polar vortices on earth and mars a comparative study of the climatology and variability from reanalyses polar vortices on mars provide case studies to aid understanding of geophysical vortex dynamics and may help to resolve long standing issues regarding polar vortices on earth due to the recent development of the first publicly available martian reanalysis dataset macda for the first time we are able to characterise thoroughly the structure and evolution of the martian polar vortices and hence perform a systematic comparison with the polar vortices on earth the winter atmospheric circulations of the two planets are compared with a specific focus on the structure and evolution of the polar vortices the martian residual meridional overturning circulation is found to be very similar to the stratospheric residual circulation on earth during winter while on earth this residual circulation is very different from the eulerian circulation on mars it is found to be very similar unlike on earth it is found that the martian polar vortices are annular and that the northern hemisphere vortex is far stronger than its southern counterpart while winter hemisphere differences in vortex strength are also reported on earth the contrast is not as large distinctions between the two planets are also apparent in terms of the climatological vertical structure of the vortices in that the martian polar vortices are observed to decrease in size at higher altitudes whereas on earth the opposite is observed finally it is found that the martian vortices are less variable through the winter than on earth especially in terms of the vortex geometry during one particular major regional dust storm on mars martian year 26 an equatorward displacement of the vortex is observed sharing some qualitative characteristics of sudden stratospheric warmings on earth

altered atmospheric responses to eastern pacific and central pacific el ninos over the north atlantic region due to stratospheric interference the two types of el nino that have been identified namely the eastern pacific ep and central pacific cp el ninos are known to exert different climatic impacts on the north atlantic region during winter here we investigate the characteristics of the teleconnection of the two el nino types with a focus on the stratosphere troposphere coupling during the ep el nino polar stratospheric warming and polar vortex weakening frequently occur with a strong tendency for downward propagation near the tropopause consequently the atmospheric pattern within the troposphere over the north atlantic sector during midwinter closely resembles the negative north atlantic oscillation pattern in contrast during cp el nino events stratospheric warming events exhibit a much weaker downward propagation tendency this difference in the stratospheric circulation response arises from the different seasonal evolution of the tropospheric wave response to the two el nino types for the ep el nino the aleutian low begins growing during december and is sustained throughout the entire winter december to february which provides favorable conditions for the continuous downward propagation of the stratospheric warming we also discuss the origin of the difference in the teleconnections from the two types of el nino associated with the distinct longitudinal position of the warm sst anomaly that determines troposphere stratosphere coupling

downward coupling between the stratosphere and troposphere the relative roles of wave and zonal mean processes abstract wave and zonal mean features of the downward dynamic coupling between the stratosphere and troposphere are compared by applying a time lagged singular value decomposition analysis to northern hemisphere height fields decomposed into zonal mean and its deviations it is found that both zonal and wave components contribute to the downward interaction with zonal wave 1 due to reflection dominating on the short time scale up to 12 days and the zonal mean due to wave mean flow interaction dominating on the longer time scale it is further shown that the two processes dominate during different years depending on the state of the stratosphere winters characterized by a basic state that is reflective for wave 1 show a strong relationship between stratospheric and tropospheric wave 1 fields when the stratosphere is leading and show no significant correlations in the zonal mean fields on the other hand winters characterized by a stratospheric state that does not reflect waves show a strong relat

meridional and downward propagation of atmospheric circulation anomalies part ii southern hemisphere cold season variability abstract as in the northern hemisphere there exists a simultaneous poleward propagation of temperature anomalies in the stratosphere and equatorward propagation in the troposphere in the southern hemisphere s cold season it takes about 110 days for anomalies of one polarity to propagate from the equator to the pole or half the period of the complete cycle nearly twice as long as in the northern hemisphere the earlier poleward propagation of temperature anomalies in upper levels compared with those in lower levels results in an apparent downward propagation in the stratosphere accompanying the poleward and downward propagating warm cold anomalies is a successive leveling steepening of isentropic surfaces reflecting a simultaneous reduction strengthening of the meridional temperature gradient and increase decrease of the vertical static stability following changes in the thermal fields are poleward and downward propagating zonal wind anomalies of the opposite sign the arrival of the pole

a blocking view of the stratosphere troposphere coupling dynamical influence from the stratosphere is known to play a role in shaping the wintertime tropospheric circulation patterns observations suggest that this influence is strongest following weak and strong polar vortex events termed sudden stratospheric warmings ssws and vortex intensification vi events respectively in this work stratosphere troposphere coupling is studied through the modulation by extreme vortex events of the northern hemispheric tropospheric blocking frequency and eddy driven jet displacements this is done using three reanalysis data sets and the centro euro mediterraneo sui cambiamenti climatici climate model with a resolved stratosphere cmcc cms coupled model control run reanalysis results suggest the existence of distinct patterns of blocking activity following extreme vortex events over the atlantic basin ssws are shown to lead by about 20 50 days the occurrence of increased reduced blocking frequency on the poleward equatorward side of the atlantic jet stream anomalies of the opposite sense with poleward reduction and equatorward enhancement of the blocking frequency occur following vi events the response over the pacific sector is less clear compared to reanalyses cmcc cms shows a similar but weaker response especially over the atlantic a possible explanation is identified in the different structure of the polar vortex and weaker wind shear anomalies with respect to reanalysis we finally highlight that patterns identified following vortex extremes show similarities with the northern annular mode over the atlantic but not over the pacific this suggests that the stratosphere troposphere coupling is more a regional than annular feature

responses of benthic foraminifera to environmental variability a case from the middle jurassic of the kachchh basin western india abstract at the western margin of the indian plate the jurassic sedimentary succession of the kachchh basin provides well developed exposures for fauna based studies based on a quantitative analyses of 67 samples spanning middle bathonian late callovian interval the paleoenvironment of the jumara section the depocenter of the kachchh basin is inferred four benthic foraminiferal assemblages are recognized by both clustering and nmds ordination methods these assemblages vary in biotic traits such as life habit and diversity as well as in abiotic traits such as sediment type nutrient availability and oxygen level the bathonian spirillina polygyrata assemblage that dominates an outer neritic oligotrophic setting has a preference for calcareous substrates in the earliest callovian the epistomina mosquensis assemblage replaced the latter as oxic conditions decreased and terrigenous influx increased two successive and less diverse assemblages had a preference for non calcareous substrates and dominated the mid early late callovian landscape these are the oxic lenticulina subalata assemblage inner to middle neritic oligotrophic setting in the mid early to mid middle callovian and the dysoxic reophax metensis assemblage mesotrophic to eutrophic middle neritic setting in the late middle to late callovian linear regression models suggested that sea level oxygenation and sediment type are the main abiotic factors controlling the distribution of the fauna moreover taxa with specific biotic traits such as shell composition calcareous vs agglutinated and selection strategy r vs k strategy occupied different environmental settings furthermore diversity and epifaunal infaunal ratio had a cyclic pattern comparable to those of third order sea level fluctuations

