is needed to determine if these results apply more generally

the dynamics of boundary layer jets within the tropical cyclone core part ii nonlinear enhancement abstract observations of wind profiles within the tropical cyclone boundary layer until recently have been quite rare however the recent spate of observations from the gps dropsonde have confirmed that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer in part i a mechanism for producing such a maximum was proposed whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration due to gradient wind imbalance were identified as being i vertical diffusion ii vertical advection and iii horizontal advection and a linear analytical model of the boundary layer flow in a translating tropical cyclone was presented and used to diagnose the properties of the jet and the near surface flow a significant shortcoming was that the jet was too weak which was argued to be due to the neglect of vertical advection here a high resolution dry hydrostatic numerical

tropical cyclone formation in a sheared environment a case study abstract the development of hurricane danny 1997 from depression to hurricane was examined using cloud to ground lightning data reconnaissance aircraft data and satellite imagery vertical wind shear between 850 and 200 hpa of 5 11 m s 1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development early in the period the storm intensified steadily in the presence of this downshear convection during the last and most intense outbreak a second vortex appeared to develop within the convection evidence is presented that the new downshear vortex became the dominant vortex and absorbed the original based on these events it is hypothesized that the presence of moderate vertical wind shear accelerated the early development process equivalent potential temperature fields within 500 m of the surface were examined only well after the period of vortex interaction did the characteristic mature tropical cyclone radial profile of eq

geologic effects on groundwater salinity and discharge into an estuary summary submarine groundwater discharge sgd can be an important pathway for transport of nutrients and contaminants to estuaries a better understanding of the geologic and hydrologic controls on these fluxes is critical for their estimation and management we examined geologic features porewater salinity and sgd rates and patterns at an estuarine study site seismic data showed the existence of paleovalleys infilled with estuarine mud and peat that extend hundreds of meters offshore a low salinity groundwater plume beneath this low permeability fill was mapped with continuous resistivity profiling extensive direct sgd measurements with seepage meters n 551 showed fresh groundwater discharge patterns that correlated well with shallow porewater salinity and the hydrogeophysical framework small scale variability in fresh and saline discharge indicates influence of meter scale geologic heterogeneity while site scale discharge patterns are evidence of the influence of the paleovalley feature beneath the paleovalley fill fresh groundwater flows offshore and mixes with saltwater before discharging along paleovalley flanks on the adjacent drowned interfluve where low permeability fill is absent fresh groundwater discharge is focused at the shoreline shallow saltwater exchange was greatest across sandy sediments and where fresh sgd was low the geologic control of groundwater flowpaths and discharge salinity demonstrated in this work are likely to affect geochemical reactions and the chemical loads delivered by sgd to coastal surface waters because similar processes are likely to exist in other estuaries where drowned paleovalleys commonly cross modern shorelines the existence and implications of complex hydrogeology are important considerations for studies of groundwater fluxes and related management decisions

environmental flow impacts on tropical cyclone structure diagnosed from airborne doppler radar composites abstractfollowing a recent demonstration of multicase compositing of axisymmetric tropical cyclone tc structure derived from airborne doppler radar measurements the authors extend the analysis to the asymmetric structure using an unprecedented database from 75 tc flights in particular they examine the precipitation and kinematic asymmetry forced by the tc s motion and interaction with vertical wind shear for the first time they quantify the average magnitude and phase of the three dimensional shear relative kinematic asymmetry of observed tcs through a composite approach the composite analysis confirms principal features of the shear relative tc asymmetry documented in prior numerical and observational studies e g downshear tilt downshear right convective initiation and a downshear left precipitation maximum the statistical significance of the composite shear relative structure is demonstrated through a stratification of cases by shear magnitude the impact of storm motion on eyewall convect

vortex rossby waves in a numerically simulated tropical cyclone part ii the role in tropical cyclone structure and intensity changes abstract in part i the author analyzed the asymmetric structure in the inner core of a numerically simulated tropical cyclone and found that the asymmetry near the eyewall in the mid lower troposphere is dominated by wavenumber 1 and 2 vortex rossby waves these waves are found to be well coupled with asymmetries in eyewall convection and thus may play an important role in the life cycle of a tropical cyclone in this paper analyses are extended to include the role of these vortex rossby waves in tropical cyclone structure and intensity changes the waves are found to transport angular momentum from the eyewall to the eye accelerating tangential winds in the eye at the expense of decelerating the tangential wind in the eyewall and thus they play an important role in the inner core dynamics of the tropical cyclone convection in the eyewall is enhanced between the downstream trough and upstream ridge in the vortex rossby waves but suppressed between the downstream ridge and upstream trough this close

quadrant dependent evolution of low level tangential wind of a tropical cyclone in the shear flow abstractthis study investigates the quadrant by quadrant evolution of the low level tangential wind near the eyewall of an idealized simulated mature tropical cyclone embedded in a unidirectional shear flow it is found that the quadrant averaged tangential wind in the right of shear quadrants weakens continuously while that in the left of shear quadrants experiences a two stage evolution a quasi steady stage followed by a weakening stage after the imposing of vertical wind shear this leads to a larger weakening rate in the right of shear and a stronger jet in the left of shear quadrants the budget analysis shows that the quadrant dependent evolution of tangential wind is controlled through the balance between the generalized coriolis force gcf i e the radial advection of absolute angular momentum and the advection terms the steady decreasing of the gcf is primarily responsible for the continuous weakening of jet strength in the right of shear quadrants for the left of shear quadrants the quas

