Environmental Research Goes on the Road

English

 

(l-r) Drs. Eyal Rotenberg and David Asaf, Prof. Dan Yakir and Yakir Preisler. Lab on wheels

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
For the past decade, an extension of the Weizmann Institute – the Yatir research station – has been monitoring the atmosphere above a patch of forest in southern Israel, producing data on the exchange of water, carbon and energy between the atmosphere and the semiarid ecosystem. This station, the sole Israeli contribution to the global chain called FLUXNET, has generated scores of doctoral theses and scientific papers, as well as adding invaluable pieces to the picture of global climate change.

Yet the future of the station was uncertain; its long-term funding threatened to dry up. That is when a generous donor named Robert Lewis, together with his sister, Cathy Wills, stepped into the breach with a promise to provide support for the station for the next ten years. In fact, Lewis was so impressed with the work being done there that he asked the head of the project, Prof. Dan Yakir of the Environmental Sciences and Energy Research Department in the Faculty of Chemistry: “What else do you need to develop this research?” Yakir’s reply was prompt: “We would like to be able to be mobile.”

Thus was the Biosphere-Atmosphere Research Mobile Lab born. The gestation period was a long one: Together with Dr. Eyal Rotenberg, Yakir and their team have spent the last two years designing and assembling the lab from the chassis up. All of the equipment has been custom-built, and a slew of engineers and experts from a dozen companies have been involved in the project. In the process, the researchers found they had to become truck drivers as well as scientists – Yakir, Rotenberg and several of the crew are now licensed, and they have begun to figure diesel and maintenance costs into their research budget.

“Eventually,” says Yakir, “the mobile lab will become our main lab, and much of the work conducted today both at Yatir and in our Weizmann Institute lab will be carried out there. In the future, it will do everything the ten-year-old Yatir station can do and more.” Along with the computers and scientific gear, the lab hauls a huge telescopic mast that can raise equipment up to 30 meters in the air – 10 meters higher than the tower at Yatir – enabling researchers to study the atmosphere above the relatively tall canopies of Israel’s northern forests.

In addition to ongoing scientific research, Yakir would like to see the mobile lab used in various educational projects at the Weizmann Institute. “It’s often hard to get students excited about global climate science,” he says. “A mobile lab outside the classroom gives them the opportunity to see the cool equipment that is used in our research, and the real-time measurements on the computer screens could make the subject both immediate and attractive.” In the meantime, the FLUXNET organization has already invited Yakir to bring the lab to Europe, where they would like it to travel between the many fixed stations to check and calibrate them.
 
 
Prof. Dan Yakir’s research is supported by the Cathy Wills and Robert Lewis Program in Environmental Science; and the estate of Sanford Kaplan.

 

 
 
 
 
(l-r) Drs. Eyal Rotenberg and David Asaf, Prof. Dan Yakir and Yakir Preisler. Lab on wheels
Environment
English
  • Carbon dioxide
  • Dan Yakir
  • Environmental Sciences and Energy Research
  • FLUXNET
  • Yatir forest

Pumping Iron

English

 

(l-r) Dr. Ishai Dror and Prof. Brian Berkowitz. Clean water

 

 

 
 
Iron and vitamin B12 are no longer just for dietary supplements. When bound together with a third material, they can break down some of the worst water pollutants, and they may thus be the key to restoring the health of the underground water supply.

Using these components, Prof. Brian Berkowitz and Dr. Ishai Dror of the Environmental Sciences and Energy Research Department (Faculty of Chemistry) have designed a treatment system that reduces the toxic chemicals in water to harmless compounds that can be further broken down naturally. Such a system could be placed in the path of underground flow to clean the water before it ever reaches the pipes, or it could be used to treat polluted water pumped from below ground.

Many of the waste chemicals that leach down into underground water reservoirs, called aquifers, can persist there for hundreds, even thousands of years. The problem, says Berkowitz, is that such man-made substances as pesticides, cleaning fluids and flame retardants don’t resemble anything found in nature, and thus few natural mechanisms exist to break them down. Unfortunately, many are considered to be carcinogenic even in extremely minuscule amounts, and Western standards allow only a few parts per billion of these pollutants to be present in drinking water.

