the effects of orography on midlatitude northern hemisphere dry climates abstract the role of mountains in maintaining extensive midlatitude arid regions in the northern hemisphere was investigated using simulations from the gfdl global climate model with and without orography in the integration with mountains dry climates were simulated over central asia and the interior of north america in good agreement with the observed climate in contrast moist climates were simulated in the same regions in the integration without mountains during all season but summer large amplitude stationary waves occur in response to the tibetan plateau and rocky mountains the midlatitude dry regions are located upstream of the troughs of these waves where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited in summer this mechanism contributes to the dryness of interior north america as a stationary wave trough remains east of the rockies but is not effective in eurasia due to seasonal changes in the atmospheric circulation the dryness

the basic ingredients of the north atlantic storm track part ii sea surface temperatures abstractthe impact of north atlantic sst patterns on the storm track is investigated using a hierarchy of gcm simulations using idealized aquaplanet and semirealistic boundary conditions in the atmospheric component hadam3 of the third climate configuration of the met office unified model hadcm3 this framework enables the mechanisms determining the tropospheric response to north atlantic sst patterns to be examined both in isolation and in combination with continental scale landmasses and orography in isolation a gulf stream sst pattern acts to strengthen the downstream storm track while a north atlantic drift sst pattern weakens it these changes are consistent with changes in the extratropical sst gradient and near surface baroclinicity and each storm track response is associated with a consistent change in the tropospheric jet structure locally enhanced near surface horizontal wind convergence is found over the warm side of strengthened sst gradients associated with ascending air and i

coastal sabkha and salt pan deposition of the lower clear fork formation permian texas abstract middle permian leonard series evaporites carbonates and red beds of the lower clear fork formation in the texas panhandle display many features common to modern coastal and continental sabkha facies similarities among lithofacies patterns and sequences sedimentary structures and anhydrite halite textures and fabrics of both the lower clear fork formation and modern sabkha facies permit construction of a model of halite deposition in coastal sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins inferred coastal sabkha and marine inner shelf environments and lithofacies recognized in the lower clear fork formation are largely based upon analogous modern depositional se tings and include the following 1 red siltstone to mudstone deposited in a wadi or desert alluvial eolian plain and inner sabkha mud flats both passing basinward into 2 chaotic mudstone halite of an inner sabkha saline mud flat which flanked 3 inner sabkha salt pans bearing banded to massive halite and laminated anhydrite and 4 nodular nodular mosaic and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments salt pans may have formed in the inner sabkha as a result of displacive gypsum anhydrite growth and jacking up of the marginal sabkha surface which impeded seaward drainage of floodwater off the sabkha modern process sediment analogs include alluvial fans saline mud flats and salt pans of the coastal sabkhas in baja mexico the trucial coast and kutch india evaporites and terrigenous clastics in bristol dry lake california exhibit many features analogous with the permian suggesting that this setting though strictly continental serves as a process analog bromide values in lower clear fork halite average 40 ppm which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis upward decreasing values in the lower clear fork upper cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite

some physical drivers of changes in the winter storm tracks over the north atlantic and mediterranean during the holocene the winter climate of europe and the mediterranean is dominated by the weather systems of the mid latitude storm tracks the behaviour of the storm tracks is highly variable particularly in the eastern north atlantic and has a profound impact on the hydroclimate of the mediterranean region a deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in mediterranean climate and the civilizations it has supported over the last 12 000 years broadly the holocene period this paper presents a discussion of how changes in climate forcing e g orbital variations greenhouse gases ice sheet cover may have impacted on the basic ingredients controlling the mid latitude storm tracks over the north atlantic and the mediterranean on intermillennial time scales idealized simulations using the hadam3 atmospheric general circulation model gcm are used to explore the basic processes while a series of timeslice simulations from a similar atmospheric gcm coupled to a thermodynamic slab ocean hadsm3 are examined to identify the impact these drivers have on the storm track during the holocene the results suggest that the north atlantic storm track has moved northward and strengthened with time since the early to mid holocene in contrast the mediterranean storm track may have weakened over the same period it is however emphasized that much remains still to be understood about the evolution of the north atlantic and mediterranean storm tracks during the holocene period

