magnetic remanence and fabric properties of laboratory deposited hematite bearing red sandstone redeposition experiments of disintegrated hematite bearing sandstone have confirmed a tangent relationship between inclinations of the drm and ambient magnetic field pronounced variations of drm intensities with field inclination are attributed to processes acting during the depositional formation of laminated sediments coinciding azimuthal distributions of remanence and maximum susceptibility directions reflect intrinsic properties of flaky hematite grains in which the magnetic moment is parallel to the direction of maximum susceptibility this parallelism probably depends on magnetic domain configurations

southern hemisphere circulation and relations with sea ice and sea surface temperature abstract relationships on the seasonal timescale between southern hemisphere 500 hpa height sea surface temperature and antarctic sea ice variability have been investigated using ncep ncar reanalyses ncep sea surface temperatures and met office sea surface temperature and sea ice data the dominant region of interannual variability in the southern hemisphere circulation over the southeast pacific ocean is found to be related to enso variability in tropical pacific sea temperatures as shown in a number of earlier papers it is also related to antarctic sea ice variability where an out of phase relationship is found between sea ice extent in the central pacific and in the southwest atlantic ocean sea ice extent is enhanced in one region when the atmospheric flow anomaly is equatorward presumably through a combination of anomalous heat flux and direct advection at the same time the atmospheric flow anomaly in the other region tends to be poleward resulting in a poleward retreat in the sea ice ed

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

reexamination of the near surface airflow over the antarctic continent and implications on atmospheric circulations at high southern latitudes abstract previous work has shown that winds in the lower atmosphere over the antarctic continent are among the most persistent on earth with directions coupled to the underlying ice topography in 1987 parish and bromwich used a diagnostic model to depict details of the antarctic near surface airflow a radially outward drainage pattern off the highest elevations of the ice sheets was displayed with wind speeds that generally increase from the high interior to the coast these winds are often referred to as katabatic with the implication that they are driven by radiational cooling of near surface air over the sloping ice terrain it has been shown that the antarctic orography constrains the low level wind regime through other forcing mechanisms as well dynamics of the lower atmosphere have been investigated increasingly by the use of numerical models since the observational network over the antarctic remains quite sparse real time numerical weather prediction for the u s antarctic program has been

acquisition of chemical remanent magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds abstract hematite bearing red beds are renowned for their chemical remanent magnetization crm if the crm was acquired substantially later than the sediment was formed this severely compromises paleomagnetic records to improve our interpretation of the natural remanent magnetization the intricacies of the crm acquisition process must be understood here we contribute to this issue by synthesizing hematite under controlled earth like field conditions 100 t crm was imparted in 90 oriented samples with varying inclinations the final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides when the magnetic field intensity is 40 t the crm records the field direction faithfully however for field intensities 40 t the crm direction may deviate considerably from that of the applied field during synthesis the crm intensity normalized by the isothermal remanent magnetization crm irm 2 5 t increases linearly with the intensity of growth field implying that crm could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties crm in hematite has a distributed unblocking temperature spectrum from 200 to 650 c while hematite with a depositional remanent magnetization drm has a more confined spectrum from 600 to 680 c because it is usually coarser grained and more stoichiometric therefore the thermal decay curves of crm with their concave shape are notably different from their drm counterparts which are convex these differences together are suggested to be a potential discriminator of crm from drm carried by hematite in natural red beds and of significance for the interpretation of paleomagnetic studies on red beds

aspects of pre tertiary paleomagnetism of spitsbergen and their tectonic implications abstract paleomagnetic investigations were carried out on cretaceous dolente dykes and sills permian limestones permo carboniferous limestones and lower devonian sandstones from different parts of spitsbergen detailed rock magnetic studies showed that the main magnetic minerals in dolentes limestones and sandstones are titanomagnetite magnetite and hematite respectively the rocks were demagnetized thermally and in alternating fields vector analysis of the demagnetization path separates the different components of nrm and establishes a characteristic remanence the paleomagnetic poles for cretaceous dolentes permo carboniferous limestones and lower devonian sandstones from spitsbergen are respectively 65 n 222 e 34 n 140 e and 12 n 135 e when compared with the european and north american apparent polar wander paths all spitsbergen poles he at a distance from both apwps suggesting that spitsbergen has been rotated and even translated in relation to europe during the opening of the labrador sea and greenland norwegian sea

