November 8, 2017, 07:13 PST

ACT-America: Settling into the rhythm of the field

By Hannah Halliday / SHREVEPORT, LOUISIANA

A C-130 gets a checkup after a flight. A dedicated flight team keeps the aircraft running and maintained. Credit: NASA/Hannah Halliday.

A C-130 gets a checkup after a flight. A dedicated flight team keeps the aircraft running and maintained. Credit: NASA/Hannah Halliday.

Fieldwork is my favorite part of my job. I have been working as a postdoc at NASA’s Langley Research Center in Hampton, Virginia, for a few days over a year, and I’m still not over the excitement of arriving somewhere new, ready to take measurements and run our instruments.

My background is in chemistry, but I slid into meteorology because I wanted to apply myself to environmental issues that had global impact. That decision put me on a path into the world of air quality research, and ultimately to NASA to work with airborne science. While I’m still new to flying for science, I love working with instruments and taking measurements. Being on an aircraft turns that feeling up to 11.

plane view
The C-130 doesn’t have many windows, but Halliday is lucky to have one beside her seat. Flights often have low-altitude runs, and offer views of the country from unique angles. This is a view of the Mississippi River from the Sunday, Nov. 5, flight. Credit: NASA/Hannah Halliday.

Atmospheric Carbon and Transport-America, or ACT-AMERICA, has been an especially cool project to be involved with because I earned my Ph.D. at Penn State, where principal investigator Ken Davis and other members of the ACT-AMERICA planning team are based. Working with ACT-AMERICA is part serious work and part fun reunion, working with people I know well on a totally new subject and project. I got to fly with the mission last spring, and I’ve come back to join them again for two weeks in Shreveport, Louisiana.

On Saturday, Nov. 4, we took a break from flying to do instrument work and maintenance. For my group, which is tasked with the Atmospheric Vertical Observations of CO2 in the Earth’s Troposphere, or AVOCET, in-situ measurements, that meant calibrating our instruments. When we calibrate, we send our instruments gases that have a known concentration and record what our instruments measure. Doing this regularly allows us to keep track and correct for the instrument drifting over time, and to maintain the accuracy and precision of our measurements.

Our two aircraft, a C-130 and a B-200, are stored in different locations when we’re at our ground sites. The calibration gas tanks are heavy, so for ease of use we’ve built our calibration gas cylinders their own little cart that they live on, which can be towed from one location to another. The cylinders are left on the cart, where we put a regulator on the calibration cylinder we want to use and run a tube into the airplane. It’s a simple solution that lets us easily and quickly use the same calibration gases on two different aircraft.

Hannah Halliday monitors incoming measurements.
Hannah Halliday, right, monitors incoming AVOCET measurements during a Nov. 2 science flight. Next to her are Theresa Klausner and Max Eckle, Ph.D. students with the German Aerospace Center, DLR, which has joined the fall flight campaign to test an instrument that measures methane and ethane. Credit: NASA/David C. Bowman.
Researchers talk during a flight.
Bianca Baier, a postdoctoral researcher with NOAA’s Earth Systems Research Lab in Boulder, Colorado, and Ken Davis, ACT-America principal investigator from Penn State, talk during a flight. Credit: NASA/David C. Bowman.

One of the reasons I love working in science is that our measurements and our work is built on a heap of clever solutions to small problems. While we also stand on the shoulders of scientific giants who had deep insights into the workings of the universe (for instance, Isaac Newton realizing that the gravity affecting an apple also affects the stars), in our day-to-day work we use the cleverness of the people who worked out the universal swage fittings, or the person who figured out how to set up our inlet system to bring air in from outside the plane when we’re at high altitude.

Calibration gas cylinders
Calibration gas cylinders on their transportation cart. During a calibration, scientists use three gases with low, middle and high concentrations, and use this information to understand how the instrument will behave when it “sees” gases in the environment. Credit: NASA/Hannah Halliday.

We’re not all brilliant all the time, but by looking at a problem long enough we can often find a clever solution to a small vexing problem (such as how to quickly transport our calibration cylinders), and that’s where our progress comes from.

On Sunday, Nov. 5, we flew a science mission, measuring the inflow of air from the Gulf of Mexico. It was a busy day for me, because I was both tending my group’s instruments and also taking flask samples for the National Oceanic and Atmospheric Administration (NOAA). NOAA uses glass-lined containers to trap air at specific locations on the flight track. They take these samples back to their lab in Boulder, Colorado, where they measure the greenhouse gases as well as other molecules that help determine whether samples were influenced by other sources, such as traffic or wildfires. My job was to follow their sampling plan, telling their mostly automated system when to collect a sample and coordinating with our in-flight calibrations.

Specialized inlets draw air into the instruments and have different designs based on the needs of the instruments.
Specialized inlets draw air into the instruments and have different designs based on the needs of the instruments. These inlets are located near the front of the aircraft so they don’t sample the exhaust from the engines. Credit: NASA/David C. Bowman.

The flights can be quite busy, and it’s a full day of activity. For the four to five hours that a typical science flight will last, we have an additional three hours of flight prep before we take off, and a debriefing meeting once we land, plus data workup and archiving the preliminary data once we’re back in our hotel rooms.

It’s satisfying work, but it’s important that we have non-flight days like Saturday to catch up on our instrument maintenance as well as personal things—exercise, laundry, even sleep. When we’re in the field there’s no set schedule like when we’re in the office, and it’s important to grab that time when we can, because flight days depend on the weather, and a good measurement day waits for no scientist, not even when they have a plane!

This piece was originally published on the NASA Earth Expeditions blog.

November 3, 2017, 07:12 PDT

ACT-America: Waiting for the great big teaspoon in the sky

By Joe Atkinson / SHREVEPORT, LOUISIANA

ACT America group with the B200 King Air and C130 Hercules in Shreveport, Louisiana. Credit: NASA/David C. Bowman.

ACT America group with the B200 King Air and C130 Hercules in Shreveport, Louisiana. Credit: NASA/David C. Bowman.

