quartz cementation in late cretaceous mudstones northern north sea changes in rock properties due to dissolution of smectite and precipitation of micro quartz crystals abstract late cretaceous mudstones from two wells located in the northern north sea and the norwegian sea have been examined with respect to quartz cement two different types of quartz cement type 1 and type 2 have been identified using sem eds cl analysis of drill bit cuttings at depths 2370 2670 m 80 85 c type 1 appears as relatively large aggregates 30 100 m of depth temperature related crypto or microcrystalline to macrocrystalline irregular quartz cement formed by local re crystallization of biogenic silica the cl responses of type 1 quartz cement give a clear indication of an authigenic origin type 2 quartz cement represents relatively high amounts of extremely fine grained micro sized 1 3 m crystals embedded as discrete short chains or small clusters nests within the illitized clay matrix the cl responses of micro quartz crystals indicate an authigenic origin the micro quartz is most probably sourced from silica released during the smectite to illite dissolution precipitation reaction the petrographic evidence indicates that most of the silica released by the smectite to illite reaction has not been exported out of the mudstones the silica released produce a subtle inter connected micro quartz network interlocked with aggregates of micro quartz and authigenic clay crystals this micro quartz cementation process causes a significant and sharp change in the mudstone stiffness at the onset of the chemical compaction regime this is indicated by an abrupt increase in well log velocity vp and change in seismic facies close to 2500 m 80 85 c

further development of a high frequency seismic source for use in boreholes a borehole sparker seismic source enclosed in a semi flexible tube has been developed to produce a short compressional seismic pulse with a frequency content in the range 250 hz to 3 5 khz with a peak power at 570 hz the pulse shape and frequency content are shown to be a function of the input power the diameter of the spark chamber the salinity of the electrolyte the material of the spark chamber and the electrode configuration when in a borehole the source produces a vertically polarized shear wave but being similar to a small explosive charge does not allow phase reversal as a means of identifying the shear wave in the received pulse train the source is shown to be ideal for tomographic imaging surveys because of its repetitive nature high frequency content and reliability very high resolution seismic reflection surveys are also shown to be possible under favourable circumstances

eddy zonal flow feedback in the southern hemisphere abstract the variability of the zonal mean zonal wind in the southern hemisphere is studied using eof analysis and momentum budget diagnostics of ncep reanalysis data 1978 97 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude jet analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of eof1 and plays an important role in the selection of the leading eof of midlatitude variability further analysis also shows a propagating feedback common to both eof1 and eof2 which is responsible for the poleward drift of wind anomalies with time the observations support the following feedback mechanism anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient that by thermal wind coincides with the latitude of the anomalous zonal jet the net propagation of baroclinic

impacts of mjo convection over the maritime continent on eastern china cold temperatures abstractthe present study shows that winter cold events over eastern china can be induced by madden julian oscillation mjo associated anomalous convection over the maritime continent we conduct

the life cycle of the northern hemisphere sudden stratospheric warmings motivated by recent evidence of strong stratospheric tropospheric coupling during the northern hemisphere winter this study examines the evolution of the atmospheric flow and wave fluxes at levels throughout the stratosphere and troposphere during the composite life cycle of a sudden stratospheric warming the composite comprises 39 major and minor warming events using 44 years of ncep ncar reanalysis data the incipient stage of the life cycle is characterized by preconditioning of the stratospheric zonal flow and anomalous quasistationary wavenumber 1 forcing in both the stratosphere and troposphere as the life cycle intensifies planetary wave driving gives rise to weakening of the stratospheric polar vortex and downward propagation of the attendant easterly wind and positive temperature anomalies when these anomalies reach the tropopause the life cycle is marked by momentum flux and mean meridional circulation anomalies at tropospheric levels that are consistent with the negative phase of the northern hemisphere annular mode the anomalous momentum fluxes are largest over the atlantic half of the hemisphere and are associated primarily with waves of wavenumber 3 and higher

observed connection between stratospheric sudden warmings and the madden julian oscillation 1 the effect of the madden julian oscillation mjo on the northern hemisphere wintertime stratospheric polar vortex and major mid winter stratospheric sudden warmings ssws is evaluated using a meteorological reanalysis dataset the mjo influences the region in the tropospheric north pacific sector that is most strongly associated with a ssw consistent with this ssws in the reanalysis record have tended to follow certain mjo phases the magnitude of the influence of the mjo on the vortex is comparable to that associated with the quasi biennial oscillation and el nino the mjo could be used to improve intra seasonal projections of the northern hemisphere high latitude circulation and in particular of the tropospheric northern annular mode at lags exceeding one month

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

modulations in the planetary wave field induced by upward propagating rossby wave packets prior to stratospheric sudden warming events a case study a diagnostic framework is introduced in which anomalous zonally averaged rossby wave activity injection into the stratosphere is decomposed into a contribution solely from zonally confined upward propagating rossby wave packets and another from interaction of the wave packets with the climatological planetary waves to pinpoint the tropospheric sources of the wave packets a particular form of wave activity flux is evaluated for the associated circulation anomalies the framework is applied to reanalysis data for the period prior to a stratospheric sudden warming ssw event in january 2006 which was associated with two successive events of above normal wave activity injection from the troposphere in the earlier event a pair of wave packets that emanated from tropospheric anomalies over the north pacific and over europe enhanced the upward wave activity injection which was augmented further by their interaction with the climatological planetary wave in contrast in the later period a wave packet that emanated from an anticyclonic anomaly over the north atlantic is found to be the primary contributor to the enhanced planetary wave activity injection while its interaction with the climatological planetary wave contributed negatively the predominant importance of the sole contribution from a single wave packet is also found in a major ssw event observed over antarctica in september 2002 these results indicate that the diagnostic framework presented in this study is a useful tool for understanding the interaction between anomalies associated with zonally confined wave packets and climatological mean planetary waves in the study of stratosphere troposphere dynamical coupling copyright 2009 royal meteorological society

