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REPORTDOCUMENTATION PAGE Form Approved O M B N o.0704-01-0188Thepubliceportingburdenforthiscollectionofnformationsestimatedtoaverage hourpe rresponse,ncludingheimeforeviewingnstructions,searchingexistingdatasources,gatheringand maintainingthedataneeded,and completingand reviewingthecollectionofinformationendcommentsregardingthisburdenestimateoranyotheraspectofthiscollectionofnformation,ncludinguggestionsoreducingheurdenoepartmentfefense.ashingtoneadquarterservicesirectorateornformationperationsndeports(0704-0188),215JeffersonDavisHighway,Suite1204,ArlingtonVA 22202-4302espondentsshould eawarehatnotwithstandingan yotherprovisionofaw ,noperson hall esubjecttoan ypenaltyforfailingtocomplywithacollectionofinformationifitdoesnotdisplayacurrentlyvalidOM BcontrolnumberPLEASEDO NOTRETURN YOURFORMTO TH EABOVEADDRESS.

1.REPORTDATEDD-MM-YYYY) 30-01-2010 2.EPORTTYPE REPRINT 3.ATESCOVERED (From-T o )

4.TITLEANDSUBTITLE Creationofartificialonosphericlayersusinghigh-powerHFwaves

-opa

5a .CONTRACTNUMBER

5b .GRANTUMBER5c .PROGRAMELEMENTUMBER 61102F

6 .A U T H O R S T .PedersenB .Gustavsson*E .Mishin E .Kendall"T .Mills

H .C .Carlson A .L .Snyder

5d .PROJECTNUMBER23115e .TASKNUMBERSD

5fWORKUNITNUMBER A 4

7.PERFORMINGORGANIZATION NAME(S)AN D ADDRESS(ES)AirForceResearchLaboratory/RVBXI29RandolphRoadHanscomAFB,MA1731-30108.PERFORMINGORGANIZATIONREPORTNUMBERA F R L - R V - H A - T R - 2011- 1031

9.SPONSORING/MONITORING AGENCYNAME(S)AN DADDRESS(ES) 10.SPONSOR/MONITOR'S ACRONYM(S)AFRL/RVBXI

11 .SPONSOR/MONITOR'S REPORTNIIMRFRIS1

12.DISTRIBUTION/AVAILABILITYSTATEMENT ApprovedforPublicRelease;distributionunlimited. 2011062711513 .SUPPLEMENTARYNOTES ReprintedfromGeophysical Research Letters,Vol.37 ,L02106,doi:l0.l029/2009GL04l895,2010 2010,AmericanGeophysicalUnion*InfoLab21,LancasterUniv.,Lancaster,U K .SR Ilnternational,MenloPark.CA A F O S R ,Arlington,VA@ N W R A .StocktonSprings,E

14 .ABSTRACTW ereportthefirstevidenceofartificialionosphericplasmasreaching sufficientdensitytosustaininteractionwithahigh-powerH Fp u m pbeamroducedbythe3. 6 MW H igh-R requencyActiveAurora lProgram ( H A A R P )transmitterinGakona,Alaska .heH F- drivenionizationprocessisinitiatednearth e2ndelectrongyroharmonicat22 0k m altitudeintheionosphericFregion.nc ehe artificialpl a sm areachessufficientdensity tosupportinteractionwiththetransm itterbeam it rapidlydescendsasanionizationwaveto-150k m altitude.lthoughtheseinitialartificiallayersappeartobedynamican dhighlystructured,thisne wabilitytoproduce significantartificialpl a sm aintheupperatm osphereopensthedoortoanewregimeinionospheric radiowavepropagationwheretransmitter-producedplasmasdominateoverhenaturalonospheric plasmaan dm ay eventually b ee m pl oye dasactive c om pone nt sf communicat ions, radar,an dothersystems.