climate links and recent extremes in antarctic sea ice high latitude cyclones southern annular mode and enso in this article we study the climate link between the southern annular mode sam and the southern sea ice extent sie and discuss the possible role of stationary waves and synoptic eddies in establishing this link in doing so we have used a combination of techniques involving spatial correlations of sie eddy streamfunction and wind anomalies and statistics of high latitude cyclone strength it is suggested that stationary waves may be amplified by eddy anomalies associated with high latitude cyclones resulting in more sea ice when the sam is in its positive phase for most but not all longitudes a similar association is observed during enso la nina years although this synergy in the sam enso response may partially reflect preferential areas for wave amplification around antarctica the short extent of the climate records does not allow for a definite causality connection to be established with sie stronger polar cyclones are observed over the areas where the stationary waves are amplified these deeper cyclones will break up and export ice equatorward more efficiently but the near coastal regions are cold enough to allow for a rapid re freeze of the resulting ice break up we speculate that if global warming continues this same effect could help reverse the current positive antarctic sie trends once the ice gets thinner similarly to what has been observed in the northern hemisphere

southern hemisphere strong polar mesoscale cyclones in high resolution datasets mesoscale cyclones are small low pressure systems usually 500 km in radius that often appear embedded in synoptic structures these events can be weak and short lived or vigorous and destructive here we use an automatic tracking scheme to investigate two subsets of southern hemisphere mesoscale cyclones that are strong and have the potential to cause damage namely polar lows i e strong and short lived and explosive cyclones i e rapid intensification but not necessarily short lived a short climatology 2009 2012 is obtained by using high resolution 0 5 antarctic mesoscale prediction system amps mean sea level pressure the results show a significant improvement of spatial detail compared to the 0 75 resolution era interim dataset with a total count approximately 46 higher in amps the subset of mesoscale cyclones that are explosive is small with a total genesis number of about 13 that of polar lows in addition only about 1 of the polar lows are explosive suggesting that cyclones that undergo rapid intensification tend to become larger longer lived and hence are no longer regarded as polar lows mesoscale cyclones are more frequent in winter with a maximum concentration around the antarctic but also occurring as far north as tasmania and new zealand analysis of sensible heat flux and sea ice extent anomalies during the genesis days shows that there is a large spread of genesis points over both positive and negative flux anomalies in winter with a somewhat random pattern in the other seasons

the polarity of the silurian magnetic field indications from a global data compilation silurian palaeomagnetic data from all continents are compiled in an attempt to define the polarity history of the earth s magnetic field during the period data sets from llandovery ludlow and pridoli strata often display evidence of field reversals i e the presence of both normal and reverse polarity magnetization directions despite the fact that the palaeomagnetic sample collections may cover only a limited stratigraphic range in each case palaeomagnetic data from rocks of wenlock age are exclusively of normal magnetic polarity a comparison of the available silurian data with published ordovician palaeomagnetic results suggests that the frequency of magnetic field reversals increased from ordovician to silurian times palaeomagnetic data sets are not yet available from a continuous silurian stratigraphic sequence of any great duration so the silurian magnetostratigraphy is still at a much more preliminary stage than that for the ordovician apart from the wenlock all silurian series have some intervals with frequent

synoptic activity in the seas around antarctica abstract the recent ncep department of energy doe reanalysis 2 update of the original ncep ncar dataset provides what is arguably the highest quality analyses spanning two decades available for the high southern latitudes it therefore offers an excellent starting point from which to assemble a modern comprehensive and reliable picture of synoptic activity in the subantarctic region this set covering the modern satellite era from january 1979 to february 2000 is used herein in addition the exploration in this study has been conducted with sophisticated feature tracking and trajectory analysis software it is shown that the high southern latitude cyclone system density is greatest in the indian ocean and to the south of australia near or to the south of 60 s the numbers in winter exceed those in summer except over a few but important regions such as the bellingshausen sea the antarctic coastal region is confirmed as one of high cyclonicity as is that in the northern part of the antarctic

