eddies and the annular modes of climate variability the dominant modes of month to month varia tion in the troposphere are realistically simulated in a gen eral circulation model whose lower boundary is prescribed with realistic topography and seasonally varying climato logical sea surface temperatures in both hemispheres these internal modes describe a nearly zonally symmetric north south shifting of the zonal jets as anomalous westerlies vac illate between high 50 60 a nd low 30 40 latitudes the eddy structures evolve with the jets and the corre sponding eddy momentum forcings support the shifts in jet position stationary synoptic wave variations mainly ac count for the total eddy forcings in the northern south ern hemisphere pronounced eddy variations occur over the north atlantic sector

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

geophone ground coupling for frequencies much lower than the coupling resonant frequency the geophone accurately follows the ground motion but for higher frequencies the coupling can alter both the amplitude and phase of the seismic signal the normal planting of vertical geophones in the field results in coupling adequate for conventional recording that uses frequencies less than 100 hz however for very loose soils or for high frequency seismic recording i recommend that the geophones be buried to place the geophones in firmer soil the coupling resonant frequency for vertical geophones is determined by the firmness of the soil and i have measured resonant frequency ranging from 100 to 500 hz at different locations because the firmness of the soil increases with depth the coupling resonant frequency can be increased by burial of the geophones or by the use of longer spikes the rocking of horizontal geophones causes a low frequency coupling resonance it is crucial that horizontal geophones be planted with their bases firmly contacting the soil geophones so planted have a resonance around 130 hz whereas those 1 cm off the ground can have a resonance of 30 hz or lower soil conditions have little effect on the resonant frequency horizontal geophones with 1 inch spikes are as well coupled as those with longer spikes but the best coupling is achieved by burial of the geophones modified journal abstract

the structure and predictability of the high latitude mode in the csiro9 general circulation model abstract the csiro9 general circulation model shows a zonally symmetric mode of variability which closely resembles the high latitude mode hlm in middle and high latitudes of the southern hemisphere the leading eof of the zonal mean zonal wind between 30 and 68 s whose amplitude has been taken as an index of the hlm shows opposing variations centered near 40 and 60 s accounting for 43 of the daily variance analysis has concentrated on composites for periods when the index changed quickly between significant peaks of the opposite sign or persisted with a large amplitude for an extended period the momentum flux variations are small at the northern and southern boundaries and the principal variations are centered near 49 s between the maxima in the zonal wind the changes in angular momentum content are around 30 smaller in the southern band eddy heat fluxes are less coherent but help in maintaining the zonal wind anomalies against friction a simple model of the zonal wind index with stochastic

sea ice atmosphere signal of the southern oscillation in the weddell sea antarctica abstract composite analysis of weekly ship and shore observations of the weddell sea pack ice for extreme events of the southern oscillation so occurring in the 1929 62 period reveals strong variations in ice water concentrations in the early and late summer melt season substantially reduced ice concentrations more open water occur in december and early january of warm el nino events yr0 compared with the summer before yr 1 and appear connected with the change to a stronger cyclonic atmospheric circulation over higher latitudes of the south atlantic similarly consistent meteorology sea ice associations appear to characterize the mid to late summer of warm so events yr0 compared with yr0 of cold events there is some evidence that the regionally dependent pressure and wind reversals and possibly the associated sea ice concentration changes in the weddell sector have become more marked during so events occurring since about the early 1950s some corroboration of changes in the sea ice

antarctic sea ice relationships with indices of the atmospheric circulation of the southern hemisphere a link between the antarctic sea ice extent and low frequency atmospheric variations particularly enso has been suggested by recent modeling and empirical studies this question is examined here using a high resolution by week by region data base of antarctic sea ice extent for the 1973 1982 period although of relatively short duration by northern hemisphere standards such a data base offers an opportunity rare in southern hemisphere climate studies the seaice variations are examined in the context of longer term indices of the large scale atmospheric circulation these are a southern oscillation index soi and an index of sea level pressure slp wavenumber one in the southern hemisphere extratropics the indices are updated through 1982 and their associations with regional scale pressure indices in the australia new zealand sector are also examined the 1973 1982 period is anomalous when compared with the period 1951 1972 correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the soi suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea ice extent removing these effects from the data and re running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance in order to reconcile these findings with previous studies that show some strong ice circulation interactions on regional scales only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further these occur preferentially in the ross and weddell sectors which constitute the regions contributing most to the variability of antarctic sea ice the analysis suggests that the sea ice extent changes lag the soi by several months but may precede changes in extratropical slp wavenumber one confirmation of these tentative regional ice extent circulation teleconnections necessarily awaits the forward extension of the high resolution sea ice data base beyond the 10 years available here