Brrrr.

I don’t know what I was expecting from Louisiana in late October, but I definitely wasn’t expecting cold and damp.

I’m here for the final leg of the fall 2017 flight campaign for Atmospheric Carbon and Transport-America, or ACT-America, a five-year NASA study looking at the transport of carbon dioxide and methane by weather systems in the eastern United States.

This is the third flight campaign of the study and the team has just arrived in Shreveport—home base for the next two weeks. Flight operations will be based out of Shreveport Regional Airport. Sleep operations are based at a hotel just a few minutes down the road in Bossier City.

NASA Langley B200
The NASA Langley B200 sits in a hangar at Shreveport Regional Airport. The B200 and the C-130 won’t fly today because the weather pattern is too similar to the one they flew through the day before. Credit: NASA/David C. Bowman.

As I’ve already mentioned, the weather so far is pretty meh. There’s a slow-moving front to thank for that. But more on the creeping front later on. First, a little taste of ACT-America’s home for the next couple of weeks.

Shreveport is the largest city in Ark-La-Tex, a region that includes Northwestern Louisiana, Northeastern Texas and South Arkansas. It and Bossier City are divided by the Red River. Shreveport is on the west, Bossier City the east. Casinos dot the riverbank—the Horseshoe, Boomtown, Eldorado, Margaritaville, Diamond Jack’s.

It’s no big surprise that you can’t go far here without finding restaurants that have Cajun and Creole dishes on the menu. The first night in town, a contingent from the ACT-America team visits the Blind Tiger in downtown Shreveport. Steaming plates of crawfish etouffe come out of the kitchen accompanied by crusty homemade croutons and mounds of rice. There’s a dish called Cajun fried corn—breaded, deep-fried corn on the cob. Louisiana beers are on tap. Gumbo is spelled gumbeaux.

The State Fair of Louisiana is taking place in Shreveport. It claims to be the largest livestock show and carnival in the state. Rick Rowe, a reporter with the local ABC affiliate, does a segment on the morning news with a man who sells fried cheese at the fair. Rowe samples a cube that’s just been pulled from the bubbling hot oil and sounds positively ecstatic as he bites through the crispy breading.

Unloading equipment and supplies
Although there won’t be a flight today, there’s still work to do. Here, Yonghoon Choi, an instrument investigator from NASA Langley, and Max Eckle, a Ph.D. student with DLR, the German aerospace agency, help unload equipment and supplies that have been trucked to Shreveport from the previous ACT-America home base in Lincoln, Nebraska. The fall flights are giving the DLR a chance to see how their methane- and ethane-detecting Quantum Cascade Laser Spectrometer operates in the field, while also allowing the ACT-America scientists to better zero in on methane sources. Credit: NASA/David C. Bowman.

The state fair isn’t the only thing going on, though. Another news segment has a meteorologist visiting a Bossier City shop that sells power equipment: lawnmowers, leaf blowers, generators, chainsaws. They have an event coming up called Sawdust Days. Folks who show up for Sawdust Days will be treated to a special demonstration by a man who does wood carvings with a chainsaw.

“He’s carved a lot of pieces right here,” the shop owner says, gesturing to a rustic-looking wooden bear that towers over him and the meteorologist, “so he’s pretty good at it.”

I turn off the TV and head to the airport to catch up with another guy who knows something about meteorology—Ken Davis, principal investigator for ACT-America and a professor of meteorology at Penn State University.

Weather is critical to ACT-America. In fact, it’s the reason that, on its first full day in Shreveport, the campaign is keeping its C-130 and B200 aircraft on the ground. Just the day before, as ACT-America moved from its previous home base in Lincoln, Nebraska, to Shreveport, the aircraft passed through the very front that’s inching through Louisiana now, bringing the chilly air and rain along with it. Instruments on both aircraft measured carbon dioxide and methane levels during the transit.

“This weather is relatively similar to what we documented yesterday,” Davis says. “If we measured it yesterday, we don’t need to measure it today.”

What the team will want to measure, though, is what happens to the greenhouse gases after the cold front stalls not too far south of Shreveport. There, it’ll get a push from warm, low-level air flowing in from the Gulf of Mexico and then move northeast as a warm front.

It’s a scenario that may take a couple of days to play out, so the next research flights may happen tomorrow, they may happen the day after tomorrow. The atmosphere will do what it wants to do, thank you. Davis likens it to a big cup of coffee.

“Over the timescale of days,” he stretches out days when he says it, “somebody’s stirring it with a great big teaspoon. And you’ve got to wait … every stir takes a couple of days. We want to measure different parts of that.”

Late night planning meeting
Hannah Halliday, left, a postdoctoral researcher at NASA Langley, and Bianca Baier, a postdoctoral researcher at the NOAA Earth System Research Laboratory in Boulder, Colorado, point out to Ken Davis a region where fires might make for interesting measurements. Credit: NASA/David C. Bowman.

Later on, at a planning meeting, they make the final decision—another down day tomorrow, then a flight the next day when the great big teaspoon in the sky has finally mixed things up just so. It’ll be a good day for airborne science.

The meeting breaks up. Folks head back to their hotel rooms.

With a free evening in front of me, I think about taking a chilly walk down the bank of the Red River to get a look at the Shreveport skyline at night. And for some reason, I’m craving a piping hot cup of coffee.

This piece was originally published on the NASA Earth Expeditions blog.

October 4, 2017, 14:16 PDT

Searching for the bluest blue

By Joaquín E. Chaves-Cedeño / South Pacific Ocean

The crew prepares to deploy the radiometer from the stern of the R/V Nathaniel Palmer to measure the optical properties of the water from the surface down all the way down to the bottom of the photic zone. Credit: Lena Schulze/FSU.

The crew prepares to deploy the radiometer from the stern of the R/V Nathaniel Palmer to measure the optical properties of the water from the surface down all the way down to the bottom of the photic zone. Credit: Lena Schulze/FSU.

