interannual enso and interdecadal enso like variability in the southern hemisphere tropospheric circulation abstract recent work has identified variability in the pacific ocean sst with a structure qualitatively similar to enso but at lower frequencies than enso zhang et al have documented the atmospheric circulation anomalies in the tropics and northern hemisphere that are associated with decadal enso like variability and compared these anomalies to those associated with the interannual enso cycle here the authors extend the study of zhang et al to the southern hemisphere using the national centers for environmental prediction national center for atmospheric research reanalysis data for 1958 96 consistent with previous studies the southern hemisphere circulation anomalies associated with enso display a teleconnection pattern from the central tropical pacific into the far southeastern pacific ocean comparatively larger circulation anomalies are found in the southern hemisphere associated with the decadal enso like variability though aloft the structure of the anomalies emphasizes the polar vortex wit

anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

decadal variability in the north pacific the eastern north pacific mode abstract decadal variability in the north pacific is studied in a series of coupled global ocean atmosphere simulations using coupled modeling surgery a set of modeling approaches that can be used to identify the origins and causes of a specific variability mode in the coupled climate system both modeling and observational studies suggest two distinctive internal modes in the north pacific the north pacific mode npm and the eastern north pacific mode enpm the enpm originates from atmospheric stochastic forcing through spatial resonance both local ocean atmosphere coupling and remote tropical teleconnective forcing can enhance the enpm but none of them is a necessary precondition the influence of the tropical forcing in the midlatitudes is dominated by atmospheric teleconnection while the oceanic teleconnection is negligible the upper ocean heat budget reveals that sst anomalies in the central north pacific and the eastern north pacific are generated by anomalous ekman advection and surface hea

balanced ocean data assimilation near the equator the question is addressed whether using unbalanced updates in ocean data assimilation schemes for seasonal forecasting systems can result in a relatively poor simulation of zonal currents an assimilation scheme where temperature observations are used for updating only the density field is compared to a scheme where updates of density field and zonal velocities are related by geostrophic balance this is done for an equatorial linear shallow water model it is found that equatorial zonal velocities can be detoriated if velocity is not updated in the assimilation procedure adding balanced updates to the zonal velocity is shown to be a simple remedy for the shallow water model next optimal interpolation oi schemes with balanced updates of the zonal velocity are implemented in two ocean general circulation models first tests indicate a beneficial impact on equatorial upper ocean zonal currents

a model of sea level rise caused by ocean thermal expansion abstract warming of the atmosphere as a result of an increased concentration of greenhouse gases is expected to lead to a significant rise is global sea level we present estimates of the component of this sea level rise caused by thermal expansion of the ocean these estimates are based on the idea that the upper layers of the main gyres of the ocean are ventilated by the subduction of water at higher latitudes and its subsequent equatorward and downward flow into the main thermocline along surfaces of constant density in this mechanism heat enters the ocean by an advection process rather than by vertical diffusion as in previous estimates of the component of sea level rise that is caused by thermal expansion after the heat initially enters the subtropical gyres by subduction it is then redistributed to preserve gradients of the depth integrated pressure field by an adjustment involving low vertical mode baroclinic waves estimates of historical sea level rise based on this simple ventilation sch

sea level rise a review of recent past and near future trends global mean sea level is a potentially sensitive indicator of climate change global warming will contribute to worldwide sea level rise slr from thermal expansion of ocean water melting of mountain glaciers and polar ice sheets a number of studies mostly using tide gauge data from the permanent service for mean sea level bidston observatory england have obtained rates of global slr within the last 100 years that range between 0 3 and 3 mm yr 1 with most values concentrated between 1 and 2 mm yr 1 however the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability sources of uncertainty in the sea level data include variations in winds ocean currents river runoff vertical earth movements and geographically uneven distribution of long term records crustal motions introduce a major source of error to a large extent these can be filtered by employing palaeo sea level proxies and geophysical modelling to remove glacio isostatic changes ultimately satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges future sea level is expected to rise by 1 m with a best guess value of 48 cm by the year 2100 such rates represent an acceleration of four to seven times over present rates local land subsidence could substantially increase the apparent slr for example louisiana is currently experiencing slr trends nearly 10 times the global mean rate these recently reduced slr estimates are based on climate models that predict a zero to negative contribution to slr from antarctica most global climate models gcms indicate an ice accumulation over antarctica because in a warmer world precipitation will exceed ablation snow melt however the impacts of attritional processes such as thinning of the ice shelves have been downplayed according to some experts furthermore not all climate models are in agreement opposite conclusions may be drawn from the results of other gcms in addition the west antarctic ice sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict because of the great uncertainty in slr projections careful monitoring of future sea level trends by upgraded tide gauge networks and satellite geodesy will become essential finally because of the high spatial variability in crustal subsidence rates wave climates and tidal regimes it will be the set of local conditions especially the relative sea level rise rather than a single global mean sea level trend that will determine each locality s vulnerability to future slr

pacific thermocline bridge revisited abstract the coupling on decadal time scales of the mid latitude and tropical pacific via an oceanic bridge in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model results indicate that in the tropics decadal anomalies of isopycnal depth are forced by ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid latitudes of either hemisphere in the coupled model temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere but are lag correlated between southern hemisphere mid and low latitudes however anomaly magnitudes on the equator are small these results suggest that the oceanic bridge to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial pacific coupling to the southern mid latitudes via temperature anomalies on isopycnals remains an intriguing possibility

