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Antarctic Forecasting - A Practitioner’s View LT CDR Matt Ruglys RNZN Joint METOC HQJFNZ

Antarctic Forecasting - A Practitioner’s View

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Antarctic Forecasting - A Practitioner’s View. LT CDR Matt Ruglys RNZN Joint METOC HQJFNZ. My background. Joined the Royal Navy in 1981 METOC training 1990 METOC, HMS ENDURANCE 1991-1993 Two deployments to the Antarctic Peninsula MetService NZ 2007-2010 - PowerPoint PPT Presentation

Text of Antarctic Forecasting - A Practitioner’s View

Antarctic Forecasting

Antarctic Forecasting -A Practitioners ViewLT CDR Matt Ruglys RNZNJoint METOCHQJFNZ

1My backgroundJoined the Royal Navy in 1981METOC training 1990METOC, HMS ENDURANCE 1991-1993Two deployments to the Antarctic PeninsulaMetService NZ 2007-2010Joined Royal New Zealand Navy 2010METOC in HMNZS OTAGO Nov 2013-Jan 2014Deployment to the Ross SeaA tale of two shipsHMS ENDURANCEIce class 1A1 (DNV)Displacement 6100tLOA 91mBeam 17.9mDraught 8.5mHMNZS OTAGOIce class 1C (Lloyds)Displacement 1900tLOA 85mBeam 14mDraught 3.6m

ChallengesSparsity of surface observationsEven greater sparsity of upper air observationsHence the determination of current weather conditions and the spatial distribution of weather elements (fronts, air masses and so on) is difficult

Surface observationsThis is a typical coverage of SYNOPS. The cluster in the Southern Ocean I think are buoys which I would not normally have expected to see but on this occasion proved to be very useful. South of 60S there are very few obs.5

Surface ObservationsBut on occasions there would be even fewer.6

Radiosonde observationsIt is even worse for upper air obs. I could use Invercargill for a short while, then Macquarie, but from then on there is really nothing until McMurdo.7Satellite ImagerySatellite imagery is essential to fill in the gaps in observationsGeostationary satellites do not cover polar regionsPolar orbiting satellites have better resolution than geostationary satellitesGenerating a time sequence is not really possibleGeostationary Satellite Imagery

Polar Orbiting Satellite Imagery

This is a composite built from a number of satellite passes at different times. As a result it is difficult to use it when analysing charts (did not stop me from trying though).10

Hand AnalysisUsing only SYNOPS and the composite satellite image I drew three hand analyses each day.11Data & CommunicationsInternet via satelliteSlow, thus file size is importantChose NAVGEM over GFS or AMPSAMPS D3 (Ross Sea)MSLP and 10m u and v winds 46MBNAVGEM Global (Ross Sea)MSLP and 10m u and v winds 1.8MBFor getting model data bandwidth is a big deal. You cant download all the fields, so you have to be very selective. Nor can I simply download a bit more when I feel like it from my desk. I would have to go to the COMMCEN with a USB stick. The COMMCEN was not manned 24 hours a day so I would have to fit in with their schedules.12OrographyOrography has a powerful modifying effect on the airflowTrans-Antarctic mountains and high ground to the west of the Ross SeaBarrier winds

When you use global model data you cant expect a high degree of orographic fidelity.13Orography

Contours in metres. From: Parish, TR; Cassano, JJ; Seefeldt, MW; Characteristics of the Ross Ice Shelf air stream as depicted in Antarctic Mesoscale Prediction System simulations; J Geophys Res III D12109, doi:10.1029/2005JD006185NAVGEM (0.5)

You can see that there is some compression of the isobars over the land to the west.15NAVGEM (0.5)

This is reflected in increased wind speeds as you would expect16AMPS D3 (3.3km)

The 3km AMPS output has a much noisier MSLP field.17AMPS D3 (3.3km)

But the winds are higher still than in the Global model output, by some 5-10kts.18

Barrier wind theory to practiceKatabatic windsBoundary layer very strong temperate inversions Katabatic winds can be very extreme, reaching storm force or greater at times Develop at very short notice Strongly channelled by local topographyLocal weather conditions can change dramatically over very short space and time scales Katabatic flows can be associated with very turbulent conditions, rapid temperature changes, and often very poor visibility in blowing snow

IR image showing katabatic drainage (dark signature & yellow arrows). Red areas show polynyas (ice-free areas) formed where strong offshore winds blow

Advection FogFog and icebergs are not a happy mix. It is perhaps ironic that icebergs are often first sighted on the passage south near the Antarctic Convergence which is also an area prone to sea fog!22Advection FogRelatively straightforwardAir temperatureDewpointSea surface temperatureBoundary LayerThe boundary layer can be difficult for both man and machineRoss Island - FEW

Ross Island early in the morning25Ross Island - FEW

This is the midnight (local) ascent from McMurdo. The dry air is reflected in the observation of FEW. There is an indication of weak mass descent at 700hPa. But surface bace Normand Point construction does not indicate any low cloud development26AMPS D5 (1.1km) cloud fraction

The AMPS 1km forecast was also for no or FEW total cloud at midday.27Ross Island - BKN

Unfortunately midday actually looked like this!28Ross Island - BKN

Not surprisingly the midday ascent shows the moist air at 910hPa.29Human ForecastersBecause of the topography land surface lower atmospheric flows relative lack of good surface weather observationsThe meteorologist is an even more important component of the forecasting system than s/he would be in other locationsBut even they will get caught out