wind and thermodynamic retrieval from single doppler measurements of a gust front observed during phoenix ii abstract the adjoint method to retrieve the three dimensional wind and thermodynamic fields is applied to single doppler observations of a gust front measured during the phoenix ii experiment this method uses a fluid dynamics model and its adjoint and combines the retrieval with data assimilation into the prediction model the wind and thermodynamic variables are determined by minimizing the difference between the model solution and the observations experiments are conducted first with radial velocity alone and then with both radial velocity and reflectivity to examine the quality of the retrieval with respect to radar location boundary conditions length of assimilation data filtering smoothing enforced by penalty functions and model accuracy verification of these experiments is provided by a dual doppler analysis test results show that the adjoint method is able to retrieve the wind and thermodynamic fields of the gust front the retrieved horizontal wind agrees very well with the dual doppler

halocline structure in the canada basin of the arctic ocean 1 we examine the varieties and spatial distributions of pacific and eastern arctic origin halocline waters in the canada basin using 2002 2003 hydrographic data the halocline structure in the canada basin is different from the eastern arctic halocline because it includes fresher pacific winter waters that form a cold halostad which lies above the eastern arctic origin lower halocline waters the structure of the halostad in the canada basin however is not spatially uniform and depends on the pathway and history of the source water pacific winter water entering through the bering strait becomes salty due to sea ice formation and this in turn is dependent on the occurrence and distribution of polynyas in particular saline water from the eastern chukchi sea forms thick halostad and causes depression of the isohalines in the southern canada basin this depression influences thermohaline structure of the oceanic beaufort gyre

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

beaufort shelf break eddies and shelf basin exchange of pacific summer water in the western arctic ocean detected by satellite and modeling analyses 1 mesoscale eddies and shelf basin exchange of pacific summer water in the western arctic ocean are examined using satellite data sets and an eddy resolving coupled sea ice ocean model several surface eddy like features along the beaufort shelf break are detected by the moderate resolution imaging spectroradiometer modis sea surface temperature and the global imager gli radiance image the quikscat sea wind vectors indicate that summertime shelf wide wind is an important factor for interannual variations in the eddy properties a realistic numerical experiment reveals that the origin of shelf break warm eddies and timing of their generation can be classified into three types type i eddies are frequently produced in the vicinity of the barrow canyon throughout the summer season by a combination of outflow of pacific summer water with a low potential vorticity from the barrow canyon and lateral velocity shear of the canyon jet surface wind variability modulates the timing of generation type ii and type iii eddies originate from an eastward current along the beaufort shelf break although origin depth and background hydrographic structure differ between them type ii eddies are spawned from the shelf slope at middepth during early summer type iii eddies are generated from the surface isopycnal front over the shelf break during late summer the shift from type ii eddies to type iii eddies is caused by surface buoyancy input in the upstream region a sensitivity experiment using different atmospheric forcing data suggest that the mechanism controlling pacific water transport from the chukchi shelf to the canada basin differs depending on surface wind fields in the shelf region the mesoscale eddies primarily induce the shelf to basin transport under weak or westerly wind conditions during summer while wind driven ekman transport is a major driver in the easterly wind regime year 2003 2007 corresponds to the former latter case

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

the retrieval of asymmetric tropical cyclone structures using doppler radar simulations and observations with the extended gbvtd technique abstract the ground based velocity track display gbvtd technique is extended to two doppler radars to retrieve the structure of a tropical cyclone s tc s circulation with this extension it is found that the asymmetric part of the tc radial wind component can be derived up to its angular wavenumber 1 structure and the accuracy of the retrieved tc tangential wind component can be further improved although two radar systems are used a comparison with the traditional dual doppler synthesis indicates that this extended gbvtd egbvtd approach is able to estimate more of the tc circulation when there are missing data previous research along with this study reveals that the existence of strong asymmetric radial flows can degrade the quality of the gbvtd derived wind fields when a tc is observed by one radar it is suggested that the gbvtd method be applied to tcs over a flat surface e g the ocean where the assumption of relatively smaller asymmetric radial winds than asymmetric tangential winds is

flow dynamics of a wide arctic canyon we extend and interpret acoustic doppler current profiler and conductivity temperature depth data collected in the summer of 1993 over barrow canyon in order to implement a high resolution 1 5 to 5 km model of the beaufort and chukchi seas this paper addresses physical processes relevant to the barrow canyon region using common dynamical analyses of both field data and numerical results the field data reveal the dominant physical processes that guide the design of our numerical experiments the observed velocity field shows an intense and variable down canyon flow with transports ranging from 0 5 to 1 4 sv a momentum analysis reveals that the cross canyon dynamic balance for the barotropic component is primarily geostrophic conversely the baroclinic cross canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying coriolis acceleration and the cross canyon pressure gradient in addition to the moderate influence of stratification froude number of 0 4 and burger number of 0 06 the barotropic pressure gradient component across the canyon inferred from the large magnitude and little vertical variability of the residuals is dynamically important for both upcanyon and downcanyon flows that occur at different locations concurrently the along canyon dynamic balance is ageostrophic since the time derivative and the coriolis term are of the same order of magnitude temporal rossby number is approximately 1 an analysis of the longitudinal density and velocity fields from the model reveals that the main driving mechanism for generating the observed upcanyon flow is the nonlinear interaction of the variable barotropic flow with the steep topography stratification is maintained by the downcanyon advection of fresh and warm water from the bering and chukchi seas and the upcanyon advection of saltier and colder water from the arctic

using high resolution simulations to quantify errors in radar estimates of tornado intensity abstractobservation experiments are performed on a set of high resolution large eddy simulations of translating tornado like vortices near surface doppler wind measurements are taken by emulating

