Solar Forecast
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Solar Forecast: How much damage and disruption might the next solar AHEAD cycle bring? On January 20, 2005, Earth was pummeled by a barrage of en- ergetic protons from the Sun that resulted in the most intense ground-level radiation in a half century. Eight months later, our star belched several powerful fl ares, one of them the fourth BY C. RENÉE JAMES largest in the past 20 years. Had its associated torrent of charged particles been directed earthward, we would have likely expe- rienced widespread power outages, disruptions in communica- tions, and, for any astronauts who happened to be out on a spacewalk, enough exposure to cause radiation sickness. All this during the Sun’s “quiet time.” For 250 years observers have kept counts of spots on the Sun, tallies that allow us to track how much commotion is taking place on our star’s surface as it waxes and wanes throughout a roughly 11-year-long cycle of activity. Far from being curious blemishes, sunspots are the most obvious clue of the Sun’s state. More sunspots mean more active cycles. The Sun is never really completely quiescent, but during each cycle’s minimum the solar disk can be blank for long stretches (as was the case earlier this year). Right now we are witnessing the dying gasps of the 23rd recorded solar cycle, one that even at its maximum was less active than the previous two cycles. Cycle 24, which should begin later this year, might be far more impressive, perhaps 50% stronger than the one just ending. On the other hand, it might be 40% weaker. The problem is that solar scientists are getting mixed signals from our star. NASA / TRACE TEAM NASA / TRACE Playing the Odds TIP OF THE ICEBERG This active region on More than a bet is riding on the strength of the upcoming activity the Sun, recorded in extreme-ultraviolet light cycle. Despite the Sun’s seemingly remote distance of 150 million by the TRACE spacecraft, triggered a solar kilometers (93 million miles), what happens on its face is con- fl are on January 20, 2005, that one scientist nected intimately with what happens here and throughout the called “in many ways one of the most spec- solar system. Activities that we take for granted — uninterrupted tacular of the Space Age.” Its rapid onset electrical power, polar-routed airline fl ights, satellite-based com- and the torrent of high-energy protons it munications, and GPS navigation, to name just a few — can be unleashed have underscored Earth’s vulner- profoundly affected by inclement space weather. And if the fore- ability to solar outbursts. cast for a more severe cycle holds true, we’ll face a higher prob- 24 July 2007 Sky & Telescope ©2007 New Track Media LLC. All rights reserved. IC OBSERVATORY IC PHOTO-ILLUSTRATION: PATRICIA GILLIS-COPPOLA; AURORA: MICHAEL KLENSCH / WWW.AGLOWPHOTO.COM; SUN COMPOSITE: SOLAR AND HELIOSPHER SUN COMPOSITE: KLENSCH / WWW.AGLOWPHOTO.COM; MICHAEL AURORA: GILLIS-COPPOLA; PATRICIA PHOTO-ILLUSTRATION: S&T ©2007 New Track Media LLC. All rights reserved. Sky & Telescope July 2007 25 psolar forecast TROUBLE BREWING When a Jupiter-size Sun (masked) Sun (masked) sunspot group rolled into view in October 2003, scientists knew something big might happen. And it did: on October 28th, this region spawned the fourth most intense X-ray outburst ever recorded — with Earth directly in the line of fi re. Visible Disk X-ray Flares Coronal Mass Ejections DODGED BULLET Six days later, the same active region exploded with an even more powerful fl are, the strongest on record. Fortunately, its pulse of radiation — and the fast-moving coronal mass ejection (CME) that it spawned — struck Earth with NASA / SOHO CONSORTIUM (8) NASA / SOHO CONSORTIUM only a glancing blow. ability of being hit by powerful outbursts like those in 2005. Sun is not completely clear. Many scientists assert that solar These are the sorts of events that scientists really wish fl ares provide their acceleration, while others point to the they could predict. Given the potential impact on our shock waves associated with coronal mass ejections. health and societal infrastructure, the more time we have Regardless, all those X-rays and SEPs take very little to prepare for them, the better. Unlike many terrestrial- time to reach Earth. “By the time you see them happening weather disasters, however, individual space-weather there,” comments Thomas Bogdan, director of the SEC, events are currently unpredictable. “they’re happening here.” Scientists can only guess, not “It’s fair to say that space-weather forecasting has only predict, when they’ll occur, by tracking the confi gurations just reached the level that terrestrial-weather forecasting of solar magnetic fi elds most likely to result in fl ares or SEP was at in the late 1950s,” comments Douglas Biesecker of events. Frighteningly, this kind of probabilistic risk analysis NOAA’s Space Environment Center in Boulder, Colorado. would not have deterred astronauts from venturing outside Scientists currently wield predictive power only for the safety of the International Space Station on January 20, the slowest of space-weather events, coronal mass ejections. 2005. Fortunately, they stayed in that day. CMEs are great bubbles of plasma containing billions of tons of charged particles that the Sun sporadically spews Like a Hurricane into space. They can reach Earth in as little as 18 hours, So what exactly is at stake when the Sun gets agitated? The sometimes “attacking” Earth’s magnetosphere with enough most obvious and widespread problems arise from the mas- ferocity to cause severe geomagnetic storms. sive CMEs. These can create geomagnetic storms, which By contrast, fl ares in the solar atmosphere can release in- are every bit as powerful as their name implies. According tense bursts of ultraviolet and X-ray energy with speed-of- to Biesecker, “Geomagnetic storms are to space weather light consequences. X-class fl ares, the most extreme cases, what hurricanes are to terrestrial weather. Pretty much can cause power-grid failures at high latitudes, communica- everything that could be affected is.” tion blackouts, satellite failures, and signifi cant radiation The good news is that CMEs — like hurricanes — give us enhancements throughout near-Earth space. This energy plenty of warning before plowing into us. The bad news is can also energize our atmosphere, causing it to expand and that CMEs’ charged particles come in dense swarms, and so create more drag on satellites in low-altitude orbits. the list of “everything that could be affected” is quite long. Also dangerous are abrupt releases of solar energetic particles For example, the frenzied electromagnetic activity dur- (SEPs), which travel at nearly the speed of light and arrive at ing a severe geomagnetic storm can induce strong electrical Earth in just minutes. What accelerates them away from the currents in long pipelines and cables (as illustrated on page 29). Currents coursing through oil pipelines can prema- EBB AND FLOW Since the late 1700s astronomers have used counts turely corrode the metal and ultimately cause leaks that are of sunspots (below) to gauge the Sun’s state during its 11-year activity costly to locate and repair. For terrestrial power supplies, cycle. The upcoming interval, Cycle 24, may be either considerably more this added rapidly varying power can destroy transformers 300 or less active than usual (see page 30), depending on which of two and create widespread blackouts at higher latitudes. leading models proves correct. But fast-moving charged particles aren’t the cause for 200 100 Sunspot number 0 17701780 1790 1800 1810SOURCE: D. HATHAWAY / NASA 1820 26 July 2007 Sky & Telescope ©2007 New Track Media LLC. All rights reserved. Sun-Earth Science Goes Global Fifty years ago, the world’s Earth works. A global scien- off on February 19th during According to executive scientists combined forces tifi c eff ort is once again being ceremonies in Vienna, Austria. director Joseph Davila (NASA/ during the International Geo- mustered for the International Sponsored by the United GSFC), the IHY is trying to physical Year, a campaign to Heliophysical Year (www Nations, the 24-month-long forge lasting partnerships learn more about how Planet .ihy2007.org), which kicked IHY will explore how the Sun among investigators in many infl uences the electromag- disciplines and in geographic netic environments around locales, such as Africa, where Earth and other planets. One few studies have been done major thrust will be to set up before. “We want the science magnetometers and other in- to continue after IHY has struments in as many diff erent ended,” he notes. countries as possible. — J. Kelly Beatty concern. The ultraviolet light and X-rays associated with an intense fl are can ionize our upper atmosphere, sometimes crippling radio communication for hours. Since a burst of light is our fi rst clue that a fl are has occurred, we have ab- solutely no way to prepare for these radio blackouts. Another concern is the satellite-based Global Positioning System, which is usually accurate to within meters but can be rendered unable to pinpoint positions to within 50 me- ters following a strong solar fl are. The reason is that fl ares generate prodigious radio energy in addition to their X-ray and ultraviolet outbursts. Once these radio waves reach Earth, they act as noise that can degrade the signals trans- mitted by GPS and other navigational systems. Only recently have researchers realized how susceptible GPS receivers are to stormy space weather. A solar fl are last December 6th created an outburst of radio noise 10 times stronger than any previously known. “At its peak,” notes Dale Gary, a physicist at the New Jersey Institute of Tech- nology, “the burst produced 20,000 times more radio emis- sion than the entire rest of the Sun.