a link between reduced barents kara sea ice and cold winter extremes over northern continents the recent overall northern hemisphere warming was accompanied by several severe northern continental winters as for example extremely cold winter 2005 2006 in europe and northern asia here we show that anomalous decrease of wintertime sea ice concentration in the barents kara b k seas could bring about extreme cold events like winter 2005 2006 our simulations with the echam5 general circulation model demonstrate that lower troposphere heating over the b k seas in the eastern arctic caused by the sea ice reduction may result in strong anti cyclonic anomaly over the polar ocean and anomalous easterly advection over northern continents this causes a continental scale winter cooling reaching 1 5 c with more than three times increased probability of cold winter extremes over large areas including europe our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it being in qualitative agreement with the simulated large scale atmospheric circulation realignment furthermore our results suggest that high latitude atmospheric circulation response to the b k sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then again back to cyclonic type of circulation as the b k sea ice concentration gradually reduces from 100 to ice free conditions we present a conceptual model which may explain the nonlinear local atmospheric response in the b k seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

tropospheric precursors and stratospheric warmings abstractmany tropospheric arctic oscillation ao events are preceded by stratospheric ao events and even earlier in time by anomalous upward energy flux associated with rossby waves in the troposphere this study identifies lower tropospheric circulation anomalies that precede large ao events in both the troposphere and stratosphere and the anomalous upward energy flux compositing analysis of stratospheric warming events identifies regional tropospheric precursors which precede stratospheric warmings the tropospheric precursor is found to vary when compositing over polar vortex displacements and splits separately prior to vortex displacements the main anomaly sea level pressure center of the tropospheric precursor is located across northwest eurasia and is associated with the siberian high prior to vortex splits a similar anomaly center is identified in the tropospheric precursor but is weaker and appears to be more strongly related to a shift in the storm tracks differences in the sea level pressu

influence of tropical pacific sea surface temperature on the genesis of gulf stream cyclones abstractthis study investigates the relationship between tropical pacific sea surface temperature sst variability and cyclogenesis over the gulf stream region of the north atlantic a cyclone identification scheme and lagrangian trajectories are used to compare preferred cyclogenesis locations and precyclogenesis flow paths associated with three patterns of tropical pacific sst variability eastern pacific ep el nino central pacific cp el nino and la nina during ep el nino and la nina winters the upper level precyclogenesis flow takes a subtropical path over north america and gulf stream cyclogenesis predominantly occurs under the north atlantic jet entrance which is the climatologically preferred location in contrast during cp el nino winters when the warmest sst anomalies occur in the central tropical pacific the precyclogenesis flow takes a northern path across north america and gulf stream cyclogenesis tends to occur farther north under the jet exit the shift in preferred cyclogenesis

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is

two types of baroclinic life cycles during the southern hemisphere summer abstract baroclinic eddy life cycles of the southern hemisphere sh summer are investigated with ncep ncar reanalysis data a composite analysis is performed for the years 1980 through 2004 individual life cycles are identified by local maxima in synoptic scale eddy energy two types of baroclinic life cycles are examined each defined by the strength of the barotropic energy conversion 2 days prior to the maximum baroclinic growth for one life cycle the barotropic conversion is anomalously weak before the maximum baroclinic growth for the other the barotropic conversion is anomalously strong these two life cycles are referred to as the weak barotropic wb and strong barotropic sb life cycles the analyses for the wb life cycle find that a poleward anomalous wave activity flux is observed within the sh tropics and subtropics just before the initial growth of the synoptic scale eddies in contrast the sb life cycle exhibits an equatorward anomalous wave activity flux prior to the initial wave de

reconstruction of sediment supply from mass accumulation rates in the northern adriatic basin italy over the past 19 000 years reconstruction of sediment supply is hampered by the incompleteness of the stratigraphic record this problem may be partly circumvented by studying mass accumulation rates in closed systems i e basins in which no sediment has bypassed the site of deposition over the time interval of interest we present time averaged basin wide mass accumulation rates and their associated uncertainties from a well documented closed basin the northern adriatic basin italy spanning the time interval from 19 ka b p to the present the sediment masses of five basin wide lithosomes and their associated uncertainties are derived by means of stochastic simulation using highresolution seismic data porosity profiles and radiocarbon datings this study demonstrates that inferring rates of sediment supply from conformity bounded stratigraphic units is feasible as indicated by the excellent agreement of our results of mass accumulation over the past 400 years with two independently derived estimates formation of the stratigraphic record is not an instantaneous process by comparing spatial patterns of mass accumulation rates on three different timescales decadal centennial and millennial we demonstrate a low preservation potential of sediments presently accumulating near the coast and a continuous cross shore and alongshore sediment transport regime the change from transient to persistent accumulation patterns in the highstand systems tract of the northern adriatic basin occurs at the centennial to millennial timescale intrabasinal erosion and recycling of sediments obscure the relation between rates of sediment supply and net basin wide mass accumulation which limits the amount of information that can be extracted from the stratigraphic record hence a mismatch between rates of sediment supply and accumulation rates is expected for unconformity bounded sequence stratigraphic units given the uncertainties associated with our estimates we are unable to reject the hypothesis that net basin wide mass accumulation rates have been constant over the time interval of 19 000 years at a 10 significance level