Berkowitz and Dror realized that a simple chemical reaction might split the molecules of these harmful substances apart in such a way that bacteria or other natural processes could finish the job. The “indigestible” part of these molecules is generally a bond between a carbon ring and a chloride or bromide ion; if the reaction could get them to accept an electron in place of the ion, the two would be separated. As an electron source, the researchers turned to elemental iron, which easily gives up its electrons. They then looked for a way to combine the iron with a common filtering material called diatomite. Diatomite, though it resembles very fine white, powdery sand, is actually composed of fossilized diatom shells, and the microscopic pores in the grains make it an excellent filter for fluids – everything from swimming pool water to beer.
 

Scanning electron microscope images of representative samples of (left) clean diatomite and (right) diatomite composite with zero valent iron (small white dots) and vitamin B12 (not visible)

 
 
At first, the iron didn’t bind well to the diatomite base; and the electron transfer was only partially successful. The scientists realized they needed a further addition to the mix – a catalyst that would help get the electrons from the iron into the polluting molecules. “Rather than invent a new catalyst, we looked to natural molecules,” says Dror. “Nature’s favorite molecule for shuttling electrons is the porphyrin.” Porphyrins are found in everything from chlorophyll to hemoglobin to vitamin B12. The scientists found that B12 – an easily available, non-toxic substance – was just what the doctor ordered. The vitamin kept the iron particles small and spaced evenly on the diatoms’ surface, creating a large surface area for the chemical reactions to take place while enabling the water to flow through the material. Now the electron transfer was highly efficient. The costs of such a system, says Berkowitz, are comparable to those of standard activated carbon filters, and the results are much better, making them attractive to industries that rely on clean water.  

Larger diatomite/iron/B12 units could be placed in trenches or batteries of deep wells dug into the path of water flowing underground, says Berkowitz. In this way, aquifers that are in danger of contamination could be restored and their precious water reserves saved. Added advantages might include the prevention of soil contamination through seepage, a reduction in the need for such energy-intensive water-purification methods as desalination and a halt to the release of toxic gases from polluted aquifers into underground basements and parking garages.
 
Prof. Brian Berkowitz’s research is supported by the Carolito Stiftung; the Angel Faivovich Foundation for Ecological Research; the Dr. Scholl Center for Water and Climate, which he heads; the Brita Fund for Scholarships, Research and Education for the Improvement of Water in Israel; the Phyllis and Joseph Gurwin Fund for Scientific Advancement; Mr. and Mrs. Michael Levine, Pinckney, NJ; and the P. & A.Guggenheim-Ascarelli Foundation. Prof. Berkowitz is the incumbent of the Sam Zuckerberg Professorial Chair in Hydrology.

 

 

 

 

 

 
Scanning electron microscope images of representative samples of (left) clean diatomite and (right) diatomite composite with zero valent iron (small white dots) and vitamin B12 (not visible)
Environment
English
  • Brian Berkowitz
  • Chemistry
  • Environmental Sciences and Energy Research
  • Nanoparticles
  • Water›Water contamination

Eat, Prey, Rain

English

Dr. Ilan Koren. In the clouds. Cloud photo: Tamar Deutsch

 
 
What do a herd of gazelles and a fluffy mass of clouds have in common? A mathematical formula that describes the population dynamics of prey animals, such 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.

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 each other’s expense, so too does rain deplete 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 shape 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 systems. 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 amount of aerosols changes, the system can shift abruptly from one state to another. The model shows 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 aerosol 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 these systems and the complex relationships between clouds, rain and aerosols, giving us a useful view of the big picture and helping us to understand how shifting aerosol levels can lead to different climate patterns.”
 
Dr. Ilan Koren’s research is supported by the Yeda-Sela Center for Basic Research. Dr. Koren is the incumbent of the Benjamin H. Swig and Jack D. Weiler Career Development Chair in Perpetuity.
 
