ACRIDICON-CHUVA - Blog

Goodbye Manaus - Hello Oberpfaffenhofen (AC21/22)

10/8/2014

The crew on the return flights. In front from left: Alex Wolf, Tina Jurkat, Bernhard Buchholz, Christiane Schulz, Frank Werner, Stefan Mertes. In back: Steffen Gemsa, Max Dollner, Stefan Grillenbeck

Transfer flights are like road movies: The journey is the reward.

To transfer HALO back to Oberpfaffenhofen it takes two 6 h flights from Manaus, with a stopover at Sal in the Cape Verde Islands. The take-off at Manaus was planned for 8:00 o’clock in the morning on October 3. Our handling agency arranged the exit documents and a flag of the Amazonian district for a last picture of HALO in Manaus. Since we had no Brazilian scientist and no military observer aboard, altogether six scientists from Germany and three crew members were operating the aircraft. Without the Brazilian observer on board, we were not allowed to take data above Brazilian territory. Our colleagues in Manaus gave us last instructions on how to turn on the instruments once we left Brazilian air space. They gave us a warm farewell and wished a good journey and received a pile of postcards that we had missed to send.

Sunset on the Sahara dust layer

Travelling with HALO without running instruments is quite relaxing. We enjoyed watching the Amazon Basin, the thick forest, and the coastline of Brazil. After three and a half hours we left Brazilian air space and were allowed to turn on the instruments. We were heading for a Sahara dust layer near Cape Verde, which gave us some time to set up the measurement. We travelled at FL410 and FL430, sampling remote aerosol concentrations at high altitudes over the Atlantic Ocean. Approximately half an hour southwest of the coast of Cape Verde we descended to FL100 going into a thick Sahara dust plume during sunset and landed at Sal at 18:00 o’clock local time. Yet another interesting data set we can carry home.

The second part of the transfer started the next day with a hectic preparation of the instruments. HALO was parked outside; fortunately we had no storm or rain that night. We had only about 1 h before take-off to turn on the instruments and get things running before sampling another dust event near Sal. Take-off was at 8:00 o’clock. We ascended to FL100 but had to realize that the dust cloud was below us. Thus our radiation measurements collected some valuable data while flying above the dust cloud.

Left: Parked outside in Sal

We ascended again to FL430 to 390 sampling high-altitude aerosol particles over Europe and trying to encounter mid latitude cirrus clouds. The final descent reminded us that this is the last mission for ACRIDICON, and as a goodbye gift HALO rewarded us with a glory in the thick water cloud cover over Oberpfaffenhofen.

Guest blogger and photographs: Tina Jurkat

The Last Mission in the Amazon (AC20 - 01 Oct 2014)

10/5/2014

The "Textbook Outflow"

AC20 was the last flight of ACRIDICON-CHUVA campaign in Brazil. Altogether we had 14 scientific flights based here in Manaus, we spent almost hundred flight hours in the air. This is quite impressive, in particular taking into account the harsh environmental and technical conditions here in the Amazon. The instruments worked surprisingly well, we had no major failures. Also, HALO itself was not grounded for technical reasons throughout the entire campaign.

We took off for AC20 with three mission objectives: (a) to have another coordinated flight with the American G1, to sample outflow (because we had the feeling that the data collected so far for the outflow mission type were not yet complete), and (c) finally to collect more cloud profile data. Because of missing clouds we failed with the attempt to collect more measurements for the coordinated flight with the G1 (mission objective a). However, in particular the outflow sampling was very successful.
We picked a textbook outflow on our way and crossed it in numerous altitudes perpendicular and parallel. We were flying above and below this poor outflow cloud. This made sense because amazingly the cloud seemed quite stable during the 2.5 hours it took us to sample it. Near the end of the sampling the outflow descended, and lost momentum.

On our way back we managed to collect another of the "ever popular" cloud profiles, see photo.

Guest blogger and photos: Manfred Wendisch

Clouds over the Atlantic (AC19 – 30 Sep 2014)

10/3/2014

Now that we had sampled the various types of continental convection, we needed to explore a contrasting regime – the convective clouds over the tropical Ocean. Here we expected to find the lowest aerosol particle concentrations, in combination with a greater input of moisture and latent heat. Again the morning sky was cloudless, and again the first few cu’s started up around 1030L.