seasonal variation of upwelling in the alaskan beaufort sea impact of sea ice cover 1 data from a mooring array deployed from august 2002 to september 2004 are used to characterize differences in upwelling near the shelf break in the alaskan beaufort sea due to varying sea ice conditions the record is divided into three ice seasons open water partial ice and full ice the basic response is the same in each of the seasons roughly 8 h after the onset of easterly winds the shelf break jet reverses followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break pacific winter water and warm at depth atlantic water the secondary circulation at the outer shelf is to first order consistent with a two dimensional ekman balance of offshore flow in the upper layer and onshore flow at depth there are however important seasonal differences in the upwelling overall the response is strongest in the partial ice season and weakest in the full ice season it is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack ice as the strength of the wind forcing was comparable over the three seasons an eof based upwelling index is constructed using information about the primary flow secondary flow and hydrography the ability to predict upwelling using the wind record alone is explored which demonstrates that 90 of easterly wind events exceeding 9 5 m s 1 drive significant upwelling during certain periods the ice cover on the shelf became landfast which altered the upwelling and circulation patterns near the shelf break

the lower palaeozoic apparent polar wander path for baltica palaeomagnetic data from silurian limestones of gotland sweden summary well dated and undeformed silurian lower wenlock limestones from gotland southern sweden yield two stable remanence components following detailed thermal and alternating field demagnetization studies 1 a low blocking temperature coercivity magnetization termed l delineated below 250dc 10mt is oriented parallel to the present earth s field dec 001 inc 67 n 4 sites a95 16d 2 a higher blocking temperature coercivity magnetization termed h unblocked between 250 400dc 10 35mt has a nne declination and shallow negative inclination dec 025 inc 19 n 5 sites a95 5d this h component direction compares favourably with a previous result from gotland based upon blanket cleaning given a lack of evidence for subsequent geological heating conodont alteration index 1 1 5 or pervasive palaeomagnetic overprinting the h palaeopole is regarded as reliable and primary early diagenetic in origin 19ds 352de dp dm 3 5 the only other well constrained mid silurian pole from baltica that from the ringerike sandstone of the oslo district is in excellent agreement with the gotland data these combined poles resolve previous problems regarding the shape and time calibration of silurian apparent polar wander relative to baltica

geophysical investigation of the honningsvag igneous complex scandinavian caledonides the honningsvag igneous complex within the mageroy nappe northern norway has marked magnetic and gravimetric signatures palaeomagnetic studies reveal a siluro devonian scandian dual polarity remanence ne and up sw and down mean declination 045 inclination 38 and a 95 8 4 rock magnetic and petrological studies indicate a pure magnetite host for the remanent magnetization component magnetic fabric ellipsoids delineate dl and d2 scandian structures affecting the area and demonstrate an internal reclined fold structure of the honningsvag igneous complex forward modelling demonstrates that a short wavelength pouitive aeromagnetic anomaly c 700 nt over the northwestern part of the complex is associated with an area of reverse remanent polarity sw and down conversely areas of normal remanence polarity ne and up most common are associated with magnetic lows or quiet zones the gravity field in the vicinity of the complex displays a symmetrical positive anomaly of approximately 200 g u wavelength 15 km this can be attributed to a density contrast of approximately 0 20 mg m 3 between the gabbros of the honningsvag complex 2 93 and surrounding metasediments 2 73 an optimal geophysical and geological model demonstrates that the complex has been tilted through 90 and now has the form of a steeply dipping reclined fold structure extending to a depth of at least 6 km palaeomagnetic remanence acquisition post dates emplacement of the mageroy nappe late dl and probably originated during post dl uplift brittle upper crust d2 deformation which continued into devonian times folded the honningsvag igneous complex and introduced a small but systematic dispersion in the palaeomagnetic remanence directions the magnetization is therefore post dl but pre d2 in age and can be termed syn scandian palaeomagnetic and isotopic evidence suggests a syn tectonic magnetization age of c 410 ma the palaeomagnetic pole n7 and e344 resembles that from the underlying kalak nappe complex it is therefore inferred that the scandian emplacement of the mageroy nappe was synchronous with a thermal event which affected the older and underlying finnmarkian defor med kalak nappe complex

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

circulation of the chukchi sea shelfbreak and slope from moored timeseries abstract data from a year long mooring array across the shelfbreak upper slope of the chukchi sea are used to describe and quantify the circulation and water masses of the region the timeseries revealed the year round existence of the eastward flowing shelfbreak jet and seaward of this the westward flowing chukchi slope current in the mean the slope current is estimated to transport 0 57 0 04 sv of pacific water while the bottom intensified shelfbreak jet transports 0 009 0 003 sv towards barrow canyon the slope current is surface intensified in summer and fall and in winter and spring it becomes middepth intensified moves shoreward and weakens two extreme states of the circulation were identified 1 an enhanced slope current and reversed westward flowing shelfbreak jet and 2 a strong eastward flowing shelfbreak jet and weak slope current the former state occurs when the wind stress curl on the chukchi shelf is positive and the latter state occurs when the curl is negative a simple theoretical model is used to determine the changes in sea surface height due to such wind stress curl forcing which is consistent with the observed changes in flow seaward of the shelf both in amplitude and phase via geostrophic set up shelfbreak upwelling occurred throughout the year but there was no correlation between the regional wind conditions and the upwelling furthermore there was no apparent relationship between upwelling and the extreme slope current shelfbreak jet events a comparison of water mass signals between the chukchi slope array and a mooring at the head of barrow canyon supports the notion that the slope current is fed by the outflow of pacific water from the canyon

the early carboniferous mageroy dykes northern norway palaeomagnetism and palaeogeography palaeomagnetic data from the 337 ma mageroy dykes northern norway are of exceptionally high quality and a positive contact test along with an existing regional result from the silurian honningsvag igneous suite attests to a primary early carboniferous magnetic signature the palaeomagnetic pole s 14 8degrees e320 1degrees dp dm 4 4 8 6degrees is the first early carboniferous pole from baltica and implies that northernmost norway greenland the barents sea and svalbard were located at tropical to low northerly latitudes at this time northward drift during carboniferous times 5 6 cm yr as demonstrated from palaeomagnetic data is also reflected in the sedimentary facies in the barents sea realm that is a change from tropical early carboniferous to subtropical 20 30degrees n carbonates and evaporites in the late carboniferous the mageroy dykes are continental tholeiites which intruded into a set of nw se trending normal faults parallel to the trollfjorden komagelva fault zone and the mageroysundet fault immediately to the north and south of mageroya respectively these and many other nw se trending faults onshore and offshore were active during late palaeozoic extension and the dykes were probably contemporaneous with the earliest syn rift sedimentation in the barents sea for example the nordkapp basin less

