nitrate fluctuations at the water table implications for recharge processes and solute transport in the chalk aquifer this study investigates fluctuations in nitrate concentration at the water table to improve understanding of unsaturated zone processes in the chalk aquifer sampling was conducted using a novel multi level sampler during periods of water table rise over 5 years at a vertical resolution of 0 05 m nitrate concentration increased as the water table seasonally recovered with similar inter annual trends with depth the rising water table activated horizontal fractures facilitating the delivery of water elevated by up to 10 mg l of nitrate with respect to the adjacent groundwater below these fractures are considered to activate via piston displacement of water from the adjoining matrix hydrograph analysis identified 16 events which significantly perturbed the water table within 24 48 h of rainfall consistent nitrate concentrations indicate recharge through persistent fracture flow from the surface was not generally the primary driver of the rapid water table response during these events instead the response was attributed to the piston displacement of porewater immediately above the water table however a single event in november 2012 delivered relatively dilute recharge indicating rapid persistent fracture flow following rainfall was possible to a depth of 14 15 m decreases in porewater nitrate concentration around fracture horizons and the dilution of many groundwater samples with respect to porewaters indicate a fresher source of water at depth this was considered most likely to be a result of near surface water bypassing the matrix because of widespread mineralization on fracture surfaces which retard water and solute exchange therefore persistent fracture flow maybe considered a frequent process operating independently of the matrix and is not necessarily event driven

a critique of emanuel s hurricane model and potential intensity theory we present a critique of emanuel s steady state hurricane model which is a precursor to his theory for hurricane potential intensity pi we show that a major deficiency of the theory is the tacit assumption of gradient wind balance in the boundary layer a layer that owes its existence to gradient wind imbalance in the radial momentum equation if a more complete boundary layer formulation is included using the gradient wind profiles obtained from emanuel s theory the tangential wind speed in the boundary layer becomes supergradient invalidating the assumption of gradient wind balance we show that the degree to which the tangential wind is supergradient depends on the assumed boundary layer depth the full boundary layer solutions require a knowledge of the tangential wind profile above the boundary layer in the outer region where there is subsidence into the layer and they depend on the breadth of this profile this effect is not considered in emanuel s theory we argue that a more complete theory for the steady state hurricane would require the radial pressure gradient above the boundary layer to be prescribed or determined independently of the boundary layer the issues raised herein highlight a fundamental problem with emanuel s theory for pi since that theory makes the same assumptions as in the steady state hurricane model our current findings together with recent studies examining intense hurricanes suggest a way forward towards a more consistent theory for hurricane pi copyright 2008 royal meteorological society

a model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

on the influences of vertical wind shear on symmetric tropical cyclone structure derived from amsu abstract axisymmetric temperatures and gradient balanced winds associated with tropical cyclones derived from the advanced microwave sounding unit are stratified by the 24 h averaged vector difference of the horizontal wind between 200 and 850 hpa or vertical wind shear using 186 total cases that are limited to tropical cyclones with intensities greater than 33 m s 1 or mature and are located over sea surface temperatures greater than 26 4 c vertical wind shear based composites are created results show that as the vertical wind shear increased the upper level warm core structure associated with the tropical cyclone descended resulting in a shallower balanced vortex these observationally based results are presented in the context of recent mesoscale modeling results of the effect of shear on tropical cyclone structure

thermal fronts and attracting lagrangian coherent structures in the north bay of bengal during december 2015 march 2016 abstract we investigate two dimensional advective stirring by satellite derived ocean surface currents in the north bay of bengal during december 2015 march 2016 using the framework of lagrangian coherent structures lcs the forward and backward finite time lyapunov exponent fftle and bftle respectively fields indicate that freshwater parcels from the river run off are subjected to intense stirring by the ocean surface currents which contain both geostrophic and wind forced ekman currents large scale thermal fronts present in the satellite based sea surface temperature sst fields are then shown to closely resemble attracting lcs alcs that govern horizontal advective stirring on subseasonal time scales statistical estimates of the angle between the thermal fronts of all spatial scales present in the sst data and the alcs from the entire north bay of bengal show a preference to align with each other significantly in the presence of sufficiently strong alcs in their neighbourhood thermal fronts are shown to have a strong preference to align with them finite time advection of fluid particles over around a week to compute the bftle fields results in the strongest alignment between the thermal fronts and neighbouring alcs the robustness of our results are established by presenting analyses of i geostrophic currents from altimeter data and ii a reanalysis based fine scale salinity field attracting lcs identified as sufficiently strong ridges in the bftle fields are argued to represent reasonable estimates of the location and orientation of fronts thermal or salinity formed by advective stirring over subseasonal time scales

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

recharge of the upper chalk aquifer at a site in hampshire england 2 solute movement abstract this paper describes a field experiment to study the movement of solutes through the unsaturated zone of the chalk using soil physical techniques to calculate water fluxes and sequential soil coring to measure solute concentrations with depth and time deuterium oxide was used as a tracer to follow water movement nitrate leaching beneath spring barley was calculated below the root zone approximately 40 kg ha 1 yr 1 of nitrate nitrogen were leached beyond root depth 1 m in the two study years at concentrations of between 20 and 75 mg l 1 and at a downward velocity of 0 85 m yr 1

the role of observed environmental conditions and precipitation evolution in the rapid intensification of hurricane earl 2010 abstractan investigation into the possible causes of the rapid intensification ri of hurricane earl 2010 is carried out using a combination of global analyses aircraft doppler radar data and observations from passive microwave satellites and a long range lightning network results point to an important series of events leading to and just after the onset of ri all of which occur despite moderate 7 12 m s 1 vertical wind shear present beginning with an initially vertically misaligned vortex observations indicate that asymmetric deep convection initially left of shear but not distinctly up or downshear rotates into more decisively upshear regions following this convective rotation the vortex becomes aligned and precipitation symmetry increases the potential contributions to intensification from each of these structural changes are discussed the radial distribution of intense convection relative to the radius of maximum wind rmw determined from doppler wind retrievals is estimated from

former carboniferous overburden in the northern appalachian basin a reconstruction based on vitrinite reflectance abstract elevated vitrinite reflectance values have been observed in the upper devonian west falls group of the northern new york appalachian basin in new york lopatin modeling suggests that the high thermal maturity of these and associated strata was caused by the presence of a devonian and carboniferous overburden that has subsequently been eroded from the northern appalachian basin devonian overburden reconstructed from extrapolation of stratigraphic data thickens from west 0 4 km to east 2 0 km across the field area in contrast carboniferous overburden reconstructed by lopatin modeling thins from west 2 0 3 4 km to east 0 7 1 2 km the inferred geometry of a northeasterly thinning wedge of sediment is compatible with the existing distribution of late paleozoic sediments in the appalachian basin and suggests the northern part of the basin experienced only moderate subsidence during carboniferous time