precursory signals of east asian winter cold anomalies in stratospheric planetary wave pattern the impacts of the stratospheric polar vortex changes on the tropospheric climate variability have been emphasized in previous studies the present study presents evidence for precursory signals of cold anomalies over east asia in the stratospheric wave pattern during november through march the leading two empirical orthogonal function eof modes of daily 50 hpa geopotential height anomalies along 65 n correspond to changes in the amplitude and phase of the stratospheric planetary wavenumber 1 respectively composite analysis is performed to unravel the temporal evolution of anomalies during 8 phases of 34 events identified based on the second eof mode with a complete life cycle for the period 1979 2016 the surface cold anomalies over eastern china emerge in phase 3 corresponding to negative and positive 50 hpa height anomalies on the north atlantic and russian far east sector respectively and peak in phase 5 corresponding to positive 50 hpa height anomalies over eurasia when the siberian high extends southeastward and the east asian trough deepens with anomalous surface northerly winds downward propagation of stratospheric signal is detected over western europe and western siberia the former is a source region of the tropospheric rossby wave trains propagating along the polar front jet and subtropical jet the downward propagation of stratospheric signal is related to the reflection of stratospheric planetary wavenumber 1 pattern and contributes to the development of the tropospheric rossby wave train that in turn leads to the strengthening of the siberian high and the deepening of the east asian trough

the february 2010 arctic oscillation index and its stratospheric connection theatmosphericdynamicsduringtheoccurrenceoftheextremenegativevalueofthe arcticoscillationindexinfebruary2010areinvestigatedusingmeteorologicalfields from era interim and era 40 reanalysis data the study focuses on the possible causes of this anomalous value finding that it was forced by a geopotential anomaly that propagated downward from the stratosphere to the troposphere in association with a major sudden stratospheric warming event which occurred at the end of january an analysis of the dynamics of this warming is also developed together with a comparison with past similar events synoptic and spectral properties of the geopotentialfieldsareanalyzed andthetimeseriesofthe baroclinicactivityindex are computed finding an abrupt increase of the middle latitude baroclinic activity immediately after the central date of the warming event a possible interpretation of this feature is proposed copyright c

does the holton tan mechanism explain how the quasi biennial oscillation modulates the arctic polar vortex idealized experiments with the whole atmosphere community climate model waccm are used to explore the mechanism s whereby the stratospheric quasi biennial oscillation qbo modulates the northernhemispherewintertimestratosphericpolarvortex overall theeffectofthecriticallineemphasized in the holton tan mechanism is less important than the effect of the mean meridional circulation associated with qbo winds for the polar response to the qbo more specifically the introduction of easterly winds at the equator near 50 hpa 1 causes enhanced synoptic scale eliassen palm flux epf convergence in the subtropics from 150 to 50 hpa which leads to the subtropical critical line moving poleward in the lower stratosphere and2 createsabarriertoplanetarywavepropagationfromsubpolarlatitudestomidlatitudesin the middle andupper stratosphere e g less equatorwardepf near 508n whichleads to enhancedplanetary wave convergence in the polar vortex region these two effects are mechanistically distinct while the former is relatedtothesubtropicalcriticalline thelatterisduetothemeanmeridionalcirculationofthe qbo allof these effects are consistent with linear theory although the evolution of the entire wind distribution is only quasi linear because induced zonal wind changes cause the wave driving to shift and thereby positively feed back on the zonal wind changes finally downward propagation of the qbo in the equatorial stratosphere upper stratospheric equatorial zonal wind and changes in the tropospheric circulation appear to be less important than lower stratospheric easterlies for the polar stratospheric response overall an easterly qbo wind anomaly in the lower stratosphere leads to a weakened stratospheric polar vortex in agreement with previous studies although not because of changes in the subtropical critical line

carbon dioxide gas permeability of coal core samples and estimation of fracture aperture width abstract the structure of cleats or natural fractures in coal seams is an important factor affecting gas permeability coal seam permeabilities have been classified into fracture and matrix flows however fractures in coal seams are generally not regular and usually are discontinuous in addition it is difficult to definitively distinguish the fracture and matrix permeabilities and to measure the fracture widths or other necessary properties of fractures for permeability estimation typically gas permeability has been determined by using the darcy equation for incompressible fluid flow and homogeneous porous media even if the gas flow through fractures has different characteristics with respect to effective stress which is given by the confined stress minus the gas pressure in this study permeability measurements were carried out with a new procedure and methodology to estimate the fracture width in coal core samples this measurement method is an improvement on conventional permeability measuring methods in this research it was identified that fracture permeability can be estimated from measurements of gas flow rates in a limited small area using a pipe attachment on the end of the surface of the core finally a linear equation composed of fracture permeability and matrix permeability is presented

palaeobiogeographic patterns of the brachiopod assemblages of the iberian subplate during the late toarcian early aalenian jurassic abstract late toarcian aalenian brachiopod assemblages recorded in different basins located in and around iberia present a pattern of spatial and temporal distribution which enables two palaeobiogeographic biochoremas to be differentiated the iberian atlantic district iad which includes the lusitanian basin asturias and the basque cantabrian basin on one hand and the iberian mediterranean district imd the latter basically comprises the iberian range and the tortosa platform of the catalonian basin changes in the composition of the assemblages throughout the stratigraphical interval studied have enabled three main stages characterizing each palaeobiochorema to be recognized the first two assemblages reflect gradual individualization and isolation with frequent endemisms these two stages correspond to the iad1 iad2 imd1 and to the imd2 assemblages respectively as from the pseudoradiosa chronozone and during the aalensis and opalinum chronozones an increase in communication between the two districts can be observed as well as between these and other remote areas this stage is represented by the iad3 and the imd3 assemblages some of the brachiopods colonizing the districts are widely dispersed due to their capacity for expansion they have been found in other tethysian basins other species are exclusive to the district basins and appear to have originated in the areas close to them for the latter species the existence of two different evolutionary factories is proposed one that supplies species to the iad mainly from generic stocks as neozeilleria soaresirhynchia or praemonticlarella and another for the species reaching the basins of the imd clearly shared by other european and north african basins the atlantic evolutionary factory remains active until the aalenian and part of the early bajocian while the mediterranean is diluted since the aalenian

upward and downward injection of rossby wave activity across the tropopause a new aspect of the troposphere stratosphere dynamical linkage propagation of zonally confined rossby wave activity between the troposphere and lower stratosphere of the southern hemisphere during austral winter and spring of 1997 is studied by using a wave activity flux and refractive index both defined for stationary rossby waves on a zonally asymmetric time mean flow a particular event of large scale quasi stationary cyclogenesis in the troposphere is discussed to which downward wave activity injection from anticyclonic anomalies upstream that had developed in the exit region of the lower stratospheric polar night jet pnj contributed substantially consistent with that downward injection phase lines of observed stream function anomalies exhibited a distinct eastward tilt with height the development of the anticyclonic anomalies occurred at the leading edge of a quasi stationary rossby wave train propagating along the pnj that had originated from a tropospheric blocking ridge farther upstream though less common than upward wave activity injection across the tropopause similar events of downward wave activity injection occurred several times during that season primarily in the regions south of australia and over the central south pacific over each of which the pnj exit overlapped with a tropospheric subpolar jet to form a vertical waveguide locally it is argued that the downward wave activity propagation is essentially due to refraction in the vertically sheared westerlies and the zonal asymmetries in the time mean flow are a likely factor for the observed geographical preference of the downward wave activity injection copyright 2005 royal meteorological society

