Fun with Aureoles and Aerosols

      Credit: Earth Science Picture of the Day/Rob Rathkowski

Earth Science Picture of the Day (EPOD)
recently ran a series of photos that illustrates nicely the impact that small airborne particles called aerosols can have on light.

As EPOD notes, the size of an aureole — the halo-like circle that appears around the sun when viewed through a haze or mist — depends on the amount of aerosol in the air. More aerosols mean more light is scattered, which produces larger aureole). Since most aerosols are concentrated near Earth’s surface, the aureole at sea level appears much larger than it would high on a mountain peak. You can try this experiment yourself to get a sense of the aerosol load in the air you’re breathing.

Aerosols are a major preoccupation for climate scientists as the particles—including dust, ash, sea salt, soot, and industrial pollutants—can scatter light and affect Earth’s energy balance. Infusions of ash and sulfate from volcanic eruptions, for example, are capable of cooling global temperatures by 0.3 degrees Celsius. Likewise, sulfate aerosols from factories and power plants can mask global warming somewhat and are often bandied around as possible components of geoengineering schemes.

Want to learn more about how aerosols scatter light? EPOD has another post on the topic that compares aureoles at sunsets in the Netherlands before (below left) and after (below right) the arrival of a massive volcanic ash cloud from the eruption of Eyjafjallajökull. Also, for optics aficionados, a site called Atmospheric Optics will walk you through a number of interesting examples of aerosols and atmospheric water and ice scattering light.

        Credit: Earth Science Picture of the Day/Kosmas Gazeas
— Adam Voiland, NASA’s Earth Science News Team

Extreme Field Campaign

A team from NASA Langley Research Center needed a high and dry place to run their Far Infrared Spectroscopy of the Troposphere (FIRST) instrument last summer and fall. They found it in Chile’s Atacama Desert. Photo courtesy of Rich Cageao, NASA Langley Research Center.

How does a group of NASA scientists end up on a barren mountaintop, a hemisphere away from home, 17,500 feet above sea level, and in need of supplemental oxygen to stay focused in the thin air? Like most things in science, this trek began with a question or two.

“The first question is: what is the science that’s important to do? The second is: how do you do it?”

Rich Cageao said it was these questions that led a group of scientists and engineers from NASA’s Langley Research Center to embark on a four-month field campaign to the Atacama Desert of Chile in 2009, from late July to early November.

To study how water vapor absorbs infrared radiation in the high atmosphere and influences the climate, the group needed a site well above sea level. Otherwise, the higher levels of water vapor near the surface would block any attempt at detailed infrared measurements, like putting a thick layer of gauze in front of a camera lens.

A modified shipping container – like the ones shipped on rail cars and tractor trailers – became a remote office for the scientists and home for their instrument called FIRST – Far Infrared Spectroscopy of the Troposphere). Trucks took it from Virginia to California; a ship took it from California to Chile; a truck again took it from sea level to an elevation equal to the base camp on Mt. Everest. And the container – outfitted with windows, a door, an opening for measurements, and oxygen – made it to and from the site in pretty good shape, despite a few snowstorms and gale-force winds.

Here the site is seen prior to grading and preparation. Photo courtesy of Rich Cageao, NASA Langley Research Center.

Once the container was in place at a graded site on a Chilean mountain called Cerro Toco, the team set to working out the kinks with the instrument and power supply. They also worked on adapting to the daily climb from base camp at 8,000 feet to the work site at 17,500 feet.

The conditions kept everyone on their toes, and nothing ever seemed routine, Cageao said. “Warm days, out of the wind, were zero degrees Centigrade. Winds were typically 25 mph, and up to 60 mph,” Cageao described the days as extremely taxing. Nothing could be called drudgery. The possibility that something could go wrong required a state of hyper-awareness. “You’re not waiting for something to happen. You never sit around.”

After site work, the instrument, housed in a converted shipping container, was put in place in Chile following a
months-long trek by truck and ship.
Photo courtesy of Rich Cageao, NASA Langley Research Center.

