thermodynamic analysis of ocean circulation abstract calculating a streamfunction as function of depth and density is proposed as a new way of analyzing the thermodynamic character of the overturning circulation in the global ocean the sign of an overturning cell in this streamfunction directly shows whether it is driven mechanically by large scale wind stress or thermally by heat conduction and small scale mixing it is also shown that the integral of this streamfunction gives the thermodynamic work performed by the fluid the analysis is also valid for the boussinesq equations although formally there is no thermodynamic work in an incompressible fluid the proposed method is applied both to an idealized coarse resolution three dimensional numerical ocean model and to the realistic high resolution ocean circulation and climate advanced model occam it is shown that the overturning circulation in occam between the 200 and 1000 m depth is dominated by a thermally indirect cell of 24 sverdrups 1 sv 106 m3 s 1 forced by ekman pumping in th

temporal change of seismic structure around iwate volcano inferred from waveform correlation analysis of similar earthquakes 1 we investigate the temporal change of crustal structure around iwate volcano northeastern japan using calculations of the cross correlation coefficients of p and s waves of pairs of similar earthquakes that occurred between 1995 2002 at the subducting pacific plate boundary while large coefficients are observed at most stations throughout the period two stations located on the southwestern slope of iwate volcano exhibit small s wave coefficients the coefficients at these two stations decreased remarkably from 1998 corresponding to a period of significant volcanic activity and an m6 1 earthquake since 2000 the coefficients have recovered gradually suggesting their correlation with the activity of iwate volcano the coefficients of p waves at these stations are large compared to those of s waves suggesting that temporal change in the crustal structure beneath these stations occurred in elastic properties to which s waves are sensitive such as rigidity related to magmatic and or seismic activity in and around the volcano

observed radar reflectivity in convectively coupled kelvin and mixed rossby gravity waves 1 propagating disturbances in the tropical atmosphere exhibiting characteristics of linear equatorial waves have been shown to be coupled to convection in some cases a rain event at a specific location can be associated with a particular wave of sufficiently large amplitude rain events spanning three years at kwajalein atoll republic of the marshall islands 8 72n 167 73e are classified by associated wave type i e kelvin or mixed rossby gravity mrg using space time spectral filtered outgoing longwave radiation olr contoured frequency by altitude diagrams cfads of radar for the classified dates were compared between the two groups the kelvin wave accumulated cfad has a distribution shifted to lower reflectivities compared to mrg suggesting that kelvin storms likely contain a larger fraction of stratiform to convective area compared to mrg storms citation swann a a h sobel s e yuter and g n kiladis 2006 observed radar reflectivity in convectively coupled kelvin and mixed rossby gravity waves geophys res lett 33 l10804 doi 10 1029 2006gl025979

late quaternary sedimentation patterns on the meriadzek terrace bay of biscay esscamp 02 core 47 n 9 w abstract foraminiferal assemblage changes size and mineralogy of lithic grains oxygen isotopes caco 3 and dolomite content were studied along a 9 m long core from the meriadzek terrace to gain insight into climate productivity and sediment source changes at this part of the northeast atlantic margin during the late quaternary an age model has been generated on the basis of radiocarbon dating downcore foraminiferal assemblages and 18 o values high sedimentation rates at this site allow very detailed records for the last glacial period down to late isotopic stage 3 sea surface temperature sst inferred from the foraminiferal assemblages 18 o curve and the temperature estimation by the simmax analog technique reveal three distinctive periods during isotopic stage 2 with late stage 2 15 3 13 4 ka being the coldest period of the last 26 ka a northward retreat of the polar front at 13 4 ka based on the sst record coincides with the strongest peak of primary productivity as indicated by the foraminiferal fluxes levels rich in large lithic grains llg interpreted as ice rafted debris ird correspond to periods of low sst and are coeval with heinrich layers 1 2 and 3 however the hematite stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our core point to an iceland and or fenno scandian rather than a laurentian or greenland origin of this material

