predicting north atlantic sea surface temperature variability on the basis of the first mode baroclinic rossby wave model 1 predictability of sea surface temperature sst variations over the north atlantic ocean is studied on the basis of the first mode baroclinic rossby wave model this simple linear wave model can explain about 10 46 of the wintertime sst variability in several regions of the north atlantic basin including the tropics between 5 n and 20 n the eastern subtropics between 27 n and 34 n and the east of newfoundland it is shown that the wintertime sst anomalies can be skillfully predicted up to 3 months ahead in the tropical atlantic 18 months in the eastern subtropical atlantic and 3 years east of newfoundland on the basis of the first mode baroclinic rossby wave adjustment

north atlantic subtropical mode waters and ocean memory in hadcm3 abstract a study of the formation and propagation of volume anomalies in north atlantic mode waters is presented based on 100 yr of monthly mean fields taken from the control run of the third hadley centre coupled ocean atmosphere gcm hadcm3 analysis of the temporal and spatial variability in the thickness between pairs of isothermal surfaces bounding the central temperature of the three main north atlantic subtropical mode waters shows that large scale variability in formation occurs over time scales ranging from 5 to 20 yr the largest formation anomalies are associated with a southward shift in the mixed layer isothermal distribution possibly due to changes in the gyre dynamics and or changes in the overlying wind field and air sea heat fluxes the persistence of these anomalies is shown to result from their subduction beneath the winter mixed layer base where they recirculate around the subtropical gyre in the background geostrophic flow anomalies in the warmest mode 18 c formed on the western

the estimation of global sea level change a problem of uniqueness an objective method of estimating regional averages of coherent sea level sl change is developed the technique is applied to a large set of sl data representative of most of the world s continental margins the results show highly coherent sl changes over many of the regions studied the method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of sl variations existing in the historical sl data set the pattern is characterized by a coherent rise of sl in all regions except alaska scandinavia both areas of notorious crustal uplift and southeast asia where sl appears to be falling the analysis suggests little or no change in sl prior to the early 1900 s the period since that time has seen an increase in sl that is optimally fit by a linear trend of 23 cm century the study results suggest that it is not possible to uniquely determine either a global rate of change of sl or even the average rate of change associated with the existing inadequate data set indeed different analysis methods by themselves can cause 50 variations in the estimates of sl trend in the existing data set a signal noise analysis suggests it should be easy to detect small future changes in the sl trends estimated for the period 1930 1980 however detection of theoretically predicted low frequency signals e g caused by co2 warming will be difficult in view of the huge low frequency natural variability associated with glacial tectonic processes

the long term hydrographic record at bermuda abstract a long by oceanographic standards time series of hydrographic observations at bermuda was begun in 1954 and continues to the present analysis of this dataset has shown the temperature and salinity variations on interannual timescales to be largely independent in the surface layer 0 200 dbar where integral timescales for salinity are 50 longer than for temperature and surface salinity changes are correlated with decadal changes in the 18 c water production temperature salinity anomalies are highly correlated in the thermocline where the interannual variability at that level is accountable to either vertical oscillations of the thermocline with amplitudes of 50 m or meridional oscillations of the horizontal gradient set up at the southern edge of the recirculation gyre of 300 kim salinity changes in the deepest layer observed at bermuda station s 1500 2500 dbar are uncorrelated with temperature masked by measurement errors in the early years of the time series inclusion of earlier

buoyancy driven interannual sea level changes in the southeast tropical pacific 1 it is commonly held that interannual to decadal sea level variability patterns mainly represent the ocean s response to wind forcing this view is based in part on modeling studies of wind driven sea level changes along the tropical pacific however because buoyancy forcing and other generating mechanisms are usually ignored this paradigm may overemphasize the role of winds focusing on the southeast tropical pacific we use a data constrained ocean state estimate to demonstrate that distinct mechanisms including the ocean s response to buoyancy forcing as well as nonlinear processes can also contribute to interannual sea level variability contrary to the notion that buoyancy driven sea level changes are dynamically passive such changes exhibit a strongly nonlocal dynamically active character made manifest in westward propagating waves as similar findings apply elsewhere accurate modeling of interannual to decadal regional sea level changes requires consideration of a variety of forcing mechanisms including but not limited to the winds

