el nino la nina and sahel precipitation during the middle holocene simulations with a synchronously coupled atmo sphere land ocean sea ice model indicate el nino la nina like events in the eastern tropical pacific ocean during the middle holocene 6 ka with similar intensities and frequencies as at present 0 ka july august september sahel precipitation shifts northward as expected from proxy data for present day interannual decadal variability of western sahel precipi tation is correlated with both pacific el nino la nina sea sur face temperature sst anomalies and the atlantic dipole teleconnections at 6 ka between sahel precipitation and el nino la nina sst anomalies are absent with tropical atlantic ssts asserting a dominant influence these results illustrate potential problems with using present day teleconnection patterns in interpreting past climate variability from proxy data

development of a sea ice model for use in zonally averaged energy balance climate models abstract a sea ice model for use in zonally averaged energy balance climate models is presented which includes the following processes surface melting basal freezing and melting lateral melting from ice flee water or growth of new ice in leads snowfall and the formation of white ice ice advection and a parameterized ice and snow thickness distribution which represents the effects of small scale dynamics the ice growth equations of hibler are solved analytically thereby permitting a gradual increase in zonal ice fraction in fall and winter both lateral and vertical melting lead to a continuous decrease of ice fraction during ice decay the correlation between ice thickness and ice thickness sensitivity to the upward heat flux at the ice base is of opposite sign seasonally and latitudinally the parameterized feedback between ice thickness and the minimum permitted lead fraction is found to be very important to the ice simulation and is a process which needs to be studied using higher resolution

effect of ocean gateways on the global ocean circulation in the late oligocene and early miocene 1 we investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns using a fully coupled climate model in an idealized setup we compare situations corresponding to the late oligocene the early miocene and present day the model results show the existence of a flow reversal through the panama seaway between the oligocene and miocene this flow reversal is induced by global tectonic changes related to the widening of the southern ocean passages and the closing of the tethys seaway it mainly involves the wind driven ocean circulation in agreement with previous model studies the global thermohaline circulation in the oligocene and miocene simulations is significantly different from the present day conveyor circulation as there is deepwater formation in both the north atlantic and the north pacific oceans in particular in the oligocene simulation the salinity contrast between the atlantic and pacific oceans is reduced because of water mass exchange through the low latitude connections between the two oceans

a mechanism of decadal variability of the sea ice volume in the northern hemisphere a long term simulation performed with a coarse resolution global atmosphere ocean sea ice model displays strong decadal variability of the sea ice volume in the northern hemisphere with a significant peak at about 15 18 years this model results from the coupling of ecbilt a spectral t21 3 level quasi geostrophic atmospheric model and clio a sea ice ocean general circulation model first the mechanism underlying the variability of ice volume in the model was studied by performing correlation analyses between the simulated variables in a second step a series of additional sensitivity experiments was performed in order to illustrate the role of specific physical processes this as allowed us to identify a feedback loop in the ice ocean system which proceeds as follows an increase in at tic sea ice volume induces an increase in the salinity there this salinity anomaly is transported to the greenland sea where it promotes convective activity this warms up the surface oceanic layer and the atmosphere in winter and induces a decrease of the ice volume completing half a cycle the changes in ice volume are driven by a geopotential height pattern characterised by centres of action of opposite signs over greenland and the barents kara central arctic area thermodynamic feedback between the ice and the atmosphere appear also to be very important for the persistence of the oscillation the dynamical response of the atmosphere to sea ice and temperature anomalies at surface plays a smaller role

effects of rheology and ice thickness distribution in a dynamic thermodynamic sea ice model realistic treatment of sea ice processes in general circulation models is needed to simulate properly global climate and climate change scenarios as new sea ice treatments become available it is necessary to evaluate them in terms of their accuracy and computational time here several dynamic ice models are compared using both a 2 category and 28 category ice thickness distribution simulations are conducted under normal wind forcing as well as under increased and decreased wind speeds it is found that the lack of a shear strength parameterization in the cavitating fluid rheology produces significantly different results in both ice thickness and ice velocity than those produced by an elliptical rheology furthermore use of a 28 category ice thickness distribution amplifies differences in the responses of the various models while the choice of dynamic model is governed by requirements of accuracy and implementation it appears that in terms of both parameterization of physical properties and computational time the elliptical rheology is well suited for inclusion in a gcm