simulation and analysis of tornado development and decay within a three dimensional supercell thunderstorm abstract a three dimensional numerical simulation using a two way interactive nested grid is to study tornado genesis within a supercell during a 40 minute period two tornadoes grow and decay within the storm s mesocyclone the tornadoes have life spans of approximately 10 minutes maximum ground relative surface wind speeds exceed 60 m s 1 during both tornadoes and horizontal pressure gradients reach 18 hpa km 1 during the second tornado comparison of the simulated storm evolution with doppler and field observations of supercells and tornadoes shows many similar features vertical vorticity in the mesocyclone and the tornado vortex at low levels is initially created by the tilting of the environmental vorticity and baroclinically generated vorticity along the forward gland gust front of the storm tornadogenesis is initiated when mesocyclone rotation increase above cloud base the increased rotation generates lower pressure in the mesocyclone increasing the upward pressure gradient forces the upwar

pathways timing and evolution of pacific winter water through barrow canyon abstract observations from a ship based campaign in july august 2009 combined with idealized numerical simulations are used to investigate the seasonal delivery of pacific winter water to barrow canyon and the subsequent adjustment of the flow down the canyon as the current advects dense water it transitions from a nearly barotropic structure near the canyon head to a strongly baroclinic flow with a subsurface maximum near the canyon mouth both the data and model indicate that the transit times along the three chukchi shelf pathways feeding barrow canyon a coastal pathway a southern hanna shoal pathway and a northern hanna shoal pathway modulate the mode of winter water that occupies the canyon at a given time in particular remnant pacific winter water carried along the rapid coastal pathway can precede the arrival of newly ventilated pacific winter water carried along the two interior pathways the observations and model indicate that the transition between water types draining from the canyon can occur rapidly over time scales of days to weeks we also demonstrate that mixing along the path of the current is unlikely to result in the observed down canyon transition from newly ventilated pacific winter water to remnant winter water further supporting the dominant role of advection while the focus here is on the transition of winter water modes the implication that seasonality within barrow canyon is tied to seasonality of the bering strait inflow together with the relative transit times along advective pathways should hold for other water types as well

circulation and thermohaline variability of the hanna shoal region on the northeastern chukchi sea shelf we analyzed velocity and hydrographic data from 23 moorings in the northeast chukchi sea from 2011 to 2014 in most years the eastern side of hanna shoal was strongly stratified year round while weakly stratified regions prevailed on the shelf south and west of the shoal stratification differences cause differential vertical mixing rates which in conjunction with advection of different bottom water properties resulted in seasonally varying along isobath density gradients in agreement with numerical models we find that bottom waters flow anticyclonically around the shoal whereas most of the shelf responded barotropically to wind forcing there was a strong baroclinic component to the flow field northeast of hanna shoal resulting in no net vertically integrated transport on average in contrast there is a net eastward transport from west of the shoal which implies convergence north of the shoal convergence and along isobath density gradients may foster cross shelf exchange north of hanna shoal modal analyses indicate that the shelf south of the shoal and barrow canyon responded coherently to local and remote winds whereas the wind current response around hanna shoal was less coherent barotropic topographic waves of 3 day period were generated episodically northeast of the shoal and propagate clockwise around hanna shoal but are blocked from entering barrow canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the shoal analysis of water properties on the western side of hanna shoal suggests that these include contributions from the western and southern portions of the chukchi sea

centrifuging of hydrometeors and debris in tornadoes radar reflectivity patterns and wind measurement errors high resolution doppler radar observations of tornadoes reveal a distinctive tornado scale signature with the following properties a reflectivity minimum aloft inside the tornado core described previously as an eye a high reflectivity tube aloft that is slightly wider than the tornado core and a tapering of this high reflectivity tube near the ground the results of simple one dimensional and two dimensional models demonstrate how these characteristics develop important processes in the models include centrifugal ejection of hydrometeors and or debris by the rotating flow and recycling of some objects by the nearsurface inflow and updraft doppler radars sample the motion of objects within the tornado rather than the actual airflow since objects move at different speeds and along different trajectories than the air error is introduced into kinematic analyses of tornadoes based on radar observations in a steady axisymmetric tornado objects move outward relative to the air and move more slowly than the air in the tangential direction in addition the vertical air relative speed of an object is less than it is in still air the differences between air motion and object motion are greater for objects with greater characteristic fall speeds i e larger denser objects and can have magnitudes of tens of meters per second estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one dimensional model doppler on wheels observations of the 30 may 1998 spencer south dakota tornado demonstrate how the apparent tornado structure can change when the radar scatterer type changes when the spencer tornado entered the town and started lofting debris changes occurred in the doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size

diagnosed three dimensional axisymmetric structure of the mulhall tornado on 3 may 1999 on 3 may 1999 an unusually large tornado that caused f4 level damage and killed several people was intercepted by the doppler on wheels dow mobile radar near mulhall oklahoma from a range of 4 to 9 km resulting in high resolution volumetric data every 55 s up to 1 5 km altitude over a period of 14 min for the first time the evolution and three dimensional structure of a tornado were deduced using the ground based velocity track display gbvtd technique after the circulation center was determined the tangential wind and radial wind were derived from the gbvtd technique at each radius and height in addition the axisymmetric vertical velocity angular momentum vorticity and perturbation pressure were deduced from the tangential and radial wind fields this study focuses on the axisymmetric aspects of this tornado the primary circulation of the mulhall tornado consisted of an 84 m s 1 peak axisymmetric tangential wind with the radius of maximum wind rmw ranging from 500 to 1000 m the secondary circulation exhibited a two cell structure characterized by a central downdraft surrounded by an annular updraft near the rmw the calculated maximum pressure deficit from a 3 km radius to the tornado center at 50 m altitude was 80 hpa the maximum vorticity during the first 8 min of observation was located inside the rmw away from the tornado center this vorticity profile satisfied the necessary condition of barotropic instability as the tornado weakened afterward the vorticity monotonically increased toward the center the computed swirl ratios were between 2 and 6 consistent with the observed multiple vortex radar signatures and the vorticity pattern swirl ratios were generally smaller during the weakening phase

spatially variable advection correction of radar data part ii test results abstract the spatially variable advection correction analysis procedure introduced in part i is tested using analytical reflectivity blobs embedded in a solid body vortex and terminal doppler weather radar tdwr and weather surveillance radar 1988 doppler wsr 88d data of a tornadic supercell thunderstorm that passed over central oklahoma on 8 may 2003 in the tdwr tests plan position indicator ppi data at two volume scan times are input to the advection correction procedure with ppi data from a third scan time intermediate between the two input times that is used to validate the results the procedure yields analyzed reflectivity fields with lower root mean square errors and higher correlation coefficients than those reflectivity fields that were advection corrected with any constant advection speed

