An Antarctic Circumpolar Wave (ACW) is simulated by a global coupled ocean-atmosphere model. Time-longitude diagrams of anomalies in sea-surface temperature (SST) and sea-surface salinity (SSS) show that anomalies propágale eastward, taking 20-30 years to encircle the pole. The time taken is 2-3 times longer than indicated by observations, due to the relatively slow speed of the modelled Antarctic Circumpolar Current (ACC). High-SSS anomalies correspond to high-SST anomalies and high-density anomalies, and thus to low sea-surface height anomalies, indicating that salinity IS a dominant factor for dynamics with in the Southern Ocean and is indispensable for understanding the mechanism of the ACW. Sea-ice formation is suppressed southward of warm, saline surface-water regions. High sea-ice concentration anomalies correspond to thick sea-ice anomalies. Empirical orthogonal function analyses of SSTanomalies for both model and observation show that the dominant mode in the Southern Ocean has a spatial pattern closely related to El Niño activity. Sea-level pressure (SLP) anomalies propagate eastward with the ACW. High SLP anomalies in the atmosphere correspond to low-density anomalies 111 the ocean. The ACC has clockwise geostrophic velocity anomalies over high-density anomaly regions with upwelling. Both heat and salt are transported from the deep layer to the surface layer by upwelling. This could suppress sea-ice formation directly. Anomalous horizontal advection of heat and salt by geostrophic velocity anomalies in the ACC appears to influence the anomalies in SST, SSS and sea ice.

The intra-annual variability of Antarctic precipitation from the European Centre for Medium-range Weather Forecasts short-term meteorological forecasts and from climate simulations by the ARPÈGE and LMD-Zoom general circulation models is presented and discussed. The spatial resolution of forecasts and simulations is high over the Antarctic region, about 100 km, so that the impact of topography and small-scale atmospheric dynamics are better resolved than with more conventional model grids (about 300 km). All the models and forecasts show that the seasonality of precipitation is spatially very variable. Meridional coast-to-interior contrasts are marked, but equally strong variations are unexpectedly found where more homogeneity might be expected because of the homogeneity of the environment, e.g. on the high Antarctic plateau. Neither the forecasts nor the simulations confirm that precipitation is mostly maximum in winter over much of East Antarctica as suggested by scarce and potentially unreliable observations (Bromwich, 1988). Spring and fall maxima are quite frequent too, though summer maxima are rare. Daily precipitation statistics show more spatial pattern, with increasingly infrequent precipitation as distance from the coast toward the interior of the ice sheet increases Several aspects of the intra-annual variability of precipitation can be interpreted in terms of atmospheric dynamics, but at both daily and seasonal time-scales the different forecasts and climate simulations often locally and regionally disagree with each other. Discrimination between models and their ability to reproduce the dynamics of Antarctic hydrology, and progress on simulating such aspects of the Antarctic climate, is limited by the lack of reliable observation of precipitation variability.

Results from a century-long integration of a coupled ocean/sea-ice model covering the Southern Hemisphere are discussed. The model has a refined grid in a 60° sector south of Australia and is driven by climatological atmospheric variables. The ocean/sea-ice system evolves into a thermal-mode behaviour, i.e. strong vertical mixing produces a well-mixed, weakly stratified upper ocean in the sea-ice zone, resulting in a thin ice cover with multiple polynyas in southern winter. The time evolution of total ice area, however, is close to estimates from satellite observations. The relative extrema of total sea-ice area are somewhat underestimated.

The surface layer of the Southern Ocean is subject to the action of wind, waves and currents. We present solutions from a fine-resolution quasi-geostrophic model with surface friction, which is driven by a specified mean and fluctuating wind field, and predicts the surface current, and also the surface Stokes drift due to the wavefield. The resulting flow patterns control the dispersion of particles at the sea surface, and, using a proven Lagrangian algorithm, batches of particles of specified draught can be injected into the flow at various locations and tracked. The simulated patterns are compared with historical data on dispersion and with drift-card and satellite-drogue studies in the Southern Ocean, iceberg tracking and other studies to show the relative importance of dispersion by synoptic variability in the atmosphere and mesoscale eddies in the ocean.

The performance of a regional atmospheric climate model (RACMO) with a horizontal resolution of 55 km X 55 km is evaluated using measured temperature and humidity profiles. Parameterisations of the physical processes are taken from the EC-HAM4 general circulation model (GCM). Sea-surface temperatures and sea-ice mask in the model are prescribed from observations. The model is forced by re-analyses of the European Centre for Medium-range Weather Forecasts (ECMWF) at the lateral boundaries.

