Tyler O'Neal, Staff Editor PROCESSORS

Georgia Tech research on large storm waves could help lessen their impact on coasts

When cyclones or other massive oceanic storms make landfall, their giant waves batter coastlines and sometimes cause widespread damage.

Now, an international team of researchers has analyzed months of data of large nearshore waves to provide new insights that could help improve the designs of a variety of coastal structures from seaports to seawalls to better withstand destructive waves.

In the study published October 28 in the journal Scientific Reports, the researchers report combining a mathematical model to describe the formation of large waves with real-world measurements taken in shallow waters just off of the coast of Ireland, where waves have been reported to hit the shore with enough force to move 100-ton rocks.

"In this work we have analyzed real data in order to show that, over the course of several months measuring different storm events, we find that the extreme waves that we have observed in the coastal data tend on average to be smaller than the rogue waves we have observed in deep water, but they have similar characteristics," said Francesco Fedele, a associate professor in the Georgia Tech School of Civil and Environmental Engineering. CAPTION Waves crashing against the Irish coast. CREDIT Frederic Dias{module In-article}

"These large nearshore waves are still caused by constructive interference - the effect of waves coming in all different directions and basically meeting at one point and piling up to form a large wave, and by second-order nonlinearities that distort the sinusoidal shape of waves to have sharper crests and shallower troughs," Fedele said.

The research team also included M. Aziz Tayfun, professor emeritus from Kuwait University, Frederic Dias, a professor at the University College Dublin, and James Herterich, a postdoctoral associate, also at the University College Dublin.

In the study, which was sponsored by Science Foundation Ireland, the researchers analyzed measurements captured by an acoustic doppler current profiler (ADCP) device that was deployed for several months on the ocean floor off Killard Point during Spring 2015 and off the Aran Islands during Spring 2017. During that time, the device was able to capture data from two intense storm events that produced large coastal waves.

The more recent storm, Doris, which hit the Irish coast in February 2017, produced waves as tall as 43 feet from peak to trough, and the earlier storm in 2015 caused waves even taller, as high as 73 feet, according to the measurements from the ADCP, which works by emitting sound pulses and measuring the strength of sounds bouncing off of floating particles to calculate the height of the water.

The researchers used that data to compare with the Tayfun-Fedele and Boccotti statistical models used to explain rogue ocean waves that occur in much deeper water. Those models were used in an analysis of the two famous real-world rogue waves, Andrea and Draupner, observed at oil platforms in the North Sea in 1995 and 2007, as well as the Killard rogue wave observed off the coast of Ireland in 2014.

"We were able to extend these statistical models, which are largely validated for waves in deep waters, to describe coastal rogue waves," Fedele said.

Comparing the simulated wave profiles of the deep-sea rogue waves and the wave profiles generated by the data collected for the nearshore waves showed a similar profile for all, suggesting that the nearshore waves generated much in the same way as the deepwater ones, Fedele said.

But for nearshore waves, the breaking of the waves bleeds away some of their energy, he said.

"Once you get into shallow waters, the enhanced nonlinearities make waves less dispersive and the tendency for waves to break intensifies.," Fedele said. "A lot of the energy is dissipated forming white caps that crash against the shore."

The research could provide an underpinning for designs of coastal structures that are built to withstand the forces of waves over time.

"For people who want to design coastal structures, you need to know what's the largest wave that will break in a coastal area over the lifetime of the structure - what's the largest wave out of however many millions of waves or more that will happen," Fedele said. "And once you have this knowledge using these statistical methods, you can design the structure to withstand the highest wave."

Fedele said the next steps of the research would involve studying more about the physical mechanics of the point when waves break, either against the shore as in the case of coastal waves, or when deep-sea rogue waves break out in the open water.

UBC Sauder research proposes a virtual speed bump for lightning-fast markets

Tyler O'Neal, Staff Editor PROCESSORS

UBC Sauder's Markus Baldauf says a tiny tweak to how certain trades happen could make for more efficient stock markets, and it's already being adopted by major players.

The blink of an eye takes just a tenth of a second, but that's an eternity in today's stock markets, where automated transactions are calculated in millionths of seconds.

Stock market traders have always relied on speed to gain competitive advantage, but over the past 10 to 15 years, the development of high-frequency trading technology has changed the game -- to the point where investors can make fortunes by buying and selling in minuscule increments of time.

Some are concerned that this so-called "arbitrage strategy" -- which involves simultaneously buying and selling to take advantage of minute differences between prices -- could affect the health of the overall market. {module In-article}

But researchers at the UBC Sauder School of Business and at Kellogg School of Management are proposing a key fix: a virtual speed bump.

"Two things that we care about as traders are liquidity and the informativeness of prices. Liquidity happens when transaction costs are small -- so if I buy something and sell it immediately afterward, how much money do I lose? If that's a small amount, then that's a good market," explains UBC Sauder assistant professor Markus Baldauf, a co-author of the study.

"If that difference is big, then that market is illiquid and that's a bad thing," he says. "We also want prices to reflect reality, and the value of companies, because they are a barometer of how well the economy is doing."

To test the impacts of high-frequency trading on these market measures, Baldauf applied a mathematical model that looked at liquidity as well as informativeness of prices -- that is, how much information security prices reflect about fundamentals.

Liquidity providers simultaneously offer to buy and sell a stock, which yields the bid-ask spread of the market. When setting their bids and offers, they balance the needs of traders to buy or sell, as well as their risk of being on the losing end of a trade.

