Topographic/bathymetric map of onshore/offshore Southern California, with height and depth in meters. The Red Mountain and Pitas Point faults are considered in this study. Triangles indicate direction of dip; faults without triangles are considered strike-slip. Letters show approximate (central) city locations: SB = Santa Barbara; V = Ventura; O = Oxnard. Inset shows the map boundary in black. IMAGE CREDIT: KENNY RYAN, UC RIVERSIDE.

Study led by UC Riverside seismologists shows modeled tsunami resulting from simulated earthquake in Ventura basin first propagates south but then turns unexpectedly toward Ventura/Oxnard

Few can forget the photos and videos of apocalyptic destruction a tsunami caused in 2011 in Sendai, Japan.  Could Ventura and Oxnard in California be vulnerable to the effects of a local earthquake-generated tsunami? Yes, albeit on a much smaller scale than the 2011 Japan earthquake and tsunami, according to supercomputer models used by a team of researchers, led by seismologists at the University of California, Riverside.

New method could improve atmospheric forecasts over months, decades, and could explain 'pause' in global warming

The atmosphere is so unstable that a butterfly flapping its wings can, famously, change the course of weather patterns. The celebrated "butterfly effect" also means that the reliability of weather forecasts drops sharply beyond 10 days.

Beyond this, there are strong fluctuations in temperature, with increases tending to be followed by decreases, and vice-versa. The same pattern holds true over months, years and decades. "This natural tendency to return to a basic state is an expression of the atmosphere's memory that is so strong that we are still feeling the effects of century-old fluctuations," says McGill University physics professor Shaun Lovejoy. "While man-made atmospheric warming imposes an overall increasing trend in temperatures, the natural fluctuations around this trend follow the same long memory pattern." 

In a new paper published online in Geophysical Research Letters, Lovejoy shows how to directly harness the atmosphere's elephantine memory to produce temperature forecasts that are somewhat more accurate than conventional numerical supercomputer models. This new method, he says, could help improve notoriously poor seasonal forecasts, as well as producing better long-term climate projections. 

Improvement on standard approach

To take advantage of the butterfly effect, Lovejoy's approach treats the weather as random and uses historical data to force the forecast to reflect a realistic climate. This allows it to overcome limitations of the standard approach, in which imperfect representations of the weather push a supercomputer model to be consistent with its model climate - rather than with the real climate. The new method also represents an improvement over other statistical forecasting techniques that exploit only the atmosphere's short-term memory, Lovejoy asserts.

Lovejoy's paper uses a simple version of his new method to show that the so-called pause in global warming since 1998 can be well explained with the help of historical atmospheric data. He also concludes that this method proves more accurate over this period than the standard supercomputer models used, for example, by the International Panel on Climate Change.

Lovejoy's model also predicts that if greenhouse gas emissions continue at the post 2000 rate, there is a 97.5% chance that the "pause" in global warming will be over before 2020.

New model predicts wind speeds more accurately with three months of data than others do with 12

When a power company wants to build a new wind farm, it generally hires a consultant to make wind speed measurements at the proposed site for eight to 12 months. Those measurements are correlated with historical data and used to assess the site's power-generation capacity.

At the International Joint Conference on Artificial Intelligence later this month, MIT researchers will present a new statistical technique that yields better wind-speed predictions than existing techniques do -- even when it uses only three months' worth of data. That could save power companies time and money, particularly in the evaluation of sites for offshore wind farms, where maintaining measurement stations is particularly costly.

"We talked with people in the wind industry, and we found that they were using a very, very simplistic mechanism to estimate the wind resource at a site," says Kalyan Veeramachaneni, a research scientist at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) and first author on the new paper. In particular, Veeramachaneni says, standard practice in the industry is to assume that wind-speed data follows a so-called Gaussian distribution -- the "bell curve" familiar from basic statistics.

"The data here is non-Gaussian; we all know that," Veeramachaneni says. "You can fit a bell curve to it, but that's not an accurate representation of the data."

Typically, a wind energy consultant will find correlations between wind speed measurements at a proposed site and those made, during the same period, at a nearby weather station where records stretch back for decades. On the basis of those correlations, the consultant will adjust the weather station's historical data to provide an approximation of wind speeds at the new site.

The correlation model is what's known in statistics as a joint distribution. That means that it represents the probability not only of a particular measurement at one site, but of that measurement's coincidence with a particular measurement at the other. Wind-industry consultants, Veeramachaneni says, usually characterize that joint distribution as a Gaussian distribution.

