Happy Earth Day! Sometimes it's a good thing to have your head in the clouds, especially when you're researching the global climate

NSF's Weather or Not!

Happy Earth Day! Sometimes it's a good thing to have your head in the clouds, especially when you're researching the global climate

National Science Foundation


Heading to the clouds! How studying stratocumulus clouds makes for an interesting flight

Interviewer: Charlie Heck

Interviewee: Bruce Albrecht

Charlie: Cali to Hawaii -- a sweet, 8-hour (give or take) flight to paradise, aboard a National Science Foundation Gulfstream V. We’re going up, up and away with University of Miami Professor Bruce Albrecht and his research team as they head to the clouds, specifically stratocumulus clouds.

Bruce: All in all these kinds of clouds cover about 20 percent of the Earth's surface. And so what that means is they're very important because they reflect the solar radiation back to space.

Charlie: It’s been nearly 40 years since Albrecht took his first measurements of clouds off the California coast. This time he returned equipped with new, state-of-the-art technologies to understand the effects of low-lying clouds on global climate.

Bruce: The low-lying clouds that we're mostly talking about are over the ocean. And they are usually within the lowest two kilometers or 6,000 feet. And in particular the stratocumulus clouds, the lumpy looking clouds that you see often off the coast of California. Their tops are pretty low, around a kilometer, a kilometer and a half and they're very good reflectors of solar radiation. These kinds of clouds cover about 20 percent of the Earth's surface. And so what that means is they're very important because they reflect the solar radiation back to space.

These stratocumulus clouds transition to more broken clouds and less cloudiness. And so this most recent experiment that we were involved with was actually looking at that transition from the stratocumulus to the broken cumulus clouds. And, as I mentioned before, these clouds are important because they're climactic impact that is a reflection of solar radiation. So as they transition from solid to the broken clouds it changes that whole amount of energy that's reflected back. And the models themselves, large scale forecast models, weather models and climate models have a very difficult time in really capturing that transition from those cloud types. So that was our goal was to try to study that transition from the solid clouds as it flows towards the equator and towards the West, at least in the Pacific, that we have this transition from the solid to the broken clouds.

And in that transition there's some important processes that go on. And one of the things that we actually sort of discovered back in the 1976 I guess with our first flight, that these little clouds, even though they're shallow and they're low, they can produce precipitation. And you wouldn't really expect that. Particularly over land you don't see that in those kind of clouds. But over the open oceans you see this precipitation that falls out. And we know that that precipitation is also affected by aerosols, the particles on which clouds form. And so our work has really looked at this transition from the point of view of, one, as the air mass moves it changes its surface temperature, it changes, its wind changes, other factors change. But the aerosol content on which the clouds feed also changes as we go downstream.

Charlie: Things have changed a lot, technology wise, since his first dance in the clouds, not the least of which is the aircraft his research team used to collect their observations and data:

Bruce: A luxury business jet that the National Science Foundation has actually, had it built and built in such a way that it could be a research aircraft. So it has special capabilities that a regular Gulf Stream V wouldn't have. So we've given up the luxury seats, and we've put in all kinds of instruments and other places where observers can go and sit on the aircraft and follow along on the mission. And the important thing about that is that this aircraft, although it's designed mostly to fly upper altitudes, it can also do work at the lower levels, the lower altitudes.

Charlie: A typical flight takes between 7-and-a-half to 8 hours for the team. They spend around 4 hours at the low level, which is about 500 feet above the surface. But the aircraft performs better at higher altitudes so the plane dips down to sample the clouds then pops back up to perform at its best. And how does it perform at its best? Well there’s a ton of great technology onboard, two things in particular: cloud radar and LIDAR or High Spectral Resolution Lidar.

Bruce: Most radars that we are accustomed to, if we see something from our news forecasts or weather forecasts or on the news are radars which detect precipitation. But the radar that was on this aircraft-- and there had been other radars like this before, but this was really the first time we've had it on this particular aircraft that is sensitive to clouds. So it can see these little clouds that you see and on a typical weather radar would not see those clouds because they wouldn't have the sensitivity needed to detect those clouds. At the same time that same layer can also see the precipitation that's in the shallow clouds. So we get a really nice picture of the clouds and precipitation.

In addition, because it has what we call a Doppler capability, it can also look at the velocity structure, the ups and downs in the cloud itself. So we can look at that turbulence that is inherent in these clouds. And then couple with that we had a light air system, which could also detect aerosols and could also look at the cloud boundaries. And so by putting that together with the radar and the LIDAR, we get a really nice picture of these cloud systems. And the nice advantage of these systems is that you don't have to fly directly in the clouds. So when we're flying above the clouds we would have the radar and the LIDAR looking downward and sampling the clouds below us.

And we discovered a couple things -- one is that some of these clouds are very, very efficient precipitators. That is that most of the water that's condensed just falls out in the form of precipitation. So the visual cloud that's left is sometimes these thin gray clouds that we really didn't even detect very much from satellites before. So the system is a little more complicated than we sort of in our...schematic of how that transition occurs. And so that was really sort of an eye-opener to all of us, each of us as we went on our missions. We had that same observation. Oh, look at these little shallow clouds that are still here, and everything else below is kind of rained out of it. And so this was sort of an eye-opener for us. And it also comes back to this idea of the interaction between aerosols, clouds and precipitation because associated with those clouds that we saw, the air was extremely clean. So when the clouds rain they take all the aerosols basically and kind of wash them out. But they were cleaner than we kind of anticipated. You know, it’s like how can they be so efficient in actually making the air so clean in that process?

