sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

combined themis and ground based observations of a pair of substorm associated electron precipitation events 1 using ground based subionospheric radio wave propagation data from two very low frequency vlf receiver sites riometer absorption data and themis satellite observations we examine in detail energetic electron precipitation eep characteristics associated with two substorm precipitation events that occurred on 28 may 2010 in an advance on the analysis undertaken by clilverd et al 2008 we use phase observations of vlf radio wave signals to describe substorm driven eep characteristics more accurately than before using a 30 kev electron precipitation flux of 5 6 107 el cm 2 sr 1 s 1 and a spectral gradient consistent with that observed by themis it was possible to accurately reproduce the peak observed riometer absorption at macquarie island l 5 4 and the associated nwc radio wave phase change observed at casey antarctica during the second larger substorm the flux levels were near to 80 of the peak fluxes observed in a similar substorm as studied by clilverd et al 2008 during the initial stages of the second substorm a latitude region of 5 l 9 was affected by electron precipitation both substorms showed expansion of the precipitation region to 4 l 12 more than 30 min after the injection while both substorms occurred at similar local times with electron precipitation injections into approximately the same geographical region the second expanded in an eastward longitude more slowly suggesting the involvement of lower energy electron precipitation each substorm region expanded westward at a rate slower than that exhibited eastward this study shows that it is possible to successfully combine these multi instrument observations to investigate the characteristics of substorms

rotating flows along indented coastlines the problem of a steady inviscid reduced gracity rotating flow in a wedge around a sharp corner is examined using two or more corner solutions plausible flow streamlines can be generated in more complicated domains as long as no two corners are closer than the rossby radius of deformation this procedure is illustrated with two examples 1 circulation in a channel mouth and 2 flow around a square bump in a coastline

developing 3 d mine scale geomechanical models in complex geological environments as applied to the kiirunavaara mine an understanding of the relationship between the geological environment and rock mass behaviour induced by mining activities can lead to hazard reduction through knowledge based design however ch

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

upper ocean modeling in a coastal bay a numerical model of the upper ocean is developed to study the dynamics and thermodynamics of the baie des chaleurs gulf of st lawrence canada the model has primitive equation dynamics with two active layers embedded with a niiler kraus niller and kraus 1977 type mixed layer model at the top proper open boundary conditions and forcing functions are constructed the model is eddy permitting with a horizontal grid spacing of 2 4 km an arakawa c grid scheme is used forced by observed wind atmospheric heat fluxes river runoff and appropriate remote forcing in particular the gaspe current gc the model demonstrates that the mean cyclonic general circulation pattern in the bay is a consequence of the intrusion of the gc the strength of the circulation depends on the resultant stress of prevailing westerly winds and the opposing gc intrusion in the mixed layer atmospheric heat fluxes and horizontal thermal advection play a key role in the thermal balance at the eastern part of the bay the local mixed layer fluctuations are controlled by wind and gc induced divergence the entrainment and its corresponding heat flux is important at the western part of the bay and changes the mean mixed layer depth on a timescale of more than a week varying gc intensifies the flow variations induced by the wind in the bay and improves simulation results as compared with observations

the problem of gulf stream separation a barotropic approach inertial separation of a western boundary current from an idealized continent is studied in a homogeneous ocean circulation model a number of processes are identified that either encourage or prevent separation at a coastal promontory in this model for a single gyre wind forcing a free slip boundary condition forces the stream to follow the coastline whereas the no slip condition allows separation at a sharp corner a prescribed countergyre to the north of the stream is not necessary to achieve separation if the no slip condition is used premature separation occurs for wind fields that do not extend beyond the latitude of the cape for a more realistic wind field and coastline two distinct states of the stream are found at small reynolds numbers the current fails to separate and develops a stationary anticyclonic meander north of the cape stronger currents separate and drive a recirculation in the lee of the continent

relating arctic pack ice stress and deformation under winter conditions 1 together thermodynamic and dynamic processes determine the thickness distribution of the ice cover on polar oceans which governs the exchange of energy between the atmosphere and the ocean key to the dynamic processes is the mechanical behavior of the ice cover during the surface heat budget of the arctic ocean sheba field experiment we deployed sensors to measure the internal ice stress at several locations within a 15 15 km area these measurements are combined with satellite derived ice motion and imagery products the objective is to make a first step toward using these data sources for evaluating sea ice dynamics models by assessing whether the stress signal can be qualitatively linked to the regional scale 10 100 km deformation activity four case studies are presented each with distinguishing characteristics consolidation of the seasonal ice zone against the alaskan coast 5 7 december 1997 advancement of the consolidation zone into the perennial ice pack 11 13 december extreme divergence 14 17 january and consolidation of the pack against wrangel island and the siberian coast 20 23 february the results of this analysis 1 demonstrate that stress measurements are related to the regional deformation behavior of the ice cover 2 confirm that regional scale ice dynamics is primarily a function of coastal geometry and sustained large scale wind direction and magnitude 3 provide continued evidence that the ice pack behaves as a granular hardening plastic and 4 encourage pursuit of efforts to use direct measurements of ice stress and deformation in the formulation and development of sea ice dynamics models