sea level variations induced by heating and cooling an evaluation of the boussinesq approximation in ocean models in this paper a sigma coordinate ocean model is modified to remove the commonly used boussinesq approximation so that the effect of thermal expansion is exactly included in the basic equations in order to cope with the seasonal heating cycle and the detection of climate change through variation in sea level height tests are performed to evaluate the differences between boussinesq and non boussinesq calculations under different heating and cooling conditions and different model domains for an idealized case of a flat bottom shallow ocean basin without wind forcing simulations of a warm eddy show that the non boussinesq dynamics have only a minor effect on the baroclinic current field however vertically averaged velocities though small compared with the baroclinic velocities are cyclonic for the boussinesq calculation and anticyclonic for the non boussinesq calculation the results indicate that global or closed basin boussinesq models should be able to simulate most of the observed steric sea level changes on seasonal or climate timescales when corrected by a spatially uniform time dependent factor calculated from the volume averaged density change the seasonal variation of the globally averaged sea level calculated from climatological data is small about 1 cm variations in steric sea level in regional models both boussinesq and non boussinesq may differ from those of global models owing to the unknown transport across their boundaries associated with the local heating and cooling a spatially uniform time dependent correction similar to that associated with thermal expansion is proposed to account for transport across open boundaries of regional models variations of sea level obtained from a boussinesq model of the atlantic ocean approximate the seasonal signal due to the heating cooling cycle of each hemisphere as observed by satellite altimeter data

role of the atmospheric and oceanic circulation in the tropical pacific sst changes a coupled climate model is used to explore the response of the tropical sea surface temperature sst to positive sst anomalies in the global extratropics the main model results here are consistent with previous numerical studies in response to prescribed sst anomalies in the extratropics the tropical ssts rise rapidly and reach a quasi equilibrium state within several years and the tropical subsurface temperatures show a slow response the annual mean hadley cell as well as the surface trades are weakened the weakened trades reduce the poleward ekman transports in the tropical ocean and furthermore lead to anomalous positive convergences of heat transport which is the main mechanism for maintaining the tropical pacific sst warming the process of an extratropical influence on the tropics is related to both the atmospheric and oceanic circulations the intertropical convergence zone itcz moves southward and eastward in the pacific corresponding to a reduction of the hadley circulation and walker circulation at the same time convective precipitation anomalies are formed on the boundary of the climatological itcz while the climatological mean convections centered in the southeast asia region are suppressed the largely delayed response of the tropical subsurface temperature cannot be explained only by the strength change of the subtropical cells stcs but can be traced back to the slow changing of subsurface temperature in the extratropics in the extratropical oceans warming and freshening reduce the surface water density and the outcropping lines of certain isopycnal layers are moved poleward this poleward movement of outcropping lines can weaken the positive temperature anomalies or even lead to negative anomalies on given isopycnal layers displayed on time dependent isopycnal layers positive subsurface temperature anomalies are present only in the region after subduction and are subsequently replaced by negative temperature anomalies in the deep tropics regions the noticeable features of the density compensation of temperature and salinity indicate that diapycnal processes play an important role in the equatorward transport of the temperature and salinity anomalies from the midlatitude

the passive and active nature of ocean heat uptake in idealized climate change experiments the influence of ocean circulation changes on heat uptake is explored using a simply configured primitive equation ocean model resembling a very idealized atlantic ocean we focus on the relative importance of the redistribution of the existing heat reservoir due to changes in the circulation and the contribution from anomalous surface heat flux in experiments in which the surface boundary conditions are changed we perform and analyze numerical experiments over a wide range of parameters including experiments that simulate global warming and others that explore the robustness of our results to more general changes in surface boundary conditions we find that over a wide range of values of diapycnal diffusivity and southern ocean winds and with a variety of changes in surface boundary conditions the spatial patterns of ocean temperature anomaly are nearly always determined as much or more by the existing heat reservoir redistribution than by the nearly passive uptake of temperature due to changes in the surface boundary conditions calculating heat uptake by neglecting the existing reservoir redistribution which is similar to treating temperature as a passive tracer leads to significant quantitative errors notably at high latitudes and secondarily in parts of the main thermocline experiments with larger circulation changes tend to produce a relatively larger magnitude of existing reservoir redistribution and a faster growing effective heat capacity of the system the effective heat capacity is found to be sensitive to both vertical diffusivity and southern ocean wind

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

steric sea level variations during 1957 1994 importance of salinity 1 spatially averaged 50 s 65 n temperature and salinity changes in the 0 3000 m layer during the 1957 1994 period resulted in a sea level rise at a mean rate of about 0 55 mm per year about 10 of this rate is due to a decrease of the volume mean salinity the magnitude of total steric sea level tssl changes and the ratio of thermosteric and halosteric anomalies to tssl anomaly are nonuniform geographically salinity effects are critically important to the tssl changes in some regions of the ocean for example the thermosteric anomaly is nearly compensated by the halosteric anomaly in the subpolar north atlantic this fact will cause erroneous heat content estimates based on altimetric observations from space if a climatological salinity is assumed based on the present historical archive of salinity data a decrease in global mean salinity has occurred this increase of fresh water would cause sea level rise at a rate of 1 3 0 5 mm yr if the added water comes from sources other than floating sea ice

adjustment of the coupled ocean atmosphere system to a sudden change in the thermohaline circulation 1 the adjustment of the coupled ocean atmosphere system to a fresh water anomaly in the north atlantic ocean is investigated using a coupled gcm in response to the anomaly the atlantic thermohaline circulation thc collapses and the associated reduction in northward heat transport causes sea surface temperatures sst to fall over the north atlantic and to increase over the tropical south atlantic atmospheric feedbacks are excited as soon as the sst anomalies reach sufficient magnitude a key stage in the adjustment process occurs 4 6 years after the perturbation is introduced when a significant sst dipole develops in the tropical atlantic this dipole causes a southward shift of the itcz and leads in year 7 to the triggering of an el nino event it is concluded that atmospheric feedbacks could spread globally the influence of a sudden change in the thc much more quickly and efficiently than could ocean processes alone