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

tectonic and geomorphic analysis of the belledonne border fault and its extensions western alps in the western alps the ne trending belledonne fault system extends from the mont blanc massifs in the ne to the vercors massif in the sw it includes the belledonne border fault defined by an alignment of micro earthquakes ml 3 5 focal mechanisms and their respective depths indicate a crustal scale ne trending dextral strike slip faulting this study aims at better constraining the geometry the fault kinematics and slip rate of the faults of the belledonne fault system by using a multidisciplinary approach that includes tectonics geomorphology and geophysics new clues of potential quaternary deformations are observed 1 the right lateral offsets of morphologic markers talwegs along the ne trending arcalod fault at the north eastern termination of the belledonne border fault 2 the left lateral offset of the valley carved by the isere glacier along the nw trending brion fault which is consistent with the fault kinematics deduced from the focal mechanisms stream network anomalies along the belledonne border fault are related to glacial erosion processes rather than faulting however fault kinematics analysis along the belledonne border fault allows us to determine a strike slip tectonic regime characterized by horizontal ene trending sigma 1 stress axis it is consistent with the mean trend of the p and t axes deduced from the focal mechanisms we display evidences that this stress state is messinian to quaternary in age and occurred after an oligocene to messinian strike slip tectonic regime characterized by horizontal wnw trending sigma 1 fault slip rates cannot be assessed because of the lack of morphologic features with constrained ages however it is likely that the presented geomorphic markers are older than wurm c 2015 elsevier b v all rights reserved

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

a climatology of sea ice embayments in the cosmonaut sea antarctica 1 the cosmonaut sea off the coast of antarctica is characterized by highly variable sea ice conditions as the sea ice expands during the austral fall and winter embayments open bodies of water surrounded on three sides by sea ice as well as polynyas often form using sea ice concentration data provided by satellite based passive microwave instruments from 1979 to 2004 we characterize these embayment events by their size and temporal evolution the data suggests a striking periodicity in the occurrence of these embayments with the exception of a quiet period between 1984 and 1987 the large embayment events seem to appear approximately every three years in the same location and persist for anywhere between mid june to mid august these results indicate there is predictability in the occurrence of embayment events adding important insight into the characterization of sea ice variability in this region

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

oceanic wave dynamics and interdecadal variability in a climate system model western boundary disturbances detected in the first multicentury integration of the national center for atmospheric research climate system model are analyzed and the role they play in the model interdecadal variability is investigated the boundary signals propagate southwestward along the coast of north america at depth they reach the equator and propagate along the equator but with decreasing amplitude away from the western boundary their southwestward propagation is associated with the evolution of the western boundary current system the gulf stream system in the upper part of the water column and the deep western boundary current at depth from weaker than average to stronger than average conditions thus the boundary disturbances seem to play an important role in the model thermohaline circulation variability at interdecadal timescales they show similarities with the boundary waves found in ocean only models exhibiting interdecadal variability and their role in the model s response to changes in the rate of sinking appears to be in agreement with the theory of the spin up of the deep ocean circulation the main result of this study is that the similarities with ocean only results and theories support the idea that interdecadal timescales of variability originate from the ocean dynamics

tropical pacific variability in the ncar climate system model a 300 yr simulation with the ncar climate system model csm version 1 captured only 60 of the observed enso signal and exaggerated the interannual variability of sst in the western tropical pacific here a simulation with a new version of the csm which significantly improves the spatial and temporal patterns of tropical pacific variability is described maximum sst variability is shifted to the central and eastern pacific a better simulation of the equatorial pacific thermocline structure results in nino 3 and nino 4 statistics com parable to the observed estimates for the last century the evolution of sst and subsurface temperature anomalies is in excellent agreement with observed events the majority of events evolve as a standing mode with weak sst anomalies occurring in the northern spring in the eastern tropical pacific and maximum anomalies covering the eastern tropical pacific ocean to the date line by the following northern winter at the same time subsurface temperature anomalies spread eastward and upward along the tropical thermocline the delayed oscillator and wyrtki s buildup hypothesis are consistent with aspects of the csm simulation on the equator a westerly wind stress anomaly in the central pacific forces off equatorial upwelling anomalies which propagate westward reaching the western boundary about one half year later this upwelling signal then propagates eastward along the equator arriving 2 months before cooling in the eastern pacific basin the tropical pacific atmospheric response to warm oceanic events also agrees with observational analyses with a negative southern oscillation pattern in sea level pressure wind stress anomalies and low level convergence to the west of the maximum sst anomalies and enhanced deep convection and precipitation in the central and eastern tropical pacific

