The central idea of ACRIDICON is to compare the interactions between aerosols, cloud, rain, and radiation in clouds that are meteorologically similar, but contain different amounts of aerosol particles. We have so far sampled moderately polluted clouds (AC07) and fairly clean clouds (AC09). Now we are hunting for really dirty clouds. One thing I had never expected in the Amazon dry season: That finding really polluted air would be a problem. In previous campaigns, there were so many fires producing so much smoke that one could almost cut the air with a knife. I remember a morning in Ji Parana in 2002, where I woke up in the hotel room, smelled smoke, went into the hall way and, looking down the hall, saw smoke haze. I first thought the hotel was on fire, but it was just the heavy smoke that covered the whole region!
Well, this year we have to look pretty hard to find really polluted air. It appears that deforestation has really gone down in recent years, and that this shows up in improved air quality. A good thing for everybody, of course, except for us smoke hunters! We are further constrained by the area that we are allowed to operate in and by the need to find just the right kind of convective clouds. This makes flight planning a bit of a gamble, especially since weather forecasting in this region is not as reliable as one would like, to put it mildly.
Today, we put our bets on an area south of Alta Floresta, where the satellites had seen a large region of smoke, not very heavy, but good enough. The forecast was not for very strong convection, but we were willing to take a chance. HALO took off at 1052L and passed through a mix of clouds. Soon we saw nicely developed cumulus to our east, and even some threatening-looking giant Cb. Promising, but here the air was too clean for our purposes.
Today, we put our bets on an area south of Alta Floresta, where the satellites had seen a large region of smoke, not very heavy, but good enough. The forecast was not for very strong convection, but we were willing to take a chance. HALO took off at 1052L and passed through a mix of clouds. Soon we saw nicely developed cumulus to our east, and even some threatening-looking giant Cb. Promising, but here the air was too clean for our purposes.
When we reached Alta Floresta, the air was dirty enough, but there were hardly any clouds! We flew over large deforested areas, and saw a few smallish fires. But, one of the actually had its smoke plume rising into a little cumulus cloud – a pyrocumulus! Even though it was small, we got quite excited and sampled through it. By this time (1250L), the clouds had started to develop quite nicely, and we began our cloud profiling routine. We went through cloud after cloud, getting shaken around, turning sharply again and again to get back into the next cloud, much to the discomfort to our Air Force observer who got quite airsick!
BUT – the strong inversion that was present at about 15,000’ made it difficult for clouds to rise through this level. Some valiantly pushed through and reached as much as 18,000’, but quickly collapsed, exhausted from their effort. It seemed that just as soon as we had made a passage through a cloud, it fell apart behind us. We joked in the cockpit that we were breaking the clouds with our airplane…
At 1515L it became clear that the clouds weren’t likely to rise any higher. Actually, there were beautiful clouds growing way higher just to the east of us – BUT – this was in a military area that we weren’t allowed to enter. How frustrating! We decided to head back to Manaus, collected some measurements in cirrus and outflow on the way back, and landed at 1652L. It was a great flight all in all, but we were still a bit disappointed because the clouds had fizzled out just below the level where ice starts to form, one of the phenomena that we are really interested in.
On this flight I took some pictures of the inside of HALO. There is one open area with a table, but the rest is packed with instruments. What a difference from the situation in the picture that was taken in 2006!