a wave cisk model of squall lines abstract the wave cisk model of raymond incorporating lag effects in the updraft and downdraft is implemented as an initial value problem in physical space examples of both midlatitude and tropical squall lines are successfully simulated diagnosis of the model shows that condensational heating in the updraft is the primary driving mechanism of a mature squall line with evaporative cooling and convective momentum transfer playing subsidiary roles however an instability involving the displacement of boundary layer air by downdrafts apparently plays an important role in squall line initiation a weakness of the model is its inability to predict the direction of squall line propagation relative to the low level wind shear this is traced to the insensitivity of the convective parameterization to midlevel entrainment however unlike strict two dimensional squall lint models the parameterization allows cross stream mass transfer to occur in the context of overall slab symmetry such transfer is dynamical

potential for estimation of snow depth on arctic sea ice from cryosat 2 and saral altika missions abstract the scattering properties of the radar signal at ka and ku band frequencies are investigated using a theoretical model and snow grain observations obtained during previous field campaigns our results show that the combination of radar altimeters operating at these two frequencies should allow for the retrieval of snow depth over arctic sea ice we estimate uncertainties of the ice surface position in relation to crossover observations over sea ice and show that the accuracy of the crossover methodology with short time gap 3 days or less is better than 3 cm comparison of the cryosat 2 altika retrieved snow depth with in situ measurements provided by operation icebridge shows a good agreement with a root mean square error rmse of 5 cm analysis of the cryosat 2 altika retrieved snow depths over three winters 2013 2015 reveals a thinner snow cover on both multi year 32 57 and first year ice 63 75 relative to the 1954 91 warren climatology suggesting the need for more contemporary year round and basin scale snow depth fields

model derived estimates of groundwater mean ages recharge rates effective porosities and storage in a limestone aquifer the edwards aquifer of south central texas u s a a highly fractured and faulted group of limestone formations is the major water supply for the san antonio area a discrete state compartment dsc model or mixing cell model based upon the conservation of environmental tritium within the aquifer was used to obtain estimates of groundwater mean ages recharge effective porosities and storage in the edwards aquifer in the vicinity of san antonio texas the model was calibrated and validated with the spatial and temporal 1953 1971 distributions of environmental 3h tritium in the groundwater the final model consisted of 34 cells eight of these cells represented the unconfined portion of the edwards aquifer in the vicinity of the balcones fault zone an area where recharge occurs via streamflow infiltration and direct infiltration of precipitation the model confirmed previous analyses of flow in the edwards system generally parallel to the balcones fault zone with restricted flow perpendicular to this zone groundwater mean ages ranged from 16 to over 130 yr the storage volume of the confined portion of the edwards aquifer is 30 9 km3 which corresponds to an average effective porosity of 4 8 range 1 9 8 the average annual recharge to the edwards aquifer during the period 1953 1971 was 0 614 km3 the study demonstrated that discrete state compartment models calibrated and validated with environmental tritium distributions can yield valuable hydrogeologic information that is difficult or expensive to obtain using traditional techniques the approach used in the study is particularly suited to limestone aquifers which are normally extremely difficult to analyze with traditional methods

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

the structure and decay of a rainband in hurricane irene 1981 abstract the mesoscale thermodynamic kinematic and reflectivity structure of a rainband observed in hurricane irene on 27 september 1981 is presented data are from 16 aircraft passes from 150 to 4700 m msl through the rainband which was located ssw of the circulation center of the northward moving hurricane cross sections of the rainband as a function of height and radial distance from the storm center reveal the following 1 little or no decrease of e in the subcloud layer associated with the weak convective cells in the rainband 2 large differences in static stability between the north and south sides of the band 3 a change of the radial wind component in the subcloud layer from flow toward the circulation center to flow away from it as the rainband weakens the decay of the rainband is believed to be related to mesoscale subsidence and the location of the rainband relative to the motion of the hurricane melting and evaporation of hydrometeors falling between the eyewall and the rainband are

effects of mackenzie river discharge and bathymetry on sea ice in the beaufort sea mackenzie river discharge and bathymetry effects on sea ice in the beaufort sea are examined in 2012 when arctic sea ice extent hit a record low satellite derived sea surface temperature revealed warmer waters closer to river mouths by 5 july 2012 mackenzie warm waters occupied most of an open water area about 316 000 km2 surface temperature in a common open water area increased by 6 5 c between 14 june and 5 july 2012 before and after the river waters broke through a recurrent landfast ice barrier formed over the shallow seafloor offshore the mackenzie delta in 2012 melting by warm river waters was especially effective when the strong beaufort gyre fragmented sea ice into unconsolidated floes the mackenzie and other large rivers can transport an enormous amount of heat across immense continental watersheds into the arctic ocean constituting a stark contrast to the antarctic that has no such rivers to affect sea ice

mechanisms for quasi stationary behavior in simulated heavy rain producing convective systems abstract in this study idealized numerical simulations are used to identify the processes responsible for initiating organizing and maintaining quasi stationary convective systems that produce locally extreme rainfall amounts of particular interest are those convective systems that have been observed to occur near mesoscale convective vortices mcvs and other midlevel circulations to simulate the lifting associated with such circulations a low level momentum forcing is applied to an initial state that is representative of observed extreme rain events the initial vertical wind profile includes a sharp reversal of the vertical wind shear with height indicative of observed low level jets deep moist convection initiates within the region of mesoscale lifting and the resulting convective system replicates many of the features of observed systems the low level thermodynamic environment is nearly saturated which is not conducive to the production of a strong surface cold pool yet the convection qui

inner core structure of hurricane alicia from airborne doppler radar observations abstract airborne doppler radar measurements are used to determine the horizontal winds vertical air motions radar reflectivity and hydrometer fallspeeds over much of the inner core region within 40 km of the eye of hurricane alicia 1983 the reconstructed flow field is more complete and detailed than any obtained previously the data show both the primary azimuthal and secondary radial height circulations the primary circulation was characterized by an outward sloping maximum of tangential wind the secondary circulation was characterized by a deep layer of radial inflow in the lower troposphere and a layer of intense outflow above 10 km altitude the rising branch of the secondary circulation was located in the eyewall and sloped radially outward discrete convective scale bubbles of more intense upward motion were superimposed on this mean rising current and convective scale downdrafts were located throughout and below the core of maximum precipitation in the eyewall precipitation particle

role of ice dynamics in anomalous ice conditions in the beaufort sea during 2006 and 2007 1 a new record minimum in summer sea ice extent was set in 2007 and an unusual polynya formed in the beaufort sea ice cover during the summer of 2006 using a combination of visual observations from cruises ice drift and satellite passive microwave sea ice concentration we show that ice dynamics during preceding years included events that preconditioned the beaufort ice pack for the unusual patterns of opening observed in both summers intrusions of first year ice from the chukchi sea to the northern beaufort and increased pole ward ice transport from the western arctic during summer has led to reduced replenishment of multiyear ice older than five years in the western beaufort resulting in a younger thinner ice pack in most of the beaufort we find ice younger than five years melts out completely by the end of summer south of 76n the 2006 unusual polynya was bounded to the south by an ice tongue composed of sea ice older than 5 years and formed when first year and second year ice melted between 76n and the older ice to the south in this paper we demonstrate that a recent shift in ice circulation patterns in the western arctic preconditions the beaufort ice pack for increased seasonal ice zone extent