quasi stationary wave variability in nscat winds planetary and interseasonal properties of the nasa scatterometer nscat winds are explored in the context of the quasi stationary waves qsws of the southern hemisphere the qsws are examined by means of zonal asymmetries of 3 month running averages of the meridional velocity derived from nscat the study period spans the entire nscat record from september 15 1996 through june 29 1997 meridional winds from the european space agency ers 2 scatterometer are used to augment 3 month averages centered on august 1996 through may 1997 the time period corresponds to the transition from year 1 to 0 of the 1997 warm event in the southern oscillation comparisons are made with qsw signals in geopotential height anomalies from the national centers for environmental prediction national center for atmospheric research climate data assimilation system the zonal anomalies of meridional wind from nscat are shown to be in approximate geostrophic balance with zonal gradients in the zonal anomalies of geopotential height at 500 and 1000 hpa

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

climate change in the western antarctic peninsula since 1945 observations and possible causes temperature records from stations on the west coast of the antarctic peninsula show a very high level of interannual variability and over the last 50 years larger warming trends than are seen elsewhere in antarctica in this paper we investigate the role of atmospheric circulation variability and sea ice extent variations in driving these changes owing to a lack of independent data the reliability of antarctic atmospheric analyses produced in the 1950s and 1960s cannot be readily established but examination of the available data suggests that there has been an increase in the northerly component of the circulation over the peninsula since the late 1950s few observations of sea ice extent are available prior to 1973 but the limited data available indicate that the ice edge to the west of the peninsula lay to the north of recently observed extremes during the very cold conditions prevailing in the late 1950s the ultimate cause of the atmospheric circulation changes remains to be determined and may lie outside the antarctic region

the role of eddies in maintaining the westerlies in the southern hemisphere winter abstract the distribution of the mean westerly wind over the globe is described for june july and august the southern winter using analyses from the european centre for medium range weather forecasts ecmwf from 1979 to 1982 the tropospheric momentum budget is analyzed from both the traditional eulerian and the transformed eulerian perspectives thus an assessment is made of the eliassen palm flux divergence and the diabatically driven residual mean circulation the vertical mean budget is also analyzed to allow deductions about the mean surface torque by the atmosphere on the earth and the grow surface stress in the southern winter transient eddies dominate the poleward momentum transports in both hemispheres and total transports are somewhat larger than found in previous studies values of the deduced mean westerly surface stress are therefore larger than most previous estimates but seem very reasonable and are probably more reliable in midlatitudes a strange vertical structure analyzed to be

interpreting recent accumulation records through an understanding of the regional synoptic climatology an example from the southern antarctic peninsula in this study we correlate temporal features within the electrical conductivity acidity traces of four shallow firn cores obtained from the southern antarctic peninsula to synoptic scale variations in the regional climate as depicted by a numerical weather prediction model it is demonstrated that the three high acidity features present within the 1992 93 accumulation correspond to periods of significant precipitation a hypothesis supported by the association of these events with strong onshore winds ideal for transporting the biogenically derived sources of precipitation acidity to the core sites the longitudinal location of depressions within the bellingshausen sea is shown to be the principal factor governing the volume of precipitation that they give over the western peninsula annual accumulation in the model is 25 lower than revealed by the cores although there are too many uncertainties to provide a definite reason for the deviation the smoothed model orography and inaccurate land sea mask are believed to be significant factors it is postulated that the acidity pattern within southern peninsula cores may reveal an el nino southern oscillation signal

