We made a hasty exit from Thule just before the first direct sunlight of the year hit the base, and, importantly for the mission, just before a large storm system rolled in that might have trapped us up there for many days had we tarried any longer. As we ascended to our highest flight level, around 13km above sea-level, the sun appeared to us, low and orange to the east.
The typical flight path on ATom is to ascend to about 13km, fly level for 10 minutes, descend to around 1.5km, fly level for 5 minutes, and then repeat along our chosen path for 8-11h (depending on air traffic control and other factors. The reason we scan up and down is that vertical structure in the atmosphere is important and can tell us a lot about the processes going on. For example, I’m very interested in new particle formation, where liquid aerosol particles form from the gas phase in-situ in the atmosphere. The amount by which this process is influenced by charged particles can have a large influence where on the vertical scale in the atmosphere we expect to see very small particles. The reason we have the pauses at the top and bottom is that we get some of the information about gases and particles from collecting filters (air is run through a membrane and particles will collect on this) and canisters (literally trapping air, usual under pressure, in a sealed container for later analysis in the lab). These take time to fill/sample and it useful to do it all at one altitude so you don’t vary too much where the sample is coming from.
As we made our first descent on this flight, the sun, which had just appeared to rise, dipped below the horizon again from out view point. It looked kind of like the sun was setting in the east, which felt bizarre. To make matters weirder, we were flying “west with the night” (if you’re at all interested in the history of aviation, bush pilots or generally bad-ass women having epic adventures do check out the book of this title by Beryl Markham), and further north so the sun appear to hover on the horizon for hours, coming in and out of view as we rose and dipped. My body, already slightly off-kilter from the many time-zone, seasonal and climatic changes, felt a bit like I imagine birds do when they get all confused during a solar eclipse. It did make for a beautiful flight though.
On the low legs, coming over to Alaska, we observed more sea-ice. At this time in the year it should be reaching its maximum, and yet it looked a lot thinner than expected with more open water and sea-smoke than is normal at this time of the year. We did a series of low approaches in Alaska: Dead-Horse, Utqiaġvik and Cold-Point, before coming in to land for real at Anchorage.
Since we hadn’t planned to be in Anchorage until the following day, there was no space for us in a heated hanger that night. It is a problem for many instruments on board if the temperatures get too low, and so we had to keep a heater on the plane all night. This meant two people needed to be on-board at all times, so teams of one scientist and one crew member took turns through the night to stay on the plane.
We had one down day in Anchorage and, after servicing my instruments, I took a drive out with a colleague, Chris, from UC Irvine to Portage Glacier. This is easily a stunning enough route to warrant driving for its own sake, with steep mountains plunging down into a sea-inlet, which at this time of year was iced over and full of slush-bergs. We, however, were on a mission. Chris operates one of the canister instruments I was talking about earlier, collecting samples of air for later analysis in the lab. In each of the stops, he has gone out in search of ground samples to add to his flight samples. The group has been taking samples near Anchorage for a number of years, so it helps to take them always in the same place for comparison.
We drove out to the frozen lake, and Chris pulled out a couple of metal canisters from the trunk. He walked out a little way onto the lake, but stopped after we noticed that the top of the ice was slushy only a few inches from the top. He took a few samples spaced apart in distance and time, then we headed back to Anchorage for some rest before the final flight of the mission!