Why doesn't matter just bunch up? The same principle that keeps neutron stars and white dwarf stars from imploding also keeps people from imploding and makes normal matter mostly empty space. The observed reason is known as the Pauli Exclusion Principle. The principle states that identical fermions -- one type of fundamental matter -- cannot be in the same place at the same time and with the same orientation. The other type of matter, bosons, do not have this property, as demonstrated clearly by recently created Bose-Einstein condensates. Earlier this decade, the Pauli Exclusion Principle was demonstrated graphically in the above picture of clouds of two isotopes of lithium -- the left cloud composed of bosons while the right cloud is composed of fermions. As temperature drops, the bosons bunch together, while the fermions better keep their distance. The reason why the Pauli Exclusion Principle is true and the physical limits of the principle are still unknown.
Sunday, February 28, 2010
Saturday, February 27, 2010
On February 21st, the Space Shuttle Endeavour and the International Space Station (ISS) flew through the sky near dawn over Whitby, Ontario, Canada. Along with star trails, both were captured in this single time exposure. Glinting in sunlight 350 kilometers above the Earth, Endeavour slightly preceeded the ISS arcing over the horizon. But the brighter trail and the brighter flare belongs to the space station just visited by Endeavour. Near the completion of the STS-130 mission, hours later Endeavour made a night landing at Kennedy Space Center.
Friday, February 26, 2010
A jewel of the southern sky, the Great Carina Nebula, aka NGC 3372, spans over 300 light-years. Near the upper right of this expansive skyscape, it is much larger than the more northerly Orion Nebula. In fact, the Carina Nebula is one of our galaxy's largest star-forming regions and home to young, extremely massive stars, including the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun. Nebulae near the center of the 10 degree wide field include NGC 3576 and NGC 3603. Near center at the top of the frame is open star cluster NGC 3532, the Wishing Well Cluster. More compact, NGC 3766, the Pearl Cluster, can be spotted at the left. Anchoring the lower left of the cosmic canvas is another large star-forming region, IC 2948 with embedded star cluster IC 2944. That region is popularly known as the Running Chicken Nebula.
Thursday, February 25, 2010
This beautiful cosmic portrait features NGC 891. The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. Also apparent in NGC 891's edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also been seen near this galaxy's disk.
Wednesday, February 24, 2010
Now, after seven years in orbit and 15 laser-operation campaigns, ICESat has stopped collecting science data. The last of three lasers on the satellite's Geoscience Laser Altimeter System (GLAS) ceased emitting light on Oct. 11, 2009. Attempts to restart the lasers have ended, and NASA is pursing options for satellite decommissioning.
"ICESat's loss is disappointing and it comes at a critical time," said Tom Wagner, cryosphere program manager at NASA Headquarters in Washington. "But we can't lose sight of the fact that ICESat and its team of talented scientists and engineers helped us see the Earth's polar ice caps in a new way. Those observations are feeding a new generation of models to help us figure out where the planet is headed."
As the world's first laser-altimeter satellite, ICESat has measured Earth's surface and atmosphere in "unprecedented 3-D detail," said Jay Zwally, ICESat's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "ICESat has been an outstanding success, despite disappointing limitations in the laser lifetimes. Scientific advances have been made in measuring changes in the mass of the Greenland and Antarctic ice sheets, polar sea ice thickness, vegetation-canopy heights, and the heights of clouds and aerosols."
In the Arctic, for example, scientists used ICESat to map Greenland's dramatic surface elevation, rising to 4,000 meters above sea level. They watched as thin, seasonal sea ice replaced thick, older sea ice as the dominant type in the Arctic Ocean. In Antarctica, scientists achieved a comprehensive inventory of lakes that actively drain or fill under the ice. At both poles, they have tracked glaciers along the coast of the Greenland and Antarctic ice sheets as they empty into the sea.
Learn more about the satellite's early days and subsequent discoveries in this Flickr image gallery.
Despite the end of ICESat's mission, NASA's observations of Earth's polar regions continue. Operation Ice Bridge began in 2009, becoming the largest airborne survey of Earth's polar ice ever flown. For the next five years, instruments on NASA aircraft will target areas of rapid change to yield an unprecedented 3-D view of Arctic and Antarctic ice sheets, ice shelves, and sea ice. The mission will bridge the gap in satellite data until the launch of ICESat-2, planned for 2015.
"Operation Ice Bridge is allowing us to get much higher resolution data over smaller, targeted regions," said Lora Koenig of NASA Goddard, and acting project scientist for the Ice Bridge mission.
