Post on 25-Feb-2016
description
UAV observations of the wintertime boundary layer over the Terra Nova Bay polynya
John Cassano and Shelley KnuthDepartment of Atmospheric and Oceanic Sciences
Cooperative Institute for Research in Environmental SciencesUniversity 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
Wingspan 3 metersWeight 15 kgPayload Capacity
2-5 kg
Endurance 12-17+ hrsRange 1000+ km
Altitude 100-6000 m
Communications via 900 MHz radio and Iridium
Flies in fully autonomous mode with user-controlled capability
Aerosonde UAV
Wind Speed/Direction Pitot with GPSRH/Temp/Pressure Standard Radiosonde Met
SensorsOcean /Ice Skin
TemperatureInfrared Thermometer
Ocean/Ice Visible Imagery
Still Digital Camera
Net Shortwave Radiation
Pyranometer
Net Longwave Radiation
Pyrgeometer
RH/T/P/wind profiles DropsondesAltitude 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 LaunchPegasus Runway (14 Sept 2009)
Aerosonde RecoveryPegasus Runway (7 Sept 2009)
• 16 flights– 8 science flights to TNB
• 11000 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 Polynya22 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
100-600 m layer: ~2 K warmingSHF Profile 1-2: ~608 W/m2 (10.6 km)SHF Profile 2-3: ~580 W/m2 (11.8 km)SHF Profile 3-4: ~83 W/m2 (24.1 km)SHF Profile 1-4: ~327 W/m2 (46.5 km)
Relative Humidity
100-600 m layer: 125% inc. in specific humidity
LHF Profile 1-2: ~63 W/m2 (10.6 km)LHF Profile 2-3: ~161 W/m2 (11.8 km)LHF Profile 3-4: ~86 W/m2 (24.1 km)LHF Profile 1-4: ~101 W/m2 (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?