Lesson 6: Proton aurora, diffuse aurora and some specific phenomena

Transcription

1 Lesson6:Protonaurora,diffuseaurora andsomespecificphenomena AGF 351 Op?calmethodsinauroralphysicsresearch UNIS, AnitaAikio UniversityofOulu Finland Photo:J.Jussila Protonaurora Distribu1onofprotonandelectronaurorabeforeanda8ersubstormonset (Fukunishi,1974).Protonauroraisveryweakcomparedtoelectronaurora! 1

2 Protonaurora H+precipita1on:charge exchangewith ionospherich=>spreadingofh+aurora intheionosphere H+precipita1onfromthe magnetospherebypitchanglediffusiondueto 1ghtfieldlinecurvature comparedtoion gyroradius wave par1cleinterac1ons ExcitedhydrogenatomsH*produce emissionshα(656.3nm)andhβ(486.1nm). Protonaurora Protonaurora(le8)withinthemainovalbeforesubstormonset(Donovan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

3 Protonaurora H+aurora(boXom)followstheconfigura1onalchangesofthemagnetotail(top) (Donovan,2011).Whenmagnetotailstretches(incl.angledecreases),fieldlines maptolowerla1tudesandh+aurorashi8sequatorward.!"#$%&#'("#)*"#+,#%'-.-%#).# -"/.)"#("&("#)*"#/%0&").)%12# 33()-")$*1&04#5-"(('-"4#")$6 Protonaurora H+aurorafromthecyanregionandelectronarcspolewardoftheionisotropic boundary(ib),whichmarkstheregionbetweendipolarandtaillikefieldlines (Donovan,2011). ionib electronarcs 3

