In­tense So­lar Flare Wor­ries Sci­en­tists

Blast of Ra­dio Waves Larger Than Thought Pos­si­ble Caused GPS Dis­rup­tions

The Washington Post Sunday - - Science - By Marc Kauf­man

Global Po­si­tion­ing Sys­tem de­vices around the world were briefly but sig­nif­i­cantly dis­rupted late last year by an un­ex­pect­edly large blast of ra­dio waves dur­ing a so­lar flare, re­searchers re­ported at a con­fer­ence last week.

The Dec. 6 so­lar flare spawned an in­tense burst of ra­dio wave ra­di­a­tion, in­clud­ing some at the same fre­quen­cies used by GPS hard­ware — cre­at­ing a “ noise” that made it im­pos­si­ble for many re­ceivers to con­tinue re­ceiv­ing sig­nals from GPS satel­lites. The ef­fect, said Cornell Univer­sity pro­fes­sor Paul Kint­ner, was “ more pro­found and wide­spread than we thought pos­si­ble.”

The event is con­sid­ered es­pe­cially wor­ri­some be­cause it oc­curred dur­ing a “ so­lar min­i­mum,” part of an 11- year cy­cle when sunspots and so­lar flares are least fre­quent. When the next “ so­lar max­i­mum” ar­rives around 2011, re­searchers said, the dis­rup­tions to GPS de­vices and other satel­lite­based nav­i­ga­tion in­stru­ments could be far more se­vere.

“ This ra­dio event was 10 to 20 times big­ger than any­thing we had mea­sured be­fore, or thought would reach Earth from the sun,” said William Murtagh of the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion’s Space En­vi­ron­ment Cen­ter, an or­ga­nizer of the Wash­ing­ton con­fer­ence on the in­creas­ingly im­por­tant field of space weather.

“ It told us that when it comes to pre­par­ing for big so­lar events, we can never let down our guard,” Murtagh said. “ We re­ally don’t know what might be com­ing at us.”

The im­pact of the De­cem­ber dis­rup­tion on trans­porta­tion and other sys­tems re­mains un­clear, in part be­cause mil­i­tary and com­mer­cial GPS users do not like to dis­cuss their vul­ner­a­bil­i­ties. But the re­searchers said many re­ceivers were use­less for 10 min­utes, and some for longer pe­ri­ods.

GPS is widely used in nav­i­ga­tion, sur­vey­ing, sit­ing sen­si­tive equip­ment such as deep- sea oil rigs and mil­i­tary op­er­a­tions of all kinds, as well as in or­ga­niz­ing the flow of elec­tric­ity through power grids and in in­ter­na­tional fi­nan­cial trans­ac­tions. Its use is grow­ing quickly with­out much aware­ness of its vul­ner­a­bil­ity, sev­eral spaceweather re­searchers said.

Sci­en­tists have known for some time that GPS — which re­lies on re­ceiv­ing pre­cisely timed ra­dio sig­nals from sev­eral of 24 or­bit­ing satel­lites — can be dis­rupted by elec­tro­mag­netic storms cre­ated in Earth’s iono­sphere by so­lar flares and erup­tions. A ma­jor elec­tro­mag­netic storm at the end of Oc­to­ber 2003, for in­stance, had some GPS units down for as much as 19 hours.

Th­ese storms are caused by electrically charged par­ti­cles and elec­tro­mag­netic fields spewed by the sun that travel rel­a­tively slowly to­ward Earth. As a re­sult, spaceweather fore­cast­ers can usu­ally give GPS users sev­eral hours’ to sev­eral days’ warn­ing that a dis­rup­tion may be com­ing.

The ra­dio waves from the Dec. 6 flare, how­ever, trav­eled at the speed of light and passed quickly through the re­gion of the at­mos­phere that usu­ally blocks in­com­ing ra­di­a­tion. As a re­sult, they be­gan jam­ming GPS re­ceivers with no warn­ing.

“ The GPS sig­nal is a rel­a­tively weak one,” said Kint­ner, who, along with a Cornell grad­u­ate stu­dent, first de­scribed the ef­fect of so­lar ra­dio waves on GPS. “ What hap­pens when there’s a so­lar ra­dio blast is that the back­ground noise to the sig­nal in­creases — like at an in­creas­ingly noisy cock­tail party. Even­tu­ally, the back­ground noise makes it so you can’t hear the per­son you’re next to.”

Anthea Coster of the Mas­sachusetts In­sti­tute of Tech­nol­ogy’s Haystack Ob­ser­va­tory said the De­cem­ber ra­dio flare was so strong that it dis­rupted the most so­phis­ti­cated GPS re­ceivers — ones far more pow­er­ful than those used in many au­to­mo­biles.

Space weather is largely driven by the sun and its 11- year cy­cle of in­creas­ing and de­creas­ing mag­netic ac­tiv­ity — which can be­come vis­i­ble as sunspots at its great­est in­ten­sity, or so­lar max­i­mum. The last max­i­mum was in 2000, and they gen­er­ally last three to five years.

Dur­ing a max­i­mum, the mag­netic field that sur­rounds the sun is reg­u­larly pierced by flares and coro­nal mass ejec­tions of en­ergy in the form of ul­tra­vi­o­let light, Xrays, highly charged pro­tons and a “ stormy” so­lar wind.

Much of the en­ergy is blocked by Earth’s mag­netic field, but some larger so­lar flares pro­duce ra­dio bursts like the one that pierced the at­mos­phere last year.

While sci­en­tists were sur­prised by the in­ten­sity of the De­cem­ber ra­dio blast, they are keenly aware that much about space weather re­mains im­per­fectly un­der­stood or sim­ply mys­te­ri­ous. They also say most of the space- weather- re­lated prob­lems likely to oc­cur in the fu­ture will hap­pen when pow­er­ful ra­di­a­tion and elec­tro­mag­netic forces hit the thou­sands of satel­lites that or­bit Earth.

Both the Air Force and NOAA have space- weather ob­ser­va­to­ries, with tele­scopes sit­u­ated around the world to keep the sun’s sur­face and its flares con­tin­u­ously in view. NOAA’s Space En­vi­ron­ment Cen­ter, which puts out reg­u­lar re­ports on space- weather dy­nam­ics and trends, is head­quar­tered in Boul­der, Colo.

Murtagh, a fore­caster in that of­fice, said be­cause space- weather records go back only a few so­lar cy­cles, “ we don’t re­ally have a good idea yet of the bound­aries of what’s pos­si­ble.”

He said if some­one had asked him on Dec. 4 if a ra­dio erup­tion of the size that reached Earth two days later was pos­si­ble, he would have said no.

“ So now,” he said, “ if I was asked if one might come that’s five or 10 times more pow­er­ful than the De­cem­ber 6 event, I would have to say: ‘ It’s pos­si­ble. We re­ally don’t know.’ ”

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