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

the summer hydrographic structure of the hanna shoal region on the northeastern chukchi sea shelf 2011 2013 abstract we used shipboard and towed ctd current meter and satellite tracked drifter data to examine the hydrographic structure in the northeastern chukchi sea in august september of 2011 2012 and 2013 in all years the densest winter water was around and east of hanna shoal in 2012 and 2013 a 15 m deep layer of cold dilute meltwater overlaid the dense water north of the shelf region between 71 2 and 71 5 n a front extends from the southwest side of hanna shoal toward the head of barrow canyon separated meltwaters from warmer saltier bering sea summer waters to the south stratification was stronger and the surface density variances in the meso and sub mesoscale range were higher north of the front than to the south no meltwater or surface fronts were present in 2011 due to a very early ice retreat differences in summer ice cover may be due to differences in the amount of grounded ice atop hanna shoal associated with the previous winter s regional ice drift along the north side of hanna shoal the model predicted clockwise barotropic flow carrying waters from the western side of the shoal appears to converge with a counterclockwise baroclinic flow on the northeast side the baroclinic tendency is confined to the upper 30 m and can include waters transported from the shelfbreak the inferred zonal convergence implies that north of the shoal a near surface waters are a mixture of waters from the western and eastern chukchi sea and b the cross isobath pressure gradient collapses thereby facilitating leakage of upper layer waters northward across the shelf

winter water formation in coastal polynyas of the eastern chukchi shelf pacific and atlantic influences water properties and formation processes of alaskan coastal winter water acww over the eastern chukchi shelf along the alaska coast the so called barrow canyon pathway are examined using data from moorings atmospheric reanalysis satellite derived sea ice production sip and a numerical tracer experiment along this pathway pacific winter water pww can be modified to produce acww through sip accompanied by production of cold saline polynya water in the coastal polynyas upwelling of warm atlantic water aw and mixing processes on the shelf three different types of acww are formed i a mixture of aw and pww ii a mixture of aw and polynya water and iii hypersaline polynya water the northeasterly winds correlated with the north south atmospheric pressure gradient between beaufort high and aleutian low are common triggers of polynya sip episodes and aw upwelling in the barrow coastal polynya bcp due to the dual impact of northeasterly winds pww modification processes in the bcp are more complicated than what occurs elsewhere in the chukchi polynya the impact of aw upwelling on the acww formation is most prominent in the bcp usually centered along the coast all types of acww are thought to be basically transported westward or northwestward with the chukchi slope current and or beaufort gyre and finally contribute to maintenance of the lower halocline layer especially over the chukchi borderland northwind ridge and southern canada basin even in the pacific sector of the arctic ocean acww properties are strongly influenced by both atlantic origin and pacific origin waters

tornadogenesis in a high resolution simulation of the 8 may 2003 oklahoma city supercell abstracta 50 m grid spacing advanced regional prediction system arps simulation of the 8 may 2003 oklahoma city tornadic supercell is examined a 40 min forecast run on the 50 m grid produces two f3 intensity tornadoes that track within 10 km of the location of the observed long track f4 intensity tornado the development of both simulated tornadoes is analyzed to determine the processes responsible for tornadogenesis trajectory based analyses of vorticity components and their time evolution reveal that tilting of low level frictionally generated horizontal vorticity plays a dominant role in the development of vertical vorticity near the ground this result represents the first time that such a mechanism has been shown to be important for generating near surface vertical vorticity leading to tornadogenesis a sensitivity simulation run with surface drag turned off was found to be considerably different from the simulation with drag included a tornado still developed in the no drag simulation but it was

circulation of winter water on the chukchi shelf in early summer abstract using a variety of data sources we investigate the properties and pathways of pacific origin winter water as it spreads across the eastern chukchi shelf in early summer the focus is on the time period june july 2011 during which an extensive shipboard hydrographic velocity survey was undertaken as part of the impacts of climate on ecosystem and chemistry of the arctic pacific environment icescape program a revised circulation scheme is constructed revealing that the transport pathways on the chukchi shelf are more complex than previously thought notably the well known branch progressing northward from the central channel bifurcates as it reaches hanna shoal flowing around both sides of the shoal and dividing into smaller filaments that continue towards barrow canyon mass is conserved in the circulation scheme with approximately 1 sverdrup flowing poleward across the chukchi shelf within these pathways then exiting barrow canyon the salinity of the winter water varied on the shelf in 2011 with saltier water found in the upstream portion of what is defined as the central pathway using sea ice concentration data and atmospheric reanalysis fields we argue that salinization of the winter water in the central pathway occurred via brine rejection as the parcels progressed north and passed through the cape lisburne polynya this demonstrates that winter water pervading the interior shelf can be transformed by convective overturning north of bering strait presumably stirring up nutrients from the sediments and thereby influencing primary productivity in the region of hanna shoal

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

turbulent kinetic energy dissipation in barrow canyon pacificwaterflowsacross theshallowchukchisea beforereachingthe arctic ocean where it isa sourceof heat freshwater nutrients and carbon a substantial portion of pacific water is routed through barrow canyon located in the northeast corner of the chukchi barrow canyon is a region of complex geometry and forcing where a variety of water masses have been observed to coexist these factors contribute to a dynamic physical environment with the potential for significant water mass transformation the measurements of turbulent kinetic energy dissipation presented here indicate diapycnal mixing is important in the upper canyon elevated dissipation rates were observed near the pycnocline effectively mixing winter and summer water masses as well as within the bottom boundary layer the slopes of shear stratification layers combined with analysis of rotary spectra suggest that near inertial wave activity may be important in modulating dissipation near the bottom because the canyon is known to be a hotspot of productivity with an active benthic community mixing may be an important factor in maintenance of the biological environment