 
Dr. Ilan Koren. In the clouds. Cloud photo: Tamar Deutsch
Environment
English
  • Aerosols
  • Cloud formation
  • Environmental Sciences and Energy Research
  • Ilan Koren
  • Mathematical model

Eat, Prey, Rain

English
 
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).

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.”
 
clouds. Photo: Tamar Deutsch
 
 
Dr. Ilan Koren’s research is supported by the Yeda-Sela Center for Basic Research. Dr. Koren is the incumbent of the Benjamin H. Swig and Jack D. Weiler Career Development Chair in Perpetuity.
 
clouds. Photo: Tamar Deutsch
Environment
English
  • Aerosols
  • Cloud formation
  • Environmental Sciences and Energy Research
  • Ilan Koren
  • Mathematical model

Self-Organizing Clouds

English
Satellite image of a marine stratocumulus system, courtesy of NASA

The low rain clouds known as marine stratocumulus are generally found off the west coast of continents along the subtropical belts, sometimes extending for thousands of kilometers over the oceans. They form amazingly organized systems. Satellite images of these cloud systems reveal a puzzling pattern: a nearly perfect grid of cloud cells with hexagonal shapes. Some parts of these cloud fields are formed of closed cells – which look, in images, like fluffy white beehives. Other areas of the fields contain open cells, in which the clouds concentrate at the edges of the cell boundaries. Such cloud systems can persist for many hours.


Scientists at the Weizmann Institute, the NOAA Earth System Research Laboratory, the Pacific Northwest National Laboratory and Peking University have now shed new light on this long-standing mystery, revealing some of the basic physical principles that control these systems. But their findings may have other implications as well: The bright cloud cover of the closed cells cools the planet by reflecting radiation back into space, while the open ones reflect much less. Understanding the dynamic process that creates these open and closed patterns may help researchers to ascertain how human activity could affect their cooling capacity.

“A similar phenomenon to these cloud cells,” says Dr. Ilan Koren of the Weizmann Institute’s Environmental Sciences and Energy Research Department (Faculty of Chemistry), “is water boiling, in which the temperature drop from the pot’s heated base to the upper surface causes the water to rise and fall in columns. This rolling, cell-like pattern, known as Rayleigh-Bénard convection, was described over a hundred years ago.” In both cases, cells are generated when the bottom is hotter than the top and heat is transferred within the system.

As in many cases of Rayleigh-Bénard convection, cloud cells appear to be well organized and to obey a strict overall pattern. Koren and Dr. Graham Feingold of the NOAA lab in Colorado studied the role of rain in the open marine stratocumulus systems, watching how these systems progress in satellite images over periods of hours and days, as well as developing models to uncover their underlying organizing principles. They found a new feedback loop – one in which rain plays a central role – that forces the cells to oscillate between two states.

 

 
Prof. Ilan Koren. Organized systems
 
Their model begins with clouds forming on the edges (the walls) of the open cells as seawater evaporates and rises. Eventually, the water turns to rain, which then generates the opposite dynamic of that which created the clouds in the first place. In the first stages of the cloud formation, the energy that is released as the rising vapor condenses enhances and amplifies the updraft. Later, however, once the rain starts to fall and evaporate below the cloud base, a cooling effect takes over.

This cooling effect forces the air to sink, evaporating the parent cloud along the way. The new downdraft zone forces the air around it to be lifted, creating the next generation of clouds in a location that was previously the empty center of the parent cell.

In this way, all the cells are linked, and thus the various cells’ oscillations will be synchronized with one another. A single cell cannot act on its own: It needs the “permission” and collaboration of all the neighboring ones. Koren: “Like the sound of many hands clapping in rhythm, or the synchronized flashing of fireflies on a summer night, such communication creates a self-organized system that oscillates in a coherent way.” Though the individual cells alternately clear up and cloud over, the system as a whole persists for days at a time, leading the scientists to refer to “dynamic stability” in the cloud cover.