a primitive equation ocean circulation model using a general vertical coordinate transformation 1 description and testing of the model the ocean general circulation model of the geophysical fluid dynamics laboratory has been modified to accommodate a generalized vertical coordinate transformation the model with a slightly modified transformation z h is applied to three simple test cases a clear improvement of barotropic and baroclinic topographic rossby waves has been achieved compared with the z coordinate model a somewhat more typical time independent problem for the overflow of dense water masses over a zonal ridge exhibits the potential benefits as well as the flaws of the new model vertically integrated mass transport is very sensitive to changes in bottom slope in regions where planetary and topographic are of comparable magnitudes this translates into large errors in the z model due to the crude approximation to the actual topography the deep flow in the z model does not follow the bottom exactly horizontal overshoots of dense water lead to convective mixing on the southern side of the ridge this can be a serious problem for modeling more realistic overflow situations with the z model increased diapycnal diffusion has been identified as the most serious problem with the terrain following coordinate system for this specific application

variability of circulation induced by the separation of gaspe current in baie des chaleurs canada observational studies the observed variability of summer circulation in the baie des chaleurs bdc canada is found to be largely controlled by the intrusion separation processes of a coastal jet gaspe current gc at the bay entrance an analysis of hydrographic and current meter data showed that the mean counter wind cyclonic circulation in the bdc from spring to the beginning of the cooling season in 1991 was ascribed to the westward intrusion of the gc the forcing mechanism of the gc on the bdc was determined by the characteristics of the coastal jet separation under the intrusion regime the gc entered into the bdc along the north coast of the bay suppressed the local wind driven eastward currents and formed a cyclonic circulation in the bay under the separation regime gc mainly passed across the entrance of the bdc with the formation of an anticyclonic recirculation at the lee of the jet near the bay entrance and a weaker cyclonic circulation in the bay dynamics of the boundary current separation is utilized to reason the observed variability of flow field in the bdc

a simple three dimensional model of the circulation off newfoundland a simple numerical model is developed to study the three dimensional structure of the steady circulation off newfoundland the model uses linear dynamics a vertical eddy viscosity to parameterize the vertical mixing and a linear parameterization of bottom friction in which the bottom stress is related to the bottom velocity realistic geometry and bottom topography are included the results presented here are for an ocean of uniform density the model is driven by specifying the sea level along the northern boundary the inflow corresponding to the inshore and offshore branches of the labrador current the model can reproduce the circulation pattern found by greenberg and petrie 1988 who used a vertically integrated nonlinear primitive equation model it also enables dynamical interpretation to be given in terms of flow along f h contours and frictional diffusion across these contours in this connection we investigate the dependence on the friction parameters of the transport through several sections we also examine the onshore offshore mass exchange over the southeastern edge of the grand banks we find that the model labrador current flowing southward along the shelf break leads to an onshelf flux in the upper part of the water column and an offshelf flux in the bottom ekman layer this is caused by the frictional torque and leads to an along slope decay of the current amplitude finally the limitations of the model and plans for its further development are discussed

simulation of the atlantic circulation with a coupled sea ice mixed layer isopycnal general circulation model part i model description abstract a diabatic ocean general circulation model based on primitive equations is described it uses isopycnals as lagrangian coordinates in the vertical and predicts a free surface prognostic fields of temperature and salinity enter the dynamics as active tracers through a realistic equation of state the surface boundary layer is parameterized by a detailed mixed layer model a sea ice model with a viscous plastic rheology is coupled to the mixed layer thermal forcing wind stress and surface input of turbulent kinetic energy are determined from monthly mean values of atmospheric quantities while the freshwater flux still is parameterized by a newtonian relaxation towards the observed surface salinity the model equations are written in layer formulation each interface represents an isopycnal as the equations are written in flux form the mass flux and the content of mass heat and salt are conserved in the model domain a potential vorticity conserving scheme is included except for the mixed

pathways and modification of the upper and intermediate waters of the arctic ocean 1 the purpose of this study is to investigate the pathways and the ventilation of source water masses of the upper and intermediate waters of the arctic ocean for the arctic and subarctic domain a coupled ice ocean general circulation model is set up to be integrated for several decades it is driven by a climatological seasonal cycle of monthly mean atmospheric data from 1980 to 1989 and by restored sea surface salinities passive tracers are used to visualize and interpret the modeled flow and to compare it with observations the model is able to reproduce known features of the arctic ocean circulation like the inflow of two branches of atlantic origin via the fram strait and the barents sea and their subsequent passage at middepths in several cyclonic circulation cells the fate of these atlantic source water masses river water and bering strait inflow water in the model are studied the branch crossing the barents sea is subject to an intense heat loss and ice formation as a result water of this branch leaves the shelf toward the central part of the arctic ocean not only at the surface but also in denser varieties which finally feed the central arctic at halocline and middepths the lightest part turns northward and finally westward joining the transpolar drift the densest part 200 1000 m depth moves eastward along the continental slope a similar path is taken by the atlantic water branch from the fram strait the inflowing branch over the barents sea turns out to be the dominant source for the lower atlantic water layer in the arctic ocean in this investigation atlantic tracers starting in fram strait need 6 years to reach the northern laptev sea slope travel times to return to fram strait are 15 20 years along the lomonossov ridge and about 30 years along the continental slope of the canadian basin tracers that mark the pacific water or the mackenzie river water flow eastward and leave the arctic mainly via the canadian archipelago the siberian river water tracers at the surface penetrate far into the canadian basin before they join the transpolar drift the travel times of the river water from the river mouths are 2 3 years to the shelf edge and 12 14 years to fram strait