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

the chukchi slope current abstract using a collection of 46 shipboard hydrographic velocity transects occupied across the shelfbreak and slope of the chukchi sea between 2002 and 2014 we have quantified the existence of a current transporting pacific origin water westward over the upper continental slope it has been named the chukchi slope current which is believed to emanate from barrow canyon the current is surface intensified order 50 km wide and advects both summer and winter waters it is not trapped to a particular isobath but instead is reminiscent of a free jet there is no significant variation in pacific water transport with distance from barrow canyon a potential vorticity analysis suggests that the flow is baroclinically unstable consistent with the notion that it meanders the current is present during all synoptic wind conditions but increases in strength from summer to fall presumably due to the seasonal enhancement of the easterly winds in the region its transport increased over the 12 year period of data coverage also likely in response to wind forcing in the mean the slope current transports 0 50 0 07 sv of pacific water this estimate allows us to construct a balanced mass budget of the chukchi shelf inflows and outflows our study also confirms the existence of an eastward flowing chukchi shelfbreak jet transporting 0 10 0 03 sv of pacific water towards barrow canyon

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

seasonal to mesoscale variability of water masses and atmospheric conditions in barrow canyon chukchi sea abstract twenty four repeat hydrographic transects occupied across barrow canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from july october as well as the occurrence of upwelling the mean sections revealed that the alaskan coastal water is mainly confined to the eastern flank of the canyon corresponding to a region of sloped isopycnals indicative of the surface intensified alaskan coastal current which advects the water the pacific origin winter water is found at depth banked against the western flank of the canyon its isopycnal structure is consistent with a bottom intensified flow of this dense water mass out of the canyon for the months that were sampled the alaskan coastal water is most prevalent in august and september while the coldest winter water is observed in the month of august it is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central chukchi shelf as opposed to the coastal pathway roughly a third of the hydrographic sections were preceded by significant up canyon winds and hence were deemed to be under the influence of upwelling during these periods anomalously salty water is found throughout the eastern flank of the canyon and on occasion atlantic water fills the deepest part of the section using atmospheric reanalysis data it is shown that upwelling occurs when the beaufort high is strengthened and the aleutian low is deepened two modes of storm tracks were identified northward progressing storms mode 1 and eastward progressing storms mode 2 both of which can drive upwelling mode 1 is prevalent in july august while mode 2 is more common in september october these seasonal patterns appear to be dictated by regional variations in blocking highs

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

surface current patterns in the northeastern chukchi sea and their response to wind forcing we measured northeastern chukchi sea surface currents using high frequency radar systems hfr during the ice free periods of august to october from 2010 2014 we analyzed these data along with regional winds using self organizing maps som to develop a set of surface current wind patterns temporal changes in the som patterns consist predominantly of two patterns comprising northeastward and southwestward surface currents a third pattern represents a transitional stage established during the onset of strong northeasterly winds these patterns are analogous to the first two eigenmodes of an empirical orthogonal function analysis of the hfr data the first principal component pc1 is significantly correlated 0 8 to that of the winds and is directly related to the time series of som derived patterns the sign of pc1 changes when the speed of local northeasterly winds exceeds 6 m s 1 at which point the northeastward surface currents reverse to the southwest this finding agrees with previous models and observations that suggest this wind threshold is needed to overcome the pressure gradient between the pacific and arctic oceans the transitional stage is characterized by alongshore currents bifurcating in the vicinity of icy cape and wind driven ekman currents north of 71 5 n its development is a manifestation of interactions amongst the poleward pressure gradient wind stress and geostrophic flow due to the coastal setdown

dual doppler analysis of winds and vorticity budget terms near a tornado abstract three dimensional dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field and vorticity generation terms in and near a weak short lived tornado the beam widths of the two doppler on wheels dow mobile radars at the range of the tornado are 250 m with gate lengths of 75 m resulting in a resolution of less than 107 m3 one of the dows collected data during the 240 s prior to the formation of the tornado enabling examination of the genesis process a single set of volumetric scans suitable for dual doppler analyses were completed by both dows permitting the calculation of vertical and horizontal vorticity divergence and stretching and tilting terms in the vorticity budget of the large but weak tornado and its surroundings but no local tendency terms analyses of the dual doppler vector wind fields document for the first time in a supercellular tornado revealed several structures expected to be associated with

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

finescale radar observations of the dimmitt texas 2 june 1995 tornado abstract the mature and dissipating stages of a strong tornado were observed from close range by the prototype doppler on wheels mobile radar volumetric observations repeated eight times over an 840 s period with resolution volumes at the center of the tornado as low as 61 m 61 m 75 m 2 8 105 m3 revealed new details about three dimensional tornado vortex structure and evolution observed structures included a conical debris envelope a low reflectivity eye multiple windfield maxima and multiple semiconcentric bands of reflectivity surrounding the eye the three dimensional structure of the debris and single doppler wind field were well characterized as well as more rapid dissipation of the tornado aloft compared to near the ground volumetric measures of tornado strength are introduced a downdraft exhibiting w 30 m s 1 indicative of a partial two cell vortex was observed only during the earliest radar scans when the tornado was near maximum intensity comparisons with simple conceptual m

tropical cyclone kinematic structure retrieved from single doppler radar observations part i interpretation of doppler velocity patterns and the gbvtd technique abstract deducing the three dimensional primary circulation of landfalling tropical cyclones tcs from single ground based doppler radar data remains a difficult task the evolution and structure of landfalling tcs and their interactions with terrain are left uncharted due to the lack of dual doppler radar observations existing ground based single doppler radar tc algorithms provide only qualitative information on axisymmetric tc center location and intensity in order to improve understanding of the wind structures of landfalling tcs using the widely available wsr 88d data along the u s coastal region a single ground based radar tc wind retrieval technique the ground based velocity track display gbvtd technique is developed part i of this paper presents 1 single doppler velocity patterns of analytic asymmetric tcs 2 derivation of the gbvtd technique and 3 evaluation of the gbvtd retrieved winds using analytic tcs the doppler velocity patterns of asymmetric tcs display more complex structu

