ATMOSPHERIC AND OCEANIC CONNECTIONS BETWEEN THE

POLAR REGIONS AND LOWER LATITUDES (IAMAS, IAPSO)

Location: Mechanical Engineering G34LR

Location of Posters: Old Gym

Thursday 22 July AM

Presiding Chair: Robin D Muench (Earth and Space Research, Seattle, USA)

JSM18/E/05-A4 Invited 0940

CHANGES IN THE NORTHERLY LIMIT OF ANTARCTIC SEA ICE SINCE THE 1930S

Peter WADHAMS (Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, UK. email: pw11@cam.ac.uk).

A paper by de la Mare (Nature, 389, 57-59, 1997) utilises positional information from whaling ships to hypothesise that the latitude of the Antarctic ice edge retreated southward significantly during the 1960s, by nearly 3 degrees. In the current investigation, other sources of information about the Antarctic ice edge location have been examined, including the work of ships of the Discovery Committee. It has been found that although a southward shift did occur, it was not as great, or as sharply defined, as postulated in the paper. A possible reason for the discrepancy is changing patterns of whaling strategy during the 1960s based on a change in species composition of the prey. The implications of a southward ice edge shift for water mass modification are also discussed.

JSM18/W/05-A4 1020

INFLUENCE OF THE VARIATION OF POLAR SEA-ICE EXTENT ON THE ATMOSPHERIC CIRCULATION, EL-NINO AND HYDROCLIMATIC REGIME OF THE YANGTZE RIVER BASIN

Gongbing Peng (Institute of Geography, Chinese Academy of Sciences, Beijing100101, P.R.China, email: zhangsh@lreis.ac.cn)

Monthly anomalous data of Antarctic sea-ice extent from Jan., 1973 to Sept., 1997 and of Arctic sea-ice extent from Aug., 1901 to Aug., 1995 are used. They are then compared with corresponding data of the atmospheric circulation, El-nino and runoff of Yichang, Hankou and Datong, which represent hydroclimetic condition of upper, middle and lower Yangtze River basin respectively. The influences of the sea-ice extent on them have been revealed by means of cross correlation calculation and synoptic-climatic analysis. Special attention has been paid to the connections of South and North Pacific subtropic highs, sea-surface temperature and trade wind of equatorial East Pacific, El-Nino, Walker and Hadley cells with Antarctic sea- ice and to that of north polar vorter, meridianal circulation of Asia, North Pacific subtropic high and El-nino with Arctic sea-ice.

The results show that the influences are significant. Several Synoptic climatic models have been established, dealing with the influence processes. It will be useful to hydroclimatic prediction.

JSM18/W/14-A4 1040

CORRELATIONS BETWEEN CHINA MONSOON PRECIPITATION AND OBSERVED ANTARCTIC SEA ICE

Lin ZHANG (Department of Polar Research and Ocean Forecasts, National Research Center for Marine Environment Forecasts, 8 D Hui Si, Hai Dian District, Beijing, China,

e-mail: linzh@polarmet1.mps.ohio-state.edu), David H. Bromwich and Keith M. Hines (both at Byrd Polar Research Center, The Ohio State University, Columbus, OH 43210, USA,

e-mail: bromwich@polarmet1.mps.ohio-state.edu)

A previous observational study found a statistically-significant correlation between East Asian monsoon parameters and 10 years of observed Antarctic sea ice. This fascinating link is re-examined with the much longer record of Antarctic sea ice now available. The SIGRID sea ice data from 1973-1986, SSMR sea ice data from 1979-1987 and SSM/I sea ice data from 1988-1997 are correlated to precipitation records available from 364 stations over China. The sea ice data are also correlated to parameters of the monsoon pressure distribution as suggested by the earlier observational study. While the earlier study used sea ice with distinctive trends in the 10-year record, the present study has a sufficient sea ice record to reasonably capture interannual variations on the order of a decade or less. This new study compliments earlier global climate modeling studies with the NCAR CCM2 as well as future modeling studies to be performed with the NCAR CCM3.

JSM18/W/17-A4 1120

THIS STUDY EVALUATES THE RELATIONSHIP BETWEEN ANTARCTIC SEA ICE AND GLOBAL CLIMATE VARIABILITY

Xiaojun YUAN, Lamont-Doherty Earth Observatory of Columbia University,

email: xyuan@Ideo.columbia.edu

This study evaluates the relationship between Antarctic Sea Ice and global climate variability. Temporal cross-correlations between Antarctic sea ice edge (SIE) anomaly and various climate indices are calculated. For the sea surface temperature (SST) in the eastern equatorial Pacific and tropical Indian Ocean, Southern Oscillation index, as well as the tropical Pacific precipitation, a coherent propagating pattern is clearly evident in all correlations with the detrended SIE anomalies (SIE*). Correlations with ENSO indices imply that up to 30% of the variance in SIE* is linearly related to ENSO. The SIE* has even higher correlations with the SST in the tropical Indian Ocean. In addition, correlation of SIE* with global surface temperature produces two characteristic correlation patterns: (1) an ENSO-like pattern in the tropics with stronger correlations in the Indian Ocean, and the Pacific and North American teleconnection (PNA) pattern in extra-tropics with stronger correlations in North America; and (2) a dipole like pattern in the tropical Atlantic with stronger correlations south of the equator. The SIE* anomalies in the western Indian Ocean, eastern Pacific and Weddell Sea of the Antarctic polar ocean sectors show the strongest polar links to extropolar climate. Linear correlations between SIE* in those regions and global climate parameters pass a local significance test at the 95% confidence level. The field significance is evaluated using colored noise that is more appropriate than white noise and shuffled noise. The fraction of the globe displaying locally significant correlations (at the 95% confidence level) between SIE* and global temperature is significantly larger, at the 99.99% confidence level, than the fraction expected given colored noise in place of the SIE*. Even so, one would still expect, by chance, to find a large number of significant correlations in any one individual correlation map.

