on the occurrence of upwelling along the east coast of india a numerical model is applied to simulate the coastal circulation of water off the east coast of india the driving mechanisms consist in general of wind stress forcing representative of that applying during the southwest monsoon season and a forced southward transport of water across a northern open boundary that models the fresh water discharge from the hugli and mahanadi rivers the model predictions both with and without northern boundary forcing are compared with recently published data on observations of upwelling along the east coast of india the simulations provide definitive evidence that with the simultaneous presence of both a forced fresh water flow and upwelling favourable winds along the east coast of india during the monsoon season the occurrence of upwelling is confined to latitudes south of visakhapatnam to the north of this latitude it is shown that the local effect of the southward forced transport of fresh water across the northern boundary remains sufficiently strong to inhibit the occurrence of upwelling and instead to lead to a sinking that is consistent with the observational data

a laboratory study of gyres and uplift near the strait of gibraltar laboratory experiments were conducted in which a rotating basin of stratified salty water in a field of gravity with a free surface was connected to a basin of fresh water by a narrow shallow channel the resulting density driven flow in the channel consisted of two currents a freshwater flow at the top from the fresh basin to the salty basin and a saltwater flow at the bottom in the opposite direction it models the flow in the strait of gibraltar which connects the atlantic ocean to the saltier mediterranean sea selective withdrawal of deep water up to and over the sill depth is observed in the stratified salty mediterranean basin the governing dimensionless numbers are the ratio of the rossby radius of deformation within the strait to the width of the strait and the ratio of rossby radius in the stratified med water to rossby radius of deformation within the strait the experiments were deliberately scaled to correspond to the parameters of the real mediterranean gibraltar region or not as we wished with the most correct parameters the water at a depth corresponding to 700 m in the mediterranean was selectively withdrawn up to sill depth and out of the salty basin the water at a depth corresponding to 900 m was not with double the correctly scaled stratification the water at a depth corresponding to 500 m was drawn out and the water at a depth corresponding to 700 m was not with no stratification water of a depth corresponding to 1200 m was drawn out the results are qualitatively consistent with the ideas of stommel et al 1973 that water at great depth in the mediterranean is drawn up and out at the strait of gibraltar although quantitatively the scaled experimental depths of withdrawal are not as great there are some indications that the gyre of atlantic water corresponding to the alboran sea gyre may enhance the selective withdrawal process but the mechanism is unclear

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

time and space variability in the eastern alboran sea from march to may 1990 an intensive field experiment was carried out from march 6 to april 30 1990 in the eastern alboran sea to understand the relationship between the large scale circulation and the location of the transition zone between new and longer resident modified atlantic water maw the detection of a strong jet 80 cm s 1 of new maw with anticyclonic curvature near the morocco coast suggests that the eastern alboran gyre eag was not fully developed a new state of the circulation in the eastern alboran basin intermediate between the eag viudez et al 1995 and the lanoix 1974 state is presented also important is that the almeria oran front was not present in the upper layer that small scale instabilities were detected in the northern region and that significant nongeostrophic flows were observed all these features are clearly indicative of the high spatial and temporal variability of a region where complex adjustments among density velocity and topography occur

northern larsen ice shelf antarctica further retreat after collapse changes of larsen ice shelf antarctica and the surrounding glaciers after its collapse in 1995 were investigated using satellite radar imagery with emphasis onchanges in the glaciers which previously nourished the ice shelf north of seal nunataks the large glaciers retreated several kilometres inland of the previousgrounding line the velocity field of drygalski glacier the largest glacier in this area was mapped by means of interferograms derived from pairs of ers syntheticaperture radar images from 1995 and 1999 the main part of the glacier showed significant acceleration of flow over these 4 years with an increase of veocity upto three fold at the terminus similar accelerations were observed by means of interferometry on several other grounded glaciers suggesting that the removal ofice shelves could lead to an effect on eustatic sea level for larsen b the northernmost surviving part of larsen ice shelf the retreat of the ice front to october2000 is documented

relationship between tidewater glacier calving velocity and water depth at the calving front an analysis of the relationship between iceberg calving rates and water depth has been completed for 22 tidewater glaciers a linear relationship provides reasonable accuracy with a correlation coefficient of 0 85 for all tidewater glaciers examined whether they be polar or temperate the polar glaciers have a slightly lower calving rate for a given water depth this relationship indicates a lower calving rate for water depths over 50 m than determined by brown and others 1982 it is based only on glaciers or ice streams and cannot be applied to ice shelves

