Month: September 2017

by Kristina Pistone / NASA Ames Research Center /

I’m not gonna lie: field work is probably my favorite part of the job as a scientist. Aside from my personal interest in visiting new places and cultures, having firsthand experience in data collection is valuable for when we return home and start doing the hard work of interpreting our observations to understand new things about Earth’s climate. While it’s often physically and mentally exhausting, being in the field provides a context that is difficult to get even from the most thorough notes by colleagues.

Thus, I was very excited to be able to participate in the ORACLES-2017 deployment in São Tomé, a tiny island in the crook of Africa’s arm, where we flew NASA’s Orion P-3 aircraft to understand how pollution affects clouds in this region. My colleagues Kirk Knobelspiesse and Michael Diamond have already posted a couple of great pieces, which include an overview of ORACLES, the general science questions we are studying, and how we go about doing that in the middle of the Atlantic Ocean.

I work primarily with 4STAR, the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research, a pretty cool instrument which we use to learn about pollution in the atmosphere. (See a more detailed post about the instrument here.) For 4STAR, deployment involves not only having an operator on every flight to make sure the instrument is in the right mode at the right time, but also cleaning and calibrating it before and after each flight to make sure everything is going as expected and that we’re able to process and interpret the data when we get home.

Of course, despite months and even years of planning and organization, sometimes field work doesn’t go quite as expected. It’s a huge feat to pull off a massive, international, multi-institutional observing campaign, especially when it’s happening on the other side of the world and in a country where the infrastructure, where it even exists, is less well-maintained than we’re used to in the United States. Even with an excellent logistics team (which we had) things can still go wrong: shipments are delayed, the weather doesn’t cooperate, hardware suddenly fails for no apparent reason and then, right as you’ve fixed it, something different breaks. Part of the job is to make things work in the face of unexpected challenges. ORACLES-2017 was no exception. While we’ll be processing and analyzing the data we collected for months to come, there were some notable ordeals.

When I arrived in the second half to relieve my colleagues, the team had already had to deal with several mechanical issues that, while minor, meant that in the name of safety we couldn’t fly on the schedule that was initially planned. The team had to develop a new flight schedule on the fly, so to speak, while still taking into account how the atmospheric conditions changed from day to day so that each flight maximized the amount of data toward our science goals.

Instruments break. When the aerosol mass spectrometer’s (AMS) instrument power supply died with three flights still remaining, we were able to get the system working again by opening 4STAR’s spare computer and donating its power supply to the other instrument team (known as HiGEAR, since they’re from the University of Hawaii and scientists love acronyms). It ended up being functional if inelegant, due to the slightly different sizes of the two computers.

On one of our non-flying days we walked to the equator, which ran south of where we were staying (a change from flight days, when we would fly over it on our way to sample clouds). A couple of locals ended up walking along with us and between their limited English and my broken Spanish-inspired Portuguese and a lot of gesturing towards the ORACLES logo on other team members’ t-shirts, I tried to explain what exactly we were doing in their country: why we’re measuring pollution and clouds, why particularly São Tomé is the place we chose to come to measure these conditions, and how understanding the conditions of ORACLES is important to our broader understanding of Earth’s climate.

I’m not sure I got all the way through those points, but I hope it was at least partially intelligible, as part of our job as scientists is to convey to non-scientists why what we do is important. And having conversations with people who otherwise might not be exposed to Earth science is particularly important to me since we all live on the same planet, and as recent events have sadly reminded us, what goes on in Earth’s climate system often has very immediate impacts on people’s lives.

One final note: a lot of us scientists, despite being Earth scientists, were super bummed to miss out on the North American eclipse last month. I think it led to a couple hours of computer screens looking like this:

But did you know that São Tomé and Príncipe played a role in another scientific eclipse event? It was one of the locations to which scientists traveled in 1919 to make observations during a different total solar eclipse that would then be used to verify Einstein’s theory of general relativity. It’s amazing to think that a hundred years ago there were scientists who probably had to overcome their own field work challenges very near to the places we were staying. Just another reminder of how global an endeavor this thing we call science is.

by Michael Diamond / SÃO TOMÉ & PRÍNCIPE /

In August, dozens of scientists from across the United States descended on the small island nation of São Tomé and Príncipe. Nestled on the equator off the coast of western central Africa, São Tomé was an ideal location to study the phenomenon we had all gathered to observe: a seasonal plume of smoke from agricultural and forest fires that gets lofted by the prevailing winds from the African continent to over the southeast Atlantic Ocean. As part of the NASA field campaign Observations of Aerosols above Clouds and their Interactions, or ORACLES, our aim was to better understand how all that smoke over the ocean affects the amount of sunlight that gets absorbed in the atmosphere and at Earth’s surface.