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 are investigated with the aid of the european centre for medium range weather forecasts analysis data and mesoscale model simulations neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event the analysis and interpretation is primarily based upon the evolution of the lower and upper level potential vorticity pv field complemented by three dimensional trajectory calculations lothar originated in the western atlantic and travelled as a shallow low level cyclone of moderate intensity towards europe this translation took place below and slightly to the south of a very intense upper level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low level pv anomaly not unlike the concept of a diabatic rossby wave no significant pv anomalies were evident at the tropopause level during this early phase of the life cycle the surface cyclone intensified rapidly when the shallow cyclone approached the jet stream axis the circulation induced by the diabatically produced low tropospheric pv anomaly on steeply sloping isentropic surfaces that transect the intense upper level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold this stratospheric pv anomaly virtually merged with the diabatically produced ephemeral pv feature to form a vertically aligned tower of positive pv at the time of maximum storm intensity a sensitivity study with a dry adiabatic hindcast simulation shows no pv tower configuration and only a very weak surface development and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid bottom up intensification of lothar a comparison of the anomalously high atlantic sea surface temperatures in december 1999 with the water vapour source regions for the latent heat release that accompanied the rapid intensification phase of lothar shows a close relationship this is of importance when discussing the possible implications of climate variability and change on the development of north atlantic winter storms copyright 2002 royal meteorological society

play analysis and leading edge oil reservoir development methods in the permian basin increased recovery through advanced technologies the permian basin of west texas and southeast new mexico remains an important oil producing province accounting for 17 of united states production 327 million bbl in 2002 with a resource base of such size increased understanding of reservoir geology and improved use of enhanced recovery practices in the basin can have a substantial impact on united states oil production thirty two oil plays covering both the texas and new mexico portions of the permian basin were defined on the basis of reservoir stratigraphy lithology depositional environment and structural and tectonic setting one thousand three hundred and thirty nine significant sized reservoirs cumulative production of 1 million bbl 1 59 105 m3 of oil through 2000 were assigned to a geologic play cumulative production from these reservoirs was 28 9 billion bbl 4 59 109 m3 or 95 of the basin s total examples of successful reservoir development practices are listed by play because methods demonstrated to work well in one reservoir should be applicable to other reservoirs in the play the permian basin is dominantly a carbonate province carbonate reservoirs account for 75 of total oil production clastics 14 mixed clastics and carbonates 8 and chert 3 the plays having the largest cumulative production are the northwest shelf san andres platform carbonate play 4 0 billion bbl 6 31 108 m3 the leonard restricted platform carbonate play 3 3 billion bbl 5 25 108 m3 the pennsylvanian and lower permian horseshoe atoll carbonate play 2 7 billion bbl 4 29 108 m3 and the san andres platform carbonate play 2 2 billion bbl 3 42 108 m3 the permian system dominates production accounting for 73 of cumulative production followed by the pennsylvanian 13 and the ordovician 6 the estimated remaining reserves from that component of the resource base that is already discovered and producing is 3 25 billion bbl 5 17 108 m3

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

climatology of cyclogenesis mechanisms in the mediterranean abstract a general climatology of the main mechanisms involved in mediterranean cyclogenesis is presented a diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons and in different cyclogenetic regions within the same season it is shown that cyclones that developed over the three most active areas in winter the gulf of genoa the aegean sea and the black sea are essentially subsynoptic lows triggered by the major north atlantic synoptic systems being affected by local orography and or low level baroclinicity over the northern mediterranean coast it is also suggested that cyclones in two or all three of these regions often occur consecutively linked to the same synoptic system in spring and summer thermally induced lows become progressively more important despite the existence of other factors such as the atlas mountains contributing to lee cyclogenesis in northern africa or the extension of the asian monsoon into the eastern