Targeted information from aircraft combined with the broad and consistent coverage from satellites contribute to a more complete understanding of Earth's response to climate change, helping scientists make better predictions of what the future might hold.
› ICESat's Notable Moments in Science Image Gallery (Flickr)
› ICESat Video Highlights
› Operation Ice Bridge
› Antarctica's Land and Ice Elevation
› NASA Provides New Perspectives on the Earth's Changing Ice Sheets
› NASA Satellite Reveals Dramatic Arctic Ice Thinning
› Map Characterizes Active Lakes Below Antarctic Ice
› NASA Ice Satellite Maps Profound Polar Thinning
› ICESat project Web site
› ICESat on Twitter
The Atlas V roared to life Thursday morning to send the Solar Dynamics Observatory into space on its mission to evaluate the complex mechanisms of the sun. Liftoff came on-time at 10:23 a.m. EST from Launch Complex 41 at Cape Canaveral Air Force Station on Florida's Atlantic Coast.
The SDO spacecraft is in good shape midway through the launch phase that will eventually place it in an elongated orbit reaching more than 21,000 miles high. Eventually, SDO's orbit will be circularized and will reach about 22,300 miles in what is called geosynchronous orbit. From that altitude, the spacecraft will point its instruments at the sun and relay the readings instantly to a ground station in New Mexico. The research is expected to reveal the sun's inner workings by constantly taking high resolution images of the sun, collecting readings from inside the sun and measuring its magnetic field activity. This data is expected to give researchers the insight they need to eventually predict solar storms and other activity on the sun that can affect spacecraft in orbit, astronauts on the International Space Station and electronic and other systems on Earth.
Live coverage of the launch is available on NASA TV and NASA's Launch Blog.
Tuesday, February 23, 2010
The video, “Piecing Together the Temperature Puzzle,” explores possible causes for rising global temperatures.
It explains what role fluctuations in the solar cycle, changes in snow and cloud cover, and rising levels of heat-trapping greenhouse gases play in contributing to global warming.
The new gallery consists of ten spectacular satellite images of our warming planet captured during the hottest decade since modern record keeping began.
The images show the kinds of events -- including melting glaciers, heat waves, and floods -- that many scientists predict will become more frequent in coming decades due to climate change.
Both the video and the image gallery are part of a new multimedia collection available with the launch of the “Our Warming World” Web page on NASA’s Global Climate Change Web site. “Our Warming World” features videos, images, articles and interactive visuals that discuss rising global temperatures and the impact of greenhouse gases as the main contributor to today’s climate change.
Visit NASA's Global Climate Change Web site to explore the image gallery:
To many people’s confusion, these weather events happened against a backdrop of increasing man-made greenhouse gas levels in the atmosphere that are gradually warming the planet. But scientists stress this weather does not mean that those gases are no longer exerting a warming influence. Nor does it go against the grain of basic global warming theory. Cold snaps and bouts of natural cooling that could last years are expected naturally even as the climate continues on a long-term warming trend, forced by man-made emissions.
It’s snow joke
So, what has been going on out there these past two months? As for the Arctic winter weather, it is exactly that -- Arctic. A pattern of high sea-level pressure over the Arctic has led to weaker westerly winds that typically pin cold air closer to the North pole. According to John M. Wallace, an atmospheric sciences professor at the University of Washington, the weakened jet stream has allowed cold Arctic air to creep into more southern latitudes over the U.S., Canada, Europe and Asia.
This pattern of pressure is called the “Arctic Oscillation.” The oscillation comes in two phases: a “negative phase” where there is relatively high pressure over the North pole and low pressure at the mid-latitudes (at about 45 degrees North); and a “positive phase” in which this pressure system is reversed. This winter, the Arctic Oscillation has been in an extremely negative state. This has caused unseasonably cold air masses to sweep over what are normally temperate latitudes, and unusually mild air masses to be brought in over much of the Arctic itself, Wallace explained.
“The unseasonable temperatures have been accompanied by well-above-normal sea-level pressure in the Arctic, especially over the Atlantic sector. That’s how scientists characterize the Arctic Oscillation,” Wallace said. “Winter isn’t over yet, we’re barely to the halfway mark. But this will be a winter to remember because of the Arctic Oscillation.”
“The bottom line is, I don’t find it extraordinary,” Wallace said. “With or without anthropogenic (man-made) warming, you’re going to have big variations in these patterns.”