the evaluation of winds from geopotential height data in the stratosphere abstract several methods of obtaining horizontal wind fields in the extratropical stratosphere from geopotential height data are evaluated and compared to geostrophic estimates with focus on the poleward fluxes of momentum and heat and on the resulting eliassen palm ep flux divergence estimates winds derived from a coupled iterative solution of the zonal and meridional momentum equations balance winds are proposed and tested in addition to winds derived from linearizing these equations about the zonal mean flow linen winds comparison of the different analysis methods are made for a general circulation model simulation of the northern hemisphere nh winter stratosphere and for nh and southern hemisphere sh winter observational data the balance and linear wind estimates of poleward momentum flux are similar and substantially smaller than geostrophic values in the high latitude stratosphere neglect of local curvature effects is the primary cause of the geostrophic overestimate the relati

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

solar signal propagation the role of gravity waves and stratospheric sudden warmings we use a troposphere stratosphere model of intermediate complexity to study the atmospheric response to an idealized solar forcing in the subtropical upper stratosphere during northern hemisphere nh early winter we investigate two conditions that could influence poleward and downward propagation of the response 1 the representation of gravity wave effects and 2 the presence absence of stratospheric sudden warmings ssws we also investigate how the perturbation influences the timing and frequency of ssws differences in the poleward and downward propagation of the response within the stratosphere are found depending on whether rayleigh friction rf or a gravity wave scheme gws is used to represent gravity wave effects these differences are likely related to differences in planetary wave activity in the gws and rf versions as planetary wave redistribution plays an important role in the downward and poleward propagation of stratospheric signals there is also remarkable sensitivity in the tropospheric response to the representation of the gravity wave effects it is most realistic for gws further tropospheric responses are systematically different dependent on the absence presence of ssws when only years with ssws are examined the tropospheric signal appears to have descended from the stratosphere while the signal in the troposphere appears disconnected from the stratosphere when years with ssws are excluded different troposphere stratosphere coupling mechanisms therefore appear to be dominant for years with and without ssws the forcing does not affect the timing of ssws but does result in a higher occurrence frequency throughout nh winter quasi biennial oscillation effects were not included

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

role of finite amplitude rossby waves and nonconservative processes in downward migration of extratropical flow anomalies abstractthere is growing evidence that stratospheric variability exerts a noticeable imprint on tropospheric weather and climate despite clear evidence of these impacts the principal mechanism wh

downward migration of extratropical zonal wind anomalies 1 we show in confirmation of previous work using one and three dimensional models that extratropical zonal wind anomalies produced by fluctuating rossby wave forcing in the troposphere appear first in the stratosphere and migrate downward into the troposphere by systematically eliminating wave reflection and downward control through an induced meridional circulation it is shown that the downward migration is dependent on neither process rather the mechanism appears to rely on local wave mean flow interaction just as in the similar downward migration evident in the tropical quasi biennial oscillation in particular these results imply that the similar downward migration observed in the arctic oscillation should not be taken to indicate any controlling influence of the stratosphere on the troposphere

influence of the vertical and zonal propagation of stratospheric planetary waves on tropospheric blockings 1 case studies are used to elucidate the relationship between stratospheric planetary wave reflection and blocking formation in the troposphere the enhanced upward propagation of a planetary scale wave packet from the eurasian sector involving a euro atlantic blocking leads to a stratospheric sudden warming ssw following the weakening of the stratospheric westerly jet due to polar warming the stratospheric planetary wave packet then propagates downward over the american sector inducing a ridge over the north pacific as well as a trough over eastern canada in the upper troposphere the ridge promotes the formation of a pacific blocking this result explains why pacific blockings tend to form after ssw and why they are associated with suppressed upward propagation of planetary waves

downward wave reflection as a mechanism for the stratosphere troposphere response to the 11 yr solar cycle abstractthe effects of solar activity on the stratospheric waveguides and downward reflection of planetary waves during nh early to midwinter are examined under high solar hs conditions enhanced westerly winds in the subtropical upper stratosphere and the associated changes in the zonal wind curvature led to an altered waveguide geometry across the winter period in the upper stratosphere in particular the condition for barotropic instability was more frequently met at 1 hpa near the polar night jet centered at about 55 n in early winter the corresponding change in wave forcing was characterized by a vertical dipole pattern of the eliassen palm e p flux divergent anomalies in the high latitude upper stratosphere accompanied by poleward e p flux anomalies these wave forcing anomalies corresponded with negative vertical shear of zonal mean winds and the formation of a vertical reflecting surface enhanced downward e p flux anomalies appeared below the negative shear zone they coincided with more

palaeoecological distribution pattern of early middle jurassic benthic foraminifera in the lusitanian basin portugal based on multivariate analysis abstract paleontologists have favoured univariate statistical methods over multivariate ones using information rich data to derive diversity measures such as the simpson s index however such palaeontological datasets may benefit from flexible multivariate methods that exploit data directly hence in this work with the aim of quantifying and characterising the spatio temporal change in the species composition and abundance of benthic foraminiferal assemblages univariate and multivariate statistical techniques are applied on a lusitanian basin dataset from the lower middle jurassic transition this paper presents the trends identified at spatial and temporal scales i e among sections corresponding to distal middle and proximal palaeogeographical positions within the platform and between two successive stratigraphic intervals upper toarcian and lower aalenian it also compares the results obtained by univariate and multivariate methods samples in the reference sections are composed by taxa typical of the jurassic carbonate marine platforms of the boreal realm such as vaginulinidae and lenticulina species univariate analysis only found significant change in species diversity between the two most distant sections and failed to detect any temporal change in contrast multivariate analysis permanova and nmds revealed that spatial change in assemblage structure 22 quadruples temporal change 5 cap analysis identified characteristic species for each section along the palaeogradient with a posterior cross validation procedure that classified correctly 97 of the samples in fact multivariate results suggest the existence of stable palaeoecological conditions across the lower middle jurassic transition in the lusitanian basin future work in the field may benefit from multivariate analysis including hydrocarbon exploration activities where only core samples are available and foraminifera are currently used

diversity dynamics and mass extinctions of the early middle jurassic foraminifers a record from the northwestern caucasus abstract the early middle jurassic foraminiferal assemblages of the northwestern caucasus including a total of 315 species and 68 genera were analysed to establish the principal diversity patterns at substage level of resolution an overall conclusion is that the number of species varied significantly in contrast to the number of genera the most diversified were late sinemurian pliensbachian late toarcian early aalenian and late bajocian assemblages significant diversity drops have been documented in the early toarcian and in the middle aalenian the first of them corresponds to the well known mass extinction which regionally was initiated in the pliensbachian and terminated when rapid late toarcian diversification began the second event could be considered as a regional evidence of a new mass extinction that appeared in the middle aalenian and was most likely associated with the aalenian bajocian regional anoxic event also recorded in the carpathian part of the western tethys the most intense foraminiferal turnovers took place in the toarcian and in the middle aalenian early bajocian the lazarus effect in spite of its high value has not much influenced the estimation of principal diversity trends