JSM18/W/15-A4 1140

ECMWF ANALYSES AND REANALYSES DEPICTION OF ENSO SIGNAL IN ANTARCTIC PRECIPITATION

David H. BROMWICH and Aric N. Rogers (both at Byrd Polar Research Center, The Ohio State University, Columbus, Ohio 43210, email: bromwich@polarmet1.mps.ohio-state.edu); Per Kållberg (European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading, U.K.,

email: per.kallberg@ecmwf.int); Richard I. Cullather (Department of Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado 80309, email: Richard.Cullather@colorado.edu); James C. White (Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80303, email: jwhite@spot.colorado.edu); Karl J. Kreutz (Climate Change Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire. Now at Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, MS #25, Woods Hole, Massachusetts 02543, email: kkreutz@whoi.edu)

The El Niño-Southern Oscillation (ENSO) signal in Antarctic precipitation is evaluated using European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses and ECMWF 15-year (1979-1993) reanalyses. Operational and reanalysis data sets indicate that the ENSO teleconnection with Antarctic precipitation is manifested through a positive correlation between the Southern Oscillation Index and West Antarctic sector (120° W to 180°, 75° S to 90° S) precipitation from the early 1980s to 1990, and a negative correlation after 1990. However, a comparison between the operational analyses and reanalyses shows significant differences in net precipitation (P-E) due to contrasts in the mean component of moisture flux convergence into the West Antarctic sector. An analysis of mean fields related to moisture convergence shows that there are significant differences in the average wind fields between the operational analyses and the reanalyses for the most reliable period of overlap (1985-1993).

Further, it is found that variations in net precipitation in this region are determined more by the structure of the flow pattern than by moisture content. Some of the differences in flow pattern are attributed to an error in the reanalysis assimilation of Vostok Station data that suppresses the geopotential heights over East Antarctica. Reanalysis geopotential heights are also suppressed over the Southern Ocean, where there is a known cold bias below 300 hPa. Deficiencies in ECMWF reanalyses result in a weaker ENSO signal in Antarctic precipitation and cause them to miss the significant upward trend in precipitation found in recent operational analyses. Ice core analyses reflect both the upward trend and ENSO teleconnection correlation pattern seen in net precipitation obtained from operational analyses. This study confirms the results of a previous study using ECMWF operational analyses that was the first to find a strong correlation pattern between the moisture budget over the West Antarctic sector and the Southern Oscillation Index.

JSM18/P/01-A4 1200

A SEARCH FOR ENSO TELECONNECTION SIGNALS IN THE ANTARCTIC PENINSULA REGIONAL ATMOSPHERIC CIRCULATION AND CLIMATE IN THE AUSTRAL WINTER 1973-93

Steve Harangozo (British Antarctic Survey, Madingley Rd, Cambridge CB3 0ET, UK)

There is an increasing amount of evidence to implicate ENSO in modulating the surface climate in some parts of Antarctica on interannual time scales. The overall importance of ENSO in modulating interannual atmospheric circulation and climate variability is, however, far from clear at present. The way in which the ENSO signal becomes manifest in the Antarctic surface climate record remains an open question. This paper will present preliminary results of a study to detect ENSO signals in the atmospheric circulation and climate in the Antarctic Peninsula region of West Antarctica. The austral winter period (June-August) when interannual circulation variability is greatest is chosen for study. The study makes use of tropical SST data along with numerical analysed atmospheric circulation data.

Some of the key findings of this study to date are that: a) considerable variability exists in the winter extratropical atmospheric circulation between different ENSO warm events in the South Pacific/West Antarctica sector, b) the tropical climate/SST state in the central-westem Pacific on seasonal time scales differs considerably between one ENSO warm event to the next and c) there is an apparent strongly linear association between seasonal climate/SST behaviour in the tropical Pacific and the South Pacific extratropical atmospheric circulation. These findings will be presented and their relevance for understanding interannual climate variability in the Antarctic Peninsula will be discussed.

JSM18/E/01-A4 1220

INTERANNUAL PERIODICITIES IN ANTARCTICA, WITH COMPARISON TO THE SOUTHERN OSCILLATION

Greig THOMPSON (350 Salen Heights Avenue South, Salem, Oregon, 97302 USA,

email: gthomp@cyberis.net) and Charles STEARNS (Space Science and Engineering Center, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706, USA)