The 2009 global temperature analysis released by NASA’s Goddard Institute for Space Studies (GISS) shows that, globally, 2009 was tied for the second hottest year on record. This comes as news reports and blogs question whether global warming is even occurring, given local weather conditions and the fact that warming did not occur at the same rate in the past 10 years as it did during the ‘80s and ‘90s. But here is the key: While the rate of warming slowed, the decade ending Dec. 31, 2009 was also the warmest since accurate records began in 1880, according to GISS. And neither the basic chemistry and physics of global warming nor the continuing increase in man-made greenhouse gas emissions has changed.
One spell is not enough
“Frequently heard fallacies are that ‘global warming stopped in 1998,’ or that ‘the world has been getting cooler over the past decade,’” GISS director James Hansen wrote in a recent essay called “The Temperature of Science.” “These statements appear to be wishful thinking -- it would be nice if true, but that is not what the data show.”
Hansen explains that the 5-year and 11-year temperature averages, i.e. the planet’s annual average temperature, averaged over 5 or 11 years, are valuable because they place less emphasis on single-year variability. These running averages show a consistent rise in the Earth’s temperature over the past 30 years. Further, if the El Nino effect (when unusually warm ocean temperatures occur in the tropical Pacific Ocean) is as strong in 2010 as expected, Hansen said there is a greater than 50 percent chance that it could be the warmest year in the period of instrumental data.
But even if it is, like the recent harsh weather, one year or one particular spell of weather will never alone prove or disprove what is happening to the climate. Even as man-made greenhouse gases exert a consistent pressure on the climate, trapping more heat close to the surface of our planet, surface temperatures from year to year will fluctuate depending on the naturally variable forces at work around the globe. In the early 1990s, the mass of sulfates blasted into the atmosphere by the eruption of the Mt. Pinatubo volcano reflected sunlight and counteracted much of the man-made warming effect for several years. In 1998 El Nino combined with the man-made effect to give us one of the warmest years ever.
Allowing for this variability, global warming theory does not posit a linear, year-to-year increase in temperatures. Nor does it say that harsh winter weather will simply end. What it does say is that increasing concentrations of gases such as carbon dioxide and methane, with unchecked growth, will contribute a greater and greater warming influence on the world’s climate.
“The bottom line is this: there is no global cooling tr end,” Hansen wrote in his 2009 temperature analysis. “For the time being, until humanity brings its greenhouse gas emissions under control, we can expect each decade to be warmer than the preceding one.”
- Climate change is not proven nor disproven by individual warming or cooling spells. It’s the longer-term trends, of a decade or more, which place less emphasis on single-year variability, that count.
- The past couple of months have seen a particularly cold winter in parts of the U.S. and elsewhere.
- This has been the result of the “Arctic oscillation” -- a see-sawing pressure system over the North pole -- that has driven cold air into more southern latitudes.
- These cold spells, and other weather changes that are a result of naturally occurring patterns, are still consistent with a globally warming world.
- Video: Global Temperature Update 2009
- Essay: If it’s that warm, how come it’s so cold? [download pdf]
- Essay: The Temperature of Science [download pdf]
- Feature story: 2009: Second warmest year on record; end of warmest decade
- Feature story: Temperature trackers watch waxings and wanings of our watery world
- Feature story:Feature story: The ups and downs of global warming
- Q&A: Just 5 Questions: The Temperature Record
Covering 71 percent of our planet's surface, the ocean acts as a global thermostat, storing energy from the sun, keeping Earth's temperature changes moderate and keeping climate change gradual. In fact, the ocean can store as much heat in its top three meters (10 feet) as the entire atmosphere does.
"The vast amount of heat stored in the ocean regulates Earth's temperature, much as a flywheel regulates the speed of an engine," said Bill Patzert, an oceanographer and climatologist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The ocean has a long history of capturing and giving up heat generated by both human activities and natural cycles; it is the thermal memory of the climate system."
Heat and moisture from the ocean are constantly exchanged with Earth's atmosphere in a process that drives our weather and climate. Scientists at NASA and elsewhere use a variety of direct and satellite-based measurements to study the interactions between the ocean and atmosphere.
"These interactions result in large-scale global climate effects, the largest of which is the El Niño-Southern Oscillation," explained Josh Willis, a JPL oceanographer and climate scientist. This climate pattern appears in the tropical Pacific Ocean roughly every four to 12 years and has a powerful impact on the ocean and the atmosphere. It can disrupt global weather and influence hurricanes, droughts and floods. It can also raise or lower global temperatures by up to 0.2 degrees Celsius (0.4 degrees Fahrenheit).