the coupling of mixed rossby gravity waves with diabatic heating during the trmm kwajex field campaign composite dynamic and thermodynamic structures of mixed rossby gravity mrg waves are presented with their coupling with diabatic heating and moisture sources sinks using tropical rainfall measuring mission kwajalein experiment trmm kwajex field campaign data a significant departure of convectively coupled waves from dry waves exists in the phases of wave component maximum low level wind convergence is accompanied by midtropospheric divergence and upper tropospheric convergence that is preceded by increase of moisture in the boundary layer these phases correspond to surface turbulent transport shallow and midlevel convections that cause moistening and heating of the lower and middle troposphere they are followed by deep convection with maximum heating centered in the upper troposphere the deep convective heating evolves to stratiform like upper tropospheric heating and lower tropospheric cooling that precedes the quick demise of convection such a structure on convectively coupled mrg waves is summarized by four phases which sheds lights on how tropical waves are coupled with convective processes in all their phases

synoptic scale disturbances near the equator abstract a spectral analysis of winds analyzed and initialized at the european centre for medium range weather forecasts reveals an abundance of power in the 850 mb meridional wind along the equator with periods near four days the power is mostly in the westward propagating component using high pass filtered data it is shown that the waves have westward phase and eastward group propagation relative to the mean wind the longest wavelengths are found over the pacific ocean while the shortest are found over the convectively variable regions of indonesia south america and africa mean phase speeds at 850 mb are positively correlated with the mean wind on the equator at 500 mb and below and negatively correlated with the mean wind above that level the effective advecting zonal wind of the disturbances seems to be the density weighted average of the lower troposphere the structure of the disturbances bears resemblance to the expected structure of an equatorially trapped mixed rossby gravity wave over t

on the transport and angular momentum balance of channel models of the antarctic circumpolar current abstract angular momentum balances are discussed both in general as well as in the context of simple channel models of the antarctic circumpolar current acc particular emphasis is placed on the close relationship between the angular momentum balance and the meridional circulation it is found that topographic form drag is established very early in the integration whereas interfacial form drag can take much longer to develop restrictions on the geostrophic portion of the meridional circulation imposed by zonally reconnecting potential vorticity contours in the upper ocean allow derivation of an estimate for the steady state transport the estimate assumes there to be little or no circumpolar flow at great depth an assumption that stems from the belief that the band of zonally reconnecting geostrophic contours in the southern ocean does not extend to the ocean floor the predicted transport is proportional to the strength of the stratification and compares favorably with numerical results in the lite

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

observation of a quasi 2 day wave during toga coare abstract detailed structure of the quasi 2 day oscillation observed in the active phase of the madden julian oscillations during the intensive observation period of tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare iop was described a variety of observational platforms is used including high resolution gms infrared histogram rain rate estimate from toga and mit radar measurements upper air soundings and boundary layer profiler winds from the integrated sounding system and surface data from the imet buoy the quasi 2 day mode had a westward propagation speed of 12 15 day 1 a horizontal wavelength of 25 30 longitude a coupling with the westward propagating n 1 inertio gravity waves was hypothesized from the space time power spectral distribution of the cloud field the wind disturbance structure was consistent with the hypothesis the vertical wave structure had an eastward phase tilt with height below 175 hpa and vice versa above indicating the wav

an observational study of easterly waves over the eastern pacific in the northern summer using fgge data abstract fgge revel iii b data provided by the european centre for medium range weather forecasts and the outgoing longwave radiation data measured by satellites are used to investigate observationally relationships between deep cloud activity and large scale meteorological fields during the northern hemisphere summer may september of 1979 over the eastern pacific aside from the summer monsoon area over southern and eastern asia the eastern pacific is the area where strong deep convection frequently develops in the northern summer this is also one of the tropical ocean areas that have been least explored meteorologically a power spectral analysis using the maximum entropy method is made for the meridional wind component at 850 mb at various grid points in the analysis domain for each mouth from may through september the waves with a period of 4 6 days are not only stronger in july and august than those of other months but active in the regions of 100 130 w in the eastern pacific and 130 160 e i

does the sensitivity of southern ocean circulation depend upon bathymetric details the response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized but eddy permitting model simulations previously ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing here it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry the key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process the addition of an embayment which insulates bottom water formation from meridional eddy fluxes acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current the degree of interaction between southern ocean eddies and antarctic shelf processes may thereby control the sensitivity of the southern ocean to change

on the cause of abrupt vegetation collapse in north africa during the holocene climate variability vs vegetation feedback the abrupt desertification over the northern africa in the mid holocene is studied in both a complex and a simple coupled climate vegetation model in contrast to the previous mechanism that relies on strong positive vegetation climate feedback and the resulted multiple equilibria we propose a new mechanism in which the abrupt desertification is caused by low frequency climate variability rather than a positive vegetation climate feedback the implication of this new mechanism to modelling and observation is also discussed