We compared simulations for January 1993 with boundary-layer profiles measured at the Swedish research station Svca (Dronning Maud Land, Antarctica) and with radiosonde measurements made at the Georg von Neumayer (GvN) and South Polar stations for the same period. This comparison was performed in order to study some model characteristics before the model is used for mass-balance calculations. The vertical temperature gradient at Svea during the night is overestimated by RACMO, but corresponds much more closely to the observations than do the ECMWF re-analyses. in the re-analyses a decoupling of the lowest model layer from the higher atmosphere occurs. The differences between the absolute temperatures at the GvN and SP stations and the absolute temperatures at the model gridpoints corresponding most closely to these sites are less than 5°C. The humidity profiles indicate that the model generally underestimates the turbulent transport of moisture from the surface to higher levels.

Data from six automatic weather stations deployed around the interior of the Lambert Glacier basin, Antarctica, at surface elevations of 1830-2741 m are used to compile a surface climatology of this part of interior Antarctica for the period 1994-96. The stations measure air pressure, near-surface wind speed and air temperature at several levels, wind direction and firn temperatures. The topography of the basin, which extends more than 800 km inland, controls the katabatic wind regime and strongly influences the surface climate of the region. Windiest sites are on the steep coastal slopes, and within the depression of the Lambert and Mellor Ice Streams where the flow is topographically channelled. Surface winds here show greater seasonal variation in speed but less variation in direction than elsewhere. The annual mean temperatures on the relatively steep slopes on the eastern side of the basin are 4-5°C warmer than at equivalent altitude on the western side. During winter, near-synchronous synoptic temperature and pressure increases occur throughout the basin to at least 1000 km from the coast. There is a consistent pattern of diurnal wind variation in the summer at all stations, with maximum wind speed at about 0900 LST (local solar time), and the most easterly direction at 1300 LST.

To evaluate the greatest impact that sea-ice anomalies around Antarctica could have on the global atmosphere, 15 year seasonal cycle simulations are conducted with the U.S. National Center for Atmospheric Research Community Climate Model version 2.1. Sensitivity simulations are performed with the following conditions: (1) all sea ice in the Southern Hemisphere is replaced by year-round open water, but the permanent ice shelves are retained (NSIS); and (2) all sea ice in the Southern Hemisphere and the major ice shelves are removed and replaced by open water (NISH). The results are compared to a standard run (CNT) with boundary conditions set for the present climate. The comparison shows that trains of positive and negative anomalies in zonal-mean fields extend into the tropical latitudes of the Northern Hemisphere. Anomalies are largest during April-October. The additional removal of the ice shelves in NISH enhances the response, as zonally averaged anomalies are similar in pattern to those in NSIS but are roughly twice as large poleward of 50° S, and only slightly larger farther north. Anomalies in the eddy fields are found in both hemispheres. in NISH, and to a lesser degree in NSIS. these anomalies appear to be related to a delayed northern advance over China during June of the rain front associated with the summer monsoon. Consequently, precipitation is enhanced in middle and southern China and decreased in northern China. Observational analyses have also found links between Antarctic sea-ice variations and modulations of the East Asian monsoon.

The Japanese Antarctic Research Expedition (JARE) has set up automatic weather stations at six sites on a 1000 km long traverse route between Syowa station (21 ma.s.l..) and Dome Fuji station (3810 ma.s.l.) since 1993. Large temperature rises in winter were observed several times in this area. There were two patterns of time delay of the temperature rises. One was that the temperature rise at Mizuho station preceded that at other stations, and the other was that the temperature rise at Dome Fuji station preceded the others. The former occurred when a disturbance came from the coast between east Enderby Land and the Amery Ice Shelf and strong winds destroyed the stable inversion layer. The latter occurred when the low-pressure center was near the coast of west Wilkes Land. in this case, temperature rise was caused by adveclion of warm air. The atmospheric pressure at Dome Fuji station and Relay Point oscillated with a period of 0.5 year and amplitude of about 15hPa. The pressure was higher in July and December, and was accompanied by a temperature rise. Fluctuations of hourly air temperature at Dome Fuji station were approximately twice as large as fluctuations at the other sites. The lapse rale of the annual mean temperature increased with elevation, while the monthly lapse rate was largest in April.

A study of the spatial and temporal distribution of methane sulphonic aeid (MSA) and nssSO42- concentrations in snow-pit samples was performed to determine the main and secondary sources, transport effects and seasonal pattern of biogenic sulphur compounds. Four snow pits, about 3 m deep, excavated at the same time at different altitudes (870-2960 m a.s.1.) in northern Victoria Land, Antarctica, gave coherent information about the effect of altitude and seasonality on the snow chemical composition. A progressive, well-defined decreasing concentration trend is shown as altitude increases, with the biggest effect in the first 1000 m a.s.1. At higher altitudes, biogenic sources make the most important contribution to the tola! sulphate balance with respect to sea-mray input. Particular attention was paid to the relationship between MSA and nssSO42- by using MSA as a univoca] biogenic marker. The nssSO42- /MSA ratio was evaluated with respect to altitude and seasonality to determine the effect of transport mechanisms (such as long-range transport and fractionation) or non-dimethyl sulphide sources on nssSO42- snow content.

