propagation of signals in basin scale ocean bottom pressure from a barotropic model 1 the exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model we find two particular cases of exchange between two basins at periods of 4 6 days the exchange is between the atlantic and pacific basins and represents a known oscillation forced by atmospheric pressure this mode represents a failure of the inverse barometer relationship due to the large scale and high frequency of atmospheric forcing and the presence of continents significant exchange between atlantic and pacific also occurs at longer periods the second case is most prominent at periods longer than 30 days strongest at periods longer than 100 days and represents a mass exchange between the southern ocean and the pacific the southern ocean part of this exchange is clearly related to the southern mode of fluctuations in antarctic circumpolar transport forced by southern ocean wind stress the reason for the exchange being with the pacific rather than other basins is explored and is found to be related to the balance of wind stress by form stress in drake passage exchange with the atlantic and indian oceans becomes dominant if drake passage topography is removed while recognizing the limitations of a barotropic model we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes accordingly we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics

variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

seasonal and interannual global surface mass variations from multisatellite geodetic data 1 monthly global surface mass distribution changes are estimated in the spherical harmonic domain with a complete spectrum up to degree and order 50 the estimates are derived by inverting gps displacement series measured at roughly 450 continuously tracking sites and ocean bottom pressure obp estimates of a data assimilated ocean circulation model from 1993 to 2004 the inversion uses a hybrid estimator after singular value decomposition of the normalized measurement equations with reduced reliance on a priori spectral information the results are then compared and combined with gravity recovery and climate experiment grace gravity data to provide enhanced spectral and geographic coverage high fidelity degree 1 surface mass variation coefficients are recovered corresponding to equivalent geocenter motion with better than 0 5 mm annual amplitude precisions in all three components a clear annual surface mass cycle occurs in both gps obp and grace derived results there is very good agreement among the low degree spherical harmonic coefficients and in global geographic pattern but with significant regional differences in amplitudes annual variations of average mass over the global oceans antarctica and greenland are then derived total surface mass over both antarctica and greenland peak in their respective summers due to increased atmospheric mass large interannual variations have also been found involving several continents in the 11 year gps obp solution the patterns of variation suggest that the recent satellite laser ranging slr observation of a reversal in trend of the earth s oblateness may be largely an interannual surface mass cycle with considerable contribution from the northern continents

atmospheric patterns forcing two regimes of arctic circulation a return to anticyclonic conditions atmospheric sea level pressure slp patterns associated with two regimes of ice ocean circulation are identified by sorting the data into bins depending on whether modeled arctic ocean circulation was anticyclonic or cyclonic the transition between regimes is a zonally symmetric slp cell with maximum amplitude at the north pole from 1946 to 1997 four anticyclonic and four cyclonic regimes track the arctic ocean slp oscillation recent slp data suggest that the ocean atmosphere system will shift or has already shifted to an anticyclonic state

recent earth oblateness variations unraveling climate and postglacial rebound effects earth9s dynamic oblateness j2 has been decreasing due to postglacial rebound pgr however j2 began to increase in 1997 indicating a pronounced global scale mass redistribution within earth9s system we have determined that the observed increases in j2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the southern pacific and indian oceans when these effects are removed the residual trend in j2 2 9 x 10 11 year 1 becomes consistent with previous estimates of pgr from satellite and eclipse data the climatic significance of these rapid shifts in glacial and oceanic mass however remains to be investigated

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

departures from the local inverse barometer model observed in altimeter and tide gauge data and in a global barotropic numerical model sea level data from the topex poseidon altimeter satellite and from subsets of the global tide gauge and bottom pressure recorder networks have been employed to study the worldwide distribution of departures from the simple local inverse barometer lib model from a combination of measurement techniques the lib model was found to provide a reasonable representation of the data within 5 10 outside of the tropics for timescales from several days to several weeks for most locations however several parts of the southern ocean and other higher latitude areas were seen from the altimetry to contain significant departures across the range of timescales accessible for study by the technique within the tropics the response of sea level to air pressure forcing was observed to be typically 50 of that of the lib model at timescales of several days with considerable spatial variation and to approximate the lib model more closely at timescales of several weeks a coarse grid global barotropic numerical model was found to reproduce qualitatively the global average response as a function of frequency to simulate many of the characteristics of the spatial variation of the response and to demonstrate the relative importance of air pressure and wind forcing at different timescales data sets from the permanent service for mean sea level and u k meteorological office were used to investigate lib departures at intraseasonal and longer timescales along continental coastlines and at ocean islands increasingly large departures were observed along many parts of the world coastline as timescales increased from months to seasons

