The take-off procedure went very smoothly, as usual. After take-off we climbed and saw that the atmosphere was extremely hazy, in particular below the clouds (see photo). It’s difficult to take an attractive picture of hazy air!

During flight we encountered a lot of fires, especially in the southern part of our track. We are very curious how these fires have influenced the cloud properties; there is exciting analysis work ahead of us. Taking good measurements is only the first step; the fun part starts if you look at the data in more detail after the campaign to make real science out of the measurements. Both parts are equally important for our job.

The picture to the right shows a small deforestation fires that has just about run its course.

At the end of flight AC17 we took the opportunity to overfly ATTO, make pictures and collect data to link the tower observations with the airborne measurements. This was not as trivial as it sounds because to fly over the tower required entering a military, restricted airspace. Our military observer was actually very helpful in obtaining the permission to fly in this area.

We had a good flight and we believe we have now reached most of the scientific objectives of the mission. Detailed analysis is required to quantitatively evaluate the results. Thanks to the whole team, namely the pilots (Stefan and Steffen), our flight technician (Alex), the military observer (Tenente Mendez) who actually was very helpful in maintaining contact with the Portuguese-only-speaking ATC operator at the ground, and the scientists (Tina, Daniel, Tobias, and Christopher)!

(Guest blogger: Manfred Wendisch; photos: Manfred Wendisch, Tina Jurkat)

The satellite communication system at the ATTO tower site has been down now for a few days, and there was no way to satisfy our curiosity about progress at the site. Finally, a few pictures were brought back with one of the weekly servicing trips. They had been taken a few days back, on 23 and 24 September. It was great to see that the tower is growing at a fast pace! At this point, the tower is about 60 m tall, and guy wires need to be installed to support it.

In science, any experiment is only considered credible, if it can be replicated. HALO’s task today was to replicate the tracer experiment AC11 from 16 September. The tracer was released again from the top of the Park Suites Hotel at about 0600L. HALO took off under the leadership of Hans Schlager at 1047L (1447Z). The team began by taking air samples for tracer measurements at 2000’and 4000’ in an area west of Manaus, and then climbed to 35,000’, heading east in the hopes of finding big cumulus clouds to investigate. The satellite image to the left shows the flight track and the Cb clouds that were sampled during this flight.

It turned out that there were no clouds big enough to be of interest in the east, so HALO turned around to go to a big cumulonimbus (Cb) cloud that had been spotted southwest of the city. The aircraft descended into the boundary layer at 4000’ to sample the air at low levels, and then began to probe clouds at 4500’ from 1700Z to 1720Z. Since the whole central Amazon Basin has been surprisingly dry now for days, fires began to be lit everywhere, particularly in the inhabited rural areas surrounding Manaus.

After these measurements at low level, HALO climbed to the top of the large Cb cloud and made measurements in its outflow anvil between FL310 (31,000’) and FL390.This took until 1846Z, and yielded beautiful data as well as beautiful views.

The next task now was to find the tracer again, that had been drifting through the air since morning. Model calculations predicted that some of it had been sucked into a big cumulus cloud west of Manaus, and to test this prediction, HALO took samples in the outflow from this cloud at FL370 between 1903Z and 1940Z. The flight concluded by additional tracer sampling at low levels and cloud probing at 6000’. Landing was at 2110Z.

Photos: Hans Schlager

AC15 was a HALO flight for early risers, the take-off was planned for 06:30 LT! To meet this schedule, the preparation of HALO and its scientific instrumentation had to start four hours before takeoff. Therefore, HALO was moved from the hangar to the apron at 03:30 am already. The scientists met at 04:00 LT at Terminal 2 to enter the airport.

The picture on the left shows the probes on the wings and the rainforest below during the albedo measurements

Why so early? Well, this special mission required cloudless conditions; clouds would actually hurt the measurements. That sounds strange for a convective cloud campaign. However, the main objective of this flight was to measure the surface albedo of the rain forest (a measure of how much of the incoming solar radiation is reflected by the ground) and compare it with the albedo of deforested areas. This type of data is needed as a crucial input for radiative transfer simulations which are needed to analyze, for example, the satellite intercomparisons performed during AC10 and AC14. In general, albedo data are required to evaluate all the radiation measurements carried out during ACRIDICON. These albedo measurements have to be performed under cloudless conditions and, therefore, we had to schedule such an early flight, well before convective clouds would evolve.

It was not quite clear whether the 06:30 take-off would actually work. Too many ifs and buts could cause unexpected delays. The fueling turned out to be a potential problem so early in the morning. However, our colleagues from DLR-FX successfully managed to maintain the schedule. The flight preparation went very smoothly, and actually we took off two minutes ahead of the planned 06:30L.

The albedo measurements were performed at low level (3,000 feet). They worked very well; the timing was perfect and we were lucky because no clouds perturbed our measurements. We collected about two hours of albedo data before the regular, daily convective cloud evolution started. After the albedo measurements, we climbed to an altitude of 43,000 feet and sampled a huge outflow, which looked almost frightening from a distance. We probed the outflow at different altitudes and subsequently descended to measure above, within, and below convective clouds at lower levels.

Altogether we had a very successful flight. As usual, the collaboration with the pilots (Stefan & Steffen) was simply great; the team of instrument operators (Chrischi, Fabian, Adrian, Florian) and the mission PI had a lot of fun. Thanks to all of you!
(Guest blogger: Manfred Wendisch. Picture credits: Manfred Wendisch, Florian Ewald, Steffen Gemsa)

The flight AC14 had two main scientific objectives. First, we wanted to collect microphysical cloud data in a coordinated flight jointly with our US colleagues flying with the G1 aircraft. Those measurements should be compared in order to assure that we can use each other’s data for further analysis of the ACRIDICON-CHUVA campaign. Furthermore, we wanted to compare the aircraft cloud data with those collected by the ground based radar. Second, we intended another meeting with the A-train satellites. Only the second objective was fully achieved. The first objective was reached only partly, because the clouds were quite shallow and could not be seen by the ground-based radar. But this is how science and in particular atmospheric observations work: Sometimes you are lucky, on other occasions you may fail.

The coordination between the two aircraft during the comparison part of the flight (first objective) is kind of tricky, because the aircraft need to be vertically separated by 1000 feet to make sure they don’t collide. On the other hand we wanted them to be collocated vertically above each other, which is a challenge because the optimal speed of the two aircraft is not exactly the same.  Somehow the pilots managed these issues; they are professionals.

For the satellite meeting all went smoothly. The timing was perfect and the clouds were well developed. After the rendezvous with the A-train we climbed to FL480 which is a new altitude record for HALO in PMS configuration. We also celebrated the HALO flight hour number 1000 during this flight.

Again, this was a nice flight with HALO. Thanks to the pilots (Steffen & Michi), the flight technician (Tommy), and the scientists in the back (Tina, Rebecca, and Frank)!

(Guest blogger and pictures: Manfred Wendisch)