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

origins of aircraft damaging clear air turbulence during the 9 december 1992 colorado downslope windstorm numerical simulations and comparison with observations results from numerical simulations of the colorado front range downslope windstorm of 9 december 1992 are presented although this case was not characterized by severe surface winds the event caused extreme clearair turbulence cat aloft as indicated by the severe structural damage experienced by a dc 8 cargo jet at 9 7 km above mean sea level over the mountains detailed measurements from the national oceanic and atmospheric administration environmental research laboratories environmental technology laboratory doppler lidar and wind profilers operating on that day and from the defense meteorological satellite program satellite allow for a uniquely rich comparison between the simulations and observations four levels of grid refinement were used in the model the outer domain used national centers for environmental prediction data for initial and boundary conditions the finest grid used 200 m in all three dimensions over a 48 km by 48 km section the range of resolution and domain coverage were sufficient to resolve the abundant variety of dynamics associated with a time evolving windstorm forced during a frontal passage this full range of resolution and model complexity was essential in this case many aspects of this windstorm are inherently three dimensional and are not represented in idealized models using either 2d or so called 2d 3d dynamics both the timing and location of wave breaking compared well with observations the model also reproduced cross stream wavelike perturbations in the jet stream that compared well with the orientation and spacing of cloud bands observed by satellite and lidar model results also show that the observed cat derives from interactions between these wavelike jet stream disturbances and mountain forced internal gravity waves due to the nearly east west orientation of the jet stream these two interacting wave modes were orthogonal to each other thermal gradients associated with the intense jet stream undulations generated horizontal vortex tubes hvts aligned with the mean flow these hvts remained aloft while they propagated downstream at about the elevation of the aircraft incident and evidence for such a vortex was seen by the lidar the model and observations suggest that one of these intense vortices may have caused the aircraft incident reports of strong surface gusts were intermittent along the front range during the period of this study the model showed that interactions between the gravity waves and flow aligned jet stream undulations result in isolated occurrences of strong surface gusts in line with observations the simulations show that strong shears on the upper and bottom surfaces of the jet stream combine to provide an episodic downburst of turbulence in the present case the perturbations of the jet stream provide a funnel shaped shear zone aligned with the mean flow that acts as a guide for the downward transport of turbulence resulting from breaking gravity waves the physical picture for the upper levels is similar to the surface gusts described by clark and farley resulting from vortex tilting the cat feeding into this funnel came from all surfaces of the jet stream with more than half originating from the vertically inclined shear zones on the bottom side of the jet stream visually the downburst of turbulence looks similar to a rain shaft plummeting to the surface and propagating out over the plains leaving relatively quiescent conditions behind

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

the evolution of hurricane humberto 2001 abstractin 2001 the national oceanic and atmospheric administration and the national aeronautical and space administration marshaled their resources to sample hurricane humberto for 3 successive days during the fourth convection and moisture experiment camex 4 humberto developed from a tropical storm into a category 2 hurricane despite the deep layer vertical shear of the environmental horizontal wind vws increasing markedly on the second and third days of sampling as exhibited in earlier studies the eyewall convection developed an azimuthal wavenumber 1 n 1 asymmetry as the vws increased horizontal divergence and vertical stability within 100 km of the eye exhibited persistent relationships to the vws vector the warm core evolved in an unexpected way the warm anomaly was initially located in the lower troposphere and built upward as the storm intensified the maximum temperature anomaly remained in the lower troposphere on all 3 days while the development of the upper tropospheric warm anom

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

a three dimensional lagrangian hurricane eyewall computation the computation of a hurricane eyewall is necessary to determine mixing between the eyewall and the neighbouring eye and environment regions we define a lagrangian eyewall region by computing the lagrangian structures of hyperbolic stability that distinguish the eyewall from surrounding regions the methods used guarantee the stability and continuity of the eyewall for time dependent velocity fields as an added benefit of our methods fast convergence gives the opportunity to utilize the methods in real time simulations the exact location of lagrangian coherent structures is accomplished through a ridge extraction algorithm which is efficient for locating the ridges found in this model a complete construction of three dimensional coherent structures is accomplished by overlaying horizontally continuous ridge curves onz levels copyright c

the thermal history of the new york basement determined from 40ar 39ar k feldspar studies constraints on the thermochronologic evolution of the new york crystalline basement are mainly restricted to the high temperature early cooling history following 1 1 ga grenville metamorphism u pb methods and the late cooling history fission track methods the thermal history for the one billion years between these intervals is herein assessed using 40ar 39ar hornblende muscovite biotite and k feldspar thermochronology hornblende preferred ages suggest cooling below 450 500 c between ca 900 and 950 ma total gas ages of biotites range from 746 1060 ma and their age spectra complexity is probably related to younger thermal events and or excess argon a single muscovite analysis yields a preferred age of 854 ma argon isotope analyses of k feldspar provide a quantitative evaluation of the thermal history between 175 and 350 c multi diffusion domain thermochronology on highly variable k feldspar results yield internally consistent thermal histories and along with geologic constraints suggest thermal maxima of 275 350 c at ca 700 470 450 and 300 ma combining all of the k feldspar analyses provides an internally consistent thermal history for the region and allows for the following inferences reheating at 700 ma associated with late precambrian rifting during the formation of the iapetus ocean apparently affected the entire adirondack region with the highest temperatures occurring in the eastern part of new york local reheating in the ordovician is inferred to have affected the eastern adirondack mountains and probably resulted from the combined effects of burial during the early paleozoic emplacement of taconic thrust sheets and migration of hot fluids along normal faults during the taconic orogeny high paleotemperatures for the devonian section of eastern new york are related to maximum burial of the basement during the carboniferous at ca 300 ma