Climatic data sets from 11 manned Antarctic stations covering the period from 1957 to 1991 were analyzed for interannual variablility and possible relationship to the El Nino - Southern Oscillation (ENSO). Time series were constructed by removing the long term individual monthly means, centering and then normalizing by the standard deviation. This was done for surface temperature, pressure, potential temperature, coastal stations temperature average, coastal station pressure average, and the potential temperature difference between Scott Base and Amundsen-Scott station at the South Pole. Single Spectrum Analysis (SSA) uses data adaptive filters to discern quasi-periodic oscillations from noise in a time series. The data adaptive filters used were described by a set of mutually orthogonal vectors determined from the constructed time series under study. These base vectors were not necessarily sinusoidal and could therefore discern nonlinear aperiodic oscillations. The Maximum Entropy Method (MEM) of spectral analysis was used to resolve dominant quasi-periodic oscillations in the constructed time series. The MEM of estimating the spectral density fits an autoregression (AR) model to a series so as to maximize a lack of information (entropy) of the patterns in the time siries. SSA indicated that for any one of the station time series at least 4.6% and at most 18% of the total variance was described by anharmonic components with a period between 18 and 59 months. Spectral analysis using MEM resolved dominant quasi-periodic oscillations of 27 and 55 month periods in the SSA-filtered Southern Oscillation Index (SOI), confirming earlier investigations. Temporal changes in the amplitudes of these oscillations coincide with ENSO events. The differenced potentia-temperature time series between the South Pole and coastal stations showed interannual oscillations with periods on the order of the ENSO events.

Thursday 22 July PM

Presiding Chair: John Turner (British Antarctic Survey, Cambridge, UK)

JSM18/W/03-A4 1400

SLOW OCEANIC TELECONNECTIONS LINKING THE ANTARCTIC CIRCUMPOLAR WAVE WITH TROPICAL ENSO

Ray G. PETERSON, Warren B.White (Scripps Institution of Oceanography University of California, San Diego La Jolla, California 92093-0230 USA email: rpeterson@ucsd.edu;

E-mail: wbwhite@ucsd.edu)

A case study for the period 1982-1994 shows that a major source for the Antarctic Circumpolar Wave (ACW) is in the western subtropical South Pacific Ocean, where interannual anomalies in sea surface temperature (SST) and precipitable water (PrWat) form. Once established, these interannual anomalies, covarying with anomalies in sea level pressure (SLP), move south into the Southern Ocean. These covarying anomalies then propagate eastward around the globe as the ACW through a combination of oceanic advection by the Antarctic Circumpolar Current and ocean-atmosphere coupling (White et al., 1998). The coincidence of interannual anomalies in SST, SLP, and PrW indicates the extra-tropical ocean and atmosphere are coupled on these time scales. Significant portions of the interannual SST signal propagating eastward around the Southern Ocean as the ACW propagate equatorward into the South Atlantic and Indian oceans, ultimately reaching the tropics in each basin some 6-8 years after appearing in the western subtropical South Pacific Ocean. 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 propagate eastward and arrive at the Indo-Pacific transition in phase with the ENSO (El Niño - Southern Oscillation) signal in covarying SST and SLP propagating eastward from the Indian Ocean to the Pacific Ocean (Tourre and White, 1997). The interannual SST and PrWat anomalies that appear initially in the western subtropical South Pacific are directly linked with ENSO on the equator through anomalous vertical convection and a regional overturning Hadley cell in the troposphere, the same cell that initiates fast planetary waves in the atmosphere (Sardeshmukh and Hoskins, 1988) that transmit ENSO signals around the southern hemisphere on much shorter time scales.

JSM18/E/03-A4 1420

EVIDENCE OF EL NINO-SOUTHERN OSCILLATION IN SURFACE METEOROLOGICAL DATA IN ANTARCTICA

Linda KELLER (Department of Atmospheric, Oceanic and Space Sciences, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin, 53706 USA), George WEIDNER and Charles Stearns (both at Space Science and Engineering Center, University of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706, USA)

Meteorological measurements have have routinely been made for some 40 years in Antarctica. For about half that period, automatic weather stations (AWS) have provided additional surface measurements at remote locations in Antarctica. Within this time span, there have been four El Nino events - 1982-83, 1986-88, 1991-92, and 1997-98. Signatures of the El Nino events have been observed in the surface meteorological data by several investigators and recently there have been studies concerning the teleconnections between the atmosphere at lower latitudes and the Antarctic atmosphere. Several studies have shown variability in meteorological data (temperature, pressure, precipitation, etc.) is correlated to the El Nino-Southern Oscillation (ENSO) phenomenon. Most of these studies have focused on particular regions of Antarctica. Since the number of surface observing stations has increased dramatically since the major ENSO event of 1982-83, we examine the records at new AWS sites for ENSO signatures along with the now longer record at long established AWS sites. In particular we are interested in comparing the two strong El Nino events of 1982-83 and 1997-98. Previous data indicated the Ross Ice Shelf is anomalously cold just prior to and during the early stages of ENSO events while stations on the high plateau of East Antarctica are anomalously cold during the later phase of the ENSO event. Results from the AWS will be included with observations from manned stations. The AWS data set for 1998 will be completed in the near future.

JSM18/E/07-A4 1440

THE AGULHAS CURRENT SYSTEM: THE INFLUENCE OF EDDIES ON THE TIME-MEAN CIRCULATION DIAGNOSED FROM TWO GENERAL CIRCULATION MODELS

WELLS, N.C. (School of Ocean & Earth Sciences, Southampton Oceanography Centre, Southampton, S014 3ZH, email: ncw@mail.soc.soton.ac.uk), Ivchenko, V.O.(Jet Propulsion Laboratory, N.A.S.A., Pasadena, CA 91109, email: Best, S.E (formerly of School of Ocean & Earth Sciences, Southampton Oceanography Centre, Southampton, S014 3ZH )

