Science Flight #5 - May 6

Seemed for us to be like a Déjà Vu: Again a frontal system with light precipitation crossed Inuvik during the night and the early morning. Similar to the flight on April 30, we intended to follow the front after it had passed and sample low clouds in its back. The forecast predicted an increasing cloud top altitude towards East and closer to the front what we could confirm pretty well during the flight. Takeoff was scheduled for 11 am. Even the front passed a little earlier, we kept to this schedule. This flight Polar 5 was to start first. Unfortunately takeoff of Polar 6 was delayed due to another aircraft. The time difference could be minimized until the begin of the cloud leg with Polar 5 already slowing down to 120 kn observation speed during the ferry.

Forecast from ECMWF

Lidar signal indicating cloud top
for the grey shaded area in the forecast.

The cloud situation we found in the measurement area was surprisingly close to the forecast. At the start of the cloud leg only a low stratiform cloud layer remained. This cloud was also present later, when flying towards North East, but showed increasing cloud top altitudes. About 25 NM after starting the cloud leg a second cloud layer in higher altitudes about 2000 m was detected by AMAli. First this layer was thin enough to be pentrated by AMALi, later it almost vanished before about 30 MN to the return point the higher cloud layer thickened. The cloud top also increased so that we had to adjust the flight altitude to 11,000 ft. 

Polar 6 could sample these clouds at three levels during the flight: (1) the lowest fog layer, (2) thin layers/sheets of cloud sometimes only haze roughly between 3000 and 3500 ft, (3) layers of Stratus translucidus and sometimes Stratus translucidus undulatus above 7300 ft to 7600 ft. Straight legs and staircases were flown to sample droplets and ice crystals. Mostly liquid droplets were found to dominate the cloud. 

During all the time the horizon looked very hazy. Cirrus, although very homogeneous, was observed by the radiation measurements above Polar 5 almost all the flight. Polar 6 also tried to sample the hazy layer above the cloud for about 15 minutes before approaching Tuk for another overpass intended to inter compare the aerosol measurements at ground and in the air.  

For details read here: http://www.uni-leipzig.de/~racepac/flights/flight_05.html