the oceanic mesoscale convective system observed with airborne doppler radars on 9 february 1993 during toga coare structure evolution and budgets data collected on 9 february 1993 during the tropical ocean and global atmosphere programme coupled ocean atmosphere response experiment toga coare with the doppler radars on board the two national oceanic and atmospheric administration wp 3d and the national center for atmospheric research electra aircraft are analysed to study the structure and evolution of an equatorial oceanic mesoscale convective system mcs observations lasted more than five hours a period during which the cloud cluster characteristics changed from convective to stratiform this mesoscale system was approximately aligned along the tropospheric wind shear but it was nearly perpendicular to the low level shear series of three dimensional fields of reflectivity air velocity components retrieved pressure and temperature perturbations show similarities with previously observed convective systems over the tropical oceans in particular although the cloud top reached 18 km altitude relatively weak vertical motions and temperature perturbations resulted from a moderate convective instability in the low levels a cold front to rear flow intensified and deepened as the overall structure evolved from convective to stratiform the vertical profiles of mean horizontal divergence evolved from low level convergence in the cross line direction for the earliest analyses to mid level convergence from all directions during the later stratiform phase vertical momentum fluxes were important and led to an increase in the cross line wind shear and a decrease in the along line one analysis of radiosounding data from the nearest stations of the toga coare array shows that the period during which airborne doppler observations were conducted was characterized by relatively strong large scale ascent and apparent sources of heat moisture and momentum these diagnosed values and the mean radarderived ones agree fairly well this shows that the early convective and late stratiform phases of the mcs are equally important for the apparent sources of heat and momentum

small scale spiral bands observed in hurricanes andrew hugo and erin abstract analysis of radar data taken from the three intense hurricanes that passed close to wsr 57 and wsr 88d radar sites at their point of landfall illustrate small scale spiral bands that are frequently observed within 100 km or so of the hurricane center faintly visible in the radar reflectivity images these bands have scales of 10 km across the band and can extend for 100 km as they spiral outward in a clockwise fashion they appear to move around the hurricane with speeds close to the tangential wind at the level of the bands and are characterized by enhanced updrafts with higher equivalent potential temperature in the regions of elevated reflectivity they induce wind speed variations of at least 8 m s 1 across the bands the authors suggest that these small scale hurricane spiral bands are similar to boundary layer rolls although they extend through depths of 5 6 km which is more than would be expected for rolls in the boundary layer near the sea the data presented here are not sufficient to

submesoscale sea ice ocean interactions in marginal ice zones signatures of ocean eddies fronts and filaments are commonly observed within marginal ice zones mizs from satellite images of sea ice concentration and in situ observations via ice tethered profilers or underice gliders however localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts here we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence we demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along mizs with spatial scales o 10 km and rossby numbers o 1 in low wind conditions cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt the horizontal eddy diffusivity of sea ice mass and heat across the miz can reach o 200 m 2 s 1 submesoscale ocean variability also induces large vertical velocities order 10 m d 1 that can bring relatively warm subsurface waters into the mixed layer the ocean sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 w m 2 we speculate that these submesoscale driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of mizs with the continuing global warming and sea ice thickness reduction in the arctic ocean submesoscale sea ice ocean processes are expected to become increasingly prominent

evidence of arctic sea ice thinning from direct observations the arctic sea ice cover is rapidly shrinking but a direct longer term assessment of the ice thinning remains challenging a new time series constructed from in situ measurements of sea ice thickness at the end of the melt season in fram strait shows a thinning by over 50 during 2003 2012 the modal and mean ice thickness along 79 degrees n decreased at a rate of 0 3 and 0 2 m yr 1 respectively with long term averages of 2 5 and 3 m airborne observations reveal an east west thickness gradient across the strait in spring but not in summer due to advection from more different source regions there is no clear relationship between interannual ice thickness variability and the source regions of the ice the observed thinning is therefore likely a result of arctic wide reduction in ice thickness with a potential shift in exported ice types playing a minor role

airborne observations of summer thinning of multiyear sea ice originating from the lincoln sea to better understand recent changes of arctic sea ice thickness and extent it is important to distinguish between the contributions of winter growth and summer melt to the sea ice mass balance in this study we present a lagrangian approach to quantify summer sea ice melt in which multiyear ice myi floes that were surveyed by airborne electromagnetic thickness sounding within nares strait during summer were backtracked using satellite imagery to a region in close proximity 3 20 km to spring ice thickness surveys carried out in the lincoln sea typical modal total myi thicknesses including 0 4 m snow ranged between 3 9 and 4 7 m in the lincoln sea during april ice only modal thicknesses were between 2 2 and 3 0 m in nares strait during august total thinning including snow and ice was 1 3 0 1 m including 0 4 0 09 m of snow melt and 0 9 0 2 m of ice melt this translates to a seasonal net heat input of 305 69 mj m2 262 60 mj m2 for ice only and seasonal net heat flux of 57 13 w m2 45 10 w m2 for ice only which is unlikely to be explained by solar radiation fluxes alone furthermore our approach provides an improvement on traditional ice mass balance buoy estimates because it integrates melt over larger spatial scales where melt can be highly variable due to differential melt experienced between melt ponds bare ice hummocks and ridges

sea ice mass balance observations from the north pole environmental observatory in recent years the periphery of the arctic sea ice cover has undergone significant changes with a reduction in summer ice extent a thinning of the ice and a shift from multiyear to first year ice here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack using autonomous measurements of sea ice mass balance deployed near the north pole results exhibit no definitive trends there is large interannual variability with surface melt ranging from 0 02 m to 0 50 m and bottom melt from 0 10 m to 0 57 m the largest amounts of bottom melt have occurred in the past few years for all 9 years the ice at the end of the melt season was at least 1 2 m thick

evaluating the recharge mechanism of the lower kuiseb dune area using mixing cell modeling and residence time data summary a mixing cell approach was extended by a method incorporating mean cell residence times derived from 14c to further constrain and validate the modeling results this extended approach was used to model the groundwater system of the lower kuiseb dune area in namibia the kuiseb river is a 560 km long ephemeral river that crosses the namib desert from east to west transmission losses from the riverbed during flood events are an important source of groundwater recharge to the underlying aquifer system the lower kuiseb area is located in a hyper arid region with annual precipitation less than 25 mm yr hydrochemical data from 13 wells in the area were used in the mixing cell model mcm end members were identified as sources for the groundwater found in the lower kuiseb including inflow from the crystalline basement plateau north of the kuiseb as well as floodwater from the kuiseb river a conceptual groundwater recharge and flow model was developed and then inverse mixing cell modeling was carried out using hydrochemical tracers this approach generally allows for several possible solutions after completing the inverse modeling a forward mixing cell model was developed by varying the mean residence time of each cell to fit calculated 14c data to the measured 14c data this new approach joins previously developed methods solely based on conservative mixing or residence time optimization based on the results of the model the fraction of floodwater in different sections of the lower kuiseb groundwater systems was calculated ranging from 61 to 98 2 in addition to floodwater groundwater inflow from the crystalline basement north of the kuiseb was shown to contribute to the lower kuiseb aquifer accounting for salinization during periods without flooding