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

eddy zonal flow interactions associated with the southern hemisphere annular mode results from ncep doe reanalysis and a quasi linear model abstract using a recent 22 yr 1979 2000 record of the ncep department of energy doe reanalysis 2 dataset hereafter ncep2 reanalysis and a two level spherical quasi geostrophic quasi linear model the eddy zonal mean flow interactions associated with the southern hemisphere annular mode sam variability have been investigated the main emphasis is to highlight the differing natures of the eddy zonal mean flow interactions i due to the high frequency 2 8 days eddies and medium frequency 8 30 days eddies and ii during the extreme and transitional phases of the sam the results show that in addition to a previously documented positive feedback due to the high frequency eddies the medium frequency eddies provide an oscillatory feedback to the sam variability leading to an enhancement of the latter s spectral power in an intermediate frequency band an examination of the latitude lag composites of the transient eddy forcing tef due to high frequency eddies during the extreme and transiti

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

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

distribution and characteristics of mesoscale cyclones in the antarctic ross sea eastward to the weddell sea abstract the mesoscale cyclone activity observed in the portion of antarctica that faces the south pacific ocean and weddell sea area is summarized from a study of 1991 in general area normalized results reveal much greater mesoscale cyclonic activity over the ross sea ross ice shelf and southern marie byrd land than on both sides of the antarctic peninsula more than 50 of the observed mesoscale vortices are of the comma cloud type the average diameter of mesoscale vortices is approximately 200 km near terra nova bay 270 km near byrd glacier and 280 km near siple coast near the antarctic peninsula the average diameter is about 370 km over the bellingshausen sea and 380 km on the weddell sea side the largest percentage of deep vortices occurs over the bellingshausen sea sector 38 of all cases where convective instability frequently occurs over the ross sea ross ice shelf and weddell sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700

twentieth century simulation of the southern hemisphere climate in coupled models part ii sea ice conditions and variability we examine the representation of the mean state and interannual variability of antarctic sea ice in six simulations of the twentieth century from coupled models participating in the intergovernmental panel on climate change fourth assessment report the simulations exhibit a largely seasonal southern hemisphere ice cover as observed there is a considerable scatter in the monthly simulated climatological ice extent among different models but no consistent bias when compared to observations the scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal winds suggesting that wind forced ice transport is responsible for much of this scatter observations show that the leading mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the atlantic sector associated with anomalies of the opposite sign in the pacific sector the observed ice anomalies also exhibit eastward propagation with the antarctic circumpolar current as part of the documented antarctic circumpolar wave phenomenon many of the models do simulate dipole like behavior in sea ice anomalies as the leading mode of ice variability but there is a large discrepancy in the eastward propagation of these anomalies among the different models consistent with observations the simulated antarctic dipole like variations in the ice cover are led by sea level pressure anomalies in the amundsen bellingshausen sea these are associated to different degrees in different models with both the southern annular mode and the el nino southern oscillation enso there are indications that the magnitude of the influence of enso on the southern hemisphere ice cover is related to the strength of enso events simulated by the different models

interpretation of recent antarctic sea ice variability 1 trends in the satellite derived antarctic sea ice concentrations 1979 2002 show pronounced increase decrease in the central pacific sector bellingshausen western weddell sector by 4 10 per decade confidence levels for these regional trends exceed 95 positive polarities of the antarctic oscillation aao lead to more less ice in the eastern ross amundsen sector bellingshausen northern weddell sector which are qualitatively opposite to the impacts of positive polarities of the el nino southern oscillation enso the mechanisms responsible for the covariability between the ice and the a aao and b enso are demonstrated over the last 24 years a positive aao trend and a slightly negative enso trend produce a spatial pattern of ice changes similar to the regional ice trends however the magnitude of the ice changes associated with the aao and enso is much smaller than the regional ice trends more local or less understood large scale processes should be investigated for the explanations