The Agulhas Retroflection region is analysed in two ocean general circulation models, (FRAM and POP). Both models are able to resolve some of prominent time-dependent features of the region, including the Agulhas rings which are shed off from the Retroflection region. In this paper an analysis of the energy budget over a 5 year period together with a stability analysis are used to determine the relative importance of barotropic and baroclinic instability processes in the two models. It is shown that both models have two quasi-zonal jets, a northerly westward flowing jet and a more southerly eastward flowing jet, which act as the entrance and exits of the Retroflection region respectively. Both jets are shown to be baroclinicly unstable, and have growth rates and wavelengths consistent with those observed in both models. It is shown that this instability process is well resolved in the POP model, but is influenced by sub-grid scale viscosity in the FRAM model. The energy budget in POP demonstrates that the westward jet is intensified by reynold's stresses which arise from the eddies in that jet, whilst the eastward jet shows that the reynold's stresses act to diffuse the jet. In both jets the eddies are produced by a mixed barotropic- baroclinic instability, though the baroclinic instability transfers are significantly smaller than the barotropic instability. In FRAM, a similar response is observed.

JSM18/W/06-A4 1500

MODELLING INTERHEMISPHERIC VARIABILITY DUE TO FLUCTUATIONS OF THE THC

Katrin MEISSNER, Holger Brix and Ruediger Gerdes (all at Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany, email: meissner@awi-bremerhaven.de)

Freshening of high latitude surface water can change the large scale oceanic transport of heat and salt. Atmospheric perturbations over the deep water production sites thus have a large scale response, establishing a kind of oceanic teleconnection with time scales of years to centuries. In a number of response experiments with a global coupled atmosphere-ocean-sea ice model, we here investigate the connections between northern and southern hemisphere sea surface conditions due to fluctuations of the thermohaline circulation. The atmospheric component of the model consists of the vertically integrated thermodynamic energy and moisture balance equations. The two-dimensional model calculates surface fresh water fluxes and surface heat fluxes over land, sea and ice areas. The sea ice component is a simple thermodynamic model while the ocean component is a full GCM based on MOM2.

JSM18/W/04-A4 1520

HOW FORM STRESS IN THE SOUTHERN OCEAN LINKS WITH SVERDRUP BALANCE IN THE SUBTROPICS

Chris W. HUGHES (CCMS - Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead, Merseyside L43 7RA, UK, Email: cwh@ccms.ac.uk), and Beverly de Cuevas (Southampson Oceanography Centre, Empress Dock, European Way, Southampton SO14 3ZH, UK,

Email: B.Decuevas@soc.soton.ac.uk)

There is a dichotomy in the way the ocean's response to wind forcing is usually interpreted, in which the Southern Ocean is considered quite separately from the rest of the world. The canonical balance for most of the world is Sverdrup balance in which the forcing is due to wind stress curl and interactions with bottom topography are ignored, coupled with viscous western boundary currents. In the Southern Ocean however, it is well established that interactions with the bottom topography are necessary to balance the zonal wind stress by topographic form stress. It will be shown here that this latter balance, which also holds in other ocean basins, implies a `spin' pressure torque which upsets the Sverdrup balance at some longitude, and balances the wind stress curl in a zonal integral. At lower latitudes the spin pressure torque is concentrated near the western boundaries, producing nearly inviscid western boundary currents. This balance will be illustrated with diagnostics from an eddy-permitting global ocean model (OCCAM)

JSM18/W/12-A4 1600

TIME-AVERAGED SUBANTARCTIC CYCLONIC ACTIVITY AS REVEALED IN A FOUR-DECADE REANALYSIS

Ian SIMMONDS and Kevin Keay (both at School of Earth Sciences, The University of Melbourne, Parkville, Victoria, 3052, Australia, email: ihs@met.unimelb.edu.au)

The high density of cyclones in the subantarctic region are known to be associated with the frequent severe weather conditions experienced over coastal Antarctic and the domain to the north. Such systems are also responsible for a large proportion of the transport of heat and moisture to the polar region effected by the atmosphere. Hence the study and documentation of the behaviour of these systems in the subantarctic is important for a number of reasons, among which is the fact that they form a 'bridge' between the Antarctic and the lower latitudes.

We present a new climatology of subantarctic extratropical cyclones. This has been compiled by applying a state-of-the-art cyclone tracking scheme to the 6-hourly NCEP global reanalyses spanning the period 1958-1997. The greatest density of cyclones (exceeding 6 x 10-3 cyclones (deg. lat.)-2) is found south of 60oS in all seasons and in the Indian and west Pacific Oceans in autumn and winter. In general, there is a net creation of cyclones (i.e., cyclogenesis exceeds cyclolysis) north of about 50oS, and a net destruction to the south of this latitude. Having said this, the most active cyclogenesis takes place south of 45oS. The NCEP reanalyses indicate that most SH cyclogenesis occurs at these very high latitudes, and the axis of the maximum lies on, or to the south of, 60oS. This is in agreement with the deductions of many modern studies of SH cyclone behaviour. The region is also host to even greater levels of cyclolytic activity.

The presentation will consider measures of the importance and influence (e.g., for eddy fluxes) of cyclonic systems. It is suggested that the 'depth' of a system is a relatively bias-free and useful measure of a cyclone's status and effect on the circulation. The greatest climatological depths are seen to lie at about 60oS, well to the north of the circumpolar trough and of the region of greatest cyclone density.