The oscillation pattern is made up of linked atmospheric and oceanic components. The atmospheric component is called the Southern Oscillation, a pattern of reversing surface air pressure that see-saws between the eastern and western tropical Pacific. The ocean's response to this atmospheric shift is known as either "El Niño" or "La Niña" (Spanish for "the little boy" and "the little girl," respectively).
Where the wind blows
During El Niño, the normally strong easterly trade winds in the tropical eastern Pacific weaken, allowing warm water to shift toward the Americas and occupy the entire tropical Pacific. Heavy rains tied to this warm water move into the central and eastern Pacific. El Niño can cause drought in Indonesia and Australia and disrupt the path of the atmospheric jet streams over North and South America, changing winter climate.
Large El Niños, such as the most powerful El Niño of the past century in 1997 to 1998, tend to force Earth's average temperatures temporarily higher for up to a year or more. Large areas of the Pacific can be one to two degrees Celsius (around two to four degrees Fahrenheit) above normal, and the average temperature of the ocean surface tends to increase. The current El Niño began last October and is expected to continue into mid-2010. Scientists at NASA's Goddard Institute of Space Studies in New York estimate that if this pattern persists, 2010 may well go down as the warmest year on record.
El Niño's cold counterpart is La Niña. During La Niña, trade winds are stronger than normal, and cold water that usually sits along the coast of South America gets pushed to the mid-equatorial region of the Pacific. La Niñas are typically associated with less moisture in the air and less rain along the coasts of the Americas, and they tend to cause average global surface temperatures to drop. The last La Niña from 2007 to 2009 helped make 2008 the coolest year of the last decade. The end of that La Niña last year and subsequent transition into an El Niño helped contribute to last year's return to near-record global temperatures.
All the ocean's a stage
Both El Niño and La Niña play out on a larger stage that operates on decade-long timescales. The Pacific Decadal Oscillation, or PDO for short, describes a long-term pattern of change in the Pacific Ocean that alternates between cool and warm periods about every five to 20 years. The PDO can intensify the impacts of La Niña or diminish the impacts of El Niño. In its "cool, negative phase," warm water, which causes higher-than-normal sea-surface heights (because warmer water expands and takes up more space), forms a horseshoe pattern that connects the north, west and south Pacific with cool water in the middle. In its "warm, positive phase," these warm and cool regions are reversed, and warm water forms in the middle of the horseshoe.
Such phase shifts of the PDO result in widespread changes in Pacific Ocean temperatures and have significant global climate implications. During the 1950s and 1960s, the PDO was strongly negative, or cool, and global temperatures seemed to level off. During most of the 1980s, 1990s and 2000s, the Pacific was locked in a strong positive, or warm, PDO phase and there were many El Niños. We are currently in the early stages of a cool PDO phase that began around 2006. Cool, negative phases tend to dampen the effects of El Niños.
Willis said the PDO, El Niño and La Niña can strongly affect global warming due to increased greenhouse gases. "These natural climate phenomena can sometimes hide global warming caused by human activities, or they can have the opposite effect of accentuating it," he explained.
"These natural signals -- El Niños, La Niñas and PDOs -- can modulate the global record for a decade or two, giving us a wild ride with major climate and societal impacts," said Patzert. "They can have a powerful short-term influence on global temperatures in any particular year or decade. This can make it appear as if global warming has leveled off or become global cooling. But when you look at the long-term trend over the past 130 years, our world is definitely getting warmer. And that's the human-produced greenhouse gas signal."
Patzert said the recent climate record is like making a drive from the coast to the mountains. "As you rise slowly to higher and higher elevations, occasionally you hit a major speed bump, such as the 1997 to 1998 El Niño, and temperatures spike; or you hit potholes, such as cooler phases of the PDO, and temperatures dip," he said. "In the end, though, we still tend toward the top of the mountain, and the trend upwards is clear. We are driving ourselves into a warmer world."
The new images from the imaging science subsystem and the composite infrared spectrometer teams also include the best 3-D image ever obtained of a "tiger stripe," a fissure that sprays icy particles, water vapor and organic compounds. There are also views of regions not well-mapped previously on Enceladus, including a southern area with crudely circular tectonic patterns.
The images and additional information are online at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
"Enceladus continues to astound," said Bob Pappalardo, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "With each Cassini flyby, we learn more about its extreme activity and what makes this strange moon tick."
For Cassini's visible-light cameras, the Nov. 21, 2009 flyby provided the last look at Enceladus' south polar surface before that region of the moon goes into 15 years of darkness, and includes the most detailed look yet at the jets.