structural and surface features of arc shaped radar echoes along an outer tropical cyclone rainband this study uses ground based dual doppler radar and surface observations to document the structural and surface features of the arc shaped radar echoes asres evident along an outer rainband of typhoon longwang as it approached northern taiwan on 1 october 2005 the particular aim of this study is to explore the possible distinction between the present case previously documented tropical cyclone rainbands tcrs and squall lines the dual doppler derived fields show that the leading precipitation of the studied asres exhibited a convective nature with a sharp horizontal gradient of reflectivity and a significant vertical extent theregionsbehindtheleadingconvectionwerecharacterizedbyband relativerear to frontflowatlowlevels and were associated with a broader area of stratiform precipitation the deep layer of front to rear flow extending from the surface to the upper troposphere was generally present ahead of the asres this flow appearstobeliftedupwardatandimmediatelyaheadoftheleadingedgeofthelow levelrear to frontflowto form rearward tilting updrafts these airflow patterns are similar to those of the convective region of squall lines but differ fundamentally from those of previously documented tcrs that were located closer to the inner core of cyclones the detailed analyses of surface fluctuations during the passage of one of the studied asresfurthershowanabruptpressurerise 2mb atemperaturedrop 48c andapronounceddeceleration of inflow air coincident with the leading heavy precipitation the evaluation presented suggests that the convectively generated cold pool may be important in influencing the structures and propagation of the studied asres

mesoscale and convective scale characteristics of mature hurricanes part i general observations by research aircraft abstract the analysis of instrumented aircraft data from four recent mature hurricanes reveals common mesoscale and convective scale features the structure and organization of the convection precipitation and wind flow are studied by combining the airborne observations using basic instrumentation with quantitative radar measurements three predominant precipitation features seen are 1 the eyewall 2 a stratiform rain region adjacent to and outside the eyewall and 3 rainbands that contain both convective and stratiform regions the eyewall is so named because it surrounds the rain free eye but several additional features distinguish it from other convective bands in the hurricane in particular the updraft tangential wind maximum and highest rainfall have preferred locations relative to each other with the updraft being radially inward from the rain and wind maxima the 10 dbz radar reflectivity contour indicative of the inner edge slopes substantially outward with height and there is evide

surface fluctuations associated with tropical cyclone rainbands observed near taiwan during 2000 08 with radar measurements and temporally high resolution surface observations this study investigates surface fluctuations associated with tropical cyclone rainbands tcrs observed in the vicinity of taiwan during 2000 08 a total of 263 tcrs identified from 37 typhoon eventsduring the studyperiod were analyzed to show the mean and common nature of perturbations of various meteorological variables associated with the passage of tcrs the main patterns of surface thermodynamic fluctuations as revealed from the composite analysis of all identified tcrs include a persistent decrease in temperature dewpoint temperature and equivalent potential temperature ue from the outer to inner edge of the rainband a wavelike variation of pressure perturbations associated with the rainband was evident with a minimum coincident with the outer edge and a maximum located inside the inner edge the kinematics of the rainband was characterized by an obvious decrease in cross band wind component relatively minor variations in along band wind component and the windveering quantitative analysesindicatethatthemajorityofthetcrs 80 90 exhibitedvariations in surface temperature pressure wind speed and wind direction less than 28c 1 5 mb 5 m s 21 and 208 respectively however acleartrendofthemagnitudeoftcrthermodynamicfluctuationsincreasingwiththe radial distance from the tropical cyclone center was observed the tcrs identified in this study were also classified into the outer and inner rainbands which are distinguishedbyaradialdistanceof3timestheradiusofmaximumwind thecompositeandmagnitudeanalyses of their surface fluctuations indicate that the outer rainbands had a higher potential than the inner rainbands to reduce the near surface ue values this observed characteristic is likely related to more pronounced evaporative cooling taking place in drier subcloud regions and the downward transport of low ue air aloft by more vigorous convective downdrafts for the outer rainband fundamentally different features of surface pressure fluctuations and mean frictional vertical velocity and relative vorticity between the outer and inner rainbands were also documented these results reflect a possibly different origin nevertheless there was no dramatic difference in the pattern of kinematic fluctuations between the outer and inner rainbands and their mean magnitudes were also found to be statistically identical which suggests that there is not an entirely clear distinction of surface characteristics for these two types of rainbands

snow contribution to first year and second year arctic sea ice mass balance north of svalbard the salinity and water oxygen isotope composition 18o of twenty nine first year fyi and second year syi arctic sea ice cores total length 32 0 m from the drifting ice pack north of svalbard were examined to quantify the contribution of snow to sea ice mass five cores total length 6 4 m were analyzed for their structural composition showing variable contribution of 10 30 by granular ice in these cores snow had been entrained in 6 to 28 of the total ice thickness we found evidence of snow contribution in about three quarter of the sea ice cores when surface granular layers had very low 18o values snow contributed 7 5 9 7 to sea ice mass balance on average including also cores with no snow using 18o mass balance calculations in syi cores snow fraction by mass 12 7 16 3 was much higher than in fyi cores 3 3 4 4 while the bulk salinity of fyi 4 9 was distinctively higher than for syi 2 7 we surmise that oxygen isotopes and salinity profiles can give information on the age of the ice and allows to distinguish between fyi and syi or older ice in the area north of svalbard this article is protected by copyright all rights reserved

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

precipitation and kinematic structure of an oceanic mesoscale convective system part i convective line structure abstract the precipitation thermodynamic and kinematic structure of an oceanic mesoscale convective system is studied using airborne doppler and in situ flight level data collected by the noaa p 3 aircraft the system a well organized stationary north south convective line was located near the east coast of taiwan in part i the basic structure of the line is documented with both datasets a procedure revealing the strengths and weakness of both approaches the doppler data reveal that the warm moist air feeding the line enters from the east side most updrafts associated with the leading edge of the convective line tilt westward below 5 km and then eastward above 5 km this change of tilt corresponds to a change in the sign of the vertical flux of east west momentum to the east of the leading edge a 10 km wide zone of strong mesoscale descent is seen the band is not a complete barrier to the low level southeasterly flow and at times and places along the line the inflowing air can move throu

from points to poles extrapolating point measurements of sea ice mass balance the amount of ice growth and ablation are key measures of the thermodynamic state of the ice cover while ice extent and even ice thickness can be determined using remote sensing techniques this is not the case for the mass balance mass balance measurements require an ability to attribute the change establishing whether a change in the thickness of the ice cover occurs at the top or bottom surface and whether it is a result of growth or ablation we have developed and implemented a tool that can be used to measure thermodynamic changes in sea ice mass balance at individual locations the ice mass balance buoy imb the primary limitation of the imb is that it provides a point measurement of the ice mass balance defined by a particular combination of snow and ice conditions determining if and how such point measurements can be extrapolated is critical to understanding the large scale mass balance of the sea ice cover we explore the potential for extrapolation using mass balance observations from the surface heat budget of the arctic sheba field experiment during sheba mass balance measurements were made at over 100 sites covering a 100 km 2 area results indicate that individual point measurements can provide reasonable estimates for undeformed and unponded multi year ice which represented more than two thirds of the ice cover at sheba and is the dominant ice type in the perennial pack a key is carefully selecting a representative location for the instrument package the contribution of these point measurements can be amplified by integrating them with other tools designed to measure ice thickness and assimilating these combined data into sea ice models