In his previous research, Koren investigated the role of tiny particles called aerosols – both natural and man-made – in cloud formation and precipitation. Because aerosols affect drop size and thus rainfall, he believes that the dynamics of marine stratocumulus systems could be especially vulnerable to the changes brought about by man-made particles in the atmosphere. This, in turn, could affect how well they reflect sunlight and cool the Earth.
 

 

Dr. Ilan Koren's research is supported by the Yeda-Sela Center for Basic Research. Dr. Koren is the incumbent of the Benjamin H. Swig and Jack D. Weiler Career Development Chair in Perpetuity.

 

 
 

 



 
 

 

 

 

 

 

Satellite image of a marine stratocumulus system, courtesy of NASA
Environment
English
  • Climate change
  • Cloud formation
  • Environmental Sciences and Energy Research
  • Ilan Koren

Cooling forests can heat too

English


The simple formula we’ve learned in recent years – forests remove the greenhouse gas CO2 from the atmosphere; therefore forests prevent global warming – may not be quite as simple as we thought. Forests can directly absorb and retain heat, and, in at least one type of forest, these effects may be strong enough to cancel out a good part of the benefit in lowered CO2. This is a conclusion of a paper that will be published tomorrow, Friday 22, in Science by scientists in the Weizmann Institute’s Faculty of Chemistry.
 

For the past 10 years, the Weizmann Institute has been operating a research station in the semi-arid Yatir Forest, a pine forest at the edge of the Negev Desert. This station is part of a world-wide project composed of over 400 stations, called FLUXNET, which investigates the relationship between forests, the atmosphere and climate around the globe. The contribution of the Yatir station, says Prof. Dan Yakir of the Environmental Sciences and Energy Research Department, is unique as it ‘is one of very few in the  semi-arid zone, which covers over 17% of the Earth’s land surface, and it has the longest record of the processes taking place in semi-arid forests.’
 
Forests counteract the ‘greenhouse effect’ by removing heat-trapping CO2 from the atmosphere and storing it in living trees. Over the years of measurement, Yakir’s group has found that the semi-arid forest, even though it’s not as luxuriant as temperate forests farther north, is a surprisingly good carbon sink – better than most European pine forests and about on par with the global average. This was unexpected news for a forest sitting at the edge of a desert, and it indicated that there is real hope for the more temperate forests if things heat up under future global change scenarios.
 
But forests do more than just store CO2, and Yakir, together with Dr. Eyal Rotenberg, decided to look at the larger picture – the ‘total energy budget’ of a semi-arid forest. The first hint they had that other processes might be counteracting the cooling effect of CO2 uptake came when they compared the forest’s albedo – how much sunlight is reflected from its surface back into space – with that of the nearby open shrub land. They found that the dark-colored forest canopy had a much lower albedo, absorbing quite a bit more of the sun’s energy than the pale, reflective surface of surrounding areas. In a cloudless environment with high levels of solar radiation, albedo becomes an important factor in surface heating.
 
Next, the researchers looked at the mechanisms for ‘air conditioning’ within the forest itself. To cool down, trees in wetter areas of the globe use water-cooled systems: They open pores in their leaves and simply let some of the water evaporate, drawing heat away in the process. But the semi-arid pine forest, with its limited water supply, is not built for evaporation. The scientists found that it uses an alternative, efficient, air-cooling system, instead. As semi-arid forests are not as dense as their temperate counterparts, the air in the open spaces between the trees comes into contact with a large surface area, and heat can be easily transferred from the leaves to the air currents. This semi-arid air cooling system is quite efficient at cooling the treetops, and this cooling, in turn, leads to a reduction in infrared (thermal) radiation out into space. In other words, while the semi-arid forest can cool itself well enough to survive and take up carbon, it both absorbs more solar radiation energy (through the albedo effect) and retains more of this energy (by suppressing the emission of infrared radiation). Together, these effects turned out to be stronger than the scientists had expected. ‘Although the numbers vary with location and conditions,’ says Yakir, ‘we now know it will take decades of forest growth before the ‘cooling’ CO2 sequestration can overtake these opposing ‘warming’ processes.’
 