Scientists planned to use this flyby to look for new or smaller jets not visible in previous images. In one mosaic, scientists count more than 30 individual geysers, including more than 20 that had not been seen before. At least one jet spouting prominently in previous images now appears less powerful.
"This last flyby confirms what we suspected," said Carolyn Porco, imaging team lead based at the Space Science Institute in Boulder, Colo. "The vigor of individual jets can vary with time, and many jets, large and small, erupt all along the tiger stripes."
A new map that combines heat data with visible-light images shows a 40-kilometer (25-mile) segment of the longest tiger stripe, known as Baghdad Sulcus. The map illustrates the correlation, at the highest resolution yet seen, between the geologically youthful surface fractures and the anomalously warm temperatures that have been recorded in the south polar region. The broad swaths of heat previously detected by the infrared spectrometer appear to be confined to a narrow, intense region no more than a kilometer (half a mile) wide along the fracture.
In these measurements, peak temperatures along Baghdad Sulcus exceed 180 Kelvin (minus 135 degrees Fahrenheit), and may be higher than 200 Kelvin (minus 100 degrees Fahrenheit). These warm temperatures probably result from heating of the fracture flanks by the warm, upwelling water vapor that propels the ice-particle jets seen by Cassini's cameras. Cassini scientists will be testing this idea by investigating how well the hot spots correspond with the jet sources.
"The fractures are chilly by Earth standards, but they're a cozy oasis compared to the numbing 50 Kelvin (-370 Fahrenheit) of their surroundings," said John Spencer, a composite infrared spectrometer team member based at Southwest Research Institute in Boulder, Colo. "The huge amount of heat pouring out of the tiger stripe fractures may be enough to melt the ice underground. Results like this make Enceladus one of the most exciting places we've found in the solar system."
Some of Cassini's scientists infer that the warmer the temperatures are at the surface, the greater the likelihood that jets erupt from liquid. "And if true, this makes Enceladus' organic-rich, liquid sub-surface environment the most accessible extraterrestrial watery zone known in the solar system," Porco said.
The Nov. 21 flyby was the eighth targeted encounter with Enceladus. It took the spacecraft to within about 1,600 kilometers (1,000 miles) of the moon's surface, at around 82 degrees south latitude.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md., where the instrument was built.
The iSWA is a robust, integrated system provides information about space weather conditions past, present, and future and, unlike many other programs currently in use, has an interface that the user can customize to suit a unique set of data requirements.
"The iSWA space-weather data analysis system offers a unique level of customization and flexibility to maintain, modify, and add new tools and data products as they become available," says Marlo Maddox, iSWA system chief developer at NASA Goddard.
iSWA draws together information about conditions from the sun to the boundary of the sun’s influence, known as the heliosphere. The iSWA systems digests information from spacecraft including the National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environmental Satellites (GOES), NASA’s Solar Terrestrial Relations Observatory (STEREO), the joint European Space Agency and NASA mission Solar and Heliospheric Observatory (SOHO), and NASA's Advanced Composition Explorer (ACE).
Citizen scientists and science enthusiasts can also use the data, models, and tools of the iSWA system. Similar to the way in which armchair astronomers have used SOHO data to discover comets, enthusiasts will find the iSWA system a wonderful resource for increasing their familiarity with the concept of space weather.
“We are continuously evolving the iSWA system, and we hope that it will benefit not only NASA satellite operators, but also that it may also help space-weather forecasting at other agencies such as the Air Force Weather Agency and NOAA," says Michael Hesse, chief of the Space Weather Laboratory at NASA Goddard.
Space-weather information tends to be scattered over various Web sites. NASA Goddard space physicist Antti Pulkkinen says the iSWA system represents “the most comprehensive single interface for general space-weather-related information,” providing data on past and current space-weather events. The system allows the user to configure or design custom displays of the information.
The system compiles data about conditions on the sun, in Earth's magnetosphere -- the protective magnetic field that envelops our planet -- and down to Earth's surface. It provides a user interface to provide NASA's satellite operators and with a real-time view of space weather. In addition to NASA, the iSWA system is used by the Air Force Weather agency.
Access to space-weather information that combines data from state-of-the-art space-weather models with concurrent observations of the space environment provides a powerful tool for users to obtain a personalized “quick look” at space-weather information, detailed insight into space-weather conditions, as well as tools for historical analysis of the space-weather’s impact.
Development of the iSWA system has been a joint activity between the Office of the Chief Engineer at NASA Headquarters and the Applied Engineering and Technology Directorate and the Science and Exploration Directorate at NASA Goddard. The iSWA system is located at NASA Goddard.