stratigraphy and depositional mosaics of lower clear fork and wichita groups permian northern midland basin texas the stratigraphy depositional environments and reservoir potential of the wichita group and overlying lower clear fork permian in the northern midland basin are described on the basis of seismic interpretations log correlations and lithologic analyses the wichita in this area is divided into a lower member of slope to basinal limestones and shales and an upper member of shelf dolomites varicolored shales and evaporites only a starved lower wichita section is present in areas to the south fusulinid evidence and physical correlations suggest that the wolfcampian leonardian boundary occurs within the wichita and ascends stratigraphically toward the north these data in conjunction with the upward shoaling aspect of the wichita establish a progradational relatio between shelf facies of the upper member and slope to basinal facies of the lower member the lower clear fork beneath the tubb member records continued southward progradation of similar shelf facies these lithologies are represented in the basin by limestones and shales beneath and possibly including lowermost dean sandstones depositional systems of the wichita and pre tubb clear fork sections are carbonate dominated rimmed shelves adjoining deeper basins periods of rapid progradation and offlapping shelf edge accretion were cyclic being coincident with periods of low sea level the tubb section records a change to a mixed siliciclastic and carbonate rimmed shelf system deposition of shelf tubb and basinal dean facies was related to a mosaic of cyclic reciprocal siliciclastic carbonate sedimentation rapid shelf outbuilding occurred at low sea level stands during the siliciclastic phases of sedimentation the formation of the shallow north platform was more a consequence of constructional sedimentary processes during the late wolfcampian and early leonardian than of structural influences over much of the northern midland basin study area potential stratigraphic hydrocarbon reservoirs are in wichita and lower clear fork strata such reservoirs occur as separate offlapping shelf marginal dolomitized oolite grainstone shoals rather than organic buildups as was described in earlier studies

internal solitons on the pycnocline generation propagation and shoaling and breaking over a slope in part 1 a study is made of the internal solitary wave on the pycnocline of a continuously stratified fluid a korteweg de vries kdv equation for the interfacial displacement is developed following benney s method for long nonlinear waves experiments were conducted in a long wave tank with the pycnocline at several different depths below the free surface while keeping the total depth approximately constant a step like pool of light water trapped behind a sliding gate served as the initial disturbance condition the number of solitons generated was verified to satisfy the prediction of inverse scattering theory the fully developed soliton was found to satisfy the kdv theory for all ratios of upper layer thickness to total depth in part 2 of this study we investigate experimentally the evolution and breaking of an internal solitary wave as it shoals on a sloping bottom connecting the deeper region where the waves were generated to a shallower shelf region it is found through quantitative measurements that the onset of wave breaking was governed by shear instability which was initiated when the local gradient richardson number became less than the internal solitary wave of depression was found to steepen at the back of the wave before breaking in contrast with waves of elevation two slopes were used with ratios 1 16 and 1 9 and the fluid was a boussinesq fluid with weak stratification using brine solutions

distribution of porosity and permeability in platform dolomites insight from the permian of west texas saller and henderson 1998 presented an article concerning porosity and permeability variations in two west texas oil fields north riley and south cowden fields these fields occur within dolomitized permian platform carbonates near the basinward shelf edge of the central basin platform a paleogeographic element that influenced permian deposition in west texas their carefully documented study outlines several anomalous aspects concerning porosity distribution they noted in particular that porosity distribution is not strictly facies dependent but that porosity tends to increase in a basinward direction they suggested that porosity developed largely during dolomitization by the action of hypersaline evaporative fluids that flowed downdip in a basinward direction during the permian these brines were generated in restricted shelf interior lagoons and moved downdip parallel with bedding in a shallow reflux type of hydrologic system driven by subsurface fluid density differences in the permian clear fork and grayburg formations as shown here in figure 1 see figure 18 in saller and henderson 1998 figure 1 part a shows the scenario proposed by saller and henderson 1998 for porosity creation dolomitization and dolomite cementation of the permian clear fork and grayburg formations of west texas they suggested that macrodissolution of calcium carbonate occurred contemporaneously with dolomitization and dolomite cementation this process of brine backreaction however would cause a net increase of porosity in the shelf interior the opposite of what is observed part b shows a two stage scenario proposed here to circumvent the problem of limestone macrodissolution by shelf interior brines that must have been initially in approximate bulk equilibrium with calcium carbonate the first stage records dolomitization by replacement of limestone with little macrodissolution in stage two evaporative shelf interior brines may have evolved in equilibrium with dolomite only and became undersaturated with calcite and aragonite reflux migration of these brines downdip may

