The International Antarctic Weather Forecasting Handbook:

IPY 2007-08 Supplement


Andrew M. Carleton

Department of Geography, and Earth and Environmental Systems Institute,

Penn State University, University Park, PA 16802, U.S.A.


Submitted March 2008

*Contribution relevant to Chapter 2 An Overview of the Meteorology and Climatology of the Antarctic.

Editors’ note: at this time, the contribution has not been adapted to the original Handbook style, especially wrt numbering of figures etc.


A teleconnection is a statistical association between the climate— temperature, precipitation, or other meteorological variables—at widely-separated locations.  The significant association can be either positive or negative, and may be present for certain decades only to be absent in others; the locations influenced can be in the same or different latitude zones (e.g., Antarctica-only teleconnections; tropical-extratropical teleconnections); and the teleconnection signal can be primarily inter-seasonal, inter-annual, or inter-decadal (Carleton, 2003).  A teleconnection manifests a recurring large-scale pattern in the atmosphere’s pressure/height field, and the accompanying variations in winds influence the advection of temperature and moisture at locations within that pattern.  Because of the persistence of teleconnection patterns on climate time scales, some predictive skill is possible for weather at the affected locations; for example, as given by the preferred longitudes of atmospheric blocking and cold-air outbreaks related to wave-number 3.  However, the predictive ability differs by teleconnection considered; in general, tropical-based (extratropical) teleconnections show persistence—and, therefore, predictability—on seasonal (monthly and shorter) time scales.  Although teleconnections may arise from any number of physical processes in the troposphere and stratosphere, the dominant ones involve interactions of heat, moisture and momentum between Earth’s surface and the atmosphere (e.g., ocean-air interactions in the tropics; snowcover/sea ice-air interactions).  In the Antarctic and sub-Antarctic, the dominant teleconnections in order of increasing time scale, are as follows: (1) Semi-Annual Oscillation (SAO)—inter-seasonal; (2) Southern Annular Mode (SAM)—annual/inter-annual; (3) El Niño Southern Oscillation (ENSO)—inter-annual; (4) Antarctic Circumpolar Wave (ACW)—interdecadal.  Regional-scale teleconnections associated with ENSO include the Pacific-South America (PSA) and Antarctic Dipole (ADP) patterns.

1          Semi-Annual Oscillation

Meteorological observations during the IGY and afterwards, confirmed the dominant twice-yearly cycle in zonal pressure/height for the sub-Antarctic, and its presence in surface temperature (and other variables) at Antarctic coastal stations as a “coreless winter” (van Loon, 1967).  The SAO results primarily from seasonal imbalances in solar radiation receipt and the outgoing long-wave radiation between Antarctica and middle southern latitudes.  It is well depicted by the latitude location of the circumpolar trough: on average, furthest away from Antarctica in January and July, but closest to the coast in March and September.  The concomitant inter-seasonal changes in the near-surface wind direction over the Antarctic seas— more westerly in the equinoctial months; more easterly in solsticial months—influence the seasonal advance and retreat of the sea ice.  The ice advances rapidly between June and September when the area of expanded near-surface westerlies accompanying poleward migration of the circumpolar trough, encourages divergence of the pack.  Ice retreat in the late spring and early summer is encouraged by the equatorward movement of the trough and the resulting ice compaction.  There is a temporal trend in the SAO in recent decades: since the mid- to late 1970s, the spring-time phase of the oscillation has been delayed into November, probably connected to increasing sea surface temperatures (SSTs) in the tropical eastern Pacific accompanying more frequent El Niño events (van den Broeke, 1998).  The resulting protracted isolation of the springtime polar vortex from middle latitudes may explain, at least in part, the worsening of the Antarctic ozone hole.