Charlie: Okay, let’s recap: Albrecht and his team are studying clouds -- these really important, effective precipitators. The team is using an NSF-funded research plane, with exciting new technology. So what’s a “day in the life” of this research mission and just how big is this team?

Bruce: Well, behind the scenes there's a fairly large crew that's involved. So, when we do a mission, there are a couple aspects of it. The first before the mission starts, we have to prepare the aircraft and all the instrumentation. So that goes on a few months before the whole mission started. And that involved all the people at the National Center for Atmospheric Research who operate this National Science Foundation GV aircraft. And so those people are behind the scenes, and they also will go out in the field. Maybe not be flying, but they're on the ground so if something happens to one of the instruments or we have to calibrate or we have to do something special that they are there and available as our technical help. Now some of those people who are involved with the instruments also fly on the airplane.

We had someone who would operate the LIDAR. We had someone who would operate the radar. So they weren't the scientists, but they were the engineers and technicians who had helped develop these observing systems. So they were on the aircraft. So on the aircraft itself, so then they're on there. But then we have-- so maybe two-- I think there's three people who are basically in that capacity. And then we have two scientists on board who would take notes and direct the flight. And then there were two pilots. So the aircraft itself when it's fully loaded with equipment doesn't really haul that many people.

But at the same time, as I said, there's a big crew that's really behind it in terms of supporting the observations. And from the scientific perspective, a very big thing that we have to do first is plan the mission. So where are we going to fly? And then once we get to Hawaii we want to sample the same cloud masses again. So we have to figure out where to fly on the way back. So we have to make those predictions. So that was done. We had a graduate student who was working at the University of Washington. And he has these models developed, which would sort of predict our trajectories for the air masses. So the air mass starts here at this time, and two days later it's going to be at this point over here where we can sample it.

Bruce: So then we would make that official prediction the day before and then decide where we were going to fly the aircraft. So that all had to be done with a whole group of us making these decisions as to where the aircraft is going to go. So, that's why I say the number of people involved is actually fairly large considering that there's only six or seven people who are actually on the aircraft as it makes the mission. And then as the aircraft, as I said before, is taking observations, those observations are sent back to the crew that's on the surface to the scientists there at the ground station. And they will receive that information and can look at that information. And they can also check via satellite with the scientists onboard. So if they see something that they say this is particularly interesting, can you modify flight plan appropriately to sample that, then that chat goes back and forth.

Bruce: As people see exciting things like these thin gray clouds, which we hadn't seen before, there was a lot of chat going on as to this is what's going on, it's really exciting. And also the people on the ground could actually see what the radar and the LIDAR were observing. It was a little bit delayed. It was like four or five minutes. But we could still see those patterns as they were coming across. So a lot of people are involved in the mission itself even though there's only a limited number that can be on the aircraft.

Charlie: Albrecht was present on two round-trip flights. So I’ll let him tell you his favorite part of the ride:

Bruce: Well, I think the most exciting thing that we saw was really from our -- we were watching the radar returns, and we were getting in there. And we could see that these clouds which we were thinking were, you know, had a certain structure to them, but they looked like little tiny thunderstorms in terms of their extent and the amount of precipitation. But they were only just these little shallow clouds. And so we were sort of really taken back by that. And I remember back my first flights I did were in 1976 when I first studied these clouds. And at that time we didn't have all this very sophisticated instrumentation. And we couldn't even see the data in real time. But I remember seeing water coming on the windshield of the airplane. This was an Electra aircraft, a four engine jet. And that was like a real big eye opener to us. We said, "Whoa, look at this." There's this water coming in here. There's all this precipitation in here, and these are just these little tiny shallow clouds. And so the experiment for that was in 1976. So then we go ahead to 2015, which is almost 20 years ago-- 20 years later. More than that. How many is that? 40 years.

Charlie: [laughter] 40 years.

Bruce: [laughter] I've been doing this too long, you know. And, again, now instead of looking at the water on the windshield, we had these radars which are showing us this precipitation which we really hadn't had a chance to look at before. So for that it was really an eye opener, exciting. So it's not like the guys who are flying through a tornado and say "Oh, I just nearly flew through a tornado." But for us excitement is in a different way with these clouds that are such efficient precipitators.

Charlie: That was Bruce Albrecht, he is a professor at the University of Miami. Nearly 40 years after taking his first aircraft measurement of clouds off the California coast, he returned, along with a pretty impressive team and state-of-the-art plane and technologies to explore the effects of low-lying clouds on global climate.

Albrecht says a few researchers were instrumental in the planning and implementation of this project and I’m always one to honor a shout out request, so here goes: members of the team include Pakita Zwydema at the University of Miami, Chris Bretherton and Robter Wood at the University of Washington and Virendra Ghate at the Argon National Laboratory.

I’m Charlie Heck, co-editor of the Science360 News Service and co-host of the Super Science Show, at the National Science Foundation.
If you have any questions about this story or suggestions for interviews about super cool NSF-funded science, send me an email before I schedule my summer vacation -- California’s looking pretty dreamy right about now! Email me at editor@science360.gov.