variability of sea surface height and circulation in the north atlantic forcing mechanisms and linkages abstract simulations with a coarse resolution global ocean model during 1958 2004 are analyzed to understand the inter annual and decadal variability of the north atlantic analyses of empirical orthogonal functions eofs suggest relationships among basin scale variations of sea surface height ssh and depth integrated circulation and the winter north atlantic oscillation nao or the east atlantic pattern eap indices the linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability in the subpolar region variations of the gyre strength ssh in the central labrador sea and the nao index are highly correlated surface heat flux is important in driving variations of ssh and circulation in the upper ocean and decadal variations of the atlantic meridional overturning circulation amoc surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the amoc in the subtropical region momentum flux plays a dominant role in driving variations of the gyre circulation and amoc there is a strong correlation between gyre strength and ssh at bermuda

on the observability of oceanic gyres abstractthis study examines the observability of a stratified ocean in a square flat basin on a midlatitude beta plane here observability means the ability to establish in a finite interval of time the time dependent ocean state given density observations over the same interval and with no regard for errors the dynamics is linearized and hydrostatic so that the motion can be decomposed into normal modes and the observability analysis is simplified an observability gramian a symmetric matrix is determined for the flows in an inviscid interior in frictional boundary layers and in a closed basin its properties are used to establish the condition for complete observability and to identify optimal data locations for each of these flows it is found that complete observability of an oceanic interior in time dependent sverdrup balance requires that the observations originate from the westernmost location at each considered latitude the degree of observability increases westward due to westward prop

interannual baroclinic rossby waves in the midlatitude north atlantic abstract twenty six year time sequences of upper thermocline temperature block averaged in 5 degree latitude and longitude squares reveal strong in phase vertical coherence and low to moderate horizontal coherence over 550 km least squares fitting theoretical cross spectra from a stochastic first baroclinic mode rossby wave model to cross spectra of the temperature time sequences yields several best fit wavenumber vectors that conform to the dispersion relation of first baroclinic mode rossby waves in a flat bottom ocean with no mean current the slope of the midocean ridge which is as important as midlatitude beta and the mean circulation were ignored about 25 55 of the cross spectral energy can be attributed to the best fit waves a composite spectrum of the baroclinic potential energy of all the demonstrated rossby waves is qualitatively similar to the spectrum of north pacific first baroclinic mode rossby waves showing a peak around 6 7 years but is 30 times larger in magnitude the geograph

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

can long term variability in the gulf stream transport be inferred from sea level recent studies by sturges and collaborators suggest a simple but powerful technique to estimate climatic changes in the transport of the gulf stream from the difference between the oceanic sea level calculated with a simple wind driven rossby wave model and the observed coastal sea level the hypothesis behind this technique is tested using 40 years of data 1950 to 1989 obtained from a three dimensional atlantic ocean model forced by observed surface data the analysis shows that variations in sea level difference between the ocean and the coast are indeed coherent with variations of the gulf stream transport for periods shorter than 1 year or longer than 4 5 years the results obtained from the three dimensional model confirm the findings of the simple rossby wave model that decadal climatic changes in the gulf stream transport vary considerably with latitude

a description of coads surface meteorological fields and the implied sverdrup transports for the atlantic ocean from 30 s to 60 n abstract using coads data spanning 1947 1988 we describe the regional nature of the atlantic ocean wind driven circulation between 30 8 and 60 n and its annual and interannual variability the sverdrup streamfunction defines the circulation gyres our focus is on three central gyres the northern hemisphere anticyclonic subtropical gyre the cyclonic tropical gyre just north of the equator and the clockwise equatorial gyre straddling the equator this rendition of the sverdrup streamfunction computed with constant drag coefficient and air density compares favorably with that from other climatologies in the straits of florida analyses suggest that differences between the annual cycle in sverdrup transport and observations may be due to regional winds farther north in the tropical gyre the sverdrup circulation argues against a continuous western boundary current transporting water from the equatorial region into the caribbean in boreal winter bringing to question the mechanisms for the known interh