But even with the cold, the wind, and the barren, almost lifeless site, Cageao couldn’t pass on the opportunity.

“We have, by nature, that feeling of, ‘we’ve got to get out there,’” he said of many scientists in the office. “We’re much happier in the field. It’s an adventure. It’s good science and it’s challenging.”

So why go to all this effort?

The Earth’s surface emits infrared radiation it has absorbed from the sun. Greenhouse gases partly trap that energy as heat, keeping the planet habitable. But with humans burning fossil fuels and altering the balance of greenhouse gases – and therefore the amount of heat trapped in the atmosphere – scientists need to understand exactly how this process works in order to improve predictions of climate change.

“The primary greenhouse gas on Earth is not CO2. It’s not methane. It’s water vapor,” Cageao said. “And when you drive up the temperature of the atmosphere, you drive up the water vapor, so you better have this right. Having it pretty close isn’t enough.”

— Patrick Lynch, NASA’s Earth Science News Team

Soaring for Science

NASA's Global Hawk autonomous plane

The newest bird in NASA’s flock — the unmanned Global Hawk — took off at 7 a.m. Pacific time today (April 2) from Dryden Flight Research Center at Edwards Air Force Base in California. The flight is the first airborne checkout of the plane since it was loaded with 11 science instruments for the Global Hawk Pacific (GloPac) mission.

Pilots are also streamlining processes to coordinate the workload while the nearly autonomous plane is flying at altitudes above 60,000 feet (almost twice as high as a commercial airliner). Operators and mission researchers are using the day to make sure all instruments are operating properly while in flight — particularly at the cold temperatures of high altitude — and communicating clearly with the plane and ground controllers. Mission participants expect to begin collecting data when actual GloPac science flights begin over the Pacific Ocean later this month.

GloPac is the Global Hawk’s first scientific mission. Instruments will sample the chemical composition of air in Earth’s two lowest atmospheric layers — the stratosphere and troposphere — and profile the dynamics and meteorology of both. They also will observe the distribution of clouds and aerosol particles. The instruments are operated by scientists and technicians from seven science institutions and are funded by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Paul Newman, the co-mission scientist for GloPac, has been blogging about the mission on Earth Observatory’s “Notes from the Field” site. Here are a few excerpts to whet your appetite…

…There is an old Latin quote: “Maxima omnium virtutum est patientia.” Or “patience is the greatest virtue.” When it comes to mounting science instruments on an aircraft, you need to continually return to that quote…

…During the integration this week, we’ve had to cut holes into the aircraft. I told Chris Naftel, the Global Hawk project manager, that we had to cut some holes into the plane for the Meteorological Measurement System. Chris replied: “I don’t want to hear anything about the holes. It pains me!” In spite of Chris’ pain, the little holes are critical for measuring winds. You’re now asking, what? Little holes? For winds? It’s actually a very slick little measurement that relies on the work of Daniel Bernoulli, a Dutch mathematician who lived in the 1700s…

Read more here …

Working (Very) Remotely

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Bryan Fabbri, Fred Denn, and Bob Arduini typically drive to their jobs at NASA’s Langley Research Center in Hampton, Va. But then there are a few days each month when they take the helicopter instead.

The three scientists are part of the small, hands-on team that maintains a suite of meteorological and climate-observing instruments on the Chesapeake Light, a platform lighthouse 15 miles off the Virginia coast in the Atlantic Ocean.

The instruments record air and sea surface temperature, the amount of sunlight and heat absorbed and reflected by the ocean surface, wind speed, aerosol composition, and on and on. The measurements are made to validate the observations made by the Langley-managed Clouds and the Earth’s Radiant Energy System (CERES).

The CERES satellite instruments have been operating for more than a decade, creating a long-term record of a key driver of Earth’s climate – the balance of incoming and outgoing solar radiation known as the “energy budget.” And the instruments that Fabbri, Denn and Arduini maintain on Chesapeake Light serve to validate the observations CERES makes over the oceans. The project is called COVE (CERES Ocean Validation Experiment) and began along with CERES more than a decade ago.