Aerosols—small airborne particles, like smoke, desert dust, and sulfates from power plants—affect the amount of energy the southeastern Atlantic Ocean gets from the sun, not only by absorbing and reflecting sunlight directly, but also through its effects on clouds. A large expanse of very bright low clouds covers much of the southeastern Atlantic, very similar to the clouds off the coast of California that create San Francisco’s characteristic fog. Smoke can change the properties of these clouds in various ways, including brightening the clouds by creating lots of small droplets, which, interestingly, make the clouds less likely to drizzle and thus stick around for a longer time. Both of those changes allow the clouds to reflect more sunlight, creating a cooling effect.

As anyone who’s been outside on an overcast day knows, clouds play a major role in regulating the amount of the sun’s energy that gets to Earth’s surface, so any changes in the clouds over the southeast Atlantic and those like them across the globe can have big implications for Earth’s energy balance. It is well-known that the heat-trapping effect of man-made greenhouse gas emissions have led to a net warming over the 20th and early 21st centuries. However, unresolved scientific questions about the potential cooling effects of aerosol-cloud interactions over the past century represent a large fraction of the uncertainty in estimates of how much humans have affected the present-day climate.

For ORACLES, NASA’s P-3 Orion aircraft was our primary transport for measuring the smoke-cloud system. On the P-3 we have a set of instruments that can be broadly separated into two categories: in-situ and remote sensing.

In-situ instruments, like those in the picture collage below, measure things in place through air inlets. For example, we have particle counters that can measure the number and size of smoke particles in a plume, and cloud probes that can measure how much liquid water is in a cloud.

In contrast, remote sensing instruments sense things remotely; that is, they tell us about the properties of clouds and smoke from far away, like how we use a telescope to observe stars. In our case, we use instruments like a radar to look at precipitation and a lidar (a laser that provides information about a what’s between the plane and the ground) to look at the smoke plume’s structure.

Of course, the in-situ instruments that measure clouds aren’t much use when flying through smoke above the clouds, and when we fly high to get good lidar profiles, we can’t get in-situ smoke measurements. In addition, some of the remote sensing instruments don’t work well when high clouds are present, and the smoke and low clouds aren’t always in the same place from one day to the next. How do we balance all these competing objectives to produce a flight that collects high-quality, usable data? That’s where the forecasting and flight-planning team comes in.

As a graduate student at the University of Washington in Seattle, my role in ORACLES is to look at model forecasts from computer simulations and satellite imagery and then use flight-planning software to create flight plans that will meet our scientific objectives. On what we call routine flights, that mostly means picking altitudes and aircraft maneuvers rather than locations, because for these flights we always stick to the same north-south track to build up statistics that can be used to compare our observations with various computer models.

One example of the choices that have to be made here is whether to do stacked legs, in which we fly over the same location at different heights, or sequential legs, which let us cover more ground because we don’t need to backtrack and instead gives us observations at slightly different locations that might be harder to interpret. A similar choice has to be made when we switch between altitudes: we can ramp down and cover a lot of ground, or do a square spiral and get a vertical profile over the same location.

Time-lapse video of a square spiral maneuver over a relatively uniform field of low clouds during the August 24^th routine flight. About 10 minutes elapse in the span of this video. Video credit: Michael Diamond.

The other type of flight we call a flight of opportunity, in which we have more latitude in choosing our flight location to sample interesting features, or to avoid pitfalls like high clouds, that are identified by the models.

We were also able to combine flight plans so that the flights of opportunity could resample air that we observed a day or two earlier. Ideally, to study how the smoke evolves during the course of its journey over the Atlantic, we would be able to follow it as the winds push it westward and downward over a period of days. Unfortunately, this is not at all practical in an aircraft with nine hours’ worth of fuel. Instead, we can run a weather forecast model to predict where the air we sampled during a routine flight will end up in a few days. Then, like an advanced game of connect-the-dots, we can design our next target of opportunity flight to hit the right location and altitude to resample that air to see how it’s evolved.

Our August 17 flight of opportunity was a bit special because, rather than return to São Tomé, the P-3 landed on Ascension Island in the middle of the South Atlantic Ocean so we could do some joint flights with a British team studying similar science questions. On the way to Ascension, we planned our track to intersect the new (forecasted) locations of a few different smoke plume air parcels that we sampled on August 15.

Now that the 2017 ORACLES deployment is over, the task ahead of us will be to analyze the data we collected in flights like the August 15-17 resampling mission to produce new scientific insights into this unique smoke-cloud system. Within a year, all of our data will become public at https://espoarchive.nasa.gov/archive/browse/oracles so that other researchers across the country and around the world will be able to contribute their own research and generate new ideas and solutions. The data from last year’s deployment, which took place in September and was based out of Walvis Bay, Namibia, is already available. However, we’re not done with data collection just yet: We’ll be heading back into the southeast Atlantic next year for one last deployment, this time in October to characterize the end of the southern African fire season.