JSM18/W/09-A4 1620

DIAGNOSIS OF THE EXTRAORDINARY WINTER 1982 - 1983 SEASONAL ANOMALY FORMATION USING CYCLONE CLIMATOLOGY PARAMETERS OF THE GLOBAL ATMOSPHERE

Victor LAGUN, (Arctic and Antarctic Research Institute, 38 Bering str., St.Petersburg, 199397, Russia; e-mail: lagun@aari.nw.ru)

On the base of 1981 -1991 NCEP dataset the global distribution of the extra-tropical cyclone parameters is calculated using original numerical method of spatial cyclone position determination. The estimated parameters include temporal and spatial frequencies, the depth, the cyclone center location and pressure in the cyclone center, the square, the linear size, the shape, the drift velocity, the life time and storm track variability. These parameters are presented as a global distribution as well as integral hemispheric and global estimations. For the winter 1982-1983 of extraordinary weather conditions the seasonal anomalies for mentioned above synoptic climatology parameters are calculated relative to the mean decadal values. Studied decade was characterized by the increasing number of the intensive extra-tropical cyclones, accompanied by the increasing tendency of the surface temperature. The global distribution of the seasonal anomalies for the cyclone frequency, for the cyclone depth and for the drift speed is analised. Regional features of the seasonal anomalies for Europe, North America and South Atlantic are discussed. The results are compared with the global diabatic energy source/sinks estimations and with the published results of this seasonal climatic event GCM simulations.

JSM18/W/01-A4 1640

HEMISPHERIC CONNECTIONS WITH TEMPORAL CHANGES IN CYCLONE BEHAVIOUR OFF THE ANTARCTIC COAST

Ian SIMMONDS and Kevin Keay (both at School of Earth Sciences, The University of Melbourne, Parkville, Victoria, 3052, Australia, email: ihs@met.unimelb.edu.au)

We present an analysis of the variability and trends exhibited by many aspects of high southern latitude mean sea level extratropical cyclones during the period 1958-1997. The investigation is undertaken by applying an automatic finding and tracking scheme to the six-hourly 'reanalyses' produced by NCEP. The outcome of this is arguably the most reliable and extensive analysis subantarctic cyclone variability undertaken to date.

The annual average number of cyclones per analysis in the 50-70˚S latitude band rose from the start of the period to a maximum of about 17 around 1970. Since then the numbers have shown an overall decline (by about 10%), the counts in the 1990s being particularly low. (Similar behavior was evident when the count was confined to the 30-50˚S latitude band.) Least squares best fit to the time series exhibited a significant slopes of -0.58 cyclones analysis-1 decade-1.

The overall structure of the time series of annual cyclone per analysis over 30-50˚S and 50-70˚S are similar, but their year-to-year changes are shown to be negatively correlated, and hence there tends to be an interannual compensation of cyclones density between the middle and higher latitudes.

A number of modelling studies have suggested that extratropical cyclone numbers may be expected to change under enhanced CO2. It is argued that under warmer conditions the specific humidity of the atmosphere increases and hence cyclonic eddies transport (latent) energy poleward more efficiently, and hence fewer are required. The SH mean annual surface temperature exhibits a minimum in the mid 1960s, and a fairly steady rise since then. The time series shows an out-of-phase relationship with that of the SH cyclone numbers and they possess a significant correlation coefficient of -0.79.

JSM18/E/06-A4 1700

EXTRATROPICAL INFLUENCES ON INTERHEMISPHERIC ASYMMETRY OF TROPICAL CLIMATE

Anthony J. BROCCOLI (NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08542, USA, email: ajb@gfdl.gov)

Evidence from a variety of climate simulations suggests a relationship between the latitude of the intertropical convergence zone (ITCZ) and the interhemispheric temperature contrast. To explore the role of extratropical forcing in this relationship, an atmospheric general circulation model is forced by prescribed sea surface temperatures (SSTs) in the extratropics and coupled to a mixed layer ocean elsewhere. The imposition of SST anomalies of opposite signs in the northern and southern extratropics induces substantial changes in tropical climate. The ITCZ shifts toward the warmer hemisphere, accompanied by tropical anomalies in meridional surface winds. Changes in atmospheric heat exchange between the tropics and midlatitudes are the likely cause of this shift. This linkage between extratropical forcing and tropical climate may be of importance in understanding past and future climates.

JSM18/L/01-A4 1720

INTERACTIONS BETWEEN THE LOWER LATITUDE CIRCULATION AND THE ANTARCTIC DURING PERIODS OF AMPLIFIED LONG WAVES

John TURNER (Ice and Climate Division, British Antarctic Survey, Cambridge, UK,

email: J.Turner@bas.ac.uk)

Understanding the teleconnections between the Antarctic and lower latitudes is very important in interpreting correctly the global climate signals found in ice cores taken from the Antarctic ice sheets. However, the ice cores contain a wide range of signals from very local climate variations to those associated with the major global cycles. Some of the most pronounced signals are associated with periods of amplified long waves when mild, moist air masses can penetrate well into the interior of the continent giving some of the largest precipitation events found over the plateau. This talk will examine the nature of the synoptic events that can occur during periods of amplified long waves, including the occurrence of major storms in the coastal region, weather systems ascending onto the plateau and rapid warming taking place at interior locations. Selected cases will be presented using satellite imagery, model output, ice core accumulation data and synoptic observations from automatic weather stations. The climatological occurrence of such events will be considered along with their relationship to conditions at lower latitudes.