mudstone compaction and its influence on overpressure generation elucidated by a 3d case study in the north sea mudstones are one of the least permeable rocks in most sedimentary sequences accordingly they can act as seals for fluid flow leading to abnormal overpressures nevertheless mudstone compaction and related permeability and porosity decrease are not adequately described in current basin modelling software because only mechanical compaction is taken into account in reality however clay minerals undergo severe chemical diagenesis which certainly influences petrophysical properties and compaction in this context a mathematical approach which has been originally developed in soil mechanics has been adapted to basin modelling the underlying mathematical equations are carefully explained in the text in the basic equation the compression coefficient is a function of void ratio and effective stress using these equations overpressure can be predicted by using petroleum systems modelling techniques this is shown for a real 3d case study in the north sea in which strong overpressure occurs a compaction model for mudstones that depends strongly on the clay content of the individual stratigraphic units is used for the calibration of porosities in the 3d case study in addition a chemical compaction model that reduces porosities by using a kinetic reaction is used for the deeper part of the basin where mechanical compaction processes are less important the pressure generation process depends strongly on permeability and compressibility of the porous medium therefore the use of mudstone compaction and permeability models is sufficient to produce pore overpressures in the case studied abnormal overpressures are generated during burial together with the petroleum generation process the mechanical and chemical compaction mechanisms ensure that the pressures are preserved in the deeper part of the basin

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

a consistent poleward shift of the storm tracks in simulations of 21st century climate 1 a consistent poleward and upward shift and intensification of the storm tracks is found in an ensemble of 21st century climate simulations performed by 15 coupled climate models the shift of the storm tracks is accompanied by a poleward shift and upward expansion of the midlatitude baroclinic regions associated with enhanced warming in the tropical upper troposphere and increased tropopause height the poleward shift in baroclinicity is augmented in the southern hemisphere and partially offset in the northern hemisphere by changes in the surface meridional temperature gradient the poleward shift of the storm tracks also tends to be accompanied by poleward shifts in surface wind stress and precipitation and a shift towards the high index state of the annular modes these results highlight the integral role that the storm tracks play in the climate system and the importance of understanding how and why they will change in the future

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

tropospheric precursors of anomalous northern hemisphere stratospheric polar vortices regional extratropical tropospheric variability in the north pacific and eastern europe is well correlated with variability in the northern hemisphere wintertime stratospheric polar vortex in both the ecmwf reanalysis record and in the whole atmosphere community climate model to explain this correlation the link between stratospheric vertical eliassen palm flux variability and tropospheric variability is analyzed simple reasoning shows that variability in the north pacific and eastern europe can deepen or flatten the wintertime tropospheric stationary waves and in particular its wavenumber 1 and 2 components thus providing a physical explanation for the correlation between these regions and vortex weakening these two pathways begin to weaken the upper stratospheric vortex nearly immediately with a peak influence apparent after a lag of some 20 days the influence then appears to propagate downward in time as expected from wave mean flow interaction theory these patterns are influenced by enso and october eurasian snow cover perturbations in the vortex induced by the two regions add linearly these two patterns and the quasi biennial oscillation qbo are linearly related to 40 of polar vortex variability during winter in the reanalysis record

compactional behavior of fine grained sediments examples from deep sea drilling project cores laboratory experiments statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep sea sediments which are in compaction equilibrium with the overburden a revised and generalized version of athy s law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles surfaces especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces the sediments analyzed almost range from systems of suspended grains to nearly perfect colloidal systems the methods and equations required to derive the relevant parameters are given for both downhole porosity density measurements and laboratory experiments

the impact of enso on wave breaking and southern annular mode events abstract this study examines the relationship between intraseasonal southern annular mode sam events and the el nino southern oscillation enso using daily 40 yr ecmwf re analysis era 40 data the data coverage spans the years 1979 2002 for the austral spring and summer seasons the focus of this study is on the question of why positive sam events dominate during la nina and negative sam events during el nino a composite analysis is performed on the zonal mean zonal wind eliassen palm fluxes and two diagnostic variables the meridional potential vorticity gradient a zonal mean quantity that is used to estimate the likelihood of wave breaking and the wave breaking index wbi which is used to evaluate the strength of the wave breaking the results of this investigation suggest that the background zonal mean flow associated with la nina el nino is preconditioned for strong weak anticyclonic wave breaking on the equatorward side of the eddy driven jet the type of wave breaking that is found

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

simple quantitative evaluation of porosity of argillaceous sediments at various depths of burial abstract relationship of porosity to depth of burial d in m geologic age a in millions of years and lithology ratio of thickness of shales total thickness of terrigenous deposits r has been developed by the writers which gives satisfactory results 0 exp 0 014 13 3 log a 83 25 log r 2 79 10 3 d where 0 initial porosity of the argillaceous sediment a nomogram has been prepared for an easy solution of the above equation