4 Origin of diffuse aurora It has been believed that diffuse aurora is caused by pitch angle scaxering of CPS electrons ( kev ) into the loss cone, but the precise mechanism has been unclear. Two classes of magnetospheric plasma waves, electrosta1c electron cyclotron harmonic (ECH) waves and whistler mode chorus waves, could be responsible for wave par1cle interac1ons that lead to P A scaxering: ω kiivii = nωec / γ, LOSS OF PARTICLES TO THE ATMOSPHERE OR TO ENERGY DIFFUSION ASSOCIATED WITH TRANSFER OF ENERGY BETWEEN PARTICLES where ω is the wave frequency, Doppler shi8ed toa anetmul1ple AND WAVES 4HE SPATIAL DISTRIBUTION OF THREE PLASMA WAVES (n=0,±1,±2,...) of the rela1vis1c electron gyrofrequency Ω and kll and vll are CAPABLE OF INTERACTING WITHecRELATIVISTIC ELECTRONS DURING A parallel components of the wave vectorstorm andis par1cle SKETCHED INvelocity &IGURE (γ is the #HORUS EMISSIONS ARE INTENSE WHISTLER MODE WAVES WHICH rela1vis1c factor). ARE EXCITED IN THE LOW DENSITY REGION OUTSIDE THE PLASMAPAUSE BY THE INJECTION OF PLASMASHEET ELECTRONS INTO THE INNER MAG Thorne et al. reported in Nature in 2010 that scapering by NETOSPHERE DURING ENHANCED STORM TIME CONVECTION #HORUS HIGHLY NON LINEAR WAVES THAT OCCUR whistler mode chorus waves (f <EMISSIONS fec) is ARE the dominant cause of IN DISCRETE MICRO BURSTS AT FREQUENCIES BETWEEN n OF THE EQUATORIAL the most intense diffuse auroral precipita1on. ELECTRON GYROFREQUENCY ;4SURUTANI AND 3MITH 3ANTOLIK ET AL = 4HESE WAVES HAVE BEEN ASSOCIATED WITH INTENSE MICROBURST PRECIPITATION WITH EFFECTIVE LOSS TIMES ^ DAY FOR -E6 ELECTRONS ;,ORENTZEN ET AL / "RIEN ET AL = AND STOCHASTIC ENERGY DIFFUSION ;(ORNE AND 4HORNE 3UMMERS ET AL =! STATISTICAL SURVEY HAS BEEN MADE OF THE SPATIAL DISTRIBUTION OF CHORUS EMISSIONS SEEN ON #22%3 AND THEIR DEPENDENCE ON MAGNETIC ACTIVITY ;;-EREDITH ET AL B=.IGHTSIDE CHORUS IS STRONGLY CONFINED TO THE EQUATORIAL REGION <15 WHILE DAYSIDE EMISSIONS ARE STRON GER AT HIGH LATITUDES >20! SIGNIFICANT CORRELATION HAS BEEN FOUND BETWEEN THE STORM TIME ACCELERATION OF ELECTRONS TO RELATIVISTIC ENERGIES THROUGHOUT THE ENTIRE OUTER RADIATION BELTS AND ENHANCED CHORUS EMISSIONS ;-EREDITH ET AL C= ec OR MICRO BURST PRECIPITATION ;/ "RIEN ET AL = SUGGESTING THAT CHORUS PLAYS AN IMPORTANT ROLE IN THE ACCEL ERATION PROCESS Origin of diffuse aurora Whistler mode chorus waves (f < f ) recorded on the ground (le8) and expected distribu1on in space in a recovery phase of a storm (right). 0LASMASPHERIC HISS IS AN INCOHERE IN THE FREQUENCY BAND BETWEEN A FEW K(Z WHICH IS GENERALLY CONFINED W ;4HORNE ET AL = 2ESONANT ELECTR CAUSE PITCH ANGLE SCATTERING AND LOS FROM THE SLOT REGION ;,YONS AND 4HO!BEL AND 4HORNE = 4HE INTENSI AND CORRESPONDING RATE OF LOSS IS ST THE RECOVERY PHASE OF STORMS ;3MIT ING SUBSTORM ACTIVITY ;-EREDITH ET A HISS CAN THEREFORE CONTRIBUTE TO THE DAYS OF ENHANCED OUTER ZONE RELATI THE PLASMAPAUSE EXPANDS OUTWARDS STORM ;3PJELDVIK AND 4HORNE = %LECTROMAGNETIC ION CYCLOTRON % FREQUENCY 0C BAND WAVES n IN BANDS BELOW THE PROTON GYROFREQUE OF ENERGETIC IONS INTO THE RING CURRE = 7AVE AMPLIFICATION IS ENHAN DENSITY ALONG THE DUSK SIDE PLASMAPA *ORDANOVA ET AL = AND DRAINAGE PLUMES THAT ARE FORMED I DURING STORM CONDITIONS ;3PASOJEV WAVES CAN CAUSE RAPID ION PRECIPIT 3PASOJEVIC ET AL = BUT C TIC ELECTRONS ;4HORNE AND +ENNEL,ORENZEN ET AL 3UMM -EREDITH ET AL A= 2%3/.!.4 7!6% 0!24)#, 2ESONANT )NTERACTIONS 7ITH -AG!S PARTICLES UNDERGO THEIR ADIAB DRIFT MOTION IN THE RADIATION BELTS THE PLASMA WAVES DESCRIBED ABOVE THE ELECTRON MOTION CAN BE VIOLATED D PLASMA WAVES WHOSE FREQUENCY MULTIPLE N ± ± OF THE REL FREQUENCY AS EXPRESSED BELOW (courtesy of J. Manninen) &IGURE 3CHEMATIC MODEL FOR THE EXPECTED DISTRIBUTION OF PLASMA WAVES DURING THE RECOVERY PHASE OF2005) THE LARGE (ALLOWEEN (Thorne, STORM 4HE PLASMAPAUSE POSITION WAS OBTAINED FROM )-!'% OBSERVATIONS COURTESY * 'OLDSTEIN WHERE [ V C ] IS THE REL AND VLL ARE COMPONENTS OF THE WA AND PARTICLE VELOCITY ALONG THE DI MAGNETIC FIELD $URING WAVE PART CAN BE A NET EXCHANGE OF MOMENTU TO PARTICLE SCATTERING IN MOMENTU OF MOMENTUM SPACE SCATTERING O CAL BAND OF FIELD ALIGNED EQUATORI 4

5 Sta?s?cs:Notepolarcaparcs 56*..7(%8%&*(#79.7(2%:;<2%4=>=? Polarcaparcs PolarUVILyman Birge Hopfieldlong(LBHl, nm)filter:fromn2molecules,intensitydependson totalenergyfluxofprecipita1ngelectrons. Kullenetal.,JGR(2002):duringnorthwardIMF(Bz<0),strongIMF magnitude,andhighsolarwindspeed.dependenceonby. 5