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

generation of moving spiral bands in tropical cyclones abstract a theory based on the shallow water equation is developed to explain the generation of moving spiral banded structures in tropical cyclones the theory proposes that fluctuation of the vorticity distribution in the compact core region can act as a source generating gravity waves that produce the banded structures this mechanism is usually called the lighthill radiation mechanism a numerical experiment using the fifth pennsylvania state university national center for atmospheric research mesoscale model mm5 code is used to test this theory the moving bands in the simulated tropical cyclone show good agreement with the theoretically calculated gravity waves that emerge from a core region with an elliptical distribution of vorticity results of the simulated cyclone also illustrate that spiral cloud bands are triggered by the propagating gravity waves

multicell squall line structure as a manifestation of vertically trapped gravity waves abstract two dimensional and three dimensional simulations of a midlatitude squall line with a high resolution non hydrostatic model suggest that the multicellular structure of the storm may be associated with gravity waves generated by convection time lapse display of model output demonstrates that the commonly described cut off process is actually a gravity wave phenomenon the convective cells arise as gravity waves which are forced by continuous strong low level convergence at the storm s gust front the waves propagate to both sides of the gust front the stronger westward front to rear mode dominates at the mature stage of the squall line continuous low level updraft is generated at the nose of the cold pool which propagates at the speed of a density current updraft cells periodically break away from this persistent low level gust front updraft and move at phase speeds of their associated gravity waves not at the surrounding airflow speeds as implied by the traditional multicell model lin

a numerical study of outer rainband formation in a sheared tropical cyclone abstractthe dynamical process of outer rainband formation in a sheared tropical cyclone tc is examined in this study using the fully compressible nonhydrostatic tc model after the easterly vertical wind shear of 10 m s 1 was imposed upon an intensifying strong tc an outer rainband characterized by a wavenumber 1 structure formed as a typical principal rainband downshear further analysis indicates that the outer rainband formation was closely connected to the activity of the inner rainband previously formed downshear moving radially outward the inner rainband tended to be filamented owing to the strong radial gradient of angular velocity as the inner rainband approached the outer boundary of the inner core convection in its middle and upwind segments reinvigorated and nascent convective cells formed upwind of the rainband caused mainly by the decreased filamentation and stabilization subsequently the rainband reorganized into a typical outer rainband three different scenarios are found to be

radar observations of intense orographic precipitation associated with typhoon xangsane 2000 abstract with measurements from two ground based doppler radars located in northern taiwan this study documents the detailed aspects of intense orographic precipitation associated with typhoon xangsane 2000 as it moved northward immediately off the eastern coast of taiwan bringing strong low level northeasterly to north northeasterly winds impinging on the mountainous northern coast with relatively good persistent coverage of radar echoes on both inland and upstream regions this particular event provides a unique description of the orographic precipitation and its relationship with orographic geometry strong upstream oncoming flow and the precipitation inherently associated with typhoon circulations in this case the heaviest precipitation was observed to occur primarily over two coastal mountain barriers mount da tun dt and the nangang keelung range nkr barrier dt is an approximately 3d mountain barrier and the nkr adjacent to the southeast of dt is a relatively lower narrower 2d moun

a compartmental mixing cell approach for the quantitative assessment of groundwater dynamics in the otway basin south australia abstract transient groundwater fluxes as calculated by a groundwater flow model modflow are used as input into a compartmental mixing cell cmc model to simulate the transport of hydrochemical and isotopic species in regional groundwater systems good agreement between modeled and measured concentrations of solutes in groundwater provides greater confidence in estimating aquifer parameters for the flow model the cmc model is currently developed for multi layered groundwater systems and allows for both recharge to the uppermost aquifer and upward or downward leakage between individual aquifers the combination of the cmc approach and modflow allows chemical and hydraulic data to be analysed simultaneously to allow for improved conceptualization of the groundwater system the use of transient fluxes reflects the temporal scale and variability of the chemical tracers as well as the temporal variability of hydraulic conditions the model is applied to a transect in the gambier embayment of the otway basin in south australia to quantify mixing between two main aquifer systems this groundwater system is hydraulically connected to the ocean in the west and as a result would have been affected by sea level changes over the last 30 000 yr radiocarbon simulations helped to quantify a major zone of downward leakage to the confined aquifer with modeled rates of leakage ranging 2 9 mm yr

boundary layer structure and dynamics in outer hurricane rainbands part i mesoscale rainfall and kinematic structure abstract results of hurricane boundary layer experiments conducted in outer rainbands of hurricanes josephine 1984 and earl 1986 are presented comparisons of precipitation and kinematic structures in these storms and in hurricane floyd 1981 indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer the two dimensional mesoscale structure suggests that these rainbands are made up of a linear aggregate of cellular reflectivity elements on the inner upshear side of the band and stratiform rain on the outer downshear side the bands are oriented perpendicular to the shear above the boundary layer and cells move downband at about 85 of the density weighted mean wind speed of the 0 2 6 km layer the boundary layer wind field is strongly influenced by the rainband with alongband and crossband wind maxima located on the outer side of the band axis and minima 4 8 km to the inner side maximum crossband convergence and cyclonic shear vor

a wide rainband in a developing tropical cyclone abstract on 18 january 1987 the three aircraft from the equatorial mesoscale experiment emex completed a mission designed to identify the mesoscale reflectivity kinematic and thermodynamic structure of a convectively active rainband on the leading edge of developing tropical cyclone irma the reflectivity structure determined from land based and aircraft radars reveals that the band consisted of an unusually wide 80 km region of convective clouds that did not maintain a linear organization high e air entered from both sides in the subcloud and lower cloud layer thermodynamically the rainband was benign in the sense that it did not produce cold downdrafts or large regions of low e air that would limit the energy of the low level inflow to the developing eyewall region kinematically the band was a preferred location for the enhancement of the wind component parallel to the band the low level flow was along rather than across the major axis of the band above 4 5 km flow was from the inner to