Left: HALO's crowded home away from home - the whole airplane didn't even fit into the hangar!

We took off at1052L (1452Z) in an easterly direction (it’s always runway 10 in Manaus) and climbed to 39,000’, heading towards the Atlantic. We soon reached Santarem, where the Tapajos River joins the Amazon. Here we were able to observe an interesting phenomenon: the “river breeze” effect. It is analogous to the sea breeze, where greater heating over land causes local convection and a line of clouds along the coast. This draws in air from the cooler sea, the “sea breeze”. Over the cooler water, air subsides resulting in the absence of clouds over the water. The rivers in the Amazon are large enough to cause the same phenomenon, which could be easily seen along the wide Rio Tapajos.

Macapá, on the mouth of the Amazon River

After Santarem, we turned northeast towards Macapa. We passed a beautiful, large pyrocumulus way below us, and I was tempted to change the flight plan and descend to investigate it. But this would have taken so much time that we would have risked our chance to work over the Ocean. After a while, we descended to make our lower-level measurements, and for all intents must have looked to the air traffic controller at Macapa like we were making an approach to land there. She asked us where we planned to land, and when we answered “Manaus” she must have thought that we were a bunch of gringos who were REALLY lost! She told us “Standby”, probably to confer with the area controllers who must have told her that we were harmless. She then asked us to call her again when we were 37 miles away on the other side of her airport, surely looking forward to be rid of us again.

Clouds poking through the polluted haze layer near Macapá

Soon we were over open water, which in this case looks like milk coffee from the giant plume of the Amazon River that stretches out over the Atlantic for hundreds of miles. Convection was not particularly abundant over the Atlantic, but we were lucky to find a long cloud street that we could use to make our cloud profiles in. It was nice to get lots of measurements by just zipping along this cloud street at different levels, back and forth.

Taking aim at a cloud top

Before we began our measurements over the sea, I had been a bit apprehensive about our prospects to get data in clean air. The air over the coastal region had still been quite polluted, and I had observed a number of brown pollution layers at various altitudes during descent. Down in the boundary layer, however, the particle concentration was about 300 per cc, typical of clean marine conditions. The clouds acted accordingly, producing ample rain at quite low altitudes.

Multiple pollution layers over the Ocean

But even some 100 nautical miles offshore, we still saw the brown pollution layers above 10,000’, which some of the taller clouds pushed through. As they were coming on easterly winds and made no sign of diminishing with distance from shore, they appear to be the result of long-distance transport of smoke from vegetation fires in Africa.

Our work over the Atlantic done, we headed back towards the Amazon at 14,000’ to measure the gradient in cloud properties from ocean to land. Over land, we happened upon a pyrocumulus over a fire northwest of Belem, which we took a few minutes to sample.

Eventually, we climbed to FL430 again for our way back. Close to Manaus we saw a large outflow from a huge Cb near Manaus, and since we had a little flight time left, we decided on the spot to make a measurement run through it.

On the approach to Manaus airport, we had a surprise: we were informed that because of “rubber removal from the runway” we had to enter a holding pattern. So we spent another 15 minutes circling at 4000’ before we could land at 2200Z. This was my last flight during ACRIDICON; tomorrow I’ll be flying back to Germany. Sitting on a cramped commercial flight, I’ll miss the excitement of being on HALO!

A Quest for Clean Air (AC18 – 29 Sep 2014)

10/2/2014

Flight preparations in the "lab/office" in the hangar

The weather patterns in Amazonia had been pretty unusual over the last few days. Even in the “dry season”, there are usually quite frequent showers and thundershowers in central and northern Amazonia – the rain forest needs a steady supply of rain. But lately it has been quite dry over almost the entire Basin, because a high pressure system has parked itself over the region. This has several consequences, none of them good for us: The high pressure suppresses the deep convection that produces the tall clouds, which we are here to investigate. The lack of rain prevents the removal of aerosol particles from the atmosphere, so that it becomes increasingly difficult to find areas with very clean air. And finally, the circulation around the high swiftly moves the dense smoke from the fires in the southern part of the Basin out in a southeasterly direction, away from us und in the direction of São Paulo. This makes it hard for us to find the other extreme: very, very dirty air. Under these circumstances, flight planning requires a lot of information from satellites and models, and also a good amount of luck.

