Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

Eat, Prey, Rain: New Model of Dynamics of Clouds and Rain Is Based On a Predator-Prey Population Model

  10:10:00 AM    Science Lover

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What do a herd of gazelles and a fluffy mass of clouds have in common? A mathematical formula that describes the population dynamics of such prey animals as gazelles and their predators has been used to model the relationship between cloud systems, rain and tiny floating particles called aerosols. This model may help climate scientists understand, among other things, how human-produced aerosols affect rainfall patterns. The research recently appeared in the Proceedings of the National Academy of Sciences (PNAS).

A new mathematical model may help climate scientists 
understand, among other things, how human-produced 
aerosols affect rainfall patterns. (Credit: © Brian 
Jackson / Fotolia)

Clouds are major contributors to the climate system. In particular the shallow marine stratocumulus clouds that form huge cloud decks over the subtropical oceans cool the atmosphere by reflecting part of the incoming solar energy back to space. Drs. Ilan Koren of the Weizmann Institute's Environmental Sciences and Energy Research Department (Faculty of Chemistry) and Graham Feingold of the NOAA Earth System Research Laboratory, Colorado, found that equations for modeling prey-predator cycles in the animal world were a handy analogy for cloud-rain cycles: Just as respective predator and prey populations expand and contract at the expense of one another, so too rain depletes clouds, which grow again once the rain runs out. And just as the availability of grass affects herd size, the relative abundance of aerosols -- which "feed" the clouds as droplets condense around them -- affects the shapes of those clouds. A larger supply of airborne particles gives rise to more droplets, but these droplets are smaller and thus remain high up in the cloud rather than falling as rain.

In previous research, Feingold and Koren had "zoomed in" to discover oscillations in convective cells in marine stratocumulus. Now they returned to their data, but from a "top down" angle to see if a generalized formula could reveal something about these systems. Using just three simple equations, they developed a model showing that cloud-rain dynamics mimic three known predator-prey modes. Like gazelles and lions, the two can oscillate in tandem, the "predator" rain cycle following a step behind peak cloud formation. Or the two can reach a sort of steady state in which the clouds are replenished at the same rate as they are diminished (as in a light, steady drizzle). The third option is chaos -- the crash that occurs when predator populations get out of hand or a strong rain destroys the cloud system.



The model shows that as the amounts of aerosols change, the system can abruptly shift from one state to another. It also reveals a bifurcation -- two scenarios at different ends of the aerosol scale that lend themselves to stable patterns. In the first, relatively low aerosol levels lead to clouds in which development depends heavily on aerosol concentrations. In the second, high levels produce saturation; these clouds depend solely on the initial environmental conditions.

Using this so-called systems approach, says Koren, "can open new windows to view and understand the emergent behavior of the complex relationships between clouds, rain and aerosols, giving us a more useful view of the big picture and helping us to understand how shifting aerosol levels can lead to different climate patterns."

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Nanodiamonds Discovered in Greenland Ice Sheet, Contribute to Evidence for Cosmic Impact

Nanodiamonds Discovered in Greenland Ice Sheet, Contribute to Evidence for Cosmic Impact

  12:11:00 AM    Science Lover

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Nanosize diamonds have been discovered in the Greenland ice sheet, according to a study reported by scientists in a recent online publication of the Journal of Glaciology. The finding adds credence to the controversial hypothesis that fragments of a comet struck across North America and Europe approximately 12,900 years ago.

Scanning transmission electron microscope image of nanodiamonds from the Greenland ice sheet. (Credit: James C. Weaver, UCSB)

"There is a layer in the ice with a great abundance of diamonds," said co-author James Kennett, professor emeritus in the Department of Earth Science at UC Santa Barbara. "Most exciting to us is that this is the first such discrete layer of diamonds ever found in glacial ice anywhere on Earth, including the huge polar ice sheets and the alpine glaciers. The diamonds are so tiny that they can only be observed with special, highly magnifying microscopes. They number in the trillions."

This discovery supports earlier published evidence for a cosmic impact event about 12,900 years ago, Kennett explained. He said that the available evidence in the Greenland ice is consistent with this layer being at or close to this age, although further study is needed.

Researchers from the University of Maine led the expedition to Greenland in 2008. Co-authors on the study, besides Kennett and the team from Maine, include scientists from many universities and research entities. James Kennett's son, Douglas J. Kennett, of the University of Oregon, is one of the 21 scientists who contributed to the report.