Different curves

The first novelty of the model that Veeramachaneni developed with his colleagues -- Una-May O'Reilly, a principal research scientist at CSAIL, and Alfredo Cuesta-Infante of the Universidad Rey Juan Carlos in Madrid -- is that it can factor in data from more than one weather station. In some of their analyses, the researchers used data from 15 or more other sites.

But its main advantage is that it's not restricted to Gaussian probability distributions. Moreover, it can use different types of distributions to characterize data from different sites, and it can combine them in different ways. It can even use so-called nonparametric distributions, in which the data are described not by a mathematical function, but by a collection of samples, much the way a digital music file consists of discrete samples of a continuous sound wave.

Another aspect of the model is that it can find nonlinear correlations between data sets. Standard regression analysis, of the type commonly used in the wind industry, identifies the straight line that best approximates a scattering of data points, according to some distance measure. But often, a curved line would offer a better approximation. The researchers' model allows for that possibility. 

Validation

The researchers first applied their technique to data collected from an anemometer on top of the MIT Museum, which was looking to install a wind turbine on its roof. Once they had evidence of their model's accuracy, they applied it to data provided to them by a major consultant in the wind industry. 

With only three months of the company's historical data for a particular wind farm site, Veeramachaneni and his colleagues were able to predict wind speeds over the next two years three times as accurately as existing models could with eight months of data. Since then, the researchers have improved their model by evaluating alternative ways of calculating joint distributions. According to additional analysis of the data from the Museum of Science, which is reported in the new paper, their revised approach could double the accuracy of their predictions.

CAPTION This is a plume of ash from the Sarychev volcano in the Kuril islands, northeast of Japan. The picture was taken from the International Space Station during the early stage of the volcano's eruption on June 12, 2009.

In June, 1991, Mount Pinatubo in the Philippines exploded, blasting millions of tons of ash and gas over 20 miles high - deep into the stratosphere, a stable layer of our atmosphere above most of the clouds and weather. Certain gases in the massive plume from this volcano acted like a sunshield by scattering some of the sun's light, preventing it from reaching the surface and causing average surface temperatures to drop worldwide by an estimated 0.5 degrees Celsius (0.9 degrees Fahrenheit).

"We've been trying to better understand how volcanoes alter the climate for about 30 years now," said Lori Glaze of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The Mount Saint Helens eruption in 1980 (Washington state) and the El Chichon eruption in 1982 (Mexico) were both similar-sized eruptions. There wasn't much of a climate effect after Mount Saint Helens, but after El Chichon, there was a big global cooling event for a couple years."

"We didn't understand why, so people started looking into that and it turned out that the El Chichon eruption included much more sulfur than Mount Saint Helens," said Glaze.

The eruptions of El Chichon and Pinatubo were powerful enough to propel their gases into the stratosphere, which gave them the potential to alter short-term climate. "Since the stratosphere is stable, if gas in volcanic plumes gets into the stratosphere, it stays there for a long time - a couple years," said Glaze. "Although there are many complications, the bottom line is that when these gases produce aerosols in the stratosphere, they scatter some of the sun's radiation, which warms the stratosphere and causes a net cooling at the surface. The gas in these volcanic plumes - primarily sulfur dioxide (SO2) and hydrogen sulfide (H2S) - which doesn't come out in large amounts -- reacts to form a layer of sulfuric acid (H2SO4) in the stratosphere. This layer scatters some of the sun's infrared radiation."

Another type of volcano called a "flood-basalt eruption" doesn't explode as dramatically, but dwarfs these examples with much bigger volumes of gas and lava erupted. "With eruptions like Pinatubo, you get one shot of sulfur dioxide and other gases into the stratosphere, but then the volcano is quiet for hundreds or thousands of years," said Glaze. "With a flood-basalt eruption, you're repeatedly ejecting these chemicals into the atmosphere over tens, hundreds, or maybe even thousands of years. Each eruption itself may not be the biggest thing you've ever seen, but you're continuously supplying gas to the atmosphere over a long period time."

There haven't been any flood-basalt volcanic eruptions in human history, which is probably a good thing. "It's almost unfathomable how big these lava flows are," said Glaze. "A large part of the western part of the state of Washington is covered in 1.5 kilometers-thick (thousands of yards) lava from the Columbia River flood-basalt eruptions." One eruption of the Columbia River basalt formation, the Roza eruption, is the focus of Glaze and her team's analysis. It happened about 14.7 million years ago and produced about 1,300 cubic kilometers (over 300 cubic miles) of lava over an estimated period of ten to fifteen years.