It doesn’t take a lot of technology to see that the ocean is blue. And when it comes to the blueness of the ocean, it doesn’t get much more blue than where I am. My current home and office is the research vessel Nathaniel B. Palmer—the largest icebreaker that supports the United States Antarctic Program—which is on an oceanographic expedition across the South Pacific Ocean. On this voyage, however, the Palmer hasn’t broken any ice.

Our Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) P06 campaign departed Sydney, Australia, on July 3, and successfully ended the first leg of this journey on August 16 in Papeete, French Polynesia, also known as Tahiti. This is where our team from NASA Goddard Space Flight Center (Scott Freeman, Michael Novak, and I) joined dozens of other scientists, graduate students, marine technicians, officers and crew members for the second and final leg that ended in the port of Valparaiso, Chile, on September 30.

The GO-SHIP program is part of the long history of international programs that have criss-crossed the major ocean basins, gathering fundamental hydrographic data that support our ever growing understanding of the global ocean and its role in regulating Earth’s climate, and of the physical and chemical processes that determine the distribution and abundance of marine life. This latter topic regarding the ecology of the ocean is what brings our Goddard team along for the ride.

The P06 ship track, for the most part, follows along 32.5° of latitude south. That route places our course just south of the center of the South Pacific Gyre—the largest of the five major oceanic gyres, which form part the global system of ocean circulation. The Gyre, on average, holds the clearest, bluest ocean waters of any other ocean basin. This blueness is the macroscopic expression of its dearth of ocean life. We have seen nary a fish or other ship since we departed Tahiti (as this is not a major shipping route). Oceanic gyres are often called the deserts of the sea. On land, desert landscapes are limited in their capacity to support life by the availability of water. Here, lack of water is not the issue. Water, however, is at least the co-conspirator in keeping life from flourishing. Physics, as it turns out, is what holds the key to this barren waterscape.

MODIS chlorophyll concentrations indicating phytoplankton, with the R/V Nathaniel B. Palmer’s ship track superimposed
This map shows MODIS chlorophyll concentrations indicating phytoplankton, with the R/V Nathaniel B. Palmer’s ship track superimposed. The deeper blue the color the less chlorophyll there is. Credit: NASA.

Due to the physics of fluids on a rotating sphere such as our planet, the upper ocean currents slowly rotate counterclockwise around the edges of the center of the Gyre—as a proper Southern Hemisphere gyre should—and a fraction of that flow is deflected inward, toward its center. With water flowing toward the center from all directions, literally piling up and bulging the surface of the ocean, albeit, by just a few centimeters across thousands of miles, gravity pushes down on this pile of water.

This relentless downward push puts a lock on life.

The pioneers of life in the ocean, tiny microscopic organisms known as phytoplankton, drift in the currents and grow on a steady mineral diet of carbon dioxide, nitrogen, and phosphorus, along with a dash of iron. (Meanwhile, they expel oxygen gas as a by-product, to the great benefit of life on Earth). Phytoplankton obtain most of their sustenance from the ocean below. What happens in this Southern Hemisphere gyre is that layers of denser water trap the nitrogen- and phosphorus-rich water to depths that are out of reach to most of the phytoplankton. And phytoplankton that do make it to that depth are too starved of sunlight to spark the engine of photosynthesis that allows them to grow.

Why are we here and where does NASA come into this story? Since the late 1970s, NASA has pursued, experimentally at first, and now as a sustained program, measuring the color of the oceans from Earth-orbiting satellites as a means to quantify the abundance of microscopic life. It’s microbiology from space, in a way. Formally, though, we call it “ocean color remote sensing.” Bound to polar orbits that allow them to scan the entire surface of the globe every couple of days, satellites whiz by at several hundred miles above the atmosphere carrying meticulously engineered spectra-radiometers, or cameras capable of measuring the quantity and quality, or color, of the light that reaches its sensors. This is where our work aboard the R/V Palmer comes into the story.

Crew members prepare an optical instrument for deployment over the side of the ship to collect optical measurements
Scott Freeman of NASA works with an R/V Nathaniel Palmer crew member to prepare an optical instrument for deployment over the side of the ship to collect optical measurements. Credit: FSU/Lena Schulze.

The data the satellites beam down from orbit do not directly measure how much plant life there is in the ocean. Satellite instruments give us digital signals that relate to the amount of light that reaches their sensors. It is up to us to translate, or calibrate, those signals into meaningful and accurate measurements of microscopic life, along with temperature, salinity, sediment load, sea level height, wind and sea surface roughness, or any other of the many environmental and geophysical variables satellite sensors can help us detect at the surface of the ocean. To properly calibrate a satellite sensor and validate its data products, we must obtain field measurements of the highest possible quality. That is what our team from NASA Goddard is here to do.

Around midday, typically the time an ocean color satellite is flying over our location, we perform our measurements and collect samples. We measure the optical properties of the water with our instruments to compare what we see from the R/V Palmer to what the satellites measure from their orbit. At the same time that we perform our battery of optical measurements, we also collect phytoplankton samples to estimate their abundance and species composition as well as the concentration of chlorophyll-a, the green pigment common to most photosynthesizing organisms, such as plants. By simultaneously collecting these two types of measurements—light and microscopic plant abundance—we are able to build the mathematical relationships that make the validation of satellite data products possible.

Mike Novack of NASA studies the optical and biological characteristics of sea water samples in the ship’s laboratory.
Mike Novack of NASA studies the optical and biological characteristics of sea water samples in the ship’s laboratory. Credit: NASA/Joaquin Chavez.

The waters of the South Pacific Gyre are an ideal location for gathering validation quality data, perhaps one of the most desirable, because there are few complicating factors and sources of uncertainty that blur the connection we want to establish between the color of the water and phytoplankton life abundance. Our measurements will extend NASA’s ocean chlorophyll-a dataset to some of the lowest such values on Earth.  The water here is blue; in fact, it’s the bluest ocean water on Earth.

This piece was originally published on the NASA Earth Expeditions blog.