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

controls on preferential recharge to chalk aquifers summary there is evidence that under certain conditions rapid preferential recharge via the fracture network can occur in chalk aquifers this has potentially important implications for contaminant migration through the chalk unsaturated zone cuz and for groundwater flooding in chalk catchments in the case of groundwater flooding deficiencies in modelling aquifer response have been attributed to inadequate representation of flow processes in the cuz in this paper we consider two complementary approaches for assessing controls on preferential recharge to chalk aquifers an empirical approach and a physically based modelling approach we show that the main controls on preferential recharge to chalk aquifers are the characteristics of rainfall events in terms of duration and intensity the physical properties of the near surface and the antecedent soil moisture in the near surface we demonstrate a number of deficiencies when past models of the cuz are applied to the problem of simulating preferential recharge notably that the assumption of instantaneous equilibrium between fractures and matrix is not valid particularly during extreme recharge events in order to simulate preferential recharge fractures and matrix must be modelled as separate but interacting domains this was achieved using a dual continua model the model was computationally demanding but was able to reproduce observed behaviour including apparently hysteretic soil moisture characteristic relationships in the near surface and rapid preferential recharge fluxes in response to high intensity rainfall events

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

some aspects of hurricane inner core dynamics and energetics abstract the energy cycle of the mature hurricane resides in the secondary circulation that passes through the storm s eyewall by equating the generation of energy in this cycle to boundary layer dissipation an upper bound on wind speed is derived this bound depends on the degree of thermodynamic disequilibrium between the tropical ocean and atmosphere on the difference between sea surface and outflow absolute temperatures and also on the ratio between the enthalpy exchange and surface drag coefficients such a bound proves to be an excellent predictor of maximum wind speeds in two different axisymmetric numerical models and does not appear to depend on the existence of the hurricane eye but further consideration of the detailed dynamics of the eye and eyewall show that the intensification of hurricanes is accelerated by feedbacks associated with a component of eye subsidence forced by radial turbulent diffusion of momentum this radial momentum diffusion is an inevitable by product of the strong fr

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

field data and flow system response in clay vertisol shale terrain north central texas usa the water budget in clay shale terrain is controlled by a complex interaction between the vertisol soil layer the underlying fractured rock land use topography and seasonal trends in rainfall and evapotranspiration rainfall runoff lateral flow soil moisture and groundwater levels were monitored over an annual recharge cycle four phases of soil aquifer response were noted over the study period 1 dry season cracking of soils 2 runoff initiation lateral flow and aquifer recharge 3 crack closure and down slope movement of subsurface water with surface seepage 4 a drying phase surface flow predominated within the watershed 25 of rainfall but lateral flow through the soil zone continued for most of the year and contributed 11 of stream flow through surface seepage actual flow through the fractured shale makes up a small fraction of the water budget but does appear to influence surface seepage by its effect on valley bottom storage when the valley soil storage is full lateral flow exits onto the valley bottom surface as seasonal seeps well response varied with depth and hillslope position flowtube model results and regional recharge estimates are consistent with an aquifer recharge of 1 6 of annual precipitation calculated from well heights and specific yield of the shale aquifer copyright 2005 john wiley sons ltd

a tracer investigation into the importance of fissure flow in the unsaturated zone of the british upper chalk abstract the displacement and recovery of surface applied 15 no 3 2 h and cl in the unsaturated zone of the british upper chalk was followed over a 4 year period recovery of cl in the chalk matrix under the treated plot was equivalent to 110 of that applied that of 2 h was 57 in the treated plot lateral flow of 2 h was evident from cores taken outside the plot and if this is included together with 2 h estimated to have been lost by evapotranspiration the recovery approached 100 recovery of 15 no 3 was 100 1 year after tracer application falling to 9 4 after 4 years no evidence of denitrification was obtained from background no 3 cores and it was concluded that the shortfall in no 3 recovery was due to uptake by grass from depths of 50 70 cm the tracer profiles and recoveries were not consistent with significant vertical macrofissure flow but the lack of seasonal periodicity in background 2 h profiles suggested that some microfissure flow could be occurring the displacement of the tracer peaks when considered with the estimates of recharge indicated that only 50 of the water filled matrix was conducting flow

heterogeneous behaviour of unconfined chalk aquifers infer from combination of groundwater residence time hydrochemistry and hydrodynamic tools chalk groundwater is an important aquifer resource in france and also in much of northwestern europe large areas between the paris basin the london basin denmark and the northwest of germany as it is intensively exploited for human use with a large proportion reserved for drinking water the improvement of the knowledge on chalk aquifer hydrodynamical functioning and groundwater geochemistry is essential for the management of this resource to achieve this aim we developed a methodology based on a combination of hydrodynamic hydrochemistry and groundwater dating tools a study site of about 500 km2 was selected in ne france where chalk outcrops at 15 sampling points including boreholes and rivers mainly from chalk aquifer drainage groundwater geochemistry were monitored monthly for 2 years from june 2017 to june 2019 groundwater level in boreholes were monitored hourly with in situ water loggers in addition two sampling campaigns for the analysis of cfcs and sf6 have been conducted in boreholes in high and low water level periods to define the groundwater residence time the aquifer at the majority of sampling sites has an inertial behavior with respect to recharge as no impact of individual rainfall event was observed rapid piezometric response following rainfalls was observed at one site suggesting the presence of locally highly developed fracture network contrariwise high spatial and temporal heterogeneities of geochemistry was observed on the study area according to the mixing process piston flow exponential or binary mixing defined at each sampling site groundwater dating indicated rather heterogeneous ages ranging from less than 20 years to more than 50 years a combination of hydrogeological setting residence time and land use information was used to explain the hydrochemical heterogeneities highlighting the main factors governing the chalk groundwater geochemistry including water level fluctuation thickness of the unsaturated zone superficial formations distribution of fracture network aquifer river relations and human activities a conceptual model was proposed to clarify the hydrogeosystem functioning of unconfined chalk aquifers the proposed methodology can be used for the study of other worldwide aquifers chalk or not with the aim to provide appropriate recommendations in terms of water management

