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.

Different cloud layers were already observed on the way to C1. Above the airport a thin cloud layer was passed and sampled afterwards by Polar 5 remote sensing instrumentation. Close to C1 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 behind C1 a second cloud layer in higher altitudes about 2000 m was detected by AMAli. First this layer was thin enough to be penetrated by AMALi, later it almost vanished before about 30 MN to C2 the higher cloud layer thickened. The cloud top also increased so that we had to adjust the flight altitude to 11,000 ft. 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. On the way back first the clouds looked almost symmetric in the lidar plot. Later, the higher cloud layer was found to be thinner compared to the time we observed it on the first leg. Four drop sondes were released to cover all different cloud structures identified on the way from C1 to C2. After finishing the leg C2-C1 we again overpassed Tuk. Here only the lower cloud layer remained with several cloud gaps where AMALi could sample the boundary layer.

Polar 6 could sample 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. Close to C1 the lowest cloud, between 3000 and 3500 ft, was penetrated for some time. An extended leg was used to analyze especially the cloud top. Later the higher cloud layer was sampled by horizontal legs and staircase pattern. On the way back Polar 6 also tried to sample the hazy layer above the cloud for about 15 minutes. Before overflying Tuk, the lowest cloud layer was sampled again by a line pattern at cloud top. The Tuk overpass was flown at about 600 ft altitude what is suitable for aerosol measurement intercomparison.