the northeast pacific ocean response to the 1982 1983 el nino the ocean s response to atmospheric forcing and to forcing along the coast by kelvin waves is examined in light of nearshore seasonal variability and the major 1982 1983 el nino in addition to driving the northeast pacific gyre and local currents the wind modifies the depth to the main thermocline changing the apparent westward phase speed of rossby waves excited by passing kelvin waves the amplitude of the passing kelvin wave determines whether the rossby wave depresses or raises the thermocline while propagating westward along the northeast pacific coast from oregon to washington model results suggest that the wind raises the main thermocline during the 1982 1983 el nino generally the coastal response off oregon and washington appears to be strongly driven by the large scale atmosphere while along the california coast and south to the equator the dominant el nino signal has an oceanic origin that signal with periods between 2 and 5 years originates in the western equatorial pacific ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50 n using data from two reduced gravity primitive equation models coupled at 18 n at shorter seasonal time scales the acceleration of the wind appears to be an important mechanism in driving coastal currents

a twentieth century reanalysis forced ocean model to reconstruct the north atlantic climate variation during the 1920s the observed north atlantic multi decadal variability for the period 1872 2009 is reconstructed with the max planck institute ocean model which is forced with an ensemble of the atmospheric twentieth century reanalysis special emphasis is put on the early part of the experiments which includes a prominent climate variation during the 1920s the experiments are in agreement with selected hydrographic records indicating a transition from cold and fresh north atlantic water properties prior to the 1920 climate variation towards warm and saline waters afterwards examining the variation reveals that sea level pressure slp anomalies prior to the 1900s resemble a negative phase of north atlantic oscillation and associated weak winds result in a weak north atlantic current nac and sub polar gyre spg this leads to a reduced transport of warm and saline waters into the higher latitudes simultaneously arctic freshwater release results in the accumulation of cold and fresh water properties which cover the upper layers in the labrador sea and subsequently suppress convection from the 1910s the arctic freshwater export is reduced and nac and spg are strengthened as a result of an increased slp gradient over the north atlantic concurrently labrador sea convection and atlantic meridional overturning circulation amoc increase the intensified nac spg and amoc redistribute sub tropical water into the north atlantic and nordic seas thereby increasing observed and modelled temperature and salinity during the 1920s

storminess and vulnerability along the atlantic coastlines of europe analysis of storm records and of a greenhouse gases induced climate scenario abstract identification of the distinctive circulation patterns of storminess on the atlantic margin of europe forms the main objective of this study dealing with storm frequency intensity and tracking the climatology of the extratropical cyclones that affect this region has been examined for the period 1940 1998 coastal meteorological data from ireland to spain have been linked to the cyclone history for the north atlantic in the analysis of storm records for european coasts the study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the north atlantic oscillation nao results indicate a seasonal shift in the wind climate with regionally more severe winters and calmer summers established this pattern appears to be linked to a northward displacement in the main north atlantic cyclone track an experiment with the echam4 a gcm at high resolution t106 has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region the experiment consists of 1 a 30 year control time slice representing present day equivalent co 2 concentrations and 2 a 30 year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent co 2 concentrations the boundary conditions have been obtained from an atmosphere ocean coupled oa gcm simulation at low horizontal resolution an algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones for most of the northern part of the study region covering ireland and scotland results describe the establishment by ca 2060 of a tendency for fewer but more intense storms the impacts of these changes in storminess for the vulnerability of european atlantic coasts are considered for low lying exposed and soft sedimentary coasts as in ireland these changes in storminess are likely to result in significant localised increases in coastal erosion

nighttime ionospheric d region parameters from vlf phase and amplitude 1 nighttime ionospheric d region heights and electron densities are determined from an extensive set of vlf radio phase and amplitude observations the d region parameters are characterized by the traditional h height in kilometers and sharpness in km 1 as used by wait and by the u s navy in their earth ionosphere waveguide programs the vlf measurements were made with several frequencies in the range 10 khz to 41 khz on long mainly all sea paths including omega la reunion and omega argentina to dunedin new zealand nau puerto rico and naa maine usa to cambridge uk and npm hawaii to san francisco because daytime vlf propagation on such paths is readily measured and predicted the differences between night and day amplitudes and phases were measured and compared with calculations for a range of nighttime ionospheric parameters this avoided the problem of uncertainties in the transmitter powers in this way the height h and the sharpness when averaged over periods of several days at least for the midlatitude d region near solar minimum were found to be 85 1 0 4 km and 0 63 0 04 km 1 respectively

instability of a buoyancy driven coastal jet the gaspe current and its st lawrence precursor the discharge of the st lawrence river drives a buoyant jet which extends along the south shore of the lower st lawrence estuary and combining with the northwest gulf of st lawrence cyclonic gyre becomes the gaspe current in both the estuarine jet and the gaspe current strong lateral and vertical shears are present satellite thermal imagery has shown that the gaspe current is unstable its instabilities are manifested as prominent wave disturbances and eddy features we use satellite thermal images from 3 different years to show that unstable disturbances are also characteristic of the estuarine jet we update previous work to show that gaspe current is both baroclinically and barotropically unstable our model studies also show that this conclusion is valid for the estuarine jet as well finally we discuss a sequence of satellite images showing the development of an unstable disturbance apparently triggered by an eastward wind pulse