Last year, the Kennetts reported the discovery of nanosize diamonds in a layer of sediment exposed on Santa Rosa Island, off the coast of Santa Barbara, Calif. They published this information with numerous co-authors in two papers last year in the Proceedings of the National Academy of Sciences and Science magazine.

According to James Kennett, the Greenland results also contradict a recent study questioning the presence of nanodiamonds in a layer of this age.

Kennett explained that the layer containing nanodiamonds on Santa Rosa Island, as well as those in the Greenland ice sheet -- both supporting a cosmic impact event -- appear to closely correspond to the time of the disappearance of the Clovis culture, the earliest well-established and well-accepted human culture living across North America. The event also corresponds with the time of extinction of many large animals across North America, including mammoths, camels, horses, and the saber tooth cat.

There is also evidence of widespread wildfires at that time, said Kennett. An associated sharp climatic cooling called the Younger Dryas cooling is also recorded widely over the northern hemisphere. This includes evidence found in ocean-drilled sediments beneath the Santa Barbara Channel. The cause of this cooling has long been debated as well as the cause of the animal extinctions and human cultural shift.

A high proportion of the nanosize diamonds in the Greenland ice sheet exhibit hexagonal mineral structure, and these are only known to occur on Earth in association with known cosmic impact events, said Kennett. This layer of diamonds corresponds with the sedimentary layer known as the Younger Dryas Boundary, dating to 12,900 years ago.

James Kennett, former director of the Marine Science Institute at UCSB, is considered by many of his peers to be an early founder of marine geology and paleoceanography. He has specialized in analyzing sedimentary layers below the ocean floor.

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New View of Tectonic Plates: Computer Modeling of Earth's Mantle Flow, Plate Motions, and Fault Zones

New View of Tectonic Plates: Computer Modeling of Earth's Mantle Flow, Plate Motions, and Fault Zones

  11:55:00 PM    Science Lover

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Computational scientists and geophysicists at the University of Texas at Austin and the California Institute of Technology (Caltech) have developed new computer algorithms that for the first time allow for the simultaneous modeling of Earth's mantle flow, large-scale tectonic plate motions, and the behavior of individual fault zones, to produce an unprecedented view of plate tectonics and the forces that drive it.

Plate boundaries, which can be seen as narrow red lines are 
resolved using an adaptively refined mesh with 1km local 
resolution. Shown are the Pacific and the Australian tectonic 
plates and the New Hebrides and Tonga microplates. 
(Credit: Georg Stadler, Institute for Computational 
Engineering & Sciences, UT Austin)

A paper describing the whole-earth model and its underlying algorithms will be published in the August 27 issue of the journal Science and also featured on the cover.

The work "illustrates the interplay between making important advances in science and pushing the envelope of computational science," says Michael Gurnis, the John E. and Hazel S. Smits Professor of Geophysics, director of the Caltech Seismological Laboratory, and a coauthor of the Science paper.

To create the new model, computational scientists at Texas's Institute for Computational Engineering and Sciences (ICES) -- a team that included Omar Ghattas, the John A. and Katherine G. Jackson Chair in Computational Geosciences and professor of geological sciences and mechanical engineering, and research associates Georg Stadler and Carsten Burstedde -- pushed the envelope of a computational technique known as Adaptive Mesh Refinement (AMR).

Partial differential equations such as those describing mantle flow are solved by subdividing the region of interest (such as the mantle) into a computational grid. Ordinarily, the resolution is kept the same throughout the grid. However, many problems feature small-scale dynamics that are found only in limited regions. "AMR methods adaptively create finer resolution only where it's needed," explains Ghattas. "This leads to huge reductions in the number of grid points, making possible simulations that were previously out of reach."

"The complexity of managing adaptivity among thousands of processors, however, has meant that current AMR algorithms have not scaled well on modern petascale supercomputers," he adds. Petascale computers are capable of one million billion operations per second. To overcome this long-standing problem, the group developed new algorithms that, Burstedde says, "allows for adaptivity in a way that scales to the hundreds of thousands of processor cores of the largest supercomputers available today."

With the new algorithms, the scientists were able to simulate global mantle flow and how it manifests as plate tectonics and the motion of individual faults. According to Stadler, the AMR algorithms reduced the size of the simulations by a factor of 5,000, permitting them to fit on fewer than 10,000 processors and run overnight on the Ranger supercomputer at the National Science Foundation (NSF)-supported Texas Advanced Computing Center.