15 .SUBJECTTERMSIonosphereolarregionsighLatitudes IonosphericrregularitiesActiveexperimentsonosphericscintillationquatorialonosphere PlasmaprocessesH Feating16.SECURITY CLASSIFICATIONOF: a.REPORT

UNCLb.ABSTRACT

UNCLc.THISPAGE

UNCL17 .LIMITATIONOFABSTRACT

U N L

18 .NUMBER OFPAGES 19a .NAMEOFRESPONSIBLE PERSON

oddR .Pedersen19B.TELEPHONENUMBERIncludeareacode)

Standard Form298 (Rev.8/98)Prescribed byANSIStdZ39.18

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8R or FullArticleGEOPHYSICALRESEARCHLETTERS,V O L .37,L02106,doi:10.l029/2009GL04l895,2010

Creationofartificialionosphericlayersusinghigh-powerHF wavesT .Pedersen,1.Gustavsson,2E .Mishin,1.Kendall,3T.Mills,1.C.Carlson,4andA.L .Snyder5Received24N ove m b e r2009:evised3December2009;accepted January2010:published30January2010.[l]eeporthefirstevidenceofartificialonosphericplasmaseachingsufficientdensityosustainnteractionwith igh-powerFumpeamroducedyhe3. 6 MWHigh-FrequencyActiveAuroralProgram (HAARP)transmitterinGakona,Alaska.TheHF-drivenonizationprocesssnitiatedearhendlectronyroharmonicat220kmaltitudenheonosphericFegion.Oncetheartificialplasmareachessufficientdensityosupportinteractionwiththetransmitterbeamitrapidlydescendsas anonizationwaveo-150 maltitude.Althoughheseinitialartificialayersappeartobedynamicandhighlystructured,thisnewabilitytoproducesignificantartificialplasmanheupperatmosphereopensthedoorto anewregimenonosphericadiowavepropagationwheretransmitter-producedplasmasdominateoverthenaturalionosphericplasmaandmayeventuallybeemployedas activecomponentsofcommunications,adar,andothersystems.itation:cdcrscn,T .,.ustavsson,. ishin,E .endall,.Mills,..arlson,nd..nyder(2010),reationofartificialionosphericlayersusinghigh-power H Fwaves,Geophys.es .Lett.,7,L02I06,doi:10.1029/2009GL041895.1 . Introduction

[2]heonosphericplasma fewhundredkilometersaboveth eearth'ssurfaceactsasareflectorfo rradiowavesinheHFfrequencyange,enablingong-distanceadiocommunications,over-the-horizonradar,an dothertechnol-ogies ofgrowingimportancefo rnational security andcounter-terrorismapplications[McNamara,991].However,henaturaldiurnal,seasonal,an dsolar-drivenvariabilityofth eionosphereimposesseverelimitationson operationofsuchsystems.Conceptstoactivelycontrolradiopropagationb y usinghigh-powerelectromagneticwavesoonizethegas-se sintheupperatmospherean dcreateartificialonosphericplasmahavebeendiscussedfo rdecades[e .g. ,Koert,991],buthaveneverbeendemonstrateddueoheargeelectricfieldhresholdsequiredorconventionalorevenunawaybreakdown[GurevichndZybin,005].Recentadvancesinhigh-powerH Fexcitationofth eonospherem a d epossi-b leb ycompletionoftheHigh-FrequencyActiveAuroral

SpaceVehiclesDirectorate. A irForceResearchLaboratory.Hanscom A F B ,Massachusetts,U S A .2lnfoLab2l.LancasterUniversity,Lancaster.U K .'SRInternational.McnloPark.California.U S A .4AirForceOff i ceofScientificResearch.Arlington,Virginia.U S A .'NorthwestResearchAssociates, tocktonSprings,Maine.U S A .Copyright2010bytheAmericanGeophysicalUnion.0094-8276/I0/2009GLO41895SO5.0O

ResearchProgramHAARP)ransmitterfacility,however,havemadeproductionofsignificantartificialonosphericplasmapossibleforth eirstt ime,openingthedoortoprac-ticalexplorationoftheseconcepts.