multistage substorm expansion auroral dynamics in relation to plasma sheet particle injection precipitation and plasma convection 1 we present observations of the auroral expansions during two substorms focusing on multistage intensifications and the morphology of the poleward boundary and relate these auroral observations to the local plasma convection and plasma sheet dynamics the observations are made by meridian scanning photometers and an all sky camera asc at ny alesund svalbard 76 magnetic latitude mlat an asc in lovozero russia 64 mlat the international monitor for auroral geomagnetic effects image magnetometer chain in svalbard and scandinavia the hydra instrument on polar located at the inner edge of the plasma sheet particle detectors on dmsp f13 and dmsp f14 traversing the ionospheric projection of the plasma sheet and the cutlass finland hf radar in each substorm the aurora between 70 and 80 mlat consisted of two branches separated by 5 in mlat the higher latitude branch at 75 78 mlat was subject to a sequence of short lived 1 2 min intensifications so called poleward boundary intensifications pbis recurring at 3 min intervals subsequent to each brightening auroral forms traveled equatorward at a speed of 1 0 1 5 km s 1 on polar the pbis are related on a one to one basis with injections of electrons in the 5 to 20 kev energy range at the inner edge of the equatorial plasma sheet with predominantly a trapped distribution delayed by 5 min electron precipitation within 60 77 mlat corresponding to a large radial extent of the plasma sheet is documented by dmsp flights in the 1800 2000 magnetic local time mlt sector in discussing the branches of the high latitude aurora within the context of current understanding of the relation of bursty bulk flows to substorm expansion phase dynamics we note the following 1 the initial auroral breakup located at 63 64 mlat near the equatorward edge of plasma sheet precipitation which was followed by 2 two successive brightenings auroral expansions appearing within 72 74 mlat 2100 mlt separated by 14 min 3 a 20 min long brightening sequence in the poleward auroral branch 75 78 mlat consisting of six discrete events pbis within the boundary plasma sheet precipitation and 4 the presence of auroral vortex motion strong field aligned current sheets in some of these pbis which were accompanied by 5 electron injections at the inner edge of the plasma sheet 6 brightenings of the lower latitude auroral branch when equatorward moving auroral forms emafs streamers arrive there and 7 localized bursts of equatorward ionospheric convection at speeds of 0 5 1 km s 1 in the latitude range of the emafs streamers the documented associations between pbis emafs plasma sheet injections and the local convection events are explained in terms of a substorm scenario involving bursty bulk flows in the late expansion phase

influence of orographically steered winds on mutsu bay surface currents 1 effects of spatially dependent sea surface wind field on currents in mutsu bay which is located at the northern end of japanese honshu island are investigated using winds derived from synthetic aperture radar sar images and a numerical model a characteristic wind pattern over the bay was evidenced from analysis of 118 sar images and coincided with in situ observations wind is topographically steered with easterly winds entering the bay through the terrestrial gap and stronger wind blowing over the central water toward its mouth nearshore winds are weaker due to terrestrial blockages using the princeton ocean model we investigated currents forced by the observed spatially dependent wind field the predicted current pattern agrees well with available observations for a uniform wind field of equal magnitude and average direction the circulation pattern departs from observations demonstrating that vorticity input due to spatially dependent wind stress is essential in generation of the wind driven current in mutsu bay

on the formulation of open boundary conditions at the mouth of a bay we describe our experience in formulating open boundary conditions to apply at the mouth of a reduced gravity model of a bay our objective is to find a way to calculate the response of the bay to wind forcing over the bay itself without being concerned about the influence of regions beyond we show that open boundaries from which kelvin waves can propagate along the coast into the model domain upstream boundaries must be treated with care we begin by considering an upstream boundary which runs perpendicular to the coast we find that if a radiation condition is applied on such a boundary then spurious kelvin waves of near inertial period can propagate in from the boundary and contaminate the solution in the interior of the model domain also if there is ekman transport at the upstream boundary away from toward the coast then upwelling downwelling will occur indefinitely and completely swamp the model solution in the bay this is similar to the solution we expect when the coastline is straight and extends to infinity in the upstream direction however it is not the same since the rate of upwelling downwelling is roughly half the theoretical value for that case for the problem of a bay we suggest that the way to deal with this is to extend the coastline out to sea on the upstream side of the mouth and apply a condition on the artificial stretch of the boundary which suppresses kelvin wave propagation but is also not prohibitively reflective to outgoing poincare waves for our problem a condition of zero normal gradient in interface displacement seems to be sufficient this condition also captures reasonably well the near inertial kelvin waves that are generated by the northwest corner of the bay which are a genuine part of the solution as long as the other boundaries are sufficiently far from the bay we have also experimented with using sponge layers rather than radiation conditions on the other boundaries we find that sponging only the interface displacement and leaving the velocities undamped gives results that compare well with those obtained using radiation conditions on the other hand sponging the velocities as well as the interface displacement leads to significantly different results this is the case even if only the pressure driven part of the velocities is sponged and the ekman part is left undamped this suggests that applying highly viscous layers around open ocean parts of model boundaries can be counter productive it is sometimes better to damp only the density field and leave the velocities undamped finally we discuss how our results apply to three dimensional general circulation type models