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

tracking a long lasting outer tropical cyclone rainband origin and convective transformation abstractthis study used radar and surface observations to track a long lasting outer tropical cyclone rainband tcr of typhoon jangmi 2008 over a considerable period of time 10 h from its for

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

kinematic structure of convective scale elements in the rainbands of hurricanes katrina and rita 2005 1 airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex show the convective scale air motions embedded in the principal rainbands of hurricanes katrina and rita these embedded convective cells have overturning updrafts and low level downdrafts originating at 2 4 km that enter the rainband on its radially outward side and cross over each other within the rainband as well as a strong downdraft emanating from upper levels 6 km on the radially inward side these vertical motion structures repeat from one convective cell to another along each rainband the resulting net vertical mass transport is upward in the upwind portion of the band and greatest in the middle sector of the principal rainband where the updraft motions contribute generally to an increase of potential vorticity below the 3 4 km level because the convective cells in the middle sector are systematically located radially just inside the secondary horizontal wind maximum shwm the local increase in vorticity implied by the convective mass transport is manifest locally as an increase in the strength of the shwm at midlevels 4 km the overturning updrafts of the convective cells tilt stretch and vertically transport vorticity such that the convergence of the vertical flux of vorticity strengthens the vorticity anomaly associated with the shwm this process could strengthen the shwm by several meters per second per hour and may explain how high wave number convective scale features can influence a low wave number feature such as the principal rainband and subsequently influence the primary vortex

sea ice draft observations in nares strait from 2003 to 2012 time series observation of sea ice draft and velocity from nares strait between 2003 and 2012 provides new insights on the statistical properties of sea ice leaving the arctic for the atlantic oceans median ice draft is 0 8 m but it varies annually from 1 5 m in 2007 2008 to 0 5 m in 2008 2009 probability density distributions of sea ice draft depend on location across the channel with thicker ice near canada and thinner ice near greenland nevertheless sea ice motion stops seasonally due to arching land fast ice that spans the 30 40 km wide channel for up to 190 days per year such as during the 2011 2012 winter in contrast the 2006 2010 period exhibits a single ice arch lasting 47 days in april may 2008 hence sea ice statistics are weighted by space not by time using sea ice velocities estimated from colocated velocity observations multiyear sea ice with drafts exceeding 5 m constitute between 9 2003 2004 and 16 2007 2008 of the observed sea ice the probability g d of this thick ridged multiyear ice decays exponentially with draft d at an e folding scale d0 of 3 0 0 2 m the trend of d0 with time is statistically indistinguishable from zero this observation suggests a steady export of multiyear sea ice at decadal time scales we speculate that our observations document the draining of the last reservoir of thick ice from the arctic ocean found to the north of ellesmere island and greenland

multi variable mixing cell model as a calibration and validation tool for hydrogeologic groundwater modeling abstract agricultural irrigation can make substantial changes to groundwater systems this study focuses on an arid area in northern nevada where 100 yr of extensive irrigation has occurred in particular the impacts of long term agricultural activities on the groundwater fluid balance geochemistry and potential changes to the water quality of a nearby river were investigated the study conducted in the fernley basin in western nevada utilized two different modeling approaches to construct a conceptual model that honors both the chemical and physical aspects of the basin groundwater flow regime a multi variable mixing cell model was constructed to represent the hydrochemical approach while a modflow model was constructed to represent the hydrogeological model a geochemical and isotopic analysis of the basin and its margin groundwater was conducted to identify all of the water sources that potentially flow through the basin and all water bodies within the basin those water bodies and sources were incorporated into a mixing cell model that allowed delineation of the general flow lines connecting the different water bodies within the basin with their sources the mixing cell model results were used to calibrate the hydrogeological model until a general agreement between the flow lines of both models was achieved the calibration of the hydrogeologic model included adjustments of the hydraulic conductivities and the use of various interpolation methods the study showed that parallel application of two different modeling approaches the mixing cell model along with a hydrogeological model provides an excellent tool for the validation of the conceptual model moreover it allowed calibration of the hydrogeologic model not only to the water heads as usually done in hydrogeological models but also to the general flow lines that honors the basin geochemistry

quantitative assessment of the flow pattern in the southern arava valley israel by environmental tracers and a mixing cell model abstract this paper demonstrates the implementation of a novel mathematical model to quantify subsurface inflows from various sources into the arid alluvial basin of the southern arava valley divided between israel and jordan the model is based on spatial distribution of environmental tracers and is aimed for use on basins with complex hydrogeological structure and or with scarce physical hydrologic information however a sufficient qualified number of wells and springs are required to allow water sampling for chemical and isotopic analyses environmental tracers are used in a multivariable cluster analysis to define potential sources of recharge and also to delimit homogeneous mixing compartments within the modeled aquifer six mixing cells were identified based on 13 constituents a quantitative assessment of 11 significant subsurface inflows was obtained results revealed that the total recharge into the southern arava basin is around 12 52 10 6 m 3 year 1 the major source of inflow into the alluvial aquifer is from the nubian sandstone aquifer which comprises 65 75 of the total recharge only 19 24 of the recharge but the most important source of fresh water originates over the eastern jordanian mountains and alluvial fans

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

ice mass balance buoys a tool for measuring and attributing changes in the thickness of the arctic sea ice cover recent observational and modeling studies indicate that the arctic sea ice cover is undergoing significant climate induced changes affecting both its extent and thickness the thickness or more precisely the mass balance of the ice cover is a key climate change indicator since it is an integrator of both the surface heat budget and the ocean heat flux accordingly efforts are underway to develop and deploy in situ observing systems which when combined with satellite remote sensing information and numerical models can effectively monitor and attribute changes in the mass balance of the arctic sea ice cover as part of this effort we have developed an autonomous ice mass balance buoy imb which is equipped with sensors to measure snow accumulation and ablation ice growth and melt and internal ice temperature plus a satellite transmitter the imb is unique in its ability to determine whether changes in the thickness of the ice cover occur at the top or bottom of the ice cover and hence provide insight into the driving forces behind the change since 2000 imbs have been deployed each spring from the north pole environmental observatory and in several other areas including a few in the beaufort sea and central basin at this point the collective time series is too short to draw significant and specific conclusions regarding interannual and regional variability in ice mass balance comparisons of available data indicate that ice surface ablation is greater in the beaufort region 67 80 cm relative to the north pole 0 30 cm consistent with a longer period of melt in the more southerly location ablation at the bottom of the ice 22 cm maximum ice thickness 235 cm and maximum snow depth 28 cm were comparable in the two regions

processes controlling surface bottom and lateral melt of arctic sea ice in a state of the art sea ice model we present a modelling study of processes controlling the summer melt of the arctic sea ice cover we perform a sensitivity study and focus our interest on the thermodynamics at the ice atmosphere and ice ocean interfaces we use the los alamos community sea ice model cice and additionally implement and test three new parametrization schemes i a prognostic mixed layer ii a three equation boundary condition for the salt and heat flux at the ice ocean interface and iii a new lateral melt parametrization recent additions to the cice model are also tested including explicit melt ponds a form drag parametrization and a halodynamic brine drainage scheme the various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics for each simulation the total melt is decomposed into its surface bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally because this study quantifies the relative importance of several processes in driving the summer melt of sea ice this work can serve as a guide for future research priorities