coherence of antarctic sea levels southern hemisphere annular mode and flow through drake passage 1 it is known from small sets of tide gauges that sub surface pressure sea level corrected for the inverse barometer effect around antarctica varies coherently around about half of the continent and that this coherent signal is related to atmospheric forcing in the form of the antarctic oscillation or southern hemisphere annular mode we here confirm that this coherence extends to a more extensive network of tide gauges and to parts of the continental shelf far from the shore as measured by bottom pressure gauges we use time series from an eddy permitting ocean model with realistic forcing to relate the coherent mode to fluctuations in transport through drake passage and confirm using a 1 resolution barotropic model that the fluctuations are predominantly due to barotropic dynamics although baroclinic dynamics are expected to play an increasing role at interannual timescales

an ocean resonance in the southeast pacific 1 satellite altimeter observations of sea surface height show an extensive region of high variability in the southeastern pacific which previous studies have suggested is a rossby wave trapped by topography here we investigate the feature using results from a high resolution global ocean model we calculate the empirical orthogonal modes and find that 29 of the ssh variability is due to a single mode we correlate the time series of the mode with the local ekman pumping and find that the correlation is largest when the wind curl is averaged over a region roughly the size of the mode we calculate the response function relating the two time series and find that it is dominated by a resonance at zero frequency with a decay time of about two days we conclude that the feature is a highly damped geostrophic mode of the ocean

a basin coherent mode of sub monthly variability in arctic ocean bottom pressure 1 a sub monthly mode of non tidal variability of ocean bottom pressure obp is observed in a 5 year record of deep sea bottom pressure at the north pole obp records from other regions in the arctic show that the north pole non tidal mass fluctuation is part of a non propagating basin coherent variation that is well represented by the ice ocean model piomas with a basin averaged winter only rms of 3 3 cm wavelet analysis of the modeled obp shows that the basin averaged mass variations are non stationary and only significant during the winter the basin averaged obp is strongly related to the meridional wind component over the nordic seas the ocean response is consistent with episodic wind forcing driving a northward geostrophic slope current the mass transport anomaly associated with the mode is significant relative to the annual net mean flow

a note on the barotropic response of sea level to time dependent wind forcing this study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind driven linear barotropic vorticity dynamics the topex poseidon altimetric observations of sea level and the wind products of the national meteorological center are used as the database for the study each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10 10 in most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation the apparent net vorticity change is more than what can be explained by the local wind stress curl in the few regions where the wind stress curl is strong enough to balance the vorticity budget predominantly in the northeast pacific and the southeast pacific the balance is basically achieved in terms of the time dependent topographic sverdrup relation namely the balance between the advection of the planetary vorticity plus the topography induced vorticity and the forcing by the wind stress curl

ocean dynamics associated with rapid j2 fluctuations importance of circumpolar modes and identification of a coherent arctic mode 1 fluctuations of the earth s dynamic oblateness j2 are a measure of global redistributions of mass between equatorial and polar regions sensitive to the component which is symmetric about the equator cox and chao recently published a time series of monthly values of j2 based on satellite orbit determination which showed rapid fluctuations from month to month as well as a large change in j2 in 1997 1998 we here investigate the ocean dynamics associated with these rapid fluctuations using a barotropic ocean model forced by atmospheric wind stress and pressure we find that the model has significant skill in reproducing the observations though not the change in 1997 1998 much of the model variability is related to coherent circumpolar fluctuations in arctic and antarctic bottom pressure which despite their apparent symmetry are forced by quite different mechanisms the antarctic mode is forced by circumpolar winds whereas the arctic mode is forced by northward winds over the entrances to the polar sea comparison with in situ observations shows that the model has skill in reproducing the polar modes arctic tide gauge records confirm the presence of a coherent mode at short periods and at long periods over at least the eurasian arctic shelf if barotropic and representative of the whole arctic this would be large enough to make a major contribution to measured j2 fluctuations but does not account for the 1997 1998 event

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

coherent sea level response to the antarctic oscillation 1 large scale sea level variations around antarctica were studied and their relationship with atmospheric variations was investigated tide gauge data at five coastal stations were used coherent sea level variations were clearly detected for all stations on intraseasonal time scales the coherent variations had significant negative correlations with an index of the atmospheric annular mode variation antarctic oscillation coherence was significant for periods from 10 to 100 days with negligible time lag the negative correlation is consistent with the mechanism that a high low westerly anomaly leads to a stronger weaker northward ekman drift and causes divergence convergence around antarctica