structure and seasonal characteristics of the gaspe current ctd and current meter data from the northwestern gulf of st lawrence were analyzed to study the structure and variability of the gaspe current since the current is buoyancy driven its properties are strongly influenced by the seasonal variation of the freshwater discharge from the st lawrence estuary from june to november maximum speed decreases from 110 cm s 1 to 60 cm s 1 high vertical shears exist in the upper 40 m of the water column during the same period the width of the current decreases and the position of the current maximum shifts from near the shore to about 14 km from the shore these changes in the structure can be understood in terms of geostrophy and baroclinic deformation radius in the temperature salinity field the most prominent change from june to november is the continuing increase of surface salinity temperature change occurs mainly in the september november period when atmospheric cooling accelerates the effect of atmospheric cooling is also reflected in the density distribution with the result that in november currents in the upper 30 m are seaward in the entire section from sept iles to marthe de gaspe while in the summer months the currents are seaward in the southern part and westward in the northern part of the section momentum balance of the current system is also investigated it was found that east of pointe des monts geostrophic balance is maintained while west of pointe des monts the observations do not seem to be consistent with the assumption of geostrophy

determination of exploitable blocks in an andesite quarry using independent component kriging abstract categorizing quarry blocks as exploitable and non exploitable for facing and building stones needs to apply multivariate geostatistical methods such as cokriging or to generate factors which are spatially independent and consequently run kriging estimation there are various methods for generating spatially independent factors such as principal component analysis but this method cannot produce factors which are totally independent so in this study an orthogonalization method independent component analysis is introduced as a novel tool in multivariate geostatistics and is used to find spatially independent factors the theory of a new estimating method independent component kriging is presented and applied to an andesite quarry located in ankara turkey one level of the quarry is chosen to be a test area from which 108 rock samples are taken at 20 m regular intervals the rock samples are tested for some of the mechanical properties of andesite that control the economy of the extraction process then the application area is divided into 1544 square blocks and the newly developed estimation method is used for estimating unknown values of variables at unsampled locations finally the blocks are classified as exploitable and non exploitable regarding ts 10835 standards

numerical experiments with a wind and buoyancy driven two and a half layer upper ocean model we describe numerical experiments with a limited domain 15 67 n 65 west to east coarse resolution two and a half layer upper ocean model the model consists of two active variable density layers a niiler and kraus 1977 type mixed layer and a pycnocline layer which overlays a semipassive deep ocean the mixed layer is forced with a cosine wind stress and haney type heat and precipitation evaporation fluxes which were derived from zonally averaged climatological levitus 1982 surface temperatures and salinities for the north atlantic the second layer is forced from below with 1 newtonian cooling to climatological temperatures and salinities at the lower boundary 2 convective adjustment which occurs whenever the density of the second layer is unstable with respect to climatology and 3 mass entrainment in areas of strong upwelling when the deep ocean ventilates through the bottom surface the sensitivity of this model to changes in its internal mixed layer and external e g a newtonian coupling coefficient parameters is investigated and compared to the results from a control experiment we find that the model is not overly sensitive to changes in most of the parameters that were tested albeit these results may depend to some extent on the choice of the control experiment

on the unsteady separation intrusion of the gaspe current and variability in baie des chaleurs modeling studies a numerical model has been used to study separation intrusion of an unsteady baroclinic coastal jet the gaspe current gc and its impact on dynamics and thermodynamics of the baie des chaleurs bdc gulf st lawrence canada the model has 2 layers with primitive equation dynamics and an embedded bulk mixed layer ml model it is forced with observed atmospheric fluxes as well as the gc the simulations show that the variability in the baie des chaleurs is controlled by the characteristics of the unsteady gc separation intrusion on the basis of the dynamic and vorticity balance analyses it is found that the separation is related to the adverse pressure gradient force which is induced by the ageostrophic terms in the momentum equations and to local vorticity intensification due to the inertial effect in the flow the simulations demonstrate characteristics of unsteady separation the presence of separation in an accelerating current as well as in a linear current with strong deceleration when momentum advection is neglected gives new insight into the mechanisms of unsteady boundary current separation unsteady separation or intrusion occurrence depends on the magnitude of the gc transport as well as its rate and duration of deceleration or acceleration the gc intrusion generates cyclonic circulation in the bdc prevailing westerly winds reduce the cyclonic circulation inside the bay but have little effect on separation intrusion near the entrance the gc either intrudes along the coastline attachment or after separation reattachment increasing vertical shear of the gc and offshore movement of the gc axis reduces the tendency to separate the finding of an asymmetric response of gc separation intrusion to symmetric gc forcing explains the monthly mean features seen in observations taken in the bay

asymmetry in the response of a stratified coastal embayment to wind forcing we investigate mechanisms that lead to asymmetry in the response of a stratified coastal embayment following the onset of a uniform steady wind that is blowing both along the axis and out of the bay we focus on bays on the east coast of newfoundland where the typical duration of wind events is 5 days and stratification representative of june conditions yields a first baroclinic mode wave speed of 0 51 m s 1 we use several numerical models ranging from a linear reduced gravity model with a single baroclinic mode to a nonlinear prognostic primitive equation model candie we investigate the effect of factors such as continuous stratification vertical mixing nonlinearity and realistic bottom topography if the linear dynamics of only the first baroclinic mode is considered the response of the idealized bay to 5 days of steady wind forcing is symmetric about the axis of the bay continuous stratification allows for higher order vertical modes these slower modes increase the response time of the bay yielding asymmetry in the circulation pattern after 5 days of constant wind forcing model results using realistic geometry demonstrate that realistic bottom topography has little effect on near surface circulation on the 5 day timescale adding nonlinearity allows a significant cross bay transport of upwelled water and leads to the characteristic along bay pattern of the surface isotherms evident in observations and can also lead to the separation of the coastal jet from the upwelling favorable shore

