errors in paleomagnetism structural control on overlapped vectors mathematical models abstract the reliability of paleomagnetic data is a keystone to obtain trustable kinematics interpretations the determination of the real paleomagnetic component recorded at certain time in the geological evolution of a rock can be affected by several sources of errors inclination shallowing declination biases caused by incorrect restoration to the ancient field internal deformation of rock volumes and lack of isolation of the paleomagnetic primary vector during the laboratory procedures overlapping of components these errors will limit or impede the validity of paleomagnetism as the only three dimension reference this paper presents the first systematic modeling of the effect of overlapped vectors referred to declination inclination and stability tests taking into account the key variables orientation of a primary and secondary overlapped to the primary vectors degree of overlapping intensity ratio of primary and secondary paleomagnetic vectors and the fold axis orientation and dip of bedding plane in this way several scenarios of overlapping have been modeled in different fold geometries considering both polarities and all the variables aforementioned allowing to calculate the deviations of the vector obtained in the laboratory overlapped with respect to the paleomagnetic reference not overlapped observations from the models confirm that declination errors are larger than the inclination ones in addition to the geometry factor errors are mainly controlled by the relative magnitude of the primary respect to the secondary component p s ratio we observe larger asymmetries and bigger magnitudes of errors along the fold location if the primary and secondary records have different polarities if the primary record declination and the fold axis orientation are perpendicular 90 errors reach maximum magnitudes and larger asymmetries along the fold surface different dips the effect of overlapping in the fold and reversal tests is also qualitatively analyzed in this paper

changes in the 300 mb north circumpolar vortex 1963 2001 abstract the mean monthly polar stereographic map analyses of the free university of berlin terminated at the end of 2001 this paper summarizes the changes in size of the 300 mb north circumpolar vortex and quadrants for the full period of record 1963 2001 where the size has been defined by planimetering the area poleward of contours in the jet stream core a contracted vortex has tended to be a deep vortex in winter but a shallow vortex in summer during 1963 2001 there was a statistically significant decrease in vortex size of 1 5 per decade the decrease in size of western hemisphere quadrants being twice that of eastern hemisphere quadrants a significant increase in arctic oscillation ao index accompanies the significant decrease in vortex size but since the vortex contracts appreciably in all four seasons whereas the positive trend in the ao index is mainly in winter the vortex cannot serve as a proxy for the ao index the evidence for vortex contraction at the time of the 1976 77 regime

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

the influence of el nino southern oscillation events on the northern hemisphere 500 hpa circumpolar vortex the relationship between el nino the southern oscillation and their joint effect enso and northern hemisphere 500 hpa midlatitude circulation for the 1946 1994 observational record is determined seasonally standardized vortex positions at a spatial resolution of 5 longitude are correlated with an equatorial pacific sea surface temperature anomaly index and the southern oscillation index soi the 500 hpa circumpolar vortex is consistently expanded over the central pacific during and for the entire year following warm enso periods the vortex is contracted over north america concurrently with warm enso and to a lesser degree during the following season expansion contraction variability is also evident over east asia although the linkages to warm or cold enso are weak sea surface temperatures have a stronger association with the vortex than does the soi

elliptical diagnostics of stratospheric polar vortices diagnostics based on the spatial moments of isopleths of a long lived tracer or of potential vorticity are presented that enable the structure and evolution of stratospheric polar vortices to be concisely summarized and quantified the area centre aspect ratio and orientation of the equivalent ellipse of the vortex on an isentropic surface are defined using the second and lower order spatial moments of contours within the vortex edge region by examining the variations of these elliptical diagnostics with time and altitude the temporal evolution and vertical structure of the polar vortices can be quantified the usefulness of the diagnostics is assessed by examining nitrous oxide data from the geophysical fluid dynamics laboratory skyhi general circulation model the diagnostics show and quantify several differences between the arctic and antarctic vortices in the skyhi model the arctic vortex moves further off the pole is generally more elongated and has a more complicated vertical structure than the antarctic vortex with larger variations of both the vortex centre and elongation with height the elliptical diagnostics also identify the occurrence of large scale rossby wave breaking events both at the vortex edge and in the subtropics in the model