response of the weddell sea pack ice to wind forcing sea ice drift in the weddell sea was studied on the basis of data from seven buoys deployed on ice floes in january february 1996 six of the buoys formed an array with initial mutual distances of 50 km which by october 1996 were stretched to 400 km in an east west direction the differential kinematical parameters i e divergence shearing rate and vorticity were estimated from the buoy array positions by applying a time dependent method the large scale drift of the array was divergent until august 1996 but after the array came under the influence of the antarctic circumpolar current the deformation was mainly shearing meteorological data from european centre for medium range weather forecasts analyses and special sensor microwave imager derived ice concentrations were interpolated at the buoy sites the drift velocity was highly wind dependent it was also wind dependent in winter when the momentum balance was mainly between the internal ice stress and the air drag the drift divergence and shearing rate were related to the wind forcing while the array vorticity correlated better with the air pressure itself we estimated the air ice drag coefficient to be 1 8 10 3 at a height of 10 m over the ice and the geostrophic drag coefficient to be 6 1 10 4 the stability effects on the coefficients were mostly felt in conditions of light winds the average ice water drag coefficient based on 5 day periods was 2 1 10 3 the ice transport through a transect crossing the weddell sea was computed on the basis of the geostrophic winds observed wind drift dependence ssm i derived ice concentrations and the literature on ice draft statistics the resulting annual mean net export in 1996 was 1600 km3 yr 1

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

paleomagnetism of the lower devonian sandstones from holy cross mountains central poland part 1 abstract paleomagnetic investigations of the emsian quartz sandstones from holy cross mountains central poland have revealed the presence of a three component natural remanent magnetization the viscous component of the nrm is carried by magnetite grains and is directed close to the present day local geomagnetic field the remaining two components are both carried by hematite presumably of two stage origin because it was not possible to apply a fold test the acquisition time of each component could only be inferred indirectly the hematite remanence of the highest 650 c blocking temperature is thought to be of post tectonic permian origin as its direction before bedding correction d 199 i 38 is almost identical with the characteristic nrm obtained lewandowski 1983 from neighbouring permian deposits the intermediate component d 231 i 0 with a blocking temperature of around 610 c after applying a bedding correction gives a paleomagnetic pole 24 n 142 e near to european middle upper devonian poles therefore it is thought that this magnetization probably reflects the ambient geomagnetic field not very long after sedimentation

palaeomagnetic argument for a stationary spitsbergen relative to the british isles western europe since late devonian and its bearing on north atlantic reconstruction abstract palaeomagnetic results from the devonian of central spitsbergen mimer valley formation billefjorden suggest an average palaeofield direction for the late devonian early carboniferous with declination 227 5 inclination 30 6 corresponding to a relative pole position at lat 24 s long 325 e this magnetization which is post tectonic is regarded as acquired chemically linked with the upper devonian svalbardian phase of deformation this result together with some recent data from central spitsbergen defines a devonian polar wander segment that accords extremely well with corresponding british data we interpret this in terms of no major displacement of central spitsbergen as compared with western europe since devonian time svalbard and the barents sea region have probably formed a fairly stable platform since the early devonian on the balance of available geological and palaeomagnetic evidence from spitsbergen the british isles and newfoundland the north atlantic region does not appear to have been subjected to strike slip motions in the order of thousands of kilometers in or since the late devonian