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

large variations in balloon ascent rate over hawaii 1 a sequence of nine weather balloons were launched recently over the island of hawaii during the nights of 12 13 and 17 december 2002 providing measurements of ascent rate horizontal wind speed and direction temperature and other quantities the measurements show short intervals of altitude with a large increase in ascent rate occurring only near the tropopause indicating regions of strong upward air velocity at this location the large ascent rates correlate well to the strength of a jet stream and with the presence of a local critical level indicating mountain waves as the primary cause no corresponding decreases in ascent rate were measured suggesting strong three dimensional effects

an experimental study on hurricane mesovortices mesovortices in the eyewall region of a hurricane are intriguing elements of the hurricane engine in situ measurements of them are sparse however and our understanding of their overall role in the physics of a hurricane is incomplete to further understand their dynamics an experimental apparatus using a homogeneous fluid water has been constructed to emulate the lower tropospheric flow of the hurricane eye eyewall region for experimental configurations possessing a central aspect ratio less than unity a primary and secondary circulation similar to the in flow layer of an intense hurricane and a similar radius to width ratio of the curvilinear shear layer bordering the eye and eyewall region the flow supports two primary quasi steady vortices and secondary intermittent vortices the vortices form through kelvin helmholtz instability of the curvilinear shear layer bordering the slowly upwelling fluid in the centre and the converging fluid from the periphery the primary vortices are maintained by convergence of circulation from the periphery and merger of secondary vortices spawned along the shear layer the horizontal flow field is measured using a particle image velocimeter despite the relatively strong secondary circulation through the parent vortex the horizontal flow is found to be approximately uniform in the direction parallel to the rotation axis the peak tangential velocity is found to occur in the mesovortices and is roughly 50 greater than the parent vortex that supports them the measurements provide insight into recent observations of excessive wind damage in landfalling storms and support the hypothesis that intense storms contain coherent vortex structures in the eyewall region with higher horizontal wind speeds locally than the parent hurricane

mechanisms of groundwater recharge and pesticide penetration to a chalk aquifer in southern england abstract in order to assess the potential for enhanced agrochemical contamination of shallow groundwaters a field study was established on the upper chalk in hampshire uk two instrumented sites 380 m apart were established on a hillslope one on the interfluve with a deep water table 18 m depth the other on the dry valley bottom where the groundwater was close to the surface 4 m depth hourly measurements of water potentials in the unsaturated zone to 3 0 m depth identified very different groundwater recharge processes between the two sites in response to the same storm event on the interfluve site with the deep water table only matrix flow through the chalk unsaturated zone at 3 m depth was identified in contrast at the dry valley bottom with a shallow water table both rapid preferential flow and matrix flow processes were observed at a 3 m depth the correlation between groundwater depth measurements and unsaturated profile moisture content measurements demonstrated the importance of the capillary fringe in sustaining a higher moisture content in the unsaturated zone at the shallow groundwater site the resulting reduced water storage capacity for vertical drainage fluxes meant that little water was required to wet the shallow profile before rapid preferential flow events demonstrated by rapid water potential responses occurred however where the groundwater was deeper intermediate storage sites located on chalk surfaces and at chalk ped block contact points remained empty and unsaturated water potential profiles showed that rainfall pulses were attenuated as these sites absorbed the downward water fluxes consequently preferential events at these deep groundwater sites are rare the importance of these intermediate storage sites in controlling recharge processes is highlighted the potential mass load of pesticide transported to the shallow groundwater in preferential events during 1996 7 was determined using bromide tracer studies water balance calculations and measured groundwater pesticide concentrations an estimated 0 1 of the applied pesticide reached the shallow groundwater along preferential pathways in 1996 7 calculations under a worst case scenario showed that this value did not increase beyond 0 2 of pesticide applied

hurricane maximum intensity past and present hurricane intensity forecasting has lagged far behind the forecasting of hurricane track in an effort to improve the understanding of the hurricane intensity dilemma several attempts have been made to compute an upper bound on the intensity of tropical cyclones this paper investigates the strides made into determining the maximum intensity of hurricanes concentrating on the most recent attempts to understand the maximum intensity problem the theories of holland and emanuel are reviewed with the objective of assessing their validity in real tropical cyclones each theory is then tested using both observations and the axisymmetric hurricane numerical models of ooyama and emanuel it is found that ambient convective instability plays a minor role in the determination of the maximum intensity and that the emanuel model is the closest to providing a useful calculation of maximum intensity several shortcomings are revealed in emanuel s theory however showing the need for more basic research on the axisymmetric and asymmetric dynamics of hurricanes as an illustration of the importance of asymmetric vorticity dynamics in the determination of a hurricane s maximum intensity it is shown using ooyama s hurricane model that the maximum intensity of a tropical cyclone may be diminished by convectively generated vorticity anomolies excited outside the primary eyewall the vorticity anomolies are parameterized by adding a concentric ring of vorticity outside the primary eyewall that acts to cut off its supply of angular momentum and moist enthalpy it is suggested that the generation of vorticity rings or bands outside the primary eyewall is a major reason why tropical cyclones fail to attain their maximum intensity even in an otherwise favorable environment the upshot of this work points to the need for obtaining a more complete understanding of asymmetric vorticity processes in hurricanes and their coupling to the boundary layer and convection

analysis of water level response to rainfall and implications for recharge pathways in the chalk aquifer se england summary water table response to rainfall was investigated at six sites in the upper middle and lower chalk of southern england daily time series of rainfall and borehole water level were cross correlated to investigate seasonal variations in groundwater level response times based on periods of 3 month duration the time lags in days yielding significant correlations were compared with the average unsaturated zone thickness during each 3 month period in general for cases when the unsaturated zone was greater than 18 m thick the time lag for a significant water level response increased rapidly once the depth to the water table exceeded a critical value which varied from site to site for shallower water tables a linear relationship between the depth to the water table and the water level response time was evident the observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix suggesting that some fissure flow was occurring the majority of rapid responses were observed during the winter spring recharge period when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest and were more likely to occur when the rainfall intensity exceeded 5 mm day at some sites a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick this response was generally associated with the autumn period the results of the cross correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

