6 September 1995
PH: This flight was devoted to smoke-cloud interactions. We headed north from Porto Velho in the hope that as we went north we would see a significant decrease in smoke and be able to look at cloud structure in cleaner air to the north and compare it with cloud structure in the smoky air further south. That didn't materialize completely. There was no sharp demarcation, just maybe a very small gradient. But we did a lot of sampling of nice cumulus, good sizes for us to work with, below cloud base, above cloud base, and at various heights in the cloud. Did some sampling on outflow of air from clouds. This was all out near 100 miles or so north of Porto Velho, which was as far north as we could go in our flight area. Then we did a descent right down to just above tree tops. But essentially no change in aerosol properties all the way down to that level. Then we headed back south and went through clouds as we encountered them on the way back and did some more in-cloud and below-cloud sampling. And we are now a short distance from Porto Velho. Okay, Art. Would you like to summarize?
AR: I can't add too much to what you said except that I would agree I didn't see too much in the way of a difference between the north and Porto Velho. And I would add that the cloud bases were about 1,500 ft lower in the north than they were in the south when we were sampling them. And generally the clouds that we sampled were narrow goose-neck, rather short-lived, clouds having lifetimes of only a few minutes and that, I'm guessing, would explain why we saw a little drizzle or rain in these things even though they were all above the freezing level at cloud top.
PH: About how deep were most of the clouds that we sampled.
AR: The deepest clouds we sampled topped out at 10,000-12,000 ft, the very, very deepest.
PH: That's the tops, the bases were 3,500 ft?
AR: That's correct. And some of those clouds we were sort of passing through the bottoms. The very deepest clouds I guessed we were not even near cloud top at the time we went through them and the last cloud that we sampled for so long topped out at around 10,000 or 11,000 ft.
PH: Okay, Ron.
RF: Well, I was pretty much just the bag man on this flight. We did get one filter sample up in that cleaner area. Not much to say about it. It was all pretty steady all the way back to Porto Velho. Good set of 47 Teflon, mercury and MOUDI for Paulo that's been running for the entire flight. And a lot of real interesting hot and cold DMPS spectra.
PH: Okay. Ray?
RW: You know, just looking out at this haze, it really looks likes it's hydrated, you know, visually. And the humidigraph isn't showing anything. And I did an experiment with the CE nephelometer, since we're not using the extinction cell in this stuff, where I varied the flow so that it was running at near ambient RH, which is close to 100%, and in a very low flow which dries the aerosol out and I get about a 50% increase in scattering based on that, which is sort of what you would expect. So I think I will continue to run the CE nephelometer unless we do individual plumes. Other than that, I took lots of bag samples and "no-bag" samples.
PH: So you think the humidigraph is not doing its job?
RW: Well, the other nephelometers show a variation of scattering with relative humidity, ambient relative humidity. It's easy to turn that on and off. But with the ramped relative humidity in that, there just doesn't seem to be anything.