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

the volcanic signal in surface temperature observations abstract climate records of the past 140 years are examined for the impact of major volcanic eruptions on surface temperature after the low frequency variations and el nino southern oscillation signal are removed it is shown that for 2 years following great volcanic eruptions the surface cools significantly by 0 1 0 2 c in the global mean in each hemisphere and in the summer in the latitude bands 0 30 s and 0 30 n and by 0 3 c in the summer in the latitude band 30 30 60 n by contrast in the first winter after major tropical eruptions and in the second winter after major high latitude eruptions north america and eurasia warm by several degrees while northern africa and southwestern asia cool by more than 0 5 c because several large eruptions occurred at the same time as enso events the warming produced by the enso masked the volcanic cooling during the first year after the eruption the timescale of the enso response is only 1 year while the volcanic response timescale is 2 years so the coo

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

cosmonaut polynya in the southern ocean structure and variability along the far eastern margin of the weddell gyre is a persistent feature in the middle of the ice pack which we previously reported and called the cosmonaut polynya a study of polynya occurrences from 1973 to 1993 reveals that since 1986 the polynya has become more active with an average size of about 7 2 104 km2 and an average location at 52 e and 65 s satellite observations indicate that the polynya has recurred several times during winter in recent years with intervals ranging from a few days to a few weeks the centroid of the polynya varies only slightly with each formation during the year and from one year to another suggesting a controlling influence of the ocean and bottom topography that may be initially induced by wind the daily time series indicates two primary modes of formation one that is initiated in the early winter during a storm at a site usually preceded by an embayment of the ice edge and another that occurs during midwinter often preceded by a coastal polynya event adjacent to cape ann the cosmonaut polynya region is characterized in this study by compression of the westward flowing coastal current and the eastward flowing southern edge of the antarctic circumpolar current following the principle of conservation of potential vorticity vertical stretching of the water column would ensue enhancing upwelling such a process accelerates the injection of relatively warm salty deep water into the surface layer inhibiting sea ice growth and causing the polynya formation this theory appears to explain the general behavior of the polynya in terms of frequency duration size and location

platform sedimentation and collapse in a carbonate dominated margin of a foreland basin jaca basin eocene southern pyrenees the eocene jaca basin is a foreland basin with well exposed carbonate platforms in the distal margin this margin underwent alternating periods of stable platform growth and platform drowning periods of drowning were accompanied by large scale collapses with generation of shelf edge truncations and resedimentation of carbonate megabreccias into a terrigenous turbiditic trough these features caused a stepped retreat of the platforms and are related to episodic variations of tectonic loading in the hinterland and correlative flexural bending of the distal basin

contraction of the 300 mbar north circumpolar vortex during 1963 1997 and its movement into the eastern hemisphere the size of the 300 mbar north circumpolar vortex and its partition into western and eastern hemispheres and quadrants 0 90 w 90 w 180 90 e 180 and 0 90 is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean monthly analyses of the institute of meteorology of the free university of berlin during 1963 1997 the trend in annual vortex size is a significant 1 4 decade vortex contraction but with the trend in the western hemisphere portion of the vortex a significant 2 1 decade compared to 0 7 decade in the eastern hemisphere portion signifying a movement of the vortex farther into the eastern hemisphere thus while on average 52 of the vortex was in the eastern hemisphere during 1963 1997 this value increased by a significant 0 4 decade during the period resulting in a substantial increase in vortex eccentricity in winter and spring the vortex has moved mainly into the asian quadrant 90 e 180 whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90 e 180 and 0 90 w and in autumn there has been a decrease in size of quadrant 90 w 180 relative to the other quadrants the standard deviation of the annual quadrant size anomalies has decreased significantly during 1963 1997 indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts on the basis of a 41 station northern hemisphere radiosonde network during 1963 1997 the annual 850 300 mbar temperature increased by a significant 0 12 c decade in the northern hemisphere as a whole and by a significant 0 17 c decade in the western half and by 0 06 c decade in the eastern half of the hemisphere the resulting association of a 1 decade decrease in 300 mbar vortex size with about an 0 1 c decade increase in 850 300 mbar temperature differs by a factor of 2 from what would be expected hydrostatically a difference that would be eliminated by an 0 4 mbar decade increase in midlatitude surface pressure during 1963 1997