September 25, 2017, 07:29 PDT

Up in smoke (and clouds) over the southeast Atlantic

By Michael Diamond / São Tomé and Príncipe

Smoke from small-scale burning on the northern side of São Tomé island. Although burning was prevalent across São Tomé, the vast majority of the smoke in our study area originated from the south-central African continent, in countries like Angola and the Democratic Republic of the Congo. Credit: Michael Diamond.

Smoke from small-scale burning on the northern side of São Tomé island. Although burning was prevalent across São Tomé, the vast majority of the smoke in our study area originated from the south-central African continent, in countries like Angola and the Democratic Republic of the Congo. Credit: Michael Diamond.

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.

Snapshot of the smoke-cloud system over the southeast Atlantic Ocean
Snapshot of the smoke-cloud system over the southeast Atlantic Ocean, taken from the window of the P-3 during the August 24th routine flight. A thick plume of milky-gray smoke overlies a blue ocean surface dotted with puffy white low clouds. Credit: Michael Diamond.

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.

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.

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.

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.

Resampling flight plan example
Example of a resampling flight plan conducted on the August 15th routine flight (dark blue line) and August 17th flight of opportunity (cyan line). The blue gradient lines represent the motion of air parcels first sampled on the 15th (dark blue) and then resampled 2 days later on the 17th (light blue). Black dots represent the location of the air parcels after 1 day. Credit: NOAA Air Resources Laboratory/Michael Diamond.

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.

This piece was originally published on the NASA Earth Expeditions blog.

September 19, 2017, 08:25 PDT

Weather or climate change?

From NASA’s Global Climate Change website team

A pre-winter storm located just off the coast of southwestern Australia was photographed from the International Space Station on March 29, 2014. A solar array panel on the orbital outpost is in the left side of the frame.

A pre-winter storm located just off the coast of southwestern Australia was photographed from the International Space Station on March 29, 2014. A solar array panel on the orbital outpost is in the left side of the frame.

One query we frequently get from the public is to explain the difference between weather and climate. It’s a great question.

Some people say “weather is what you get” and “climate is what you expect.” In a nutshell, “weather” refers to the more local changes in the climate we see around us, on short timescales from minutes to hours to days to weeks. Examples are familiar – rain, snow, clouds, winds, storms, heat waves and floods. “Climate” refers to longer-term averages (they may be regional or global), and can be thought of as the weather averaged over several seasons, years or decades. Climate change is harder for us to get a sense of because the timescales involved are much longer, and the impact of climate changes can be less immediate. 

Dr. Eric Fetzer, a scientist at NASA’s Jet Propulsion Laboratory, explains it this way: “Weather describes how the atmosphere behaves over weeks or less. Climate is how it behaves over time periods of about a month or longer. So climate refers to seasonal and longer periods, out to centuries and millennia.”

In addition to long-term climate change, there are shorter term climate variations. This so-called climate variability can be represented by periodic or intermittent changes related to El Niño, La Niña, volcanic eruptions, or other changes in the Earth system.

As always, we welcome your questions and comments.

August 7, 2017, 10:31 PDT

The next big question in sea level science

Projecting regional changes

By Laura Faye Tenenbaum

Lower Manhattan, where the Regional Sea Level Changes and Coastal Impacts Conference was held, lies within a few feet of sea level. Credit: NASA.

Lower Manhattan, where the Regional Sea Level Changes and Coastal Impacts Conference was held, lies within a few feet of sea level. Credit: NASA.

“Sea level scientists have a pretty good grasp on global mean sea level,” said Steve Nerem, a professor in the Aerospace Engineering Sciences Department at the University of Colorado and the team leader for NASA’s Sea Level Change Team (N-SLCT). “It’s the regional sea level change that’s the next big question, the next big step for sea level science,” he added.

Nerem and much of the rest of the N-SLCT were in New York City this July where more than 300 scientists from 42 countries gathered at Columbia University for a weeklong Regional Sea Level Changes and Coastal Impacts Conference. The international conference was organized by the World Climate Research Programme (WCRP), Climate and Ocean – Variability, Predictability, and Change (CLIVAR), and the UNESCO Intergovernmental Oceanographic Commission and was co-sponsored by NASA.

Regional sea level change is more variable, over both space and time, than global sea level change and can diverge by up to 7 inches (20 centimeters) or more from the global mean. Additionally, making regional projections about future sea level differs from making global mean sea level projections. This is due to the fact that different processes contribute to sea level change in coastal regions.

Global sea level rise is caused by thermal expansion of warmer water plus contributions from ice sheets and glaciers. Regional sea level change, especially along coastlines, is influenced by additional factors, including vertical land movements, waves and tides, and winds and storms. So in order to estimate sea level inundation and flood risk, scientists have to understand all the factors that contribute to extreme water levels such as local sea level rise, land subsidence, tides, waves and storm surge.

“Where I live, it’s hard to separate the pure science from the applications. With all this flooding, the broader significance of your work is very clear.”
- Ben Hamlington, upcoming NASA Sea Level Change Team leader

Members of the N-SLCT understand the importance of studying coastal sea level change and improving the accuracy of regional projections. Ben Hamlington, assistant professor in the Ocean, Earth and Atmospheric Sciences Department at Old Dominion University in Norfolk, Virginia, and upcoming team leader for N-SLCT is serious about understanding sea level.

“The overarching theme of my scientific research,” he said, is “to consistently improve regional sea level projections.” Manhattan, where the conference was held, for example, lies within a few feet of sea level, and furthermore, the U.S. East Coast has some of the highest amounts of projected sea level increase.

“Global means aren’t very useful for someone who’s on the coast of Virginia where I live,” Hamlington said. A main part of the challenge of predicting regional sea level is that what causes the sea level changes and the flooding varies dramatically from place to place. Hamlington described a term called “nuisance flooding,” which is a type of persistent tidal flooding that leads to public inconveniences like road closures and backed-up storm water systems.