The Community Coordinated Modeling Center is funded by the Heliophysics Division in the Science Mission Directorate at NASA Headquarters, and the National Science Foundation.
› iSWA space-weather forecasting tool Web site
Monday, February 22, 2010
Sunday, February 21, 2010
Saturday, February 20, 2010
The figure shows the day of the week favored by rainfall and by lightning in each summer from 1998 to 2009 in the southeastern United States (click here for a map of the area included in the analysis). The "clock plots" on the left and right indicate the day of the week when mean activity was at a maximum. The numbers indicate the year the data comes from. The rain estimates are based on TRMM and other satellite observations. The lightning data were collected by ground stations that are part of the National Lightning Detection Network. Credit: NASA/Bell
To find out more, I ran some questions about the connection between pollution and lightning by Bell via email:
What On Earth: Why does air pollution have any bearing on lightning or rainfall, and why is the connection more noticeable over the Southeast than other parts of the country?
Thomas Bell: Our explanation is that the storms need to start their growth in a hot, humid environment to give the pollution “something to work with.” The pollution causes the storm to climb to higher altitudes, because it causes the cloud droplets being formed in the storm to be smaller than they would be in a clean environment. They’re lighter and are carried up higher than usual, where they freeze (releasing latent heat), which pumps the storm up more than would happen in clean air.
The environment needs to be hot in order to have the capacity to push the storm up to altitudes where freezing can occur. The environment also needs to be humid because when the storm grows more vigorously it “sucks” air at its base up more strongly, pulling in more moisture, which then provides additional energy to the storm as the moisture condenses during its climb. The western half of the country is fairly dry—even though it can be hot, there isn’t much “fuel” (moisture) to feed a storm when it tries to grow more vigorously. The Southeast is especially hot and humid in the summer, so that’s where the effect shows up best, according to our theory.
What On Earth: Are there particular types of air pollution that have more or less impact on rain and lightning?
Thomas Bell: We don’t have a good answer to this as yet. The pollution should be the kind that affects cloud droplet growth. If we had to finger something, we’d probably choose the kinds of particulates that are emitted by diesel engines, because it seems that the weekly cycle in pollution is due, to a considerable extent, to the weekly cycle in transportation (probably trucking). More trucks are on the roads from Tue-Thu than they are the rest of the week. But this is more conjecture than a well-documented explanation.
For more context on Bell's findings, see these earlier Image of Week entries, take a look at these news stories, or read these peer-reviewed journal articles. And, when you've done all that, head over to the Earth Science Picture of the Day page (which we've written about previously) and enjoy these spectacular pictures of lightning. Here's an eerie one taken in the German town of Bad Mergentheim:
A image from a simulation that shows the spread of black carbon aerosols in Asia. Areas where the air was thick with the pollution particles are white, while lower concentrations are transparent purple. (Credit: Earth Observatory)
As NASA atmospheric scientist Eric Wilcox recently told Time magazine, emerging evidence suggests that a short-lived type of air pollution called black carbon—known popularly as soot—can exacerbate global warming by absorbing incoming solar radiation.
Yet pinning down precisely how much the black carbon exacerbates warming is no easy task, research conducted by Goddard Institute for Space Studies climatologist Dorothy Koch suggests. The study, published in Atmospheric Chemistry and Physics tracked how the predictions from 17 global black carbon models compared with actual measurements collected by airplane, satellite, and ground-based sensors. It shows, among other things, that models generally underestimate black carbon’s warming effect on climate.
Koch tested all the models in three ways. In the simplest of the three, she compared the models’ predictions to the amount of black carbon measured at the surface, finding that they matched real life reasonably well.
Her second test compared the models’ predictions to black carbon measurements made higher in the atmosphere using airplanes, and the results were much less clear cut. Though the models usually had too much black carbon over pollution sources, most had too little over remote regions such as the Arctic.
Koch’s final and most important test looked at how much solar radiation black carbon actually absorbs, an indicator of the amount of warming the particles actually produce. Again, the results were mixed. The models were largely accurate over North America and Europe, but were not for areas that have high levels of black carbon such as Central Africa, Southeast Asia, and the Amazon.
We concluded from this study that most models have enough black carbon at ground level in polluted regions, too much in the atmosphere above source regions, but not enough in the Arctic where black carbon may play an important role in contributing to Arctic warming and ice/snow melt. The models' soot generally does not absorb enough sunlight and therefore these models would underestimate black carbon heating effects. This probably results from underestimating the absorbing properties of the particles rather than the amount (mass) of black carbon.