deep burial diagenesis its implications for vertical movements of the crust uplift of the lithosphere and isostatic unroofing a review abstract various techniques of study of strata exposed at the surface in undeformed areas of the appalachian basin and ozark done imply that these strata have been heated to temperatures that suggest a former great depth of burial the data reveal that the strata have been much more deeply buried than previously thought if such former deep burial has taken place then subsequent uplift and erosion must also have taken place to bring these formerly deeply buried strata to the present land surface unexpectedly large amounts of uplift and erosion ranging from 4 3 to 7 km have re exposed these formerly deeply buried rocks this leads to the surprising conclusion that isostatic unroofing has stripped off thick sections of strata whose presence was previously unsuspected therefore the lithosphere in its isostatic unroofing of thick sequences of sedimentary strata has undergone much larger vertical motions than many geologists had previously estimated case histories in this review include strata of the silurian of the northern appalachian basin and of the ordovician of the ozark dome which reached interpreted maximum burial depths of 5 and 4 3 km respectively devonian strata in the catskill mountains of new york imply a former depth of burial of 6 5 km lower ordovician carbonate sequences of the northern appalachian basin imply a depth of burial in excess of 7 km middle ordovician strata from the same basin signify a depth of burial of approximately 5 km and devonian strata a paleodepth of 4 5 5 km such former great depths of burial of undeformed strata which are now exposed at the surface reflect large scale vertical movements of the crust and uplift of the lithosphere these drastic changes represent isostatic unroofing with widespread implications for paleogeography of a kind unrecognized at present

the significance of flow in the matrix of the chalk unsaturated zone the significance of flow in the matrix of the chalk unsaturated zone in comparison with flow in fractures has been the subject of much debate in this article important elements of the literature are discussed in detail and several simple modelling analyses based on steady state flow are presented a study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles unless unrealistically small fracture spacings are assumed the effect of air phase continuities e g bedding planes on matrix flow has also been examined these discontinuities are frequently interrupted by points of connectivity between matrix blocks an issue therefore is the relationship between connectivity and its effect on inter block conductance a simple analysis of the laplace equation shows that just 1 connectivity represents an effective pathway equivalent to 18 of the local rock hydraulic conductivity obviously when there is no fracture flow solute spreading is significantly reduced however dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow all of the above studies suggest that flow in the matrix of the chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system

infiltration processes in karstic chalk investigated through a spatial analysis of the geochemical properties of the groundwater the effect of the superficial layer of clay with flints summary in the paris basin in upper normandy france the chalk plateaus are covered with thick deposits of loess and clay with flints from a few meters to approximately 40 m thick locally a perched groundwater is sometimes observed in the superficial layers in which evapotranspiration processes seem to occur this study s objective was to understand the effects of the thick clay with flints layers on the infiltration processes to achieve this we adopted a spatial approach comparing the maps of the geochemical properties of the chalk groundwater and the maps of the thickness of clay with flints the french national groundwater database ades acces aux donnees des eaux brgm provided the mean geochemical properties in the chalk aquifer of upper normandy this database was used to prepare maps of the environmental tracers ca 2 hco 3 mg 2 cl na no 3 and so 4 2 the data are spatially well organized using principal component analysis pca these maps were compared with the maps of the thickness of clay with flints a focus on the coastal basins northern upper normandy shows a very strong spatial correlation between the maps of clay with flints thickness and all of the maps of the major ions the thickness of clay with flints is negatively correlated with the autochthonous ions hco 3 and ca 2 and is positively correlated with the allochthonous ions cl na so 4 2 and no 3 these results highlight that the thickness of clay with flints controls recharge two types of infiltration processes are proposed 1 thicker clay with flints allows storage in the perched groundwater which allows evapotranspiration resulting in high concentrations of allochthonous ions and a decrease in the dissolution potential of water and low concentrations of autochthonous ions the infiltration of the perched groundwater is thus delayed and concentrated 2 thinner clay with flints causes the infiltration to be more diffuse with low evapotranspiration and thus low concentrations of allochthonous ions in the chalk groundwater more there is more dissolution and higher concentrations of autochthonous ions in the chalk groundwater

a lagrangian trajectory view on transport and mixing processes between the eye eyewall and environment using a high resolution simulation of hurricane bonnie 1998 the transport and mixing characteristics of a large sample of air parcels within a mature and vertically sheared hurricane vortex are examined data from a high resolution 2 km horizontal grid spacing numerical simulation of real case hurricane bonnie 1998 are used to calculate lagrangian trajectories of air parcels in various subdomains of the hurricane namely the eye eyewall and near environment to study the degree of interaction transport and mixing between these subdomains it is found that 1 there is transport and mixing from the low level eye to the eyewall that carries air possessing relatively high values of equivalent potential temperature e which can enhance the efficiency of the hurricane heat engine 2 a portion of the low level inflow of the hurricane bypasses the eyewall to enter the eye and this air both replaces the mass of the low level eye and lingers for a sufficient time order 1 h to acquire enhanced entropy characteristics through interaction with the ocean beneath the eye 3 air in the mid to upper level eye is exchanged with the eyewall such that more than half the air of the eye is exchanged i n5hi nthis case of a sheared hurricane and 4 that one fifth of the mass in the eyewall at a height of 5 km has an origin in the mid to upper level environment where e is much less than in the eyewall which ventilates the ensemble average eyewall e by about 1 k implications of these findings for the problem of hurricane intensity forecasting are briefly discussed