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

measurement of diagenetic compaction strain from quantitative analysis of fault plane dip we developed a new technique for quantifying the amount of porosity loss during diagenetic transformation of opal a to opal ct the technique is based on 3d seismic data from offshore norway where the widely developed biosiliceous sediments of the brygge formation are deformed by a polygonal fault system evidence is shown from two study areas that the dip of the polygonal fault planes reduces abruptly across the opal a to opal ct diagenetic boundary suggesting that the fault planes were passively rotated into shallower dips due to diagenesis the reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis using an independent assessment of the magnitude of the porosity loss we are able to validate the method based on fault plane dips and also to evaluate whether the porosity loss results in an exclusively vertical strain additionally the impact of silica diagenesis on the shear strength of the sediments and fault growth is investigated we present evidence suggesting that deviations from classical mohr coulomb behaviour may be expected during the combined processes of diagenesis and porosity collapse and may indeed be sufficient to promote continued fault growth

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

salt as a 3d element in structural modeling example from the central european basin system abstract based on a well constrained 3d structural model of the central european basin system 3d modeling has been carried out to understand the regional scale regularities between movements of the upper permian zechstein salt and the major post permian tectonic events the 3d reconstruction of the paleo thickness of upper permian salt at the end of the permian period demonstrates that areas of thickened upper permian salt correlate with the present day distribution of the largest salt structures within the central european basin system this spatial correlation implies that the distribution of salt thickness at the end of deposition partially controlled the structural style of the basin during post permian phases of salt tectonics moreover the results of 3d salt redistribution for post permian times indicate that the initiation of salt movements took place in the triassic the triassic extensional events triggered several phases of salt movements within the coeval depocenters of the central european basin system such as the glueckstadt graben the horn graben the norwegian danish basin the fjerritslev trough and the himmerland graben and the polish basin during the late jurassic early cretaceous extensional transtensional tectonic event the strongest salt movement occurred within the central graben the lower saxony basin and the pompeckj block the intensity of the late jurassic early cretaceous phase of salt tectonics is essentially declining from the marginal areas of the central european basin system towards the horn graben the glueckstadt graben and adjacent areas the late early cretaceous early late cretaceous is characterized by tectonic quiescence without strong salt movements over the entire study area the next regional phase of salt movements was triggered by late cretaceous early cenozoic inversion involving almost the entire central european basin system in terms of renewed salt movements inversion related thick skinned salt tectonics is observed along the nw se trending elbe fault system and the teisseyre tornquist zone where strongest compressional deformations were localized on the contrary a thin skinned character of salt movements was prevailing within the largest part of the north german basin post inversion cenozoic subsidence was also accompanied by salt activity related either to diapiric rise due to regional shortening and or to local roughly e w directed extension the cenozoic phase of salt movements was especially prominent within the marginal troughs of the glueckstadt graben

the deep structure of the south atlantic kwanza basin insights from 3d structural and gravimetric modelling abstract we present results from 3d gravimetric modelling of the kwanza basin offshore angola accomplished to investigate the deep crustal structure beneath the basin and discuss our findings with respect to their implications for the opening of the central south atlantic the kwanza basin is located in the southern part of the central south atlantic although the post rift evolution of the kwanza basin is well studied little is known about the basin s early history this is mainly due to the missing knowledge of its crustal structure owing to the masking effect of an up to 4 km thick salt layer which seismically obscures the underlying basement to get an insight into the deeper structure of this part of the angolan margin we combined 3d structural isostatic and gravimetric modelling 2d seismic reflection data was used to determine the structural setting and the configuration of the stratigraphic units in the sedimentary part of the basin whereas its crustal structure was constrained by isostatic and gravity modelling our modelling results indicate that high density lower crustal bodies similar to ones found in the northern part of the central segment are present in the southern part and thus seem to be a general feature of the crust of the central south atlantic thinning of the crust occurs gradually rather than in an abrupt manner and block faulting seems to have played a significant role during rifting as is indicated by a strongly structured upper crust in contrast we find little evidence for ductile thinning or exhumation of the deeper lithosphere as previously suggested for the northern segment of the central south atlantic in its southern segment it appears more likely that magmatic intrusions prevented mantle exhumation by sealing crustal detachment faults and giving the margin a distinct magmatic signature

shale compaction and statistical physics summary after a short historical outline of the development of the ideas on the compaction of clays and shales it is shown that the exponential porosity depth dependence of compacted shales expressed by athy s law can be derived using standard methods of statistical physics the main result of the paper states that the exponential compaction law expresses the maximum entropy equilibrium state of the pores in the rock that is compaction is an irreversible process where clay particles tend towards a statistically defined final equilibrium connections with the classical theory of consolidation are pointed out

poleward shift of subtropical jets inferred from satellite observed lower stratospheric temperatures abstractone pronounced feature in observed latitudinal dependence of lower stratospheric temperature trends is the enhanced cooling near 30 latitude in both hemispheres the observed phenomenon has not to date been explained in the literature this study shows that the enhanced cooling is a direct response of the lower stratospheric temperature to the poleward shift of subtropical jets furthermore this enhanced lower stratospheric cooling can be used to quantify the poleward shift of subtropical jets using the lower stratospheric temperatures observed by satellite borne microwave sounding units it is shown that the subtropical jets have shifted poleward by 0 6 0 1 and 1 0 0 3 latitude in the southern and northern hemispheres respectively in last 30 years since 1979 indicating a widening of tropical belt by 1 6 0 4 latitude

eddy zonal flow feedback in the northern hemisphere winter abstract the variability of the zonal mean zonal wind in the northern hemisphere winter december march is studied using eof analysis and momentum budget diagnostics of ncep ncar reanalysis data 1976 2001 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude westerlies analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes selects the leading eof of midlatitude variability like the southern hemisphere the baroclinic eddies reinforce the zonal wind anomalies while external rossby waves damp the wind anomalies in the northern hemisphere the quasi stationary eddies also reinforce the zonal wind anomalies but the baroclinic eddies are most important for the positive eddy zonal flow feedback the observations support the following feedback mechanisms 1 above normal baroclinic wave activity is generated in the region of enhanced wester

