mississippian wood grained chert and its significance in the western interior united states abstract wood grained chert is nodular chert which has internal light and dark colored concentric three dimensional compositional banding resembling grain in wood the light colored bands are dolomitic and the dark colored bands are quartzose with carbonaceous matter wood grained chert is recognized in the mississippian lodgepole deseret and great blue limestones and some correlatives of these formations in montana utah and idaho the deseret starved basin model sandberg and gutschick 1980 gutschick and sandberg 1983 provides a paleogeograpic framework that restricts the wood grained cherts in this basin to the foreslope between the oxygenated carbonate platform margin 300 m basin wood grained chert may mark th approximate position of the lower limit of the pycnocline in the deseret starved basin upwelling of nutrient rich water along the foreslope generated high biological productivity which in turn supplied abundant biogenic silica and organic matter to the sediments of the foreslope and basin siliceous microfossils dissolved and provided a source of silica for the formation of porcellanite opal ct nodules within the foreslope sediments during burial and compaction calcium carbonate diffused into the nodules from the surrounding mixed calcareous siliceous muds and early diagenetic conversion of opal ct to quartz released magnesium reduction of sulfate a dolomite inhibitor in the associated anoxic organic rich sediments below the pycnocline permitted dolomite formation dolomite precipitated in bands as a result of a periodic supersaturation precipitation nucleation d pletion process ostwald prager theory of liesegang band formation possibly augmented by competitive particle growth petrographic evidence and the apparent inverse relationship between band spacing and time support our theory

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

an idealized nonlinear model of the northern hemisphere winter storm tracks abstract in this paper a nonlinear dry model forced by fixed radiative forcing alone has been constructed to simulate the northern hemisphere winter storm tracks a procedure has been devised to iterate the radiative equilibrium temperature profile such that at the end of the iterations the model climate closely resembles the desired target climate this iterative approach is applied to simulate the climatological storm tracks in january it is found that when the three dimensional temperature distribution in the model resembles the observed distribution the model storm tracks are much too weak it is hypothesized that this is due to the fact that eddy development is suppressed in a dry atmosphere owing to the lack of latent heat release in the ascending warm air to obtain storm tracks with realistic amplitudes the static stability of the target climate is reduced to simulate the enhancement in baroclinic energy conversion due to latent heat release with this modification the storm tracks in the

evolution of the tropospheric split jet over the south pacific ocean during the 1986 89 enso cycle abstract a case study investigation into the meridional and horizontal circulation over the south pacific ocean is presented for the 1986 89 el nino southern oscillation enso cycle using the european centre for medium range weather forecasts ecmwf analyses annual average fields are created for the years before and after the 1987 minimum warm phase and 1989 maximum cold phase in the southern oscillation index the analyses reveal a shift in the split jet stream over the south pacific sector 180 120 w from a strong subtropical jet stj and weak polar front jet pfj during the warm phase to a weak stj and strong pfj during the cold phase analysis of the momentum budget reveals how the split jet in the upper troposphere over south pacific ocean evolved during the 1986 89 enso cycle during the warm phase the strong stj is associated with advection of the mean flow momentum flux from the australian sector which is approximately balanced by a large negative ageostrophic term the pfj is primaril

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

indices of the southern hemisphere zonal wind abstract the time and spatial variation of the southern hemisphere 500 hpa zonal wind has been examined using spectral analysis bandpass filtering and empirical orthogonal function eof analysis applied to a 15 year sample of australian hemispheric analyses spectral analysis of the entire 15 year record of the 500 hpa zonal mean westerly wind shows significant peaks only on the seasonal and interannual time scales the mean segmented spectra for each season failed to show any additional significant peaks at higher frequencies or any significant differences between seasons the primary pattern of variation revealed by eof analysis shows similar behavior on synoptic to seasonal time scales with compensating departures occurring at intervals of 20 latitude the first eof has opposing peaks near 40 and 60 s and shows an equivalent barotropic pattern when correlated with individual grid point values at 500 hpa and mean sea level pressure correlations of the zonal pattern with regional anomalies reveal

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

northern winter stationary waves theory and modeling a review is provided of stationary wave theory the theory for the deviations from zonal symmetry of the climate to help focus the discussion the authors concentrate exclusively on northern winter several theoretical issues including the external rossby wave dispersion relation and vertical structure critical latitude absorption the nonlinear response to orography and the interaction of forced wave trains with preexisting zonal asymmetries are chosen for discussion while simultaneously presenting a decomposition of the wintertime stationary wave field using a nonlinear steady state model