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

hydrodynamics of floodplain wetlands in a chalk catchment the river lambourn uk variations in floodplain channel water levels and valley floor groundwater levels measured in piezometers and boreholes are examined at selected points along the course of the river lambourn a chalk river in southern england a local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river s perennial profile variations in hydraulic gradient between local borehole levels and or floodplain channel water levels are described for three sites in the seasonal section of the channel at bockhampton east garston and west shefford the results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain however as the floodplain widens and the alluvial gravel aquifer increases in size the gravel aquifer accounts for a substantial down valley component of groundwater flow with a diffuse vertical water flux in the lower catchment the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water table variability providing a stable hydrological regime for valley bottom wetlands catchment controls upon the local valley bottom wetland regime are demonstrated with the application of a simple groundwater model developed using modflow the model is used to simulate groundwater discharge to the river in the upper and lower catchment in addition to the water level regime at selected points in the valley bottom in the lower catchment the results demonstrate the importance of taking catchment scale water flow into account when managing isolated wetlands in a permeable catchment

ecology and evolution of devonian trees in new york usa abstract the first trees in new york were middle devonian earliest givetian cladoxyls duisbergia and wattieza with shallow rooted manoxylic trunks cladoxyl trees in new york thus postdate their latest emsian evolution in spitzbergen progymnosperm trees svalbardia and callixylon archaeopteris appeared in new york later mid givetian than progymnosperm trees from spitzbergen early givetian associated paleosols are evidence that wattieza formed intertidal to estuarine mangal and callixylon formed dry riparian woodland also from paleosols comes evidence that wattieza and callixylon required about 350 mm more mean annual precipitation than plants of equivalent stature today that wattieza tolerated mean annual temperature 7 c less than current limits of mangal 20 c and callixylon could tolerate temperatures 14 c less than modern mangal devonian mangal and riparian woodland spread into new york from wetter regions elsewhere during transient paleoclimatic spikes of very high co 2 3923 238 ppmv and subhumid mean annual precipitation 730 147 mm conditions which were more likely extrinsic atmospheric perturbations rather than consequences of tree evolution for most of the middle devonian co 2 was lower 2263 238 ppmv and paleoclimate in new york was semiarid mean annual precipitation 484 147 mm such transient perturbations and immigration events may explain the 40 million year gap between the late emsian 400 ma evolution of trees and famennian 360 ma co 2 drawdown and expansion of ice caps

tropical cyclone eye thermodynamics in intense tropical cyclones sea level pressures at the center are 50 100 hpa lower than outside the vortex but only 10 30 hpa of the total pressure fall occurs inside the eye between the eyewall and the center warming by dry subsidence accounts for this fraction of the total hydrostatic pressure fall convection in the eyewall causes the warming by doing work on the eye to force the thermally indirect subsidence soundings inside hurricane eyes show warm and dry air aloft separated by an inversion from cloudy air below dewpoint depressions at the inversion level typically 850 500 hpa are 10 30 k rather than the 100 k that would occur if the air descended from tropopause level without dilution by the surrounding cloud the observed temperature and dewpoint distribution above the inversion can however be derived by 100 hpa of undilute dry subsidence from an initial sounding that is somewhat more stable than a moist adiabat it is hypothesized that the air above the inversion has remained in the eye since it was enclosed when the eyewall formed and that it has subsided at most a few kilometers the cause of the subsidence is the enclosed air s being drawn downward toward the inversion level as the air below it flows outward into the eyewall shrinkage of the eye s volume is more than adequate to supply the volume lost as dry air is incorporated into the eyewall or converted to moist air by turbulent mixing across the eye boundary the moist air below the inversion is in thermodynamic contact with the sea surface its moisture derives from evaporation of seawater inside the eye frictional inflow of moist air under the eyewall and from moist downdrafts induced as condensate mixes into the eye the moist air s residence time in the eye is much shorter than that of the dry air above the inversion the height of the inversion is determined by the balance between evaporation inflow and inward mixing on one hand and loss to the eyewall updrafts on the other

processes of water movement through a chalk coombe deposit in southeast england the processes of water movement through the coombe deposit in a chalk dry valley near eastbourne in southeast england were investigated using simple methods based on regular weekly measurements of rainfall soil water content and soil water potential the drainage flux recharge through the soil was determined using the water balance method during the winter and the zero flux plane zfp method after the appearance of the zfp in the spring the unsaturated hydraulic conductivity was derived applying darcy s law in a novel way using the measured potential gradients and weekly drainage fluxes the derived conductivity characteristics were adequate to identify the flow mechanisms to illustrate the difference in behaviour between the horizons of the soil profile and to give some indication of pore water velocities the mean daily drainage flux at 2 85 m depth during the recharge period from 10 october 1980 to 29 may 1981 was 1 6 mm d 1 weekly mean rates of up to 3 7 mm d 1 were observed but peak short term rates must have considerably exceeded this figure it was shown that in the lower part of the coombe deposit when drainage fluxes are large much of the flux passes through a very small proportion of the wetted cross sectional area of the soil this gives rise to pore water velocities of at least 3 m d 1 at a depth of 2 85 m and 0 5 m d 1 between 0 5 m and 2 5 m depth these results show that pollutants may be moved very rapidly through the profile in this and similar material the core sampling techniques normally used to monitor pollutant movement in the chalk are unlikely to succeed in detecting this movement not only because it is transient but also because it occupies only a very small proportion of the water filled pores

comment and reply on time temperature burial significance of devonian anthracite implies former great 6 5 km depth of burial of catskill mountains new york

dynamic instabilities of simulated hurricane like vortices and their impacts on the core structure of hurricanes part i dry experiments abstract a series of numerical simulations of dry axisymmetric hurricane like vortices is performed to examine the growth of barotropic and baroclinic eddies and their potential impacts on hurricane core structure and intensity the numerical experiments are performed using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 with a 6 km horizontal grid to examine internal effects on the stability of vortices all external forcings are eliminated axisymmetric vortices that resemble observed hurricane structures are constructed on an f plane and the experiments are performed without moist and boundary layer processes three vortices are designed for this study a balanced control vortex is built based on the results of a full physics simulation of hurricane floyd 1999 then two other axisymmetric vortices exp 1 and exp 2 are constructed by modifying the wind and mass fields of the control vortex the exp 1 vortex is designed t