JSM18/E/04-A4 1740

HIGH LATITUDE THERMAL VARIABILITY IN RELATION TO LOWER LATITUDE

Tarzadin ULAANBAATAR (Department of Earth Sciences, National University of Mongolia,

email: numelect@magicnet.mn )

A best way to show the climate teleconnection of high and lower latitudes is the creation of climate model covered Earth's surface by simple climatological parameters.

In result of my research works was born a 3D mathematical model of the air temperature regime on and near the Earth's surface. According to this model a thermal field exists near the Earth, i. e. this field includes the troposphere, earth surface and shallow layers of lithosphere, which is called heliogeothermosphere as wishing by Author. It is limited from depth of yearly thermal influences into the shallow lithosphere to tropopause. In this interval the heliogeothermosphere consists of isothermal surfaces due to decreasing the temperature by atmospheric height. Shape of the heliogeothermosphere is more ellipsoid than Earth's. So, the isotherms cut the Earth's surface at certain geographical latitudes. In order to facilitate calculation we used following approach that we do not account atmospheric turbulence and its chemical content, therefore, the temperature gradient or distance between the isotherms is not changed. The isothermal surfaces show the connection of the high and lower latitudes. Temperature gradient fluctuates only in relation of sea level.

In this paper is presented that at a little fluctuation of the isothermal surface in lower latitudes drives dramatical shift of the geographical, climate and permafrost zones at high latitudes. Furthermore, the nature of thermal regime on and near the Earth's surface by length of daylight, daily and yearly motions of the Earth, terrain height, altitude of sun, geographical latitude and albedo of different objects) are shown in forms of equations and their terms.

Friday 23 July AM

Presiding Chair: Charles R Stearns (University of Wisconsin, Wisconsin, USA)

JSM18/W/02-A5 Invited 0900

DECADAL CLIMATE FLUCTUATIONS IN THE ARCTIC AND CONNECTIONS TO LOWER LATITUDES

Lawrence A. MYSAK and Silvia A. Venegas, Mcgill University, Dept. of Atmospheric and Oceanic Sciences, 805 Sherbrooke St., W Montreal, QC H3A 2K6 Canada.

E-mail: mysak@zephyr.meteo.mcgill.ca

During the past two decades there has been considerable research on identifying the nature and causes of interannual and interdecadal climate variability in the Arctic and high northern latitudes through the analysis of various atmospheric, oceanic, sea ice and hydrologic data sets. With the availability of longer records, it has become clear that the dominant signal of variability in the Arctic and subarctic has a decadal timescale. For example, the time expansion coefficients of the first empirical orthogonal function modes for the sea ice concentration (SIC), sea level pressure (SLP), 500-hPa height and 850-hPa temperature north of 45 degrees each exhibit an oscillatory pattern since the 1960s, with a period of around 10 years.

To further elucidate the nature of this decadal clmate oscillation, we performed a combined complex empirical orthogonal function analysis of 40 years of SIC and SLP data which span the Arctic poleward of 45 N. The analysis indicates the over most of the duration of this climate cycle, the ice cover anomalies are created by the atmosphere (i.e., are wind generated), and change through ocean advection. However, it is suggested that during relatively short intervals the atmosphere could respond rapidly to changing sea ice conditions in the Greenland Sea, which results in reversals of the phases of the North Atlantic Oscillation, a familiar climate feature in the winter SLP. The evolving patterns of the SIC and SLP anomalies over the 10-year cycle can be succinctly described in terms of a new feedback, which has remnants of, but is quite distinct from that proposed some time ago by Mysak and his collaborators.

JSM18/W/07-A5 0940

CONNECTIONS BETWEEN AIR TEMPERATURE ANOMALIES IN THE ARCTIC AND LOWER LATITUDES: NATURAL AND GREENHOUSE COMPONENTS

N.Ye. KHARLANENKOVA, G.V. Alekseyev, R.V. Bekryayev (Arctic and Antarctic Research Institute, 38 Bering Street, St. Petersburg, Russia 199397, e-mail:alex@aari.nw.ru)

The spatial distribution of air temperature anomalies in the Arctic and adjacent latitudes at strong (exceeding RMS) deviations of air temperature means in the N 85-200 area based on the 1890-1998 data is characterized in the winter by two modes with the opposite in the sign anomalies. During the anomalously warm winter months the positive temperature anomalies occupy the Arctic region being most significant over the adjoining climatic cold sources on the Asian and North American continents whereas the weak negative anomalies are located above the temperate latitudes of the Atlantic and the Pacific Oceans (COWL structure). At strong negative anomalies of mean temperature in the winter negative anomalies are located above the Arctic region and the adjoining continental cold sources while the weak positive anomalies are observed above the oceans (WOCL-structure). Two types in the distributions of surface pressure and geopotential anomalies correspond to such temperature anomalies. In particular, the increase in the pressure difference between the centers of the Azore and Icelandic Highs (the North Atlantic oscillation index (NAO)) is obvious during winter warming with the reverse process occurring during cooling. The climatic signal from the other non-arctic impact on the Arctic atmosphere related to the ENSO phenomenon, is also noticeable, although it is much weaker compared to the NAO signal in the variability of mean winter air temperature at Arctic latitudes with a time scale of 5-6 years. The spectral analysis of relations between the air temperature anomalies in different latitudinal zones of the Northern Hemisphere revealed that both negatively and positively correlated components distributed by the periods of oscillations are present in the series of anomalies. A relative contribution of the former and the latter to the total dispersion of oscillations varies within a year with the positive correlation typically observed at low frequencies and negative at higher frequencies. It is demonstrated that the inverse relation between the air temperature anomalies in the Arctic area and in lower latitudes is mainly caused by the winter air exchange between them whereas the direct relations at low frequencies indicate the influence of global factors primarily of the increase in CO2 content. The conclusions derived from the analysis of climatic data are confirmed by the analysis of data from long-term numerical experiments using the atmospheric circulation model. This study is supported by the INTAS N 97-1277 Project.

