April 26, 2017

Glacier Shape Influences Susceptibility to Melting

Kangerlugssuup Sermerssua Glacier
Terminus of Kangerlugssuup Sermerssua glacier in west Greenland

A new NASA-funded study has identified which glaciers in West Greenland are most susceptible to thinning in the coming decades by analyzing how they’re shaped. The research could help predict how much the Greenland Ice Sheet will contribute to future sea level rise in the next century, a number that currently ranges from inches to feet.

“There are glaciers that popped up in our study that flew under the radar until now,” said lead author Denis Felikson, a graduate research assistant at The University of Texas Institute for Geophysics (UTIG) and a Ph.D. student in The University of Texas Department of Aerospace Engineering and Engineering Mechanics. Felikson’s study was published in Nature Geoscience on April 17.

The Greenland Ice Sheet is the second largest ice sheet on Earth and has been losing mass for decades, a trend scientists have linked to a warming climate. However, the mass change experienced by individual coastal glaciers, which flow out from the ice sheet into the ocean, is highly variable. This makes predicting the impact on future sea-level rise difficult.

“We were looking for a way to explain why this variability exists, and we found a way to do it that has never been applied before on this scale,” Felikson said.

Of the 16 glaciers researchers investigated in West Greenland, the study found four that are the most susceptible to thinning: Rink Isbrae, Umiamako Isbrae, Jakobshavn Isbrae and Sermeq Silardleq.

Umiamako Isbrae, Sermeq Silardleq and Jakobshavn Isbrae are already losing mass, with Jakobshavn being responsible for more than 81 percent of West Greenland’s total mass loss over the past 30 years.

Rink has remained stable since 1985, but through shape analysis researchers found that it could start to thin if its terminus, the front of the glacier exposed to ocean water, becomes unstable. This is a strong possibility as the climate continues to warm.

"Not long ago we didn't even know how much ice Greenland was losing, now we're getting down to the critical details that control its behavior," said Tom Wagner, director of NASA’s cryosphere program, which sponsored the research.

The analysis works by calculating how far inland thinning that starts at the terminus of each glacier is likely to extend. Glaciers with thinning that reaches far inland are the most susceptible to ice mass loss.

Just how prone a glacier is to thinning depends on its thickness and surface slope, features that are influenced by the landscape under the glacier. In general, thinning spreads more easily across thick and flat glaciers and is hindered by thin and steep portions of glaciers.

The research revealed that most glaciers are susceptible to thinning between 10 and 30 miles inland. For Jakobshavn, however, the risk of thinning reaches over 150 miles inland—almost one-third of the way across the Greenland Ice Sheet.

“Jakobshavn is particularly vulnerable to thinning because it flows through a very deep trough that extends deep into the ice sheet interior, making the ice thick and the surface flat,” Felikson said.

Felikson said these calculations will help identify which areas of Greenland may be most susceptible to melting and thus contribute most to future sea level rise. However, while the method can point out vulnerable areas, it can’t predict how much mass loss is likely to occur.

Still, knowing which glaciers are the most at risk can help scientists allocate limited resources, said co-author Timothy Bartholomaus, an assistant professor at the University of Idaho. “The approach we demonstrate here allows us to identify which outlet glaciers are not yet changing rapidly, but might,” Bartholomaus said. “With that knowledge, we can anticipate potential sea-level rise and set up the observational campaigns in advance to understand these glacier changes.”

Among other sources of data, Felikson and his team used a bedrock topography map created with data from NASA’s Ocean Melting Greenland project to determine the thickness of the ice and a digital elevation model from the Greenland Ice Mapping Project, which uses measurements from the Japanese-provided Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA’s Terra satellite, to separate glacier catchments.

Ginny Catania, an associate professor in the University of Texas Jackson School of Geosciences and research associate at UTIG, said the group has plans to apply the shape analysis technique to other glaciers. “Our plan is to extend the analysis so that we can identify glaciers in Antarctica and around the rest of Greenland that are most likely to be susceptible to change in the future,” she said.

Study collaborators include researchers at Iceland’s Institute of Earth Sciences, the University of Copenhagen, the University of California, the University of Kansas, Oregon State University and the University of Oregon. The research was funded by NASA and The University of Texas Aerospace Engineering and Engineering Mechanics Department.

Image Credit: Denis Felikson, Univ. of Texas
Explanation from: https://www.nasa.gov/feature/goddard/2017/glacier-shape-influences-susceptibility-to-melting

Taking AIM at Night-Shining Clouds: 10 Years, 10 Science Highlights

Noctilucent Clouds
Noctilucent clouds appeared in the sky above Edmonton, Alberta, in Canada on July 2, 2011

Launched on April 25, 2007, NASA’s Aeronomy of Ice in the Mesosphere, or AIM, mission, has provided a wealth of new science on the dynamics and composition of Earth’s upper atmosphere. Designed to study noctilucent, or night-shining, clouds, AIM’s data have helped scientists understand a host of upper-atmosphere phenomena, from radio echoes to giant, planet-scale atmospheric waves.

