Polar Prediction The Scientific Challenges - Antarctica John Turner British Antarctic Survey Cambridge, UK

Outline The physical environment Observations High latitude synoptic and mesoscale weather systems Aspects of the Antarctic atmospheric circulation –The wind field –Atmosphere-ocean-ice interactions –The pole of variability –The Southern Annular Mode High-low latitude links

The Southern Ocean

East Antarctica West Antarctica Antarctic Peninsula Trans-Antarctic Mountains

The Underlying Orography

The Antarctic Orography

The Antarctic Research Stations

AWS Systems

Mean winter surface pressure The circumpolar trough rings the Antarctic between deg S

The Wave Number 3 Pattern and the Amundsen Sea Low ASL Baines and Fraedrich (1989) They showed that the wave 3 pattern was a result of flow separation around coastal irregularities, with the ASL being present because of strong flow around the northward extension of the orography near 150º E and the presence of the Ross Sea embayment.

The Pole of Variability SD of the winter MSLP SD of the winter MSLP for a circular Antarctic on (left) and off (right) the Pole

Automatically derived summer season depression tracks around the Antarctic Jones and Simmonds (1993)

A mesocyclone inland of Halley at a time when AGO 84 was to be serviced by a team flying from Halley

Polar lows over the South Pacific. 14:00 11 January 1995.

A vortex over Halley that had gale force winds Halley

Can we now predict polar lows? The current 14 km horizontal resolution of the ECMWF forecast model should resolve these systems The University of Trier is trying to create a climatology of Southern Hemisphere mesoscale systems

The Wind Field Cape Denison – Home of the Blizzard During the expedition of Douglas Mawson they recorded: A world record mean annual average wind speed of 19.4 m/s Gale force winds on all but one of 203 consecutive winter days

Streamlines of the Near-surface Winds From a 48 hr model integration carried out by Parish and Bromwich (1991)

The Representation of Strong Wind Events in Analyses Reanalysis fields only reliable around the Antarctic since 1979

Dumont d’Urville Annual mean wind speed = 18.1 kts Mean of 86.9 gale days per year Mean of 16.2 storm days per year

At this time the station reported a 10 minute mean wind speed of 51 kts from 140 degrees. ERA had 34.6 kts from 127 deg.

At this time the station reported a 10 minute mean wind speed of 57 kts from 160 degrees. ERA had 39.7 kts from 138 deg.

At this time the station reported a 10 minute mean wind speed of 61 kts from 180 degrees. ERA had 18.1 kts from 172 deg.

The Differences Between DD Wind Speeds and Analysed Winds RMS differences (kts). (bias) {number of events} 125 km 25 km 125 km

Higher Horizontal Resolution Runs

Atmosphere-Ocean-Ice Interactions ASL

The Large Temperature Variability at Faraday/Vernadsky Station July Mean temperature Correlation of Faraday winter temperature and sea ice extent over the Bellingshausen sea

Sea Ice Advances and Retreats in 1993 At 77.5 W Horiz scale = 800 km Shading indicates the meridional component of the wind m/s

The Trend in July Sea Ice Concentration

The Trend in June Sea Ice Concentration

The Trend in May Sea Ice Concentration

The Trend in April Sea Ice Concentration

The Trend in March Sea Ice Concentration

The Trend in February Sea Ice Concentration

Atmosphere-Ocean-Ice Interactions Along the Coast of the Western Peninsula 25 August 2010

Antarctic Temperature and Wind Changes Since 1980 The Impact of the Ozone Hole

Upper Tropospheric Height Anomalies Associated with El Nino Events The PSA signal is less robust than the PNA because of the strength of the Southern Hemisphere westerlies

The South Pacific Surface Pressure and Height Anomalies Associated with El Nino Events

The Southern Annular Mode Trend in the SAM since 1957 A positive SAM and a positive (La Nina) SOI can give a deeper Amundsen Sea Low We only have about 10 days skill in predicting the SAM.

The Ozone Hole Has Changed the Atmospheric Circulation Around Antarctica We have strong winds over the Southern Ocean because of the pressure difference between the Antarctic and mid-latitudes L H H H

Scientific Challenges Representing the fine scale processes in models – orography, the wind field, polar lows How can we represent realistically the strong wind events? For forecasting over the Antarctic continent there is still a reliance on nowcasting with satellite imagery How can we improve the prediction of weather systems over the plateau? The large natural variability of the Antarctic climate system hinders prediction Atmosphere-ocean-ice interactions are important in some areas. There are some indications of persistence in sea ice anomalies that may be of value for prediction. We need better understanding of the interaction of the major modes of variability – the SAM and ENSO

First Meeting of the European Polar Lows Working Group, April 1989, Cambridge, UK

Thank you