[3]lectromagneticwaveswithordinary(O )modepolar-izationreeflectedro mlasmasthepointherans-mittedwavefrequency/requalsth elocalplasmafrequencyfs9y/NlkHz(forNeincm "1),whichdependsonlyonth eplasmadensityNe.High-powerradiowavesc an transfersig-nificantenergytotheonosphericplasmawhen/7-matchesplasmaigen-frequenciesearf,hepperhybridre -quencyfuh Jf}+f2e,rmultiplesoftheelectrongyrofrequencyf.Thisenergycan heatth eonosphericelectronpopulationohousandsofK elvinaboveambientan d ls oaccelerateelectronsosuprathermalenergiesnheangeofafew tofe w dozen eV .Su p ra therma lelectronsexcite opticalemissionsuponm p a c twithheneutralgasses[Bernhardte taL ,988],nd c an actuallycreatene w plasmawhentheirenergyexceedstheionizationpotentialsofthegasses(~ 12-18eV )[GustavssonetaL ,2006].

[4]asedonenergybudgetestimates,creationofartifi-cialonization yH FheatinghasbeenpredictedooccurwhenpowerdensitiesntheH Fbeamreach G W effectiveradiatedpowerERP),similaroha tofth esolarextremeultravioletlu xcreatinghenaturalonosphereCar/50/1. 1993],However,heeffectsofionizationproductionhavegenerallybeenoosma l lo edetectablenheonosphereuntilheecentupgradeofth eHAARPacilitynGakona,Alaska(62.4N4 5W)o3.6MWpower,providingE R Pinth erangeof400-4000M W .nitialexperimentsafterth eupgradeshowedindicationsofenhancedplasmadensitiesnear200 maltitudeonhebottomsideofth eonosphericFregion,whichapparentlyde-focusedthetransmitterbeamintoaring surroundingabrightcentralspotvisibleinopticalmeasurements[PedersentaL,009].nhiseportw epresenthefirstevidenceofartificialonizationeachingth ethresholdofself-perpetuation,wheretheartificialplasmabecomessufficientlydensetosustainnteractionwithth etransmitterb e a m .Thisbreaksth edependenceon th enaturalionospherean dallowsth eartificialplasmato descendasan ionization"wave"towardhigherpowerdensitiesclosertothetransmitter,formingaglowingartificialayernear15 0m altitudenheonospheric"valley"egion, minimumnnaturalplasmadensity.2. Observations

[ 5 ]hemostpronouncedcasesofartificialayeror m a-tioninth evalleyregionoccurredbetween4-6UTon March17 ,2009,correspondingtotwilightan dearlyeveninghours

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0020 ISO 24 0Secondsafler05:13:00 UT17 March2009 0 2 4 6 8 10 Volume EmissionRate Figure.left)magesofartificialopticalemissions sviewedfrom th eremo tesiteat557 . 7 nm (top,withaltitudesalongheAARPieldinendicated),andromheHAARP iteookingupheieldin ewithhighesolutionat557.7nm 2ndow)and427.8nm 3rdow).Averagecalibratedntensitiesat427.8nm orth ecentralegionofth eimagesar eshowninth e4t hro w as afunctionofsecondsaftertheransmitterurnedon t5:13:00U T .right)The557.7nm magesor210shavebeencombinedusing to -mographicalgorithmoprovideacross-sectionofth eopti-calvolumeemissionat enhemagneticmeridianplane.TheHAARPmagneticieldin endcontoursofnominaltransmitterpowernercentelativeopeakower t23 0k m altitudehavebeensuperimposedon th etomographiccrosssection. inAlaskaocalime.Theransmitterwaspointed themagneticzenithaz=202el=76)andoperatedwithO-modepolarization tullpowerof~440M W E R Palter-natingbetween4m inatul lpoweran d4m inofftoallowrecoveryfromartificiallynducedeffects.Theransmitterfrequencyalternatedbetween3.16and2.85MHzeveryother"on"periodocompareeffectsawayfromandnear2fce .After05:05U T th eionosphericcriticalfrequencyfoFT droppedbelow3.16MHzandonly2.85M H zwasutilized.Thetransmitterbeamha daul lwidthathalfmaximumof18degreesalongth ema g net i cmeridianat 2.85M H z .Op ti ca lobservationswerecarriedou twitharemotewide-fieldi ma g erlocated-160k m N ofHAARP,an dwithmultiplewide-an dnarrow-fieldsystemsat th eHAARPsiteobserving557.7nm emissionsfromth eSstateofa to mi coxygencorrespondingto>4 eV electronenergyan d427.8nm Nlemissionsindicat-ingionizationproductionat > 18eV .Figure showsaseries ofopticalmagesviewedobliquelyfromtheremotesiteat 557.7nm(toprow)andlookingup th emagneticfieldro m HAARP(557.7an d 427.8nm inth e2n d and3r drows)duringan artificiallayercreationeventfrom 05:13-05:17U T .E m i s -sionintensitiesaveragedoverthecentralpartofthe427.8nm imagesar eshownnth efourthrow.

