DC-8 Flight Report for January 16, 2000

The Hostetler lidar and DIAL reported seeing a PSC near 23 km altitude at about 0830 to 0845 UT. The ir scattering ratio was about 0.4. Sunlight made the depolarization difficult to quantify, but the clouds appear to DIAL to be depolarizing in both the infrared and visible. This cloud is well out on the edge of the vortex, as predicted. From 0850 on a depolarizing PSC was present near 20 km, where MTP temperatures were on the NAT condensation line. After approximately 0900, a PSC appeared at 18 km or maybe below. At that time three layers of PSC were present at 17 to 18 km, 19 to 20 km, and 20 to 21 km. All three layers were depolarizing in the infrared. The ASUR instrument reports that ClO is present in the lower stratosphere in the vortex, but it did not see any when we left Kiruna and were outside the vortex. At 0945, as we approached the beginning of the sunrun, PSCs were seen from 17 to about 19 km altitude. The ir scattering ratio was about 0.25, and they were depolarizing. The infrared depolarization ratio was about 0.1. At the turn to begin the sun run, numerous waves were present in the cloud deck below us. A possible stratospheric ice cloud was present well to the south of the aircraft. During the sun run a contrail was present on the horizon. The PSC continued and filled the region from 17 to about 20 km. At the POAM footprint the PSC seemed to be present only as a thin layer near 20 km. As we turned north the PSC faded, but something remained from 20 to 23 km, possibly in two layers. It was also slightly depolarizing. We could see these clouds visually. Toward the north they appear as a red or purple glow above the dark blue shadow of the Earth. To the west, two layers of PSC were clear on the horizon. As we approached Novaya Zemlya, Hostetler reported that we encountered a thin but highly backscattering cloud (ratio of 2.5) near 20 km. As we continued onward several thin layers appeared between 18 and 20 km. AROTEL reports seeing waves in the vertical temperature profiles. At 1125 a PSC was observed near 16 km, in addition to the others. Again, these layers were highly depolarizing. Possibly these clouds are enhanced by flow over the island; however, they continued upwind of the island in a less intense fashion. Likewise, they continued upwind of Frans Josef Land. Generally clouds seemed to be continuous from about 17 to 20 km and were still present at 1330 UT. As we approached Spitsbergen the PSCs disappeared. This disappearance coincided with the predicted edge of the vortex; however, AROTEL and MTP temperatures are quite low in this region, lower than forecast and as low or lower than in regions in which PSCs were seen. Numerous waves were seen in AROTEL and in situ data near Spitsbergen; however, it is not clear that any PSCs were present. There were some variations in the scattering seen by DIAL, but these may have been in the sulfate aerosols. At 1530 UT we saw very high numbers of condensation nuclei in situ which correspond with a low ozone layer at 15 km seen by DIAL. This low ozone layer corresponds with an enhanced backscatter, but it is too warm to be a PSC. MTP sees very little structure in the vertical temperature profile in this region and it is quite warm (around 220 K). All of this seems to correspond to a pool of warm air that was forecast off the coast of Norway in the 1200 UT ASM forecast. We had to cut the flight slightly short due to a cabin pressure problem, and therefore missed the opportunity to observe the large gravity wave over Norway.