vertical mixing and cabbeling in layered models abstract a consistent scheme for vertical mixing in layered numerical models is derived in this paper the fact that the vertical coordinate density depends on the properties being transported namely salinity and potential temperature renders the inclusion of vertical mixing in layered models a subtle problem the approach the authors have taken is based upon the entrainment into a layer being proportional to the turbulent activity in that layer across each interface there are then two entrainment velocities one upward velocity that is the entrainment of fluid into the layer above the interface and one downward velocity being the entrainment velocity into the layer below the interface this double entrainment accounts for both the diffusive and the advective consequences of turbulent mixing the proposed scheme works without approximation for a nonlinear equation of state and can readily handle the production of density caused by cabbeling several examples are given

sensitivity of simulated cfc 11 distributions in a global ocean model to the treatment of salt rejected during sea ice formation we show that simulated oceanic absorption of an atmospheric gas is very sensitive to the representation of a process that occurs beneath sea ice as sea ice forms salt is rejected locally increasing surface sea water density this dense water can sink to the pycnocline at the base of the mixed layer previous studies have not considered the impact of this subgrid scale process on transient tracers in the ocean to assess the potential importance of this process to the oceanic absorption of atmospheric gases we performed two idealized simulations a control simulation in which salt rejected during sea ice formation is placed in the model s 25 m thick surface layer and a test simulation in which salt rejected during sea ice formation is distributed uniformly through the upper 160 m beneath the forming sea ice our treatment of rejected salt is highly idealized and is intended to demonstrate the need for a physically based parameterization of subgrid scale convection for use in ocean general circulation models that takes into account the subgrid scale heterogeneity of surface buoyancy forcing distributing rejected salt more deeply during periods of ice formation helps to maintain vertical density gradients inhibiting grid scale convection especially in the southern ocean this greatly diminishes simulated ocean uptake of cfc 11 and generally improves simulated cfc 11 and salinity fields the modeled global ocean inventory of cfc 11 for year 1990 is about 30 lower and modeled column inventories in the southern ocean are up to 90 lower in our test simulation relative to our control simulation we infer that a more detailed treatment of subgrid scale processes occurring beneath sea ice may diminish simulated oceanic absorption of anthropogenic co2 especially in the southern ocean

coupled model simulations of boreal summer intraseasonal 30 50 day variability part 1 systematic errors and caution on use of metrics boreal summer intraseasonal 30 50 day variability bsisv over the asian monsoon region is more complex than its boreal winter counterpart the madden julian oscillation mjo since it also exhibits northward and northwestward propagating convective components near india and over the west pacific here we analyze the bsisv in the cmip3 and two cmip2 coupled ocean atmosphere models though most models exhibit eastward propagation of convective anomalies over the indian ocean difficulty remains in simulating the life cycle of the bsisv as few represent its eastward extension into the western central pacific as such few models produce statistically significant anomalies that comprise the northwest to southeast tilted convection which results from the forced rossby waves that are excited by the near equatorial convective anomalies our results indicate that it is a necessary but not sufficient condition that the locations the time mean monsoon heat sources and the easterly wind shear be simulated correctly in order for the life cycle of the bsisv to be represented realistically extreme caution is needed when using metrics such as the pattern correlation for assessing the fidelity of model performance as models with the most physically realistic bsisv do not necessarily exhibit the highest pattern correlations with observations furthermore diagnostic latitude time plots to evaluate the northward propagation of convection from the equator to india and the bay of bengal also need to be used with caution here incorrectly representing extratropical tropical interactions can give rise to apparent northward propagation when none exists in association with the eastward propagating equatorial convection despite these cautions the use of multiple cross checking diagnostics enables the fidelity of the simulation of the bsisv to be meaningfully assessed

influence of various forcings on global climate in historical times using a coupled atmosphere ocean general circulation model the results of a simulation of the climate of the last five centuries with a state of the art coupled atmosphere ocean general circulation model are presented the model has been driven with most relevant forcings both natural solar variability volcanic aerosol and anthropogenic greenhouse gases sulphate aerosol land use changes in contrast to previous gcm studies we have taken into account the latitudinal dependence of volcanic aerosol and the changing land cover for a period covering several centuries we find a clear signature of large volcanic eruptions in the simulated temperature record the model is able to simulate individual extreme events such as the year without a summer 1816 warm periods in the early seventeenth century and the second half of eighteenth century occur in periods of increased solar irradiation strong warming is simulated after 1850 in particular over land going along with an increase of the positive north atlantic oscillation nao phase consistent circulation anomalies are simulated in multidecadal means with similarity to observed and reconstructed anomalies for example during the late seventeenth and early eighteenth century the model is able to reproduce some of the observed or reconstructed regional patterns we find that cooling around 1700 and at the end of the eighteenth century is less than in other studies due to the relatively small variations in solar activity and the relatively modest volcanic forcing applied here these cooling events are not restricted to europe and north america but cover most of the northern hemisphere colder than average conditions for example during the late seventeenth and early eighteenth centuries go along with a decrease in pressure difference between low and high latitudes and a decrease of the north atlantic oscillation this favours positive sea ice anomalies east of greenland and around iceland leading to widespread negative temperature anomalies over europe we also find characteristic blocking patterns over western europe in particular during autumn which contribute to the advection of cold air