JSM18/W/10-A5 1000

A POSITIVE FEEDBACK MECHANISM BETWEEN THE OKHOTSK SEA ICE AND THE ALEUTIAN LOW

Yoshihiro TACHIBANA (JISAO Univ. of Washington, Box 354235, 4909 25 Ave NE Seattle, WA 98195-4235, USA, e-mail: tachi@atmos.washington.edu), Meiji Honda (Institute for Global Change Research/FRSGC, Tokyo, 105-6791, Japan, e-mail: meiji@frontier.esto.or.jp), Tatsuro Watnabe (Japan Sea National Fisheries Research Institute, Nigata 951-8121, Japan, e-mail: tatsuro@jsnf.affrc.go.jp)

We found a positive feedback that the Okhotsk sea ice enhances the Aleutian low while the enhanced Aleutian low also enlarges the sea ice in the Okhotsk Sea, using AGCM and ice-ocean model separately. The AGCMs with the boundary condition of widely covered ice over the Okhotsk Sea, and with that of slightly covered ice, respectively showed enhanced Aleutian low, and weakened one because of the different heat flux from the ocean due to the difference of ice coverage. Using the results of these two AGCMs as the boundary conditions of ice-ocean models in the Okhotsk Sea, we could simulate much larger ice area with the boundary condition of the strong Aleutian low than that of the weak Aleutian low. This ice difference is mainly because of the difference of northwestern wind that brings movement of sea ice toward the southern Okhotsk Sea and that brings cold air advection from Siberia toward the Okhotsk Sea, since Okhotsk Sea is to the west of the Aleutian low. Therefore, once the ice widely covers the Okhotsk S ea, the Aleutian low will be strengthened and this will also rebound upon the ice again. In consequence, the Okhotsk sea ice amplifies the interannual variabilities of both the Aleutian low and the ice itself.

JSM18/W/11-A5 1020

ARCTIC IMPACT ON THE NORTH ATLANTIC

MYAKOSHIN O.I., Alekseev G.V., Zakharov V.F. (The Arctic and Antarctic Research Institute Bering St. St., 38, 199347 St. Petersburg, Russia e-mail:alexgv@aari.nw.ru)

The North Atlantic region has a strong influence on Arctic climate, which is transferred through the atmospheric circulation variations connected with the dynamics of the North-Atlantic atmospheric action centers and through variations of the Atlantic water inflow to the Arctic Ocean. For the last 100 years significant natural climate fluctuations were observed in this region such as the warming of the 1930-1940s, the GSA and cooling in the late 1960s-early 1970s accompanied by the sea ice area variations. The climatic phenomenon of the GSA and the related cooling in the North Atlantic in the late 1960s-early 1970s developed under the influence of the increased inflow of freshened polar water and sea ice from the Arctic Ocean [Steffansson, 1969; Dickson et al., 1988; Mysak et al., 1990, S.Hakkinen, 1993]. However, the cause of this increase has not yet been unambiguously explained. An analysis of climatic conditions in the Arctic in the 1950s-1990s and the Soviet oceanographic survey data of the Arctic Ocean in 1955-1979 suggest the increased freshened influence of the Arctic Ocean on the North Atlantic region to be predominantly connected with more intense summer melting of snow, ice caps and sea ice in the Arctic in the late 1950s-1960s. During this period positive summer air temperature anomalies in the Arctic were observed, which were the largest in the Canadian-Greenland region where enormous snow and ice supplies accumulate. Favorable conditions for sea ice melting were observed in the Arctic Basin along with the increased river water flow to the Arctic Ocean. Since summer melting of snow and ice and the summer inflow of river water comprises the major portion of the total inflow of freshwater to the Arctic Ocean, the consequences of the increased summer inflow in the 1950s-1960s was manifested in a significant freshening of the upper layer in the Arctic Ocean in the early 1970s, especially in the region of the East Greenland Current outflow. What are the grounds to suggest a possible recurrence of the climatic scenario of the late 1960s-early 1970s in the North Atlantic? First, this is the increase of the summer air temperatures in the Arctic in the 1990s. Second, this is the increase of the sea ice export through Fram Strait [Vinje et al., 1997] and the increased sea ice cover extent in the West Atlantic in the mid-1990s. Third, there is a tendency for the decreased salinity of the upper layer in the Nordic Seas and finally a conclusion of the mathematical climate theory [Dymnikov, Volodin, 1998] about the similarity of the climatic system response to the natural and external impact.

JSM18/W/08-A5 1100

CHANGES OF THE DEPOSITION OF SOLUBLE AND INSOLUBLE AEROSOLS ON EAST ANTARCTIC ICE DURING THE TERMINATION OF THE GLACIAL PERIOD AS RECORDED IN THE DOME SUMMIT SOUTH ICE CORE (DSS), LAW DOME, ANTARCTICA.