2          Southern Annular Mode

Along with the term “Antarctic Oscillation”, the SAM refers to a long-known pattern of stronger (weaker) westerlies in adjacent broad latitude zones (e.g., middle latitudes and the sub-Antarctic; subtropics and middle latitudes).  This “zonally-varying mode” is the dominant teleconnection pattern on annual to inter-annual time scales (Carleton, 2003).  The SAM manifests large-scale anomalies in near-surface pressure, such that lower (higher) pressure over Antarctica (middle latitudes) results in stronger westerlies in the sub-Antarctic, and vice versa.  Thus, a simple index of SAM is given by the pressure difference between Antarctic coastal stations and stations in middle latitudes.  The differences in poleward momentum transport accompanying opposite phases of the SAM index influence the frequencies and tracks of synoptic-scale and meso-scale cyclones over middle and higher southern latitudes.  For example, in SAM positive winters, mesocyclones occur frequently through Drake Passage, whereas a latitudinally split pattern is evident there in SAM negative winters (Lubin et al., 2008).  In recent decades, the SAM index has become increasingly positive; it has accompanied cooling over much of Antarctica and greater zonally-averaged sea-ice extent, except for the western Peninsula region.  In the latter location, the strong warming and reduced sea ice can be at least partly explained by more frequent north-westerly winds connected to the strengthened SAM.

3          El Niño - Southern Oscillation

ENSO is the dominant global-scale teleconnection, originating in ocean-air interactions in the tropical Pacific (Turner, 2004).  Interestingly, several studies suggest a climatic precursor (pressure, winds) to ENSO in the southern Indian Ocean and south-west Pacific sectors of the sub-Antarctic (Carleton, 2003).  It is possible that the latter influence on ENSO occurs via the so-called Indian Ocean Dipole (IOD), marked by opposite anomalies of SST between the western and eastern tropical Indian Ocean.  The two opposing phases of ENSO usually are defined by the SST anomaly in the tropical eastern Pacific; the “warm event”, or El Niño, and “cold event”, or La Niña.  ENSO phases can vary in intensity from mild (e.g., 2003) to extreme (1982, 1997), and may follow one another in rapid succession (1991-95).  The ENSO teleconnection to southern high latitudes occurs primarily as a standing wave train of anomalies that extends south-eastward through the Amundsen and Bellingshausen seas, crosses the Antarctic Peninsula, and projects into the south-west Atlantic; or Pacific-South America (PSA) pattern (Mo and Higgins, 1998).  There is some dependence of the El Niño teleconnection on the exact location of convection in the eastern tropical Pacific (Turner, 2004).  The sub-Antarctic branch of PSA (Figure 1 (Teleconnections)) comprises a strong out-of-phase association in sea-level pressure (SLP) between the Amundsen/Bellingshausen seas and the Weddell Sea, or Antarctic Dipole (ADP) (Figure 1 (Teleconnections)), also evident in surface temperature and sea ice anomalies (Yuan and Martinson, 2001).  In a typical El Niño, the Amundsen Sea low (Weddell Sea low) is weaker (stronger) than normal; the reverse in La Niña.  The impact of the resulting variation in near-surface meridional winds is evident from long-term shipboard observations of sea-ice extent and concentration for the western Weddell: in El Niño, more ice yet lower concentration due to advection by southerly winds; in La Niña, less ice but higher concentration due to northerly winds (Carleton, 1988).  The opposite tends to be the case for the Amundsen/Bellingshausen sector.  Over East Antarctica, strong changes in temperature and pressure accompany the evolution of an El Niño; from positive anomalies in the year preceding the event, to negative anomalies in the year of and also following the event (Smith and Stearns, 1993).  During El Niño, more frequent blocking in longitudes of eastern Australia and the Tasman Sea results in colder conditions and more sea ice in the western Ross Sea sector, as well as a greater frequency of mesocyclones and katabatic wind events.  When blocking in this region is accompanied by enhanced troughing in the southern South America and south-west Atlantic sector on monthly-to-seasonal time scales, it comprises the positive mode of the Trans-Polar Index (TPI) teleconnection of wave-number 1 (Carleton, 1989) (Figure 1 (Teleconnections)).  The reverse pattern of anomalies comprises the TPI negative mode.  Like the ENSO teleconnection to southern high latitudes; shown, for example, in the poleward transport of moisture to the West Antarctic ice sheet in the Pacific sector (Bromwich et al., 2000), the TPI varies in strength— and climatic importance—between groups of decades.