the impact of stratospheric ozone changes on downward wave coupling in the southern hemisphere the impact of stratospheric ozone changes on downward wave coupling between the stratosphere and troposphere in the southern hemisphere is investigated using a suite of goddard earth observing system chemistry climate model geos ccm simulations downward wave coupling occurs when planetary waves reflected in the stratosphere impact the troposphere in reanalysis data the climatological coupling occurs from september to december when the stratospheric basic state has a well defined high latitude meridional waveguide in the lower stratosphere that is bounded above by a reflecting surface called a bounded wave geometry reanalysis data suggests that downward wave coupling during november december has increased during the last three decades the geos ccm simulation of the recent past captures the main features of downward wave coupling in the southern hemisphere consistent with the modern era retrospective analysis for research and application merra dataset wave coupling in the model maximizesduringoctober novemberwhenthere isa boundedwavegeometryconfiguration however thewave couplingin the modelis stronger than in the merra dataset and starts earlier and ends later in the seasonal cycle the late season bias is caused by a bias in the timing of the stratospheric polar vortex breakup temporal changes in stratospheric ozone associated with past depletion and future recovery significantly impact downward wave coupling in the model during the period of ozone depletion the spring bounded wave geometry which is favorable for downward wave coupling extends into early summer due to a delay in the vortex breakup date and leads to increased downward wave coupling during november december during the period of ozone recovery the stratospheric basic state during november december shifts from a spring configuration back to a summer configuration where waves are trapped in the troposphere and leads to a decrease in downward wave coupling model simulations with chlorine fixed at 1960 values and increasing greenhouse gases show no significant changes in downward wave coupling and confirm that the changes in downward wave coupling in the model are caused by ozone changes the results reveal a new mechanism wherein stratospheric ozone changes can affect the tropospheric circulation

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

impacts of early autumn arctic sea ice concentration on subsequent spring eurasian surface air temperature variations this study reveals a close relation between autumn arctic sea ice change sic in the laptev sea eastern siberian sea beaufort sea and subsequent spring eurasian surface air temperature sat variation specifically more less sic over the above regions in early autumn generally correspond to sat warming cooling over the mid high latitudes of eurasia during subsequent spring early autumn arctic sic affects spring eurasian sat via modulating spring arctic oscillation ao associated atmospheric changes the meridional temperature gradient over the mid high latitudes decreases following the arctic sea ice loss this results in deceleration of prevailing westerly winds over the mid latitudes of the troposphere which leads to increase in the upward propagation of planetary waves and associated eliassen palm flux convergence in the stratosphere over the mid high latitudes thereby westerly winds in the stratosphere are reduced and the polar vortex is weakened through the wave mean flow interaction and downward propagation of zonal wind anomalies a negative spring ao pattern is formed in the troposphere which favors sat cooling over eurasia the observed autumn arctic sic spring eurasian sat connection is reproduced in the historical simulation 1850 2005 of the flexible global ocean atmosphere land system model spectral version 2 fgoals s2 the fgoals s2 also simulates the close connection between autumn sic and subsequent spring ao further analysis suggests that the prediction skill of the spring eurasian sat was enhanced when taking the autumn arctic sic signal into account

dynamics and predictability of downward propagating stratospheric planetary waves observed in march 2007 abstractthe predictability of a downward propagating event of stratospheric planetary waves observed in early march 2007 is examined by conducting ensemble forecasts using an agcm it is determined that the predictable period of this event is about 7 days regression analysis using all members of an ensemble forecast also reveals that the downward propagation is significantly related to an amplifying quasi stationary planetary scale anomaly with barotropic structure in polar regions of the upper stratosphere moreover the anomaly is 90 out of phase with the ensemble mean field hence the upper stratospheric anomaly determines the subsequent vertical propagating direction of incoming planetary waves from the troposphere by changing their vertical phase tilt which depends on its polarity furthermore the regressed anomaly is found to have similar horizontal structure to the pattern of greatest spread among members of the predicted upper stratospheric height field and the spread growth rate reaches a m

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

delta influenced foraminiferal facies and sequence stratigraphy of paleocene deposits in spitsbergen abstract the paleocene firkanten formation of the central basin of spitsbergen is a succession of terrigenous clastic sediments interpreted as a major depositional sequence formed in deltaic coastal plain delta front and prodelta environments the present study combines diagnostic features of foraminiferal facies with sedimentary data to elucidate this sequence stratigraphic development deposition was initiated by an early paleocene transgression which led to the deposition of a delta plain to coastal marine sediment package forming the low stand and transgressive systems tracts these includes coal swamp lacustrine lagoonal and barrier deposits the lagoonal shales are characterised by an agglutinated foraminiferal assemblage of extremely low diversity indicative of hyposaline conditions shoreface sandstones overlying the lagoonal strata are interpreted as sand barriers reworked by the advancing transgression these sandstones are succeeded by a package of prodelta silty shales which in the lower part includes the maximum transgressive interval the foraminiferal assemblage of the prodelta shales is also agglutinated but reveals increased diversities suggesting open marine conditions the prodelta shales and overlying delta front sandtones form a succession of coarsening upwards parasequences of deltaic progradation representing the regressive systems tract the entirely agglutinated low diversity nature of the foraminiferal assemblages is in part attributable to the deltaic impact the restricted character of the faunas is additionally accentuated by the effects of the paleogene boreal province

influences of enso on stratospheric variability and the descent of stratospheric perturbations into the lower troposphere abstractthe linkage between el nino southern oscillation enso and north atlantic oscillation nao through the stratospheric pathway is examined using a global coupled climate model gfdl climate model version 3 cm3 with increased vertical resolution and extent in the stratosphere as compared to an earlier model gfdl climate model version 2 cm2 it is demonstrated that the relationship between enso and nao is stronger in cm3 than in cm2 it is found that enso plays an important role in modulating the frequency of occurrence of the stratospheric polar vortex anomalies through enhancement attenuation of the amplitudes of zonal wavenumbers 1 and 2 especially in late winter a higher frequency of weak strong stratospheric vortex events is simulated in cm3 during el nino la nina episodes the weak vortex events during el nino winters are preceded by enhancement of the zonal wave 1 pattern and weakening of zonal wave 2 pattern these modified tropospheric planetary waves propagate upward and then w