“AIM started out studying clouds that form on the edge of space, about 50 miles above Earth, to understand why they form and how they vary,” said Jim Russell, principal investigator of the AIM mission at Hampton University in Hampton, Virginia. But he says that 10 years of data from AIM has far exceeded the initial expectations. “We’ve made great strides in answering this question and learned far more about the atmosphere than we ever imagined when the mission was conceived.”

Noctilucent clouds form in Earth’s mesosphere. They’re made of ice crystals, which reflect sunlight to give off the clouds’ signature blueish glow. Though scientists had ideas about how and why these clouds form before AIM launched, the mission’s 10 years’ worth of data have confirmed their origins.

“The accepted theory was that the ice formed around meteoric smoke — very small, nanometer-scale particles that are remnants of meteors burning up in the atmosphere,” said Diego Janches, project scientist for the AIM mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “With AIM, we were able to study the presence and variability of that smoke.”

Over the next few years, AIM will enter a new phase of science. Because of the way the spacecraft’s orbit has shifted over time, AIM is now in an ideal position to study gravity waves, oscillations in the air usually caused by weather and winds near Earth’s surface.

“These gravity waves affect the entire circulation of the middle and upper atmosphere,” said Cora Randall, principal investigator of AIM’s Cloud Imaging and Particle Size, or CIPS, experiment at University of Colorado Boulder. “These are really important for the global atmospheric structure and composition, and even affect the polar vortex.”

AIM’s CIPS instrument can detect tiny changes in ultraviolet light reflected off of Earth’s atmosphere about 30 miles above the surface. Those tiny changes can reveal the gravity waves coming from below, much like ripples on the surface of a pond can be traced back to a dropped pebble.

AIM’s new measurements of these gravity waves, along with observations from ground-based missions and other satellite missions, will give scientists new insight into the behavior of the uppermost atmosphere at the edge of space.

“By taking these measurements at the same time, we’ll hopefully be able to link processes in the stratosphere to changes in the thermosphere even higher up,” said Janches.

AIM’s data have led to more than 200 papers on Earth’s upper atmosphere. A handful of key scientific discoveries:

  • Overturning assumptions about the sun and noctilucent clouds: Observations from the 1980s and ’90s suggested that the appearance of noctilucent clouds is linked to the sun’s activity, which rises and falls in about 11-year patterns. But AIM’s data tell a different story: noctilucent clouds have been steadily increasing over the past decade, despite the sun’s regular changes in activity. The precise reason for this is still unknown.
  • Noctilucent cloud and greenhouse gases: Scientists suspected that increased sightings of noctilucent clouds could be related to increasing greenhouse gases. Combining AIM’s data with 36 years of measurements from satellite instruments showed a correlation between more frequent noctilucent clouds and increases in water vapor, a greenhouse gas, and decreasing upper-atmosphere temperatures — a side effect of warming near the surface.
  • Meteors help create noctilucent clouds: The ice crystals that form noctilucent clouds must form on a foundation of some kind. AIM’s data showed that this base is actually smoke from meteors — tiny microparticles produced when meteors burn up in Earth’s atmosphere.
  • Tracking meteoric smoke: Before AIM’s launch, scientists primarily watched meteoric smoke — the tiny particles created when meteors burn up in the atmosphere — from just a few viewpoints with sounding rockets. AIM’s measurements have given scientists a new tool to watch this meteoric smoke, revealing for the first time the dynamics of how meteoric smoke moves through the atmosphere.
  • Understanding the upper atmosphere: AIM helped scientists track how heat moves in the upper atmosphere, showing that heating in the mesosphere is more likely linked to circulation in the atmosphere rather than direct heating from the sun.
  • Studying atmospheric waves caused by Earth’s rotation: AIM measures planetary waves, planet-scale waves caused by Earth’s rotation, that can influence weather across the globe. Over its 10-year mission, AIM has observed three of the four most extreme springtime planetary wave events seen since satellite observations began in 1978, raising questions about possible changes in the dynamics of the atmosphere.
  • Teleconnection between the poles: AIM’s data showed that conditions in the stratosphere near the North Pole influence conditions in the mesosphere near the South Pole days or weeks later — even going so far as to influence the transition between seasonal conditions.
  • How Earth’s weather affects the upper atmosphere: AIM’s measurements have also helped scientists track how air in the atmosphere moves vertically, as well as between the hemispheres. This helps scientists understand how events near Earth’s surface — like thunderstorms — might trigger changes in the upper atmosphere.
  • Understanding the atmosphere from bottom to top: This new understanding of vertical linkages in the atmosphere was integrated into the first weather model that describes the entire atmosphere from the surface all the way to the upper mesosphere.
  • The source of radar echoes: AIM solved the mystery of radar echoes in certain regions of the atmosphere during the summer. The same ice layer that produces noctilucent clouds is to blame for radar echoes, and the size of the ice crystals can even play a role.