linear simulation of the stationary eddies in a gcm part ii the mountain model abstract the validity of linear stationary wave theory in accounting for the zonal asymmetries of the winter averaged tropospheric circulation obtained in a general circulation model gcm is ascertained the steady linear primitive equation model used towards this end has the same vertical and zonal resolution as the spectral gcm but is finite differenced in the meridional direction it is linearized about a zonally symmetric basic state and forced by topography and 3 dimensional diabatic heating and transient flux convergence fields all of which are taken from the gcm as in part i in which we studied a gcm with a flat lower boundary we obtained the best correspondence between the gcm and the linear solutions when strong rayleigh friction is included in the linear model not only near the surface but in the interior of the tropical troposphere as well there is sufficient quantitative correspondence between the gcm and the linear solution to justify decomposing the linear simulation into parts for

a case study of saharan cyclogenesis a case of saharan cyclogenesis associated with the equatorward intrusion of a trough at the end of the atlantic storm track is investigated it is shown that a potential vorticity anomaly resulting from a baroclinic wave life cycle associated with the polar jet interacts with the low level baroclinicity over subtropical africa beneath the subtropical jet it is suggested that low latitude synoptic scale cyclogenesis events of this type can be triggered only by upper level potential vorticity anomalies if they have a sufficient depth scale and that the interaction may be aided by the presence of low static stability associated with a well mixed boundary layer a weak cold front also forms during the cyclogenesis event associated with the convergence of the baroclinicity of the polar trough front with the baroclinicity of the subtropical heat low

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

permian clear fork group north robertson unit integrated reservoir management and characterization for infill drilling part ii petrophysical and engineering data located in the permian basin of west texas north robertson unit nru produces from highly heterogeneous carbonate reservoirs of the permian leonardian clear fork group and lowermost glorieta formation discovered in 1955 the productive area encompasses 5366 ac 2173 ha along the northern border of the central basin platform and contains an estimated 262 mmbbl original oil in place ooip total recovery from the unit including 30 yr of primary production and 10 yr of waterflood production is only 10 1 ooip a recent integrated reservoir characterization effort in nru suggests that previous recovery efforts were inadequate to achieve maximum production from the reservoir analysis of petrophysical properties in the clear fork has allowed for pore level modeling leading to identifying rock types and delineating flow units maps constructed of various reservoir parameters including ooip primary and secondary ultimate recovery and flow capacity were compared with rock type distribution within individual flow units and the results of reservoir simulation to estimate portions of the unit suitable for targeted 10 ac 4 ha infill development related data also suggested the importance of completion techniques in helping improve conformity between producers and injection intervals in pay intervals in nearby wells results of 14 producing wells and 4 injector wells drilled on the basis of the new reservoir model and improved completion techniques were impressive and confirmed the value of using such an approach to optimize the economics and production of infill development in such a complex reservoir

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

linear stationary wave simulations of the time mean climatological flow abstract a spectral coordinate model linearized about a zonal mean flow is used to investigate the maintenance of the december february climatological stationary waves the model is generally run with 15 levels in the vertical and a t31 truncation the sum of the response to orography diabatic heating and transient eddy flux convergences specified from data gives a generally good northern hemisphere simulation at 200 mb with some deterioration in the lower troposphere the same is true for the southern hemisphere but only when the forcing terms from recent years are used the response is broken down into that associated with particular orographic features tropical and midlatitude heating and transient vorticity and heat flux convergence all of these are shown to be significant in particular orography accounts for approximately 30 of the total 200 mb planetary wave response in midlatitudes the diabatic heating maxima in the two storm tracks are important this heating is related to latent and se