on models of bomb 14c in the north atlantic coarse resolution general circulation ocean models show a tendency to accumulate an excess of bomb 14 c on the eastern margin of the subtropical gyres while observations suggest an excess is found in the west here simulations of the bomb 14 c transient in the north atlantic ocean are made using coarse resolution 1 0 1 2 and eddy permitting 1 3 2 5 tracer transport models the former employs large horizontal diffusivities to parameterize eddy transfer both models employ the same air sea exchange parameterization with a specified tropospheric history of 14 c the coarse resolution model accumulates 14 c evenly over the whole subtropical gyre while the eddy permitting model has a pronounced maximum column inventory in the western part consisent with the observed patterns the prescence of explicit eddies enhances the ventilation of density surfaces in the recirculation zone on the western margin of the gyre suggesting that the zonal gradient hinted at in the observations is intimately tied to properties of geostrophic eddy dynamics which are not captured parametrically in the coarse resolution model

model studies of near inertial motion on the continental shelf off northeast spain a three dimensional two dimensional one dimensional model comparison study 1 a three dimensional nonlinear model of the balearic sea region is used to examine the spatial distribution of wind induced near inertial internal waves results from the model are compared with those from two dimensional cross section and single point models in the case of motion induced by a wind pulse there is no significant along shelf flow and comparable solutions are obtained from the three and two dimensional models however when forced with a realistic wind a significant along shelf flow is produced that is larger in the cross section model than in the three dimensional model because of the absence of an along shelf pressure gradient associated with this change in flow are important differences in across shelf currents and temperature fields that influence the distribution of near inertial motion since the point model cannot take account of internal pressure gradients near inertial internal waves are absent however when some account of barotropic pressure gradients related to local wind stress are included currents and inertial oscillations were in better agreement with the three dimensional model than with the cross section model although the major features of the wind induced deepening of the thermocline could be reproduced by the single point model the absence of internal waves and mixing associated with them lead to a sharper thermocline than in the three dimensional model comparison of two and one dimensional models with the full three dimensional model shows some severe limitations in the simpler models

investigation of the dynamic sea ice component of a coupled atmosphere sea ice general circulation model this paper discusses the development of a coupled atmospheric ice model with a comprehensive ice dynamics cavitating fluid rheology and an open water parameterization the results center on the ice thickness and concentration distribution in the arctic basin where the inclusion of ice rheology has maximum impact the influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean ice drag coefficient under winter wind stress conditions the model had a tendency to buildup ice on the siberian coast the introduction of a partial slip condition at land ice boundaries in the model designed to prevent this buildup is discussed and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0 4 the ice model results are compared with the available observational data sets on ice thickness concentration and ice velocity fields to test the validity of the model simulations

energetic electron precipitation characteristics observed from antarctica during a flux dropout event data from two autonomous vlf radio receiver systems installed in a remote region of the antarctic in 2012 is used to take advantage of the juxtaposition of the l 4 6 contour and the hawaii halley antarctica great circle path as it passes over thick antarctic ice shelf the ice sheet conductivity leads to high sensitivity to changing d region conditions and the quasi constant l shell highlights outer radiation belt processes the ground based instruments observed several energetic electron precipitation events over a moderately active 24 hour period during which the outer radiation belt electron flux declined at most energies and subsequently recovered combining the ground based data with low and geosynchronous orbiting satellite observations on 27 february 2012 different driving mechanisms were observed for three precipitation events with clear signatures in phase space density and electron anisotropy comparison between flux measurements made by polar orbiting operational environmental satellites poes in low earth orbit and by the antarctic instrumentation provides evidence of different cases of weak and strong diffusion into the bounce loss cone helping to understand the physical mechanisms controlling the precipitation of energetic electrons into the atmosphere strong diffusion events occurred as the 30 kev flux than was reported by poes more consistent with strong diffusion conditions

interdecadal dynamics of the north pacific ocean abstract an isopycnal ocean model forced by ncep ncar reanalysis wind stresses and heat fluxes is used to study the interdecadal variability of the pacific ocean in the 1958 97 period a reasonable agreement is found between the model s modes of variability and those obtained by other researchers from both 100 years of observations and theoretical predictions in agreement with previous observational work decadal and interdecadal timescales have different descriptions and from this study it is suggested that they indeed have different dynamics this study focuses on the dynamics of the ocean s interdecadal variability that is of timescales of about 20 yr the decadal timescale that is 10 yr is briefly outlined and compared with previous studies it is found that atmospheric heat fluxes play a key role in establishing the interdecadal sst pattern in the midlatitudinal north pacific these fluxes would excite a high baroclinic mode igniting a series of events that move around the basin in midlatitu