In a job that usually demands a lot of time crunching data in front of a computer screen, the regular trips to the lighthouse offer a chance for something different. They also highlight a side of science that isn’t often discussed: the grunt work of making sure your instruments are working properly…or haven’t corroded in the humid salt-air…or haven’t blown off the platform with an open-ocean gust. If the sensors aren’t working properly, CERES observations over the ocean would be much more difficult to validate.

It doesn’t hurt that this important work means getting out in the middle of the ocean every now and then.

“You can’t beat that part of it,” Fabbri said. “I get a little stir crazy. I like getting out of the office and out there to work on the instruments. It doesn’t hurt to take the helicopter out.”

— By Patrick Lynch, NASA’s Langley Research Center

Are the Oceans Really Stuffed to the Gills with Carbon Dioxide?

Two months ago, NASA’s Timothy Hall and colleagues published a study that described how they had estimated the amount of manmade carbon dioxide absorbed by the ocean since the start of the industrial era.

Oceans absorb about a third of the carbon dioxide that humans release into the atmosphere, so sorting out a long-term record of carbon uptake is of great interest to climate scientists.

To create their record of the ocean’s uptake of carbon, Hall and Samar Khatiwala, the lead author of the study, devised a clever mathematical technique that proved to be a considerable advance. When Hall’s study appeared in the journal Nature, he assumed the creation of this new long-term, continuous record would headline the news.

But journalists gravitated toward something else entirely: a brief mention that the amount of carbon dioxide absorbed by the ocean seemed to be experiencing, as the researchers put it, “a small decline in the rate of increase in the last few decades.”

“Seas Grow Less Effective at Absorbing Emissions”, one headline trumpeted. Another article compared the world’s oceans to a fish “stuffed to the gills” with carbon dioxide and another reported a “sudden and dramatic drop in the amount of carbon dioxide being absorbed by the sea.

Given the caveats included in the original study, all of this caught Hall slightly off guard. I’ll let Hall, who summarized his reactions to the coverage for What On Earth, pick the story up from here:

My coauthors and I had viewed the ability to estimate the history of ocean uptake of anthropogenic carbon as the highlight of the paper. Previously, observationally-based estimates had only provided a few snapshots in time, and we were proud of the cleverness of our techniques.

It seems clever mathematical techniques, however, don’t make good press releases. Interestingly, coverage of the paper has not focused on the fact that we can estimate the uptake history. Instead it has focused on apparent reductions in the rate of uptake over the last 2 decades.

The figure below shows our estimate of ocean uptake since 1775. The first impression is the rapid increase since 1950, coinciding with the rapid rise in carbon emissions to the atmosphere. The oceans have prevented about 1/3 of anthropogenic carbon emissions from accumulating in the atmosphere. A closer reading of the curve reveals a reduction in the uptake’s rate of increase after about 1980, even while emissions continue to increase.

Scientists have long suspected that ocean carbon uptake would eventually be unable to keep pace with rising emissions. Basic aqueous chemistry tells us that, as dissolved carbon in seawater increases, seawater becomes less able to absorb new carbon. Eventually, the absorption saturates. The slowing down of the increase rate may be an early signal of this saturation.

However, recent changes in uptake were not our focus when we performed the study, and more importantly we did not analyze the statistical significance of the slowdown. We plan further analysis on these trend variations. What we can say is that there are physical reasons to suspect a reduction in the ocean’s capacity to keep pace with increasing carbon emissions, and that there are now strong observational hints for recent reductions.

Hall advises reading this story, which also appeared in Nature. It’s less dramatic and more technical than most of media accounts, but it is a more accurate representation of the paper.

–Adam Voiland, NASA’s Earth Science News Team
   Image Credit: (EPOD/K. Chrisodoulopoulus)