origin of upper ocean warming and el nino change on decadal scales in the tropical pacific ocean the cause of decadal scale variability in the tropical pacific ocean such as that marked by the 1976 77 shift in the el nino southern oscillation1 2 3 4 5 6 7 is poorly understood unravelling the mechanism of the recent decade long warming in the tropical upper ocean is a particularly important challenge given the link to el nino variability but establishing the hypothesized interannual decadal oceanic connections between middle latitudes and tropics has proved elusive8 here we present observational evidence that pacific upper ocean warming and decadal changes in the el nino southern oscillation after 1976 may originate from decadal mid latitude variability in the middle 1970s the north pacific ocean is observed to have undergone a clear phase transition a see saw subsurface temperature anomaly pattern that rotates clockwise around the subtropical gyre at middle latitudes a subsurface warm anomaly formed in the early 1970s from subducted surface waters and penetrated through the subtropics and into the tropics thus perturbing the tropical thermocline and driving the formation of a warm surface water anomaly that may have influenced el nino in the 1980s the identification of this teleconnection of extratropical thermal anomalies to the tropics through a subsurface ocean bridge may enable improved prediction of decadal scale climate variability

model assessment of decadal variability and trends in the tropical pacific ocean abstract in this report global coupled ocean atmosphere models are used to explore possible mechanisms for observed decadal variability and trends in pacific ocean ssts over the past century the leading mode of internally generated decadal 7 yr variability in the model resembles the observed decadal variability in terms of pattern and amplitude in the model the pattern and time evolution of tropical winds and oceanic heat content are similar for the decadal and enso timescales suggesting that the decadal variability has a similar delayed oscillator mechanism to that on the enso timescale the westward phase propagation of the heat content anomalies however is slower and centered slightly farther from the equator 12 vs 9 n for the decadal variability cool sst anomalies in the midlatitude north pacific during the warm tropical phase of the decadal variability are induced in the model largely by oceanic advection anomalies an index of observed sst over a broad triangular region of the tropi

global and full depth ocean temperature trends during the early twenty first century from argo and repeat hydrography the early 21st century s warming trend of the full depth global ocean is calculated by combining the analysis of argo top 2000m and repeat hydrography into a blended full depth observing system the surface to bottom temperature change over the last decade of sustained observation is equivalent to a heat uptake of 0 72 0 09 w m 2 applied over the surface of the earth 90 of it being found above 2000m depth we decompose the temperature trend point wise into changes in isopycnal depth heave and temperature changes along an isopycnal spiciness to describe the mechanisms controlling the variability the heave component dominates the global heat content increase with the largest trends found in the southern hemisphere s extratropics 0 2000m highlighting a volumetric increase of subtropical mode waters significant heave related warming is also found in the deep north atlantic and southern ocean 2000m 4000m reflecting a potential decrease in deep water mass renewal rates the spiciness component shows its strongest contribution at intermediate levels 700m 2000m with striking localised warming signals in regions of intense vertical mixing north atlantic and southern oceans finally the agreement between the independent argo and repeat hydrography temperature changes at 2000m provides an overall good confidence in the blended heat content evaluation on global and ocean scales but also highlights basin scale discrepancies between the two independent estimates those mismatches are largest in those basins with the largest heave signature southern ocean and reflect both the temporal and spatial sparseness of the hydrography sampling

a note on the representation of steric sea level in models that conserve volume rather than mass this note discusses the representation of steric sea level in ocean circulation models changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column models usually make the boussinesq approximation and conserve volume rather than mass and so do not properly represent expansion or contraction this means that although expansion contraction is included in the equation of state it is not accounted for by the model dynamics in this note we examine the equation governing the time evolution of the sea level displacement it is shown that requiring conservation of mass rather than volume introduces a new term to this equation a simple example is used to show the relationship of the new term to the surface buoyancy flux the equilibrium response to the new term has two parts one part consists of the goldsbrough and stommel gyres for which in the ocean interior vortex stretching due to the local expansion contraction of the water column is balanced by changes in planetary vorticity the other part corresponds to the inverse barometer the effect is to adjust sea level by a globally uniform but timevarying factor determined by the net expansion contraction of the global ocean since this correction is globally uniform it has no dynamical significance both the goldsbrough stommel gyres and the inverse barometer solution are missing from models as currently formulated this does not represent a serious error however if comparison is made with observations of sea level model calculated sea level should be adjusted by a globally uniform time varying factor determined by the net expansion contraction of the global ocean this would be important for assessing the likely rise in sea level in response to global warming

subduction and transport in the indian and pacific oceans in a 2 co2 climate abstract subduction water mass transformation and transport rates in the indo pacific ocean are diagnosed in a recent version of the canadian centre for climate modelling and analysis coupled model it is found that the subduction across the base of the winter mixed layer is dominated by the lateral transfer particularly within the relatively dense water classes corresponding to the densest mode and intermediate waters however within lighter densities including those characterizing the lighter varieties of mode waters the vertical transfer has a strong positive input to the net subduction the upper ocean volume transports across 30 n and 32 s are largest within the density classes that correspond to mode waters in the north pacific the buoyancy flux converts the near surface waters mostly to denser water classes whereas in the southern ocean the surface waters are transformed both to lighter and denser water classes depending on the density in response to a doubling of co2 the subduction tr

interannual and decadal temperature variability in the southwest pacific ocean between 1955 and 1988 abstract the spatial and temporal variability of the southwest pacific ocean is examined with the aim of describing the physical processes operating on interannual and decadal timescales the study takes advantage of a new temperature atlas of the upper 450 m of the southwest pacific ocean obtained from 40 000 bathythermograph profiles between 1955 and 1988 rotated principal components analysis was used to filter the important spatial and temporal scales of temperature variability in the data three different analyses are presented they include two intraocean analyses and a joint analysis of subsurface ocean temperature sea level pressure and surface winds the dominant el nino mode describes the large vertical excursions of the thermocline in the western tropical pacific in response to atmospheric forcing at a 3 6 month lag more importantly most of the retained modes outside of the equatorial region have time variations that correlate with el nino one ocean mode with a spatial pattern represen

