Solar changes help create cold northern winters

Fluctuations in ultraviolet light can set up frigid, snowy conditionsWeb edition : Monday, October 10th, 2011

Harsh winters in the United States and northern Europe may partly be the result of changes in ultraviolet radiation coming from the sun.

A new climate simulation study shows how fluctuations in ultraviolet light linked to the sun’s 11-year activity cycle could change winter weather patterns across the Northern Hemisphere. The work appears online October 9 in Nature Geoscience.

“We hope this will open the door to improving ultralong-range predictions,” says co-author Adam Scaife, a climate modeler at the Met Office’s Hadley Centre in Exeter, England.

Scientists have long noted anecdotal links between low solar activity and cold European winters: Part of the Little Ice Age, which gripped the region between about 1550 and 1850, coincided with a record low number of sunspots, which are one measure of solar activity.  But until now, Scaife says, no one had found a physical explanation for how subtle changes in radiation hitting the top of Earth’s atmosphere could translate to changes in weather patterns at the surface.

The answer came from the Solar Radiation and Climate Experiment satellite. From 2004 to 2007, during the low points of the last solar cycle, the satellite measured a surprising drop-off in the amount of ultraviolet radiation coming from the sun, roughly five times greater than previously thought. “I thought, if that’s true, that’s going to do something interesting to the climate system,” Scaife says.

To test what might happen, the scientists put the big ultraviolet decline into the Met Office’s climate model, a massive computer program that can simulate how the ocean and atmosphere respond to such changes. With less ultraviolet radiation, the simulation suggested, parts of the upper atmosphere cooled more than usual and allowed winds to blow more from the east. The anomaly then got bigger and started to burrow down through the atmosphere to altitudes where weather patterns form.  There, the changes affected how storms would normally grow, allowing cold weather to form over northern Europe and the United States.

These changes occurred only in winter, and not during every solar cycle minimum the model analyzed. But over time, the scientists found, more winters saw these cold patterns form during solar minimum than during solar maximum. “It’s changing the odds of what kind of winter you’re going to get by a significant amount,” Scaife says.

At the same time, weather patterns over southern Europe and Canada were milder than normal, essentially canceling out the chill of northern Europe and the United States. The new work thus can’t say much about whether changes in solar radiation affect global temperatures, Scaife says. Other natural factors also affect the severity of winters, including volcanic eruptions and semi-regular weather patterns like El Niño.

Kunihiko Kodera, a sun-climate researcher at Nagoya University in Japan, says the new model seems to capture all the steps in the atmosphere, but small details as to how warm or cold it got over particular landmasses may make it difficult to predict localized weather changes.

If the Met Office computer model can accurately reproduce past forecasts, the researchers hope to start incorporating solar variability into long-term weather predictions. Solar activity is currently increasing toward an expected weak maximum in 2013.

Found in: Earth and Earth Science

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When matter melts: Scientists map phase changes in quark-gluon plasma

ScienceDaily (June 24, 2011) — In its infancy, when the universe was a few millionths of a second old, the elemental constituents of matter moved freely in a hot, dense soup of quarks and gluons. As the universe expanded, this quark-gluon plasma quickly cooled, and protons and neutrons and other forms of normal matter "froze out": the quarks became bound together by the exchange of gluons, the carriers of the color force.

"The theory that describes the color force is called quantum chromodynamics, or QCD," says Nu Xu of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the spokesperson for the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at DOE's Brookhaven National Laboratory. "QCD has been extremely successful at explaining interactions of quarks and gluons at short distances, such as high-energy proton and antiproton collisions at Fermi National Accelerator Laboratory. But in bulk collections of matter -- including the quark-gluon plasma -- at longer distances or smaller momentum transfer, an approach called lattice gauge theory has to be used."

Until recently, lattice QCD calculations of hot, dense, bulk matter could not be tested against experiment. Beginning in 2000, however, RHIC was able to recreate the extreme conditions of the early universe in miniature, by colliding massive gold nuclei (heavy ions) at high energies.

Experimentalists at RHIC, working with theorist Sourendu Gupta of India's Tata Institute of Fundamental Research, have recently compared lattice-theory predictions about the nature of the quark-gluon plasma with certain STAR experimental results for the first time. In so doing they have established the temperature boundary where ordinary matter and quark matter cross over and change phase. Their results appear in the journal Science.

Phase diagrams

The aim of both the theoretical and experimental work is to explore and fix key points in the phase diagram for quantum chromodynamics. Phase diagrams are maps, showing, for example, how changes in pressure and temperature determine the phases of water, whether ice, liquid, or vapor. A phase diagram of QCD would map the distribution of ordinary matter (known as hadronic matter), the quark-gluon plasma, and other possible phases of QCD such as color superconductivity.

"Plotting a QCD phase diagram requires both theory calculations and experimental effort with heavy-ion collisions," says Xu, who is a member of Berkeley Lab's Nuclear Science Division and an author of the Science paper. Experimental studies require powerful accelerators like RHIC on Long Island or the Large Hadron Collider at CERN in Geneva, while calculations of QCD using lattice gauge theory require the world's biggest and fastest supercomputers. Direct comparisons can achieve more than either approach alone.