6 Cuspaurora Causedbyprecipita1ngmagnetosheathelectronsandions Duetodaysidereconnec1on(FTEs),alsomixtureofmagnetosphericand magnetosheathplasmapopula1ons Rela1velylowenergiesofthesepar1clesmeansthattheaurorais dominatedby630.0and636.4nm(redline)emissionsofatomicoxygen Sincetheradia1velife1meofthe 1 Dstateis110s,theexcitedatomic oxygenmoveswiththethermosphericwind(e.g.for500m/sthe distancetraveledisabout55kmfromthesiteofexcita1on) nmemissionmeasuredby ASCatLYRat07:34UTand mappedtoanal1tudeof250km. F o vcorrespondsto80 o zenith angle(sandholtetal.,jgr2000). North southauroraandplasmabubbles Burstybulkflows(BBFs)inthemagnetotailaretransienthighspeed(v x 400km/s)flowswhichcontaindepleted(lowNe)flux tubes. Sergeevetal..(2000) 6

7 North south aurora and plasma bubbles Bursty bulk flows (BBFs) in the magnetotail are transient high speed (vx 400 km/s) flows which contain depleted (low Ne) flux tubes. Nakamura et al.. (2001) The main explana1on for BBFs is the plasma bubble model by Pon1us and Wolf (1990): The bubble moves earthward due to Epol (interchange instability), and is associated with F A currents. North south aurora and plasma bubbles North south aurora was suggested by Henderson et al. (1998) to be asociated with bursty bulk flows (BBFs) in the magnetotail. The bubble model is the most plausible model to explain BBFs and observa1ons confirm that the upward FAC of the bubble is associated with N S aurora KAURISTIE ET AL.: TO THE INNER PLASMA SHEET (also called streamers) (e.g. Kauris1e et BBF al.,intrusion 2003; Pitkänen et al., 2011). Auroral streamer SIA 9-3 jup (Kauris1e et al., 2003) Figure 1. Auroral streamers observed by the UV imager onboard the Polar satellite (top) and by the ASC at MUO (bottom). The pink circle in the first plot of the top panel show the field of view of the MUO ASC. The blue diamonds in the bottom panel plots show the scanning line of the KIL MSP. but while the first one had classical substorm characteristics the second one appeared as a convection bay without global scale energy loading-unloading behavior. The overall description of the global conditions during the convection bay is given in the study by Sergeev et al. [2001] which compares and contrasts this activation with the preceding substorm period. During UT Polar UVI took images of a nice set of auroral streamers. Simultaneously Geotail, which was surveying the corresponding conjugate region in the inner plasma sheet, recorded several Earthward directed plasma flow bursts (data not shown here). One of the streamers appeared as a brightening at the oval poleward boundary (MLAT!72!) around 1945 UT, intruded to the Scandinavian sector (in MLT) and reached the itation. b2i boundaries are typically observed at the equatorial slope of the Hb band [Donovan et al., 2003], like in the two cases of Figure 2. The third circle (with the question mark) shows the 30 kev isotropic boundary position as observed by the NOAA-14 spacecraft at the time of prime interest at 1945 UT. This observation was made 2 MLT hours to the east of KIL, around 00 MLT meridian which most probably is the main cause for the disagreement in the locations: maximum of Hb emission at KIL was about one degree equatorward of the isotropic boundary at the midnight meridian. [12] The right panel of Figure 2 shows the intensity versus latitude variations of the magnetic north component 7

8 Seasonaleffectsonenerge?celectronprecipita?on Newelletal.publishedin1996inNatureanar1cle: Suppressionofdiscreteauroraebysunlight Theyfoundthat: thebeamsofacceleratedelectronsthatcauseintense discreteauroraeoccurmainlyindarkness:thewinter hemisphereisfavouredoverthesummerhemisphere,and nightisfavouredoverday(byafactorof3) discreteaurorararelyoccurinthepresenceofdiffuseaurora Also,otherphenomenarelatedtoelectrosta1caccelera1on showthesameseasonalvaria1on: intenseelectricfieldsinauroralaccelera1onregion (Marklundetal.,1994) upflowingionbeams(collisetal.,1998) auroralkilometricradia1on(kumamotaandoya,1998) Seasonaleffectsonenerge?celectronprecipita?on Probabilityofobservingacceleratede (monoenerge1c)aurora (forenergyfluxes>5erg/cm 2 s 1 ) Darkness Sunlight Newelletal.(1996) 8

9 Seasonaleffectsonauroralpar?cleprecipita?on ConclusionbyNewelletal.(1996):Ionosphericconduc?vity playsarole,e.g.bytheionosphericfeedbackinstability. Anotherexplana1onsuggestedisthatforma1onofparallel electricfieldrequireslowbackgrounddensi?esathigh al?tudes(densitycavi1es),whichmightformpreferen1ally whenionosphericelectrondensi1esarelowintheen1refield line. 9