[6 ]arlynheperiod,heopticalemissions rediffusean doughlyproportionaloheransmitterbeamntensity.Inhesecondminute,hediffuseemissionshaveorganizedthemselvesnt oasharp-edged entraldiskwithndicationsof aringsurroundingit.Verybrightfield-alignedfilamentsbegintoappearinhecenterofth edisknddescendnal -titude.nhe3r dminute,th ei lam entsar everyntensean dth eemissionshavedescendedtonearly15 0kmaltitude.T he

centralegionmmediatelysurroundinghefilamentsalsobeginsogrowdark, rendwhicheachestsextrementh e4thminute,whereemissionsnth ecenterofthebeamhaveformed brightspotnear15 0kmaltitude,eavinganemptyingnear200 m .Theocalizedspotandingar eclearlyshownn crosssectionhroughatomographicreconstructioneneratedro m57 . 7nmmagesromhe 2sites(Figure ,right).Themagneticfieldlineandnominalcontoursoftransmitterbeampowernpercentelativeo230k m altitudeat th ebeamcenterhavebeensuperimposedon th ecrosssection.

[7 ]lthoughth eacceleratedelectronsexcitingtheopticalemissionscantravel~10kmorsoalongth emagneticieldfrom theirsource,theisolatedspotnear15 0k m inthebeamcenterindicatesthatastronginteractionwithth e2.85MHztransmitterbeam istakingplaceatthisaltitude.Notethatth enaturalplasmadensityatthataltitudeatthist i meofnightisbelow2. 5x04cm "r~200kHz,anorderofmagnitudetoooworinteraction.

[8]onogramsecordingheapparentangeofpointswhereheplasmafrequencymatchesthesweptonosondeprobefrequencywereacquiredat m inintervalsthroughoutth eexperim ent.lonogramsjustbeforean dduring atransmitter"on"cy cl ethatstartedat05:21UTar edisplayedinFigure2. The"offionogram(Figure2,eft)showsonlytheback-groundF-regiononosphere,whichpeaksnear250km.Densitieselow200mirtualeightreelowhe

1H zdetectionhresholdnhem o d eutilized.Aftersev-eralminutesofheating,howeverFigure2,middle),clearlayersofne wechoesar eseenat-200 m nd16 0kmvir-tualange,closelycorrespondingoheobservedopticalstructures.Althoughth eHAARPtransmitterinterfereswith ionosondereceptionnearfa,X-modeechoesgreen)eflectfromhesamedensityevels thigherfrequenciesabovethisg a p , nd aneelatedoO-modeechoesb yheex-pression/,=y+Jf+y)"~f+ y.Thisndicatesthatth eO-mode riticalrequencynheseayerseached2. 6 and.0MHz.rueheightprofilesnvertedromhesetracesusingheUniversityofMassachusettsLowellSAOExplorerprogramareshownnheightpanel,although

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05:20UT 05:26UT 0526UT1 2Frequency(MHz) 2Frequency (MHz) 12 3 4 Frequency (MHz)Figure2.left)onogramhowingnlyackground-regionechoeswhilethetransmitterwasoff.(middle)Afterseveralminutesofheating,henteractionregiondescendsto loweraltitudes,an dtw olowerlayersofechoesbecomeap -parentnear16 0an d20 0k m virtualheight,(right)Usingbothth eO-mode(redan dpink)an dX-mode(green)echoesallowsth e g ap resultingfrom interference at the transmitterfrequencyto b ebridgedan d densitytrueheightprofiles to b edeterminedfor th evariouslayers.