Yakir and Rotenberg then asked one more question: If planting semi-arid forests can in fact lead to warming over a good part of their life cycles, what happens when the opposite process – desertification – takes place? By applying what they had learned to existing data on areas that have turned to desert, they found that desertification, instead of hastening global warming, as is commonly thought, has actually mitigated it, at least in the short term. By reflecting sunlight and releasing infrared radiation, desertification of semi-arid lands over the past 35 years has slowed down global warming by as much as 20%, compared with the expected effect of the CO2 rise over the same period. And in a world in which desertification is continuing at a rate of about six million hectares a year, that news might have a significant effect on how we estimate the rates and magnitude of climate change. Yakir: ‘Overall, forests remain hugely important climate stabilizers (not to mention the other ecological services they provide), but there are tradeoffs, such as those between carbon sequestration and surface radiation budgets, and we need to take these into consideration when predicting the future.’

 
Prof. Dan Yakir’s research is supported by the Avron-Wilstaetter Minerva Center for Research in Photosynthesis; the Sussman Family Center for the Study of Environmental Sciences; the Angel Faivovich Foundation for Ecological Research; and the Cathy Wills and Robert Lewis Program in Environmental Science.
 
 
The Weizmann Institute of Science in Rehovot, Israel, is one of the world's top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to 2,600 scientists, students, technicians and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials and developing new strategies for protecting the environment.
 
 
Weizmann Institute news releases are posted on the World Wide Web at http://wis-wander.weizmann.ac.il/, and are also available at http://www.eurekalert.org/
 
 
Environment
English
  • Carbon dioxide
  • Dan Yakir
  • Environmental Sciences and Energy Research
  • FLUXNET
  • Forest

Cross Flow

English
 
Drs. Hezi Gildor and Riyad Manasrah

 

 Last spring, a small research boat made an unusual trip – from one side to the other of the northwestern-most tip of the Red Sea. On this crossing (of the Gulf of Eilat or the Gulf of Aqaba, depending on one's map) were researchers from Jordan, Israel and the U.S. who had recently joined forces to study how water flows and mixes in the unique body of water that lies between Jordan and Israel.

Dr. Hezi Gildor of the Weizmann Institute's Environmental Sciences and Energy Research Department; Dr. Riyad Manasrah of the Marine Science Station in Aqaba, Jordan; Prof. Amatzia Genin of the Interuniversity Institute for Marine Sciences and the Hebrew University of Jerusalem, Eilat; and Dr. Stephen Monismith of Stanford University are conducting this research through the NATO Science for Peace and Security Program. Their efforts should greatly improve scientists' understanding of water currents and circulation. But the group has an immediate, practical goal as well: A detailed understanding of water movement in the Gulf can help the environmental agencies on both sides (which already cooperate to protect its unique ecology) plan a response to spills or prevent pollution from spreading.

Recent research by Gildor and Dr. Erick Fredj of the Jerusalem College of Technology has already revealed a surprise: Floating material such as oil might remain near the spill site for an extended period of time, rather than dispersing throughout the surface area of water. Using data collected from two on-shore high-frequency radar stations, Gildor created a computer map of the currents. He then added evenly spaced "particles" to a computer water-flow simulation to see where they would go. The calculation, which showed the particles moving with the currents over several days, revealed that some of the particles tended to move closer together, forming large clumps; at the same time, barriers created by the current separated particle clusters and prevented them from dispersing or mixing with other clusters. Large bodies of water don't normally lend themselves to experiments, but a set of aerial photos taken soon after a rare winter flood provided evidence for the accuracy of the model: The images show well-defined brown stains in the blue water – silt that had washed down from the nearby desert mountains into the Gulf and collected in the areas predicted in the model. In addition to the two radar stations on the Israeli side, a third is now set to go online on the Jordanian side, which will greatly increase the data available to the scientists.

"The Gulf of Eilat," says Gildor, "offers scientists an exceptional research opportunity. Although it is relatively small, it is also quite deep, and many types of ocean phenomena take place in its waters. Because of its limited size and the fact that it's almost entirely surrounded by land, detailed measurements can be obtained at a higher resolution than is possible in the open ocean. Also, there's the added advantage of being close to shore."