contribution of glacier melt to sea level rise since ad 1865 a regionally differentiated calculation the contribution of glacier melt including the greenland ice sheet to sea level change since ad 1865 is estimated on the basis of modelled sensitivity of glacier mass balance to climate change and historical temperature data calculations are done in a regionally differentiated manner to overcome the inhomogeneity of the global distribution of glaciers a distinction is made between changes in summer temperature and in temperature over the rest of the year our best estimate of the ice melt in the period 1865 1990 in terms of sea level change equivalent is 5 7 cm 2 7 cm for glaciers and 3 0 cm for the greenland ice sheet additional calculations show that simpler methods like using annual or even global mean temperature anomaly give estimates that differ by up to 55 consequently a regionally differentiating approach is advised for making projections of glacier melt with gcm output

sea level change due to oscillations in seafloor spreading rate abstract we present a theory for divergent seafloor spreading which predicts that transient surges in spreading rate would cause geodynamic sea level rise rates approximately equal to the transient surge velocity at the ridge crest multiplied by the aspect ratio of the spreading plate i e a surge velocity of 3 cm yr acting on a plate thickness 100 km and width 3000 km would produce a geodynamic sea level rise rate of 1 mm yr this rate is geologically significant and it is suggested that the calving of ice by flotation due to geodynamic sea level rise may feedback positively on a thermal sea level rise and provide a mechanism whereby plate tectonics can actually drive climatic change the theory depends on the assumption that plate motion is governed by thermally driven ridge push forces balanced by frictional drag at the base of the plate

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

generation mechanism of spiciness anomalies an ogcm analysis in the north atlantic subtropical gyre oceanic teleconnections between the low and midlatitudes are a key mechanism to understanding the climate variability spiciness anomalies density compensated anomalies have been shown to transport temperature and salinity signals when propagating along current streamlines in the subtropical gyres of the atlantic and pacific oceans the generation mechanism of spiciness anomalies in the north atlantic subtropical gyre is investigated using an analytical model based on the late winter subduction of salinity and temperatureanomalies along isopycnal surfaces the keystone ofthis approachisthe change ofthe coordinates frame from isobaric to isopycnic surfaces suited for subduction problems the isopycnal nature of spiciness anomalies and the use of a linear density equation allows for the analytical model to depend only upon surface temperature and salinity anomalies the mean thermocline currents and the surface density ratio this model clarifies and above all quantifies the mechanism by which surface temperature and salinity anomalies are modulated by density ratios to produce fully different isopycnal temperature and salinity anomalies

control of mode and intermediate water mass properties in drake passage by the amundsen sea low the evolutionof the physical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage region is examined on time scales down to intraseasonal within the 1969 2009 period both samw and aaiw experience substantial interannual to interdecadal variability significantly linked to the action of the amundsen sea low asl in their formation areas observations suggest that the interdecadal freshening tendency evident in samw over the past three decades has recently abated while aaiw has warmed significantly since the early 2000s the two water masses have also experienced a substantial lightening since the start of the record examination of the mechanisms underpinning water mass property variability shows that samw characteristics are controlled predominantly by a combination of air sea turbulent heat fluxes cross frontal ekman transport of antarctic surface waters and the evaporation precipitation balance in the subantarctic zone of the southeast pacific and drake passage while aaiw properties reflect air sea turbulent heat fluxes and sea ice formation in the bellingshausen sea the recent interdecadal evolution of the asl is consistent with both the dominance of the processes described here and the response of samw and aaiw on that time scale

decadal variations in the subtropical cells and equatorial pacific sst 1 a mechanism for generating decadal sea surface temperature sst variability in the equatorial pacific is investigated using an ocean general circulation model forced by observed wind stress equatorial sst variability is governed by different ocean dynamics on interannual and decadal time scales at interannual time scales equatorial sst anomalies are mainly driven by equatorial winds at decadal time scales on the other hand they are forced both by equatorial winds and by off equatorial winds in the tropics while the contribution from midlatitude winds poleward of 25 is negligible trade wind variations in the off equatorial tropics force equatorial sst variability by spinning up and down the subtropical cells that transport cold water into the equatorial upwelling zone equatorial sst anomalies induced by this mechanism lag behind the response to local equatorial winds by about two years

variation of the mean sea level from topex poseidon data variations of the 10 day averaged sea level extracted from topex poseidon t p altimeter data are examined from october 1992 to february 1995 data are corrected from instrumental drifts and recent precise orbit and ocean tide corrections are used when data from the less accurate first eight cycles are excluded and atmospheric pressure effects are not corrected the 10 day mean sea level varies by 5 0 mm rms its variations can be described by a 4 1 1 mm yr drift a small annual signal of 2 7 mm amplitude and a residual signal of 3 5 mm rms amplitude and gaussian statistics close to formal error estimates the mean sea level rise is difficult to explain by drifts of geophysical corrections though the case for the wet tropospheric correction and that for the orbit are uncertain pressure effects should be corrected relative to the global pressure averaged over the ocean the latter shows a seasonal signal of 1 cm amplitude and apparent fluctuations of 30 to 70 day periods these fluctuations could result from errors in the atmospheric pressure fields but they seem to be mostly related to large regional pressure evolutions evidence is also found for a sampling effect by the t p orbit of pressure signals at shorter than 10 day periods pressure effects on sea level are then assumed to be an inverse barometer relative to 10 day global atmospheric pressure over the ocean which allows analysis of the geographical repartition of the mean sea level evolution due to other effects the mean sea level rise is comparable in the northern 4 2 2 5 mm yr and southern 3 7 1 9 mm yr hemispheres it seems mostly related to interannual variations of the tropical ocean 41 of the global signal and of the northern hemisphere subtropical gyres 30 of the global signal residual noise on these regional values seems inversely proportional to the square root of the number of data points in each area the hemispheric seasonal pressure variation relative to the globally averaged pressure over the ocean is less than 3 mm amplitude in our calculation it is implicitely assumed that it induces a small interhemispheric water mass exchange the amplitudes of the seasonal hemispheric sea level variations are 27 and 18 mm in the northern and southern hemispheres respectively these amplitudes are very close to being inversely proportional to the ocean surface in each hemisphere the maxima of sea level in these hemispheres are reached in the last weeks of september and march respectively at subpolar latitudes semiannual components are observed in each hemisphere which are consistent with those of sea surface temperature