ungulate community richness grazer extinctions and human subsistence behavior in southern africa s cape floral region precipitation primary productivity and herbivore biomass are linked to ungulate richness the number of species in african ecosystems this study compares the richness of late middle to late pleistocene and holocene ungulate assemblages in southern africa s cape floral region cfr regression analysis demonstrates that pleistocene ungulate assemblages are significantly richer than their holocene counterparts elevated pleistocene ungulate richness is not explained by differential time averaging the presence of extinct taxa in pleistocene assemblages or by middle stone age msa to later stone age lsa technological change but instead by a greater number of grazing species in pleistocene faunal communities based on modern african analogs this implies that the pleistocene assemblages examined here sample time intervals characterized by elevated primary productivity particularly of grassland habitats greater ungulate biomass and altered rainfall regimes declining ungulate richness from the pleistocene to the holocene supports the hypothesis that the extinction of specialized grazers at the pleistocene holocene transition in the cfr was driven by declining productivity and availability of grassland habitats the contrast between rich pleistocene ungulate communities and impoverished holocene ungulate communities may also explain important differences in msa and lsa subsistence behavior it is proposed that intensified exploitation of fish shellfish tortoises and seabirds by lsa foragers during the holocene reflects an expansion of diet breadth in response to diminished ungulate biomass on the landscape rather than fundamental behavioral cognitive advances

inertial wind path and sea surface temperature patterns near the gulf of tehuantepec and gulf of papagayo during the northern hemisphere winter the surface atmospheric pressure on the gulf of mexico side of central america is often higher than that on the pacific side the resultant southward pressure gradient drives strong southward winds through a gap in the sierra madre mountain range at the isthmus of tehuantepec the atmospheric jet is narrow in comparison with the relevant radius of deformation so when it leaves the coast and flows out over the gulf of tehuantepec it is an inertial jet therefore the jet is expected to be deflected into a clockwise inertial circle by the coriolis force a similar process should also occur for central american atmospheric jets through mountain range gaps near the gulf of papagayo satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature sst near the gulf of tehuantepec and the gulf of papagayo consecutive daily satellite images when the coastal southward tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path a simple 1 layer analytical ocean model suggests in agreement with observations that the wind can drive surface quasi geostrophic currents of 1 m s 1 since the wind path is circular the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle the satellite sea surface temperature measurements also suggest that the wind driven surface ocean current is unstable in addition stronger gradients in sst to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface ekman flow

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

deep sea circulation in the alboran sea alboran sea circulation between 220 and 1100 m depth is studied interaction between three types of water masses in this area causes a complicated flow pattern atlantic water flowing as a jet through the strait of gibraltar into the mediterranean often forms an anticyclonic gyre to the depth of 200 m and its features are now well documented a few works based on geostrophic calculations and bernoulli s equation treat the deep flow nine free floats were released at different depths and locations from january to may 1982 and acoustically tracked every 2 hours for 40 to 90 days acoustical tracking was done from three listening stations moored in the area the tracks of the floats at all depths from 220 to 1100 m revealed broad and slow approximately 2 5 cm s cyclonic circulation located under the surface anticyclonic gyre part of the flow following the bottom topography turned near the moroccan continental slope as a jet approximately 5 cm s to gibraltar and part turned to the east following the southern boundary of the deep channel to the isle of alboran

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

the strait surface outflow a three dimensional primitive equation model is used to simulate the flow through a narrow strait the flow within a strait has a simple two layered structure with the interface located approximately at the middepth however the flow experiences a sharp transition at the strait s exit the flow jumps from a subcritical velocity inside the strait to a supercritical velocity immediately outside the strait correspondingly the density interface also slopes sharply upward to the surface after exiting the strait the surface outflow tends to form an anticyclonic gyre to the right of the strait s exit most of the outflow water is trapped within the gyre although some manages to escape through a narrow coastal current these model results compare well with observations in the tiran strait and in the gibraltar strait and alboran sea the model study indicates that the flow transition at the strait s exit and the formation of an anticyclonic gyre are unique features of the nonlinear self advection of the density current

a simple law for ice shelf calving a major problem for ice sheet models is that no physically based law for the calving process has been established comparison across a diverse set of ice shelves demonstrates that iceberg calving increases with the along flow spreading rate of a shelf this relation suggests that frictional buttressing loss which increases spreading also leads to shelf retreat a process known to accelerate ice sheet flow and contribute to sea level rise

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

the intrusion of a density current along the coast of a rotating fluid when light rotating fluid spreads over heavier fluid in the vicinity of a vertical wall coast a boundary jet of width forms the leading edge or nose of which propagates with speed along the coast a certain fraction 8 of the boundary transport is not carried by the nose but is deflected backwards detrained and left behind the propagating nose theoretical and experimental results for and are given for a quasi equilibrium constant regime over longer time intervals the laboratory observations suggest that the nose slows down and stagnates whereupon the trailing flow separates from the coast and an intermittent boundary current forms these processes may be relevant to the mixing of oceanic coastal currents and the maintenance of the mean current