One such phenomenon is usually found only in places that are much harder to study, such as the waters off the Antarctic coast. Called a density current, it takes place when cold air from a nearby land mass cools the top layer of ocean, making it denser and heavier than the water below. This layer then sinks, creating a vertical current. Although density currents are confined to narrow belts of sea near land, they are important drivers of the global ocean currents that, in turn, affect global climate patterns. The Gulf of Eilat, although it is much closer to the equator than other areas that experience this phenomenon, has all the right conditions for density currents: On the one hand, the shallow strait at the entrance to the Red Sea prevents the deep, cold water of the outer ocean from flowing into the Gulf. On the other hand, the Gulf water is surrounded by desert, where atmospheric temperatures can drop to near freezing on winter nights, thus cooling the surface water. Gildor and his research team found that pulses of density current regularly occur off Eilat's shore in wintertime, and they used their observations to create a high-resolution computer model of these flows.

The Gulf is an invaluable natural laboratory – one that Gildor is turning into an important basis for improving ocean modeling – and collaboration between scientists on both sides is crucial to conducting research in its waters. Gildor: "There's no physical line down the middle of the Gulf, and its water doesn't recognize political borders. To really understand it, we need to be able to study this body of water as a whole."   
 

Dr. Hezi Gildor's research is supported by the Sussman Family Center for the Study of Environmental Sciences; and the estate of Sanford Kaplan. Dr. Gildor is the incumbent of the Rowland Schaefer Career Development Chair in Perpetuity.

 
(l-r) Drs. Hezi Gildor and Riyad Manasrah. Sailing toward a common goal
Environment
English
  • Environmental Sciences and Energy Research
  • Hezi Gildor
  • International collaboration

Have Dust – Will Travel

English

Dr. Ilan Koren. From the Sahara to the Amazon

 

 

 

 

 

 

 

 

 

 

 

 

 

Commonly viewed as a household nuisance, dust as we know it hardly seems worthy of serious study. Humble image notwithstanding, airborne dust has a dramatic global impact, affecting everything from the weather to marine food chains.

 
An additional, surprising role for dust was identified in the 1990s: As torrential rains in the Amazon region continuously wash minerals out of the soil, they are replaced by new minerals carried in dust blown over 5,000 km across the Atlantic Ocean from the largest desert in the world – the Sahara. Scientists believe that without a steady supply of vital minerals, the Amazon region would become a wet, but largely lifeless, desert.
 
In winter, seasonal winds lift dust into the air in the Sahel, the southern part of the Sahara, and carry it to the rainforest in South America. How much dust is expelled from the Sahara and how much of it reaches the Amazon rainforest? What turns particular desert regions into good sources of dust? These questions lie at the basis of research led by Dr. Ilan Koren of the Weizmann Institute’s Environmental Sciences and Energy Research Department. In a study conducted with the late Dr. Yoram Kaufman of NASA and other colleagues from Israel, the United Kingdom, the United States and Brazil, and published in Environmental Research Letters, the scientists focused on a particular desert region considered the largest source of dust in the world – the Bodele Valley, covering a 20,000-sq-km area in northern Chad.
 
Koren’s goal was to quantify, for the first time, the Bodele Valley’s contribution to the Amazon rainforest. An additional goal was to try to explain what turns this small valley into a leading “exporter” of dust. He and his colleagues combined the data collected by two different types of satellite sensors: One made it possible to cover a wide area and evaluate the extent of dust clouds and their movement; the other supplied precise optical information about the dust’s properties. In addition, satellite photographs taken at regular intervals allowed the scientists to evaluate the speed and direction of the winds and calculate the size of the dust “shipments.” Additional measurements at two spots above the Atlantic helped evaluate the amount of dust that is “lost” on the way to South America.
 