“Basically it means your path to work has to change because a certain road is blocked or impassable. You can still get to work, but it might take longer,” he explained. Right now, these nuisance-flooding events occur multiple times a year. But as sea level continues to rise, the nuisance flooding will get more and more frequent and will become even more of a problem. “Where I live, it’s hard to separate the pure science from the applications. With all this flooding, the broader significance of your work is very clear,” he said.

In Norfolk, Virginia, glacial isostatic adjustment (GIA) is around 0.04 inches (1 millimeter) per year, another millimeter per year of subsidence is due to slow subsidence into the Chesapeake Bay Meteor Impact Crater plus ground water pumping. Finally add 0.08 inches (2 millimeters) per year from the ocean rising and “You get the long-term tide gauge rate of relative sea level rise of just lower than 0.20 inches (5 millimeters) per year over the last 100 years. That’s a pretty high rate of sea level rise over a long period of time,” Hamlington explained. “Beyond nuisance flooding, there are also extreme events,” he continued. “During a storm event, you can get several feet of water in some parts of Norfolk.”

Actionable science

Stakeholders and decision makers are the ones driving the demand for improved regional sea level projections, Hamlington continued. “They’re the ones driving the discussion toward regional projections and that’s what’s needed for planning efforts.” These stakeholders include state and local public works officers responsible for infrastructure such as stadiums, roads, seawalls, and dykes plus pumps, water utilities, other utilities, businesses, and coastal inhabitants.

Scientists are responsible for helping society. This is why decision makers and scientists have come together to co-produce actionable science, to discuss how to communicate and collaborate, and to ensure that sea level science is being understood by the adaptation community.

“This is one of the biggest sea level conferences that we’ve had, when everybody who is working in different areas of the field comes together,” said Nerem. There were presentations on a variety of techniques to measure sea level change: tide gauges, measurements in marshes, paleo-sea level, corals, but from the perspective of the N-SLCT, “ We’re really focused on how to use remote sensing, satellite altimetry from Jason-1, 2 and 3 and Gravity Recovery and Climate Experiment (GRACE) combined with GPS measurements to improve regional sea level measurements and projections.”

Nerem’s project targets regions around the globe that are susceptible to inundation but don’t have much measurement infrastructure, such as Bangladesh. Many of these regions do not have detailed digital elevation models or 50 years of tide gauge measurements like we do in the United States.  “If we use our satellite techniques and test them in a place we understand, then we can go out where we don’t have that infrastructure and assess future sea level change in those regions.”

The N-SLCT hopes to leverage the satellite observations as much as possible to try to better understand future regional sea level change. This will help decision makers, coastal managers and stakeholders better adapt and prepare for the impacts of sea level rise.

According to Nerem, “We would like to produce a new assessment of future regional sea level change that benefits from the extensive record of satellite measurements collected by NASA.”

Thank you for reading,
Laura

June 5, 2017, 09:31 PDT

Sun and sky, snow and ice

Reflections at the top of the world

By Laura Faye Tenenbaum

Hiking up to Greenland’s ice sheet, the sun remains low on the horizon even during midday.

Hiking up to Greenland’s ice sheet, the sun remains low on the horizon even during midday.

It was 11:30 in the morning and GLISTIN-A instrument engineer Ron Muellerschoen and I were in northern Greenland at the Thule Air Base pier looking over the frozen Wolstenholme Bay. We’d been talking about the time Ron was wearing shorts here during the summer, but today it was the typical -22 Fahrenheit (-30 Celsius.) And even though over the past week we’d somehow gotten used to the cold and I was wearing a big parka, my legs were starting to get cold after walking for an hour. So we decided to head back.

As we turned around to go, I was struck in the face by the sun’s rays reflecting off the ice-covered ground. The brightness was astounding. And in that instant the meaning of “albedo” was seared into my brain in a way that went beyond reading about the science or looking at illustrations and animations.

There was something special about the experience of having the rays of the sun, which was sitting low in the high latitude sky, hit the ice surface at that extremely low angle and reflect off into my eyes.

Albedo is a measure of how reflective a surface is, how much light energy bounces off and reflects away and how much light energy gets absorbed. (Think hot asphalt on a sunny day. Black asphalt has a low albedo and absorbs light energy, while the brightest white has the highest albedo and reflects the light.)

Walking in Greenland
Team Oceans Melting Greenland (OMG) stands on the Greenland Ice Sheet. Notice the long shadows made by small rocks on the ground.
Albedo is part of what has stabilized Earth’s climate for millennia, because under normal conditions, the white of the polar ice reflects light energy back to space, keeping average global temperature stable. The more area covered by ice, the more heat reflected back to space. The more ice that melts, the more heat absorbed. Increasing temperatures are melting more ice, which exposes darker brown and green land and dark blue ocean. Those darker surfaces have a lower albedo, so they absorb more of the heat from the sun’s rays.

I stood for a moment, looking at the ground — a hard, dry, crusty mixture of ice and snow that made an exceptionally satisfying crunch crunch noise as our boots marched through it — and tried to figure out the color: 50 shades of white. I settled on white/light blue/silvery sparkle. Due to the low angle of the sun, the tiniest rough edge the size and shape of a pebble on the ground’s textured surface left a long, dark shadow.

No matter where we were or how we stood or what time of day, all day, every day, there were always long shadows — crazy long shadows. At 78 degrees north latitude, a full 12 degrees above the Arctic Circle, the sun will never be overhead. Never. I know that seems unbelievable, but even during the summer solstice, when Earth’s North Pole is tilted toward the sun, or during the four summer months of 24-hour daylight, the sun is always low, low, low at this latitude.

Low on the horizon

In that moment, I also understood another science question that had been bothering me. I’d been wondering why the meter-thick sea ice hadn’t yet begun to melt. Even though it was the end of March, even though the equinox had passed, the sun was out and the days were getting longer. In fact, up here the days were getting much longer, very quickly. On March 23, just three days after the equinox, we were already having 14-hour days with sunsets lasting past 9 p.m. That’s because in these high latitudes, the day length can increase by as much as 40 minutes per day. And by mid-April, just a few weeks after spring equinox, there will be 24 hours of daylight and the sun won’t set again until September. 