single subduction zone for the generation of devonian ophiolites and high p metamorphic belts of the variscan orogen nw iberia within the variscan orogen early devonian and late devonian high p belts separated by mid devonian ophiolites can be interpreted as having formed in a single subduction zone early devonian convergence nucleated a laurussia dipping subduction zone from an inherited lithospheric neck peri gondwanan cambrian back arc slab retreat induced upper plate extension mantle incursion and lower plate thermal softening favouring slab detachment within the lower plate and diapiric exhumation of deep seated rocks through the overlying mantle up to relaminate the upper plate upper plate extension produced mid devonian suprasubduction ocean floor spreading devonian ophiolites while further convergence resulted in plate coupling and intraoceanic ophiolite imbrication accretion of the remaining cambrian ocean heralded late devonian subduction of inner sections of gondwana across the same subduction zone and the underthrusting of mainland gondwana culmination of nw iberian allochthonous pile oblique convergence favoured lateral plate sliding and explained the different lateral positions along gondwana of terranes separated by palaeozoic ophiolites

detection of a large scale mass redistribution in the terrestrial system since 1998 earth9s dynamic oblateness j2 had been undergoing a decrease according to space geodetic observations over the past 25 years until around 1998 when it switched quite suddenly to an increasing trend that has continued to the present the secular decrease in j2 resulted primarily from the postglacial rebound in the mantle the present increase whose geophysical cause s are uncertain thus signifies a large change in global mass distribution with a j2 effect that considerably overshadows that of mantle rebound

the partition of regional sea level variability abstract the existing altimetric record offers an unprecedented view of sea level variability on a global scale for more than 2 decades optimal inference from the data involves appropriate partition of signal and noise in terms of relevant scales physical processes and forcing mechanisms such partition is achieved here through fitting a general circulation model to altimeter and other datasets to produce a best estimate of variability directly forced by the atmosphere the signal of primary interest here in this context noise comes primarily from instrument errors and meso scale eddies as expected but spatial smoothing effectively reduces this noise a separate constraint is thus formulated to measure the fit to monthly large scale altimetric variability that unlike the daily pointwise constraint shows a high signal to noise ratio the estimate is explored to gain insight into dynamics forcing and other factors controlling variability contributions from thermo steric halo steric and bottom pressure terms are all important depending on region but slopes of steric spectra red and bottom pressure spectra white are nearly invariant with latitude much variability can be represented by a seasonal cycle and linear trend plus a few eofs that can be associated with known modes of climate variability and or with topographic controls both wind and buoyancy forcing are important the response is primarily basin bound in nature but uneven patterns of propagation across basin boundaries are clearly present with the pacific being able to affect large portions of the indian and atlantic basins but the atlantic affecting mostly the arctic

a test of the ability of topex poseidon to monitor flows through the drake passage topex poseidon t p altimeter data from the drake passage dp area of the southern ocean near to the highest latitudes accessible by the satellite are found to agree as well in general to data from an extensive set of in situ instrumentation as has been observed for other parts of the ocean root mean square rms differences between subsurface pressures ssp measured by altimetry and bottom pressures bp measured by in situ devices are approximately 2 mbar in the northern dp and 4 mbar in the south after application of a 20 day low pass filter two mbar accuracy would suggest that altimetry could be capable of providing useful additional information on antarctic circumpolar current acc transport fluctuations through the dp on seasonal and interannual timescales the larger rms differences on what is considered to be the more important southern side are explainable in terms of baroclinic variability at the southern end of the world ocean circulation experiment woce sr1 section the first woce conductivity temperature depth data sets from sr1 have confirmed the existence of a major baroclinic eddy feature in the south which could account to a great extent for the larger rms values better southern dp locations could possibly have been chosen for woce however further recent in situ measurements from other locations near to the dp have shown that the southern dp acc related signals in ssp or bp are only slightly larger than t p accuracy which suggests that as yet they cannot be adequately monitored by means of altimetry alone whichever location is chosen even if the altimetric and in situ observations were perfect would they provide information directly relatable to transport variability through the passage this question has been studied by means of fine resolution antarctic model fram numerical modeling investigations which have demonstrated the complexity of the correlation between the variability in dp transport and ssp or sea level within fram northern ssp or bp variations are virtually uncorrelated with transport fluctuations and the modelling has confirmed the importance of southern measurements as inferred from in situ measurements over a decade ago it is evident that for the foreseeable future an extensive set of in situ instrumentation will be required in addition to the altimetry if further insight into circulation in this part of the southern ocean is to be obtained