Analyses of the findings produced unexpected results: The Bodele Valley, which accounts for about 0.2% of the Sahara’s area, is responsible for 56% of the dust reaching the Amazon rainforest. Moreover, the total amount of dust arriving in South America from the Sahara each year is about 50 million tons – a much higher figure than the previously estimated 13 million tons and one that matches the amount thought to be needed to sustain the rainforest.
 
Why does the Bodele Valley supply such a significant amount of Amazon dust? “I looked at the satellite photos, and the answer was staring me in the eye,” says Koren, referring to Bodele’s unique geological shape. It is flanked on both sides by enormous basalt mountain ridges, with a narrow opening in the northeast. Winds that “drain” into the valley focus on this funnel-like opening, creating a large wind tunnel that directs the surface winds toward the dust source and accelerates them.
 
Though dust may not be a profitable export item, understanding its long-distance movement is a matter of global importance. 
 
Dr. Ilan Koren’s research is supported by the Sussman Family Center for the Study of Environmental Sciences; and the Samuel M. Soref and Helene K. Soref Foundation.

 

 
Dr. Ilan Koren. Crucial African export
Environment
English
  • Environmental Sciences and Energy Research
  • Ilan Koren

Hard Rain

English

 

A Weizmann Institute scientist and his colleagues caused a storm in the atmospheric research community a few years back when they suggested that tiny airborne particles known as aerosols may be among the main culprits in human-generated climate change. Aerosols affect cloud cover, and their impact on the local scale may be even greater than the greenhouse effect. 
 
Scientists have known for a while that such particles can have a number of different influences on cloud shape and formation. The problem is that some of these effects are warming and some are cooling; some seem to nudge the system toward greater rainfall and others toward less. Previously, because of limited methods for measuring the various effects, as well as the difficulty of creating an accurate model that could combine them all, the issue remained cloudy, if not downright foggy. Now Dr. Ilan Koren of the Environmental Sciences and Energy Research Department, working with Dr. Yoram Kaufman of the NASA/Goddard Space Flight Center, USA, has managed to weave together two opposing effects of atmospheric aerosols to provide a comprehensive picture of how they may be affecting our climate. 
 
Cloud formation begins with small amounts of such aerosols as sea salt and desert dust. The tiny particles serve as seeds around which water vapor in the air condenses, forming water droplets. When droplets are formed, heat is released, and this heat helps to drive the light droplets upward. As they rise, the small droplets collide, forming larger droplets. When the droplets reach a critical size, gravitation takes over and they fall from the cloud as rain. 
 
Koren's earlier studies had found evidence to suggest that the extra cloud-forming seeds planted in the atmosphere from man-made aerosol emissions (such as forest fires and burning fuel) lead to more but smaller water droplets, as the available water is divided among more seeds. Droplet collision becomes less efficient and rainfall is then suppressed. The lighter droplets are lifted farther up into the atmosphere, creating larger and taller clouds that persist for longer. Not only does this alter the global water cycle, but the increased cloud cover reflects more of the sun's radiation back into space, creating a local cooling effect on Earth.
 
To complicate matters, Koren, in another study, showed that certain types of aerosols – those containing black carbon (found, for instance, in airborne soot from burning coal) – can also decrease cloud cover, ultimately leading to a warming effect. This occurs because black carbon absorbs part of the sun's radiation, resulting in the atmosphere heating up and Earth’s surface cooling down, thereby preventing the conditions needed to form rain clouds. Fewer clouds mean weaker reflection of sunlight; less reflection of sunlight and absorption of radiation lead to warming.
 
Many policymakers and scientists have claimed, perhaps over-optimistically, that the effects of aerosols are mainly cooling, and that they may even help cancel out the greenhouse gases effect. Koren argues that it is the local effect that is worrisome: Clouds may retain their moisture over regions where they would normally precipitate, such as rainforests, or move to drop their rain over regions where it is not needed, such as oceans. Alternately, these effects could lead to the warming up of cold climate regions and the cooling down of hot ones. Such changes on top of global warming could have disastrous repercussions in the long run. 
 