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

factors controlling the thermo mechanical deformation of oil shales implications for compaction of mudstones and exploitation abstract six permian to miocene organic matter rich mudstones were subjected to unconfined compression tests under three thermo mechanical regimes the aims of this study were to assess the role of factors that control deformation and highlight implications for mudstone compaction and oil shale exploitation axial strain ranged from 1 9 to 23 at 25 c 5 3 70 mpa 12 79 at 25 310 c 31 42 mpa and 1 38 40 at 25 350 c 0 8 mpa the axial strain data showed that the principal factor controlling mudstone compaction is temperature with a secondary role for effective stress during high temperature tests dehydration of smectite in the 94 150 c interval resulted in a distinct axial strain effect decomposition of organic matter and other minerals caused visible strain only above 280 c tests up to 350 c resulted in mass loss of 4 54 43 8 wt with 1 1 8 wt due to organic matter a strong positive correlation was found between the petroleum generation indices 4 6 55 8 and expulsion efficiencies 38 6 96 2 while compaction 0 68 51 4 correlated with axial strain 1 38 40 solid volume loss 2 55 12 15 due to petroleum generation from kerogen resulted in an increase in porosity 1 56 6 36 low rate heating and low retorting temperature are necessary to optimise yield from oil shale exploitation

rossby wave propagation from the arctic into the midlatitudes does it arise from in situ latent heating or a trans arctic wave train abstractthe relationship between latent heating over the greenland barents and kara seas gbks hereafter and rossby wave propagation between the arctic and midlatitudes is investigated using glo

a statistical analysis of relationships between western north pacific tropical cyclones and extratropical circulation patterns accompanying the madden julian oscillation abstractrelationships between the madden julian oscillation mjo and the extratropical circulation have been studied extensively and applied in operational settings to improve subseasonal predicti

why might stratospheric sudden warmings occur with similar frequency in el nino and la nina winters 1 the effect of el nino southern oscillation enso on the frequency and character of northern hemisphere major mid winter stratospheric sudden warmings ssws is evaluated using a meteorological reanalysis data set and comprehensive chemistry climate models there is an apparent inconsistency between the impact of opposite phases of enso on the seasonal mean vortex and on ssws el nino leads to an anomalously warm and la nina leads to an anomalously cool seasonal mean polar stratospheric state but both phases of enso lead to an increased ssw frequency a resolution to this apparent paradox is here proposed the region in the north pacific most strongly associated with precursors of ssws is not strongly influenced by el nino and la nina teleconnections in the observational record both la nina and el nino lead to similar anomalies in the region associated with precursors of ssws and consistent with this there is a similar ssw frequency in la nina and el nino winters a similar correspondence between the penetration of enso teleconnections into the ssw precursor region and ssw frequency is found in the comprehensive chemistry climate models the inability of some of the models to capture the observed relationship between la nina and ssw frequency appears related to whether the modeled enso teleconnections result in extreme anomalies in the region most closely associated with ssws finally it is confirmed that the seasonal mean polar vortex response to enso is only weakly related to the relative frequency of ssws during el nino and la nina

the continuum of northern hemisphere teleconnection patterns and a description of the nao shift with the use of self organizing maps abstract in this study the method of self organizing maps soms is used with ncep ncar reanalysis data to advance the continuum perspective of northern hemisphere teleconnection patterns and to shed light on the secular eastward shift of the north atlantic oscillation nao that began in the late 1970s a 20 pattern som analysis of daily wintertime northern hemisphere sea level pressure reveals a continuum of patterns that correspond closely with well known teleconnection patterns this analysis also reveals that interdecadal variability of the hemispheric sea level pressure field may be understood in terms of changes in the frequency distribution within the continuum of sea level pressure patterns described by the som based on the continuum perspective illustrated with the som the above secular shift of the nao may be understood as a change in dominance from westward displaced negative nao like patterns to eastward displaced positive nao like patterns though westward and eastward displaced nao

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

interpreting transient carbonate compensation depth changes by marine sediment core modeling 1 with the advent of computationally fast intermediate complexity models of earth s climate and carbon cycle the marine record can be interpreted much more directly than before specifically the mechanistic simulation of deep sea sediment cores provides an important step in bridging the model data divide here i use this methodology to help interpret the excursion in carbonate compensation depth ccd during the paleoceneeocene thermal maximum that is recorded in cores recovered from walvis ridge in the south atlantic by explicitly simulating the expected geological record of a massive co2 release in an earth system model i show how reduction in the intensity of subsurface mixing of the sediment by benthic animals substantially magnifies the recorded shoaling of the ccd conversely to quantify correctly the carbon release consistent with the observed ccd changes one must account for any bioturbational changes a reduction in sediment mixing intensity also appears to be important to reproducing the sharpness of the contact between carbonate rich late paleocene sediments and the overlying early eocene clay layer at walvis ridge assuming a relatively rapid approximately 1 ka duration co2 release further helps to account for some of the paleoceanographic observations finally interbasin differences in bioturbational regime help resolve some of the observed disparity in carbonate preservation between walvis ridge and sites outside of the atlantic although changes in ocean ventilation and circulation are also likely to play a critical role in this