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

dependence of multiple climate states on ocean mixing parameters multiple equilibria of the climate system inferred from paleo reconstructions have also been observed in both ocean only and coupled ocean atmosphere general circulation models these multiple states are thought to be associated with different modes of operation of the meridional overturning circulation in the north atlantic it has recently been suggested that the stability of these states depends on the amount of vertical mixing in ocean models here we investigate the dependence of the hysteresis behaviour of the thermohaline circulation to sub gridscale mixing processes in the ocean using a simplified coupled ocean atmosphere model we find that both vertical and horizontal diffusivities have considerable influence on the stability of the different circulation modes they also change the transition points from one circulation pattern to another larger vertical diffusivities lead to higher values of additional precipitation into the north atlantic being necessary to stop the formation of deep water however for slightly increased evaporation the state without deep water formation becomes increasingly unstable for stronger vertical diffusion larger values of horizontal mixing lead to a narrowing of the phase space for which two equilibria are stable these results suggest that it is currently not possible given the large uncertainty in ocean mixing to quantitatively determine possible thresholds for the transition of the north atlantic thermohaline circulation between on and off modes this presents a policy predicament as it makes it extremely difficult to assign a probability for the future occurence of such nonlinear climate transition

the impact of turbulence and convection on transport in the southern ocean volume transport in the presence of fully resolved convection and turbulence is investigated in a reentrant channel model of the southern ocean the response of the meridional overturning and zonal transport to variations in wind and buoyancy forcing is quantified our simulations show two overturning cells a buoyancy driven lower cell and a wind driven upper cell the lower overturning cell is much larger in meridional extent and magnitude than the upper cell the mean component of the overturning transport is smaller than the fluctuating component in the lower overturning cell indicating that transport is dominated by eddies and or turbulent convective flow in contrast the upper cell can be primarily described as a mean flow indicating minimal eddy compensation both cells strengthen with increasing winds with the upper cell being more sensitive to increasing wind intensity than the lower cell scaling for the mean upper overturning is also derived and matches previous theories which predict a linear sensitivity of the upper cell to wind zonal transport remains insensitive to increasing wind stress suggesting that the system is eddy saturated when turbulence and eddies are resolved these results suggest that fine scale flows control zonal transport and abyssal meridional overturning in the southern ocean while wind stress drives the upper meridional overturning transport highlighting the importance of accurately characterizing turbulence and convection in large scale models

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

the effects of mesoscale eddies on the stratification and transport of an ocean with a circumpolar channel abstract the effects of eddies in a primitive equation ocean model configured in a single hemisphere domain with circumpolar channels at their poleward ends are investigated in particular two regimes for the mass balance in the channel are investigated with small overlying winds the channel stratification is largely set by diffusion operating in the gyre portion of the domain the depth scale varies with a fractional power of the diffusivity but has little dependence on the wind stress as the winds are increased the depth becomes increasingly controlled by a tendency toward small residual circulation in this limit a scaling theory is derived for the stratification in the channel that predicts the overall depth of the thermocline as a power of the wind stress and that allows the eddy length scale to differ from the channel length scale the predicted depth depends on the details of the closure chosen for the eddy buoyancy flux but in general it varies as some fractional power of the wind stress a

isopycnal averaging at constant height part i the formulation and a case study simple eulerian averaging of velocities density and tracers at constant position is the most natural way of averaging however eulerian averaging gives incorrect watermass distributions and properties as well as spurious diabatic circulations such as the deacon cell instead of averaging at constant height averaging along isopycnals removes such fictitious mixing and diabatic circulations such isopycnal averaging is normally performed at constant latitude that is averaging along isopynals as they heave up and down as a result height information is lost and the sea surface becomes much warmer or lighter than with simple eulerian averaging in fact averaging can be performed along arbitrarily aligned surfaces this study considers a particular case in which isopycnal averaging is performed at constant height thus this new isopycnal averaging follows isopycnals as they meander horizontally at constant z height information is now retained at the cost of losing latitudinal information the advantage of this averaging is that it avoids the problem of giving a surface that is too warm associated with this new isopycnal averaging a vertical transport streamfunction in r z space can be defined in analogy to the conventional meridional overturning streamfunction in y r space here in part i this constant height isopycnal averaging is explained and illustrated in an idealized zonal channel model in part ii the relationship between the two different isopycnal averagings and the eulerian mean eddy flux divergence is explored