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

sensitivity of sea ice to physical parameterizations in the giss global climate model 1 the giss coupled model is used to investigate the sensitivity of sea ice to each of the following parameterizations 1 two sea ice dynamics cf cavitating fluid vp viscous plastic 2 the specification of oceanic isopycnal mixing coefficients in the gent and mcwillams isopyncal mixing gm and 3 the wajsowicz viscosity diffusion wv the large scale sea ice properties are highly sensitive to sea ice dynamics with the inclusion of resistance to shear stress vp captures the major observed sea ice drift features and improves the simulations of sea ice concentrations thickness and export through fram strait relative to cf gm significantly improves the simulation of vertical temperature distributions in the southern ocean although it leads to a dramatic reduction of antarctic sea ice cover the reduced oceanic isopycnal mixing coefficients lead to arctic sea ice that tends to be less and thinner in almost the entire arctic except in the north pacific and labrador sea while antarctic sea ice that extends more equatorward throughout the circumpolar regions the responses of sea ice to wv show an enlargement and thickening of sea ice in the arctic within the ice packs around the antarctic and a reduction and thinning of sea ice in the northern weddell and ross seas on the basis of these experiments two composite experiments with the best parameterizations are investigated the atmospheric responses associated with sea ice changes are discussed while improvements are seen there are still many unrealistic aspects that will require further improvements to sea ice and ocean components

on the improvement of sea ice models for climate simulations the sea ice model intercomparison project experiments with dynamic thermodynamic sea ice models indicate a strong dependence of the net freezing rate sea ice transport and variability on dynamic model parameters although current dynamic thermodynamic sea ice models show relatively good agreement with observations an optimization seems to be necessary especially for the parameterizations of dynamic processes presently only a few coupled climate models use dynamic thermodynamic sea ice models in order to promote by means of coordinated numerical experiments the development of an optimal sea ice model for climate research the sea ice ocean modelling panel of the arctic climate system study acsys a project of the world climate research programme has initiated the sea ice model intercomparison project simip the first results from this model hierarchy approach are presented

influence of present day and glacial surface conditions on the antarctic oscillation southern annular mode 1 based upon coupled climate simulations driven by present day and glacial boundary conditions we demonstrate that the internal variability associated with the pronounced south polar climate anomalies that characterized the glacial climate regime was largely confined to the winter season in particular the intensity and spatial structure of the antarctic oscillation southern annular mode is found to display a strong seasonal cycle in the summer season we demonstrate that this mode of internal climate variability is extremely robust in response to a change from modern to glacial conditions in that it seems not to depend upon the latitudinal position of the baroclinic zone nor on the strength of the mean atmospheric zonal circulation in winter however and under glacial conditions this mode is characterized by a significantly modified atmospheric circulation that differs dramatically in terms of its internal variability from that characteristic of modern conditions

what sets the mean transport through drake passage twelve experiments with two coarse resolutions of a global ocean model using a variety of surface forcings are analyzed to address the question of what sets the mean transport through drake passage seven of the experiments do not have an active sea ice model but the remaining five do previous theories have suggested that the drake passage transport is governed by the cape horn sverdrup transport or alternatively is proportional to the square root of the meridional ekman transport at the latitude of drake passage the results presented here do not support either of these theories the drake passage transport depends quite strongly on the isopycnal diffusivity parameter in the model and less strongly on the background vertical diffusivity and horizontal viscosity parameters however when the magnitudes of these parameters are fixed the results show a very strong correlation between drake passage transport and both the strength of the meridional ekman transport at the latitude of drake passage and the thermohaline circulation off the antarctic shelf the relationships are monotonic but not linear the best estimate is that the meridional ekman transport drives 100 sv of drake passage transport while the remaining 30 sv are driven by the global thermohaline circulation