4          Antarctic Circumpolar Wave (ACW)

The ACW is a high latitude wavenumber-2 anomaly pattern— two enhanced ridges and two intensified troughs for the hemisphere— that move eastward across the Southern Ocean on sub-decadal time scales (8 years per complete “cycle”; 4 years per wave couplet) (White and Peterson, 1996).  Spatially, ACW is strongest in the south-west Pacific through South Atlantic sectors of the sub-Antarctic, where it may link with the ENSO teleconnection (Peterson and White, 1998).  Each wave couplet (low pressure, high pressure) has internally-consistent anomalies of meridional wind, temperature, upper-ocean salinity, and sea ice conditions.  For the area east of the low/west of the high, these anomalies are as follows: northerlies; warm air; oceanic downwelling and reduced salinity; ice retreat to higher latitudes.  For the area west of the low/east of the high, the anomalies comprise: southerlies; cold air; upwelling and increased salinity; ice advance towards lower latitudes. Because of the longer time scale of the ACW, predictability of these regional anomalies is possible several seasons ahead; however, the temporal variability in strength of the pattern between decades (e.g., early 1980s-early 1990s: strong; before and after: weak) somewhat limits its climatic value.

Figure 1 (Teleconnections) Schematic of sea-level pressure and geopotential height anomalies in the south-east Indian Ocean/South Pacific/South Atlantic sectors associated with a typical  El Niño event, and their representation in the PSA, ADP, and TPI patterns.  The geostrophic wind anomalies-- arrows-- accompany similar sea ice conditions as those associated with the ACW (refer text).  The anomaly patterns shown essentially are reversed in La Niña events.

Editors’ note: Reader: please note that this figure is an interim sketch – to be replaced by the Editors, at the author’s request with a more stylised version as resources permit.

References cited by Carleton

Bromwich, D.H., A.N. Rogers, P. Källberg, R.I. Cullather, J.W.C. White, and K.J. Kreutz (2000), ECMWF analyses and reanalyses depiction of ENSO signal in Antarctic precipitation.  J. Climate 13: 1406-1420.

Carleton, A.M. (1988),  Sea-ice – atmosphere signal of the Southern Oscillation in the Weddell Sea, Antarctica.  J. Climate 1: 379-388.

Carleton, A.M. (1989), Antarctic sea-ice relationships with indices of the atmospheric circulation of the Southern Hemisphere.  Clim. Dyn. 3: 207-220.

Carleton, A.M. (2003), Atmospheric teleconnections involving the Southern Ocean.  J. Geophys. Res. 108, 8080, doi: 10.1029/2000JC000379.

Lubin, D., R.A. Wittenmyer, D.H. Bromwich, and G.J. Marshall (2008), Antarctic Peninsula mesoscale cyclone variability and climatic impacts influenced by the SAM.  Geophys. Res. Lett. 35, L02808, doi: 10.1029/2007GL32170.

Mo, K.C., and R.W. Higgins (1998), The Pacific-South American modes and tropical convection during the Southern Hemisphere winter.  Mon Wea. Rev. 126: 1581-1596.

Peterson, R.G., and W.B. White (1998), Slow oceanic teleconnections linking the Antarctic Circumpolar Wave with the tropical El Niño-Southern Oscillation.  J. Geophys. Res. 103: 24,573-24,583.

Smith, S.R., and C.R. Stearns (1993), Antarctic pressure and temperature anomalies surrounding the minimum in the Southern Oscillation Index.  J. Geophys. Res. 98: 13,071-13,083.

Turner, J. (2004), Review, The El Niño Southern Oscillation and Antarctica.  Int. J. Climatol. 24: 1-31.

Van den Broeke, M.R. (1998), The semi-annual oscillation and Antarctic climate.  Part 2: Recent changes.  Antarct. Sci. 10: 184-191.

Van Loon, H. (1967), The half-yearly oscillations in middle and high southern latitudes and the coreless winter.  J. Atmos. Sci. 24: 472-486.

White, W.B., and R.G. Peterson (1996), An Antarctic circumpolar wave in surface pressure, wind, temperature, and sea-ice extent.  Nature 380: 699-702.

Yuan, X., and D.G. Martinson (2001), The Antarctic Dipole and its predictability.  Geophys. Res. Lett. 28: 3609-3612.