A view from the window of the P-3. A layer of smoke is visible over patchy clouds. This is somewhere over the Atlantic Ocean, quite possibly near the [0˚, 0˚] point, where the Prime Meridian crosses the Equator. Credit: NASA/Kirk Knobelspiesse

by Kirk D. Knobelspiesse / SÃO TOMÉ & PRÍNCIPE /

We can’t build a scale model of planet Earth to study in a laboratory, but we can on a computer. But how do we know a computer model we’ve built is right—or even how to build it in the first place? For atmospheric scientists like myself, the answer is measurements: from satellites, from instruments on the ground, and from airplanes.

This is how I find myself on the small African island of São Tomé, curled up inside the ‘bomb bay’ of a NASA P-3 aircraft pouring liquid nitrogen into a specialized camera called the Research Scanning Polarimeter (RSP). This is a long way from home: I work at the NASA Goddard Space flight center in Greenbelt, Maryland.

So, why São Tomé? We’re pretty close to a phenomenon that beguiles climate models and is difficult to observe by satellites – so we need to fly there instead. It all starts with ocean currents, which bring cold, deep ocean water to the surface (known as upwelling). There’s a strong current off the southwest coast of Africa called the Benguela current. The upwelled water, in turn, causes a low, semi-permanent cloud deck to form at certain times of the year – much like June Gloom in Southern California, for example. From a climate perspective, these clouds can be cooling because they reflect the sun’s energy back to space. What’s unique about where we are is that there is a tremendous amount of biomass burning nearby in sub-Saharan Africa, from both agricultural fires and natural forest fires. The smoke from these fires gets blown west, out over the clouds.

Atmospheric scientists call suspended particulate matter “aerosols”—and smoke is a type of aerosol. When suspended above clouds, aerosols can do a couple of things that impact climate. Most directly, smoke aerosols make the clouds look darker, meaning that less of the sun’s energy is reflected back to space. But the aerosols can also modify cloud properties by serving as seeds for cloud droplet formation, for example, or modifying the temperature of the atmosphere, changing how clouds form.

We know all of these things happen, and we include them in our climate models. The uncertainty boils down to how often they occur, and to what magnitude. The root of the problem is that we don’t have all the measurements we need. Satellites provide a nice snapshot, and many of our colleagues at NASA and elsewhere develop instruments especially devoted to the measurement of clouds and aerosols. They don’t, however, simultaneously measure all of the things we need to know, such as the optical and chemical properties of smoke and its exact location, or smoke in the act of modifying cloud properties.

This is why field campaigns, which make targeted observations to resolve specific scientific questions, are so important. I’m here as part of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign. (Yes, we love our tortured acronyms.). Last year, we sent two airplanes stuffed to the gills with instruments to Walvis Bay, Namibia, and we flew northwest to our area of interest. This year, we’re flying south and west from São Tomé. We’ll return again next year.

This year we’re working with one aircraft: the NASA P-3. The P-3 is a four-engine turboprop designed as a maritime surveillance aircraft for the US Navy. It is ideal for our purposes because of its endurance, size and ability to fly at very low altitudes. We have a wide variety of instruments on the P-3. Some are in situ, meaning they sample the air as the P-3 flies through a cloud or the aerosols, and they tell us size, chemical composition, and other information specific to the aircraft location. Others are remote sensing instruments, meaning they observe the scene from a distance (usually above). Examples include a downward looking precipitation radar, or a lidar, similar to a radar but using a pulsed laser beam instead of radio waves.

The Research Scanning Polarimeter (RSP) also falls in the remote sensing category. It is a passive scanner, meaning it makes a measurement of light reflected from a location under the aircraft at many different angles. One thing we’re looking at is the cloud bow, which is similar to a rainbow, but involves refraction of light from cloud—not rain—droplets. Precise measurements of the cloudbow can tell us the size of the cloud droplets at the top of a cloud, which in turn indicates the cloud meteorological state, whether or not the aerosols are interacting with the cloud, and so forth. We can also determine optical properties of aerosols above the cloud, but analysis of the data requires lots of computing power and can’t be performed easily in the field. My primary role in ORACLES is to improve this analysis, and along with my colleague, Michal Segal Rozenhaimer, we’re looking into using a type of artificial intelligence to “train” a computer to analyze our data.

This is largely done at home, so here in the field my job is to be one of the team members that ensures the RSP is working properly. This means operating the instrument in flight, participating in creating flight plans, and, yes, periodically pouring liquid nitrogen inside. (The instrument sensors work best when they’re very cold.) So even if the “bomb bay” is cramped and noisy, and I’m quite literally thousands of miles from home, I feel very fortunate to be here and a part of this field campaign.