prolonged effect of the stratospheric pathway in linking barents kara sea sea ice variability to the midlatitude circulation in a simplified model to better understand the dynamical mechanism that accounts for the observed lead lag correlation between the early winter barents kara sea bks sea ice variability and the later winter midlatitude circulation response a series of experiments are conducted using a simplified atmospheric general circulation model with a prescribed idealized near surface heating over the bks a prolonged effect is found in the idealized experiments following the near surface heating and can be explicitly attributed to the stratospheric pathway and the long time scale in the stratosphere the analysis of the eliassen palm flux shows that as a result of the imposed heating and linear constructive interference anomalous upward propagating planetary scale waves are excited and weaken the stratospheric polar vortex this stratospheric response persists for approximately 1 2 months accompanied by downward migration to the troposphere and the surface this downward migration largely amplifies and extends the low level jet deceleration in the midlatitudes and cold air advection over central asia the idealized model experiments also suggest that the bks region is the most effective in affecting the midlatitude circulation than other regions over the arctic

the connection between extreme stratospheric polar vortex events and tropospheric blockings the variations of tropospheric blockings and their connections with the stratospheric polar vortex during different stages of the life cycle of extreme stratospheric polar vortex events i e strong vortex sv events and weak vortex wv events are investigated the blocking frequency decreases over the euro atlantic sector and increases over the western north pacific during the onset and maturation stages of sv events there are more blocking days over the western north pacific and weakened upward planetary wave fluxes in the stratosphere during the maturation stage of shorter time scale sv events than during longer time scale sv events and the weakening of the upward planetary wave fluxes mainly results from the linear wave interference effect the blocking frequency is increased over the euro atlantic sector during the decline stage of sv events this increase is found to be related to the descending stratospheric zonal wind anomalies and the poleward displacement of the eddy driven jet stream which lasts for about 10 days and is associated with the descending positive stratospheric northern annular mode nam anomalies the increased blocking frequency leads to an enhancement of the planetary wave fluxes in the stratosphere via both the linear wave interference for shorter time scale sv events and nonlinear wave interference for longer time scale sv events effect the changes of the blocking frequency during the growth stage of wv events are almost opposite to those observed during the onset and maturation stages of sv events the blocking frequency decreases over the euro atlantic sector after the central dates of wv events which are related to the descending stratospheric zonal wind anomalies and the equatorward displacement of the eddy driven jet stream preceded by the descending negative stratospheric nam anomalies about 10 days we found that the nonlinear wave interference begins to make a considerable contribution to the weakening of the upward wave fluxes in the stratosphere after the central date of wv events and this is not emphasized in previous literature

observational evidence of a stratospheric influence on the troposphere by planetary wave reflection abstract recent studies have pointed out the impact of the stratosphere on the troposphere by dynamic coupling in the present paper observational evidence for an effect of downward planetary wave reflection in the stratosphere on northern hemisphere tropospheric waves is given by combining statistical and dynamical diagnostics a time lagged singular value decomposition analysis is applied to daily tropospheric and stratospheric height fields recomposed for a single zonal wavenumber a wave geometry diagnostic for wave propagation characteristics that separates the index of refraction into vertical and meridional components is used to diagnose the occurrence of reflecting surfaces for zonal wavenumber 1 this study suggests that there is one characteristic configuration of the stratospheric jet that reflects waves back into the troposphere when the polar night jet peaks in the high latitude midstratosphere this configuration is related to the formation of a reflecting surface for vertical propagation

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

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

diagnostic case studies of the northern annular mode abstract recent observational studies of the northern annular mode nam indicate that significant case to case variability exists in the structural evolution of individual events in particular certain nam events remain confined to stratospheric altitudes whereas others readily penetrate downward into the troposphere we perform observational diagnostic analyses that are targeted at identifying the physical mechanisms behind this distinction our results thereby provide a test of the different existing theories regarding stratospheric influences upon tropospheric climate we contrast robust stratospheric nam events with differing tropospheric signals in order to identify the underlying dynamical reasons for the observed differences piecewise potential vorticity pv inversions and eliassen palm flux analyses are performed to study the roles of different forcing mechanisms during nam onset our results indicate that variations in the tropospheric response are readily explained on the basis of piecewise

life cycles of north atlantic teleconnections under strong and weak polar vortex conditions this paper investigates the role of the strength of the polar stratospheric winter vortex in the dynamics of the life cycles of north atlantic teleconnections a new set of teleconnection patterns was produced from low pass filtered daily 300 hpa height data of ncep national centers for environmental prediction reanalysis data 1958 1998 all teleconnections are meridional dipoles which to a certain degree resemble the north atlantic oscillation based on surface pressure data there are two distinct teleconnections one over the eastern and one over the western north atlantic during episodes of weak polar vortex and only one over the central north atlantic during strong polar vortex episodes the teleconnections have periods of about two weeks stream function tendency analysis of the life cycles shows that the relatively simple resulting teleconnections evolve from very complex structures during the growth phase of the teleconnection indices there are strong and systematic differences between the two polar vortex regimes while in the weak vortex regime the anomaly growth is mainly driven by transient eddy vorticity fluxes from the low frequency domain in the strong vortex regime there is also low frequency advection of relative vorticity resulting from the interaction of low frequency eddies with stationary eddies copyright 2006 royal meteorological society

the tropospheric jet response to prescribed zonal forcing in an idealized atmospheric model abstract this paper explores the tropospheric jet shift to a prescribed zonal torque in an idealized dry atmospheric model with high stratospheric resolution the jet moves in opposite directions for torques on the jet s equatorward and poleward flanks in the troposphere this can be explained by considering how the critical latitudes for wave activity absorption change where the eastward propagation speed of eddies equals the background zonal mean zonal wind while the increased zonal winds in the subtropics allow the midlatitude eddies to propagate farther into the tropics and result in the equatorward shift in the critical latitudes the increased winds in the midlatitudes accelerate the eastward eddy phase speeds and lead to the poleward shift in the critical latitudes in contrast the jet moves poleward when a westerly torque is placed in the extratropical stratosphere irrespective of the forcing latitude the downward penetration of zonal winds to the troposphere displays a poleward slope for the

hydrodynamics of coalbed methane reservoirs in the black warrior basin key to understanding reservoir performance and environmental issues abstract the black warrior basin of the southeastern united states hosts one of the world s most prolific and long lived coalbed methane plays and the wealth of experience in this basin provides insight into the relationships among basin hydrology production performance and environmental issues along the southeast margin of the basin meteoric recharge of reservoir coal beds exposed in an upturned fold limb exerts a strong control on water chemistry reservoir pressure and production performance fresh water plumes containing na hco3 waters with low tds content extend from the structurally upturned basin margin into the interior of the basin northwest of the plumes coal beds contain na cl waters with moderate to high tds content carbon isotope data from produced gas and mineral cements suggest that the fresh water plumes have been the site of significant bacterial activity and that the coalbed methane reservoirs contain a mixture of thermogenic and late stage biogenic gases water produced from the fresh water plumes may be disposed safely at the surface whereas underground injection has been used locally to dispose of highly saline water wells in areas that had normal hydrostatic reservoir pressure prior to development tend to produce large volumes of water and may take up to 4 a to reach peak gas production in contrast wells drilled in naturally underpressured areas distal to the fresh water plumes typically produce little water and achieve peak gas rates during the first year of production environmental debate has focused largely on issues associated with hydrologic communication between deep reservoir coal beds and shallow aquifers in the coalbed methane fields of the black warrior basin a broad range of geologic evidence suggests that flow is effectively confined within coal and that the thick intervals of marine shale separating coal zones limit cross formational flow

