The International Antarctic Weather Forecasting Handbook:

IPY 2007-08 Supplement


Neil Adams

Australian Bureau of Meteorology,

GPO Box 727 Hobart TAS 7001

E-mail: N.Adams@bom.gov.au

Submitted April 2008

*Contribution relevant to Sections 7.7.1 Mawson Station; 7.8.4 Davis Station and 7.10.1 Casey Station but dealing more generally with forecast techniques for the Casey-Hobart air-link and for intra-continental Antarctic flights.

Editors’ note: it is understood that a more detailed update (albeit on minor aspects) on Australian station-specific forecast parameters will be provided by Adams. And so the information below has not, at this time, been segmented into the various sub-sections relevant to the original Handbook style.

Since the last edition of the Handbook the Australian Government has invested heavily in developing an Antarctic air-transport system, and since the 2005/06 summer two CASA-212 aircraft have deployed from Hobart to Antarctica to provide intra-continental logistical and scientific support for the Australian Antarctic program (AAp). The 2007/08 summer saw the introduction of the Hobart-Casey air-link using an Airbus A319. Twenty flights of the A319 are expected each summer between Hobart and Casey to support the AAp. In addition the Australian Customs Service utilise the aircraft to monitor whaling and fishing activities in the Southern Ocean, as far south as the sea-ice zone around East Antarctica. The Australian Bureau of Meteorology has built on the systems and processes developed to support the QANTAS Antarctic tourist over-flights, which have been in continuous operations since the 1994/95 summer season to support the AAp air-transport system. The C212 aircraft are a medium sized, unpressurised twin tubo-prop engined aircraft with a cruise speed of around 150 knots and cruising ceiling near 12000 ft. Their typical range with a full payload is around 800 nm or five hours of flying. For the transit flight to Antarctica the aircraft depart Hobart with internal fuel tanks to extend their flying time out to around 12 hours. These extended flights across the Southern Ocean have a service ceiling of 12000 ft (although a small amount of oxygen allows limited climbs to 16000 ft), severe limitations on head-wind, a ban on flying into known icing conditions, and the requirement to land in Antarctica under Visual Meteorological Conditions (VMC) with good surface and horizon definition, and so provide a challenging forecasting task. The take-off from Hobart requires a dry runway and temperatures below 21oC. Every aspect of the flight from take off, through cruise to landing has restrictive weather requirements that may abort a take-off. The initial plan was to fly direct from Hobart to Casey, however the distance, coupled with the almost continuous presence of significant head winds (average over flight of > 5 knots) meant that over the last three seasons only one transit flight direct to Casey has occurred. The aircraft now plan the transit flight via Dumont d'Urville. To give an indication of the difficulty in getting the aircraft to Antarctica, in the 2007/08 season the aircraft were in Hobart from 20 October attempting the flight but were unable to depart for Dumont d'Urville until suitable weather appeared on 25 November.

The flight distances are significant, (Figure 1 (Update ‑ Australia)), with the Hobart to Dumont d'Urville leg some 2689 km (1450 nm) so for the forecaster to assimilate detailed weather information, and in particular Numerical Weather Prediction (NWP) output over the entire flight is a challenge. Automated extraction software has been developed to allow the forecaster to view NWP output along the aircraft route through space and time.

Figure 1 Update ‑ Australia) Site map showing distances between Hobart in southeast Australia and Antarctic stations. The C212 aircraft fly non-stop from Hobart to Dumont d'Urville, then onto Casey

Figure 2 (Update ‑ Australia) is an example of the space/time-height cross-section of temperature and wind for a Hobart to Dumont d'Urville flight, with Figure 3 (Update ‑ Australia) showing the humidity cross-section for the same flight. Figure 4 (Update ‑ Australia) shows the track and times for the cross sections shown in Figure 2 (Update ‑ Australia) and Figure 3 (Update ‑ Australia). These forecasts coupled, with satellite imagery for the route and for the landing site at Dumont d'Urville have allowed the forecasters to successfully provide accurate route information for the pilots in their Southern ocean crossing.

Figure 2 (Update ‑ Australia) Cross-section forecast of wind speed and direction, temperature and mean sea level pressure along the flight path from Hobart to Dumont d'Urville. (See Figure 4 for track and time details for the cross-section).

Satellite imagery plays a crucial role in assisting the pilots whilst on route. The Casey High Resolution Picture Transmission (HRPT) system provides multi spectral Advanced Very High Resolution Radiometer (AVHRR) data that is extremely useful in determining possible areas of cloud or fog that may affect the landing site. Figure 5 (Update ‑ Australia) shows the multi-spectral image available on the morning of the successful flight in 2006, with Figure 6 (Update ‑ Australia) the image available just prior to landing. These images are generated from the two visual channels and the near-infrared channel from the NOAA‑17 (Figure 5 (Update ‑ Australia)) and NOAA‑18 (Figure 6 (Update ‑ Australia)) satellites. These images clearly differentiate between surface ice (continental and sea) and low cloud, with ice showing up yellow and cloud blue/white in the NOAA-17 images, and surface ice white and low cloud yellow in the NOAA-18 imagery.

Figure 3 (Update ‑ Australia). Cross-section forecast of relative humidity and precipitation along the flight path from Hobart to Dumont d'Urville. (See Figure 4 for track and time details for the cross-section). The zero degree and minus fifteen degree isotherms are highlighted to indicate the region in which aircraft icing may be an issue

Figure 4 (Update – Australia) Way-points used in generating figures 2 and 3, for the flight from Hobart to Dumont d'Urville.

Figure 5 (Update – Australia). NOAA-17 false colour image, using channels 1, 2, and  6 valid 2325 UTC 17 November 2006. Continental and sea ice show up yellow, cloud blue/white and water black.

One major issue with the polar orbitting satellites is the lack of passes during the middle of the day to provide on route guidance to the pilots, and updates on the Dumont d'Urville landing site. Geostationary data is available hourly and with the recently available MTSAT high bit-rate data false colour remapped imagery is able to provide a lower resolutin view of the entire route from Hobart to Casey. Figure 7 (Update ‑ Australia) is an example of the false colour imagery available form the MTSAT imagery. These images only use two channels (visual and near infrared), however the quality of the imagery is extremely valuable in maintaining a weather watch for the flights.

Figure 6 (Update – Australia). NOAA-18 false colour image, using channels 1, 2, and  3 valid 0643 UTC 18 November 2006. Continental and sea ice show up grey/white, cloud yellow and water blue.

Figure 7 (Update – Australia). An example of the MTSAT false colour image generated from the visual and near infrared channels.