modes of seawater intrusion during transgressions analytical methods and numerical experiments are used to study salinization of groundwater in response to sea level rise the system that is studied involves a saturated porous medium with an inclined upper surface the upper surface is progressively inundated during sea level rise to simulate transgression the landward migration of the shoreline four modes of seawater intrusion are distinguished 1 horizontal intrusion for slow transgression and a relatively high permeability substrate 2 vertical intrusion by seawater fingering for fast transgression and a sand silt substrate 3 vertical intrusion by diffusion for fast transgression and a low permeability clay substrate 4 vertical intrusion by combined diffusion and low salinity fingering for fast transgression and a clay layer at the seafloor overlying an aquifer these four modes are characterized by the development of very distinctive transition zones between the fresh and salt groundwater domains an analytical expression is derived for the critical transgression rate which separates horizontal mode 1 from dominantly vertical modes 2 4 intrusion for modes 3 and 4 salinization significantly lags behind sea level rise the results are consistent with observations of fossil fresh brackish groundwater beneath many continental shelves and shallow seas

homogenization and effective parameters for the henry problem in heterogeneous formations 1 general upscaling of density dependent flow is investigated for the classical two dimensional henry problem of saltwater intrusion in coastal aquifers combined theoretical and numerical results are here presented effective flow and transport parameters for saline intrusions could be derived for statistically isotropic and anisotropic heterogeneous permeability fields by use of homogenization theory applying also to the preasymptotic regime our numerical results indicate that heterogeneities in permeability affect foremost the transient evolution of saltwater intrusion whereas the steady state saltwater distribution is less sensitive to spatially varying permeabilities and longitudinal dispersion for the isotropic media the effective permeability is found to correspond to the geometric mean as under conditions without fluid density contrast the extension of results to anisotropic media requires nontrivial corrections for the effective permeability which include the variance of log k and the directional correlation lengths the appropriate dispersion coefficients for the problem correspond to the local dispersion coefficients rather than macrodispersion coefficients these results are discussed in light of the specific flow configuration posed in the henry problem

mesoscale aspects of the downshear reformation of a tropical cyclone the downshear reformation of tropical storm gabrielle 2001 was investigated using radar reflectivity and lightning data that were nearly continuous in time as well as frequent aircraft reconnaissance flights initially the storm was a marginal tropical storm in an environment with strong 850 200 hpa vertical wind shear of 12 13 m s 1 and an approaching upper tropospheric trough both the observed outflow and an adiabatic balance model calculation showed that the radial vertical circulation increased with time as the trough approached convection was highly asymmetric with almost all radar return located in one quadrant left of downshear in the storm reconnaissance data show that an intense mesovortex formed downshear of the original center this vortex was located just south of rather than within a strong downshear left lightning outbreak consistent with tilting of the horizontal vorticity associated with the vertical wind shear the downshear mesovortex contained a 972 hpa minimum central pressure 20 hpa lower than minimum pressure in the original vortex just 3 h earlier the mesovortex became the new center of the storm but weakened somewhat prior to landfall it is argued that dry air carried around the storm from the region of upshear subsidence as well as the direct effects of the shear prevented the reformed vortex from continuing to intensify despite the subsequent weakening of the reformed center it reached land with greater intensity than the original center it is argued that this intensification process was set into motion by the vertical wind shear in the presence of an environment with upward motion forced by the upper tropospheric trough in addition the new center formed much closer to the coast and made landfall much earlier than predicted such vertical shear induced intensity and track fluctuations are important to understand especially in storms approaching the coast

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

quantification of point source groundwater discharges to the ocean from the shoreline of the big island hawaii aerial thermal infrared imaging has revealed that submarine groundwater discharge sgd along the western coast of the big island of hawaii is often focused as point source discharges that create buoyant groundwater plumes that mix into the coastal ocean we quantified the sgd fluxes associated with several plumes using natural geochemical tracers offshore transects of 222rn and 224ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area using a series of simultaneous mass balance equations for water salt and radon we determined the groundwater fluxes of six plumes near kona hawaii the average sgd fluxes ranged from 1100 m3 d21 to 12 000 m3 d21 of total fresh saline sgd the fresh meteoric groundwater equivalents for the same flows modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition ranged from 630 m3 d21 to 8600 m3 d21 these fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh sgd rates in this region

driving mechanisms for groundwater flow and salt transport in a subterranean estuary this paper presents field measurements and numerical simulations of groundwater dynamics in the intertidal zone of a sandy meso tidal beach the study focusing on vertical hydraulic gradients and pore water salinities reveals that tides and waves provide important forcing mechanisms for flow and salt transport in the nearshore aquifer such forcing interacting with the beach morphology enhances the exchange between the aquifer and ocean the spatial and temporal variations of vertical hydraulic gradients demonstrate the complexity and dynamic nature of the processes and the extent of mixing between fresh groundwater and seawater in a subterranean estuary these results provide evidence of a potentially important reaction zone in the nearshore aquifer driven by oceanic oscillations land derived contaminants may undergo important biogeochemical transformations in this zone prior to discharge