By mid-April the meter-thick layer of frozen seawater that covers the sea surface and fills the fjords will completely melt and expose the dark blue ocean underneath. But today, even in this brilliant sunshine, even on this day of 14-hour sunlight, the ocean was still completely frozen over. 

Greenland ice
The sun sits low in the sky even during midday. This iceberg calved off one of Greenland's coastal glaciers, floated into Wolstenholme Fjord and then became trapped in sea ice.
Just the other day in fact, a group of us walked about 3 miles (5 kilometers) across the frozen ocean into the middle of Wolstenholme Fjord to visit icebergs trapped in the frozen seawater. We hadn't worried at all about breaking through. 

But “Why?” I’d been wondering. Why, with all this extra sunshine, was the sea surface still so frozen? And why did that hard, dry, crusty mixture of ice and snow still remain on the ground?

In that instant, as the glint of the sunlight reflecting off the icy ground hit my face, I knew exactly why. It was the extraordinarily low angle of the sunlight that bounced right off the stunning bright whiteness of the ice. The sunlight was not absorbed by the ice and snow and instead was reflected away. It wouldn’t be until another month or so that the sun would get a little higher in the sky. And although the sun would never be directly overhead up here, it would be high enough to begin melting the ice.

No matter how much a person studies Greenland, or the northern latitudes, or albedo, or Earth in general, going into the field to experience those things can change your entire understanding of the world and how it works. I stood there for a moment, just allowing the high-latitude sun’s cold rays to glance off the snowy ice and shine straight into my face.

NASA’s Oceans Melting Greenland (OMG) team is here in Greenland; here to find out specifically how much ice the island is losing due to warmer ocean waters around the coastline. There is almost no ocean data in remote places like this, but OMG is busy working to change that, studying the complex ocean processes that affect Greenland's coastline because gathering data is critical to understanding Earth’s complex climate. This information will help us understand the amount of sea level rise we're going to have around the world.

Thank you for reading,

Laura

May 15, 2017, 12:00 PDT

Are you ready to work?

Dive into a sea of Oceans Melting Greenland data

By Laura Faye Tenenbaum

NASA's modified G-III aircraft, with the GLISTIN-A radar instrument visible below, on the runway at Thule Air Base, Greenland.

NASA's modified G-III aircraft, with the GLISTIN-A radar instrument visible below, on the runway at Thule Air Base, Greenland.

"Get to work." The phrase stuck in my head.

I had just walked out of a two-and-a-half-hour debriefing with NASA’s Oceans Melting Greenland (OMG) Principal Investigator Josh Willis, but the whole meeting could be summed up in those three little words of his: Get to work.

It was as though he’d been ringing one of those big ol’ dinner gongs. Data! Hot off the press! Come and get your data! Calling all oceanographers, geologists, paleo-climate scientists: come and get a big ol’ helping of free data.

He made me hungry for data, too.

OMG has just returned from its second spring season. Every April for five years, just before the ice starts to melt, OMG flies a radar instrument over almost every glacier in Greenland that reaches the ocean and collects elevation measurements within a 6.2-mile (10-kilometer)-wide swath for each glacier individually so we can measure how quickly each one is thinning. That’s literally hundreds of glaciers.

“We have more than 70 of these swaths that cover a couple hundred glaciers to create new elevation maps that are high accuracy, high resolution and high quality,” Willis said.

Greenland probe map
The blue squares on this Greenland map show 250 planned locations for probes dropped by plane into ocean waters near the coast. Called Aircraft Expendable Conductivity Temperature and Depth probes, they measure ocean temperature and salinity.

OMG also has bathymetry data from sonar and gravimetry. And we have a year’s worth of Airborne Expendable Conductivity Temperature Depth Probes AXCTD data collected last September plus hundreds of vertical profiles of temperature and salinity taken from ship surveys. “We have temperature measurements in many glacial fjords that have never had a historical temperature profile before. And none of that data is being used to its fullest extent yet.” OMG will set the baseline so we know what the water temperatures are today, and as we look to the future, we can watch them warm. That’s huge. 

I recounted all the times I’ve told someone that many parts of the ocean are still so unknown. I thought about all the times I’ve written about the OMG aircraft flying into remote, uncontrolled airspace, or researching the ocean water-ice interface around Greenland: So many of these places still nameless, still anonymous, still unidentified, still unknown. It’s mind blowing.

And somewhere in all this new data is information about the correlation between the ocean water and the ice as well as the answer to the question of how each glacier may or may not be affected by the waters offshore. “We know that warm water reaches a lot of glaciers. And there have been surveys in few places, but we’ve never had a comprehensive survey of the shelf water before,” Willis said.

OMG is mapping out the edges of glaciers and watching them change year on year on year. The mission measures glacial elevation in the last few kilometers before the glacier hits the water to see exactly how much the glacier shrank or retreated or both. In a few cases, the opposite might happen. Over a single year, a glacier might not have had as much calving or it might have slowed down, which would cause it to thicken and advance.

Aerial shot of a Greenland fjord
Aerial shot of a Greenland fjord shows, at the top, the glacier's origin in the ice sheet, and, at the bottom, its termination point, where it enters a frozen ocean.