Another question many have debated is: How can such tiny, localized particles affect weather systems thousands of kilometers away? The skeptics have claimed that, though aerosols undoubtedly play a role in cloud formation, it is negligible compared to that of key meteorological players such as temperature, pressure, the water vapor content of the air and wind strength.
 
To prove his theory, Koren needed a way to separate meteorolog-ical from aerosol influences. He and Kaufman used a network of ground sensors (AERONET) to measure the effect of aerosol concentration on cloud cover and the amount of radiation absorbed by aerosols at various locations across the globe and at different times of the year. Radiation absorption is relatively unaffected by meteorology, so if the skeptics were right and meteorology is the main influence, the correlation between aerosol absorption and cloud cover should have been hard to discern. But this was not the case. They observed the dual effect they had predicted: As the amount of aerosols increased, the amount of cloud cover increased; and as the amount of radiation absorption by aerosols increased, the amount of cloud cover decreased – for all locations, for all seasons. In light of this mathematical analysis, it becomes harder to deny that aerosols are, in fact, a major player in climate change. These results have recently been published in the journal Science.
 
“I would like to think that this study has finally cleared the air,” says Koren. “Hopefully policymakers will start to tackle the issue of climate change from a different perspective, taking into account not only the global impact of aerosols but local effects too.”    
 
Dr. Ilan Koren’s research is supported by the Samuel M. Soref and Helene K. Soref Foundation; and the Sussman  Family Center for the Study of Environmental Sciences.

Sattelite image of the Mediterranean

 

 

Satellite images of clouds

 

 

 

Dr. Yoram Kaufman

 

 

Dr. Ilan Koren. Clear data on clouds
Environment
English
  • Atmosphere
  • Climate change
  • Environmental Sciences and Energy Research
  • Ilan Koren

Moving Mountains

English
Dr. Einat Aharonov. How the mountain moved

 

 

 

 

 

 

 

 

 

 

The mountains skipped like rams…
                       

– Psalm 114

 

“Moving mountains” is synonymous with doing the impossible. Yet at least once in the past, one mountain actually picked up and moved a fair distance away. This feat took place around 50 million years ago, in the area of the present-day border between Montana and Wyoming. Heart Mountain was part of a larger mountain range when the 100-km- (62-mile-) long ridge somehow became detached from its position and shifted about 50 km to the southwest. Scientists first realized that the peak was not in its original spot when they discovered that the rock formation underneath was younger than the mountain sitting on top of it. Later satellite images helped them to place the original position of the mountain. This “migrating mountain” has garnered interest from geologists and geophysicists around the world, who have tried to solve the mystery behind the largest known instance of land movement on the face of any continent. Dr. Einat Aharonov of the Weizmann Institute’s Environmental Sciences and Energy Research Department, working in collaboration with Dr. Mark Anders of Columbia University in New York, published a paper in the scientific journal Geology that offers an explanation for the phenomenon.
 
In the scenario put forward by Aharonov and Anders, the mountain range was permeated with vertical cracks in the rock, called dikes, filled with hot lava boiling up from deep in the earth. This particular range had a relatively large number of these dikes, creating conduits in the rock leading from the lava source many thousands of meters below the surface upward to a 3-kilometer-deep aquifer – a porous, water-soaked layer of limestone. There, the sizzling lava would have heated the water to extreme temperatures, causing the pressure in the trapped fluid to rise tremendously. The scientists developed a mathematical model (based on the number of dikes in the mountain and their structure) that enabled them to calculate the temperatures and pressures that would have been created deep within the base of the mountain. The results showed that the hot lava would have turned the water in the aquifer layer into a sort of giant pressure cooker, releasing enough force to literally move a mountain.   
 
Dr. Einat Aharonov's research is supported by the Sussman Family Center for the Study of Environmental Sciences. Dr. Aharonov is the incumbent of the Anna and Maurice M. Boukstein Career Development Chair.
 
Heart mountain. Older on top
 

 

 
Dr. Einat Aharonov. How the mountain moved
Environment
English
  • Einat Aharonov
  • Environmental Sciences and Energy Research

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