Wondering how climate modelers can continue to close the gap between model predictions and reality? Koch put forward some advice on how to fine-tune the next generation of aerosols models. Her top three:
1) Account for mixing between black carbon and other components of the atmosphere,
2) Incorporate better measurements of particle size and source amount in some regions.
3) Continue to mine ongoing satellite and field campaigns for data about black carbon.
Friday, February 19, 2010
Prometheus is one of Saturn's innermost moons. It orbits the gas-giant at a distance of about 140,000 kilometers (86,000 miles) and is 86 kilometers (53 miles) across at its widest point. The porous, icy world was originally discovered in images taken by NASA's Voyager 1 spacecraft back in 1980.
Cassini's narrow-angle camera captured two black-and-white images of the moon on Dec. 26, 2009, and the imaging team combined the images to make this new stereo view. It looks different from the "egg-cellent" raw image of Prometheus obtained on Jan. 27 because that view shows one of the short ends of the oddly shaped moon. In this 3-D image, the sun illuminates Prometheus at a different angle, making the moon's elongated body visible.
The Cassini Equinox Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. For more information about the Cassini Equinox Mission visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
Thursday, February 18, 2010
Beginning each fall, sea ice spreads across the surface of the Arctic Ocean until it becomes confined by surrounding continents. Only a few passages -- including the Fram Strait and Nares Strait -- allow sea ice to escape.
"There are a couple of ways to lose Arctic ice: when it flows out and when it melts," said lead study researcher Ron Kwok of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We are trying to quantify how much we're losing by outflow versus melt."
Kwok and colleagues found that ice arches were missing in 2007 from the Nares Strait, a relatively narrow 30- to 40-kilometer-wide (19- to 25-mile-wide) passage west of Greenland. Without the arches, ice exited freely from the Arctic. The Fram Strait, east of Greenland, is about 400 kilometers (249 miles) wide and is the passage through which most sea ice usually exits the Arctic.
Despite Nares' narrow width, the team reports that in 2007, ice loss through Nares equaled more than 10 percent of the amount emptied on average each year through the wider Fram Strait.
"Until recently, we didn't think the small straits were important for ice loss," Kwok said. The findings were published this month in Geophysical Research Letters.
"One of our most important goals is developing predictive models of Arctic sea ice cover," said Tom Wagner, cryosphere program manager at NASA Headquarters in Washington. "Such models are important not only to understanding changes in the Arctic, but also changes in global and North American climate. Figuring out how ice is lost through the Fram and Nares straits is critical to developing those models."
To find out more about the ice motion in Nares Strait, the scientists examined a 13-year record of high-resolution radar images from the Canadian RADARSAT and European Envisat satellites. They found that 2007 was a unique year – the only one on record when arches failed to form, allowing ice to flow unobstructed through winter and spring.
The arches usually form at southern and northern points within Nares Strait when big blocks of sea ice try to flow through the strait's restricted confines, become stuck and are compressed by other ice. This grinds the flow of sea ice to a halt.
"We don't completely understand the conditions conducive to the formation of these arches," Kwok said. "We do know that they are temperature-dependent because they only form in winter. So there's concern that if climate warms, the arches could stop forming."
To quantify the impact of ice arches on Arctic Ocean ice cover, the team tracked ice motion evident in the 13-year span of satellite radar images. They calculated the area of ice passing through an imaginary line, or "gate," at the entrance to Nares Strait. Then they incorporated ice thickness data from NASA's ICESat to estimate the volume lost through Nares.
They found that in 2007, Nares Strait drained the Arctic Ocean of 88,060 square kilometers (34,000 square miles) of sea ice, or a volume of 60 cubic miles. The amount was more than twice the average amount lost through Nares each year between 1997 and 2009.
The ice lost through Nares Strait was some of the thickest and oldest in the Arctic Ocean.
"If indeed these arches are less likely to form in the future, we have to account for the annual ice loss through this narrow passage. Potentially, this could lead to an even more rapid decline in the summer ice extent of the Arctic Ocean," Kwok said.
For more information about NASA and agency programs, visit: http://www.nasa.gov .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
NASA's Earth Science News Team: Your research suggests that the climate science community ought to shift its focus from looking at the impacts of individual chemicals to economic sectors. Why?