decadal variability in high northern latitudes as simulated by an intermediate complexity climate model a 2500 year integration has been performed with a global coupled atmospheric sea ice ocean model of intermediate complexity with the main objective of studying the climate variability in polar regions on decadal time scales and longer the atmospheric component is the ecbilt model a spectral t21 three level quasi geostrophic model that includes a representation of horizontal and vertical beat transfers as well as of the hydrological cycle ecbilt is coupled to the clio model which consists of a primitive equation free surface ocean general circulation model and a dynamic thermodynamic sea ice model comparison of model results with observations shows that the ecbilt clio model is able to reproduce reasonably well the climate of the high northern latitudes the dominant mode of coupled variability between the atmospheric circulation and sea ice cover in the simulation consists of an annular mode for geopotential height at 800 hpa and of a dipole between the barents and labrador seas for the sea ice concentration which are similar to observed patterns of variability in addition the simulation displays strong decadal variability in the sea ice volume with a significant peak at about 18 years positive volume anomalies are caused by 1 a decrease in ice export through fram strait associated with more anticyclonic winds at high latitudes 2 modifications in the freezing melting rates in the arctic due to lower air temperature and higher surface albedo and 3 a weaker heat flux at the ice base in the barents and kara seas caused by a lower inflow of warm atlantic water opposite anomalies occur during the volume decrease phase of the oscillation

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

atmospheric circulation and its effect on arctic sea ice in ccsm3 simulations at medium and high resolution the simulation of arctic sea ice and surface winds changes significantly when community climate system model version 3 ccsm3 resolution is increased from t42 2 8 to t85 1 4 at t42 resolution arctic sea ice is too thick off the siberian coast and too thin along the canadian coast both of these biases are reduced at t85 resolution the most prominent surface wind difference is the erroneous north polar summer anticyclone present at t42 but absent at t85 an offline sea ice model is used to study the effect of the surface winds on sea ice thickness in this model the surface wind stress is prescribed alternately from reanalysis and the t42 and t85 simulations in the offline model ccsm3 surface wind biases have a dramatic effect on sea ice distribution with reanalysis surface winds annual mean ice thickness is greatest along the canadian coast but with ccsm3 winds thickness is greater on the siberian side a significant difference between the two ccsm3 forced offline simulations is the thickness of the ice along the canadian archipelago where the t85 winds produce thicker ice than their t42 counterparts seasonal forcing experiments with ccsm3 winds during spring and summer and reanalysis winds in fall and winter relate the canadian thickness difference to spring and summer surface wind differences these experiments also show that the ice buildup on the siberian coast at both resolutions is related to the fall and winter surface winds the arctic atmospheric circulation is examined further through comparisons of the winter sea level pressure slp and eddy geopotential height at both resolutions the simulated beaufort high is quite weak weaker at higher resolution eddy heights show that the wintertime beaufort high in reanalysis has a barotropic vertical structure in contrast high ccsm3 slp in arctic winter is found in association with cold lower tropospheric temperatures and a baroclinic vertical structure in reanalysis the summertime arctic surface circulation is dominated by a polar cyclone which is accompanied by surface inflow and a deep ferrel cell north of the traditional polar cell the arctic ferrel cell is accompanied by a northward flux of zonal momentum and a polar lobe of the zonal mean jet these features do not appear in the ccsm3 simulations at either resolution

deciphering the role of southern gateways and carbon dioxide on the onset of the antarctic circumpolar current 1 growth of antarctic ice sheet during the cenozoic 34 million years ago appears as a potential tipping point in the long term cooling trend that began 50 ma ago for decades the onset of the antarctic circumpolar current acc following the opening of the drake passage and of the tasman seaway has been suggested as the main driver of the continental scale antarctic glaciation however recent modeling works emphasized that the eocene oligocene atmospheric carbon dioxide co2 lowering could be the primary forcing of the antarctic glaciation questioning the acc theory here we investigate the response of the acc to changes in co2concentrations occurring from the late eocene to the late oligocene we used a fully coupled atmosphere ocean model foam with a mid oligocene geography we find that the opening of southern oceanic gateways does not trigger the onset of the acc for co2typical of the late eocene 840 ppm a cooler background climatic state such as the one prevalent at the end of the oligocene is required to simulate a well developed acc in this cold configuration the intensified sea ice development around antarctica and the resulting brine formation lead to a strong latitudinal density gradient in the southern ocean favoring the compensation of the ekman transport and consequently the acc our results imply that the acc has acted as a feedback rather than as a driver of the global cooling