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

barrow canyon volume heat and freshwater fluxes revealed by long term mooring observations between 2000 and 2008 1 barrow canyon in the northeast chukchi sea is a major conduit for pacific water to enter the interior arctic basins assemblies of annual september 2000 to august 2008 temperature salinity and velocity data acquired from a mooring array in the mouth of barrow canyon and high resolution hydrographic and velocity transects along the mooring array in 2002 2010 and 2011 have enabled a direct computation of volume heat and freshwater fluxes annual mean volume transport through barrow canyon was 0 45 sv which consisted of 0 44 sv of pacific water and 0 01 sv of atlantic water annual mean pacific water transport through barrow canyon represents 55 of the long term mean pacific water inflow through the bering strait during summer more of the pacific inflow was advected to an eastern path as the alaskan coastal current that flows along the alaskan coast to barrow canyon the freshwater flux through barrow canyon was 904 km3 yr which is equivalent to 5 of the freshwater content of the canada basin the annual averaged heat flux displayed substantial interannual variability ranging from 0 93 to 3 02 tw which could melt 88 000 290 000 km2 of 1 m thick ice a relationship exists between the measured barrow canyon transport and local winds such that under southerly winds the northward flow of water through the canyon increases such wind conditions are induced by the weaker sea level pressure contrast between the arctic and north pacific caused by a decrease in the pressure over the arctic and an increase over the north pacific

role of shelfbreak upwelling in the formation of a massive under ice bloom in the chukchi sea abstract in the summer of 2011 an oceanographic survey carried out by the impacts of climate on ecosystems and chemistry of the arctic pacific environment icescape program revealed the presence of a massive phytoplankton bloom under the ice near the shelfbreak in the central chukchi sea for most of the month preceding the measurements there were relatively strong easterly winds providing upwelling favorable conditions along the shelfbreak analysis of similar hydrographic data from summer 2002 in which there were no persistent easterly winds found no evidence of upwelling near the shelfbreak a two dimensional ocean circulation model is used to show that sufficiently strong winds can result not only in upwelling of high nutrient water from offshore onto the shelf but it can also transport the water out of the bottom boundary layer into the surface ekman layer at the shelf edge the extent of upwelling is determined by the degree of overlap between the surface ekman layer and the bottom boundary layer on the outer shelf once in the ekman layer this high nutrient water is further transported to the surface through mechanical mixing driven by the surface stress two model tracers a nutrient tracer and a chlorophyll tracer reveal distributions very similar to that observed in the data these results suggest that the biomass maximum near the shelfbreak during the massive bloom in summer 2011 resulted from an enhanced supply of nutrients upwelled from the halocline seaward of the shelf the decade long trend in summertime surface winds suggests that easterly winds in this region are increasing in strength and that such bloom events will become more common

acceleration of a stratified current over a sloping bottom driven by an alongshelf pressure gradient abstract an idealized theoretical model is developed for the acceleration of a two dimensional stratified current over a uniformly sloping bottom driven by an imposed alongshelf pressure gradient and taking into account the effects of buoyancy advection in the bottom boundary layer both downwelling and upwelling pressure gradients are considered for a specified pressure gradient the model response depends primarily on the burger number s n f where n is the initial buoyancy frequency is the bottom slope and f is the coriolis parameter without stratification s 0 buoyancy advection is absent and the alongshelf flow accelerates until bottom stress balances the imposed pressure gradient the e folding time scale to reach this steady state is the friction time h r where h is the water depth and r is a linear bottom friction coefficient with stratification s 0 buoyancy advection in the bottom boundary layer produces vertical shear which prevents the bottom stress from becoming large

mobile doppler radar observations of a tornado in a supercell near bassett nebraska on 5 june 1999 part ii tornado vortex structure abstract this is part ii of a paper detailing an analysis of high resolution wind and reflectivity data collected by a mobile w band doppler radar the analysis depicts the near surface life history of a tornado in a supercell in north central nebraska on 5 june 1999 the structure of the tornado vortex near the ground is described from a sequence of sector scans at 10 15 s intervals during much of the lifetime of the tornado the formation of the tornado vortex near the ground is described in part i the wind and reflectivity features in the tornado evolved on timescales of 10 s or less a time history of the azimuthally averaged azimuthal and radial wind profiles and the asymmetric components of the azimuthal and radial wind fields in the tornado were estimated by applying the ground based velocity track display gbvtd technique to the doppler wind data if the magnitude of the asymmetric part of the radial wind component were indeed much less than that of the azimuthal wind component a necessary req

wind driven modification of the alaskan coastal current 1 across shelf transects over the eastern flank of barrow canyon were obtained in august 2005 with an autonomous underwater vehicle auv here the shelf topography creates a choke point in which a substantial portion of pacific inflow from the bering strait is concentrated within 30 km of the coast providing an ideal setup for monitoring the flow with the auv four transects extending 10 km offshore of barrow alaska inshore of the 80 m isobath were used in conjunction with a process oriented numerical model to diagnose the wind driven modification of the alaskan coastal current poleward transports of 0 12 sv were consistent among all sections although the transport weighted temperature was about 1 c colder in the transect obtained during peak winds an idealized numerical model reproduces the observed hydrographic structure and across shelf circulation reasonably well in that 1 winds were not sufficient to reverse the poleward flow 2 upwelling was most pronounced in the nearshore and 3 the onshore return flow occurred throughout the interior as opposed to the bottom boundary layer the across shelf circulation provides a possible mechanism for a meltwater intrusion observed on the offshore side of the auv transect made during peak winds also of interest is that the observed anticyclonic shear was much stronger u y f than previously measured in the region