One of the basic requirements of any phase diagram is to establish its scale. A phase diagram of water might be based on the Celsius temperature scale, defined by the boiling point of water under normal pressure (i.e., at sea level). Although the boiling point changes with pressure -- at higher altitudes water boils at lower temperatures -- these changes are measured against a fixed value.

The scale of the QCD phase diagram is defined by a transition temperature at the zero value of "baryon chemical potential." Baryon chemical potential measures the imbalance between matter and antimatter, and zero indicates perfect balance.

Through extensive calculations and actual data from the STAR experiment, the team was indeed able to establish the QCD transition temperature. Before they could do so, however, they first had to realize an equally significant result, showing that the highly dynamical systems of RHIC's gold-gold collisions, in which the quark-gluon plasma winks in and out of existence, in fact achieve thermal equilibrium. Here's where theory and experiment worked hand in hand.

"The fireballs that result when gold nuclei collide are all different, highly dynamic, and last an extremely short time," says Hans Georg Ritter, head of the Relativistic Nuclear Collisions program in Berkeley Lab's Nuclear Science Division and an author of the Science paper. Yet because differences in values of the kind observed by STAR are related to fluctuations in thermodynamic values predicted by lattice gauge theory, says Ritter, "by comparing our results to the predictions of theory, we have shown that what we measure is in fact consistent with the fireballs reaching thermal equilibrium. This is an important achievement."

The scientists were now able to proceed with confidence in establishing the scale of the QCD phase diagram. After a careful comparison between experimental data and the results from the lattice gauge theory calculations, the scientists concluded that the transition temperature (expressed in units of energy) is 175 MeV (175 million electron volts).

Thus the team could develop a "conjectural" phase diagram that showed the boundary between the low-temperature hadronic phase of ordinary matter and the high-temperature quark-gluon phase.

In search of the critical point

Lattice QCD also predicts the existence of a "critical point." In a QCD phase diagram the critical point marks the end of a line showing where the two phases cross over, one into the other. By changing the energy, for example, the baryon chemical potential (balance of matter and antimatter) can be adjusted.

Among the world's heavy-ion colliders, only RHIC can tune the energy of the collisions through the region of the QCD phase diagram where the critical point is most likely to be found -- from an energy of 200 billion electrons volts per pair of nucleons (protons or neutrons) down to 5 billion electron volts per nucleon pair.

Says Ritter, "Establishing the existence of a QCD critical point would be much more significant than setting the scale." In 2010, RHIC started a program to search for the QCD critical point.

Xu says, "In this paper, we compared experimental data with lattice calculations directly, something never done before. This is a real step forward and allows us to establish the scale of the QCD phase diagram. Thus begins an era of precision measurements for heavy-ion physics."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Sourendu Gupta, Xiaofeng Luo, Bedangadas Mohanty, Hans Georg Ritter and Nu Xu. Scale for the phase diagram of quantum chromodynamics. Science, 24 June 2011 DOI: 10.1126/science.1204621

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Study examines changes in medical students’ views about internal medicine careers

ScienceDaily (Apr. 25, 2011) — Compared with 1990, more medical students in 2007 viewed internal medicine as a potentially meaningful career; however, the majority of students are choosing other specialties, according to a report in the April 25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

"The United States faces a troubling shortage in its primary care medical workforce," the authors write as background information in the article. "According to the Institute of Medicine, the United States is not prepared to meet the health care needs of the growing number of older adults."

Mark D. Schwartz, M.D., of the New York University School of Medicine, and colleagues examined data collected during two previous national studies of senior medical students that addressed student characteristics, specialties chosen and perceptions of internal medicine among other questions. The 1990 survey included 1,244 students at 16 schools and the 2007 survey included 1,177 students at 11 schools.

The two groups of students were of similar age, marital status and parental status. Compared with the 1990 survey group, the 2007 survey group included more women (52 percent vs. 37 percent) and students reporting more educational debt, with an average of $101,000 compared with $63,000 in 1990.

The proportion of students planning careers in internal medicine (combining all types of internal medicine including subspecialty and medicine-pediatrics) was similar in 1990 and 2007 (24 percent and 23 percent respectively); however, the percentage of students planning general internal medicine training declined from 9 percent in 1990 to 2 percent in 2007.

Additionally, the appeal of being a primary care physician as an influence toward internal medicine declined from 57 percent in 1990 to 33 percent in 2007. Although most students in both cohorts were attracted toward careers in internal medicine by the "esteem" offered by the specialty (68 percent of students in 1990 and 82 percent in 2007), some students were less attracted to internal medicine by the "types of patients cared for by internists." Students in 1990 and in 2007 also felt that workload and stress are greater in internal medicine that in other fields.