Nadine Unger: There's nothing "wrong" with dividing climate impacts up by chemical species, but it's not particularly useful for policy makers. They need to know which human activities are impacting the climate and what the effect will be if they attempt to curb emissions from a particular sector. Also, there's a great deal of complexity in our emissions that they need to be mindful of if we want to mitigate climate change efficiently.
NASA: What sort of complexity?
Nadine Unger: Some sectors of the economy produce a mixture of pollutants -- particularly aerosols -- that cause cooling rather than warming in the short term. Since warming can accelerate as we remove aerosols, we've been inadvertently geoengineering for decades with aerosol emissions.
Take the heavy industry and shipping sectors, for example. These sectors burn a great deal of coal and bunker fuel, which releases carbon dioxide, which causes greenhouse warming. But they also release sulfates, which cause cooling by blocking incoming radiation from the sun and by changing clouds to make them brighter and longer-lived. In the short term, the cooling from sulfates actually outweighs the warming from carbon dioxide, meaning the net impact of the shipping and heavy industry sectors today is to cool climate.
Compare that to cars and trucks, which emit almost no sulfates but a great deal of carbon dioxide, black carbon, and ozone -- all of which cause warming and happen to be very bad for human health. Cutting transportation emissions would be unambiguously good for the climate in the short term, while cutting heavy industry emissions would have less of an impact right now.
NASA: You keep mentioning "short-term" impacts. Could the climate impacts of some sectors of the economy change over longer time periods?
Nadine Unger: Yes. Greenhouse gases have a much longer lifespan -- or residence time -- in the atmosphere than aerosols, which typically rain out after a few days or weeks. This means that the impact of greenhouse gases can accumulate and intensify over time, while the aerosol effects become comparatively less important on longer time scales due to the accumulation of carbon dioxide.
NASA: You've mentioned industry, shipping and on-road transportation. What other sectors of the economy did you analyze?
Nadine Unger: Aviation, household fossil fuels, railroads, household biofuels (mainly wood and dung used for home cooking and heating), animal husbandry, the electric power sector, waste and landfills, agriculture, biomass burning...
NASA: What is biomass burning?
Nadine Unger: Mainly tropical forest fires, deforestation and savannah and shrub fires. We also looked at agricultural waste burning, which relates to seasonal clearing of the fields common in many countries in Africa and South America.
NASA: So, does this mean that pollution from industry and biomass burning is good for the climate?
Nadine Unger: No, not at all. Both of those sectors contribute to warming over the long term, so we'll have no choice but to reduce our emissions over time. But these sectors do mask warming from greenhouses gases in the short term. Just because an activity causes cooling in the short-term does not mean that it is ‘good’ for the climate. The emissions might disturb other aspects of the climate system including the amount of rainfall in a region and therefore the water supply to humans.
NASA: Where did you get all the information about emissions?
Nadine Unger: We used emission inventories assembled by colleagues. For instance, a colleague from the University of Illinois -- Tami Bond -- has some of the best information on some types of aerosols, such as black carbon.
NASA: But how can you estimate the impacts of emissions that haven't happened yet?
Nadine Unger: We used a computer model at GISS to look at future at climate impacts if we continued emitting pollutants at today's rate. Using this approach, we looked specifically at two snapshots in time: 2020 and 2100.
NASA: What can we do if we want to minimize climate change in the near term?
Nadine Unger: Well, our analysis suggests that on-the-road transportation and household biofuels are very attractive sectors to target. We can reduce human warming impacts most rapidly by tackling emissions from these sectors. In order to protect climate in the longer term, emissions from power and industry must be reduced.
NASA: Are there any uncertainties in your results?
Nadine Unger: There are. There's a large amount of uncertainty about how aerosols affect climate, especially through the indirect effects on clouds. Hopefully, NASA's Glory mission will help reduce the uncertainties associated with aerosols.
NASA: What direction do you see your research going next?
Nadine Unger: Our focus has been on global climate so far, but in future work we'll assess regional climate impacts, as well as other disturbances to the climate system, such as effects on the water supply and land ecosystems.
In addition, we plan to investigate many of the sectors in greater detail. In the power sector, for example, we might look specifically at power stations that operate with coal or natural gas. And in the on-road transportation sector, we might break out heavy- from light-duty vehicles.
Finally, we're planning to partner with environmental economists to determine the damage costs of emissions from all the sectors due to both climate and air quality impacts, results that we can use to develop alternative mitigation scenarios.
Road Transportation Emerges as Key Driver of Warming in New Analysis from NASA
Attribution of Climate Forcing to Economic Sectors
Nadine Unger Bio
Other Research by Nadine Unger
Clean the Air, Heat the Planet