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

a 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

on the role of the antarctic continent in forcing large scale circulations in the high southern latitudes abstract the antarctic topography and attendant katabatic wind regime appear to play a key role in the climate of the high southern latitudes during the nonsummer months persistent and often times intense katabatic winds occur in the lowest few hundred meters of the antarctic atmosphere these slope flows transport significant amounts of cold air northward and thereby modify the horizontal pressure field over the high southern latitudes three year seasonal cycle numerical simulations using the ncar community climate model version 1 ccm1 with and without representation of the antarctic orography were performed to explore the role of the elevated terrain and drainage flows on the distribution and evolution of the horizontal pressure field the katabatic wind regime is an important part of a clearly defined mean meridional circulation in the high southern latitudes the position and intensity of the attendant sea level low pressure belt appears to be tied to the antarctic orography the seasonal movemen

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

magnitude frequency relationships of debris flows and debris avalanches in relation to slope relief abstract probability of occurrence hazard intensity and encounter probability are key parameters in the quantitative risk analysis qra of landslides all are strongly dependent on magnitude of the landslides as a result magnitude frequency analysis should be a part of qra deriving representative magnitude frequency relationships for debris avalanches and debris flows however is difficult one key problem is illustrated with the example of a unique database from the coastal region of british columbia canada which was compiled entirely from detailed ground investigations the magnitude of debris avalanches and debris flows is not an independent statistical quantity but a function of the scale of a given slope as characterized by the slope length thus attempting to derive probability and magnitude for a given location or sub region from a regionally derived magnitude frequency curve may lead to incorrect predictions the same problem is pertinent to the application of the same approach to any type of landslide in which the largest combined dimension of the source volume including entrainment is of the same order as the length of the slope it is recommended that greater emphasis be placed on site specific geological observations at the expense of generalized statistics

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

climatic signals of the antarctic ocean a preliminary examination of the winds and sea surface temperatures in the 120 year record of ocean climate produced by the historical sea surface temperature project has provided evidence of two distinct ocean wide modes of variability one of these has a typical time scale of a few years and is closely related to the ei nino phenomenon the other has a time scale of the order of 30 100 years and has exhibited sharp changes in higher southern latitudes however the uneven distribution of the marine observations in space and time is a potential source of spurious anomaly changes a comparison of average ship winds for different sized areas with winds derived for the same areas from weather charts is presented to illustrate the limited significance that can be attached to the local anomalies this points up a need for the joint interpretation of anomaly changes over wider areas as resulting from changes in the characteristic behavior of synoptic pressure systems a tentative explanation of the nearly simultaneous changes in the winds and sea surface temperatures of the latitude belt 40 s to 50 s is derived from wyrtki s 1960 1961 circulation model for the southern ocean that region apparently plays a leading role in the long term fluctuations of ocean climate through the antarctic intermediate water and sub antarctic mode water these water masses acquire their characteristics from the surface energy balance and sea ice processes in high southern latitudes and occupy a deep layer extending up to just below the thermocline in the tropical ocean it is suggested that they could be a pathway for climatic signals from the antarctic ocean to the rest of the globe

a climatology of anticyclones and blocking for the southern hemisphere abstract an automated procedure for locating and tracking high pressure centers is applied to 10 years of twice daily ecmwf analyses during 1980 89 to survey the behavior of anticyclones in the southern hemisphere anticyclones are concentrated in the 25 45 s band with preferred regions consistent with previous studies except in the new zealand nz south pacific sector where a double occurrence maximum noted in earlier studies was only weakly evident marked interannual variability was found in this region with the poleward branch of maximum occurrence south of 50 s present in only 3 out of 10 years mean central pressure maximized about 10 south of the time averaged ridge with highest values in winter anticyclones poleward of 50 s involve an anomalous breakdown of the westerlies with mean central pressures there 20 30 hpa higher than climatology highs tend to form and intensify in western regions of ocean basins and weaken and dissipate in the east of these oceans regions southeast of australi

empirical orthogonal functions and multiple flow regimes in the southern hemisphere winter abstract we present a new empirical orthogonal function eof analysis of winter 500 mb geopotential height anomalies in the southern hemisphere an earlier eof analysis by two of the present authors prefiltered the anomalies to exclude wavenumbers 5 and higher we do not the different preprocessing of data affects the results all three distinct planetary flow regimes identified in the winter circulation of the southern hemisphere by a pattern correlation method are captured by the new set of eofs only two of those regimes were captured by the earlier set the new results therefore lend further support to the idea that eofs point to distinct planetary