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Space Weather in Focus: A Decade in Review

2010; American Geophysical Union; Volume: 8; Issue: 10 Linguagem: Inglês

10.1029/2010sw000636

1542-7390

Ernie Tretkoff,

Space Science and Extraterrestrial Life

In the past decade, many events, discoveries, and publications have brought attention to how the Sun affects technologies, increasing awareness of space weather's effects among scientists, policy makers, and the public. As the decade comes to a close, Space Weather staff writers wondered what comes into focus after a quick scan of the past 10 years. After many excellent suggestions from Space Weather's editorial advisory board and our editor were reviewed, five snapshots were selected as representative of the most significant developments in space weather from 2001 to 2010. The items below are in no particular order. The Sun has a cycle of activity averaging 11 years in duration, during which it goes through phases of higher and lower magnetic activity, as evidenced by numbers of sunspots. Causing much discussion and speculation in the space weather community and in media coverage, the most recent minimum was abnormally long. Cycle 23, which started in 1996, began to wane after the solar maximum in 2000. For the next 8 years, there were few sunspots and few solar flares. In 2008 no sunspots were observed on 266 days of the year. Solar cycle 23 finally ended in December 2008, more than 12 years after it began. Scientists are uncertain as to why cycle 23's solar minimum was so prolonged. Some even suggested the Sun might be in another extended minimum similar to the Maunder Minimum, which occurred from 1645 to 1715, coinciding with the Little Ice Age. One effect of the extended solar minimum has been an increase in cosmic ray intensity at Earth. Galactic cosmic rays consist of protons as well as some heavier nuclei that are accelerated to high energy outside our solar system. These high-energy charged particles are a hazard to astronauts and can damage satellites. Most cosmic rays don't reach Earth, however, because they are repelled by the Sun's magnetic field, which creates the heliosphere, a giant magnetic bubble around the solar system. But when solar activity is low, the Sun's magnetic field is weaker, so more cosmic rays can penetrate the heliosphere and reach Earth. When cosmic rays hit Earth's atmosphere, they create showers of secondary particles that can be detected. Scientists have found that cosmic ray intensities were high during the recent solar minimum. “The intensity of galactic cosmic rays varies inversely with solar activity: As solar activity decreases to a minimum every 11 years or so, galactic cosmic rays increase to a maximum,” explains John Bieber of the University of Delaware, who has studied cosmic rays. “However, during the recent solar minimum, neutron monitors recorded a new space age high approximately 3% higher than any prior peak” in the past 50 years, he said. Neutron monitors detect cosmic rays with energy above 500 megaelectron volts but not lower-energy cosmic rays. Therefore, “the 3% increase measured by neutron monitors portends a much larger increase at lower energies,” said Bieber. The high cosmic ray intensities during the recent minimum suggest that it may be necessary to reconsider how much shielding astronauts require. “Radiation exposure is one of the most intractable problems facing human exploration in deep space. The new observations indicate that mission plans need to accommodate larger radiation doses from galactic cosmic rays than would be expected from observations made in the past,” said Bieber. The solar cycle can also affect Earth's climate, as small variations in solar activity can cause warming or cooling of the planet. Research spurred by the mysteriously long solar minimum could help scientists better understand and predict the solar cycle and thus its effects on Earth. Solar activity has slowly picked up after cycle 24 began in December 2008. The next solar maximum is predicted for 2013. In 2003 some unusual space weather came hand in hand with Halloween's usual ghosts, witches, and trick-or-treaters. Between 19 October and 5 November, 17 major solar flares erupted, some of them accompanied by fast coronal mass ejections (CMEs). CMEs that reached Earth caused some severe geomagnetic storms on 29 and 30 October. This outbreak of solar flares and geomagnetic turbulence is colloquially known as the “Halloween storms.” Flares associated with this event occurred in the declining phase of the solar cycle, when the Sun had been relatively quiet with only a few sunspots. In mid-October several large sunspot clusters appeared; although some solar activity does often occur late in the solar cycle as the Sun is winding down from its peak, this amount of activity was unusual. “In my opinion, what typifies the Halloween storm period is the number of large active regions involved, the extended period of activity, and the many, many moderate to large storms of all types,” said Doug Biesecker of NOAA's Space Weather Prediction Center (SWPC), which issued an advisory bulletin before the solar flares reached Earth. The flares and resulting storms were monitored by satellites observing the Sun and the Earth's environment, noted Pål Brekke of the Norwegian Space Centre. “We managed to follow the storms from where they were ‘born’ until they hit the Earth. The Earth has been hit by many similar storms before, but these were much better observed. Typically we have 1–2 similar strong storms every cycle. But the Halloween storms were somewhat unique since so many were lumped together within 2 weeks,” he said. The Halloween storms caused a variety of effects at Earth and on satellites. For instance, on Earth, geomagnetically induced currents caused a brief power outage in Sweden. Many airplane flights scheduled to fly over the polar regions had to be rerouted to avoid disruption to their communications links, causing longer