Today, finally, came the day we all had been waiting for! At 0915L I drove to the airport with the flight crew and met the other scientists who had been at work since 0700 to get the instruments prepared. The science team consisted of myself, our Brazilian scientist Rachel Albrecht, Florian Ewald, Daniel Fütterer, and Emma Järvinen.
The aircraft was already parked on the apron, since in spite of the fact that we had contracted (and paid) for a hangar, that hangar was still filled with an old ATR52 that was being repaired and painted. But actually, it was quite comfortably cool inside HALO, thanks to an efficient air conditioner. In the hectic hours before takeoff, the cabin is so crowded with all the scientists getting their instruments ready that it is almost impossible to move around, and I sat down in the hangar instead.
The aircraft was already parked on the apron, since in spite of the fact that we had contracted (and paid) for a hangar, that hangar was still filled with an old ATR52 that was being repaired and painted. But actually, it was quite comfortably cool inside HALO, thanks to an efficient air conditioner. In the hectic hours before takeoff, the cabin is so crowded with all the scientists getting their instruments ready that it is almost impossible to move around, and I sat down in the hangar instead.
I was a bit anxious at this time: Was the aircraft really going to work? Would the instruments perform? Would we be able to convince ATC to let us do the “crazy” flight patterns that our work required? Would I be able to navigate the aircraft through the complex manoeuvers that cloud profiling required? Would the pilots consider the cloud passages safe enough to make these runs time after time? Would too much ice accumulate on the aircraft to keep working?
Looking at the sky I could see that the cirrus in Manaus region was quite dense, which might be a problem for some of our radiation measurements and might suppress cumulus convection. But, to my relief, cumulus had been building since about 1030L (1430Z) and the sky beckoned us to start cloud sampling.
Takeoff was at 1606Z and we climbed out into a quite hazy sky. The haze topped out at about FL130 and we saw abundant cu’s all around us. After climbing to FL300 through some cumulus outflows we held this altitude for about 5 min, and then descended again into the boundary layer (BL). We reentered the haze at 11,000’, passed cloud base at 4000’, and at 1652Z crossed the Rio Tapajos, a major tributary of the Amazon, at about 2000’ above ground. The hazy air contained about 2000 particles per cc. There was a small fire with a smoke plume along the river and the vegetation alternated between forest and regions of savanna vegetation, which is called cerrado in Brazil.
At 1703Z we began our climb again, passed cloud base at 4100’, and did another up and down profile to FL300. At 1704Z we turned west in the BL at Alta Floresta (ATF) and flew over large deforested areas to our cloud profiling region about 30 nm west of ATF. Cloud bases here were at 5800’ indicating that we were in a slightly different airmass from before. We began cloud profiling at 1750Z with a 5000’ run below cloud base at SAT 19°C and CN ~2000/cc. For the actual profiling, we made 23 passages through clouds at 16 different levels. Some of these passages were only slightly bumpy, but other shook us around quite a bit. At the lowest levels we encountered only water cloud drops, then a zone with water and ice between FL220 and FL300, and only ice particles above this level. In the higher ice clouds, we had some encounter with static electricity, which made us a little nervous, and we made sure to stay away from the bigger cumulonimbus clouds to avoid any chance of lightning. Then, according to our plan, we had wanted to sample the ice cloud region at the temperature around -40°C, but we did not see any young cloud elements at this level, which seemed safe to enter, and so we decided to head north towards Manaus. Massive cloud anvils to the west above us looked threatening enough to hasten our departure.
On the way west and north, we passed through large areas of cloud outflow at FL330 to FL430, which contained lots of ice particles, but also very high concentrations (~5000/cc) of small aerosol particles that we think are produced in these cumulus towers. They appear to consist mostly of organic matter. As we went further north, the bigger ice particles from the clouds appeared to mix with particles from the cirrus clouds that had been prevailing in the region.
The long transect through outflow – in the cockpit we called it “grey soup” – ended when we entered a large clear area about halfway to Manaus, where we observed a beautiful sunset. Another large outflow just south of Manaus, then a turn over MNS, and north towards Boa Vista. We descended to reach ARVUM, our northernmost point, at 8000’ where particle concentrations were only ~500/cc. Since it was quite dark at this time, we felt that it was not safe to descend any further and headed back to SBEG, where we landed at 2329Z.
We were greeted by the rest of the science team and excitedly told our stories from the flight. All in all, we had an extremely successful flight that put to rest all of the worries that I had before we took off. The instruments worked (well, most of them) and the flight management between science and flight crews functioned very smoothly. ATC turned out to be very cooperative and the only hiccups were due to the occasional loss of communication because of the limited range of radio contact. Our Brazilian scientist, Rachel Albrecht, and Tenente Fialho managed to iron out some linguistic communication problems and succeeded in obtaining the magic word “Autorizado!” We wrapped up the day talking over well-deserved beers in the meeting room. “Thank you” to the team that had made it all possible, especially to our Brazilian partners!
(Photo credits to Meinrat Andreae, Steffen Gemsa, Florian Ewald, Emma Järvinen, and Daniel Fütterer)
(Photo credits to Meinrat Andreae, Steffen Gemsa, Florian Ewald, Emma Järvinen, and Daniel Fütterer)