mechanisms of decadal north atlantic climate variability and implications for the recent cold anomaly decadal sea surface temperature sst fluctuations in the north atlantic ocean influence climate over adjacent land areas and are a major source of skill in climate predictions however the mechanisms underlying decadal sst variability remain to be fully understood this study isolates the mechanisms driving north atlantic sst variability on decadal time scales using low frequency component analysis which identifies the spatial and temporal structure of low frequency variability based on observations large ensemble historical simulations and pre industrial control simulations we identify a decadal mode of atmosphere ocean variability in the north atlantic with a dominant time scale of 13 18 years large scale atmospheric circulation anomalies drive sst anomalies both through contemporaneous air sea heat fluxes and through delayed ocean circulation changes the latter involving both the meridional overturning circulation and the horizontal gyre circulation the decadal sst anomalies alter the atmospheric meridional temperature gradient leading to a reversal of the initial atmospheric circulation anomaly the time scale of variability is consistent with westward propagation of baroclinic rossby waves across the subtropical north atlantic the temporal development and spatial pattern of observed decadal sst variability are consistent with the recent observed cooling in the subpolar north atlantic this suggests that the recent cold anomaly in the subpolar north atlantic is in part a result of decadal sst variability

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

bermuda s tale of two time series hydrostation s and bats abstract this paper describes the oceanic variability at bermuda between 1989 and 1999 recorded in two overlapping hydrographic time series station s and bermuda atlantic time series study bats which are 60 km apart both show that a multidecadal trend of deep warming has reversed likely as a result of the increased production of labrador sea water since the early 1980s in addition to recording similar changes in watermass properties the two time series show similar mean vertical structure and variance as a function of pressure for temperature salinity and density above 1500 dbar the seasonal cycles of these water properties at the two sites are statistically indistinguishable the time series differ in the individual eddy events they record and in their variability below 1500 dbar the two time series are used to investigate the propagation of eddy features coherence and phase calculated from the low mode variability of density show westward propagation at 3 cm s 1 of wavelengths around 300

wind forcing of the atlantic thermocline along 32 n at low frequencies abstract the bermuda tide gauge record extends back to the early 1930s that sea level fluctuations there are highly coherent with dynamic height from hydrographic data has two interesting implications first it should contain information about the low frequency circulation of the atlantic furthermore because dynamic height contains information on heat storage it might on the limited timescales accessible in the record also contain clues about climate a simple model of wind forcing of the atlantic from the african coast to bermuda uses the levitus mean density data to estimate the long rossby wave speed as a function of longitude sea level and thermocline variability estimated this way are in remarkably good agreement with observations at periods of more than a few years duration the peak to peak sea level signal is 18 cm which is nearly 25 of the slope across the gulf stream at this latitude the model results suggest that the variability is largest somewhat to the east of bermuda fluctuatio

solar modulation of north atlantic central water formation at multidecadal timescales during the late holocene article i nfo understanding natural climate variability in the north atlantic region is essential not only to assess the sensitivity of atmosphere ocean climate signal exchange and propagation but also to help distinguish between natural and anthropogenic climate change the north atlantic oscillation is one of the controlling modes in recent variability of atmosphere ocean linkages and ice freshwater fluxes between the polar and north atlantic ocean through these processes the nao influences water mass formation and the strength of the atlantic meridional overturning circulation and thereby variability in ocean heat transport however the impact of the nao as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on eastern north atlantic central water production central water circulation and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain here we use a 1200 yr long benthic foraminiferal mg ca based temperature and oxygen isotope record from a 900 m deep sediment core off northwest africa to show that atmosphere ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre further we link the variability of the nao over the past 165 yrs and solar irradiance late holocene and their control on subpolar mode water formation to the multidecadal variability observed at mid depth in the eastern subtropical gyre our results show that eastern north atlantic central waters cooled by up to 0 8 0 7 c and densities decreased by 0 3 0 2 during positive nao years and during minima in solar irradiance during the late holocene the presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross gyre climate signal propagation during the late holocene 2011 elsevier b v all rights reserved