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L02106 P E D E R S E NET A L . :A R T I F I C I A LO N O S P H E R I CL A Y E R S I1211 It.

Figure3.ime-vs-altitudeplotof557.7nmopticalemissionsalongtheHAARPfieldin ewithcontoursshowinghe altitudeswheref=3.16MHz(blue),^,=2.85MHz(red),/,/,=2.85MHz(green),nd2/=2.85MHz(dashedwhite). Horizontalblipssuch stheon eee nnear20 0maltitude t5:05UTar estarspassingthroughheview.th eopsidesoftheprofiles reextrapolated yhesoft-ware nd renotobservablewithheonosondeechnique.T henescapableconclusionro mhecombinedoptical nd ionosondemeasurementssthatartificialonosphericayerswereproduced t200 nd150maltitude,ndha the densitynheoweroftheayersactuallyexceededbothfran dhebackgroundfF2.[ 9 ]hi sphenomenonwasreproducedonmultiplenights,b utnhefollowingsectionwepresent broaderviewofseveralepetitionsoftheexperimentonth enightofMarch17 .igure showssequentialaltitudeprofilesextractedfrom theobliqueopticalmagesalongtheprojectionofth eH A A R P magneticfieldline,overlaidwithcontoursofplasmafrequencyobtainedb yinversionof th e1-minonograms.

[ 1 0 ]nthisnight,artificialopticalemissionsat557 . 7nm wereirstdetectedabovehewilightduringa4-min"on"periodat04:49U T at2.85M H z ,buta gapinth eopticaldatapreventedfullanalysis of thisperiod.Nevertheless,th eiono-sonderecordedincreaseddensitiesonth ebottomsidean dnth evalleyegion sevidenced ydescendingcontoursof//,nhebottomsideand2.85MHznhevalleyegion.Transmissionsawayro m 7faat3.16M H zwereattemptedin3experimentcyclespriorto04:45U T ,butproducedno significanteffectsan dwerediscontinuedafterthe4thcycleat04:57U T .A t2.85MHzat05:05U T ,however,strongemissionsstartedoutas diffuseglow,hengatherednt o th espot-within-ringbullseyestructurewhilegraduallydes-cendinginaltitude.onogramsshowedasecondarybottom-sideayergraduallydescending,withhecontourof/,/,approaching200m .

[ 1 1 ]he next "on"periodstartingat 05:13UTcorrespondstotheimagespresentednFigure :nitialdevelopmentissimilartoth epreviousperiodfo rthefirst2mi n. ,withasec-ondarylayer againdescendingnear20 0k m a t-240m/s.A sth eemissionseached80 maltitude,however,he557 . 7nm intensitysuddenlyncreasedby factorof 6andheateofdescentroseto-260m/s,withth einteractionregiondes-

cendingto-150k m altitudeoverth enext90 secondsorso .H e r eth eionogramsindicatedth epresenceofplasmadensityup to3.1 H z, wellnexcessoff.Duringthe4 thminute, th eemissionsappeartoquenchhemselvessomewhatnd retreatinaltitudebeforeth een dofth etransmission.During acontinuous"on"periodbeginning t05:21UT,hesamepatternsealized,withheemissionsbrighteningatabout18 0 mndapidlydescendingo-150 m .nhiscaseth eemissionsappeartoquenchhemselvesseveralimes,initiatingth edescendingprocessoveragainfrom higheralti-tudes,althoughsomeof th eapparentverticalmotioninth eopticaldatatowardth een doftheperiodrepresentshorizontaldisplacement.Theonosondedataindicatethatartificiallyproducedplasmadensityinexcessofthe2.85M H ztransmit-terfrequencyw aspresentmostofth etimeopticalemissionswereseennear15 0k m altitude,as shownb y thered contoursbetween50and6 0maltitude.nceheackgroundionosphereadecayedelow\,htbout5:40T ,productionofbothopticalemissionsandartificialono-sphericlayersended.Justprior to theendoftheopticalemi s-sions,theauthorspresentatHAARPduringtheexperimentwentoutsideandwereabletoobservetheartificialopticalemissionswiththenakedeye,anndicatoroftheextraordi-naryintensityoftheemissionsproduced[cf .PedersenandGerken,2005] .