Regional assessments of impacts due to global climate change are a high priority in the international programs on global-change research. in the polar regions, climate models indicate an amplification of global greenhouse warming, but there are large differences between the results of various models, and uncertainties about the magnitude and timing of the expected changes. Also, the observed high-latitude climate trends over the past few decades are much more regional and patchy than predicted by the models. As a first step in assessing possible climate impacts, model results are compared with observations of changes in temperature, precipitation, sea-ice extent, the permafrost regime and other cryospheric parameters. While considerable uncertainties remain in the long-term prediction of change, there is some agreement between model results and observed trends by season on shorter time-scales, The warming observed over the land masses of the Arctic over the past few decades is matched by corresponding observed decreases in snow cover the glacier mass, balances, by thawing of the permafrost, and to a lesser degree by reductions in sea-ice extent. in Antarctica, warming in the Antarctic Peninsula and Ross Sea regions is associated with large decreases in ice-shelf areas and reduced ice thicknesses on the lakes in the McMurdo Dry Valleys. Major future impacts due to global greenhouse warming are likely to include permafrost thawing on and and its consequences for ecosystems and humans; changes in the productivity of marine ecosystems in the Arctic and Southern Ocean: economic impacts on fisheries, petroleum and other human activities; and social impacts on northern indigenous populations. Some of these impacts will have positive ramifications, but most are likely to be detrimental. While uncertainties exist about the future, climate change in the polar regions during the past few decades can be shown to have had major impacts already which will become much mole pronounced if present trends continue.

Surface temperature data for the occupied Antarctic stations (for the period 1959-96) and Southern Ocean island stations (1949-96), and sea-ice-extent data (1973-96) are analyzed to provide trends over the indicated time intervals. The mean trend (mean slope of linear regressions through the annual mean station data) for the Antarctic stations indicates a warming of 1.2°C (100 a)−1. The slope of the linear regression fit to a composite of the mean station anomaly data indicates a warming rate of 0.9°C (100 a)−1. For the Southern Ocean island station data, warming rates of 1.0° and 0.7°C (100 a) −1 are indicated by the two methods. For the sea-ice data, no significant trend is detectable over the satellite era, 1973-96, but for the longer period commencing in the mid-1940s there is some evidence of a decrease in sea-ice extent from whaling records recently published.

Atmospheric aerosol particles have been sampled since 1985 at the Brazilian Antarctic station, Comandante Ferraz (62°05' S, 58°23 5'W) Stacked niter units were used to collect particles with an aerodynamic diameter of less than 10μm. The elemental concentration was measured by particle-induced X-ray emission, yielding data for 23 elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, K, V, Cr, Mn, Fe, Ni, Cu, Zn Sc, Br Kb, SrZr and Pb. The detection limit was typically near 5 ng m −3 for elements with atomic number (z) less than 20, and Oingm for 21 < z <.30. Principal-factor and cluster analyses identified four sources for the Antarctic aerosol: fine and coarse sea salt, soil dust and sulphates. The fine-mode non-sea-salt sulphate concentration showed a clear seasonal pattern accompanying the biological cycle of algae, with minimum during winter. Some elements, such as Ni and Pb, showed very high enriched concentrations relative to the bulk sea-water composition. This indicates the existence of sources of regional or long-range transported pollution.

We compare observed temperature variations in Antarctica with climate-model runs over the last century. The models used are three coupled global climate models (GCMs) — the UKMO, the CSIRO and the MPI forced by the CO2 increases observed over the last century, and an atmospheric model experiment forced with observed sea-surface temperatures and sea-ice extents over the last century. Despite some regions of agreement, in general the GCM runs appear to be incompatible with each other and with the observations, although the short observational record and high natural variability make verification difficult. One of the best places for a more detailed study is the Antarctic Peninsula where the density of stations is higher and station records are longer than elsewhere in Antarctica. Observations show that this area has seen larger temperature rises than anywhere else in Antarctica. None of the three GCMs simulate such large temperature changes in the Peninsula region, in either climate-change runs radiatively forced by CO2 increases or control runs which assess the level of model variability.

Temperature records from slations on the west roast 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.