interpentadal variability of steric sea level and geopotential thickness of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited and objectively analyzed historical hydrographic observations for the north atlantic ocean for two periods 1955 1959 and 1970 1974 difference fields of steric sea level and geopotential thickness for the north atlantic ocean in the 0 to 1500 m depth range between the 1955 1959 and 1970 1974 pentads were computed we find that in the central portion of the subtropical gyre steric sea level decreased by up to 17 5 dyn cm whereas in the western subarctic gyre north of the gulf stream steric sea level increased by an amount up to 7 5 dyn cm from the earlier to the later pentad a decrease in steric sea level 5 dyn cm occurred along the eastern boundary of the north atlantic

a study of temperature changes in the upper north atlantic 1950 94 in this paper decadal evolution of warm and cold anomalies in the subtropical and subpolar gyres of the north atlantic in the 300 500 m and 100 250 m depth ranges is described a series of pentadally averaged objective maps of upper ocean thermal anomalies from bathythermograph data are presented warm and cold anomalies in the western subtropical gyre are succeeded by similar anomalies in the subpolar gyre and the east atlantic and subtropical return flow major warm and cold anomalies in the 1950s and 1970s respectively are similar to those described previously in ssts although there is more temporal continuity in the subsurface anomalies two very strong events in the subtropical gyre are identified a cold anomaly in 1966 72 and an intense warm anomaly in 1988 94 that show the greatest temperature anomalies in the north atlantic during the period of the study interisotherm thickness anomalies are shown for the subtropical gyre during these periods in the warm period mode waters are both warmer 188 198c and of greater volume than on average and lie in a narrow band south of the gulf stream above a depressed thermocline with warm temperature anomalies to at least 800 m depth in the cold period the predominant mode water temperature is closer to 178c but there is reduced water formation overall with a raised thermocline and cold temperature anomalies down to 600 m depth the bowl of the gyre is flat during the cold period and the implied recirculation may be weaker and extend farther to the south the changes appear to be consistent with the intensification of the subtropical gyre in the warm period and a spindown in the cold period although the relative roles of wind stress and air sea heat fluxes in these changes need to be determined

temperature fluctuation in muddy intertidal sediments forth estuary scotland abstract temperatures in muddy intertidal sediments exhibit rapid changes which occur principally during tidal inundation observations of sub surface temperature were made from an instrument tower in the forth estuary scotland observed rates of temperature change were compared with theoretical rates which would result from molecular diffusion of heat through the mud the discrepancy between observation and theory was likely to be due to rapid non diffusive heat transfers resulting from the movement of water through non capillary pore spaces created by faunal activity

mechanisms of eddy driven variability of the florida current abstractin this study mechanisms causing year to year changes in the florida current seasonality are investigated using controlled realistic numerical experiments designed to isolate the western b

annual variation of the kuroshio transport in a two layer numerical model with a ridge abstract a two layer numerical model driven by the wind stress is used to explain the observed annual variation of the kuroshio transport south of japan special attention is given to the effect of a ridge representing the izu ogasawara ridge on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion for annual variation lower layer motion is found in areas surrounding the ridge because isostasy a state of no motion in the lower layer is not achieved within such a short timescale thus the lower layer flow impinges on the bottom slope this impinging process generates anomalies of the upper layer thickness especially on the eastern side of the ridge thereafter anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic rossby wave forced above the ridge as anomalies of the upper layer thickness move westward above the ridge isostasy is accomplished with res

modelling hydrographic changes in the labrador sea over the past five decades abstract inter annual to inter decadal changes of hydrographic structure and circulation in the subpolar north atlantic are studied using a coarse resolution ocean circulation model the study covers 1949 through 2001 inclusive a time mean state nudging method is applied to assimilate the observed hydrographic climatology into the model the method significantly reduces model biases in the long term mean distribution of temperature and salinity which commonly exist in coarse resolution ocean models by reducing the time mean biases we also significantly improve the model s representation of inter annual to inter decadal variations in the central labrador sea the model broadly reproduces the heat and salt variations of the labrador sea water lsw as revealed by hydrographic observations model sensitivity experiments confirm that the low frequency hydrographic changes in the central labrador sea are closely related to changes in the intensity and depth of deep convection changes in surface heat flux associated with the winter north atlantic oscillation nao index play a major role in driving the changes in t s and sea surface height ssh changes in wind stress play a secondary role in driving these changes but are important in driving the changes in the depth integrated circulation the total changes in both ssh and depth integrated circulation are almost a linear combination of the separate influences of variable buoyancy and momentum fluxes