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

relation of size and displacement of the 300 mbar north circumpolar vortex to qbo el nino and sunspot number 1963 2000 the size of the 300 mbar north circumpolar vortex and its eastern western date line and greenwich hemisphere components is estimated for the period 1963 2000 by planimetering the area poleward of 300 mbar contours in the main belt of westerlies on the mean monthly polar stereographic analyses of the institute of meteorology of the free university of berlin on the basis of the superposed epoch method there is little evidence of a relation between vortex size and phase of the qbo but significant at the 90 level or better is the tendency for the vortex to be less displaced into the eastern hemisphere in the east wind phase of the qbo for the vortex to be expanded near the time of nino 3 sea surface temperature maximum el nino but contracted 3 4 seasons after and for the vortex to be displaced farther into the date line hemisphere when there is an el nino there is also an impressive tendency for the winter vortex to be less displaced into the eastern hemisphere at the time of el nino the tendency for the vortex to be contracted near sunspot maximum and expanded near sunspot minimum is significant at only about the 80 level because of the small sample size

relation between 300 mb north polar vortex and equatorial sst qbo and sunspot number and the record contraction of the vortex in 1988 89 abstract the size of the 300 mb north circumpolar vortex and quadrants has been estimated between 1963 and 1989 by planimetering the area poleward of contours in the main belt of westerlies on the 300 mb mean monthly polar stereographic maps analyzed by the meteorological institute free university of berlin the annual mean vortex was most contracted in 1989 6 4 less than average size and next most contracted in 1988 4 6 less than average size there have been three extensive vortex displacements during this period the last toward the north pacific and associated with the strong el nino of 1982 83 based on 108 seasonal deviations there has been a significant correlation of 0 39 between sea surface temperature sst in the eastern equatorial pacific and vortex size three seasons later that is the vortex has tended to be contracted following el nino there has been a highly significant correlation of 0 45 between this sst and the size of quadrant 90 w 180 in the same season that is this el n

surface oceanography of broke west along the antarctic margin of the south west indian ocean 30 80 e abstract hydrographic ctd and adcp data were collected during the broke west research voyage january march 2006 in the south west indian ocean sector of the antarctic margin these data describe the large scale circulation water masses fronts and summertime stratification in the surface layer over the continental shelf slope and rise region between 30 and 80 e that forms ccamlr statistical area 58 4 2 the surface circulation matched the full depth circulation and consisted of the eastward flowing southern antarctic circumpolar current front to the north and the westward flowing antarctic slope current associated with the antarctic slope front along the continental slope to the south two sub polar gyres were detected south of the southern boundary of the antarctic circumpolar current the eastern weddell gyre in the cosmonaut sea 30 50 e and the greater prydz bay gyre in the cooperation sea 60 80 e in the eastern weddell gyre the seasonal mixed layer depths were shallower warmer and fresher relative to the regions to the east which were deeper cooler and more saline this spatial variability is found to be strongly correlated to the large scale pattern of sea ice melt retreat in the months preceding the voyage and the accumulated wind stress thereafter areas of upwelling warm deep waters into the surface layer are presented from positive anomalies of potential temperature and nutrient concentrations nitrate and silicate these anomalies were strongest in the eastern weddell gyre in the vicinity of the cosmonaut polynya embayment north of cape anne and near the southern boundary of the antarctic circumpolar current in the eastern sector of the survey the summertime stratification seasonal mixed layer seasonal pycnocline and tmin layer are discussed relative to the distributions of chl a and acoustically determined antarctic krill euphausia superba densities elevated chl a concentrations were found in the surface layer of the marginal ice zone and it is proposed that these are retained south of the fast narrow jet of enhanced antarctic slope current on the upper continental slope there is qualitative evidence of these maxima being subducted and transported north in the seasonal pycnocline in response to ekman convergence from the easterly winds in this region the seasonal mixed layer within the sub polar gyres had relatively low chl a concentrations with sub surface maxima in the seasonal pycnocline and the top of the tmin layer surface concentrations increased once again north of the southern boundary in the north east of the survey krill and chl a concentrations were both co located and decoupled at different locations across the survey there was no clear oceanographic boundary influencing the distribution of the krill surveyed though further work is necessary to properly synthesize this and other biological patterns with the oceanographic processes given the varying time and length scales and intrinsic sampling limitations