flights and greater fuel costs. Further, aurorae, normally seen only at high latitudes near the poles, were reported as far south as Texas and Florida. In Earth's orbit, astronauts on the International Space Station had to take cover in a heavily shielded area of the station to avoid high doses of radiation. A number of satellites experienced anomalies, and a Japanese Earth observation satellite was permanently damaged. Deep-space and near-Earth science missions were also affected. Space weather observing satellites, including Solar and Heliospheric Observatory (SOHO) and Advanced Composition Explorer (ACE), were temporarily disrupted. ACE was unable to collect accurate solar wind data during some portions of the storms. The storms also provided a test for technologies that can be affected by space weather. For example, the Halloween storms occurred at a time when the U.S. Federal Aviation Administration's Wide Area Augmentation System (WAAS), an air navigation aid, was coming of age. “The storms gave the WAAS a few days of very difficult conditions in which to function, and the system operated as it was designed [to] but needed to alter its operating mode to account for a very disturbed ionosphere and unbounded vertical errors,” said Joseph Kunches of NOAA's SWPC. “The space weather conditions also impacted a variety of other systems—satellites, power grids, and more—and challenged the robustness of some of the most advanced technologies of the day.” These effects drew significant media attention, bringing space weather into sharp focus in the public eye. Further, the Halloween storms were brought up in congressional testimony, making policy makers—some for the first time—aware of space weather. In 1996 the X PRIZE Foundation announced that it would offer a $10 million reward to the first nongovernmental organization that launched a manned spacecraft into space twice within 2 weeks. Named for the family who sponsored the prize, the Ansari X PRIZE lay unclaimed until 2004, when the team behind SpaceShipOne flew to an altitude of more than 100 kilometers on 29 September and then again on 4 October, the anniversary of the 1957 Sputnik launch. The spaceship was designed by aerospace engineer Burt Rutan of Scaled Composites, LLC, with financial backing from billionaire software developer Paul Allen. The spacecraft was piloted by Mike Melvill on 29 September 2004 and by Brian Binnie on 4 October 2004. The Ansari X PRIZE was modeled after earlier aviation prizes, especially the Orteig Prize, which Charles Lindbergh won for his solo flight across the Atlantic Ocean in 1927. Just as that prize ushered in a new era in aviation, the Ansari X PRIZE has brought about new interest in commercial spaceflight. With new frontiers come new risks, including human interaction with adverse space weather. Flights outside of Earth's atmosphere are exposed to cosmic radiation and solar energetic particles. Commercial space travelers would face these risks, so the ability to predict space weather events could become crucial for more people. In addition to the X PRIZE flights, other developments reflect recent increased interest in commercial spaceflight. For instance, in 2001 businessman Dennis Tito became the first space tourist by paying for a trip to the International Space Station. Since then, several other civilians have become space tourists—including Anousheh Ansari, one of the X PRIZE's namesakes—and more could follow. Virgin Galactic, which is developing SpaceShipTwo to carry passengers on suborbital spaceflights, reports that more than 370 people have made deposits on the $200,000 tickets to space. Virgin Group Ltd. founder Richard Branson commented in a statement after an October test glide flight of SpaceShipTwo, “Now, the sky is no longer the limit and we will begin the process of pushing beyond to the final frontier of space itself over the next year.” The ability to predict solar activity and provide appropriate shielding will be important so that those taking advantage of the growing commercial spaceflight opportunities will be safe from radiation hazards. Over the past decade, use of the Global Positioning System (GPS) for navigation and other critical applications has grown explosively. Also during the decade, scientists discovered that this vital technology can be particularly vulnerable to unpredictable solar activity. The new threat comes from solar radio bursts. Solar radio bursts are often emitted along with solar X-rays from solar flares. These bursts can last from tens of seconds to hours and emit radio waves over a wide range of frequencies, including those used by GPS. Solar radio bursts disrupt GPS by adding noise to the signals that GPS receivers pick up. Solar radio bursts were detected in the early 1940s, but it is only recently that their effects on GPS have become recognized. In September 2005 a solar radio burst's effects on GPS were discovered by Alex Cerruti, then a graduate student at Cornell University, and his colleagues. While studying the ionosphere, Cerruti and colleagues watched the GPS receiver they were using suddenly drop out. After further investigation, they found that a solar radio burst had occurred at the time of the GPS dropout and that other GPS receivers were affected at the same time. The researchers confirmed the effect that solar radio bursts can have on GPS during a much larger burst in December 2006. This especially large solar radio burst, which produced 10 times more radio noise than any previously recorded solar flare, affected most GPS receivers over a wide geographic range on the dayside of Earth (including the continental United States), causing outages for several minutes. “Loss of GPS signals causes degraded positioning performance, and in the case of receivers tracking less than 4 satellites, causes the receiver to fail to produce a navigation solution or time estimate,” said Cerruti, who is now at MITRE Corporation. “What was surprising was the extreme magnitude of the December 2006 events—no one had anticipated a record-setting solar radio burst at the GPS frequencies,” said Cerruti. Large solar radio bursts, which are difficult to predict, are most likely to occur during active phases of the solar cycle. “Statistically one should expect more large bursts and hence more severe effects on GPS as activity increases. But the large bursts of December 2006 occurred near solar minimum, so clearly one has to be cautious,” said Dale Gary of the New Jersey Institute of Technology, one of the researchers on the team that observed the 2006 event. He estimates that bursts of that size could occur on average about once every 25 years. There are ways to improve the resiliency of GPS, noted Cerruti. “Standard techniques to improve receiver noise figures (such as proper antenna and preamp selection), as well as weak-signal-tracking algorithms, all help to improve the resiliency of GPS receivers to interference.” He added, “More research needs to be done to see if one can predict the occurrence and strength of solar radio bursts.” Because many technologies and critical infrastructure are interdependent, a space weather event that damages one system could have wide-ranging effects, possibly leading to severe societal and economic consequences. While scientists have known this for some time, the past decade saw several successful efforts to communicate this information to the public. A 2008 National Research Council (NRC) report, Severe Space Weather Events—Understanding Societal and Economic Impacts, drew attention to how space weather can disrupt daily life. The report resulted from a workshop that brought together researchers and industry experts to discuss space weather's potential effects on critical technology and infrastructure. A key focus of the report was to describe the ways in which many technologies are vulnerable to space weather. For instance, in 1989 a geomagnetic storm caused widespread blackouts in Quebec, Canada. Larger solar storms could potentially cause even more widespread and long-term damage, the report notes: A geomagnetic storm that knocked out large portions of the power grid could cost trillions of dollars in economic loss. “The report highlighted the fact that industry is affected by space weather; it is not a subject just for research. Research directed toward mitigating the effects of space weather phenomena has the potential of aiding industrial management decisions,” said Peggy Shea, emeritus researcher at the Air Force Research Laboratory and senior researcher at the University of Alabama's Center for Space Plasma and Aeronomic Research in Huntsville. “Another highlighted aspect was the connections and interdependencies across the economy,” she said. “For example, loss of power can ultimately affect communications, transportation, emergency services, and banking and finance. Examples such as these bring to attention the far-reaching consequences of a major space weather event to our everyday lives.” Congress cited the NRC report in a bill designed to protect the power grid from geomagnetic storms and other threats. The bill, which was passed by the House of Representatives in June 2010 but has not been voted on in the Senate, would give the Federal Energy Regulatory Commission (FERC) authority to develop and enforce standards for power companies to protect electric grids. “As a result of the workshop, and the report that resulted from it, much greater public, industry, and government attention was called to the relationship between space weather and critical infrastructures, particularly the power grid,” said study director Sandra Graham, senior program officer for the NRC Space Studies Board. “This raised awareness has had an enormous impact on the public and private debate about infrastructure protection, and the results of that are beginning to be seen in congressional action, industry planning, and government emergency planning.” Several other publications that influenced the space weather community during the past decade include the NRC decadal survey in 2003 (The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics) and a 2006 NRC workshop report entitled Space Radiation Hazards and the Vision for Space Exploration: Report of a Workshop. The decadal survey identified scientific challenges and helped prioritize missions, facilities, and research to meet those challenges, such as the need to replace the aging ACE satellite, which currently provides key solar wind data for space weather models and forecasting. The 2006 report focused on the need to improve the ability to predict the space environment for astronauts traveling outside Earth's atmosphere, in particular, to the Moon or Mars. The space weather community has also benefited from the launch, in 2003, of the present journal, Space Weather: The International Journal of Research and Applications, which provides a place for those interested in space weather to report on and read about new developments related to the Sun's activity and its effects on technologies. In addition, the general public has been increasingly exposed to space weather through media outlets, including news articles in a wide variety of publications and television programs. Recent popular books such as Stuart Clark's The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began have also drawn attention to space weather. Partly because of these publications and other media attention, the decade has been one of increasing awareness among scientists, policy makers, and the public of the potential effects of space weather on modern society. These five snapshots show that scientists have learned a lot in the past decade about the Sun and its effects on technologies on Earth and in space. New focus has been placed on space weather as awareness has grown, but there is still much work to be done as the Sun becomes more active and the new decade begins. Ernie Tretkoff is a staff writer for the American Geophysical Union. E-mail: [email protected]