body wave amplitude and travel time correlations across north america relationships between travel time and amplitude station anomalies are examined for short and long period sh waves and short period p waves recorded at north american wwssn and canadian seismic network stations data for two azimuths of approach to north america are analyzed to facilitate intercomparison of the data the s wave travel times and amplitudes are measured from the same records and the amplitude data processing is similar for both p and s waves short period p and s wave amplitudes have similar regional variations being relatively low in the western tectonic region and enhanced in the shield and mid continental regions the east coast has intermediate amplitude anomalies and systematic large azimuthal travel time variations there is a general correlation between diminished short period amplitudes and late s wave arrival times and enhanced amplitudes and early arrivals however this correlation is not obvious within the eastern and western provinces separately and the data are consistent with a step like shift in amplitude level across the rocky mountain front long period s waves show no overall correlation between amplitude and travel time anomalies

on the propagation of baroclinic waves in the general circulation the propagation of long first mode baroclinic planetary waves in eddy resolving quasigeostrophic general circulation models is studied recent topex poseidon observations argue oceanic first mode planetary waves move with speeds other than those predicted by simple theory these data have prompted theoretical analyses of wave propagation in a mean flow with the results suggesting mean shear can have a controlling effect on the planetary wave guide some of the predicted effects appear to be relevant to the observations while others are less obvious this coupled with other explanations for the observations motivates the calculations based on these experiments the authors suggest that the predicted effects of mean shear on wave propagation are consistent with those computed in a fully geostrophically turbulent ocean these are that a two layer model misses the dominant component of long wave interaction with a mean flow a three layer model captures this interaction qualitatively and the correction to wave propagation is in the direction opposite to the mean flow quantitative comparisons between the theory and the numerical experiments are good in the northern latitudes and questionable in the southern latitudes reasons for the southern discrepancy are offered

sea level on the u s east coast decadal variability caused by open ocean wind curl forcing one of the puzzling features of sea level on the east coast of the united states is the decedal scale variability the fluctuations are 10 15 cm peak to peak at periods longer than a few years the authors find that this variability in the frequency band treated with the model is largely caused by a deep sea signal generated by the wind stress curl over the north atlantic a simple forced long rossby wave model of the response of the thermocline to wind forcing is used computing long wave speeds from observed hydrographic data the authors model the response of the ocean at periods longer than 3 years for the full width of the atlantic and for the north south extent of the main anticyclonic gyre 188 388n the model output in deep water shows remarkably good agreement with tide gauges both at bermuda 328n and puerto rico 188n as well as with dynamic height fluctuations of 20 cm peak to peak once these fluctuations reach the western side of the ocean the authors estimate coastal sea level by constructing a complementary coastal model the coastal model is geostrophic and conserves mass within a nearshore region that encompasses the gulf stream by extending this nearshore region as far south as 148 188n and using only the oceanic fluctuations to force the variability in the stream between 80 and 90 of the variance of sea level at coastal tide gauges can be explained sea level along the coast is used to test the model assumptions the basic results however seem important because they are constrained only by open ocean wind forcing and not by input boundary conditions

an idealized model study of the mass and heat transports between the subpolar and subtropical gyres abstract the response of an ocean model of the subtropical and subpolar gyres to idealized surface forcing anomalies that mimic the thermal and mechanical forcing associated with the north atlantic oscillation nao is analyzed emphasis is given on the subpolar gyre and the mechanisms that drive the mass and heat exchanges between the two gyres first steady anomalies are applied surface heat flux anomalies induce density gradient anomalies at depth which drive current anomalies reinforcing the north eastward mean current separating the two gyres the northward heat transport of these anomalous currents is 10 times stronger than that associated with the transport of temperature anomalies by the mean current the heat transport anomalies between the two gyres balances the prescribed surface heat flux after 6 7 yr a similar mechanism is at work when a decadal harmonic forcing is considered but the lag is shortened to 3 4 yr the model response to a wind stress curl anomaly shows a similar behavior to