"To rebuild the generalist physician workforce, improving students' experience of internal medicine in medical school is no longer sufficient," the authors conclude. "Bolder reform will be required to improve the educational pipeline, practice and payment of generalist internal medicine physicians."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by JAMA and Archives Journals.

Journal Reference:

M. D. Schwartz, S. Durning, M. Linzer, K. E. Hauer. Changes in Medical Students' Views of Internal Medicine Careers From 1990 to 2007. Archives of Internal Medicine, 2011; 171 (8): 744 DOI: 10.1001/archinternmed.2011.139

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Huge dry ice deposit on Mars: NASA orbiter reveals big changes in Red Planet's atmosphere

ScienceDaily (Apr. 22, 2011) — NASA's Mars Reconnaissance Orbiter has discovered the total amount of atmosphere on Mars changes dramatically as the tilt of the planet's axis varies. This process can affect the stability of liquid water, if it exists on the Martian surface, and increase the frequency and severity of Martian dust storms.

Researchers using the orbiter's ground-penetrating radar identified a large, buried deposit of frozen carbon dioxide, or dry ice, at the Red Planet's south pole. The scientists suspect that much of this carbon dioxide enters the planet's atmosphere and swells the atmosphere's mass when Mars' tilt increases. The findings are published in the journal Science.

The newly found deposit has a volume similar to Lake Superior's nearly 3,000 cubic miles (about 12,000 cubic kilometers). The deposit holds up to 80 percent as much carbon dioxide as today's Martian atmosphere. Collapse pits caused by dry ice sublimation and other clues suggest the deposit is in a dissipating phase, adding gas to the atmosphere each year. Mars' atmosphere is about 95 percent carbon dioxide, in contrast to Earth's much thicker atmosphere, which is less than .04 percent carbon dioxide.

"We already knew there is a small perennial cap of carbon-dioxide ice on top of the water ice there, but this buried deposit has about 30 times more dry ice than previously estimated," said Roger Phillips of Southwest Research Institute in Boulder, Colo. Phillips is deputy team leader for the Mars Reconnaissance Orbiter's Shallow Radar instrument and lead author of the report.

"We identified the deposit as dry ice by determining the radar signature fit the radio-wave transmission characteristics of frozen carbon dioxide far better than the characteristics of frozen water," said Roberto Seu of Sapienza University of Rome, team leader for the Shallow Radar and a co-author of the new report. Additional evidence came from correlating the deposit to visible sublimation features typical of dry ice.

"When you include this buried deposit, Martian carbon dioxide right now is roughly half frozen and half in the atmosphere, but at other times it can be nearly all frozen or nearly all in the atmosphere," Phillips said.

An occasional increase in the atmosphere would strengthen winds, lofting more dust and leading to more frequent and more intense dust storms. Another result is an expanded area on the planet's surface where liquid water could persist without boiling. Modeling based on known variation in the tilt of Mars' axis suggests several-fold changes in the total mass of the planet's atmosphere can happen on time frames of 100,000 years or less.

The changes in atmospheric density caused by the carbon-dioxide increase also would amplify some effects of the changes caused by the tilt. Researchers plugged the mass of the buried carbon-dioxide deposit into climate models for the period when Mars' tilt and orbital properties maximize the amount of summer sunshine hitting the south pole. They found at such times, global, year-round average air pressure is approximately 75 percent greater than the current level.

"A tilted Mars with a thicker carbon-dioxide atmosphere causes a greenhouse effect that tries to warm the Martian surface, while thicker and longer-lived polar ice caps try to cool it," said co-author Robert Haberle, a planetary scientist at NASA's Ames Research Center in Moffett Field, Calif. "Our simulations show the polar caps cool more than the greenhouse warms. Unlike Earth, which has a thick, moist atmosphere that produces a strong greenhouse effect, Mars' atmosphere is too thin and dry to produce as strong a greenhouse effect as Earth's, even when you double its carbon-dioxide content."

The Shallow Radar, one of the Mars Reconnaissance Orbiter's six instruments, was provided by the Italian Space Agency, and its operations are led by the Department of Information Engineering, Electronics and Telecommunications at Sapienza University of Rome. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter project for NASA's Science Mission Directorate at the agency's headquarters in Washington. Lockheed Martin Space Systems in Denver built the spacecraft.

For more information about the Mars Reconnaissance Orbiter mission, visit http://www.nasa.gov/mro .

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Journal Reference:

Roger J. Phillips, Brian J. Davis, Kenneth L. Tanaka, Shane Byrne, Michael T. Mellon, Nathaniel E. Putzig, Robert M. Haberle, Melinda A. Kahre, Bruce A. Campbell, Lynn M. Carter, Isaac B. Smith, John W. Holt, Suzanne E. Smrekar, Daniel C. Nunes, Jeffrey J. Plaut, Anthony F. Egan, Timothy N. Titus, and Roberto Seu. Massive CO2 Ice Deposits Sequestered in the South Polar Layered Deposits of Mars. Science, 2011; DOI: 10.1126/science.1203091

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