Mark A.J. CURRAN, Vin Morgan and Li Jun (Antarctic CRC & Australian Antarctic Division GPO Box 252- 80, Hobart, 7001. Tasmania. Australia email: mark.curran@utas.edu.au) Jorgen Peder Steffensen (Dept. of Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100, Copenhagen Ø, Denmark)

Ice cores from polar ice sheets contain a wealth of information on past atmospheric conditions. Stratigraphical profiling of ice core impurities, along with the stable isotope ratio climate proxy *18O, make it possible to infer changes in the amount and composition of airborne material during past climate changes.

The Greenland ice core records all show that sudden climate oscillations (Dansgaard/Oeschger events) occurred during the last glacial period. The last of these oscillations was the warm Bolling/Allerod period (ca 14,500 B.P. - 12,500 B.P.) which was followed by a period of cold glacial conditions for ca 1200 years (Younger Dryas) before the final climate transition into the Holocene. Some of the fast climatic oscillations have also been recorded in Arctic ice cores, but in Antarctica they appear much less pronounced.

The *18O record shows that DSS core data extends back through the Holocene and the transition period and into the last Glacial cycle. We present dust (insoluble microparticle) and major chemical ionic species concentrations from the Law Dome Summit core, through the Last Glacial Maximum-Holocene transition period. This data will be compared with records from other Antarctic and Greenland core sites.

JSM18/P/02-A5 1120

PARTICLE FORMATION IN THE MARINE BOUNDARY LAYER OVER ANTARCTICA: IMPLICATIONS IN CLIMATE CHANGE

V.K. SAXENA (Cloud-Aerosol Interactions Lab (CAIL), North Carolina State University, Raleigh, NC 27695-8208, U.S.A., email: saxena@eos.ncsu.edu)

We have characterized particle formation during flights (LC-130 aircraft) in the marine boundary layer over McMurdo and during ground based observations at Palmer Station. The following two features were observed at McMurdo: (1) The Aitken nuclei concentration showed a steady decrease up to 300m MSL and then a monotonic increase with altitude, the maximum (~1300cm-3) was recorded at 2,500m MSL. (2) The cloud condensation nuclei (CCN) concentration varied from 50 to 325cm-3, the minimum occurred at 640 m MSL and the maximum at 830m MSL. At Palmer Station, we observed significantly different particle concentrations during January and February 1994. The January month was characterized by: (i) relatively constant temporal CCN concentrations, (ii) relatively constant equivalent potential temperatures, (iii) partly cloudy skies with respect to wind direction during the daytime, and (iv) winds predominantly from the east-southeast through the Southeast. In contrast, the month of February was characterized by: (i) relatively variable temporal CCN concentrations, (ii) variable equivalent potential temperatures, (iii) variable cloudy to overcast skies with respect to wind direction during the daytime, and (iv) winds predominantly from the northeast, southwest and northwest. Exceptionally elevated CCN concentrations were observed on Jan 17, 19, 20 and Feb 7, 1994 when the cloud base descended to the ground and dissipated under prevailing meteorological conditions. The most spectacular CCN enhancement event occurred on Jan 20 when the CCN concentrations were enhanced by factors of 4 and 7 respectively at 0.25% and 1.25% supersaturation (with respect to water) compared with the pre-event concentrations. Implications of these findings in enhancing the Antarctic cloud cover and its impact on the local radiation budget are discussed.

JSM18/W/13-A5 1140

VARIABILITY OF METHANESULPHONIC ACID (MSA) IN A 27 YEAR ICE CORE RECORD FROM LAW DOME, EAST ANTARCTICA

Mark A.J. CURRAN (Antarctic CRC & Australian Antarctic Division, GPO Box 252-80, Hobart, Tas. 7001 Australia, email: mark.curran@utas.edu.au), Katrina L. Phillips (IASOS, University of Tasmania, GPO Box 252-77, Hobart, Tas 7001 Australia), Tas D. van Ommen and Vin Morgan (Antarctic CRC & Australian Antarctic Division, GPO Box 252-80, Hobart, Tas. 7001 Australia), Anne Palmer (IASOS, University of Tasmania, GPO Box 252-77, Hobart, Tas 7001 Australia)

MSA is an atmospheric oxidation product of dimethylsulphide (DMS), and a component of Antarctic precipitation. DMS is produced by certain species of algae, via the breakdown of the algal metabolite dimethylsulphoniopropionate (DMSP). Antarctic ice core records of MSA thus provide a proxy for biological activity in the Southern Ocean, and a potential source of information on climate variability such as ENSO events and sea ice extent, and other factors influencing biological activity.

A 27 year record of MSA and other trace ions was extracted from a Dome Summit South (DSS) ice core, Law Dome, East Antarctica. The MSA record exhibited a persistent seasonality, with a distinct summer maximum usually flanked by two smaller peaks. This seasonal signal is apparently unique to Law Dome. The smaller peaks appear to occur in spring and late summer (or early autumn). The origin of the smaller peaks will be addressed by considering the seasonal and spatial variation in the source of DMS from the Southern Ocean and transport to Law Dome. The implications of using this MSA record as a proxy for ENSO and sea ice extent will be covered. The potential influence of post-depositional migration of MSA in the ice core record will be discussed.

Friday 23 July PM

Prisiding Chair: C.R. Stearns

PANEL DISCUSSION 1400

how do we establish polar and tropical interactions

DAVID BROMWICH, Ohio State University, Columbus Ohio, USA. PETER WADDAMS, Scott Polar Research Institite, Cambridge, UK. IAN SIMMONDS, University of Melbourne, Parkville, Victoria, Australia. LAWRENCE MYSAK, McGILL University, Montreal, Canada