Next, think about how traders respond to information that should cause prices to shift. Liquidity providers race to reprice their bids and offers. But at the same time, arbitrage traders race to hit the original quotes at the stale prices. This all happens in milliseconds.

To protect against the risk of losing those races, liquidity providers charge a larger spread between buyers and sellers. In other words, having the arbitrage traders in the race makes markets less liquid. It can also lead to less informative prices.

The researchers proposed a way to reduce the impact of arbitrage traders: impose a short delay on the processing of their orders, which throws an extremely high-speed wrench into their market-skimming strategy, and still allows regular traders to make their moves. As Baldauf puts it, "The race is basically the outcome of a coin toss, but we want to tilt it slightly in favor of the liquidity provider."

Baldauf says that while some experts have proposed sweeping changes that could have a significant impact on markets, his team's proposed change is smaller and more surgical -- so it would still achieve the same aims without incurring larger risks.

Already several exchanges have shown interest in the approach, among them the Cboe EDGA equities exchange, which earlier this year approached the U.S. Securities Exchange Commission about slowing liquidity-removing orders by as little as a few milliseconds.

"We often take trading rules and norms in markets as given, but really we can change them. It's up to policymakers and regulators to say, 'What are the rules of the game, and should we change them?'" says Baldauf, who adds that markets evolve just as languages do.

"We find that a small tweak to the existing system can create big changes, and that regular investors and institutional investors will be better off as a result."

German researchers confirm particular form of magnetic instability; discovering an overlooked piece of the solar dynamo puzzle

Tyler O'Neal, Staff Editor PROCESSORS

A previously unobserved mechanism is at work in the Sun's rotating plasma: a magnetic instability, which scientists had thought was physically impossible under these conditions. The effect might even play a crucial role in the formation of the Sun's magnetic field, say researchers from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Leeds and the Leibniz Institute for Astrophysics Potsdam (AIP) in the journal Physical Review Fluids (DOI: 10.1103/PhysRevFluids.4.103905).

Just like an enormous dynamo, the sun's magnetic field is generated by electric currents. In order to better understand this self-reinforcing mechanism, researchers must elucidate the processes and flows in the solar plasma. Differing rotation speeds in different regions and complex flow in the sun's interior combine to generate the magnetic field. In the process, unusual magnetic effects can occur - like this newly discovered magnetic instability. The most sunspots and, thus, the greatest magnetic activity are located close to the solar equator. Scientists have now demonstrated for this region a specific magnetic instability, that was considered impossible so far.{module In-article}

Researchers have coined the term "Super HMRI" for this recently observed special case of the magnetorotational instability (MRI). It is a magnetic mechanism that causes the rotating, electroconductive fluids and gases in a magnetic field to become unstable. What is special about this case is that the Super HMRI requires exactly the same conditions that prevail in the plasma close to the solar equator - the place where astrophysicists observe the most sunspots and, thus, the Sun's greatest magnetic activity. So far, however, this instability in the Sun had gone completely unnoticed and is not yet integrated into models of the solar dynamo.

It is, nonetheless, known that magnetic instabilities are crucially involved in many processes in the universe. Stars and planets, for example, are generated by large rotating disks of dust and gas. In the absence of a magnetic field, this process would be inexplicable. Magnetic instabilities cause turbulence in the flows within the disks and thus enable the mass to agglomerate into a central object. Like a rubber band, the magnetic field connects neighboring layers that rotate at different speeds. It accelerates the slow particles of matter at the edges and slows down the fast ones on the inside. There the centrifugal force is not strong enough and the matter collapses into the center. Near the solar equator, it behaves precisely the other way around. The inner layers move more slowly than the outer ones. Up to now, experts had considered this kind of flow profile to be physically extremely stable.

The researchers at HZDR, the University of Leeds and AIP still decided to investigate it more thoroughly. In the case of a circular magnetic field, they had already calculated that even when fluids and gases were rotating faster on the outside, magnetic instability could occur. However, only under unrealistic conditions: the rotational speed would have to increase too strongly towards the outer edge.

Trying another approach, they now based their investigations on a helical magnetic field. "We didn't have any great expectations, but then we were in for a genuine surprise," HZDR's Dr. Frank Stefani remembers - because the magnetic instability can already occur when the speed between the rotating layers of plasma only increases slightly - which happens in the region of the Sun closest to the equator.

"This new instability could play an important role in generating the sun's magnetic field," Stefani estimates. "But in order to confirm it, we first need to do further numerically complicated calculations." Prof. Günther Rüdiger of AIP adds, "Astrophysicists and climate researchers still hope to better understand the cycle of sunspots. Perhaps the 'Super HMRI' we have now found will take us a decisive step forward. We'll check it out."

With its various specialisms in magnetohydrodynamics and astrophysics, the interdisciplinary research team has been investigating magnetic instabilities - in the lab, on paper and with the aid of sophisticated simulations - for more than 15 years. The scientists want to improve physical models, understand cosmic magnetic fields and develop innovative liquid metal batteries. Thanks to close cooperation, in 2006, they managed to experimentally prove the theory of magnetorotational instability for the first time. They are now planning the test for the special form they have predicted in theory: In a large-scale experiment that is currently being set up in the DRESDYN project at HZDR, they want to study this magnetic instability in the lab.