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

the response of the southern annular mode the east australian current and the southern mid latitude ocean circulation to global warming 1 climate models predict an upward trend of the southern annular mode sam in response to increasing atmospheric co2 concentration however the consequential impact of this change on oceanic circulation has not been explored here we analyse the outputs of a series of global warming experiments from the csiro mark 3 climate model we show that although for the zonal wind stress change the maximum is located at approximately 60 s in terms of the change in surface wind stress curl the maximum is situated at approximately 48 s this change in the wind stress curl causes a spin up of the entire southern midlatitude ocean circulation including a southward strengthening of the subtropical gyres particularly the east australia current eac the intensified eac generates a warming rate in the tasman sea that is the greatest in the southern hemisphere sh with significant implications for sea level rise the pan southern ocean scale suggests a broad impact on the marine ecosystem of the entire southern midlatitude ocean

a palaeomagnetic study of devonian sandstone from central spitsbergen summary samples from the devonian red bed succession of wood bay formation from central spitsbergen were thermally demagnetized the vector subtraction analytical method of separation of nrm components revealed stable magnetic directions ascribed to a devonian palaeofield the mean palaeomagnetic direction d 58 i 12 yields the palaeomagnetic pole position 12 n 135 e close to the lower devonian pole for great britain indicating that spitsbergen was as similarly related to continental europe as the british islands at that time

southern hemisphere winter extratropical cyclone characteristics and vertical organization observed with the era 40 data in 1979 2001 abstract the mean characteristics and trends of southern hemisphere sh winter extratropical cyclones occurring at six levels of the troposphere over the period 1979 2001 have been investigated using the 40 yr ecmwf re analysis era 40 data cyclonic systems were identified with the melbourne university cyclone finding and tracking scheme this study shows that mean sea level pressure mslp cyclones are more numerous more intense smaller deeper and slower moving than higher level cyclones the novel vertical tracing scheme devised for this research revealed that about 52 of sh winter mslp cyclones have a vertically well organized structure extending through to the 500 hpa level about 80 of these vertically coherent sh cyclones keep their westward tilt until the surface cyclones reach their maximum depths and the mean distance is 300 km between the surface and the 500 hpa level cyclone centers when the surface cyclones obtain their maturity according to the authors definition of vertical orga

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

a climatology of southern hemisphere extratropical cyclones a climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years 1975 89 of once daily australian bureau of meteorology hemispheric analyses is presented contour maps of the positions of formation cyclogenesis dissipation cyclolysis together with other cyclone statistics are presented the distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough during the winter and intermediate seasons two mid latitude branches are evident in the cyclone density originating in the tasman sea and south american sectors both spiraling poleward and merging with the circumpolar core in the southern oceans systems were observed to move in an castsouth east direction away from their location of formation exhibiting peak speeds of migration in the mid latitudes little seasonality was evident in the densitiy distribution of cyclones through the southern oceans but a considerable amount was found in their central pressure

the role of eddies in the southern ocean temperature response to the southern annular mode the role of eddies in modulating the southern ocean response to the southern annular mode sam is examined usinganoceanmodelrunatmultipleresolutionsfromcoarsetoeddyresolving thehigh resolution versionsof the model showan increase in eddy kinetic energy that peaks 2 3 yr after a positive anomalyin the sam index previous work has shown that the instantaneous temperature response to the sam is characterized by predominant cooling south of 458s and warming to the north at all resolutions the model captures this temperatureresponse this responseis also evidentin the coarse resolution implementation of the model with no eddy mixing parameterization showing that eddiesdo not play an important role in the instantaneous response on the longer time scales an intensification of the mesoscale eddy field occurs which causes enhanced poleward heat flux and drives warming south of the oceanic polar front this warming is of greater magnitude and occurs for a longer period than the initial cooling response the results demonstrate that this warming is surface intensified and strongest in the mixed layer non eddy resolving models are unable to capturethedelayededdy driventemperatureresponsetothesam theauthorsthereforequestiontheability