the pacific center of action of the northern hemisphere annular mode real or artifact the leading empirical orthogonal function eof of the sea level pressure slp field referred to as the arctic oscillation ao or northern hemisphere annular mode nam consists of a dipole between the polar cap region and the surrounding zonal ring centered along 458n embedded within the outer ring are centers of action over the euro atlantic and pacific sectors in which slp fluctuates in phase that the observed slp fluctuations at these two centers of action are virtually uncorrelated raises the question of whether the pacific center in the annular mode could be an artifact of eof analysis it is argued that sea level pressure fluctuations at the pacific and euro atlantic centers of action of the ao nam would be more strongly correlated were it not for the fact that slp variability over the north pacific is dominated by a pattern in which fluctuations over the north atlantic and north pacific are inversely related evidence of the coexistence of such a pattern which resembles an augmented version of the pacific north american pattern is presented

using mean flow change as a proxy to infer interdecadal storm track variability abstract several recent studies based mainly on analyses of reanalysis data have suggested that the northern hemisphere storm tracks have intensified during the second half of the twentieth century however comparisons with rawinsonde observations over land areas suggest that eddy variance covariance statistics may contain spurious jumps that had led to an exaggeration of the storm track secular trend in this study storm track variations are inferred from mean flow anomalies using canonical correlation analysis cca a cca model relating storm track anomalies to mean flow anomalies is derived using recent more reliable data the model is then applied to infer storm track anamalies using mean flow anomalies for earlier periods when storm track analyses are deemed more suspect or even nonexistent results of the cca analyses suggest that the strong secular trend observed over the atlantic basin and europe is consistent with mean flow anomalies while cca predictions based on mean flow changes sugg

relation between annular modes and the mean state southern hemisphere summer abstract the annular modes emerge as the leading mode of extratropical month to month climate variability in both hemispheres here the influence of the background state on the structure and dynamics of the southern hemisphere annular mode sam during the austral summer when the climatology is characterized by a single well defined eddy driven jet is studied subsets of the climatology are constructed for early and late summer and for contrasting polarities of the enso cycle the analysis is based both on observations and on perpetual state gcm experiments the main differences between the subsets involve variations of the latitude of the mean jet it is found that in all the cases the sam is characterized by latitudinal shifts of the jet about its mean position reinforced by a positive momentum flux feedback from baroclinic waves this result is consistent with previous studies of the dynamics of the zonally averaged circulation but is found here to hold over all longitudes and for different positi

geologic controls on the recent evolution of oyster reefs in apalachicola bay and st george sound florida abstract apalachicola bay and st george sound contain the largest oyster fishery in florida and the growth and distribution of the numerous oyster reefs here are the combined product of modern estuarine conditions in the bay and its late holocene evolution sidescan sonar imagery bathymetry high resolution seismic profiles and sediment cores show that oyster beds occupy the crests of a series of shoals that range from 1 to 7 km in length trend roughly north south perpendicular to the long axes of the bay and sound and are asymmetrical with steeper sides facing to the west surface sediment samples show that the oyster beds consist of shelly sand while much of the remainder of the bay floor is covered by mud delivered by the apalachicola river the present oyster reefs rest on sandy delta systems that advanced southward across the region between 6400 and 4400 yr bp when sea level was 4 6 m lower than present oysters started to colonize the region around 5100 yr bp and became extensive by 1200 and 2400 yr bp since 1200 yr bp their aerial extent has decreased due to burial of the edges of the reefs by the prodelta mud that continues to be supplied by the apalachicola river oyster reefs that are still active are narrower than the original beds have grown vertically and become asymmetrical in cross section their internal bedding indicates they have migrated westward suggesting a net westerly transport of sediment in the bay

the wintertime southern hemisphere split jet structure variability and evolution a persistent feature of the southern hemisphere upper level time mean flow is the presence of a split jet across the south pacific east of australia during the austral winter the split jet is composed of the subtropical jet stj on its equatorward branch and the polar front jet pfj on its poleward branch the ncep ncar reanalysis is used to investigate the structure and evolution of the split jet results show that the presence absence of the pfj determines the degree of split flow given that the stj is a quasi steady feature a splitflow index sfi is developed to quantify the variability of the split jet in which negative values represent strong split flow and positive values nonsplit flow correlations with teleconnection indices are investigated with the sfi positively correlated to the southern oscillation index and negatively correlated to the antarctic oscillation the sfi is used to construct composites of heights temperature and wind for split flow and non split flow days the composites reveal that relatively cold conditions occur in the south pacific in association with nonsplit flow regimes and split flow regimes occur when relatively warm conditions prevail in the latter situation cold air bottled up over antarctica helps to augment the background tropospheric thickness gradient between antarctica and the lower latitudes with a resulting increase in the thermal wind and the pfj it is surmised that frequent cold surges out of antarctica moving into the south pacific are associated with non split flow regimes in this context the variability of the split jet responds to large scale baroclinic processes and is further modulated by synoptic scale disturbances