global sea level change determination and interpretation the notion of sea level rise brings to the popular mind the specter of deep inundation of coastal regions one pictures skyscrapers emerging from the waters like so many sleeping flamingos standing in the shallows of a lake of course if all of the world s ice sheets suddenly melted or collapsed this vision would apply to new york city and its coastal counterparts but there is a general consensus that such a calamity is not an immediate threat houghton et al 1990 the actual situation for the recent historical past and near future appears to be more benign but with nonetheless extremely significant even devastating impacts due to erosion and flooding of coastal areas

the reflectivity of magmatic underplating using the layered mafic intrusion analog abstract the reflection characteristics of layered mafic intrusions provide an analog for characterizing the reflectivity of magmatic underplates one dimensional seismic models of a variety of mafic intrusions with different parent magmas demonstrate that cumulate layering may typically be strongly reflective with reflection coefficients as high as 0 18 a seismic profile across the bjerkreim intrusion in southern norway shows that even a moderately reflective cumulate sequence with reflection coefficients on the order of 0 05 produces detectable reflections two dimensional models demonstrate that the subhorizontal cumulate layering in typical mid to upper crustal intrusions is conducive to seismic imaging but more complicated geometries such as concentric layering created during synmagmatic deformation complicate the seismic image reflection coefficients predicted for granulite facies mineral assemblages are similar to those predicted for the igneous assemblages reflection coefficients predicted for cumulates intruded or re equilibrated at eclogite facies conditions may be either decreased or enhanced with respect to the igneous assemblages depending on the abundance of plagioclase in the cumulate layers and the pressure results suggest that magmatic underplating should not be invoked as an explanation for non reflective crust except in cases where eclogitization has occurred

on the dynamics of interdecadal thermocline depth and sea surface temperature variability in the low to mid latitude pacific ocean the role of upper ocean dynamics in generating interdecadal sea surface temperature sst variations is investigated with the help of the australian bureau of meteorology research centre coupled general circulation model cgcm and a first baroclinic mode shallow water ocean model swm an empirical orthogonal function analysis is performed on the lowpass filtered sst and vertically averaged temperature in the upper 300 m anomaly data output from a 100 year cgcm simulation the dominant mode sst spatial pattern and time variability is consistent with the interdecadal pacific oscillation the swm is forced by wind stresses from the cgcm 100 year simulation to investigate the role of oceanic rossby and kelvin wave propagation on thermocline depth variations the swm produces variability similar to the cgcm interdecadal variability we conclude that large scale wind forced upper ocean dynamics play a dominant role in generating interdecadal upper ocean temperature variations on decadal and longer timescales

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

a simple model of the decadal response of the ocean to stochastic wind forcing abstract a simple linear model is used to estimate the decadal response of the extratropical ocean to wind stress forcing assuming a flat bottom a mean state at rest and no dissipation the barotropic fields are governed by a time dependent sverdrup balance the baroclinic ones by the long rossby wave equation the ocean is bounded by a coast in the east and a radiation condition is used in the west at each frequency the baroclinic response consists of a forced response plus a rossby wave generated at the eastern boundary for zonally independent forcing the response propagates westward at twice the rossby phase speed the wind stress is assumed to be stochastic with a white frequency spectrum so the model represents the continuous excitation of the ocean interior by the weather fluctuations the model predicts the shape and level of the frequency spectra of the oceanic pressure field and their variation with longitude and latitude the baroclinic response is spread over a continuum of frequencies

warming of the global ocean spatial structure and water mass trends abstractthis study investigates the multidecadal warming and interannual to decadal heat content changes in the upper ocean 0 700 m focusing on vertical and horizontal patterns of variability these results support a nearly monotonic warming over much of the world ocean with a shift toward southern hemisphere warming during the well observed past decade this is based on objectively analyzed gridded observational datasets and on a modeled state estimate besides the surface warming a warming climate also has a subsurface effect manifesting as a strong deepening of the midthermocline isopycnals which can be diagnosed directly from hydrographic data this deepening appears to be a result of heat entering via subduction and spreading laterally from the high latitude ventilation regions of subtropical mode waters the basin average multidecadal warming mainly expands the subtropical mode water volume with weak changes in the temperature salinity s relationship known as spice variability howeve