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

topographic effects on the mean tropospheric flow patterns around antarctica abstract topographically induced flows around antarctica in a rotating tank experiment with both homogeneous and stratified fluid are analyzed and compared with the mean tropospheric circulation a circular tank of fluid was brought to a state of near rigid clockwise rotation and a topographic model of the antarctic continent was then rotated counterclockwise to simulate a mean westerly zonal wind stratification was chosen to give the same ratios of topographic and dynamical length scales as in the atmosphere as was the rossby number based on the ratio of rotation rates after the onset of the relative rotation of the antarctic model cyclonic eddies evolved in the coastal areas with in the homogeneous case anticyclonic eddies over the antarctic dome after about ten tank rotation periods a dominant wavenumber 3 structure with cyclonic eddies in the ross and weddell seas and prydz bay is observed as an approximately steady state flow over the topography is relatively stagnant with weak anticycloni

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

midlatitude fronts and variability in the southern hemisphere tropical width abstractthis study examines the relationship between midlatitude synoptic activity and variations in the width of the tropics in the southern hemisphere for the period 1979 2016 the edge of the tr

seasonal southern hemisphere multi variable reflection of the southern annular mode in atmosphere and ocean reanalyses variations of southern hemisphere sh climate variables are often linked to the southern annular mode sam variability we examined such linkage by seasons using state of the art atmosphere and ocean sea ice reanalyses the associated sam related anomaly sra fields of the climate variables denoting anomalies corresponding to the same variation in sam are overall consistent across the reanalyses among the atmospheric products 20crv2 differs from era interim and cfsr in the sea level pressure sras over the amundsen sea resulting in less warming over the antarctic peninsula among the ocean reanalyses orap5 and c glors exhibit the largest consistency the major difference between them and the lower resolution cfsr and soda reanalyses is deeper penetration of anomalous meridional currents compared to the other ocean reanalyses cfsr exhibits stronger and spatially more coherent surface current sras resulting in greater sras of sea ice motion and ice thickness along the ice edges the sras of sensible and total surface heat fluxes are reduced in cfsr due to ocean atmosphere coupling significant sea ice concentration sras are present on the west side of peninsulas along the east antarctica coast in spring and winter most notably in orap5 and c glors implying changes in new ice production and shelf water formation most atmosphere and ocean variables manifest an annular sra pattern in summer and a non annular pattern in the other seasons with a wavenumber 3 structure strongest in autumn and weakest in summer the wavenumber 3 structure should be related to the zonal wave three pattern of the sh circulation the relation of which to sam needs further exploration

regions of rapid sea ice change an inter hemispheric seasonal comparison this bi polar analysis resolves ice edge changes on space time scales relevant for investigating seasonal iceocean feedbacks and focuses on spatio temporal changes in the timing of annual sea ice retreat and advance over 1979 80 to 2010 11 where arctic sea ice decrease is fastest the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later compared to 1979 80 resulting in a 3 month longer summer ice free season in the antarctic peninsula and bellingshausen sea region sea ice retreat is more than 1 month earlier and advance 2 months later resulting in a more than 3 month longer summer icefree season in contrast in the western ross sea antarctica region sea ice retreat and advance are more than 1 month later and earlier respectively resulting in a more than 2 month shorter summer ice free season regardless of trend magnitude or direction and at latitudes mostly poleward of 70 n s there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance but little correspondence between advance and subsequent retreat these results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat further model calculations suggest different net ocean heat changes in the arctic versus antarctic where autumn sea ice advance is 1 versus 2 months later ocean atmosphere changes particularly in boreal spring and austral autumn i e during march may are discussed and compared as well as possible inter hemispheric climate connections

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

zonal flow vacillation and eddy forcing in a simple gcm of the atmosphere abstract zonal flow vacillation with very long time scales is observed in a 3070 day simple gcm simulation with zonally symmetric forcing the long lasting zonal wind anomalies suggest that zonal flow vacillation is self maintained wave mean flow interactions are investigated by composite analysis and transform eulerian momentum budget analysis nonlinear life cycle simulations are conducted to demonstrate that each extreme phase of the zonal flow vacillation is a quasi stable state and is self maintained by the embedded synoptic eddies the firm eof mode of zonal mean wind shows an out of phase relation between anomalies at 60 s and at 40 s with a barotropic structure this structure is similar to the dominant vacillation pattern observed in the southern hemisphere the composite jet stream in the high low index phase of zonal flow vacillation shifts poleward equatorward from the time mean location and becomes broader narrower and weaker stronger composite eddies in the high index phase tilt nw

