May 1, 2012

The Science Behind Solar Storms

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There’s a Storm Brewing: Sun Cycles

The Sun is like a giant heat engine, said Dr. Steven Lantz, senior associate at the Cornell Center for Advanced Computing. Heat can move by one of three processes: conduction, convection and radiation.

From the radiation zone, photons moves into the convection zone where the heat transfer methods changes from radiation dominant to convection dominant. Finally at the visible photosphere, the heat-transfer method switches back to radiation and escapes from the sun.  The sun’s internal motions create a dynamo process that generates a magnetic field.

“The internal motions are doing work on the magnetic forces that are already present and somehow multiplying those fields and making them stronger until they become dynamically important in the whole thing,” Lantz said.

“In the Earth, magnetic poles are permanent for long periods of times, like tens of thousands of years, but in the Sun polar rearrangement happens in an 11 year period known as the Sun cycle,” Lantz said.

The period of greatest solar activity in the solar cycle is called a solar maximum, or solar max. According to Prof. Michael Kelley, electrical and computer engineering, the number of sunspots has a direct correlation to the frequency of geomagnetic storms. During a solar max, sunspots appear with greater frequency. A sunspot is a region of concentrated magnetic field large enough to swallow several Earths.  Sunspots come in pairs in much the same way that magnetic fields come in poles. There is a positive and a negative sunspot that are connected by a magnetic loop that is only visible when viewed through  x-ray telescopes.

Generally, emissions from the Sun come in the form of less aggressive solar winds composed of benign plasma particles. But when churning plasma extensively twists the loops, positive and negative ends cross and they short circuit with a tremendous explosion that blasts heated plasma blobs into space.

“It’s analogous to a rubber band snapping that has been wound too tightly.  It’s trying to find a way to untwist and get to a lower energy level, and in the process of that material can fly off,” Lantz said.

Space Weather: Solar Flares and Coronal Mass Ejections

Solar Storms carry a one-two punch:  first is the solar flare that releases an outburst of x-rays that can reach Earth within minutes and second is the more ominous Coronal Mass ejection which arrives a few days later.  The CME is a wave of billions of tons of electrically charged particles that can hit like a cosmic tsunami.

“We used to think solar flares were the main reason we had magnetic storms. Now the thinking is that coronal mass ejections are the source,” Kelley said. He explained that solar flares are primarily an x-ray event, whereas CMEs consist of actual mass from the Sun moving towards the Earth. Using tools called coronagraphs which block out most light from a star, scientists are able to study CMEs.

“A normal solar wind takes a couple of days to get to Earth. Coronal mass ejections are high velocity, so we usually have a day’s notice,” Kelley said. “When a coronal mass ejection hits the Earth, you will have a geomagnetic storm.”

Earth’s Solar Shield: The Geomagnetic Field

Geomagnetic storms are one of the two main components of space weather. “Space weather is a generic term used to describe what happens in space around Earth that affects humans,” Kelley said. Disturbances of the ionosphere, or upper layer of the atmosphere, caused by solar flares and CMEs are called ionospheric storms.

The impact of the storm depends on two factors: the coronal mass ejection’s magnetic force and the Earth’s magnetic force. The CME races towards Earth while rotating between its positive and negative charges. The Earth also has a positive and negative charge.  If the two forces align, such as a positive CME hits the Earth’s positive magnetic charge, the force will be repelled. But if the opposite happens, and a negative charge from one hits the positive charge of the other, the CME will strike with full force.

“The solar wind particles are always careening in and headed towards the Earth.  And for the most part, these energetic particles are deflected by the Earth’s magnetic fields.  The magnetic field takes on a special shape in the consequence of deflecting the energy particles and it gets compressed on the solar side and extended on the anti solar side, and that’s the magnetosphere.  The magnetosphere serves to deflect most of the solar winds around the Earth, which makes for a nice habitable environment down here.”

In most cases the solar winds deflects back towards its tail region and out to space because of the Earth’s shielding. The only issue is when there are strong irregularities in the solar wind such as with the coronal mass ejections.

“The shielding is imperfect in that the particles have a fairly easy time making it down to the poles. From that you get auroras precipitating.” David Hysell, earth and atmospheric sciences, said.

Auroras: The Solar Storm’s Silver Lining

Crowning the Earth at both its poles are magnificent halos of light known as auroral ovals. To anyone far enough North or South these lights appear across the sky at night, when daylight cannot outshine them, as brilliant, dancing curtains. But unlike most curtains, auroras reveal more than they conceal.

Auroras make visible the imperceptible magnetic field lines that envelope our planet — and in spectacular fashion. They hang draped across the night sky in dazzling displays of greens and reds and so trace the Earth’s otherwise unseen field lines. But how are they produced?

It begins when the sun ejects energized particles in what we call solar wind. This solar wind approaches Earth and funnels down along the magnetic field lines that stretch out from our planet’s poles. (That is why auroras only occur around Earth’s northern and southern extremities.) When that wind impacts the Earth’s upper atmosphere and those charged particles collide with the neutral particles in Earth’s magnetosphere, those formerly neutral particles that become excited. Those newly ionized particles emit excess energy in the form of light and we call the effect produced “auroras,” after the Roman goddess of dawn. It is similar to what happens in a fluorescent light tube except on a global scale.