a progress report on the alpern coal classification abstract the alpern coal classification has already been largely utilized and successfully applied both to laurasian north atlantic and gondwana coals it was accepted on basic principles by the international committee for coal petrology and as the official contribution of france it has been recently also partly adopted by the economic commission for europe of the united nations in geneva 1988 this paper deals with the improvement of the previous versions of the classification mainly by introducing new statistical data in order to establish more accurately proposed rank limits a ternary division for rank is maintained with the categories low rank coal or lignite instead of brown coal because high rank lignites may be black not brown medium rank coal or bituminous coal and high rank coal or anthracite the prefixes hypo meso and meta are used for rank subdivision thus avoiding non coherent previous prefixes such as sub bituminous and semi anthracite the selected rank parameters are moisture holding capacity ash free and calorific value moist ash free for lignites mean random reflectance for bituminous coals and anthracites correlations for bed moisture ash free and calorific value dry ash free are given for lignites correlations for volatile matter content mean maximum vitrinite reflectance and hydrogen content are also given for bituminous coals and anthracites type is determined from maceral data and is divided into vitric vitrinite v 60 fusic v liptinite l and liptic v i the ash content and the washability potential at 10 ash level are used to determine grade or facies and allow the distinction between transportable clean coals and non washable coals the run of mine ash content dry basis permits the division between coal middlings and shale if the type is liptic the subdivisions sapropelic coals and oil shales are used these are not washable but are solid fuels with a positive energy potential if the coals to be classified are clean or washed the vertical axis becomes free and can be used for example for swelling properties in bituminous coals the system has been recently computerized and allows for data to be displayed effectively for all relevant fields of application computer output examples are presented for coals from a euramerican and a gondwana basin

el nino southern oscillation signals in sea level surface mass redistribution and degree two geoid coefficients 1 we use a coupled earth system model to simulate and quantify the impact of the el nino southern oscillation enso on monthly to interannual variations of steric and eustatic global mean sea level gmsl surface mass loading and on the corresponding degree two geoid coefficients c21 s21 and c20 gmsl is dominated by eustatic variations on monthly to interannual timescales but less than 10 of the eustatic variance is related to enso in contrast steric gmsl correlates linearly in phase with enso with an explained variance of nearly 46 together these results imply that total gmsl variations are only weakly correlated with enso despite this small correlation we find a distinct enso pattern of sizable surface mass load anomalies over the continents this pattern is similar to typical enso related precipitation anomalies over the oceans the pattern features a global albeit weaker response with generally increased loading in the arctic and pacific oceans and decreased loading in the atlantic and indian oceans these surface loading anomalies lead to statistically significant enso related variations in the s21 and c20 geoid coefficients but not in c21 in analyzing the individual subsystem contributions we find that s21 is influenced by both ocean mass redistribution and soil moisture loading whereas c20 is mainly influenced by soil moisture loading our results highlight the importance of high amplitude regional loading anomalies that integrate to low degree geoid anomalies

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

quasi biennial modulation of the southern ocean coherent mode empirical orthogonal function eof analysis of two independent southernocean sea level datasets for the period 1992 2002 shows that the coherent oceanicmode a zonally symmetric counterpart to the atmospheric southern annular mode sam consistently emerges as the predominant mode of variability and is revealedto be a reliable proxy for circumpolar transport upon subannual to interannualtime scales cross validation of the coherent mode from each dataset and that ofa global barotropic model demonstrates a high degree of correspondence betweensea level observations and model estimations and also indicates that the coherentoceanic mode is largely barotropically driven upon subannual time scales whilstbaroclinic oceanic effects predominate at longer periods both the coherent modeand transport are shown to be modi ed by the stratospheric quasi biennial oscilla tion qbo and a mechanism is described by which qbo dependent planetary waveactivity may be guided from the stratosphere towards the surface by high latitudeeasterly and westerly jets inducing wind anomalies that force sea level variabilitythrough equatorward ekman transport a longer 18 year tide gauge record fromthe vernadsky faraday station and a 22 year time series of sea level estimationsfrom an ocean general circulation model are used to show that qbo inducedsea level and transport variability may be modulated upon longer time scales by aquasi decadalcycleofsolaractivity copyright c 2010royalmeteorologicalsociety

time variable gravity signal of an anomalous redistribution of water mass in the extratropic pacific during 1998 2002 1 cox and chao 2002 reported the detection of a large anomaly in the time series of earth s dynamic oblateness j2 the lowest degree gravity spatial harmonic in the form of a positive jump since 1998 overshadowing the decreasing secular trend in j2 caused primarily by the postglacial rebound pgr here we report that recent data show that j2 has been rapidly returning toward normal with pgr considered since early 2001 in search of the geophysical and climatic causes for this 1998 2002 j2 anomaly we report an oceanographic event that took place in the extratropic north and south pacific basins that was found to match remarkably well with the time evolution of the anomaly we examine the leading nonseasonal extratropic pacific empirical orthogonal function principal component modes in the sea surface height ssh data from topex poseidon sea surface temperature sst data from the national center for environmental predictions and output fields of the estimating the circulation and the climate of the ocean ecco ocean general circulation model ogcm including ocean bottom pressure obp and temperature and salinity profiles the phenomenon appears to be part of the pacific decadal oscillation and temporal correlations are made however quantitatively the obp field of the ecco model predicts a j2 anomaly that is smaller in magnitude than the observed by a factor of about 3 we discuss various possibilities for reconciling this discrepancy in terms of inadequacies of present ogcms and considering other geophysical contributions a complete resolution of the j2 enigma awaits further studies