a squall line like principal rainband in typhoon hagupit 2008 observed by airborne doppler radar this study examines the structure and dynamics of typhoon hagupit s 2008 principal rainband using airborne radar and dropsonde observations the convection in hagupit s principal rainband was organized into a well defined line with trailing stratiform precipitation on the inner side individual convective cells had intense updrafts and downdrafts and were aligned in a wavelike pattern along the line the line averaged vertical cross section possessed a slightly inward tilting convective core and two branches of low level inflow feeding the convection the result of a thermodynamic retrieval showed a pronounced cold pool behind the convective line the horizontal and vertical structures of this principal rainband show characteristics that are different than the existing conceptual model and are more similar to squall lines and outer rainbands the unique convective structure of hagupit s principal rainband was associated with veering low level vertical wind shear and large convective instability in the environment a quantitative assessment of the cold pool strength showed that it was quasi balanced with that of the low level vertical wind shear the balanced state and the structural characteristics of convection in hagupit s principal rainband were dynamically consistentwith the theory ofcold pooldynamicswidely appliedtostrong andlong livedsquall lines theanalyses suggest that cold pool dynamics played a role in determining the principal rainband structure in addition to storm scale vortex dynamics

perennial pack ice in the southern beaufort sea was not as it appeared in the summer of 2009 1 in september 2009 we observed a much different sea icescape in the southern beaufort sea than anticipated based on remotely sensed products radarsat derived ice charts predicted 7 to 9 tenths multi year my or thick first year fy sea ice throughout most of the southern beaufort sea in the deep water of the canada basin in situ observations found heavily decayed very small remnant my and fy floes interspersed with new ice between floes in melt ponds thaw holes and growing over negative freeboard older ice this icescape contained approximately 25 open water predominantly distributed in between floes or in thaw holes connected to the ocean below although this rotten ice regime was quite different that the expected my regime in terms of ice volume and strength their near surface physical properties were found to be sufficiently alike that their radiometric and scattering characteristics were almost identical

arctic ocean heat impact on regional ice decay a suggested positive feedback abstractbroad long living ice free areas in midwinter northeast of svalbard between 2011 and 2014 are investigated the formation of these persistent and reemerging anomalies is linked hypothetically with the increased seasonality of arctic sea ice cover enabling an enhanced influence of oceanic heat on sea ice and in particular heat transported by atlantic water the memory of ice depleted conditions in summer is transferred to the fall season through excess heat content in the upper mixed layer which in turn transfers to midwinter via thinner and younger ice this thinner ice is more fragile and mobile thus facilitating the formation of polynyas and leads when openings in ice cover form along the atlantic water pathway weak density stratification at the mixed layer base supports the development of thermohaline convection which further entrains warm and salty water from deeper layers convection induced upward heat flux from the atlantic layer retards ice formation either keeping ice thick

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

spiral rainbands in a numerical simulation of hurricane bill 2009 part i structures and comparisons to observations abstractthis study examines spiral rainbands in a numerical simulation of hurricane bill 2009 this paper the first part of the study evaluates the structures of spiral rainbands and compares them to previous observations four types of spiral rainbands are identified principal secondary distant and inner rainbands principal rainbands tend to be stationary relative to the storm center while secondary rainbands are more transient and move around the storm center both principal and secondary rainbands are tilted radially outward with height and have many of the commonly observed kinematic features such as overturning secondary circulation and enhanced tangential velocity on their radially outward sides principal rainbands are bounded by very dry air on their radially outward sides distant rainbands are radially inward tilting convective features that have dense cold pools near the surface inner rainbands are made of shallow convection that appears to have originated from near the eyewall dif

arctic sea ice conditions in spring 2009 2013 prior to melt 1 measurements from nasa icebridge airborne surveys in march april 2009 2013 over the western arctic ocean are presented in the context of previous observations to assess changes in the characteristics of the sea ice cover during the last decade taking into account spatial and temporal limitations in the available data following a precipitous drop in the amount and thickness of multiyear my ice in 2007 2008 the characteristics of the ice cover have remained largely consistent through march 2013 the central arctic continues to be dominated by my ice with mean and modal thicknesses of 3 2 m and 2 4 m respectively the southern beaufort and chukchi sea region is a complex mixture of 75 first year ice and 25 my ice icebridge observations indicate that the mean thickness in the beaufort and chukchi seas may have decreased from 2 5 m to as low as 1 6 m over the 5 year period

positive trend in the mean speed and deformation rate of arctic sea ice 1979 2007 using buoy data from the international arctic buoy program we found that the sea ice mean speed has substantially increased over the last 29 years 17 per decade for winter and 8 5 for summer a strong seasonal dependence of the mean speed is also revealed with a maximum in october and a minimum in april the sea ice mean strain rate also increased significantly over the period 51 per decade for winter and 52 for summer we check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing instead they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline increasing deformation means stronger fracturing hence more lead opening and therefore a decreasing albedo this accelerates sea ice thinning in summer and delays refreezing in early winter therefore decreasing the mechanical strength of the cover and allowing even more fracturing larger drifting speed and deformation and possibly a faster export of sea ice through the fram strait the september minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the arctic sea ice cover

geochemical calculations and observations on salt water intrusions i a combined geochemical minxing cell model abstract a combined geochemical mixing cell flow model has been developed the geochemical model is based on the computer program eq 3 6 wolery 1982 has been modified to include cation exchange reactions and is incorporated in a one dimensional mixing cell model for stationary one dimensional transport dispersion or diffusion is calculated by mixing the cell contents with neighbouring cells relationships between mixing factors and dispersivity and diffusion coefficients are derived the model is used to simulate concentration changes during salt water intrusions fundamental differences are shown to exist between diffusion of salt water from a stagnant water body and dispersive intrusions during marine transgressions or flooding events with dispersive flow characteristic water compositions develop in space and time as a result of cation exchange with diffusion these steep concentration gradients are smoothed out and mixed compositions occur the concept that characteristic concentrations occur during dispersive flow is used to obtain paleohydrological information in a dutch polder the depth of the fresh salt water interface before polder development is deduced from a simulation of observed exchange reactions in the polder groundwater