cretaceous tertiary tectonic inversion of the cotiella basin southern pyrenees spain the cotiella nappe includes one of the most important mesozoic basins of the southern pyrenees which was subsequently inverted during the tertiary compression the late cretaceous cotiella basin is here interpreted as the western sector of the cretaceous cotiella boixols basin 100 20 km wide located in the central part of the southern pyrenees the present day complex structure of the cotiella nappe is the result of the inversion process linked to the emplacement of basement thrust sheets of the axial zone in its western sector the cotiella nappe consists of several superimposed thrust sheets with complex geometry becoming simpler towards the east with a single thrust surface and smaller displacements the cotiella boixols basin underwent strong subsidence during the early cretaceous at its eastern sector and its depocentre migrated westward during the late cretaceous the reconstruction of the sedimentary basin to the pre compressional stage shows that during the mesozoic the cotiella boixols basin was located to the south of a basement high which later became the pyrenean axial zone from a balanced cross section it can be inferred that the cotiella north verging extensional system was connected with the north pyrenean rift by means of a 10 km deep horizontal detachment the compressional tertiary detachment within the upper crust was shallower than the extensional detachment and individualised four basement thrust sheets which form the axial zone antiform

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

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

a climatology of sea ice embayments in the cosmonaut sea antarctica 1 the cosmonaut sea off the coast of antarctica is characterized by highly variable sea ice conditions as the sea ice expands during the austral fall and winter embayments open bodies of water surrounded on three sides by sea ice as well as polynyas often form using sea ice concentration data provided by satellite based passive microwave instruments from 1979 to 2004 we characterize these embayment events by their size and temporal evolution the data suggests a striking periodicity in the occurrence of these embayments with the exception of a quiet period between 1984 and 1987 the large embayment events seem to appear approximately every three years in the same location and persist for anywhere between mid june to mid august these results indicate there is predictability in the occurrence of embayment events adding important insight into the characterization of sea ice variability in this region

a high resolution simulation of convective roll clouds during a cold air outbreak 1 a ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two dimensional structures known as roll clouds or cloud streets in this paper we present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds the simulations were initialized and validated using observations of roll clouds over the labrador sea the model results indicate that the secondary flow associated with the roll clouds results in significant differences in the temperature humidity and momentum fields between the updrafts and downdrafts the model was also able to reproduce the observed downstream evolution of the clouds as the organization of the convection changed from two dimensional rolls to three dimensional closed cells

paleomagnetically derived folding rates southern pyrenees spain well dated syntectonic unconformities with the spanish pyrenees allow characterization of sedimentation and deformation within an orogenic foreland the spanish pyrenees are composed of a south vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the mediano anticline the largest of the transverse folds folding began in the early eocene and ended by 42 ma at which time an anticline 20 km long and 5 km in wavelength had been produced angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development fold growth resulted from west ward salt movement driven by prograding sediments and was characterized by 2 3 m y intervals of slow continuous limb tilting 2 2 4 2 m y preserved as progressive unconformities within syntectonic strata because the emplacement of the cotiella montsec thrust sheet was episodic intervals of slow fold growth were punctuated by intervals lasting

chronostratigraphy of the boltana anticline and the ainsa basin southern pyrenees the ainsa basin south central pyrenees is an exceptional example of a syntectonic foreland basin where structures oblique to the pyrenean trend are well preserved the absence of a complete chronostratigraphic frame motivated us to perform a detailed magnetostratigraphic study in the ainsa basin including the shallow marine continental transition three sections covering almost the entire eocene sedimentary fill were sampled ara coscollar and mondot covering 2450 m of the sedimentary pile with more than 1000 demagnetized specimens sample spacing of 2 7 m data from previous magnetostratigraphic studies eripol section allow us to complete the eocene record with an 840 m long profile within the bartonian priabonian interval overlying the sampled sequence characteristic remanent magnetization chrm directions were effectively isolated between 300 and 500 c magnetite is the main magnetic carrier with variable iron sulfide content and occasional hematite fold tests indicate a prefolding magnetization biostratigraphy based on shallow benthic foraminifera 15 localities and a locality with abundant charophyte gyrogonites help to constrain the local magnetostratigraphic record 20 reversals between the early ilerdian and the middle priabonian a global correlation based on a magnetostratigraphic composite section derived from this work allows us to propose a complete chronostratigraphic frame for the ainsa basin infill between 55 and 45 ma accumulation rates range from 2 to 53 cm k y responding to retrogradational to progradational features during the early lutetian and a progressive increase from the middle lutetian onward related to overall continentalization of the basin westward migration of subsidence is associated with progressively younger synsedimentary structures nucleating westward of the older ones in the south pyrenean basin