unsaturated flow and solute transport through the chalk tracer test and dual permeability modelling a tracer test was carried out in the unsaturated chalk at the fleam dyke research site in cambridgeshire uk to investigate the role of the chalk fractures and matrix in unsaturated flow and solute transport the experiment under natural rainfall conditions involved distributing deuterated water on a grass covered lysimeter a cube of volume 125 m3 and on an adjacent 4 m 4 m field plot tracer migration was monitored through regular core sampling and collection of lysimeter drainage water the presence of occasional secondary peaks in sampling of the vertical tracer profile suggested the occurrence of fracture flow allowing some tracer to bypass the chalk matrix however in the 15 months following application none of the tracer was detected in the lysimeter drainage at 5 m depth modelling of the tracer results was undertaken with the 1 d numerical transient dual permeability model macro 5 0 initially developed for macroporous soils modelling results showed that macro 5 0 could reliably simulate transient recharge through the chalk the simulations suggested that fracture flow is important at the site but that it is only initiated at 1 m depth or deeper the extent of fracture flow appeared to be highly variable in different layers of the profile varying between 40 and 85 of the cumulative flux mainly depending on the saturated hydraulic conductivity of the matrix diffusion between the fractures and the matrix tended to equalize solute concentrations in both flow domains although solute bypass through the fractures occurred in some chalk strata besides diffusive exchange the modelling stressed the importance of advective exchange of solutes the results suggest that the chalk aquifer at the fleam dyke site is only moderately vulnerable to pollution even though for moderate rainfall conditions some bypass flow was possible

two distinct regimes in the kinematic and thermodynamic structure of the hurricane eye and eyewall abstract using aircraft flight level data the present work demonstrates that the kinematic and thermodynamic distributions within the eye and eyewall of strong hurricanes are observed to evolve between two distinct regimes in the first regime angular velocity is greatest within the eyewall and relatively depressed within the eye in the second regime radial profiles of angular velocity are nearly monotonic with maxima found at the eye center considering sequential profiles within individual hurricanes the authors find that the evolution of the kinematic distribution is often marked by a transition from the first regime to the second the transition can occur in less than 1 h also noted during the transition are dramatic changes in the thermodynamic structure of the hurricane prior to the transition regime 1 the eye is typically very warm and dry and the equivalent potential temperature is often elevated within the eyewall and relatively depressed within the eye after the transition regime 2

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

transient simulations of flow and transport in the chalk unsaturated zone chalk is a fractured porous medium composed of matrix blocks bounded by interconnected fractures furthermore there are a number of commonly observed and apparently contradictory phenomena these include a fast water table response slow solute migration and very little solute dispersion to the authors knowledge no unified physically based numerical model has been able to reconcile all of these points in this paper these issues were addressed through the development of a transient dual permeability model of flow and transport the behaviour of the model was explored through a hypothetical scenario the one dimensional model featured a fixed water table at 10 m depth a recharge time series derived using the penman grindley model in conjunction with daily precipitation and monthly potential evaporation data from the kennet valley berkshire was applied at the top of the model a conservative solute that could be tritium chloride or nitrate was applied to the recharge for 1 year subsequent years involved the input of clean water the simulations suggested that although transient effects have been previously neglected overlying soil and gravelly chalk layers are likely to cause significant attenuating effects on flow such that most flow occurs through the matrix fracture flow was found to be episodic and infrequent and represented between 17 and 30 of the annual recharge

a numerical study of an extreme cold air outbreak over the labrador sea sea ice air sea interaction and development of polar lows in this paper the ability of the mm5 mesoscale forecast model to simulate the air sea interaction boundary layer development and mesoscale structure associated with a cold air outbreak over the labrador sea is investigated the case chosen was one for which research aircraft data and satellite imagery are available for validation the default surface layer parameterization included in the model is shown to grossly overestimate the magnitude of the air sea interaction resulting in forecasts of boundary layer growth and mesoscale development that differ substantially from observations it is also shown that a representation of the inhomogeneities in sea ice cover results in a significant improvement in simulations of the air sea interaction boundary layer development and mesoscale structure both within the marginal ice zone and downstream over the open ocean finally the mesoscale cyclones or polar lows observed in the wake of the cold air outbreak are shown to be coupled to the evolution of an upper tropospheric potential vorticity anomaly that was advected over the region the model simulations suggest that mm5 most probably due to inaccuracies in and the limited resolution of the analyzed fields that supply the initial and boundary conditions to the model was unable to correctly simulate the development and track of this anomaly and this ultimately led to an incorrect forecast of the polar lows finite amplitude behavior

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

lagrangian coherent structures near a subtropical jet stream direct lyapunov exponents and stability results are used to extract and distinguish lagrangian coherent structures lcs from a three dimensional atmospheric dataset generated from the weather research and forecasting wrf model the numerical model is centered at 19 788n 155 558w initialized from the global forecast system for the case of a subtropical jet stream near hawaii on 12 december 2002 the lcs are identified that appear to create optical and mechanical turbulence as evidenced by balloon data collected during a measurement campaign near hawaii

surface zone flow along unsaturated rock fractures although fractures in rock are well recognized as pathways for fast percolation of water processes which permit fast flow along unsaturated fracture pathways remain to be identified and understood earlier aperture based models of flow in partially saturated fractures permit fast flow only through a continuous network of locally saturated segments film flow was recently identified as a mechanism capable of sustaining fast flow along truly unsaturated fractures when the matric potential is very close to zero another mechanism for fast flow along unsaturated fractures is introduced in this study surface zone flow which can be important when the permeability of the rock along fractures fracture skin is significantly greater than that of the bulk rock matrix in such systems the fracture surface zone provides low resistance pathways through which fast flow relative to the bulk matrix rock can occur even when the fractures are at very low water saturation initial experimental tests of surface zone fast flow were performed surface zone fast imbibition of water was measured on a welded tuff and a rhyolite however because 1 imbibition rates are also strongly influenced by rock wettability 2 these initially air dry rocks exhibited finite contact angles upon exposure to water and 3 we lack methods to reliably measure permeabilities of thin regions on rock surfaces quantification of permeability contrasts was not possible in these initial tests