the use of burrows to detect compaction and sliding in fine grained sediments an example from the cretaceous of s e france in the french southern alps alternating pelagic limestones and marls of hauterivian age contain a dense network of burrows differences between the original and preserved forms of the burrows provide evidence of sediment deformation a total compaction from early dewatering of sediment to deep burial compression caused flattening of burrows parallel to bedding its relation to carbonate is measured and a tentative mathematical relation is proposed b synsedimentary slumping is shown by total disordering of the bioturbation network in the displaced layers c a more characterized deformation is occasionally visible only on the upper part of some limestone beds the sliding is indicated by the dip of burrows in the same direction as the flow d similar embryonic flows occur in the middle of rare limestone beds it is thus suggested that this can account for some of the double beds that occur in pelagic alternations of calcareous and marly beds

1 d modelling rock compaction in sedimentary basins using a visco elastic rheology abstract recent experimental studies on unlithified sediments suggest that the compaction is in part viscous at the basin scale and on a geological time scale processes such as pressure solution can be approached by creep deformation subjected to a viscous rheology in the present work we have studied porosity reduction and fluid pressure development resulting from the visco elastic compaction of a sedimentary basin during its formation model equations include continuity equations darcy s law and a visco elastic rheology law which relates the strain rate to the effective stress and to the rate of change of this effective stress under the assumption that permeability is a power law function of porosity the equations become essentially non linear model results illustrate how the decrease of porosity starts at the base of the basin and spreads upward with increasing time in a wide range of input parameter values calculations indicate a zone of almost linear increasing of pore pressure just below the basin surface a transition zone of rapidly increasing fluid pressure with a large pressure gradient and a zone of lithostatic fluid pressure below this is consistent with the general features of zoning of fluid pressure distribution in overpressured areas but zones with high pressure also correspond to low porosity at depth the relative thickness of the zones depends on time subsidence velocity and the physical parameters of sediments which can be combined in order to define a characteristic compaction length and a characteristic compaction time in the upper zone the decrease of porosity results in a boundary layer within this layer the porosity decreases from its initial value down to its minimum value the deeper zone appears when the time of formation of the given depth basin exceeds the characteristic compaction time and the thickness of the basin is in order of compaction length zones of fluid overpressure may also develop due to the spatial variations of the physical properties of the sediments

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

application of cross hole seismic measurements in site investigation surveys application of the cross hole seismic method to site investigation surveys for civil engineering developments is illustrated by case histories from the united kingdom using the borehole sparker probe developed in mccann et al 1975 as the seismic source at newborough anglesey it is shown that this source generates both a compressional wave and a vertically polarized shear wave in the borehole the measured velocity values are used to determine the dynamic elastic moduli of the saturated sand deposit at this site at cocking sussex and east fleet dorset the presence of an air filled void between two boreholes is shown to have a significant effect on the velocity of propagation and amplitude of the transmitted seismic signals this work is extended at maidstone kent where the technique is used to confirm the presence of a cavity below the foundation of a house in the hot dry rock geothermal project at rosemanowes cornwall increased fracturing of the granitic rock mass following explosive stimul

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

basin evaluation using burial history calculations an overview burial history calculations available to the petroleum geologist include plots of burial history and geohistory porosity and conductivity as a function of depth and lithology as well as the results obtained from algorithms to handle unconformities and backstripped crustal subsidence calculations that predict the breakdown of kerogen to hydrocarbons in terms of time and temperature and methods for determining heat flow from geologic models and vitrinite reflectance data inputs required for these calculations include depths of formation tops ages of formation tops lithologies of formations depths of water at deposition of the different formations porosities of the formations as a function of depth bottom hole temperatures and or formation temperatures and any ke ogen content and vitrinite reflectance values as functions of depth sources of many of these data may be well logs well reports geologic papers and or seismic sections the paper considers how parameters can be extracted from burial history calculations to construct maps that can be compared to the current locations of oil and gas fields and so used to locate and rank prospective acreage these parameters include the potential source rock maturity of a formation plotted as a function of time and depth the thermal history of any hydrocarbons associated with the potential source rock the rate of sediment accumulation of a formation as a function of time and subsidence rate of a formation as a function of time subsidence rate includes total subsidence compaction induced subsidence isostatic response to sediment load and backstripped crustal subsidence total subsidence minus the effects of compaction and isostatic response

the continuum and dynamics of northern hemisphere teleconnection patterns this study presents an alternative interpretation for northern hemisphere teleconnection patterns rather than comprising several different recurrent regimes this study suggests that there is a continuum of teleconnection patterns this interpretation indicates either that 1 all members of the continuum can be expressed in terms of a linear combination of a small number of real physical modes that correspond to basis functions or 2 that most low frequency patterns within the continuum are real physical patterns each having its own spatial structure and frequency of occurrence daily ncep ncar reanalysis data are used that cover the boreal winters of 1958 97 a set of nonorthogonal basis functions that span the continuum is derived the leading basis functions correspond to well known patterns such as the pacific north american teleconnection and north atlantic oscillation evidence for the continuum perspective is based on the finding that 1 most members of the continuum tend to have similar variance and autocorrelation time scales and 2 that members of the continuum show dynamical characteristics that are intermediate between those of the surrounding basis functions the latter finding is obtained by examining the streamfunction tendency equation both for the basis functions and some members of the continuum the streamfunction tendency equation analysis suggests that north pacific patterns basis functions and continuum are primarily driven by their interaction with the climatological stationary eddies and that north atlantic patterns are primarily driven by transient eddy vorticity fluxes the decay mechanism for all patterns is similar being due to the impact of low frequency period greater than 10 days transient eddies and horizontal divergence analysis with outgoing longwave radiation shows that tropical convection is found to play a much greater role in exciting north pacific patterns a plausible explanation for these differences between the north atlantic and north pacific patterns is presented