A key to the model was the incorporation of data on a multitude of scales. "Many natural processes display a multitude of phenomena on a wide range of scales, from small to large," Gurnis explains. For example, at the largest scale -- that of the whole earth -- the movement of the surface tectonic plates is a manifestation of a giant heat engine, driven by the convection of the mantle below. The boundaries between the plates, however, are composed of many hundreds to thousands of individual faults, which together constitute active fault zones. "The individual fault zones play a critical role in how the whole planet works," he says, "and if you can't simulate the fault zones, you can't simulate plate movement" -- and, in turn, you can't simulate the dynamics of the whole planet.

In the new model, the researchers were able to resolve the largest fault zones, creating a mesh with a resolution of about one kilometer near the plate boundaries. Included in the simulation were seismological data as well as data pertaining to the temperature of the rocks, their density, and their viscosity -- or how strong or weak the rocks are, which affects how easily they deform. That deformation is nonlinear -- with simple changes producing unexpected and complex effects.

"Normally, when you hit a baseball with a bat, the properties of the bat don't change -- it won't turn to Silly Putty. In the earth, the properties do change, which creates an exciting computational problem," says Gurnis. "If the system is too nonlinear, the earth becomes too mushy; if it's not nonlinear enough, plates won't move. We need to hit the 'sweet spot.'"

After crunching through the data for 100,000 hours of processing time per run, the model returned an estimate of the motion of both large tectonic plates and smaller microplates -- including their speed and direction. The results were remarkably close to observed plate movements.

In fact, the investigators discovered that anomalous rapid motion of microplates emerged from the global simulations. "In the western Pacific," Gurnis says, "we have some of the most rapid tectonic motions seen anywhere on Earth, in a process called 'trench rollback.' For the first time, we found that these small-scale tectonic motions emerged from the global models, opening a new frontier in geophysics."

One surprising result from the model relates to the energy released from plates in earthquake zones. "It had been thought that the majority of energy associated with plate tectonics is released when plates bend, but it turns out that's much less important than previously thought," Gurnis says. "Instead, we found that much of the energy dissipation occurs in the earth's deep interior. We never saw this when we looked on smaller scales."

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Warmest Year-to-Date Global Temperature on Record

Warmest Year-to-Date Global Temperature on Record

  10:49:00 AM    Science Lover

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The combined global land and ocean surface temperature made this July the second warmest on record, behind 1998, and the warmest averaged January-July on record. The global average land surface temperature for July and January-July was warmest on record. The global ocean surface temperature for July was the fifth warmest, and for January-July 2010 was the second warmest on record, behind 1998.

The global average land surface temperature for July and January-July was warmest on record. (Credit: NOAA)

The monthly analysis from NOAA's National Climatic Data Center, which is based on records going back to 1880, is part of the suite of climate services NOAA provides government, business and community leaders so they can make informed decisions.

Global Temperature Highlights 

• The combined global land and ocean average surface temperature for July 2010 was the second warmest on record at 61.6°F (16.5°C), which is 1.19°F (0.66°C) above the 20th century average of 60.4°F (15.8°C). The averaged temperature for July 1998 was 61.7°F (16.5°C). 

• The July worldwide land surface temperature was 1.85°F (1.03°C) above the 20th century average of 57.8°F (14.3°C) -- the warmest July on record. Warmer-than-average conditions dominated land areas of the globe. The most prominent warmth was in Europe, western Russia and eastern Asia. Cooler-than-average regions included central Russia, Alaska and southern South America.

• According to the Finnish Meteorological Institute, Finland set a new all-time maximum temperature on July 29 when temperatures soared to 99.0°F (37.2°C), surpassing the previous record set in July 1914 by 2.3°F (1.3°C).

• Western Russia was engulfed by a severe heat wave during much of July. On July 30, Moscow set a new all-time temperature record when temperatures reached 102°F (39°C), exceeding the previous record of 99.0°F (37.2°C) set four days earlier. Before 2010, the highest maximum temperature recorded in Moscow was 98.2°F (36.8°C), set nine decades ago.

• According to the Beijing Climate Center, the July 2010 average temperature across China was 73.0°F (22.8°C), which is 2.5°F (1.4°C) above the 1971-2000 average and the warmest July since 1961.