Image Credit: NASA/Dave Hughes
Explanation from: https://www.nasa.gov/feature/goddard/2017/taking-aim-at-night-shining-clouds-10-years-10-science-highlights

NASA's Fermi Catches Gamma-ray Flashes from Tropical Storms

Typhoon Bolaven
Typhoon Bolaven, August 2012

About a thousand times a day, thunderstorms fire off fleeting bursts of some of the highest-energy light naturally found on Earth. These events, called terrestrial gamma-ray flashes (TGFs), last less than a millisecond and produce gamma rays with tens of millions of times the energy of visible light. Since its launch in 2008, NASA's Fermi Gamma-ray Space Telescope has recorded more than 4,000 TGFs, which scientists are studying to better understand how the phenomenon relates to lightning activity, storm strength and the life cycle of storms.

Now, for the first time, a team of NASA scientists has analyzed dozens of TGFs launched by the largest and strongest weather systems on the planet: tropical storms, hurricanes and typhoons.

"One result is a confirmation that storm intensity alone is not the key factor for producing TGFs," said Oliver Roberts, who led the study at the University College Dublin, Ireland, and is now at NASA's Marshall Space Flight Center in Huntsville, Alabama. "We found a few TGFs were made in the outer rain bands of major storms, hundreds of kilometers from the powerful eye walls at their centers, and one weak system that fired off several TGFs in a day."

Scientists suspect TGFs arise from the strong electric fields near the tops of thunderstorms. Under certain conditions, these fields become strong enough to drive an "avalanche" of electrons upward at nearly the speed of light. When these accelerated electrons race past air molecules, their paths become deflected slightly. This change causes the electrons to emit gamma rays.

​Fermi's Gamma-ray Burst Monitor (GBM) detects TGFs occurring within about 500 miles (800 kilometers) of the location directly beneath the spacecraft. In 2012, GBM scientists employed new techniques that effectively upgraded the instrument, increasing its sensitivity and leading to a higher rate of TGF detections.

This enhanced discovery rate helped the GBM team show that most TGFs also generate a strong pulse of very low frequency radio waves, signals previously attributed only to lightning. Facilities like the Total Lightning Network operated by Earth Networks in Germantown, Maryland, and the World Wide Lightning Location Network, a research collaboration run by the University of Washington in Seattle, can pinpoint lightning- and TGF-produced radio pulses to within 6 miles (10 km) anywhere on the globe.

"Combining TGF data from GBM with precise positions from these lightning detection networks has opened up our ability to connect the outbursts to individual storms and their components," said co-author Michael Briggs, assistant director of the Center for Space Plasma and Aeronomic Research at University of Huntsville (UAH).

The team studied 37 TGFs associated with, among other storms, typhoons Nangka (2015) and Bolaven (2012), Hurricane Paula (2010), the 2013 tropical storms Sonia and Emang and Hurricane Manuel, and the disturbance that would later become Hurricane Julio in 2014.

"In our study, Julio holds the record for TGFs, firing off four within 100 minutes on Aug. 3, 2014, another the day after, and then no more for the life of the storm," Roberts said. "Most of this activity occurred as Julio underwent rapid intensification into a tropical depression, but long before it had even become a named storm."

What the scientists have learned so far is that TGFs from tropical systems do not have properties measurably different from other TGFs detected by Fermi. Weaker storms are capable of producing greater numbers of TGFs, which may arise anywhere in the storm. In more developed systems, like hurricanes and typhoons, TGFs are more common in the outermost rain bands, areas that also host the highest lightning rates in these storms.

Most of the tropical storm TGFs occurred as the systems intensified. Strengthening updrafts drive clouds higher into the atmosphere where they can generate powerful electric fields, setting the stage for intense lightning and for the electron avalanches thought to produce TGFs.

TGFs were discovered in 1992 by NASA's Compton Gamma-Ray Observatory, which operated until 2000.

The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Image Credit: Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC
Explanation from: https://www.nasa.gov/feature/goddard/2017/nasas-fermi-catches-gamma-ray-flashes-from-tropical-storms