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

cambrian ordovician paleogeography of baltica recent paleomagnetic data and existing paleontological evidence show that baltica occupied temperate southern latitudes during cambrian and early ordovician time but was inverted with reference to its present orientation hence the currently opposed margins of the baltic and laurentian shield were not conterminous in the early paleozoic laurentian and baltic late precambrian rifting episodes may therefore have occurred along unrelated continental margins closure of the tornquist sea was accompanied by the counterclockwise rotation of baltica relative to avalonia in early to middle ordovician time this rotation initiated in late cambrian early ordovician time was coeval with the finnmarkian orogeny in the northern scandinavian caledonides

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

a theoretical and experimental comparison of the anisotropies of magnetic susceptibility and remanence in rocks and minerals summary susceptibility thermo remanent magnetization trm and isothermal remanent magnetization irm anisotropy ellipsoids have been determined for several rock samples the results indicate that the ellipsoid of initial susceptibility is less anisotropic than the trm and low field irm ellipsoids which are found experimentally to be of identical shape this suggests that palaeomagnetic data for anisotropic rocks may be corrected by using the anisotropy ellipsoid determined from magnetically non destructive low field irm measurements such irm measurements can also be used to obtain anisotropy axes of samples which are inherently anisotropic but which have a susceptibility which is too weak to be accurately measured the results for a series of artificial anisotropic samples containing magnetite particles of different sizes in the range 0 2 90 m were very similar to those for the rocks in contrast a comparison of the susceptibility and irm ellipsoids for anisotropic samples containing particles from a magnetic tape gave very different results in accordance with theory such results imply that susceptibility and irm ellipsoids could be used to determine whether anisotropic rocks contain uniaxial single domain particles magnetization confined to the easy axis or whether the particles are essentially multidomain

the influence of an alongshelf current on the formation and offshore transport of dense water from a coastal polynya the influence of an ambient alongshelf current on the formation and offshore transport of dense water from an idealized coastal polynya is examined by using a primitive equation numerical model brine rejection during ice formation within the polynya is modeled by a prescribed surface buoyancy flux over a limited region along a straight coastline a uniform alongshelf current is imposed at one end of the model domain the basic ocean response is unchanged by the ambient current i e an unstable density front forms around the polynya perimeter and breaks up into small scale 15 30 km eddies that carry the dense water away from the polynya the ambient current continuously carries water out of the polynya region thereby both increasing the alongshelf density flux and reducing the typical density anomaly generated the total volume of dense water formed is not appreciably altered the influence of a submarine canyon located downstream of the polynya in the direction of the imposed alongshelf current is examined almost no dense water enters a canyon oriented normally or diagonally to the coast because the ambient flow tends to follow isobaths and carries virtually all of the dense water around and past the canyon an appreciable fraction of densified water may flow down a canyon oriented parallel to the coast the details depending on the canyon geometry and the strength of the ambient current thus both the density anomalies produced by coastal polynyas and the pathways of dense water transport are sensitive to ambient shelf currents potentially providing a source of interannual variability in dense water formation and export from the shelf

assessing the role of oceanic heat fluxes on ice ablation of the central chukchi sea shelf abstract we investigate the role of oceanic heat flux convergence in the summertime retreat of sea ice in the presence of a mean background flow prior studies indicated that eddies generated along the marginal ice zone front carry substantial quantities of heat laterally beneath the ice but the direct importance of these fluxes to the summertime retreat of sea ice was not well established we use the regional ocean model system roms with an idealized configuration of the chukchi sea shelf and without wind forcing to 1 determine the contributions to ice melt from the oceanic heat flux compared to that from the net atmospheric heat flux through the ice surface 2 evaluate the role of mesoscale fluctuations versus the mean background flow in providing this sub surface heat flux and 3 evaluate the role of the underlying bathymetry in modifying the subsurface heat flux to the ice analyses show that the three main water masses melt water bering sea water and winter water establish frontal systems the shelf water front and the ice edge melt water front that control baroclinic processes which in turn regulate the quantity of heat fluxed laterally and vertically to the ablating ice edge we identify and characterize distinct oceanic zones associated with these fronts the shelf water transition zone and the melt water transition zone that are delineated by flow dynamics and hydrographic structure the integrated heat flux along the modeled ice edge is significant lateral eddy transport of heat is as large as 2 tw of which 50 is fluxed upwards into the near surface melt water we introduce a parameterization for the vertical heat transport to the ice through the near surface meltwater lens that is a function of the along front current velocity and the cross front temperature gradient such a parameterization could improve coarse scale ocean and climate models that lack the resolution necessary for reproducing such small scale processes the results of this study may be informative to investigations of ice edge biological processes

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

dual doppler and single doppler analysis of a tornadic storm undergoing mergers and repeated tornadogenesis abstract dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field in and near a tornado occurring near kiefer oklahoma on 26 may 1997 analyses of the dual doppler vector wind fields document in detail for the first time several structures associated with the tornado a proximate updraft region a rear flank downdraft wrapping around the tornado a double gust front structure occluding near the tornado and a region of enhanced vorticity separated from the tornado that may have been associated with cyclic tornadogenesis the analyses are compared to conceptual and computer models of tornadic storms a subsequent tornadogenesis was observed with radar every 18 s providing a finescale temporal view of the genesis process the genesis process was complex and the evolution of tornado intensity parameters was not monotonic in time low level rotation contracted and intensified then broadened then contracted and intensified a se

characteristics and dynamics of wind driven upwelling in the alaskan beaufort sea based on six years of mooring data abstract six years of mooring data from the alaskan beaufort sea slope together with meteorological observations and reanalysis fields are used to quantify the occurrence of wind driven upwelling and the associated atmospheric forcing the canonical upwelling event composited from 115 individual events reveals that when the easterly wind is strongest the entire shelfbreak jet is reversed to the west at the end of the event a bottom intensified eastward flowing rebound jet spins up that is stronger than the normal shelfbreak jet the cross isobath flow has a three layer structure with onshore flow in the surface layer offshore flow in the middle of the water column and onshore flow near the bottom this is because the reversed shelfbreak jet is oriented slightly onshore which overwhelms the cross isobath surface ekman transport the vertically integrated along isobath momentum balance supports this interpretation and indicates that the rebound jet is driven by the zonal gradient in sea surface height during over two thirds of the events atlantic water aw is upwelled to the shelfbreak while for the remaining events only pacific water pw is upwelled the primary driving factor behind this is the seasonal variation in the pw aw interface depth offshore of the shelfbreak which is controlled by the local wind stress curl during summer when pw type events dominate ekman pumping associated with negative wind stress curl deepens the interface depth limiting access to the atlantic layer over the remainder of the year when aw events dominate ekman suction associated with positive wind stress curl raises the interface these variations are due to the influence of the two regional atmospheric centers of action the aleutian low and the beaufort high