thermocline forced by varying ekman pumping part ii annual and decadal ekman pumping abstract thermocline variability forced by zonally uniform ekman pumping with annual to decadal periods is investigated both analytical and numerical solutions are obtained by the method of characteristics as found in part i there is little thermocline variability in the ventilated zone or pool zone in contrast strong variability may exist in the shadow zone for annual forcings nonlinearity is negligible however the linear solution is influenced substantially by the basic state thermocline structure as a result local responses dominate for a shallow interface while remote rossby waves dominate for a deep interface under a strong decadal forcing nonlinearity may become important the time mean thermocline in the shadow zone is shallower than the steady thermocline under the mean ekman pumping particularly in the western part of a shadow zone where the mean deviation may reach the order often meters this shallower mean thermocline is caused by the nonlinear rossby wave

the effect of bottom pressure decoupling on the speed of extratropical baroclinic rossby waves abstract in layered models of the ocean the assumption of a deep resting layer is often made motivated by the surface intensification of many phenomena the propagation speed of first mode baroclinic rossby waves in such models is always faster than in models with all the layers active the assumption of a deep resting layer is not crucial for the phase speed enhancement since the same result holds if the bottom pressure fluctuations are uncorrelated from the overlying wave dynamics in this paper the authors explore the relevance of this behavior to recent observational estimates of too fast waves by chelton and schlax the available evidence supporting this scenario is reviewed and a method that extends the idea to a continuously stratified fluid is developed it is established that the resulting amplification factor is at leading order captured by the formula where cfast is the enhanced phase speed cstandard the standard phase speed 1 z is the standard first mode for the velocity and pressur

on the relationship between decadal buoyancy anomalies and variability of the atlantic meridional overturning circulation abstractowing to the role of the atlantic meridional overturning circulation amoc in ocean heat transport amoc variability is thought to play a role in climate variability on a wide range of time scales this paper focuses on the potential role of the amoc in climate variability on decadal time scales coupled and ocean only general circulation models run in idealized geometries are utilized to study the relationships between decadal amoc and buoyancy variability and determine whether the amoc plays an active role in setting sea surface temperature on decadal time scales decadal amoc variability is related to changes in the buoyancy field along the western boundary according to the thermal wind relation buoyancy anomalies originate in the upper ocean of the subpolar gyre and travel westward as baroclinic rossby waves when the buoyancy anomalies strike the western boundary they are advected southward by the deep western boundary current leading to latitudinally coherent amoc variability the amoc i

sofar floats reveal midlatitude intermediate north atlantic general circulation part ii an eulerian statistical view abstract part i of this paper has given a descriptive view of the trajectories of 26 sofar floats drifting near 700 m depth in the central north atlantic during the mid 1980s as part of the topogulf experiment here an eulerian analysis of the 53 4 collected float years is performed by grouping data in 2 latitude 4 longitude boxes the mean circulation lacks a significant southward sverdrupian flow and shows instead zonal bands of alternating westward and eastward currents except in the canary basin west of the ridge and north of 38 n the general northeastward flow of the gulf stream system is recovered while south of 38 n the westward recirculation observed from historical float data between 70 and 55 w is shown to extend as far as 40 w a mean azores current is observed both west of the ridge near 33 n and east of 30 w near 34 n in between east of the ridge a tongue of high eddy energy indicates stronger eddy activity and local instabilities of the azores current eddy kinetic energy and e

decadal wind forcing of the north atlantic subtropical gyre abstract in the central north atlantic ocean there are large decadal scale fluctuations of sea level and of the depth of the thermocline this variability can be explained by low frequency rossby waves forced by wind the authors have used a simple model of ocean fluctuations driven by the coads wind stress curl and find that their model results and hydrographic data to the limited extent they can be compared meaningfully agree rather well the variation in wind curl over the ocean leads to surprisingly large north south variability in the computed oceanic response over the subtropical gyre the peak to peak sea level differences are as great as 20 cm and persist for many years these large variations could induce major errors in calculations of the mean ocean flow when hydrographic sections from many years are combined it appears possible however to correct for these wind induced effects to allow the lower frequency signals to be determined the westernmost edge of our oceanic calculations is at the