multi year predictability in a coupled general circulation model multi year to decadal variability in a 100 year integration of a bmrc coupled atmosphere ocean general circulation model cgcm is examined the fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial indo pacific ocean the relative importance of decadal variability is enhanced in off equatorial wings in the subtropical eastern pacific the model and observations exhibit enso like decadal patterns analytic results are derived which show that the patterns can in theory occur in the absence of any predictability beyond enso time scales in practice however modification to this stochastic view is needed to account for robust differences between enso like decadal patterns and their interannual counterparts an analysis of variability in the cgcm a wind forced shallow water model and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal enso like patterns like the interdecadal pacific oscillation and pacific decadal oscillation in this theory enso driven wind stress variability forces internal equatorially trapped kelvin waves that propagate towards the eastern boundary kelvin waves can excite reflected internal westward propagating equatorially trapped rossby waves rws and coastally trapped waves ctws ctws have no impact on the off equatorial sub surface ocean outside the coastal wave guide whereas the rws do if the frequency of the incident wave is too high then only ctws are excited at lower frequencies both ctws and rws can be excited the lower the frequency the greater the fraction of energy transmitted to rws this lowers the characteristic frequency reddens the spectrum of variability off the equator relative to its equatorial counterpart at low frequencies dissipation acts as an additional low pass filter that becomes more effective as latitude increases at the same time enso driven off equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the enso forcing the resulting off equatorial variability is therefore more coherent with low pass filtered decadal enso indices e g nino3 sea surface temperature sst than with unfiltered enso indices consequently large correlations between variability and nino3 extend further poleward on decadal time scales than they do on interannual time scales this explains why decadal enso like patterns have a broader meridional structure than their interannual counterparts this difference in appearance can occur even if enso indices do not have any predictability beyond interannual time scales the wings around 15 20 s and sub surface variability at many other locations are predictable on interannual and multi year time scales this includes westward propagating internal rws within about 25 of the equator the slowest of these take up to 4 years to reach the western boundary this sub surface predictability has significant oceanographic interest however it is linked to only low levels of sst variability consequently extrapolation of delayed action oscillator theory to decadal time scales might not be justified

warming and circulation change in the eastern south pacific ocean deep ocean temperature salinity and dissolved oxygen observations in the eastern south pacific ocean collected during the late austral fall in 1995 are compared with observations made there 28 years earlier during the same season and similar el nino southern oscillation phase warming observed above 800 m at 43 s reflects the production of warmer subantarctic mode water in recent decades warming observed above 1600 m at 28 s is due to downward isotherm displacement and southward movement of water masses by 100 200 km as revealed by joint analysis of temperature and oxygen data such changes would be expected for a weaker subtropical gyre in the south pacific an observed oxygen decrease between about 1800 m and 2900 m at 28 s may indicate enhanced southward boundary current flow at mid depths off chile

coupled pattern analysis of sea surface temperature and topex poseidon sea surface height abstract though thermal effects dominate steric changes in sea level the long period contribution of thermal expansion to sea level is uncertain nerem et al found that a global map of sea surface temperature sst trends and a corresponding map of topex poseidon derived sea surface height ssh trends were strongly correlated this result is explored with a coupled pattern analysis cpa between five years of global sst and ssh which allows for matching of modes of common temporal variability the dominant mode found is an annual cycle that accounts for nearly all 95 3 of the covariance between the fields and has a strong sst ssh spatial correlation 0 68 the spatial correlation is strong in both the atlantic 0 80 and the pacific 0 70 good temporal and spatial agreement between the ssh and sst fields for the primary seasonal mode suggests that a robust regression between fields may have some physical significance with respect to thermal expansion and that the regression coefficient might be

connections between the pacific ocean tropics and midlatitudes on decadal timescales abstract connections between the tropical and midlatitude pacific on decadal timescales are examined using a 137 yr run of a fully coupled ocean atmosphere general circulation model it is shown that the model does a credible job of simulating both enso scale and decadal scale variability and that there are statistically significant correlations between the midlatitudes and tropics on decadal timescales three physical mechanisms linking the regions are examined 1 oceanic advection along isopycnal surfaces from the midlatitude subduction regions to the tropics 2 coastally trapped or kelvin wave propagation between the tropics and midlatitudes and 3 near simultaneous communication between the regions affected by changes in the atmosphere it is found that communication via the atmosphere explains the strongest correlations found in the model further evidence is presented that is consistent with the idea that midlatitude sea surface temperature anomalies drive changes in the trade wind system that a

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

decadal scale variability of upper ocean heat content in the tropical pacific 1 decadal scale variability of upper ocean heat content ohc in the tropical pacific is investigated and is compared with that of enso scale the decadal scale ohc anomaly with a period of about 13 years shows anticlockwise propagations in the tropical north pacific like as that of enso scale it is also shown that the entire equatorial ohc anomaly leads nino 3 index anomaly by about a quarter about 3 years of the period of the decadal variability in the tropical pacific this time lag of a quarter of the period is consistent with the idea of the recharge oscillator model for enso dynamics further it is shown that the magnitude of leading ohc anomalies in the entire equatorial pacific is linearly related to the subsequent magnitudes of nino 3 and nino 3 4 indices this relationship is also similar with that of enso scale but there are several different points between them particularly in contrast with the enso scale the amplitude is larger in central equatorial pacific nino 3 4 region than in the eastern region nino 3 region

multidecadal fluctuations in the relationship between equatorial pacific heat content anomalies and enso amplitude 1 observations over the past 20 years indicate that equatorial pacific ocean heat content variations associated with el nino southern oscillation enso cycles lead sea surface temperature sst anomalies in the equatorial cold tongue by about 7 months however an asymmetry exists in the relationship between sst and heat content positive sst anomalies related to el nino are stronger than negative sst anomalies related to la nina for the same magnitude but opposite sign heat content anomaly in this study we analyse a multi century simulation using the csiro mark 3 coupled climate model to show that a similar asymmetry exists in some decades but not in others this non stationarity appears to be a consequence of modulations by a mode of multidecadal variability which affects the temperature of upwelled water and the efficiency with which upwelling generates sst anomalies

a delayed action oscillator shared by biennial interannual and decadal signals in the pacific basin 1 biennial interannual and decadal signals in the pacific basin are observed to share patterns and evolution in covarying sea surface temperature sst 18 c isotherm depth z18 zonal surface wind zsw and wind stress curl wsc anomalies from 1955 to 1999 each signal has warm sst anomalies propagating slowly eastward along the equator generating westerly zsw anomalies in their wake these westerly zsw anomalies produce cyclonic wsc anomalies off the equator which pump baroclinic rossby waves in the western central tropical north pacific ocean these rossby waves propagate westward taking 6 12 and 36 months to reach the western boundary near 7 n 12 n and 18 n on biennial interannual and decadal period scales respectively there they reflect as equatorial coupled waves propagating slowly eastward in covarying sst z18 and zsw anomalies taking 6 12 and 24 months to reach the central eastern equatorial ocean these equatorial coupled waves produce a delayed negative feedback to the warm sst anomalies there the decrease in rossby wave phase speed with latitude the increase in meridional scale of equatorial sst anomalies with period scale and the associated increase in latitude of rossby wave forcing are consistent with the delayed action oscillator dao model used to explain el nino however this is not true of the western boundary reflection of rossby waves into slow equatorial coupled waves this requires modification of the extant dao model we construct a modified dao model demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal

rossby wave coastal kelvin wave interaction in the extratropics part i low frequency adjustment in a closed basin abstract the interaction of open and coastal oceans in a midlatitude ocean basin is investigated in light of rossby and coastal kelvin waves the basinwide pressure adjustment to an initial rossby wave packet is studied both analytically and numerically with the focus on the low frequency modulation of the resulting coastal kelvin wave it is shown that the incoming mass is redistributed by coastal kelvin waves as well as eastern boundary planetary waves while the incoming energy is lost mostly to short rossby waves at the western boundary the amplitude of the kelvin wave is determined by two mass redistribution processes a fast process due to the coastal kelvin wave along the ocean boundary and a slow process due to the eastern boundary planetary wave in the interior ocean the amplitude of the kelvin wave is smaller than that of the incident planetary wave because the initial mass of the rossby wave is spread to the entire basin in a midlatitude ocean basin the slow eastern boundary planetary wave

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

a predictability study of simulated north atlantic multidecadal variability the north atlantic is one of the few places on the globe where the atmosphere is linked to the deep ocean through air sea interaction while the internal variability of the atmosphere by itself is only predictable over a period of one to two weeks climate variations are potentially predictable for much longer periods of months or even years because of coupling with the ocean this work presents details from the first study to quantify the predictability for simulated multidecadal climate variability over the north atlantic the model used for this purpose is the gfdl coupled ocean atmosphere climate model used extensively for studies of global warming and natural climate variability this model contains fluctuations of the north atlantic and high latitude oceanic circulation with variability concentrated in the 40 60 year range oceanic predictability is quantified through analysis of the time dependent behavior of large scale empirical orthogonal function eof patterns for the meridional stream function dynamic topography 170 m temperature surface temperature and surface salinity the results indicate that predictability in the north atlantic depends on three main physical mechanisms the first involves the oceanic deep convection in the subpolar region which acts to integrate atmospheric fluctuations thus providing for a red noise oceanic response as elaborated by hasselmann the second involves the large scale dynamics of the thermohaline circulation which can cause the oceanic variations to have an oscillatory character on the multidecadal time scale the third involves nonlocal effects on the north atlantic arising from periodic anomalous fresh water transport advecting southward from the polar regions in the east greenland current when the multidecadal oscillatory variations of the thermohaline circulation are active the first and second eof patterns for the north atlantic dynamic topography have predictability time scales on the order of 10 20 y whereas eof 1 of sst has predictability time scales of 5 7 y when the thermohaline variability has weak multidecadal power the hasselmann mechanism is dominant and the predictability is reduced by at least a factor of two when the third mechanism is in an extreme phase the north atlantic dynamic topography patterns realize a 10 20 year predictability time scale additional analysis of sst in the greenland sea in a region associated with the southward propagating fresh water anomalies indicates the potential for decadal scale predictability for this high latitude region as well the model calculations also allow insight into regional variations of predictability which might be useful information for the design of a monitoring system for the north atlantic predictability appears to break down most rapidly in regions of active convection in the high latitude regions of the north atlantic

on the predictability of decadal changes in the north pacific the predictability of decadal changes in the north pacific is investigated with an ocean general circulation model forced by simplified and realistic atmospheric conditions first the model is forced by a spatially fixed wind stress anomaly pattern characteristic for decadal north pacific climate variations the time evolution of the wind stress anomaly is chosen to be sinusoidal with a period of 20 years in this experiment different physical processes are found to be important for the decadal variations baroclinic rossby waves dominate the response they move westward and lead to an adjustment of the subtropical and subpolar gyre circulations in such a way that anomalous temperatures in the central north pacific develop as a delayed response to the preceding wind stress anomalies this delayed response provides not only a negative feedback but also bears the potential for long term predictions of upper ocean temperature changes in the central north pacific it is shown by additional experiments that once these rossby waves have been excited decadal changes of the upper ocean temperatures in the central north pacific evolve without any further anomalous atmospheric forcing in the second part the model is forced by surface heat flux and wind stress observations for the period 1949 1993 it is shown that the same physical processes which were found to be important in the simplified experiments also govern the evolution of the upper ocean in this more realistic simulation the 1976 77 cooling can be mainly attributed to anomalously strong horizontal advection due to the delayed response to persistent wind stress curl anomalies in the early 1970s rather than local anomalous atmospheric forcing this decadal change could have been predicted some years in advance the subsequent warming in the late 1980s however cannot be mainly explained by advection in this case local anomalous atmospheric forcing needs to be considered

a conceptual model of ocean heat uptake under climate change abstracta conceptual model of ocean heat uptake is developed as a multilayer generalization of gnanadesikan the roles of southern ocean ekman and eddy transports north atlantic deep water nadw formation and diapycnal mixing in controlling ocean stratification and transient heat uptake are investigated under climate change scenarios including imposed surface warming increased southern ocean wind forcing with or without eddy compensation and weakened meridional overturning circulation moc induced by reduced nadw formation with realistic profiles of diapycnal mixing ocean heat uptake is dominated by southern ocean ekman transport and its long term adjustment controlled by the southern ocean eddy transport the time scale of adjustment setting the rate of ocean heat uptake increases with depth for scenarios with increased southern ocean wind forcing or weakened moc deepened stratification results in enhanced ocean heat uptake in each of these experiments the role of diapycnal mixing in settin