variation in permeability with lithotype and maceral composition of cretaceous coals of the canadian cordillera abstract the permeability of high and medium volatile bituminous cretaceous coal at the megascopic and microscopic scale is investigated utilizing a pressure decay permeameter the order of decreasing permeability with lithotype is bright average 4 1 md banded 0 79 md fibrous 0 50 md banded dull 0 14 md and dull 0 016 md bright coals are the most permeable because of associated macro fracturing cleat banded dull coal permeability generally increases with increasing vitrinite content the lowest permeabilities occur in dull coals with a high mineral and inertinite content fibrous coal has a higher permeability than dull coal of the same rank due to the abundance of macroporous fusinite in fibrous coal dull coal permeability decreases with an increase in rank but these results are overshadowed by compositional variability between samples pressure decay measurements are more reliable for dull lithotypes as these lithotypes do not fracture as easily during sample preparation although measured permeabilities are optimistic due to the relaxation of stress upon exposure of coal to atmospheric pressure the results obtained are representative of the range of permeabilities of coal lithotypes and provide insight into the variability in permeability that may exist at high effective stress in the subsurface

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

coupled fluid flow and geomechanics modeling of stress sensitive production behavior in fractured shale gas reservoirs abstract compared with conventional reservoirs gas flow in shale formation is affected by additional nonlinear coupled processes such as matrix fracture deformations we present a fully coupled fluid flow and geomechanics model to accurately characterize the complex production behaviors of fractured shale gas reservoirs the flow equations are discretized using a mimetic finite difference method and poro elasticity equations by a galerkin finite element approximation a unified apparent permeability model is implemented to quantify the combined impacts of the non darcy flow adsorbed layer and pore structure alterations on matrix permeability the discrete fracture matrix dfm model based on a conformal unstructured grid is employed to explicitly represent fractures the nonlinear contact problem between the two fracture surfaces is introduced to describe the fracture mechanics behavior a splitting node technique is used to deal with the discontinuities in the displacement field across the fracture interface under the effects of pressure decline and high confining stresses on the fracture faces proppant compaction and embedment may occur causing fracture closure and thus substantial production loss hence we also develop a comprehensive proppant fracture model which is based on the theories of elasto plastic contact mechanics to capture the complex interactions between proppant and fracture the multiphysics numerical model enables us to investigate which factors have the most influential effect on the gas recovery of shale formations high fidelity numerical solutions are provided to characterize the rate transient signatures in the presence of the different flow and geomechanical mechanisms

comparing and contrasting extreme stratospheric events including their coupling to the tropospheric circulation recent work has emphasized the importance of stratosphere troposphere coupling associated with extreme values of the polar vortex strength and stratospheric planetary wave heat flux during northern hemisphere winter here using era interim reanalysis data the evolution of the two types of events are compared the life cycle of total anomaly plus climatology positive negative heat flux events are associated with vertically deep high latitude planetary wave structures and exhibit largely equal but opposite signed impacts including a net deceleration acceleration of the polar vortex due to ep flux convergence divergence and an equatorward poleward tropospheric jet shift in the north atlantic the tropospheric wave pattern is westward propagating high latitude stratospheric vertical zonal wind shear plays a key role during both events a comparison of the stratospheric events reveals that planetary wave events contribute to the development of vortex events in particular total negative heat flux events precede strong vortex events showing that strong vortex events represent true dynamical events involving significant wave mean flow interaction coupling with the north atlantic jet occurs preceding vortex events when wave 1 dominates the total eddy heat flux in the lower stratosphere since interference with wave 2 makes the impacts less clear the tropospheric impacts in the north atlantic associated with planetary wave events are found to be comparable if not larger than those following vortex events

volumetric strain associated with methane desorption and its impact on coalbed gas production from deep coal seams the permeability of deep 1000 m 3300 ft coal seams is commonly low for deep coal seams significant reservoir pressure drawdown is required to promote gas desorption because of the langmuir type isotherm that typifies coals hence a large permeability decline may occur because of pressure drawdown and the resulting increase in effective stress depending on coal properties and the stress field during production however the permeability decline can potentially be offset by the permeability enhancement caused by the matrix shrinkage associated with methane desorption the predictability of varying permeability is critical for coalbed gas exploration and production well management we have investigated quantitatively the effects of reservoir pressure and sorption induced volumetric strain on coal seam permeability with constraints from the adsorption isotherm and associated volumetric strain measured on a cretaceous mesaverde group coal piceance basin and derived a stress dependent permeability model our results suggest that the favorable coal properties that can result in less permeability reduction during earlier production and an earlier strong permeability rebound increase in permeability caused by coal shrinkage with methane desorption include 1 large bulk or young s modulus 2 large adsorption or langmuir volume 3 high langmuir pressure 4 high initial permeability and dense cleat spacing and 5 low initial reservoir pressure and high in situ gas content permeability variation with gas production is further dependent on the orientation of the coal seam the reservoir stress field and the cleat structure well completion with injection of n2 and displacement of ch4 only results in short term enhancement of permeability and does not promote the overall gas production for the coal studied

nonlinear relation of the arctic oscillation with the quasi biennial oscillation a nonlinear principal component analysis nlpca is applied to a set of monthly mean time series from january 1956 to december 2007 consisting of the arctic oscillation ao index derived from 1 000 hpa geopotential height anomalies poleward of 20 n latitude and the zonal winds observed at seven pressure levels between 10 and 70 hpa in the equatorial stratosphere to investigate the relation of the ao with the quasi biennial oscillation qbo the nlpca is conducted using a new compact neural network model the nlpca modeling of the dataset of the ao index and qbo winds offers a clear picture of the relation between the two oscillations in particular the phase of covariation of the oscillations defined by the two nonlinear principal components of the dataset progresses with a predominant 28 4 month periodicity this predominant cycle is modulated by an 11 year cycle the variation of the ao index with the qbo phase also shows that the average ao index is positive when the westerly qbo phase descends past 30 hpa and conversely the average ao index is negative when the easterly qbo phase descends past 30 hpa this relationship is evident during the boreal cold season from november to april but non existent during the boreal warm season from may to october

carbon isotope stratigraphy and ammonite faunal turnover for the middle jurassic in the southern iberian palaeomargin variations in the stable carbon isotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle here we report carbon isotope compositions of middle jurassic marine carbonates from the betic cordillera southern spain which represents an ideal region to link the stable carbon isotope curves directly to ammonite zones and subzones and thereby for the first time achieve an accurate chronostratigraphic calibration the five sections studied represent basin and high swell deposits of the southern iberian palaeomargin we find a similar 13 c of carbonates between different oceanic areas suggesting a homogeneous carbon isotope oceanic reservoir through the middle jurassic the aalenian bajocian transition is a critical period in ammonite evolution hence the early jurassic fauna are replaced by new ammonite families which become dominant throughout the middle and late jurassic for this reason we compared the 13 c values of carbonates with ammonite diversity and extinction rates at different taxonomical levels in order to explore the possible relationship between the carbon cycle and ammonite evolution the carbon isotope values of carbonates are not exactly linearly correlated with the extinction rate and ammonite diversity but the main faunal turnovers follow minimum 13 c values where extinct taxa are replaced by new ones likewise radiation episodes are associated with increasing 13 c values and with transgressive sea level rise all these data support the idea that perturbations in the global carbon cycle reflect rapid palaeoenvironmental changes we made detailed analyses of these faunal turnovers using them as a proxy to identify major palaeoenvironmental crises in their ecosystems forced by modification in the carbon cycle

