After the last front passed Inuvik a high pressure system spread over the Mackenzie Delta. A wide field of persistent boundary layer clouds was predicted in the weather forecast suitable for our measurements. Unfortunately, these clouds were also quite stable above the airport. With the aviation weather indicating icing conditions above YEV, we were not permitted to start until the cloud base stepped up and we could start and approach the measurement area flying below the clouds. The low clouds were investigated North East of the Mackenzie Delta. Two cloud legs in north-south direction, one at 133° W and one at 129° W were defined. In between Polar 6 was intended to measure aerosol and trace gases while Polar 5 continued with remote sensing of the clouds and the atmosphere.

Polar 5 flow atop of the cloud layer short after the start. The flight altitude was adjusted to 11,000 ft to cover a little more of the partly hazy cloud free air. In the beginning the boundary layer clouds were quite homogeneous. Within the cloud leg, we observed that the cloud top altitude decreased toward the north. Not much later, further north, the end of the cloud field was already visible. It was rather a large cloud gap, as towards North-East again clouds were present. In the cloud free area, the characteristics of the sea ice/open water mixture could be measured, what will be helpful for the data analysis. On the way to the second cloud leg, we observed an increasing cloud top altitude again. In this area also an enhanced aerosol concentration above the clouds was indicated by AMALi. Some thin haze layers at about 10,000 ft altitude were also observed from the remote sensing on Polar 5. In coordination Polar 6 tried to sample these clouds in situ as Polar 6 was just about to finish an extended profiling of the cloud free atmosphere. On the second cloud leg, the situation remained stable with no significant changes. Similar to the first cloud leg a drop sonde was released indicating cloud top temperature of about -10°C. Due to some instrument problems, Polar 5 had to repeat the sampling of this cloud leg and separated from Polar 6. On the direct way home to Inuvik another significant change of the aerosol concentration above the clouds was detected by the lidar. This change was visible throughout the column up to 11,000 ft. Finally, the cloud field ended about half the way from coastline to Inuvik.

Today Polar 6 did fly ahead of Polar 5. The clouds were sampled three times. First when breaking through to cloud top after the start. Here is became apparent that the layer is very thin. Rime ice accumulation was observed. Again also the air close to cloud top was sampled on a longer leg. On the way north, the same cloud was investigated again by a staircase experiment. As the cloud was relatively thin and decreased towards the end of the leg, only few levels were flown. Between first and second cloud leg an aerosol profile with different steps was measured. During the climbing different haze layers were observed and sampled. The descent to cloud top again took longer than expected. The cloud Polar 6 found on the second cloud leg did differ significantly from the first cloud. It appeared much thicker and contained much more supercooled liquid water. These conditions quickly lead to icing of the plane. So only a short period of 8 minutes was spent inside. On the way back to Inuvik, Polar 6 flow along cloud top for an entrainment study but also sampled a possible aerosol layer above the cloud deck. Altitudes change frequently without reason for following the upper cloud edge contour.