3. Discussion[12] enterpretheseobservations sollows:nearth e

doubleesonancewhere/VsimultaneouslymatchesbothfH an d2fce,electronsar eefficientlyaccelerated[e.g . ,Kosch etai,007] ndonizeth eneutralgas,addingtoth ea m b i -entplasmadensity.Thispushesthedensitycontoursdo wnoverafe w minutestoform adescendingartificialionosphericlayernear200k m ,sufficientlydensetosustaininteractionat fi,butnot/,j.Thispart of th eprocesswasseenineach of th e

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L02106 PEDERSENE TA L . :ARTIFICIALONOSPHERICLAYERS L02106 2.85MH zcasesonMarch1 7 aswellasearlier experiments,an dappearsinionogramsasasecondary bottomsidelayer.

[ 1 3 ]stheinteractionaltitudedescends,thepowerdensi-tyinthetransmitterbeam goesupasi,alreadyreaching132%at200k m comparedto23 0k m .Thisprocesscon-tinuesuntilabout180k m (163%power),whentheplasmafrequencynthedescendinglayerreaches ff.hiswouldcorrespondtoformationofthe brightfield-alignedstructuresintheopticalimages.Stimulationoftheplasmaresonanceno wb e c om e spossible,providinganadditionalpotentialmechanism fo raccelerating evenmoreelectrons.Propaga-tionoftransmitterpower toaltitudesabovetheartificiallayerisno wblockedinthe center ofthebeam,withan yH Fpowerno tabsorbedbeingreflectedbackdownan daddingtothe fieldstrengthbelowthereflectionpoint.W it hthisnewelec-tronsource,the localizedartificialplasmano w becomesc om -pletelyself-sustaining,andrapidlypropagatesdownwardasanionizationwavefronttowardthetransmitter,appearingasalayerofechoesintheionogramsnear150km .Fo rareal-isticdensitygradientof1 0 5cm "3over 0 k m ,theobserved propagationmpliesanionizationproductionratein excessoflossesby about2. 6 0 3cm"1.T hedescentoftheartificialionizationstallsat-150kmaltitude,nearthetran-sitionrom atomicoxygentoshort-livedmolecularions,whichdecayatratesexceeding eventhe enhancedionizationproductionate,nowdrivenby235% nominaltransmitterpower.

[ 1 4 ]hecompletequenchingoftheartificialonizationuponreaching -150km altitudeismoredifficulttoexplain,butasseeninthe427.8nm intensity(Figure ,bottom),the overallonizationrateaveragedoverthecentralegionofthebeam appearstogodownsteadilyasthecentralregiondescendsinaltitude,an dthematchingfrequencyfo r2fc ein-creasesto-2.95MH zat150k m altitude.Excitationnearthe2 f resonanceha sasignificantfrequency dependence [Mishinet ai,2005;Koschet ai,2007].Thislikelyreducestheefficiencyofelectronaccelerationevenathigherpowerlevelsandcontributestothe artificialplasmadensityproduc-tionbalancechangingoverfrom anetsurplusevidencedby downwardmotionofthelayertoanetloss,whichrapidlyleavesitunabletointeractwiththetransm itterbeam andmaintainitself.Thiscanbetestedinutureexperimentsby increasingthetransmitterfrequencyasthelayerdropstomaintain/rnear2fc e .Inanycase,asseenintheperiodafter5:21U T whenthetransmitterremainedoncontinuously, the interactionquenchesitself after afe wminutesat150km and startsoveragainnear/,/,nthebackgroundonosphere.When/,/,isnolongeravailabledu etodecayoftheback-ground,theprocessisnolongerabletorestartitself.