the influence of stratospheric vortex displacements and splits on surface climate abstracta strong link exists between stratospheric variability and anomalous weather patterns at the earth s surface specifically during extreme variability of the arctic polar vortex termed a weak vortex event anomalies can descend from the upper stratosphere to the surface on time scales of weeks subsequently the outbreak of cold air events have been noted in high northern latitudes as well as a quadrupole pattern in surface temperature over the atlantic and western european sectors but it is currently not understood why certain events descend to the surface while others do not this study compares a new classification technique of weak vortex events based on the distribution of potential vorticity with that of an existing technique and demonstrates that the subdivision of such events into vortex displacements and vortex splits has important implications for tropospheric weather patterns on weekly to monthly time scales using reanalysis data it is found that vortex splitting events are correl

observed decadal changes in downward wave coupling between the stratosphere and troposphere in the southern hemisphere abstractdownward wave coupling dominates the intraseasonal dynamical coupling between the stratosphere and troposphere in the southern hemisphere the coupling occurs during late winter and spring when the stratospheric basic state forms a well defined meridional waveguide which is bounded above by a reflecting surface this basic state configuration is favorable for planetary wave reflection and guides the reflected waves back down to the troposphere where they impact wave structures in this study decadal changes in downward wave coupling are analyzed using the modern era retrospective analysis for research and applications merra dataset a cross spectral correlation analysis applied to geopotential height fields and a wave geometry diagnostic applied to zonal mean zonal wind and temperature data are used to understand decadal changes in planetary wave propagation it is found that downward wave 1 coupling from september to december has increased over the last three decades owing to significant

nature and origin of fractures in permian coals from the bowen basin queensland australia a field investigation into the development of cleat and other fractures within permian coal measures was undertaken in the bowen basin of eastern queensland australia to provide predictive information on coal permeability for use in coalbed methane exploration data were collected from five open cut and three underground mines in the southern and central bowen basin covering the upper permian german creek formation and rangal coal measures fractures noted in the coals fall readily into the four categories of faults and shear zones extension and compression related joint sets mining induced fractures and coal cleats four geometric varieties of coal cleats were identified class a orthogonal sets class b sinusoidal sets class c polygonal sets and class d chaotic sets superimposed or overprinted type a sets were also observed locally on a regional scale the cleats typically parallel dip face cleats and strike butt cleats but local departures from this pattern occur in proximity to faults where face and butt cleat directions were often reversed rotated or multimodal field data suggest that coal cleats of classes a b and c were formed by brittle fracturing of the coal during burial wheras class d and superimposed cleats were formed during later compressional events constraints on the timing of deformation events affecting the bowen basin and geochemical data provided by other workers indicate that the cleats were formed within 5 ma of formation of precursor peats but were in many instances modified by later structural events

the whole atmosphere response to changes in the earth s magnetic field from 1900 to 2000 an example of top down vertical coupling we study the effects of changes in the earth s magnetic field between 1900 and 2000 on the whole atmosphere 0 500 km altitude based on simulations with the whole atmosphere community climate model extension magnetic field changes directly affect the temperature and wind in the upper atmosphere 110 km via joule heating and the ion drag force however we also find significant responses in zonal mean temperature and zonal wind in the southern hemisphere sh middle to high latitude troposphere stratosphere and mesosphere of up to 2 k and 2 m s as well as regionally significant changes in northern hemisphere nh polar surface temperatures of up to 1 3 k in december january february in the sh changes in gravity wave filtering in the thermosphere induce a change in the residual circulation that extends down into the upper mesosphere where further changes in the mean wind climatology are generated together with changes in local planetary wave generation and or amplification and gravity wave filtering this induces further changes to a residual circulation cell extending down into the troposphere however inaccuracies in the simulated sh upper mesospheric wind climatology probably mean that the simulated temperature and wind responses in the sh lower and middle atmosphere are also inaccurate the nh middle atmosphere response is zonally asymmetric consisting of a significant change in the positioning and shape of the upper stratospheric polar vortex which is dynamically consistent with the surface temperature response however the downward coupling mechanism in the nh is generally less clear

foraminifera from the aalenian and the bajocian gssp middle jurassic of murtinheira section cabo mondego west portugal biostratigraphy and paleoenvironmental implications the detailed study of benthic foraminifera in 28 samples from late toarcian aalenian early bajocian hemipelagic sediments of the murtinheira section cabo mondego lusitanian basin west portugal has permitted the recognition of the assemblage composition and the analysis of their evolution throughout this time interval the representatives of the suborder lagenina dominate all the assemblages and in the majority of them the most abundant species is lenticulina munsteri the late toarcian and early aalenian assemblages are very similar from the comptum subzone a gradual replacement of the early jurassic forms by characteristic middle jurassic taxa takes place during the late aalenian early bajocian interval a significant number of last occurrences los of taxa are recorded the assemblages composition the estimation of the relative taxa abundances and the data obtained from the calculation of several diversity indexes together with the previous sedimentological and paleontological works in this area indicate that these assemblages were developed in a shelfal basin environment this platform showed normal marine salinity values good oxygenation and was always located above calcite compensation depth ccd however the environmental conditions were not always the best for the development of rich and diverse foraminiferal assemblages these conditions were probably unstable during the late toarcian aalensis subzone early aalenian lower part of the comptum subzone from the comptum subzone to the lower part of the limitatum subzone late aalenian conditions were more stable and more favourable for the development of foraminiferal communities however in the aalenian bajocian transition the environmental conditions changed again and affected the development of this group in the limitatum subzone a decrease in the diversity of the assemblages was recorded this fact seems to be related to a global perturbation in the carbon cycle that could have affected the foraminifera together with other marine and continental organism groups

distribution and palaeoecology of middle jurassic foraminifera from the lower inferior oolite of the cotswolds abstract foraminifera extracted from limestones of the lower inferior oolite scissum murchisonae zones are analysed in terms of the sample correlation coefficient r of species pairs and the limestone petrography in each limestone sample microfaunal composition is related to 1 grain size 2 the proportion of lime mud to spar cement in the matrix 3 allochem composition the nature of these inter relationships provides a basis for determining assemblages most likely to represent a biocoenosis three palaeocommunities are reconstructed 1 primary weed fauna 2 weed sediment fauna 3 interstitial reef fauna each community was likely to have been strongly influenced by the availability of phytal or non phytal habitats in common with recent carbonate foraminifera a morphogenetic study of lenticulina muensteri roemer demonstrates that variation was generated within numerous geometrically distinct growth series where uncoiling could proceed systematically for a given coil diameter variants were subject to postmortem size geometry sorting the affinity and evolutionary development of lower inferior oolite foraminifera are evaluated by comparison with assemblages described from other locations and stratigraphic levels in nw europe the appearance of similar faunas at the lower middle jurassic boundary is correlated with the simultaneous development of shallow marine environments which favoured species capable of adapting to both phytal and non phytal micro habitats

