antarctic forecasting - a practitioner’s view

Antarctic Forecasting -A Practitioner’s View

LT CDR Matt Ruglys RNZNJoint 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• Joined Royal New Zealand Navy 2010• METOC in HMNZS OTAGO Nov 2013-Jan 2014– Deployment to the Ross Sea

A tale of two ships

• HMS ENDURANCE• Ice class 1A1 (DNV)• Displacement 6100t• LOA 91m• Beam 17.9m• Draught 8.5m

• HMNZS OTAGO• Ice class 1C (Lloyds)• Displacement 1900t• LOA 85m• Beam 14m• Draught 3.6m

Challenges

• Sparsity of surface observations• Even greater sparsity of upper air observations• Hence the determination of current weather

conditions and the spatial distribution of weather elements (fronts, air masses and so on) is difficult

Surface observations

Surface Observations

Radiosonde observations

Satellite Imagery

• Satellite imagery is essential to fill in the gaps in observations

• Geostationary satellites do not cover polar regions

• Polar orbiting satellites have better resolution than geostationary satellites

• Generating a time sequence is not really possible

Geostationary Satellite Imagery

Polar Orbiting Satellite Imagery

Hand Analysis

Data & Communications

• Internet via satellite• Slow, thus file size is important• Chose NAVGEM over GFS or AMPS• AMPS D3 (Ross Sea)– MSLP and 10m u and v winds – 46MB

• NAVGEM Global (Ross Sea)– MSLP and 10m u and v winds – 1.8MB

Orography

• Orography has a powerful modifying effect on the airflow

• Trans-Antarctic mountains and high ground to the west of the Ross Sea

• Barrier winds

Orography

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:10.1029/2005JD006185

NAVGEM (0.5°)

NAVGEM (0.5°)

AMPS D3 (3.3km)

AMPS D3 (3.3km)

Barrier wind – theory to practice

Katabatic winds

• Boundary 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 topography• Local 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 Fog

Advection Fog

• Relatively straightforward– Air temperature– Dewpoint– Sea surface temperature

Boundary Layer

• The boundary layer can be difficult for both man and machine

Ross Island - FEW

Ross Island - FEW

AMPS D5 (1.1km) – cloud fraction

Ross Island - BKN

Ross Island - BKN

Human Forecasters

• Because of the – topography – land surface – lower atmospheric flows – relative lack of good surface weather observations

• The meteorologist is an even more important component of the forecasting system than s/he would be in other locations

• But even they will get caught out