[ 1 5 ] enotethatwhilewehavediscussedevolutionoftheartificialionizationin termsofaltitude,thereisaparallelspatialevolutionoccurringsimultaneously,withthebrightfilamentsappearingawayrom thebeam centeran dgener-allymovinginwardbeforeextinguishingthemselves.Also,althoughwehavereferredtotheregionsofartificiallyen-hancedplasmadensityas"layers,"basedontheirappear-ancenheonosondedata,heopticalm a g e s learly showahighdegreeofspatialtructure,withtheareasof

greatestdensityenhancementlikelylocatedinsidethevery brightfield-alignedfilamentsafewk m indiameter.[ 1 6 ] hiletheexactmechanismsproducingtheartificialionizationlayersintheseexperimentsremaintobedeter-minedan dthepatchyan dunstablenatureoftheenhance-mentsposedifficultieso eovercomebeforepractical applicationsbecomefeasible,theseexperimentshavedem-

onstratedtheirstproductionofself-sustaining rtificial ionosphericplasmandepresent majorbreakthroughlaying the groundwork fo ravarietyofcontrollednear-spaceradiopplicationsbasedon newechnologyofartificialionospheric lasmaproduction.[n]cknowledgments .A A R PsaDepartmentofDefensepro-gram operatedjointlyby the U .S. A irForce and U . S .N avy .W o rk atA F R L wa ssupportedby the A irForceOff i ceofScientificResearch.W ethank the H A A R P rogramorransmittert ime,heoperatorsnd rewofth eH A A R Pfacilityand remoteopticalsitefo rtheirsupport,and L. M c N a m a r afo rhelpfuldiscussions.

ReferencesBcrnhardt,P .A .,L .M.Duncan,and C. A .T cplcy(1988).Artificialairglowexcited yhigh-powerH Fwaves.Science ,42(4881),022-1027,doi:10.1126/scicnce.242.4881.1022.Carlson.H .C,Jr.(1993),High-powerH Fmodification:Geophysics,spanofE M f fects ,ndenergy udget .Adv.pacees.,i(10),5-24 ,doi:10.1016/0273-1177(93)90046-E. Gurcvich,A .V. ,an dK .P.Zybin(2005),Runawaybreakdownandhe mysteriesoflightning.Phvs .odav ,8(5),7-43,doi:10.1063/1.1995746.Gustavsson,B T .B.Lcyser,M.Kosch,M.T.Rictveld,A .Stcen,B .U .E . Brandstrom,and T .A so(2006),Electron gyroharmonic effectsin ionizationand electronacceleration during high-frequencypum pingintheionosphere, Phvs.Rev.Lett. ,97 ,95002,doi:10.1103/PhysRcvLctt.97.195002.Kocrt, .(1991),Artificialonosphericmirrorcomposedof aplasmalayerwhichca nbetilted.Patent5,041,834,U . S .PatentandTrademarkOff . .W ashington,D.C. Kosch,M.J., T .Pedcrsen, .Mishin, .-l.O y a m a ,J.Hughes,A . enior,B. W atkins,andB.Bristow(2007),Coordinatedopticaland radarobser-vationsofionosphericpumpi ngfor afrequencypassthroughth esecondelectrongyro-harm onicatH A A R P ,J. eophvs .es.,12 , 06325,doi :IO. l029/2006JA O l2l46. M cN am ara ,L.F.(1991),Th eIonosphere: ommunicat ions.urveillance,and Direct ionFinding. ricgcr.Malabar,Fla.Mishin,E.V.,M.J.Kosch,T .R .Pedcrsen,andW .J.Burke(2005),H F-induccdairglowatmagnetic zenith:Thermaland parametricinstabilitiesnearelectrongyroharmonics,Geophv s .es .ett.,2 .L23I06.doi:IO.I029/2005GL023864.Pedcrsen, T .R ., and E .A .Gcrkcn (2005), Creationofvisibleartificialopticalemissionsin theauroraby high-powerradiowaves,Nature.433(7025). 498-500,doi:10.1038/naturc03243. Pedcrsen,T .,B.Gustavsson,E.Mishin,E.acKenzic.H .C.Carlson.M.Starks.and T .Mills(2009),Opticalringformationand ionizationpro-ductioninhigh-powerH Fheating experimentsatH A A R P ,Geophvs.Res.Lett. .36 .LI8107,doi:10.1029/2009GL040047.

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