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

tropospheric impact of reflected planetary waves from the stratosphere 1 a reflection of stratospheric planetary waves and its impact on the troposphere during a stratospheric sudden warming of march 2007 are investigated zonal propagation and reflection of the planetary waves is clearly seen in the longitude height sections of the eddy geopotential height and the vertical and zonal component of the three dimensional wave activity flux a wave packet propagating upward and eastward from eurasian continent was reflected by a negative wind shear in the upper stratospheric westerly jet caused by stratospheric warming waves then propagated downward to the american atlantic sector of the troposphere which led to the formation of a deep trough over the atlantic and brought cold weather to the northeastern part of the american continent

the effect of reflecting surfaces on the vertical structure and variability of stratospheric planetary waves the effects of an upper stratospheric reflecting surface on the vertical structure of stratospheric planetary waves are considered a diagnostic of the basic state wave propagation characteristics which is particularly useful for determining the existence and location of turning surfaces for meridional and vertical propagation is developed the diagnostic used is a more accurate indicator of wave propagation regions than the index of refraction because it diagnoses meridional and vertical propagation separately the diagnostic is tested on a series of simple models both steady state and time dependent it is found that the stratospheric waveguide sets the meridional wavenumber of the waves regardless of the characteristics of their tropospheric forcing making it easier to understand the effects of damping and turning surfaces on the vertical structure of the waves the diagnostic is then applied to observations of the southern hemisphere winter of 1996 it is shown that the differences in vertical wave structure between middle and late winter can be explained as a linear response to the seasonal evolution of the basic state which involves a formation of a reflecting surface in late winter it is also shown that on daily timescales wave mean flow interactions cause significant changes in the basic state propagation characteristics for periods of a few days these changes along with the time variations in the forcing of the waves are responsible for the observed daily timescale variations in wave structure the fact that the observed evolution of the waves and the basic state are consistent with linear or quasi linear wave theory depending on the timescale looked at supports the applicability of the theory as well as the validity of the observations

the life cycle of northern hemisphere downward wave coupling between the stratosphere and troposphere abstractthe life cycle of northern hemisphere downward wave coupling between the stratosphere and troposphere via wave reflection is analyzed downward wave coupling events are defined by extreme negative values of a wave coupling index based on the leading principal component of the daily wave 1 heat flux at 30 hpa the life cycle occurs over a 28 day period in the stratosphere there is a transition from positive to negative total wave 1 heat flux and westward to eastward phase tilt with height of the wave 1 geopotential height field in addition the zonal mean zonal wind in the upper stratosphere weakens leading to negative vertical shear following the evolution in the stratosphere there is a shift toward the positive phase of the north atlantic oscillation nao in the troposphere the pattern develops from a large westward propagating wave 1 anomaly in the high latitude north atlantic sector the subsequent equatorward propagation leads to a positive anomaly in midlatitudes the near surface tempera

intraseasonal dynamical evolution of the northern annular mode abstract the northern hemisphere annular mode nam accounts for a significant fraction of the extratropical wintertime atmospheric variability the dynamics of nam events have been studied on monthly time scales but little is known about the physical mechanisms that give rise to nam variability on shorter time scales composite diagnostic analyses based on daily nam indices are performed with a goal of identifying the dominant processes responsible for the growth and decay of large amplitude positive and negative nam events on short intraseasonal time scales transformed eulerian mean piecewise potential vorticity inversions and regional plumb flux diagnoses are employed to deduce the proximate forcings of the zonal mean wind tendency during maturing and declining nam stages a remarkable degree of reverse symmetry is observed between the zonal mean dynamical evolution of positive and negative nam events anomalous equatorward and downward poleward and upward eliassen palm fluxes are observed during

downward wave coupling between the stratosphere and troposphere the importance of meridional wave guiding and comparison with zonal mean coupling the nature of downward wave coupling between the stratosphere and troposphere in both hemispheres is analyzed using the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 dataset downward wave coupling occurs when planetary waves reflected in the stratosphere impact the troposphere and it is distinct from zonal mean coupling which results from wave dissipation and its subsequent impact on the zonal mean flow cross spectral correlation analysis and wave geometry diagnostics reveal that downward wave 1 coupling occurs in the presence of both a vertical reflecting surface in the mid to upper stratosphere and a high latitude meridional waveguide in the lower stratosphere in the southern hemisphere downward wave coupling occurs from september to december whereas in the northern hemisphere it occurs from january to march a vertical reflecting surface is also present in the stratosphere during early winter in both hemispheres however it forms at the poleward edge of the meridional waveguide which is not confined to high latitudes the absence of a high latitude waveguide allows meridional wave propagation into the subtropics and decreases the likelihood of downward wave coupling the results highlight the importance of distinguishing between wave reflection in general which requires a vertical reflecting surface and downward wave coupling between the stratosphere and troposphere which requires both a vertical reflecting surface and a high latitude meridional waveguide the relative roles of downward wave and zonal mean coupling in the southern and northern hemispheres are subsequently compared in the southern hemisphere downward wave 1 coupling dominates whereas in the northern hemisphere downward wave 1 coupling and zonal mean coupling are found to be equally important from winter to early spring the results suggest that an accurate representation of the seasonal cycle of the wave geometry is necessary for the proper representation of downward wave coupling between the stratosphere and troposphere

bi decadal variability excited in the coupled ocean atmosphere system by strong tropical volcanic eruptions decadal and bi decadal climate responses to tropical strong volcanic eruptions sves are inspected in an ensemble simulation covering the last millennium based on the max planck institute earth system model an unprecedentedly large collection of pre industrial sves up to 45 producing a peak annual average top of atmosphere radiative perturbation larger than 1 5 wm 2 is investigated by composite analysis post eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean atmosphere system with an average length of 20 25 years the study provides a new physically consistent theoretical framework to interpret decadal northern hemisphere nh regional winter climates variability during the last millennium the fluctuation particularly involves interactions between the atlantic meridional overturning circulation and the north atlantic gyre circulation closely linked to the state of the winter north atlantic oscillation it is characterized by major distinctive details among them the most prominent are a a strong signal amplification in the arctic region which allows for a sustained strengthened teleconnection between the north pacific and the north atlantic during the first post eruption decade and which entails important implications from oceanic heat transport and from post eruption sea ice dynamics and b an anomalous surface winter warming emerging over the scandinavian western russian region around 10 12 years after a major eruption the simulated long term climate response to sves depends to some extent on background conditions consequently ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post eruption decadal evolution of nh regional winter climates