evaluation of coupled ocean atmosphere simulations of the mid holocene using palaeovegetation data from the northern hemisphere extratropics we have used the biome4 biogeography biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean atmosphere general circulation models to mid holocene changes in orbital forcing in the mid to high latitudes of the northern hemisphere all the models produce a a northward shift of the northern limit of boreal forest in response to simulated summer warming in high latitudes the northward shift is markedly asymmetric with larger shifts in eurasia than in north america b an expansion of xerophytic vegetation in mid continental north america and eurasia in response to increased temperatures during the growing season c a northward expansion of temperate forests in eastern north america in response to simulated winter warming the northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in north america are supported by palaeovegetation data the expansion of xerophytic vegetation in mid continental north america is consistent with palaeodata although the extent may be over estimated the simulated expansion of xerophytic vegetation in eurasia is not supported by the data analysis of an asynchronous coupling of one model to an equilibrium vegetation model suggests vegetation feedback exacerbates this mid continental drying and produces conditions more unlike the observations not all features of the simulations are robust some models produce winter warming over europe while others produce winter cooling as a result some models show a northward shift of temperate forests consistent with though less marked than the expansion shown by data and others produce a reduction in temperate forests elucidation of the cause of such differences is a focus of the current phase of the palaeoclimate modelling intercomparison project

permian clear fork group north robertson unit integrated reservoir management and characterization for infill drilling part i geologic analysis north robertson unit nru produces from highly heterogeneous shallow marine platform carbonate reservoirs of the permian leonardian clear fork and lowermost glorieta formations discovered in 1955 the productive area encompasses 5366 ac 2173 ha along the northern border of the central basin platform cbp in the permian basin of west texas clear fork glorieta production is widespread in this portion of the basin with most fields including nru now under waterflood primary production was on 40 ac 16 ha spacing with enhanced recovery dependent upon a combination of 20 ac 8 ha infill drilling and waterflooding total recoveries in these fields have been typically below 25 with many waterfloods performing below prediction due to a high level of lateral and vertical reservoir heterogeneity detailed geological and petrophysical analysis of new and existing cores from nru performed as part of a combined industry u s department of energy doe sponsored project has resulted in greatly improved reservoir characterization of the clear fork productive interval ultimately allowing for the quantification and mapping of specific productive intervals within the 1000 ft 300 m gross reservoir interval relevant data have been used to identify optimal sites for strategic 10 ac 4 ha infill development aimed at maximizing the efficiency and profitability of future oil reserve growth within the unit a total of 14 producing wells and 4 injector wells were drilled on the basis of the new geologic engineering model results of these wells were impressive and confirmed the value of targeted infill development in such a complex reservoir part i of this article summarizes field data and geologic information essential to the reservoir characterization effort in nru part ii of this article to appear in the november issue of the bulletin will discuss petrophysical and engineering data as well as the targeted infill drilling effort and its results

holocene climate variability as derived from alkenone sea surface temperature and coupled ocean atmosphere model experiments holocene climate modes are identified by the statistical analysis of reconstructed sea surface temperatures ssts from the tropical and north atlantic regions the leading mode of holocene sst variability in the tropical region indicates a rapid warming from the early to mid holocene followed by a relatively weak warming during the late holocene the dominant mode of the north atlantic region sst captures the transition from relatively warm cold conditions in the eastern north atlantic and the western mediterranean sea the northern red sea to relatively cold warm conditions in these regions from the early to late holocene this pattern of holocene sst variability resembles the signature of the arctic oscillation north atlantic oscillation ao nao the second mode of both tropical and north atlantic regions captures a warming towards the mid holocene and a subsequent cooling the dominant modes of holocene sst variability emphasize enhanced variability around 2300 and 1000 years the leading mode of the coupled tropical north atlantic holocene sst variability shows that an increase of tropical sst is accompanied by a decrease of sst in the eastern north atlantic an analogy with the instrumental period as well as the analysis of a long term integration of a coupled ocean atmosphere general circulation model suggest that the ao nao is one dominant mode of climate variability at millennial time scales