Auroras are not just sights to behold, they are rich with important information for scientists interested in studying and preparing for solar storms.

Cornell Research: Analyzing Space Weather

Cornell and several other institutions including NASA teamed up and launched a rocket on Feb. 18 to analyze the components of an aurora. From this study, scientists looked to learn how phenomena like solar storms affect and obstruct radio communications in the upper atmosphere, and in particular, how satellite signals get corrupted by solar disturbances, said Steven Powell, senior engineer of electrical and computer engineering and principal investigator of the mission.

The research team launched the rocket from Poker Flat Research Range in Alaska about 35 miles north of Fairbanks. The region was far enough north to witness the northern aurora, known as the aurora borealis, and remote enough to have minimal interference by light pollution, as dark conditions are optimal for looking at the aurora. The launched rocket allowed researchers to take a vertical profile or cross-section of the aurora, unlike a satellite which would have only flown at a single altitude.

The launch and mission took only about 10 minutes, Powell said, though they waited about three weeks or so for ideal launch conditions. The rocket reached a maximum height of 325 kilometers and travelled downrange roughly the same distance. While aloft the rocket measured the energy levels of the particles it encountered using ion detectors and energy spectrum analyzers to observe the kind of energy exchange taking place in the upper layers of Earth’s atmosphere.

“The electric field measurement can be as easy as like a voltmeter measuring the electricity of the aurora,” Powell said, “it measures subtle fluctuations in the magnetic field as modulated by the charged particles from the sun.”

Powell likened these fluctuations to the optical effect of starlight twinkling, scientifically known as scintillation. Just as waves of starlight will fade and fluctuate upon interaction with the atmosphere, so too can radio waves from solar-atmospheric disturbances.

Aside from refining computer models of how radio waves travel in the upper atmosphere, Powell said that there is an even more practical side to the research: learning how signals from satellites such as global positioning systems (GPS) get degraded.

“We want people to be able to recognize those fluctuations and be aware of it if you are, for example, landing your plane at that time,” Powell said. Researchers want not only to recognize when signals are being degraded but to improve the radio receivers themselves by making them more accurate and less likely to be affected by this degradation when it does occur.

Cornell has an active program of GPS research shared by the Schools of Electrical and Computer Engineering and Mechanical Engineering.  This program was started several years ago in the ECE School by the late Prof. Paul Kintner, who also began the rocket project.

Auroras are just one type of solar-atmospheric phenomena, Powell said, “and a pretty dramatic example at that.” But some violent solar storms can be even more dramatic.

Solar Storm Aftermath: Potential tech devastation

“The energy that drives the auroral displays is delivered by the ‘punch’ of a CME to the upper ionosphere,”  Prof. Donald Farley, electrical and computer engineering, said in an email. “This same “punch” can also cause serious problems to GPS navigation.  The Global Positioning System radio signals from the satellite network pass through the ionosphere on their way to the Earth and are slightly refracted.  A disturbed ionosphere causes the apparent position of the satellites to jitter around slightly, or scintillate.

“The energetic particles associated with a really severe solar storm can also increase radio wave absorption in the ionosphere enough to completely prevent the GPS signals from reaching the Earth for a few minutes,” Farley said.

Electrical power systems are vulnerable to changing magnetic fields according to Kelley. “Communication, navigation systems, and satellites are among the many things affected by space weather,” Kelley said. Transformers are not designed for very low frequencies, so the magnetic field changes associated with magnetic storms can be problematic. “There is an entire industry that advises power companies about when to be worried about a magnetic storm. A day’s notice can be given so power companies can take the appropriate steps,” he said.

“Larger [solar] storms can knock out power systems and satellite communications,” said Robert Miceli, grad.

Carrington Flare: The Perfect Storm

The most powerful solar storm in recorded history occurred in 1859. Named after the English astronomer who first observed it, the Carrington Event caused the northern lights to be seen all across the globe —  even as far south as the Caribbean.

“People didn’t have power lines back then, but they had telegraph lines.  There were huge amounts of electricity coming out from them and they were setting fires and shorting themselves out and not working,”  Lantz said. “So this very primitive technology made of wood and wires was fried, so you can well imagine in the much more technological era that we live in now, that the consequences would be graver and really hard to recover from,”

“There should be a concern for an economic catastrophe if we had something like the 1859 event happen again. There could be places in the world that wouldn’t have power for years,” Kelley said. Transformers are built to last forever. Because of this, factories produce a very small number of transformers every year. If thousands of transformers needed to be replaced at once, it would take a very long time to recover.

According to NASA, the next solar maximum will occur in the Spring of 2013. The current predicted number of 61 sunspots for the upcoming solar maximum makes it the smallest cycle in about 100 years. While there is no need to worry about failing power grids just yet, Kelley said, “The Big One is going to happen at some point and right now we are not prepared for it.”

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Original Author: Nicolas Ramos

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