evidence for detrital remanent magnetization carried by hematite in devonian red beds from spitsbergen palaeomagnetic implications summary palaeomagnetic investigation of the devonian red bed succession of central spitsbergen the wood bay formation uncovered stable magnetic directions associated with blocking temperatures above 600 c rock magnetic properties are characterized by features commonly found in hematite bearing red sandstones the scattered directional distribution of stable magnetic components show large non systematic spatial variations hardly compatible with magnetic overprinting processes petrographic observations friend suggest a detrital origin of the hematite granules present probably derived from a lateritic source area a depositional origin of magnetizations carried by hematite is also inferred from almost coinciding azimuthal distributions of remanent directions and maximum axis of susceptibility ellipsoids effects of the depositional environment upon the acquisition of drm carried by hematite is discussed subjective pattern recognition of directional distributions from sampling areas on both sides of the dicksonfjorden enables a tentative stratigraphic correlation reflecting the presence of pre middle carboniferous faulting downthrowing to the east a clockwise post devonian rotation of the central spitsbergen uncertain magnitude is inferred from an estimate of the devonian palaeomagnetic meridian

southern hemisphere synoptic behavior in extreme phases of sam enso sea ice extent and southern australia rainfall abstract the association between southern hemisphere cyclones and anticyclones and the el nino southern oscillation enso southern annular mode sam antarctic sea ice extent sie and rainfall in perth and melbourne is explored those cities are respectively located in the southwestern and southeastern corners of australia where substantial decreasing rainfall trends have been observed over the last decades the need for a more unified understanding of large scale anomalies in storm indicators associated with the climate features itemized above has motivated this study the main aim is to identify cyclone anomalous areas that are potentially important in characterizing continental rainfall anomalies from a hemispheric perspective focusing on midlatitude australia the study covers the satellite era from 1979 to 2003 and was conducted for the southern winter when midlatitude rainfall is predominantly baroclinic the results indicate a well organized hemispheric cyclone pattern associated with en

south atlantic volcanic margins the early cretaceous south atlantic continental break up and initial sea floor spreading were accompanied by large scale transient volcanism emplacing the parana etendeka continental flood basalts and voluminous extrusive constructions on the conjugate margins south of the torres arch abutment plateau on the north namibia margin we interpret four main tectono magmatic crustal units 1 oceanic crust 2 thickened oceanic crust covered by huge seaward dipping wedges 3 a c 150 km wide break up related rift zone partly covered by the dipping wedges and 4 thicker continental crust partly deformed by palaeozoic extension east of the early cretaceous rift similar settings also characterize other south atlantic margin segments we infer an up to 300 km wide and 2400 km long rift zone representing lithospheric extension leading to breakup and formation of the south atlantic volcanic margins comparison with other volcanic margins demonstrates in spite of local and regional differences gross similarities in tectono magmatic style crustal units and dimensions

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

the unusual midwinter warming in the southern hemisphere stratosphere 2002 a comparison to northern hemisphere phenomena a strong midwinter warming occurred in the southern hemisphere sh stratosphere in september 2002 based on experiences from the northern hemisphere nh this event can be defined as a major warming with a breakdown of the polar vortex in midwinter which has never been detected so far in the sh since observations began at the earliest in the 1940s minor midwinter warmings occasionally occurred in the sh but a strong interannual variability as is present in winter and spring in the nh has been explicitly associated with the spring reversals a detailed analysis of this winter reveals the dominant role of eastward traveling waves and their interaction with quasi stationary planetary waves forced in the troposphere such wave forcing finally leading to the sudden breakdown of the vortex is a familiar feature of the northern winter stratosphere therefore the unusual development of this antarctic winter is described in the context of more than 50 arctic winters concentrating on winters with similar wave perturbations the relevance of preconditioning of major warmings by traveling and quasi stationary planetary waves is discussed for both hemispheres