compaction processes and rock properties in uplifted clay dominated units the egersund basin norwegian north sea abstract a thick succession of fine grained sediments in any sedimentary basin can serve as source if organic rich and top seals both sealing and petroleum generation capacity of any fine grained succession is dependent on compaction history mechanical and chemical compactions of the sediments in the egersund basin a thick succession of fine grained sediments of upper jurassic lower cretaceous age overly middle jurassic reservoir sands the egersund basin however has experienced a complex depositional and tectonic history particularly late exhumation neogene which complicates the overall burial thermal and pressure history in this study petrophysical and acoustic properties bulk density and p wave velocity of 10 exploration wells from two neighboring blocks in the egersund basin were utilized to investigate compaction processes in the area in addition x ray diffraction xrd and scanning electron microscopy sem analyses from selected wells and available total organic carbon toc data were used as guide to interpret the compaction processes and resulting rock properties the results show that the transition from mechanical to chemical compaction is not sharp the onset of chemical compaction imposes a measurable deviation in the burial depth trends of the petrophysical properties expected from purely mechanical compaction the continuation of the depth related trends however indicates that chemical compaction may occur in concurrent with continuing mechanical compaction the observed compaction varies between the different clay dominated stratigraphic units indicating that the major control on both mechanical and chemical compaction is the primary sediment composition

can the increase in the eddy length scale under global warming cause the poleward shift of the jet streams abstractthe question of whether an increase in the atmospheric eddy length scale may cause a poleward shift of the midlatitude jet streams is addressed an increase in the length scale of the eddy reduces its zonal phase speed and so causes eddies to dissipate farther from the jet core if the eddy dissipation region on the poleward flank of the jet overlaps with the eddy source latitudes shifting this dissipation to higher latitudes will alter which latitudes are a net source of baroclinic eddies and hence the eddy driven jet stream may shift poleward this behavior does not affect the equatorward flank of the jet in the same way because the dissipation region on the equatorward flank is well separated from the source latitudes an experiment with a barotropic model is presented in which an increase in the length scale of a midlatitude perturbation results in a poleward shift in the acceleration of the zonal flow initial investigations indicate that this behavior is also important in both observationa

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

intraseasonal and interdecadal jet shifts in the northern hemisphere the role of warm pool tropical convection and sea ice abstractthis study uses cluster analysis to investigate the interdecadal poleward shift of the subtropical and eddy driven jets and its relationship to intraseasonal teleconnections for this purpose self organizing map som analysis is applied to the ecmwf interim re analysis era interim zonal mean zonal wind the resulting som patterns have time scales of 4 8 5 7 days and undergo notable interdecadal trends in their frequency of occurrence the sum of these trends closely resembles the observed interdecadal trend of the subtropical and eddy driven jets indicating that much of the interdecadal climate forcing is manifested through changes in the frequency of intraseasonal teleconnection patterns two classes of jet cluster patterns are identified the first class of som pattern is preceded by anomalies in convection over the warm pool followed by changes in the poleward wave activity flux the second class of patterns is preceded by sea ice and stratospheric polar vortex anomalies when the arctic se

is the atmospheric zonal index driven by an eddy feedback abstract the authors address the question of whether or not eddy feedback plays an important role in driving the anomalous relative angular momentum associated with the zonal index zi in the atmosphere for this purpose composites of anomalous relative angular momentum and anomalous eddy angular momentum flux convergence eddy forcing are examined with national centers for environmental prediction national center for atmospheric research reanalysis data by using an empirical orthogonal function analysis it is found that zi behavior dominates the summer season of both hemispheres and also the winter season of the southern hemisphere for the summer season the zi is characterized by meridional displacements of the midlatitude eddy driven jet and for the southern hemisphere winter it is characterized by a simultaneous movement of the subtropical and eddy driven jets in the opposite direction for the zi of each of the above seasons unfiltered eddy forcing did not exhibit a prominent eddy feedback h

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

cluster analysis of northern hemisphere wintertime 500 hpa flow regimes during 1920 2014 abstractclusters in the northern hemisphere wintertime 10 day low pass filtered 500 hpa height field are identified using the method of self organizing maps soms results are based on 1 a 57 winter record of era and 2 a 93 winter record of the noaa twentieth century reanalysis 20cr the clusters derived from soms appear to be more robust and more linearly independent than their counterparts derived from ward s method and clusters with comparable numbers of member days are more distinctive in terms of the standardized euclidean distances of their centroids from the centroid of the dataset the reproducible som clusters in the hemispheric domain are 1 the negative polarity of the north atlantic oscillation nao 2 a pattern suggestive of alaska blocking with a downstream wave train extending over north america and the north atlantic 3 an enhancement of the climatological mean stationary wave pattern in the western hemisphere that projects positively upon the pacific north america pna pattern