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks abstract the heat and vorticity transports by synoptic scale eddies at various levels between 1000 and 100 mb have been compiled for each winter month of the 1966 84 period using time filtered daily analyses produced by the u s national meteorological center these circulation statistics were used to compute the three dimensional distributions of the quasigeostrophic geopotential tendency and vertical motion induced by baroclinic and barotropic eddy processes in individual months the latter fields serve as the basis for describing the synoptic scale eddy forcing associated with the leading modes of month to month variability of the storm tracks over the north pacific and north atlantic these modes are associated with the meridional displacements of the storm track axes from their climatological positions the placement of a storm track at a certain latitude in a certain month is accompanied by enhanced convergence of eddy heat fluxes poleward of in the tropospheric column poleward of the storm tra

variability of the southern hemisphere winter split flow a case of two way reinforcement between mean flow and eddy anomalies abstract a new split jet index is defined in this study and composites based on this index show that the split flow regime is characterized by a cold warm cold tripolar temperature anomaly in the south pacific that extends equatorward from the southern hemisphere sh high latitudes while nonsplit flow occurs when the phase of the tripolar temperature anomaly is reversed analyses of the heat budget reveal that the temperature anomalies associated with the split nonsplit flow are mainly forced by mean flow advection instead of local diabatic heating or convergence of eddy heat fluxes localized eliassen palm e p flux diagnostics suggest that the zonal wind anomalies are maintained by the eddy vorticity flux anomalies these diagnostic results are confirmed by numerical experiments conducted using a stationary wave model forced by observed eddy forcings and diabatic heating anomalies the model results show that the effects of the vorticity flux dominates over those of the heat flux which tend to damp

seasonal prediction skill and predictability of the northern hemisphere storm track variability in project minerva the seasonal prediction skill and predictability of the northern hemisphere storm track anomalies in boreal winter december january february djf is examined using seasonal ensemble reforecasts for 1982 2009 from the ecmwf integrated forecast system at two different atmospheric resolutions in project minerva it is found that the predictable signals of storm track variations are associated with the two leading eof modes of ensemble averaged djf variances of the high pass filtered daily meridional winds at 250 hpa level derived from each of the hindcast ensemble members these two eof modes are highly correlated both temporarily and spatially between two sets of reforecasts the first mode eof1 mainly shows a latitudinal shift of the storm tracks over the central eastern north pacific and the north america continent the second mode eof2 is primarily the pulsing signal exerting on the mean storm track background of the north pacific the model predictive skill is verified against observations the first mode has higher prediction skills and larger skillful regions than the second one in particular the first predictable mode is generated by the enso induced wave train starting from tropical central pacific and propagating to north america the skillful region lies in the north pacific to the west of california corresponding to the southern lobe of eof1 the second predictable mode is generated by the north pacific mode which evokes a distinctive wave train emanating from the tropical western pacific and propagating northeastward its skillful region of the storm track prediction is confined to a small area of canada western coastlines

the influence of persistent anomalies on southern hemisphere storm tracks abstract empirical orthogonal function eof analysis has been applied to nine years of daily 500 hpa data for the southern hemisphere from which synoptic scale variations had been removed by application of a 10 day low pass fitter this resulted in 11 principal modes accounting for 66 of the variance which were then regionalized through application of a varimax rotation these rotated patterns included a high latitude mode covering the antarctic eight others defining regional perturbation in the principal storm tracks at high latitudes and two residual patterns not used for this investigation persistent anomalies were defined as spells where the time coefficient of the rotated eof was greater than 1 standard deviation or less than 1 standard deviation for a period of 10 days or more and 220 of these spells were obtained for the nine eofs used in the analysis storm tracks were identified in two ways 1 from high pass filtering of the daily 5oo hpa geopotential height anomalies to include periods

characteristics of wave packets in the upper troposphere part ii seasonal and hemispheric variations abstract gridded 300 hpa meridional wind data produced by the ecmwf reanalysis project were analyzed to document the seasonal and hemispheric variations in the properties of upper tropospheric wave packets the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed on based on indices that show the coherence of wave propagation as well as examination of correlation maps schematic waveguides were constructed for the summer and winter seasons of both hemispheres along which waves preferentially propagate with greatest coherence in the summers the waveguides basically follow the position of the midlatitude jets in the northern hemisphere winter the primary waveguide follows the subtropical jet over southern asia into the pacific but there is a secondary branch running across russia joining the primary waveguide near the entrance to the pacific storm track over the atlantic the waveguide passes east southeastward toward north africa then bac

organization of storm track anomalies by recurring low frequency circulation anomalies abstract from previous studies it is known that anomalous momentum fluxes by bandpass eddies are important in maintaining long lasting tropospheric flow anomalies evidence is presented that suggests that these anomalous fluxes do not occur at random but happen because the structure of storm track activity is modified by the presence of prominent low frequency large scale circulation anomalies this behavior is noted in an extended integration of a perpetual january simulation with a general circulation model gcm because nonlinear feedbacks between low and high frequency variability make it difficult to establish causal relationships between these two ranges of variability a model is constructed that approximates the storm track activity that would be expected to accompany a given low frequency without including the feedback of the high frequencies onto the low frequency state this model is based on the linearized primitive equations and uses a series of short integrations from random initial condi