• The worldwide ocean surface temperature was 0.97°F (0.54°C) above the 20th century average of 61.5°F (16.4°C) and the fifth warmest July on record. The warmth was most pronounced in the Atlantic Ocean.

• La Niña conditions developed during July 2010, as sea surface temperatures (SST) continued to drop across the central and eastern equatorial Pacific Ocean. According to NOAA's Climate Prediction Center, La Niña is expected to strengthen and last through the Northern Hemisphere winter 2010-2011.

• For the year-to-date, the global combined land and ocean surface temperature of 58.1°F (14.5°C) was the warmest January-July period on record. This value is 1.22°F (0.68°C) above the 20th century average.

Polar Sea Ice and Precipitation Highlights

• Arctic sea ice covered an average of 3.2 million square miles (8.4 million square kilometers) during July. This is 16.9 percent below the 1979-2000 average extent and the second lowest July extent since records began in 1979. The record low July was set in 2007. This was the 14th consecutive July with below-average Arctic sea ice extent. July 1996 was the last year that had above-average sea ice extent.

• Antarctic sea ice extent in July was above average, 4.8 percent above the 1979-2000 average -- resulting in the largest July sea ice extent on record.

• According to Australia's Bureau of Meteorology, the continent received an average of 34.4 mm (1.35 inches) of precipitation during July 2010 -- this is 55 percent above the 1961-1990 average and the highest value since 1998.

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Tiny Marine Microbes Exert Influence on Climate

Tiny Marine Microbes Exert Influence on Climate

  9:51:00 AM    Science Lover

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New research indicates that the interactions of microscopic organisms around a particular organic material may alter the chemical properties of the ocean and ultimately influence global climate by affecting cloud formation in the atmosphere.

Microchannel used to created patches of DMSP. (Credit: Photo by Tanvir Ahmed and Roman Stocker)

Justin Seymour, a research fellow at the University of Technology Sydney, is the lead author of a paper published in the July 16 issue of Science that describes how a relative of the smelly chemical that sea birds and seals use to locate prey, dimethylsulfide (DMS), may serve a similar purpose at the microbial scale, helping marine microorganisms find food and cycle chemicals that are important to climate.

"We found that ecological interactions and behavioral responses taking place within volumes of a fraction of a drop of seawater can ultimately influence important ocean chemical cycling processes," said Seymour.

Using microfluidic technology, the team of researchers led by Professor Roman Stocker of the Massachusetts Institute of Technology's Department of Civil and Environmental Engineering, recorded microbes swimming toward the chemical dimethylsulfoniopropionate (DMSP) as it was released into a tiny channel occupied by the microbes.

The fact that the microbes actively moved toward the DMSP indicates that the tiny organisms play a role in ocean sulphur and carbon cycles, which exert a powerful influence on Earth's climate. How fast the microorganisms consume DMSP -- rather than converting it into DMS -- is important because DMS is involved in the formation of clouds in the atmosphere. This in turn affects the heat balance of the atmosphere.

Seymour, Stocker, Professor Rafel Simó of the Institute for Marine Sciences in Barcelona, and MIT graduate student Tanvir Ahmed carried out the research in the MIT laboratory of Stocker, who pioneered the use of microfluidics and video microscopy in the study of ocean microbes. The new study is the first to make a visual record of microbial behaviour in the presence of DMSP.

"It's important to be able to directly look at an environment in order to understand its ecology," Stocker said. "We can now visualize the behavior of marine microorganisms much like ecologists have done with macro-organisms for a long time."

To do this, the team recreated a microcosm of the ocean environment using a microfluidic device about the size of a flash drive with minuscule channels engraved in a clear rubbery material. The scientists injected DMSP into the channel in a way that mimics the bursting of an algal cell after viral infection -- a common event in the ocean -- then, using a camera attached to a microscope, they recorded whether and how microbes swam towards the chemical.

The researchers found that some marine microbes, including bacteria, are attracted to DMSP because they feed on it, whereas others are drawn to the chemical because it signals the presence of prey. This challenges previous theories that this chemical might be a deterrent against predators.

"Our observations clearly show that, for some plankton, DMSP acts as an attractant towards prey rather than a deterrent," said Simó, an expert on the role of DMSP in the sulfur cycle, "By simulating the microscale patches of the chemical cue and directly monitoring the swimming responses of the predators towards these patches, we get a much more accurate perception of these important ecological interactions than can be obtained from traditional bulk approaches."