The hangar is pretty crowded!

The cleanest air and the most rain in Amazonia is usually found in the northwestern-most part of the Basin, in the region of São Gabriel da Cachoeira. This place is reputed to have no dry season – it supposedly always rains there. The weather forecast models had also suggested the best chance for convection in the western part of Amazonia, near the border to Colombia, and the air pollution models predicted clean air. So, that’s where we decided to go.

The morning did not start very promising: Until about 0900L, the sky was clear blue without any cloud at all! It took until about half an hour before our takeoff at 1426Z (1026L) for the first little cumulus clouds to pop up. We climbed through a pretty hazy layer that reached up to about 10,000’. Reassuringly, some clouds already poked up through this layer, and eventually we found ourselves flying over a good crop of mid-sized cu’s. We descended into the boundary layer east of São Gabriel and found air as clean as one can hope for in the dry season, with about 700 particles per cc.

Left: A VERY blue sky in the morning!

The first cloud is poking out of the haze layer

Clean air over the western Amazon

The cloud with the mature anvil is on the right, the one that is still actively growing in the back left

We sampled lots of mid-sized clouds along the way, at altitudes up 14,000’, and began our systematic cloud profiling at 1638Z. As we kept climbing to higher altitudes, we were happy to see that the clouds were climbing along with us, and eventually we found ourselves at 37,000’. Here we could sample three clouds, one that was still actively growing, another that was just in the process of topping out, and a third that had already converted to an outflow anvil.

This concluded our mission goals and we headed back towards Manaus. Luck had been with us! On the way back, we had to detour around a huge cloud complex that we estimated to reach above 50,000’. This shows that the few thunderstorms that can break through the inversion barrier can then develop into real monsters! We landed again in Manaus at 2113Z.

Landing in Manaus

The AC17 Team

10/1/2014

I just found this great picture of the AC17 Team doing the Brazilian thumbs-up salute

Christopher Heckl, Tina Jurkat, Daniel Fütterer, Steffen Gemsa, Manfred Wendisch, Stefan Grillenbeck, Tobias Kölling, Alex Wolf

Land Use Change, and HALO visits ATTO (AC17 - 27 Sep 2014)

9/30/2014

So far we have had successful flights for all the five mission types of the campaign, except one which we call the “cloud contrast mission”. This mission was proposed by our Brazilian colleagues who are interested in measuring the convective cloud properties over rain forest and compare it with those collected over deforested areas. Certain differences are expected mainly because of different surface properties (e.g., temperature, latent, and sensible heat fluxes). Therefore, we planned a flight pattern covering different surface types, i.e., extended legs at different altitudes over rainforest, deforested areas and transition zones. As a second mission objective we wanted to compare the airborne data with measurements of the GPM (Global Precipitation Measurement) satellite. Thus, we planned to meet the satellite during the second part of our flight, an exercise that the pilots have already lots of experience with. Last but not least we wanted to fly over the ATTO site, to link the airborne with the tower measurements. As a side product, we wanted to take nice pictures of the tower during the flight.
Before taking-off we experienced tropical insects in the hangar, “slightly larger” compared to what we know from Europe (see photo).

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.

The Amazon forest in the ATTO 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)

ATTO Keeps Growing (26 Sep 2014)

9/29/2014

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.

Tracer Transport Take Two (AC16 - 25 Sep 2014)

9/29/2014

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.

Sampling Smoking Clouds

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

Early Bird Gets the Albedo (AC15 - 23 Sep 2014)

9/25/2014

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

A smoke plume rises from a deforestation fire and grows into a pyrocumulus cloud (1715Z)

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.

Approaching an outflow

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.

At one point in the flight, HALO came back along the same track and found its own contrail!

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)

Two Airplanes and a Satellite (AC14 - 21 Sep 2014)

9/24/2014

Fueling before start, the umbrella helps in the Brazilian sun

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.

Cloud probes mounted on the wing for the intercomparison of cloud measurements

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.

A baby pyro-cumulus

Above cirrus! HALO record altitude with PMS configuration: FL480

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)