Although flood-basalt eruptions were enormous, they were not as explosive as eruptions like Pinatubo. The molten rock (magma) in flood-basalt eruptions flowed easily. This allowed gas that was trapped in it to be released easily as well. This magma produces "fire-fountain" eruptions - a fountain of lava rising hundreds of meters (hundreds of yards) into the air. Often these eruptions begin along a crack in the Earth, called a fissure, up to several kilometers (a few miles) long, producing a dramatic glowing curtain of lava. Fire-fountain eruptions are seen on a smaller scale today in places like Hawaii and Mount Etna in Sicily, Italy.

The magma that powers Pinatubo-type eruptions is thicker, and flows more slowly. Gas dissolved in this thick magma can't escape as easily, so when pressure is suddenly released at the beginning of these eruptions, it's like popping the cork on a bottle of champagne - all the gas rushes out at once, producing an explosive eruption.

Since "fire-fountain" eruptions aren't as explosive, scientists wonder whether the gases from them are propelled high enough to reach the stratosphere, allowing the very large fire-fountain eruptions that produced the flood basalts to potentially alter the climate. The answer depends not only on how vigorous the eruption is - taller fire fountains produce higher gas plumes - but also on where the stratosphere begins.

The boundary between the unstable lower atmosphere (troposphere) and the stable stratosphere is called the tropopause. Because warmer air expands more and rises higher than cooler air, the tropopause is highest over the equator and gradually becomes lower until it reaches its minimum height over the poles. Thus a fire-fountain plume from a volcano at high latitudes near the polar-regions has a better chance of reaching the stratosphere than one from a volcano near the equator.

The height of the boundary has also changed over time, as the contents of the atmosphere have changed. For example, carbon dioxide gas traps heat from the sun, so when there was more carbon dioxide in the atmosphere, temperatures were warmer and the tropopause was higher.

The question of whether large fire-fountain eruptions can change climate was raised by a similar but much smaller-scale fire-fountain eruption in Iceland, according to Glaze. "The Laki eruption in 1783 to 1784 injected sulfur dioxide into the upper troposphere and lower stratosphere through repeated eruptions over a period of eight months, affecting climate in the northern hemisphere during 1783 and possibly through 1784," said Glaze. Ben Franklin, living in France at the time, noticed the haze and severe winter and speculated on whether Icelandic volcanoes could have changed the weather, according to Glaze.

To answer this question, Glaze and her team applied a supercomputer model they developed to calculate how high volcanic plumes rise. "This is the first time a model like this has been used to calculate whether the plume of ash and gas above a large fire-fountain volcano like the Roza eruption could reach the stratosphere at the time and location of the event," said Glaze.

Her team estimated the tropopause height given the eruption's latitude (about 45 degrees North) and the contents of the atmosphere at the time of the eruption and found that the eruption could have reached the stratosphere. Glaze is lead author of a paper on this research published August 6 in the journal Earth and Planetary Science Letters.

"Assuming five-kilometer-long (3.1 mile-long) active fissure segments, the approximately 180 kilometers (about 112 miles) of known Roza fissure length could have supported about 36 explosive events or phases over a period of maybe ten to fifteen years, each with a duration of three to four days," said Glaze. "Each segment could inject as much as 62 million metric tons per day of sulfur dioxide into the stratosphere while actively fountaining, the equivalent of about three Pinatubo eruptions per day."

The team verified their model by applying it to the 1986 Izu-Oshima eruption, a well-documented eruption in Japan that produced spectacular fire fountains 1.6 kilometers (almost a mile) high. "This eruption produced observed maximum plume heights of 12 to 16 km (7.4 to 9.9 miles) above sea level," said Glaze. When the team input fountain height, temperature, fissure width, and other characteristics similar to the Izu-Oshima eruption into their model, it predicted maximum plume heights of 13.1 to 17.4 km (8.1 to 10.8 miles), encompassing most of the observed values.

"Assuming the much larger Roza eruption could sustain fire-fountain heights similar to Izu-Oshima, our model shows that Roza could have sustained buoyant ash and gas plumes that extended into the stratosphere at about 45 degrees north," said Glaze.

Although the team's research suggests the Roza eruption had the potential to alter climate, scientists still have to search for evidence of a climate change around the time of the eruption, perhaps an extinction event in the fossil record, or indications of changes in atmospheric chemistry or sea levels, according to Glaze.