haline circulation induced by formation and melting of sea ice a three dimensional coupled ice ocean model is developed and basic numerical experiments for examining effects of freshwater budget associated with formation and melting of sea ice on the thermohaline circulation are performed motion of sea ice affects the freshwater budget in two ways first it horizontally transports freshwater in the form of sea ice second it alters the conditions of sea ice which influence heat budget at the sea surface and thus the rate of formation and melting to separate such effects of ice motion two experiments are designed in one case ice motion is removed and in the other case it is included there appear significant differences in the thermohaline circulation between the two cases these differences are due to the difference in horizontal distribution of salinity which is maintained by the cycle of formation transport and melting of sea ice and the corresponding freshwater budget experiments for investigating dependence of the thermohaline circulation on the distribution of winds and consequent ice motion are also carried out it is demonstrated that wind induced ice motion has major influences on how saline water produced by sea ice formation at high latitudes extends

an autumn instability event in the gasp aacute current abstract the gaspe current is a buoyant jet driven primarily by the freshwater discharge from the st lawrence estuary previously many incidents of unstable wave development in the3 gaspe current have been reported under summer high runoff conditions here we present satellite infrared images and discuss the occurrence and evolution of an autumn episode of current instability in the fall runoff is lower this event is notable in that the pattern observed differs considerably from that of summer events apparently due to the offshore shift that of the core of the jet in early autumn a stability analysis suggests that the gaspe current instabilities may grow slightly faster in autumn conditions the possible role of wind forcing in triggering wave growth is discussed

modeling the circulation of western bank on the scotian shelf through sequential application of a variational algorithm and a nonlinear model 1 a new approach is presented for the modeling of the quasi stationary circulation through the sequential application of a variational algorithm and a nonlinear diagnostic model the model loop begins with data assimilation of temperature salinity surface elevation and velocity data in a simplified geostrophic model in which transport and continuity equations are treated as weak constraints the temperature salinity fields and balanced open boundary conditions points are then used as input to a nonlinear primitive equation model which employs a turbulent closure scheme the nonlinear model is then run to produce a diagnostic flow field a radiation open boundary condition is applied at the outflow points of the open boundaries these two steps are organized into an iteration cycle by using output from the nonlinear model as input to the variational model the proposed approach combines the advantages of variational data assimilation in simplified models with a complicated fully nonlinear primitive equation model we apply the approach to western bank on the scotian shelf comparisons with observed current from western bank in september and october 1998 show that the sequential application of the variational approach and the fully nonlinear model allow determination of the quasi stationary circulation whose agreement with the observations is 10 30 better than circulation determined from the variational or the nonlinear model alone our calculations of the cross shelf transport across western bank show that it varies from 0 20 sv to 0 35 sv over a 2 week period the combined models also allow us to determine the character of the circulation over the bank the role of wind forcing and the implications for resident biological populations index terms 4219 oceanography general continental shelf processes 4255 oceanography general numerical modeling 4223 oceanography general descriptive and regional oceanography 4263 oceanography general ocean prediction keywords numerical modeling scotian shelf variational algorithm shelf circulation

a comparison of sea ice dynamics models at high resolution abstract an elastic viscous plastic evp model for sea ice dynamics has recently been proposed as a computationally efficient alternative to the viscous plastic vp model widely in use the evp model features a fully explicit discretization that improves the model s efficiency particularly on high resolution grids and adapts easily to parallel computation comparison of two high resolution arctic sea ice simulations identical except for the ice dynamics indicates that the evp model reproduces the vp model behavior on timescales relevant to climate studies the ice concentration and thickness distributions over a 1 yr integration period are remarkably similar in the two models although the evp model responds more rapidly and accurately to strong synoptic weather systems than does the vp model compared to drifting arctic buoys a close look at rates of strain shows that elastic waves in the evp model do not significantly alter the ice behavior in highly compact areas where the waves most benefit nu

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

review of recent developments in tidal hydrodynamic modeling i spectral models in this paper we present a brief overview with a comprehensive set of references to recently published papers for detail of a range of techniques used in tidal hydrodynamic modeling and recent progress in the field although the paper aims to introduce the topic to someone new to the area the main emphasis is on new developments in near coastal shallow sea tidal modeling and consequently we concentrate on three dimensional modeling which has progressed significantly in recent years the paper gives a brief account of methods used to discretize the hydrodynamic equations in the horizontal namely finite difference finite element and boundary fitted coordinates and through time the representation of tidal current structure in a three dimensional model using a spectral method in the vertical is also described in this method the subgrid scale vertical diffusion of momentum which has a major influence on tidal current profiles is parameterized using a flow dependent eddy viscosity recent work on

application of the gwr method to the tropical indian ocean the gravity wave retardation gwr method is a simple technique that allows layer models to include bottom topography here the method is applied and its accuracy is evaluated for monthly climatological wind forcing in an indian ocean model with realistic bottom topography this is an extension of previous studies where the gwr method was applied to idealized wind forcing in oceans with idealized basin geometry comparison to a model integration with a flat bottom demonstrates that gwr integrations with speedup factors of up to 16 indeed capture the influence of the bottom relief and have less error in the deep volume transports for a speedup factor of that magnitude a gwr integration is also found to have less error than a reduced gravity model simulation it is concluded that integrations using the gwr method give remarkably good results for the upper layer circulation as well as the deep flow with a speedup factor of up to 8