the asian australian monsoon and el nino southern oscillation in the ncar climate system model features associated with the asian australian monsoon system and el nino southern oscillation enso are described in the national center for atmospheric research ncar global coupled climate system model csm simulation characteristics are compared with a version of the atmospheric component of the csm the ncar ccm3 run with time evolving ssts from 1950 to 1994 and with observations the csm is shown to represent most major features of the monsoon system in terms of mean climatology interannual variability and connections to the tropical pacific this includes a representation of the southern oscillation links between strong asian australian monsoons and associated negative sst anomalies in the eastern equatorial pacific the equatorial sst gradient across the pacific in the csm is shown to be similar to the observed with somewhat cooler mean ssts across the entire pacific by about 18 28c the seasonal cycle of ssts in the eastern equatorial pacific has the characteristic signature seen in the observations of relatively warmer ssts propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder ssts propagating westward in the second half of the year like other global coupled models the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1 2 months later than observed the seasonal cycle of precipitation in the tropical eastern pacific is also similar to other global coupled models in that there is a tendency for a stronger than observed double itcz year round particularly in northern spring but with a well reproduced annual maximum of itcz strength north of the equator in the second half of the year time series of area averaged ssts for the nino3 region in the eastern equatorial pacific show that the csm is producing about 60 of the amplitude of the observed variability in that region consistent with most other global coupled models global correlations between nino3 time series global surface temperatures and sea level pressure slp show that the csm qualitatively reproduces the major spatial patterns associated with the southern oscillation lower slp in the central and eastern tropical pacific when nino3 ssts are relatively warmer and higher slp over the far western pacific and indian oceans with colder water in the northwest and southwest pacific indices of asian australian monsoon strength are negatively correlated with nino3 ssts as in the observations spectra of time series of indian monsoon australian monsoon and nino3 sst indices from the csm show amplitude peaks in the southern oscillation and tropospheric biennial oscillation frequencies 3 6 yr and about 2 3 yr respectively as observed lag correlations between the nino3 sst index and upper ocean heat content along the equator show eastward propagation of heat content anomalies with a phase speed of about 0 3 m s21 compared to observed values of roughly 0 2 m s21 composites of el nino la nina events in the csm show similar seasonal evolution to composites of observed events with warming cooling of greater than several tenths of a degree beginning early in northern spring of year 0 and diminishing around northern spring of year 11 but with a secondary resurgence in the csm events later in northern spring of year 11 the csm also shows the largest amplitude enso sst and low level wind anomalies in the western tropical pacific with enhanced interannual variability of ssts extending northeastward and southeastward toward the subtropics compared to largest interannual sst variability in the central and eastern tropical pacific in the observations

satellite derived maps of arctic and antarctic sea ice motion 1988 to 1994 standard image processing methods applied to 85 5 ghz special sensor microwave imager ssm i data provide previously unseen details about sea ice motion in the arctic and southern oceans means calculated from daily ice motions for 1988 1994 confirm the basic circulation patterns established from drifting stations and buoys but extend these observations to illustrate less well known transport patterns in the arctic coastal zones and sub arctic seas in the antarctic the gridded motion fields show a nearly continuous westward transport along the antarctic coast with well defined regions of exchange between this east wind drift and the antarctic circumpolar current this detailed view of mean ice motion in the southern ocean is unique and presents a comprehensive overview not previously available for antarctic ice motions

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

polar climate instability and climate teleconnections from the arctic to the midlatitudes and tropics abstract it is generally accepted that the ocean thermohaline circulation plays a key role in polar climate stability and rapid climate change recently reported analyses of the impact of anomalous freshwater outflows from the north american continent onto either the north atlantic or arctic oceans demonstrate that in either case a clear reduction in the atlantic meridional overturning circulation accompanied by an increase in sea ice extent is predicted the results also reconcile proxy inferred younger dryas greenland temperature variations the aim of the present work is to provide a detailed investigation of the pathways along which the signal associated with overturning circulation anomalies propagates into both the midlatitudes and the tropics and the effect such teleconnections have on the tropical ocean atmosphere system the authors consider both the impact of substantial slowing of the overturning circulation due to freshwater forcing of the north atlantic as well as its recovery after the a