There are literally hundreds of glaciers to research and dozens of papers buried in that data. And anybody who wants to can sift through it and publish. “You could get a Ph.D. done really fast,” Willis added enticingly. Here are some recommendations for interesting scientific research:

  • OMG’s temperature data could be used to write oceanography papers about where the warm water is on the shelf and to map out and catalogue which glaciers terminate in deep Atlantic water and which ones sit in shallow water. OMG has enough data to catalogue the depth of the faces of two-thirds of the glaciers around Greenland.
  • Paleo-climatologists and geologists can use new clearly mapped-out OMG bathymetry data to study how ancient glaciers carved troughs in the sea floor. Looking at maps of the seafloor will help us understand the implications for Greenland’s ancient ice sheet. Some flat-bottomed troughs, for example, show evidence of where little ancient rivers must have carved their way through to erode the paleo-glaciers. And sea floor sediments could be analyzed to find out how far the ancient glaciers advanced.
  • Overview papers that compare and contrast the east, west, north and south coasts of Greenland would be incredibly useful to have.
  • Some elevation maps made from historical datasets as well as a few decades’ worth of temperature measurements already exist for some isolated regions across Greenland. Using these historical maps, it’s now possible to compare them with current measurements of temperature and elevation in these locations to observe the changes.
  • OMG is also gathering oceanography data around Greenland. Since the Atlantic Ocean water is very warm and salty and the Arctic Ocean water is cold and fresh, the ratio of those two could be analyzed. Warm Atlantic Ocean water has been in the coastal area around Greenland forever, but how much Atlantic water makes it onto the shelf and reaches the glaciers? This is affected by the bathymetry and the winds, which affect the local currents. And according to Willis, “There’s really still a lot to learn.”

Already there are four downloadable datasets right here! So, come and get it, all you hungry Ph.D. oceanographers.

Get to work.

I can't wait to read your papers,

Laura

April 19, 2017, 10:59 PDT

A vast, melting desert

NASA flies northward to monitor Greenland’s glaciers

By Laura Faye Tenenbaum

Scientists strike out for a wall of ice in the far north, where rapidly changing glaciers are being tracked by a project called "Oceans Melting Greenland." Credit: NASA/JPL. View larger image.

Scientists strike out for a wall of ice in the far north, where rapidly changing glaciers are being tracked by a project called "Oceans Melting Greenland." Credit: NASA/JPL. View larger image.

I looked out the window of NASA’s modified G-III aircraft across the expanse. I knew what I would see. I knew it would look like white pillow-y ripples going on and on and on, way farther than anyone could see, like a vast field of white sand dunes stretching away into the distance.

The Oceans Melting Greenland (OMG) aircraft was flying across the entire top half of Greenland from the northwest coast to the northeast coast to make the day’s first science measurements. And the first science flight line was all the way across the Greenland Ice Sheet, across 620 miles (1,000 kilometers) of ice that’s up to 2 miles thick and hundreds of thousands of years old. And although I’d flown in Greenland a bunch of times before, I’d only ever flown over the coastal areas, where glaciers around the ice sheet’s edges carve their way through the Greenland terrain, to cut out deep, narrow fjords over centuries’ time.

Everything here is vast and expansive: the size, the views, the enormous quantity of ice.

Two days before, I’d trekked up to the ice sheet with a few members of the OMG team. We stood in the insanely cold, dry, biting air (Greenland is one of the least humid areas on planet Earth, with the cleanest, clearest air) and gazed into the incomprehensible distance. It was easy to use a snow boot to scrape the 2 inches or so of fine, dry, powdery snow away from the ice sheet to uncover the hard, greenish blue ice.

On the edge of the ice sheet, a slice of ancient ice layers was exposed like a glistening wall, and we’d walked past it on the way up to the top of the sheet. The ice wall was so vertical and so sheer, the snow that hid the other parts of the edge had fallen away, and we could see its smooth surface shining like a gem: striped blue and green. That ice is hundreds of thousands of years old, made from snow that fell year after year after year, eventually becoming compressed and preserved in this cold, dry desert environment. 

Standing on top of the ice sheet, I imagined it under my feet, going down and down and down for a mile or more. 

A mile—or more—of ice.

An exposed wall reveals ice that is hundreds of thousands of years old on the edge of the Greenland ice cap. Credit: NASA/JPL.
An exposed wall reveals ice that is hundreds of thousands of years old on the edge of the Greenland ice cap. Credit: NASA/JPL.

Everything here is vast and expansive: the size, the views, the enormous quantity of ice. Flying over them, the glaciers look like hundreds of broad frozen rivers, each one up to a few miles across, each one channeling its way from the interior of the landmass toward the sea over thousands of years. Each glacier carved out a fjord through the rock and out to sea in the same way a river erodes its channel, except it’s so much bigger, so much slower and the erosional power of the ice is so much more intense. From up here, the glacier’s impossibly slow creep seems frozen in both space and time. But the glaciers are moving. Stress fractures or crevasses, which are easy-to-observe evidence of glacier movement, form as the glaciers slope downhill toward the sea. And of course, we also have scientific measurements. Detailed satellite images show that the terminal edges of many glaciers such as Jakobshavn have receded by as much as 0.4 miles (600 meters) per year in recent times. Scientists also have time-lapse footage of seaward glacier flow.

But having evidence of glacier flow, and even glacier recession, is only part of the story. As a warmer atmosphere and a warmer ocean around the coastline continue to melt the massive amount of ice that covers Greenland, the ice ends up flowing into the ocean, which causes sea level rise worldwide.

A glacier flows toward a frozen fjord on the Greenland coast, as seen from NASA's modified G-III aircraft. Credit: NASA/JPL
A glacier flows toward a frozen fjord on the Greenland coast, as seen from NASA's modified G-III aircraft. Credit: NASA/JPL.
OMG is hoping to gather enough information about the melting glaciers to better predict sea level rise. And that explains why we were here in our NASA G-III on a March morning, flying lines over Greenland’s receding glaciers with our GLISTIN-A Ka-band interferometer radar instrument. “We want the big picture,” said Josh Willis, OMG principal investigator, “and these lines give us data for almost every glacier that reaches the water.  If the ocean is eating away at the edges of the ice sheet, we’ll see it. Bigtime.”

As we flew over, the GLISTIN-A instrument received data from a 12-kilometer swath of whatever is below and off to the sides of it, in this case glaciers. Using these data, we can measure, with great precision, the height of each glacier we fly over. See, when the end of an individual glacier melts and calves into the ocean, the whole glacier speeds up and flows even faster downhill toward the ocean because there’s less friction against the sides and bottom to slow it down. The faster it moves, the more it stretches — like pulled taffy — and when a glacier is all stretched out, its elevation is lower. And because OMG will fly the same science lines along the same coastal glaciers every year for five years in a row, we’ll be able to find out how much elevation each glacier has lost, how fast it’s flowing into the ocean and how much ice has been lost.