"These scientists have used impressive technology to study interactions between organisms and their chemical environment at the scales they actually take place," said David Garrison, director of the National Science Foundation (NSF)'s biological oceanography program. "The research will give us new insights on the workings of microbial assemblages in nature."

The research also indicates that marine microorganisms have at least one behavioral characteristic in common with larger sea and land animals: we're all drawn to food.

The team plans to extend the research from the laboratory to the ocean environment; the team is working on an experimental system that can be used on board oceanographic ships working with bacteria collected directly from the ocean.

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Source: "Chemoattraction to Dimethylsulfoniopropionate Throughout the Marine Microbial Food Web," by Justin R. Seymour, Rafel Simó, Tanvir Ahmed and Roman Stocker. Science, 16 July 2010.

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Surprisingly Regular Patterns in Hurricane Energy Discovered

Surprisingly Regular Patterns in Hurricane Energy Discovered

  11:37:00 PM    Science Lover

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Researchers at the Mathematics Research Centre and Universitat Autònoma de Barcelona have discovered the mathematical relation between the number of hurricanes produced in certain parts of Earth and the energy they release. The distribution is valid for all series of hurricanes under study, independent of when and where they occurred.

Meteorologist puts his finger on the eye of a 
hurricane. Earth image: visibleearth.nasa.gov. 
(Credit: iStockphoto/Eric Hood)

The research, published in Nature Physics, suggests that the evolution of hurricane intensity will be very difficult to predict.

It is well known that there are fewer probabilities of a devastating hurricane developing than of a modest one. However, the exact relation between the number of hurricanes and energy released was not known until now. Researchers from the Mathematics Research Centre (CRM) and the Department of Physics of Universitat Autònoma de Barcelona have analysed data corresponding to tropical cyclones (generic name used for hurricanes) which have appeared in different parts of the planet between 1945 and 2007. Scientists have discovered that this relation corresponds to a power-law, a precise mathematical formula cyclones obey in a surprising manner, regardless of where on the planet and when they appear.

This fundamental discovery has led researchers to more general conclusions on the behaviour of hurricanes. The first conclusion states that a hurricane's dynamics can be the result of a critical process, therefore making it impossible to predict its intensity. One of the aspects traditionally studied by organisations monitoring the danger of hurricanes is the prediction of their intensity, since this determines which alert and prevention systems are to be used in populated areas. Despite the efforts of scientists and resources invested, until now results have been very poor, although predictions on hurricane trajectory have improved considerably. The fact that hurricanes follow this power-law, as do other natural phenomena where large amounts of energy are released, e.g. earthquakes, questions the ability to predict the evolution of their intensity. In these types of processes, the dynamics behind large hurricanes are the same as those producing tropical storms of less importance and range. The way in which a small storm evolves and transforms into a catastrophic hurricane depends on whether the fluctuations amplifying the storm are stronger than those which tend to dissipate it. However, there is no specific aspect pointing to which will be the dominant fluctuations, since the system at that moment is in a critical situation, i.e. on the verge of either dissipating or growing.

The second conclusion of the study is related to the effects of global warming on the behaviour of tropical cyclones: a recent increase in activities in the North Atlantic has shown to follow the same pattern as other high-activity periods in the past. Although there has been a dramatic increase in the number of hurricanes occurring in the North Atlantic since mid-1990s when compared to the period starting in the 1970s, the distribution of hurricanes in the 1950s was similar to today's activity level. Therefore, this increase cannot be explained solely on the basis of climate change. Even so, the research points to the existence of a relation between global warming and the distribution of tropical cyclones. The number of hurricanes is inversely proportional to the energy released, except for the highest values of energy, where the relation is suddenly interrupted. Researchers have observed that the cut-off point where the power-law does not represent the behaviour of hurricanes is influenced by factors such as average sea surface temperature and the El Niño phenomenon. Thus at a higher temperature, for example, the cut-off point rises to higher energy values.

The research was carried out by Álvaro Corral, researcher at Mathematics Research Centre (consortium formed by the Institute of Catalan Studies and the Catalan Government, located at the UAB Research Park; CRM is also a CERCA center); Albert Ossó, UAB student in Physics; and Dr Josep Enric Llebot, professor at the UAB Department of Physics.

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