stratigraphic completeness tiered trace fossils provide a measuring stick trace fossil associations commonly display a characteristic vertical zonation tiering within the substrate when burrows of a particular tier become truncated by turbidites tempestites or other results of catastrophic events they provide a simple but quantitative caliper for estimating stratigraphic incompleteness the minimum amount of penecontemporaneous sea floor erosion can be determined by types and sequences of trace fossils preserved below event deposits

the winter atmospheric response to sea ice anomalies in the barents sea abstractthe atmospheric response to sea ice anomalies over the barents sea during winter was determined by boundary forcing the community atmosphere model cam with daily varying high and low sea ice concentration sic anomalies that decreased realistically from december to february the high and low sic anomalies produced localized opposite signed responses of surface turbulent heat flux and wind stress that decreased in magnitude and extent as winter progressed responses of sea level pressure slp and 500 mb height evolved from localized opposite signed features into remarkably similar large scale patterns resembling the negative phase of the north atlantic oscillation nao hilbert empirical orthogonal function heof analysis of the composite high sic and low sic slp responses uncovered how they differed the hemispheric pattern in the leading heof was similar for the high sic and low sic responses but the high sic response cycled through the pattern once per winter whereas the low sic respon

the role of linear interference in the annular mode response to extratropical surface forcing abstract the classical problem of predicting the atmospheric circulation response to extratropical surface forcing is revisited in the context of the observed connection between autumnal snow cover anomalies over siberia and wintertime anomalies of the northern annular mode nam previous work has shown that in general circulation model gcm simulations in which autumnal siberian snow forcing is prescribed a vertically propagating rossby wave train is generated that propagates into the stratosphere drives dynamical stratospheric warming and induces a negative nam response that couples to the troposphere important questions remain regarding the dynamics of the response to this surface cooling it is shown that previously unexplained aspects of the evolution of the response in a comprehensive gcm can be explained by examining the time evolution of the phasing and hence the linear interference between the rossby wave response and the background climatological stationary wave when the wave response a

north atlantic storm track sensitivity to projected sea surface temperature local versus remote influences abstractthis study investigates the sensitivity of the north atlantic storm track to future changes in local and global sea surface temperature sst and highlights the role of sst changes remote to the north atlantic results are based on three related coupled climate models the community climate system model version 4 ccsm4 the community earth system model version 1 community atmosphere model version 5 cesm1 cam5 and the norwegian earth system model version 1 intermediate resolution noresm1 m analysis reveals noticeable intermodel differences in projected storm track changes from the coupled simulations i e the difference in 200 hpa eddy activity between the representative concentration pathway 8 5 rcp8 5 and historical scenarios in the ccsm4 coupled simulations the north atlantic storm track undergoes a poleward shift and eastward extension in cesm1 cam5 the storm track change is dominated by an intensification and eastward extension in noresm1 m the storm track change i

the relationship of undrained shear strength and porosity with depth in shallow 50 m marine sediments abstract in this paper we review the relationship between undrained shear strength and porosity with depth of marine sediments in the upper 50 m below the seafloor based on a compilation of data from 46 ocean drilling program odp legs we find that only about half of the drill sites show the anticipated increase in strength 59 and associated decrease in porosity 49 down hole moreover a significant correlation coefficient for both strength and porosity with depth is found at only 31 of the sites four categories of sediments are distinguished based on the significance of correlation coefficients we observe an influence of sediment composition and texture on the relationship between strength and porosity with depth fine grained siliciclastic sediments clayey and silty sediments and nannofossil oozes with less than 50 carbonate frequently show significant correlation coefficients for strength and porosity with depth while fine grained carbonates with high carbonate concentrations calcareous muds and nannofossil oozes with an average carbonate content of 87 as well as reef facies carbonates lack significant trends down hole moreover correlation patterns vary considerably with geological or tectonic setting for instance delta deposits of the amazon fan and sediments from the atlantic passive continental margins frequently show significant correlation coefficients for both properties extensional arcs often show significant correlation only for one property shear strength or porosity correlation patterns are discussed in the light of sediment composition geological and tectonic setting the methods used for shear strength measurement and previous work published on compaction behaviour

the role of linear interference in northern annular mode variability associated with eurasian snow cover extent one of the outstanding questions regarding the observed relationship between october eurasian snow cover anomalies and the boreal winter northern annular mode nam is what causes the multiple week lag between positive eurasian snow cover anomalies in october and the associated peak in rossby wave activity flux from the troposphere tothe stratospherein december thisstudy exploresthe following hypothesis about thislag in order toachieve amplificationofthe waveactivity the vertically propagatingrossbywave train associated with the snow cover anomaly must reinforce the climatological stationary wave which corresponds to constructive linear interference between the anomalous wave and the climatological wave it is shown that the lag in peak waveactivityflux arisesbecause the rossby wave train associatedwiththe snowcover isin quadrature orout of phasewiththeclimatologicalstationarywavefromoctobertomid november beginninginmid novemberthe associated wave anomaly migrates into a position that is in phase with the climatological wave leading to constructive interference and anomalously positive upward wave activity fluxes until mid january climate models from the coupled model intercomparison project 3 cmip3 do not capture this behavior this linear interferenceeffectisnot onlyassociatedwith stratospheric variabilityrelatedtoeurasiansnowcoveranomalies but is a general feature of northern hemisphere troposphere stratosphere interactions and in particular dominated the negative nam events of the fall winter of 2009 10