field monitoring and dual permeability modelling of water flow through unsaturated calcareous rocks summary environmental monitoring was carried out in order to investigate the role of topsoil rock matrix and fractures in controlling the water flow in unsaturated zone of calcareous rocks and in determining the timing and the magnitude of groundwater recharge a comprehensive dataset of climate data soil moisture and rock pressure heads was used to evaluate a physically based 1d dual permeability model in order to simulate the water flow in the vertical profile to the groundwater table the parameters of water retention and unsaturated hydraulic conductivity curves in soil and rock matrix were estimated using two evaporation experiments in the laboratory and the tension infiltrometer in the field the other sensitive parameters of the model were calibrated using an optimization procedure based on combinations of randomly sampled parameters once the model had been calibrated it was used to obtain insights into the hydrological processes through the unsaturated profile down to the water table the soil acts as a attenuation layer determining the timing and the magnitude of drainage fluxes towards the unsaturated rock zone the low permeability petrocalcic horizon below the soil which frequently occurs in semi arid regions plays a key role in controlling the water exchanges between the soil and the rock most water flow in the top of the rock profile occurs through the fractures this fracture flow becomes less along the profile as a part of it gradually infiltrates into the unsaturated rock matrix fracture water infiltrates entirely into the matrix only when the unsaturated rock zone is very thick so that in sites with a shallow water table fracture flow may be the dominant groundwater recharge mechanism the flow through the matrix is continuous over time and at the water table it becomes constant and independent of large seasonal and annual variations in rainfall the flow through the unsaturated matrix is the dominant groundwater recharge mechanism in dry summers and in drought years the continuous matrix water flow sustains the recharge thus maintaining high groundwater levels when more water is extracted this is important in regions where groundwater from unconfined calcareous aquifers are important water resources the recharge through the fractures is sensitive to the annual rainfall pattern and also contributes to the groundwater in years when the rainfall is greater

hydrological processes in the chalk unsaturated zone insights from an intensive field monitoring programme as part of the nerc lowland catchment research programme locar the pang lambourn catchments berkshire uk have been extensively instrumented to provide an improved understanding of the hydrological processes in the unsaturated zone of the chalk a subject of much debate over the past 30 years to quantify the movement of water through the unsaturated zone it is necessary to measure matric potential and water content as well as input and output fluxes from precipitation evapotranspiration and groundwater recharge previous studies have indicated the need for fine temporal resolution data to monitor this system effectively due to the challenges faced in meeting this objective a monitoring scheme was designed that combines a variety of instrumentation to provide the required range accuracy and spatial and temporal resolution of data this paper firstly presents an overview of the monitoring programme and a critical discussion of the instrumentation used subsequently the field data are used to characterise the hydrological properties of the unsaturated zone and to gain insight into recharge processes the interpretation of the data presented in this paper indicate that in the chalk unsaturated zone at west ilsley matrix flow is the dominant recharge mechanism

polygonal eyewalls asymmetric eye contraction and potential vorticity mixing in hurricanes hurricane eyewalls are often observed to be nearly circular structures but they are occasionally observed to take on distinctly polygonal shapes the shapes range from triangles to hexagons and while they are often incomplete straight line segments can be identified other observations implicate the existence of intense mesovortices within or near the eye region is there a relation between polygonal eyewalls and hurricane mesovortices are these phenomena just curiosities of the hurricane s inner core circulation or are they snapshots of an intrinsic mixing process within or near the eye that serves to determine the circulation and thermal structure of the eye as a first step toward understanding the asymmetric vorticity dynamics of the hurricane s eye and eyewall region these issues are examined within the framework of an unforced barotropic nondivergent model polygonal eyewalls are shown to form as a result of barotropic instability near the radius of maximum winds after reviewing linear theory simulations with a high resolution pseudospectral numerical model are presented to follow the instabilities into their nonlinear regime when the instabilities grow to finite amplitude the vorticity of the eyewall region pools into discrete areas creating the appearance of polygonal eyewalls the circulations associated with these pools of vorticity suggest a connection to hurricane mesovortices at later times the vorticity is ultimately rearranged into a nearly monopolar circular vortex while the evolution of the finescale vorticity field is sensitive to the initial condition the macroscopic end states are found to be similar in fact the gross characteristics of the numerically simulated end states are predicted analytically using a generalization of the minimum enstrophy hypothesis in an effort to remove some of the weaknesses of the minimum enstrophy approach a maximum entropy argument developed previously for rectilinear shear flows is extended to the vortex problem and end state solutions in the limiting case of tertiary mixing are obtained implications of these ideas for real hurricanes are discussed

airborne doppler observations of the inner core structural differences between intensifying and steady state tropical cyclones abstractdifferences in the inner core structure of intensifying in intensity increase of at least 20 kt 24 h 1 where 1 kt 0 51 m s 1 and steady state ss intensity remaining between 10 kt 24 h 1 tropical cyclones tcs are examined using composites of airborne doppler observations collected from noaa p 3 aircraft missions the in dataset contains 40 eyewall passes from 14 separate missions while the ss dataset contains 53 eyewall passes from 14 separate missions intensifying tcs have a ringlike vorticity structure inside the radius of maximum wind rmw lower vorticity in the outer core a deeper stronger inflow layer and stronger axisymmetric eyewall upward motion compared with steady state tcs there is little difference in the vortex tilt between 2 and 7 km and both in and ss tcs show an eyewall precipitation and updraft asymmetry whose maxima are located in the downshear and downshear left region the azimuthal coverage of eyewall and outer core precipitation is greater for in tcs

eye excess energy and the rapid intensification of hurricane lili 2002 abstract over 4 5 days noaa and u s air force personnel in reconnaissance aircraft deployed 44 global positioning system dropwindsondes gps sondes in the eye of hurricane lili 2002 the vertical profiles derived from these gps sondes were used to determine the evolution of the height of the inversion presence and height of the hub cloud the height of the lifted condensation layer and the depth of the mixed layer as lili deepened underwent rapid intensification ri and eventually rapid decay the lower portion of the eye moistened and the lapse rate became moist adiabatic the inversion layer rose as lili intensified and then quickly fell over 1500 m at the beginning of ri comparison of the equivalent potential temperature e of the eye with that in the eyewall revealed that like many other hurricanes the eye was a reservoir for the warmest e the authors define a variable called eye excess energy that is a function of the difference in e between the eye and the eyewall and the depth over