"For my personal research, I would like to take these results and look at some of the really large ancient fissure eruptions on Venus and Mars," said Glaze. "There are other gases in volcanic plumes like water vapor and carbon dioxide. These gases don't have significant effect on Earth because there is so much in the atmosphere already. However, on Venus and Mars, the effect of water vapor becomes very important because there is so little of it in their atmospheres. Venus is one of my favorite places to study and I want to ask if there was active volcanism on Venus today, what should we be looking for?"

The surface of Venus is hidden under a thick cloud layer, so a volcanic plume might not be visible from space, but there is the possibility that an active volcano could produce noticeable changes in atmospheric chemistry.

UW Professor Fred Ogden anticipates his discovery will greatly improve the reliability and functionality for hundreds of important water models used around the country and the world.

A University of Wyoming professor has made a discovery that answers a nearly 100-year-old question about water movement, with implications for agriculture, hydrology, climate science and other fields.

After decades of effort, Fred Ogden, UW’s Cline Chair of Engineering, Environment and Natural Resources in the Department of Civil and Architectural Engineering and Haub School of Environment and Natural Resources, and a team of collaborators published their findings in the journal Water Resources Research this spring. The paper, titled “A new general 1-D vadose zone flow solution method,” presents an equation to replace a difficult and unreliable formula that’s stymied hydrologic modelers since 1931.

“I honestly never thought I would be involved in a discovery in my field,” Ogden says.

He anticipates this finding will greatly improve the reliability and functionality for hundreds of important water models used by everyone from irrigators and city planners to climate scientists and botanists around the country and the world, as well as trigger a new surge in data collection.

In 1931, Lorenzo Richards developed a beautiful, if numerically complex, equation to calculate how much water makes it into soil over time as rainfall hits the ground surface and filters down toward the water table. That equation, known as the Richards equation and often shortened to RE, has been the only rigorous way to calculate the movement of water in the vadose zone -- that is, the unsaturated soil between the water table and the ground surface where most plant roots grow.

Calculating the movement of water in the vadose zone is critical to everything from estimating return flows and aquifer recharge to better managing irrigation and predicting floods. But RE is extremely difficult to solve, and occasionally unsolvable. So, while some high-powered computer models can handle it over small geographic areas, simpler models or those covering large regions must use approximations that compromise accuracy.

For decades, hydrologists and other scientists have pursued a better way to estimate vadose zone water. Cornell University Environment and Ecology Professor Jean-Yves Parlange and Australian soil physicist John Robert Philip battled one another in the literature, proposing new equations and disproving each other -- from the 1950s until Philip’s untimely death in a traffic accident in 1999. Princeton Environmental Engineering and Water Resources Director Michael Celia published a partial solution in 1990 that is not reliable in all circumstances.

Ogden first worked on the problem in 1994 as a postdoctoral researcher. He teamed with Iranian hydrology engineer Bahram Saghafian, who was finishing a Ph.D. at Colorado State University, to publish an equation that estimates water “suction” in the vadose zone. In the early 2000s, Ogden advised a Ph.D. candidate named Cary Talbot, a researcher with the U.S. Army Corps of Engineers, on a project seeking a solution to the RE. The two developed a new way to represent vadose zone water.

In more recent years, the search continued, and a major National Science Foundation research grant in 2011 enabled Ogden to bring additional experts to the quest and use UW’s supercomputing power to test prospective solutions.

Then, late last fall, just before the large American Geophysical Union annual meeting, Ogden and his research team discovered a novel solution, an elegant new equation that he thought would equal the RE in accuracy while greatly reducing the computing power needed to run it. He tested this solution with precipitation data from his field site in Panama.

“We ran eight months of Panama data with 263 centimeters of rain through our equation and Hydrus,” Ogden says.

Hydrus is an existing supercomputer model that uses RE. The results his model generated had only 7 millimeters, or two tenths of 1 percent, difference from the results of the Hydrus model that employs Celia’s solution of the RE.

“They were almost identical. That’s when I knew,” he says. “I felt like the guy who discovered the gold nugget in the American River in California.”

What’s next for the new equation? First, it is the centerpiece of Ogden’s ADHydro model, a massive, supercomputer-powered model that’s first simulating the water supply effects of different climate and management scenarios throughout the entire upper Colorado River Basin. From there, Ogden hopes other models will incorporate it, too.

“I think, for rigorous models, it’s going to become the standard,” he says. “With help from mathematicians and computer scientists, it will just get faster and better.”

Furthermore, new pushes for data collection often follow technological advances, Ogden explains. He hopes this discovery will bring soil science back into relevance for water managers and lead to new soil data collection.

“We now have a reliable way to couple groundwater to surface through the soil that people have been looking for since 1931,” Ogden says, almost in awe of the moment.

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