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

solute transport in the vadose zone and groundwater during flash floods events were investigated in the lower reach of the kuiseb river namibia and in controlled column experiments simultaneous measurements of water level and electrical conductivity of the ood water in the stream channel and in the groundwater together with variations in the vadose zone water content temperature and pressure proles allowed a detailed analysis of the various mechanisms governing solute transport in the subsurface during ash oods the results indicated that on the land surface ash oods emit at their wetting fronts instantaneous compression waves that propagate downward through the unsaturated zone to the water table these compression waves generate abrupt solute displacement events in the groundwater immediately after the arrival of the ood on the land surface long before deep percolation and groundwater recharge begin each ood event launches into the vadose zone a wetting front that propagates down through the vadose zone and recharges the groundwater upon arrival at the water table therst wetting front of each ood season leaches out soluble salts that have accumulated in the vadose zone during the dry season however water percolation through the unsaturated zone does not leach out the entire soluble salt capacity of the sediment even if percolation takes place under high water head ooding conditions for long periods the incomplete leaching of the unsaturated zone by the percolating water releases soluble salts into the groundwater during every recharge event as a result of the rise of the water table into the vadose zone this process results in a temporal increase of the groundwater electrical conductivity ec

arctic sea ice melt in 2008 and the role of solar heating there has been a marked decline in the summer extent of arctic sea ice over the past few decades data from autonomous ice mass balance buoys can enhance our understanding of this decline these buoys monitor changes in snow deposition and ablation ice growth and ice surface and bottom melt results from the summer of 2008 showed considerable large scale spatial variability in the amount of surface and bottom melt small amounts of melting were observed north of greenland while melting in the southern beaufort sea was quite large comparison of net solar heat input to the ice and heat required for surface ablation showed only modest correlation however there was a strong correlation between solar heat input to the ocean and bottom melting as the ice concentration in the beaufort sea region decreased there was an increase in solar heat to the ocean and an increase in bottom melting

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

estimation of spatial recharge distribution using environmental isotopes and hydrochemical data ii application to aravaipa valley in southern arizona u s a abstract in part i a mathematical model was developed to estimate the spatial distribution of annual recharge rates into an aquifer using environmental isotopes and hydrochemical data in part ii the model is applied to real data from the aravaipa valley in southern arizona these data suffer from a paucity of hydrologic information but contain numerous isotopic and hydrochemical analyses the model is able to extract from the available data both qualitative and quantitative information about recharge into and flow through the shallow unconfined aquifer in the valley the model shows that this aquifer is replenished primarily by lateral recharge from the pediments and the tributary stowe gulch basin as well as by upward leakage from the underlying confined aquifer recharge from the aravaipa creek is relatively minor lateral recharge from the eastern pediments into the unconfined aquifer exceeds that from the western pediments by a factor of two the western pediments are a major source of recharge for the confined aquifer these results are tentative because independent means to verify them are currently lacking we are encouraged however that the mass balance errors of water and dissolved constituents do not exceed 4 and that the flow rate obtained from darcy s law at one location within the unconfined aquifer in which transmissivity is known agrees with model prediction while chemical reactions are ignored in the model some of the isotopic and chemical species show sufficient spatial variability due to mixing to justify the approach this is supported by analyses of equilibrium water mineral interactions conducted by wateqf

surface pressure features of landfalling typhoon rainbands and their possible causes abstract this study uses temporally high resolution surface observations doppler radar and micro rain radar to document the finescale features of the two landfalling rainbands associated with typhoon longwang 2005 as they passed over northern taiwan the present case allows a unique opportunity to investigate well defined convectively active tropical cyclone rainbands over land in particular the surface pressure fluctuations observed during the passage of the two rainbands and their possible causes are explored the rainbands were predominantly convective in nature with embedded stratiform precipitation outside their inner outer edge analyses of surface observations show similar surface pressure fluctuations during the rainband s passage low high pressure with relatively strong weak cross band flow and warmer colder temperature was located inside the outer inner edge maximum minimum pressure perturbations were observed to be 1 5 1 mb with smaller magnitudes 0 4 mb outside th

the organization of convection in the rainbands of tropical cyclone laurence abstract a slow moving weak tropical cyclone passed near darwin australia in december 1990 rainbands were observed by a doppler weather radar and a 50 mhz wind profiler for over 24 h the principal bands were seen to be organized on two distinct scales bands of stratiform precipitation formed at a radius of about 100 km from the center of the storm and moved outward at about 6 m s 1 these decayed after they moved past darwin over land a distinct midlevel jet extended along the bands within the bands convective lines formed at regular intervals propagated against and outward with respect to the mean flow and acted as a partial barrier to the radial inflow deep active convection was confined to these lines the vertical motion in the convection showed a distinct acceleration above the freezing level with measured updrafts of up to 10 m s 1 the convection elevated the tropopause height over the rainband it is hypothesized that an inertia gravity wave propagating from near the storm eye was resp

structural changes of an outer tropical cyclone rain band encountering the topography of northern taiwan this study utilized ground based doppler radar observations to document the detailed structures of an outer tropical cyclone rainband tcr of typhoon longwang 2005 as the rainband passed over the topography of northern taiwan on 1 october 2005 the tcr was oriented northeast southwest and was roughly parallel to the mountain barrier with a higher lower terrain height in its southern northern landfalling segment during the pre landfall stage the tcr was characterized by convective precipitation on its inner side where the front to rear flow met with the rear to front flow to lift air upward with overturning updraft like signatures significant relatively minor changes in the tcr s structures were evident in the southern northern landfalling segment during the landfalling stage in particular the southern landfalling segment exhibited a much stronger front to rear flow that passed through the region of the rainband resulting in the absence of low level organized convergence and a relatively disorganized nature of precipitation this structural change was shown to be closely related to a significant decrease in the cross barrier flow due to the orographic blocking that occurred as easterly ambient winds encountered local high mountains in the vicinity of the rainband segment as the tcr propagated over the western side of the major topography the low level rear to front flow reappeared due to the collapse of low level orographic blocking and the convergence between the front to rear flow and the rear to front flow tended to rebuild a well organized convective circulation along the rainband results from this case study provide insight into processes that contribute to rapid structural changes in a landfalling tcr over mountainous regions

a mesoscale gravity wave event observed during ccope part ii interactions between mesoscale convective systems and the antecedent waves abstract this paper presents the results of a very detailed investigation into the effects of preexisting gravity waves upon convective systems as well as the feedback effects of convection of varying intensity upon the waves the analysis is based on the synthesis of synoptic surface and barograph data with high resolution surface mesonetwork radar and satellite data collected during a gravity wave event described by koch and golus in part i of this series of papers use is also made of the synoptic barograph data and satellite imagery to trace the waves beyond the mesonetwork and thus determine their apparent source region just upstream of the mesonetwork it is shown that two of the gravity waves modulated convection within a weak squall line as they propagated across the line the other six waves remained closely linked with convective systems that they appeared to trigger however it is shown that the waves were not excited by convection furthermore the waves retained their signatures in the su

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

regional variability in sea ice melt in a changing arctic in recent years the arctic sea ice cover has undergone a precipitous decline in summer extent the sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing the amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014 there are large regional and temporal variations in both surface and bottom melting combined surface and bottom melt ranged from 16 to 294 cm with a mean of 101 cm the mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm on average surface melting decreases moving northward from the beaufort sea towards the north pole however interannual differences in atmospheric forcing can overwhelm the influence of latitude substantial increases in bottom melting are a major contributor to ice losses in the beaufort sea due to decreases in ice concentration in the central arctic surface and bottom melting demonstrate interannual variability but show no strong temporal trends from 2000 to 2014 this suggests that under current conditions summer melting in the central arctic is not large enough to completely remove the sea ice cover