This paper investigales the climate change in two atmosphere ice-ocean coupled climate models — the UKMO and the CSIRO— in the Antarctic region over the next century. The objectives were to sec if an enhanced level of greenhouse-gas forcing results in a surface temperature signal above background variability, and to see if this pattern of change resembles the change seen to date in Antarctica, especially the warming around the Peninsula. The models show that although reduced sea-ice compactness is responsible for regions of enhanced air-temperature anomalies, these ice-compactness anomalies are determined by different mechanisms in the respective models. The pattern of warming in both models does not match the differential rates of warming seen in the observations of temperature change over the Antarctic continent in the lait few decades. Also the level of background ocean variability in the Drake Passage and Weddell Sea region hampers the clear definition of a signal over the Antarctic Peninsula in the coupled models. Although no winter enhancement in warming over the Peninsula region IS found, an autumn anomaly is seen in one of the models. The mechanism for this feature IS documented, and an explanation of why it does not persist throughout the winter season is presented.

An updated compilation of oxygen-isotope ratio data for 562 sites in Antarctica shows a significant increase in the number of sites and an improvement in the representation of the coastal zone oyer previous versions. The data hase consists of ratio values (δ18O; multi-year mean 18O/16O relative to Standard Mean Ocean Water, in ‰) compiled as the dependent variable, together with data for the so-called independent variables: latitude, surface elevation, mean annual surface temperature and mean annual shortest distance to open ocean denoted by the 20% sea-ice concentration boundary. The problem of covariation between so-called independent variables is minimized using stepwise regression analyses. A general model is described using all the field data, and the regional variation at drainage-system scale is assessed by contrasting models for two physiographically distinct regions. in addition, entity-specific models are determined using data subsets for the conterminous grounded-ice and ice-shelf areas. Inversions of the specific models are applied to a 100 km grid data base to produce two contoured distributions of the ratio, one based on field data, and the other on remotely sensed data. The difference between these produces residuals that, relative to the summation of standard errors of the models, are small in most of the interior area of the ice sheet, and large in several areas of mountain and coastal regions, where interpolation and extrapolation of field data are particularly unreliable. Remotely sensed data generally produce ratio values which are isotopically cooler.

Daily precipitation fields and annual means from the European Centre for Medium-range Weather Forecasts re-analysis exercise are used to examine the distribution and variability of precipitation across the Antarctic Peninsula. The annual mean precipitation field from the model agrees well with the available ice-core data and suggests that the maximum accumulation for the area is on the western side of the barrier at about the 200 m level where the annual total is close to 1.3 m w.e. The Peninsula is shown to be a very effective barrier to the zonal movement of precipitating weather systems, which results in quite different atmospheric flow regimes being responsible for significant precipitation events on other side of the divide. Frontal depressions are the primary source of large daily snowfall totals on both sides of the Peninsula. On the southern coast of the Bellingshausen Sea, major snowfall events are often linked to strong northerly flow when the atmospheric circulation is blocked. Predominantly northerly flow is also responsible for significant snowfall on the Ronne Ice Shelf, which often occurs in association with lee cyclogenesis events to the east of the- Peninsula.

Long-term observatinns of precipitating clouds were carried out by a vertical pointing radar and plan-position indicator PPI) radar at Syowa station (69.0°S, 40.5°E), Antarctica, in 1989. The observations revealed that there were three abundant snowfall seasons at Syowa station and the amount of snowfall was uniform in all seasons except summer. The amounts of precipitation in autumn, winter and spring were 74, 74 and 53 mm (liquid water equivalent), respectively. The amounts of precipitation in autumn and winter were large at Syowa station in 1989. However, the amount of precipitation on the inland ice is expected to be small in winter, indicated by the distributions of precipitation measured by the PPI radar.

The occurrence frequencies of cloud vortices which brought snowfall to Syowa station increased in the autumn and spring seasons, corresponding to the activity of the circumpolar trough. However, the activities ofcloud systems that bring precipitation weaken in Spring when the sea-ice area expands to low latitudes, because of a lower supply of heat and vapor. Thus the activities of cloud vortices are also weakened above the sea ice.

The surface energy balance was calculated to estimate sublimation and melt on the surface and terminus of Canada Glacier, Taylor Valley, Antarctica, during the 1994-95 and 1995-96 austral summers. Our results indicate that sublimation accounted for roughly 80% of the observed 1994-95 summer ablation and 40% of the observed 1995-96 summer ablation on the surface of the glacier. Sublimation Oil the terminus cliffs appears to be less significant than sublimation on the glacier surface, probably accounting for at most 10-15% of the measured ablation. Based on these results, both surface and terminus cliff melt were calculated and compared with gauged flow in the Glaciol streams. We found thai while the terminus cliffs represent only 2% of the total ablation zone, they account for 10— 40% of the total meltwater runoff. Given pur current instrumentation, we can estimate meltwater discharge from the glacier with an accuracy of ±20%.

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 Niño-Southern Oscillation signal.