NASA's OMG is monitoring the speed of glaciers around Greenland's coastline. Credit: NASA/JPL
NASA's OMG is monitoring the speed of glaciers around Greenland's coastline. Credit: NASA/JPL.
Over my headset, I can hear the pilots discussing the flight path with the instrument engineers. Out the window, I can see Greenland’s northernmost glaciers below us; white upon white upon white.

They sure appear stable, still, enduring. But they’re not. They’re melting.

They sure appear stable, still, enduring. But they’re not. They’re melting.

And northern Greenland, along with the rest of the higher latitudes in the Northern Hemisphere, is experiencing some of the most intense impacts of global climate change right now, today.

OMG.

Thank you for reading.

Laura

Find out more about Oceans Melting Greenland. View and download OMG animations and graphics.

March 16, 2017, 12:10 PDT

Journey through the atmosphere

Guest post by Ellen Gray

Clouds above the Pacific Ocean on the ATom leg from Nadi, Fiji, to Christchurch, New Zealand, on February 6. Credit: Roisin Commane.

Clouds above the Pacific Ocean on the ATom leg from Nadi, Fiji, to Christchurch, New Zealand, on February 6. Credit: Roisin Commane.

The world seems smaller to Steve Wofsy than it used to. He’s the lead scientist for NASA’s Atmospheric Tomography (ATom) mission, an airborne mission to survey the gases on the world’s atmosphere that has just finished up a round-the-world flight.

Atmospheric scientist Steve Wofsy bundled up for the flight from Anchorage, Alaska, to Kona, Hawaii.
Atmospheric scientist Steve Wofsy bundled up for the flight from Anchorage, Alaska, to Kona, Hawaii, on February 1. Credit: Roisin Commane.
I met with Steve in February in Christchurch, New Zealand, at a hotel an easy ten-minute walk from the international airport. The proximity was key because that's where NASA's DC-8 research plane sat amid large warehouse-sized hangars and equipment on a section of the airport run by the U.S. National Science Foundation for research expeditions to Antarctica.

Writer Ellen Gray with NASA’s DC-8 in Christchurch, New Zealand, on February 7.
Writer Ellen Gray with NASA’s DC-8 in Christchurch, New Zealand, on February 7. Credit: Roisin Commane.
Christchurch is at the halfway point of the latest ATom mission, a 28-day near-circumnavigation of the globe. Their journey began Jan. 29 in Palmdale, California, and went north to the Arctic Ocean before zipping down the Pacific Ocean to Hawaii then Fiji on the way to New Zealand. 

NASA’s DC-8, a flying laboratory filled with instruments to measure the atmosphere, in Nadi, Fiji.
NASA’s DC-8, a flying laboratory filled with instruments to measure the atmosphere, in Nadi, Fiji, February 5. Credit: Roisin Commane.
“One day we were in Alaska and the next we were in Hawaii,” he said of the eight-hour research flight that took them from the near darkness of the Arctic winter and snow-covered runways to the belching volcanoes of the Hawaiian Islands where seasons are more of a suggestion of the calendar. When we spoke in New Zealand it was in Southern Hemisphere summer, a breezy 65 F degrees on the coast. Going from the Arctic to the Antarctic and then back again in less than a month, “it really drives home how small our planet is,” he said.

Wofsy is tall and lanky and at 70 is still an active professor and researcher at Harvard University. He began thinking about a mission like ATom 30 years ago to take a slice of the atmosphere from pole to pole to see what gases were there both naturally and from pollution, how they behaved, and how they collectively affected Earth’s climate. Building on years of research and airborne field work, including a mission Wofsy led to sample the air above the Pacific from pole to pole, ATom brings more than 22 instruments and a hundred scientists from universities and agencies around the world to begin to close the loop on some outstanding questions.

Of particular interest are three greenhouse agents: ozone that occurs in the lower atmosphere as a result of human pollution, methane that also primarily comes from human activities, and black carbon, tiny black particles that come from fires that absorb heat and interact with clouds. These three make up the number two, three, and four most important human-emitted greenhouse agents after carbon dioxide, which is also being measured.

"Together they account for almost as much warming of the surface as carbon dioxide," Wofsy explained to me.

What sets them apart is how long they stay in the atmosphere. Unlike carbon dioxide which persists for over a century before being removed from the atmosphere, ozone in the lower atmosphere reacts with other gases within a year and methane sticks around for more than a decade. This means that reducing human emissions of these two gases could make a difference in the greenhouse effect in our lifetimes. But because they're both reactive, their concentration in the atmosphere can vary a lot from place to place. Hence the importance of the up-close, around-the-world measurements made by the instruments on the ATom mission to get a handle on how much is there now and how it may change in the future.

The sky was overcast when we went out to see the plane. NASA’s DC-8 looks like an older-model commercial aircraft from the outside (which it was), but from the inside its all science. Instead of rows of seats, large metal frame structures – racks to hold the instruments and computers – dominate the view with only a pair of seats next to each one. A few scientists were onboard fine-tuning their instruments or resupplying gases and filters.

Instead of hunting for particular gases in particular pollution-prone regions, Wofsy and the science team want to measure everything they can, not just the greenhouse gases — from soot and remnant gases of fires burned on land, sulfur dioxide from volcanoes and coal-burning power plants, and industrial air pollutants. They are flying near some major land masses, but more importantly, they’re flying high over the ocean, the remotest and supposedly cleanest parts of the atmosphere to see how far humanity’s fingerprints on the air have traveled.

The answer: pretty far. This February, above the Arctic, they saw traces of Asian pollution. Above both the Pacific and Atlantic, they saw traces of African fires.

ATom left New Zealand for the southern tip of Chile and then completed the circuit flying north over the middle of the Atlantic Ocean. They arrived back in California at the end of February, finishing their second of four deployments, one to take place in each season. The mission takes to the air next this October.