UAV observations of the wintertime boundary layer over the Terra Nova Bay polynya John Cassano and Shelley Knuth Department of Atmospheric and Oceanic Sciences Cooperative Institute for Research in Environmental Sciences University of Colorado

Project Overview Use Aerosonde unmanned aerial vehicles (UAVs) to make meteorological measurements in the vicinity of Terra Nova Bay Why Terra Nova Bay? – Location of recurring polynya – Region of strong katabatic winds – Source region for Antarctic bottom water Prior to this project there were no in-situ atmospheric measurements of the wintertime atmosphere over the Terra Nova Bay polynya

MODIS-Terra 04-Oct 2005

Science Questions What atmospheric processes control the size of the Terra Nova Bay polynya? – Winds? – Surface energy budget? How do changes in the atmospheric state alter the amount of heat and moisture removed from the ocean in the polynya? – What impact does this have on the development of Antarctic bottom water? How does the presence of the polynya modify the katabatic airstream as it passes over the polynya?

Aerosonde UAV

Wingspan3 meters Weight15 kg Payload Capacity2-5 kg Endurance hrs Range1000+ km Altitude m Communications via 900 MHz radio and Iridium Flies in fully autonomous mode with user-controlled capability Aerosonde Aerosonde UAV

Wind Speed/DirectionPitot with GPS RH/Temp/PressureStandard Radiosonde Met Sensors Ocean /Ice Skin Temperature Infrared Thermometer Ocean/Ice Visible ImageryStill Digital Camera Net Shortwave RadiationPyranometer Net Longwave RadiationPyrgeometer RH/T/P/wind profilesDropsondes Altitude and Surface WavesLaser Altimeter Aerosonde Measurements

The Challenges Cold temperatures – Impacted: Engine Parts failure Communication failures Wind – Take-off / landing – In flight winds Aircraft icing

Aerosonde Launch Pegasus Runway (14 Sept 2009)

Aerosonde Recovery Pegasus Runway (7 Sept 2009)

16 flights – 8 science flights to TNB km (7000 miles) 130 flight hours

14 September 2009 First successful TNB flight 15 hour flight 1230 km (750 miles) Max wind speed 29.1 m/s (65 mph)

Aerial Photos Local test flight 9 Sept 2009 Aerial survey of Pegasus runway Flown at 1000 m altitude

Pegasus Runway Mosaic courtesy of Jim Maslanik

Aerial Photos of TNB Polynya 22 September 2009

Complex rafting and finger rafting: Produces accumulation of ice mass within thin-ice locations Image width: 70m Photo location shown in MODIS satellite image Courtesy of Jim Maslanik

Nilas ice forming in area of relatively calm winds. Sea smoke is also present. Frazil ice in location of strong winds, including waves with white caps. Courtesy of Jim Maslanik

Frazil and pancake ice accumulating to form a band of thicker ice Courtesy of Jim Maslanik

Pancake ice, with largest floes averaging about 2m diameter Courtesy of Jim Maslanik

Ridging within consolidated pack ice. Ridging indicates thicker ice compared to locations with rafted ice. Courtesy of Jim Maslanik

TNB Air Mass Modification 24 September 2009 Two plane mission to Terra Nova Bay Determine modification of katabatic air stream as it passes over polynya

Cross-wind Leg: Wind Speed

Temperature m layer: ~2 K warming SHF Profile 1-2: ~608 W/m 2 (10.6 km) SHF Profile 2-3: ~580 W/m 2 (11.8 km) SHF Profile 3-4: ~83 W/m 2 (24.1 km) SHF Profile 1-4: ~327 W/m 2 (46.5 km)

Relative Humidity m layer: 125% inc. in specific humidity LHF Profile 1-2: ~63 W/m 2 (10.6 km) LHF Profile 2-3: ~161 W/m 2 (11.8 km) LHF Profile 3-4: ~86 W/m 2 (24.1 km) LHF Profile 1-4: ~101 W/m 2 (46.5 km)

Wind Speed

Future Work Estimate surface turbulent sensible and latent heat fluxes – Bulk method – Compare to fluxes estimated from air mass modification (profiles) Estimate turbulent momentum flux to surface What are the dynamics responsible for the downwind modification of the katabatic jet? Is polynya opening / closing driven by winds or changes in the surface energy budget? Repeat UAV observations when high vertical resolution mooring is present in TNB

Questions?