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

structure and variability of the alboran sea frontal system physical characteristics of the alboran sea in the western mediterranean were examined in october 1977 during a survey by ship and aircraft the main features observed were a distinct oceanic front coinciding with the jet of incoming north atlantic water and an associated anticyclonic gyre in the western half of the basin the front was confined to the upper 200 m and was a continuous feature extending from the strait of gibraltar 500 km eastward to the prime meridian of particular interest was the observed variability of the anticyclonic gyre in 10 days between two surveys the center of the gyre shifted 50 km westward this shift may correspond to changes in strength of the north atlantic inflow as inferred by local wind and the average atmospheric pressure over the western mediterranean

future sea level rise from tidewater and ice shelf tributary glaciers of the antarctic peninsula abstract iceberg calving and increased ice discharge from ice shelf tributary glaciers contribute significant amounts to global sea level rise slr from the antarctic peninsula ap owing to ongoing ice dynamical changes collapse of buttressing ice shelves these contributions have accelerated in recent years as the ap is one of the fastest warming regions on earth further ice dynamical adjustment increased ice discharge is expected over the next two centuries in this paper the first regional slr projection of the ap from both iceberg calving and increased ice discharge from ice shelf tributary glaciers in response to ice shelf collapse is presented an ice sheet model forced by temperature output from 13 global climate models gcms in response to the high greenhouse gas emission scenario rcp8 5 projects ap contribution to slr of 28 16 to 32 16 mm by 2300 partitioned approximately equally between contributions from tidewater glaciers and ice shelf tributary glaciers in the rcp4 5 scenario sea level rise projections to 2300 are dominated by tidewater glaciers 8 18 mm in this cooler scenario 2 4 1 mm is added to global sea levels from ice shelf tributary drainage basins as fewer ice shelves are projected to collapse sea level projections from ice shelf tributary glaciers are dominated by drainage basins feeding george vi ice shelf accounting for 70 of simulated slr combined total ice dynamical slr projections to 2300 from the ap vary between 11 2 and 32 16 mm sea level equivalent sle depending on the emission scenario used these simulations suggest that omission of tidewater glaciers could lead to a substantial underestimation of the ice sheet s contribution to regional slr

mass changes of outlet glaciers along the nordensjkold coast northern antarctic peninsula based on tandem x satellite measurements we analyzed volume change and mass balance of outlet glaciers of the northern antarctic peninsula over the period 2011 to 2013 using topographic data of high vertical accuracy and great spatial detail acquired by bistatic radar interferometry of the tandem x terrasar x satellite formation the study area includes glaciers draining into the larsen a larsen inlet and prince gustav channel embayments after collapse of buttressing ice shelves in 1995 the glaciers became tidewater calving glaciers and accelerated resulting in increased ice export downwasting of most glaciers is going on but at reduced rates compared to previous years in accordance with deceleration of ice flow the rate of mass depletion is 4 2 0 4 gt a 1 with the largest contribution by drygalski glacier amounting to 2 2 0 2 gt a 1 on the technological side the investigations demonstrate the capability of satellite borne single pass radar interferometry as a new tool for accurate and detailed monitoring of glacier volume change

flow speed within the antarctic ice sheet and its controls inferred from satellite observations accurate dynamical models of the antarctic ice sheet with carefully specified initial conditions and well calibrated rheological parameters are needed to forecast global sea level by adapting an inverse method previously used in electric impedance tomography we infer present day flow speeds within the ice sheet this inversion uses satellite observations of surface velocity snow accumulation rate and rate of change of surface elevation to estimate the basal drag coefficient and an ice stiffness parameter that influences viscosity we represent interior ice motion using a vertically integrated approximation to incompressible stokes flow this model represents vertical shearing within the ice and membrane stresses caused by horizontal stretching and shearing combining observations and model we recover marked geographical variations in the basal drag coefficient relative changes in basal shear stress are smaller no simple sliding law adequately represents basal shear stress as a function of sliding speed low basal shear stress predominates in central east antarctica where thick insulating ice allows liquid water at the base to lubricate sliding higher shear stress occurs in coastal east antarctica where a frozen bed is more likely examining thwaites glacier in more detail shows that the slowest sliding often coincides with elevated basal topography differences between our results and a similar adjoint based inversion suggest that inversion or regularization methods can influence recovered parameters for slow sliding and finer scales on broader scales we recover a similar pattern of low basal drag underneath major ice streams and extensive regions in east antarctica that move by basal sliding