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

a mesoscale gravity wave event observed during ccope i multiscale statistical analysis of wave characteristics abstract this paper is the first in a series of three papers concerning a gravity wave event that occurred over the north central united states on 11 12 july 1981 the event is analyzed with superb detail resulting from the availability of digitized radar surface mesonetwork and other special data from the cooperative convective precipitation experiment ccope in montana the subject matter of this paper consists of 1 a statistical determination of the wave characteristics 2 a demonstration that the observed phenomena display a nature consistent with that of gravity waves and 3 a discussion of the principles and limitations of statistical methods for detecting and tracking mesoscale gravity waves two distinct wave episodes of 8 h duration within a longer 33 h period of wave activity are studied in detail both episodes contain strongly coherent bimodal wave activity the primary secondary wave mode isolated from autospectral and perturbation map analyses displays mean periods of 2 5 0 9 h

midlevel vorticity structure of the 10 11 june 1985 squall line abstract the comprehensive analysis of the kinematic structure of the mature phase of the 10 11 june 1985 squall line system was used to examine the midlevel vertical vorticity structure of the storm to show that relative vertical vorticity in the stratiform region at midlevels was organized into bands both cyclonic and anticyclonic oriented parallel to the convective line with anticyclonic vorticity between the rear of the convective line and the heaviest stratiform precipitation and cyclonic vorticity farther back since previous studies have not found anticyclonic vorticity over such a large portion of the stratiform region at midlevels and since the concentration of anticyclonic vorticity may have been detrimental to the longevity of the storm by limiting the development of an inertially stable cyclonic circulation the tilting and stretching terms of the vertical vorticity equation were computed to determine how the observed vertical vorticity pattern was maintained tilting of horizontal vorticit

secondary wind maxima in hurricanes airflow and relationship to rainbands abstract aircraft flight level data from 787 radial legs in 20 hurricanes are analyzed to identify the composite kinematic structure in the hurricane eyewall and especially with secondary horizontal wind maxima shwm that occur outside the eyewall similar to previous studies analysis of the flight level wind data in the eyewall reveals radial convergence near the radius of maximum wind rmw and the highest frequency of updraft and the largest upward mass transport radially inward of the rmw more than 20 of the flight legs contain substantial secondary horizontal wind maxima of specified strength and length the kinematic structure associated with shwm is similar to that of the hurricane eyewall with radial convergence near the radius of maximum wind and a preferred location for maximum upward motions and upward mass transport just inside the rmw statistical analysis confirms the similarity in characteristics between radial and vertical velocities of the eyewall and near the shwm in addition for

gravity waves and convection in colorado during july 1983 abstract in order to gain insight into the complex dynamics of a convective system interacting with a gravity wave train we have carried out an experiment in northeast colorado during july and august 1983 utilizing data from several program areas in noaa pressure data from the profs mesonetwork of microbarograph stations were combined with velocity profiles from the wave propagation laboratory uhf wind profiler st radar at stapleton airport in denver and convective cell location data from the nws limon weather radar several events were clearly visible in the microbarograph data from which four called events a b c and d in late july were selected for further study these events differed from each other in fundamental ways in each event the waves represent oscillations of a substantial depth of the troposphere and seem to appear and disappear together with the convective cells in events a and b the waves have a critical level and are probably unstable modes generated by wind shear in the jet s

impacts of human activities on recharge in a multilayered semiarid aquifer campo de cartagena se spain the development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration environmental tracers provide key information but their interpretation is complicated by more complex groundwater flow patterns in multilayered aquifers the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long screened boreholes we use environmental tracers 14c 13c 2h 18o 3h to investigate the long term evolution of recharge in the five layer campo de cartagena aquifer in south eastern spain in addition to high resolution temperature loggings to identify the depth of origin of groundwater despite the complex background this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns the tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge nonetheless both pre anthropization and post anthropization recharge regime could be identified and quantified by radiocarbon before the development of agriculture recharge varied from 17 mm year 1 at the mountain ranges to 6 mm year 1 in the plain whereas the mean annual rainfall is about 300 mm in response to the increase of agricultural activity recharge fluxes to the plain were amplified and nowadays reach up to 210 mm year 1 in irrigated areas these values are strengthened by global water budget and local unsaturated zone studies copyright 2013 john wiley sons ltd

reflectivity ice scattering and lightning characteristics of hurricane eyewalls and rainbands part i quantitative description abstract covering december 1997 through december 1998 261 overpasses of 45 hurricanes by the tropical rainfall measuring mission trmm satellite are used to document the observed radar reflectivity values passive microwave ice scattering magnitudes and total lightning cloud to ground plus in cloud these parameters are interpreted as describing convective vigor or intensity with greater reflectivities particularly aloft greater ice scattering lower 85 and 37 ghz brightness temperatures and increased lightning frequency indicating more intense convection for each parameter the full distribution of values observed during the trmm satellite s first year is presented for specific regions properties of three regions of the hurricane eyewall inner rainband and outer rainband are treated separately and compared to other tropical oceanic and tropical continental precipitation systems reflectivity profiles and ice scattering signatures are found to be fairly similar for both hurricane and non

did unusually sunny skies help drive the record sea ice minimum of 2007 1 we conduct experiments with an ice ocean model to answer the question whether and to what degree unusually clear skies during the summer of 2007 contributed to the record sea ice extent minimum in the arctic ocean during september of 2007 anomalously high pressure over the beaufort sea during summer 2007 appears associated with a strong negative cloud anomaly this anomaly is two standard deviations below the 1980 2007 average established from a combination of two different satellite based records cloud anomalies from the modis sensor are compared with anomalies from the ncep ncar reanalysis and are found in good agreement in spatial patterns and magnitude however these experiments establish that the negative cloud anomaly and increased downwelling shortwave flux from june through august did not contribute substantially to the record sea ice extent minimum this finding eliminates one aspect of the unusual weather that may have contributed to the record minimum

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer

temporal changes of the primary circulation in tropical cyclones abstract more than 900 radial profiles of in situ aircraft observations collected in 19 atlantic hurricanes and tropical storms over 13 years confirm that the usual mechanism of tropical cyclone intensification involves contracting maxima of the axisymmetric swirling wind radar shows that annuli of convective echoes accompany the wind maxima these features called convective rings exist and move inward because latent heat released in the rings leads to descent adiabatic warming and rapid isobaric height falls in the area they enclose the radial change in rate of isobaric height fall is concentrated at the inner edge of the wind maximum causing the gradient wind to increase there and the maximum to contract vigorous convection organized in rings invariably causes well defined inward moving wind maxima but when convection is weak the rings are also weak or even absent in this case the swirling wind may be nearly constant with radius and change slowly in time hurricanes that have a single vigor