an ocean resonance in the indian sector of the southern ocean 1 satellite altimeter observations of sea surface height show an extensive region of long wavelength fluctuations in the indian sector of the southern ocean a previous study showed that a similar feature found in the south pacific is due to a trapped geostrophic mode of the ocean here we investigate the feature in the indian sector and find that it is due to a similar mode with a decay time of approximately 3 5 days these previously unsuspected large scale modes of the ocean will have a significant effect locally on the satellite based gravity measurements currently underway

three forms of variability in argentine basin ocean bottom pressure ocean bottom pressure data are examined from a year long deployment of two bottom pressure recorders separated by 417 km in the argentine basin three forms of variability are found at high frequencies periods shorter than 2 hours the signal appears to be due to gravity wave propagation with the waves preferentially coming from the west at intermediate frequencies periods between 2 hours and 12 days the two records are highly coherent and in phase reflecting large scale coherent fluctuations which are well reproduced in a barotropic ocean model however the dominant mode is at a period of 20 days with a phase lag of about 90 100 degrees between the two records consistent with the a mode of variability previously inferred from satellite altimetry and current meters although the slightly shorter period is consistent with the suggestion that more than one mode contributes to the altimeter observations comparison with altimetry demonstrates that aliasing of higher frequency signals is not a significant source of error and confirms that a previously used altimetry mapping technique reduces the apparent amplitude of the mode the pressure records show a transport change of about 280 sv over one 12 day period and altimetry suggests that regions of higher variability exist the mode is only weakly excited in barotropic models but is strongly excited in a baroclinic model with a realistic eddy field suggesting that it is intrinsically linked to interactions between eddies mean flow and topography

wind forced intraseasonal sea level variability of the extratropical oceans abstract seven years worth of sea level observations from the topex poseidon altimeters and wind observations from the european remote sensing satellites ers 1 2 scatterometers were used to investigate the dynamics of large scale intraseasonal sea level variability at mid and high latitudes coherent patterns of sea level variability with spatial scales of 1000 km and timescales of 20 days to 1 year are identified in three particular regions the bellingshausen basin west of drake passage the australian antarctic basin and the central north pacific ocean 30 50 n near the date line significant coherence is found between wind stress curl and the sea level variability a simple barotropic vorticity equation in which the time rate of relative vorticity variation is balanced by the wind stress curl and a damping term is used to simulate the sea level anomalies with a significant degree of correlation with the observations although the coherence between the simulation and the observation is signifi

a near uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the arctic ocean and the nordic seas across the arctic ocean and the nordic seas a basin wide mode of ocean bottom pressure and sea level fluctuation is identified using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint the variation extends across the interconnected deep ocean basins of these semi enclosed arctic seas collectively called the arctic mediterranean with spatially near uniform amplitude and phase the basin wide fluctuation is barotropic and dominates the region s large scale variability from sub monthly to interannual timescales the fluctuation results from bifurcating coastally trapped waves generated by winds along the continental slopes of the arctic mediterranean and its neighboring seas including the north atlantic ocean the winds drive ekman transport across the large bathymetric gradients forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions the anomalies rapidly propagate away as barotropic coastally trapped waves with the coast and continental slope as respective boundaries the waves subsequently bifurcate at the shallow straits connecting the arctic mediterranean with the rest of the globe the straits transmit the shallow anomalies but not the deep variations thereby inhibiting the anomalies mutual cancelation by geographically separating the two anomalies that enter the deep arctic basins equilibrate uniformly across the domain characterized by a homogeneous depth integrated planetary potential vorticity distribution the potential vorticity s steep gradient that borders the basins shields the region from neighboring shallow variations giving rise to the observed spatially confined fluctuation compensating anomalies outside the arctic adjust similarly across the rest of the globe but are comparatively negligible in amplitude because of the global ocean s larger area relative to that of the deep arctic mediterranean the study from a technical perspective illustrates the utility of a model s adjoint in identifying causal mechanisms underlying a complex system