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

a new middle to late eocene continental chronostratigraphy from ne spain abstract the calibration of the european paleogene mammal biochronology with the international reference geochronological scale is unconstrained due to the lack of direct marine continental correlations and insufficient robust magnetostratigraphic data for mammal fossil bearing sequences the currently accepted european continental biochronology argues for a correlation of the paleogene mp14 to mp16 mammal reference levels with the bartonian stage and of the mp17 to mp20 levels with the priabonian however new magnetostratigraphic data of the continental sediments of the south central pyrenees substantially challenge this chronology our new results from the la pobla de segur basin and sierra de sis have been integrated into the framework of previous marine continental stratigraphic correlations and magnetostratigraphic data of the south central pyrenees in this new chronology mp14 and mp15 reference levels correspond to the lutetian whereas mp16 and early mp17 correlate with the early bartonian this calibration represents a significant revision of currently accepted marine continental correlations in europe but is not in conflict with the available biostratigraphic data of the south pyrenean ebro foreland basin and other western european reference basins

a numerical study of the western cosmonaut polynya in a coupled ocean sea ice model 1 employing results from a 0 4 40 level fully global coupled ocean sea ice model we investigated the role of physical processes emanating from atmosphere ocean and ice in the initiation maintenance and termination of a sensible heat polynya with a focus on the western cosmonaut polynya that occurred during may july 1999 the cosmonaut polynya first appeared in early may 1999 in the form of an ice free embayment transformed into an enclosed polynya on 5 9 july and disappeared by late july when the ice from the surrounding regions began to encircle the embayment except for the differences in ice concentrations the time of appearance size and shape of the cosmonaut polynya simulated by the model are in approximate agreement with the special sensor microwave imager ssm i observations between may and july 1999 the cosmonaut sea experienced two synoptic storms both lasting 5 days followed by the passage of the first storm on 12 19 june there was a remarkable growth in the size of the embayment by 21 103 km2 associated with this the sea surface temperature sst rose by 0 15 c the upward heat flux jumped from 5 to 94 w m 2 and a net freshwater flux into the ocean increased by 2 cm d 1 by running the model simulation with a 20 wind speed increase it is demonstrated that the twofold increase in sst and upward heat flux increased the embayment area by 15 103 km2 and decreased the ice concentration by approximately 10 from the control run a similar but somewhat weaker wind event that took place on 30 june to 10 july had less influence on the embayment area although the upward heat flux 65 w m 2 was comparable to the first event by examining the vertical displacement of the 1 6 c isotherm depth prior to during and after these two storms we demonstrate that the impetus provided by these storms was able to raise the 1 6 c isotherm depth by 30 m through wind driven mixing making sufficient oceanic heat input from beneath the mixed layer available to prevent freezing and or delay ice formation while ice in the adjacent regions continued to grow a sudden shift in the ice drift direction from southwest to northeast 3 july followed by the second storm accompanied by large air sea temperature differences caused the enclosure of the embayment subsequent formation of the polynya and its termination

long term variation of the antarctic circumpolar wave 1 during the period 1968 1999 the character of circum antarctic anomalies in sea level pressure sea ice edge and sea surface temperature changed substantially an antarctic circumpolar wave acw is only clearly visible in the period 1985 1994 before and perhaps after this the signal particularly in sea level pressure is quite different with no clear sign of precession accompanying the change from precessional to nonprecessional modes is a change in the spatial pattern of variability and a change in the predictability of atmospheric anomalies from oceanic forcing evidence from general circulation model integration suggests that during the precessional mode of the acw there is enhanced predictability as would be required to support a coupled ocean atmosphere interaction

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

size variations and long wave circulation within the january northern hemisphere circumpolar vortex 1946 89 abstract the close association between size variations in the northern hemisphere circumpolar vortex and surface and middle troposheric thermal characteristics makes vortex measurement a valuable tool in monitoring and understanding climate change unfortunately as with most hemispheric circulation indices measures of total vortex size offer little insight into regional changes in the vortex traditional approaches to vortex size calculation which are based upon planimeter measurements on a polar stereographic projection limit the ability to examine regional contributions to the total vortex and cannot be used to assess specific linkages between vortex expansion and contraction and the broader class of long wave circulation phenomena furthermore because the scale of the polar stereographic projection varies from one latitude to another interannual variations in planimeter vortex size measurements are influenced somewhat by the position of the vortex relative to the north pole many of these problem

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget