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Radio “screams” portend severe solar storms

May 30, 2007
Courtesy ESA
and World Science staff
Updated May 31

Re­search­ers say they have dis­cov­ered that the Sun gives off “screams” of ra­di­o waves that can pro­vide ad­vance warn­ing of haz­ard­ous radia­t­ion storms from the star.

In these storms, called cor­o­nal mass ejec­tions, the Sun spouts off great amounts of gas that can re­sult in harm to hu­man in­fra­struc­ture, as well as to as­tro­nauts in space.

In this an­i­ma­tion, the sun launches a cor­o­nal mass ejec­tion. Its shock ac­cel­er­ates elec­tri­cal­ly charged par­t­i­cles. When these ar­rive at Earth, they are de­flect­ed by our plan­et's glob­al mag­net­ic field, rep­re­sented by the large, pur­ple bub­ble. The par­t­i­cles next ar­rive at Mars. Mars on­ly has lo­cal mag­net­ic fields (pur­ple bub­bles). These lo­cal fields are be­lieved to be rem­nants of a glob­al mag­net­ic field, which van­ished bil­lions of years ago, and they don't de­flect the par­t­i­cles very well. Sci­en­tists be­lieve such par­t­i­cle storms, and so­lar wind, may have grad­u­al­ly re­moved much of the Mar­tian at­mos­phere after Mars' glob­al mag­net­ic field van­ished. (Cred­its: ESA, NA­SA)


A cor­o­nal mass ejec­tion be­gins when the Sun casts off around a bil­lion tons of elec­tric­ally con­duct­ing gas, or plas­ma, in­to space at mil­lions of kilo­me­tres (miles) per hour. 

The cloud is laced with mag­net­ic fields that can smash in­to Earth’s mag­net­ic field and dump en­er­gy in­to it, caus­ing mag­net­ic storms. These in turn can cause wide­spread black­outs by over­load­ing pow­er line equip­ment.

Some of these events al­so br­ing in­tense radia­t­ion storms that can dis­a­ble satel­lites or cause can­cer in un­pro­tected as­tro­nauts. As the gas ejec­tion blasts through space, it plows in­to a slower stream of plas­ma blown con­stantly from the Sun in all di­rec­tions, called the so­lar wind. 

The more sud­den plas­ma ejec­tion causes a shock wave in the so­lar wind. A strong enough shock ac­cel­er­ates elec­tric­ally charged par­t­i­cles that make up the so­lar wind to high speeds, form­ing the radia­t­ion storm. 

The trick is to iden­ti­fy which ejec­tions “pro­duce dan­ger­ous radia­t­ion, so we can warn as­tro­nauts and sat­el­lite ope­rators,” said Natchimuthuk Gopal­swamy of NASA’s God­dard Space Flight Cen­ter in Green­belt, Mar­y­land, lead au­thor of the stu­dy.

Gopal­swamy added that his team may have found a way to do just that. Cor­o­nal mass ejec­tions with pow­erful shocks, ca­pa­ble of caus­ing radia­t­ion storms, “scream” in ra­di­o waves as they slam through the so­lar wind, ac­cord­ing to the team. They pre­sented the find­ings at the Amer­i­can As­tro­nom­i­cal So­ci­ety’s an­nu­al meet­ing May 27-31 in Hon­o­lu­lu.

The re­search­ers used da­ta from the So­lar and He­lio­spheric Ob­serv­a­to­ry (SO­HO) space­craft of the Eu­ro­pe­an Space Agen­cy and NASA, as well as the lat­ter agen­cy’s Wind space­craft. They stud­ied 472 cor­o­nal mass ejec­tions from 1996 to 2005 that were fast and cov­ered large ar­eas of sky. They found that those that gen­er­at­ed a ra­di­o sig­nal al­so pro­duced radia­t­ion storms, but those with­out a ra­di­o sig­nal did­n’t. 

Strong shocks ac­cel­er­ate elec­tric ally charged sub­a­tom­ic par­t­i­cles called elec­trons in the so­lar wind, which in turn pro­duce the ra­di­o sig­nal, the as­tro­no­mers said. The same strong shock must al­so ac­cel­er­ate atom­ic nu­clei in the so­lar wind, which pro­duce the radia­t­ion storm, ac­cord­ing to the team.

“S­ince the ra­di­o sig­nal moves at the speed of light while the par­t­i­cles lag be­hind, we can use [the] ra­di­o noise to give warn­ing that it is gen­er­at­ing a radia­t­ion storm that will hit us soon,” said Gopal­swamy. “This will give as­tro­nauts and sat­el­lite ope­rators any­where be­tween a few tens of min­utes to a cou­ple of hours to pre­pare.”


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Researchers say they have discovered that the Sun gives off “screams” of radio waves that can provide advance warning of hazardous radiation storms from the star. In these storms, called coronal mass ejections, the Sun spouts off great amounts of gas that can result in harm to human infrastructure, as well as to astronauts in space. A coronal mass ejections begins when the Sun launches around a billion tons of electrically conducting gas, or plasma, into space at millions of kilometres (miles) per hour. The cloud is laced with magnetic fields that can smash into Earth’s magnetic field and dump energy into it, causing magnetic storms. These in turn can cause widespread blackouts by overloading power line equipment. Some of these events also bring intense radiation storms that can disable satellites or cause cancer in unprotected astronauts. As the gas ejection blasts through space, it plows into a slower stream of plasma blown constantly from the Sun in all directions, called the solar wind. The more sudden plasma ejection causes a shock wave in the solar wind. A strong enough shock accelerates electrically charged particles that make up the solar wind to high speeds, forming the radiation storm. The trick is to identify which ejections “produce dangerous radiation, so we can warn astronauts and satellite operators,” said Natchimuthuk Gopalswamy of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, lead author of the study. Gopalswamy added that his team may have found a way to do just that. Coronal mass ejections with powerful shocks, capable of causing radiation storms, “scream” in radio waves as they slam through the solar wind, according to the team. They presented the findings at the American Astronomical Society’s annual meeting May 27-31 in Honolulu. The researchers used data from the Solar and Heliospheric Observatory (SOHO) spacecraft of the European Space Agency and NASA, as well as the the latter agency’s Wind spacecraft. They studied at 472 coronal mass ejections from 1996 to 2005 that were fast and covered large areas of sky. They found that those that generated a radio signal also produced radiation storms, but those without a radio signal didn’t. Strong shocks accelerate electrically charged subatomic particles called electrons in the solar wind, which in turn produce the radio signal, the astronomers said. The same strong shock must also accelerate atomic nuclei in the solar wind, which produce the radiation storm, according to the team. “Since the radio signal moves at the speed of light while the particles lag behind, we can use [the] radio noise to give warning that it is generating a radiation storm that will hit us soon,” said Gopalswamy. “This will give astronauts and satellite operators anywhere between a few tens of minutes to a couple of hours to prepare.”