the 30 may 1998 spencer south dakota storm part ii comparison of observed damage and radar derived winds in the tornadoes abstract a violent supercell tornado passed through the town of spencer south dakota on the evening of 30 may 1998 producing large gradients in damage severity the tornado was rated at f4 intensity by damage survey teams a doppler on wheels dow mobile radar followed this tornado and observed the tornado at ranges between 1 7 and 8 0 km during various stages of the tornado s life the dow was deployed less than 4 0 km from the town of spencer between 0134 and 0145 utc and during this time period the tornado passed through spencer and peak doppler velocity measurements exceeded 100 m s 1 data gathered from the dow during this time period contained high spatial resolution sample volumes of approximately 34 m 34 m 37 m along with frequent volume updates every 45 50 s the high resolution doppler velocity data gathered from low level elevation scans when sample volumes are between 20 and 40 m agl are compared to extensive ground and aerial damage surveys performed by the national weather servic

using a low order model to detect and characterize tornadoes in multiple doppler radar data a new multiple doppler radar analysis technique is presented for the objective detection and characterization of tornado like vortices the technique consists of fitting radial wind data from two or more radars to a simple analytical model of a vortex and its near environment the model combines a uniform flow linear shear flow linear divergence flow all of which compose a broadscale flow and a modified combined rankine vortex representing the tornado the vortex and its environment are allowed to translate the parameters in the low order model are determined by minimizing a cost function that accounts for the discrepancy between the model and observed radial winds since vortex translation is taken into account the cost function can be evaluated over time as well as space and thus the observations can be used at the actual times and locations where they were acquired the technique is first tested using analytically simulated observations whose wind field and error characteristics are systematically varied an advanced regional prediction system arps high resolution numerical simulation of a supercell and associated tornado is then used to emulate an observation dataset the method is tested with two virtual radars for several radarsampling strategies finally the technique is applied to a dataset of real dual doppler observations of a tornado that struck central oklahoma on 8 may 2003 the method shows skill in retrieving the tornado path and radar grid scale features of the horizontal wind field in the vicinity of the tornado the best results are obtained using a two step procedure in which the broadscale flow is retrieved first

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

summertime circulation in the eastern chukchi sea abstract the transport of pacific origin water across the eastern chukchi sea during summer is studied using shipboard hydrographic and acoustic doppler current profiler data from multiple surveys the study identifies two major transport pathways in this region the well known alaskan coastal current acc flows poleward along the alaska coast while a more recently discovered and slower current flows northward through the central channel between herald and hanna shoals the two currents separate past point hope and appear to merge again in barrow canyon via previously unresolved pathways flowing west to east across the chukchi sea the collective flow that transports pacific water from bering strait to barrow canyon is termed the bering to barrow current system bbcs the coastal branch of the bbcs which encompasses the acc is a weakly baroclinic flow with a maximum speed in excess of 80 cm s inside barrow canyon the central channel branch of the bbcs is considerably weaker with a maximum flow speed under 20 cm s a portion of the pacific water that flows towards herald canyon to the west may also contribute to the bbcs the amount but the amount is within the margin of error of our data the difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the bbcs summer water masses occupy most of the southern and central chukchi sea while winter water masses occupy hanna shoal and shelfbreak regions in the northern chukchi sea during summer the total bbcs volume transport in summer is measured at four different locations in the eastern chukchi sea and found to be generally consistent the overall mean transport is 0 86 sv compared to the summer bering strait transport of 1 08 sv this study suggests that the bbcs is the main transport pathway delivering pacific water masses into the western arctic basin

tropical cyclone kinematic structure retrieved from single doppler radar observations part ii the gbvtd simplex center finding algorithm abstract this paper is the second of a series and focuses on developing an algorithm to objectively identify tropical cyclone tc vorticity centers using single doppler radar data the first paper dealt with the formulation of a single doppler radar tc wind retrieval technique the ground based velocity track display gbvtd and the results are verified using analytical tcs it has been acknowledged that the quality of the gbvtd retrieved tc circulation strongly depends on accurately knowing its center position however existing single doppler radar center finding algorithms are limited to estimate centers for axisymmetric tcs the proposed algorithm uses a simplex method to objectively estimate the tc vorticity center by maximizing gbvtd retrieved mean tangential wind when tested with a number of axisymmetric and asymmetric analytical tcs the accuracy of the tc centers estimated by the gbvtd simplex algorithm is 340 m from the true center when adding 5 m s 1 random noise to the doppler velocities

structural trends in central britain from images of gravity and aeromagnetic fields digital image processing techniques have been used to analyse the regional gravity and aeromagnetic datasets in central britain colour and shaded relief images have been generated which convey information on both anomaly amplitude as colour and anomaly gradient as relief and highlight structural trends lineaments and textural contrasts not easily discernible on standard contour maps we have identified some of the more important features and have tried to relate these to the evolution of the crust in each region on a broad scale the images emphasize caledonoid ene trends to the north of the solway line and both tornquist se and caledonoid ne to ene trends to the south the pattern of magnetic anomalies over central england seems to define the extent of the shallow late precambrian early palaeozoic basement of the midlands microcraton and delineates crustal elements and characteristic trends within it magnetic lineaments and the grain of gravity anomalies trending in northeasterly and northwesterly directions on either side of the microcraton seem to relate to structures which originated during the evolution of the welsh and eastern english caledonides respectively where lower palaeozoic and precambrian rocks form the concealed basement as in most of england the gravity lineaments tend to reflect the influence of basement fractures on the subsequent pattern of sedimentation whereas many of the features on the magnetic images are more directly related to structures within the basement itself