tropical pacific decadal variability and the subtropical tropical cells abstract the decadal scale variability in the tropical pacific has been analyzed herein by means of observations and numerical model simulations the two leading modes of the sea surface temperature sst variability in the central western pacific are a decadal mode with a period of about 10 yr and the enso mode with a dominant period of about 4 yr the sst anomaly pattern of the decadal mode is enso like the decadal mode however explains most variance in the western equatorial pacific and off the equator a simulation with an ocean general circulation model ogcm forced by reanalysis data is used to explore the origin of the decadal mode it is found that the variability of the shallow subtropical tropical overturning cells is an important factor in driving the decadal mode this is supported by results from a multicentury integration with a coupled ocean atmosphere general circulation model cgcm that realistically simulates tropical pacific decadal variability finally the sensitivity of the shal

decadal upper ocean temperature variability in the tropical pacific decadal variability in upper ocean temperature in the pacific is studied by using observations and results from model experiments especially propagation of upper ocean thermal anomalies from the midlatitudes to the tropics is studied as a possible source for decadal equatorial thermocline variability in the observations propagation along the subtropical gyre of the north pacific is clear however no propagation into the equatorial region is found model experiments with an ocean model forced with observed monthly wind and wind stress anomalies are performed to study the apparent propagation distinct propagation of thermal anomalies in the subtropics is found in the model although the amplitude of the anomalies is small the anomalies clearly propagate into the tropics but they do not reach the equatorial region the small response at the equator to extratropical variability consists of a change in the mean depth of the thermocline it appears that most variability in the subtropics and tropics is generated by local wind stress anomalies the results are discussed by using results from a linear shallow water model in which similar features are found

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

postglacial rebound and sea level contributions to changes in the geoid and the earth s rotation axis summary the rate of change of the spherical harmonic degree 2 component of the earth s gravitational potential coa 20 and polar wander velocity are two signals which are sensitive to late pleistocene deglaciation current changes in sea level and deep mantle viscosity diierent load and earth models have been used in earlier papers to predict the component of these geophysical signals caused by the collapse of the last great ice sheets and recent melting of polar ice caps in this paper we present a systematic analysis of the dependence of the predictions on parameters of the ice and earth model we show that the key parameters of the ice model which govern the predictions are the mass the location of the centre of mass and the midpoint of the deglaciation phase of secondary importance is the length of the deglaciation phase and the mean ice load prior to the last glacial maximum these conclusions enable us to make a more robust inference of mantle viscosity than has been made before allowing for the uncertainties in the model of late pleistocene and present deglaciation as previous authors have shown the lower mantle viscosity is the most important rheological parameter and therefore thecoa 20 observation complements sea level observations which are primarily sensitive to lithospheric thickness and the viscosity of the upper part of the mantle using realistic constraints on the sizes locations and timing of deglaciation of the late pleistocene ice sheets and current changes in polar ice caps the observation of coa 20 is used to infer lower mantle viscosity as a function of the present rate of sea level change if the present rate of non steric sea level change is 1 mm yr 1 and that change has been occurring for less than 1000 years then the lower mantle viscosity satis es log10 glm 21 82 0 15 which is consistent with inferences drawn from recent sea level analyses and con rms other analyses of thecoa 20 observation if the polar wander signal is produced entirely by postglacial rebound and current sea level change no more than 20 per cent of the present contribution to global sea level change comes from greenland the above conclusions also hold if the density discontinuities at 420 and 670 km are modelled as phase boundaries rather than material chemical boundaries

enso like interdecadal variability in the pacific ocean as simulated in a coupled general circulation model spatial and temporal structures of interdecadal variability in the pacific ocean are investigated using results from an atmosphere ocean coupled general circulation model aogcm the model shows a basin wide spatial pattern of the principal sea surface temperature sst variability similar to the observed one both interdecadal and interannual temporal structures of the sst variability agree well between the observation and the aogcm on the other hand a slab ocean model coupled to the same atmospheric model as the aogcm fails to simulate the observed temporal structure therefore the timescale of the coupled variability is associated with dynamical processes in the ocean a distinct interdecadal mode of the coupled atmosphere upper ocean temperature variability is found in the aogcm with a spatiotemporal structure coherent with the sst variability the mode accompanies an el nino southern oscillation enso like spatial pattern of sst and the surface wind and behaves like a delayed oscillator in enso a wedge shaped anomaly pattern of the upper thermocline temperature is formed in the eastern pacific and its northern subtropical signal propagates westward enhanced by a subtropical wind forcing at the central basin arrival of the subtropical signal at the western pacific around 20 n switches the anomaly of subsurface temperature in the equatorial region through anomalous oceanic heat transport along the western boundary the travel time of the trans pacific signal in the subtropics appears to be responsible for the timescale of this mode the aogcm successfully simulated the second mode of sst with a major variation in the midlatitude north pacific as in the observed sst in the upper ocean heat content we found another distinct mode which is characterized by a midlatitude subtropics dipole pattern migrating around the north pacific subtropical gyre however the associated sst variation of this mode shows a poor correspondence in the dominant interdecadal modes for the observed sst

formation mechanism for isopycnal temperature salinity anomalies propagating from the eastern south pacific to the equatorial region abstract equatorward propagation of temperature salinity or spiciness anomalies on an isopycnal surface emanating from the eastern subtropical south pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy resolving quasi global ocean general circulation model because of density compensating meridional distributions of temperature and salinity the meridional density gradient is weak at the sea surface in the eastern subtropical south pacific with these mean fields cool sea surface temperature anomalies sstas can make the outcrop line of an isopycnal surface migrate equatorward more than 5 and induce warm and salty anomalies on the isopycnal surface subducted warm salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature salinity anomalies although the associated effects are unclear if these anomalies could further induce warm eastern equatorial sstas that are positively correlated wit