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Flux Transfer Events at the Magnetopause and in the Ionosphere

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Flux Transfer Events at the Magnetopause and in the Ionosphere GEOPHYSICAL RESEARCH LETTERS, VOL. 17, NO. 12, PAGES 2241-2244, NOVEMBER 1990 FLUX TRANSFER EVENTS AT THE MAGNETOPAUSE AND IN TttE IONOSPHERE R. C. Elphic Los AlamosNational Laboratory M. Lockwood RutherfordAppleton Laboratory and Blackett Laboratory, Imperial College S. W. H. Cowley BlackettLaboratory, Imperial College P. E. Sandholt PhysicsDepartment, University of Oslo Abstract.On December1, 1986the ISEE 1 and2 spacecraft In aneffort to capturethe effects of FTEs bothat themagne- pairpassed through the dayside magnetopause at a location topauseand in theionosphere simultaneously, a joint EIS- whichmapped approximately to ionosphericfield-line foot- CAT/ISEE campaignwas initiatedin 1986. This campaign pointsnear the fields of viewof theEISCAT radar and pho- calledfor enhancedtracking of the ISEE 1 and2 spacecraft tometersand an all-sky cameraon Svalbard. The magne- near the magnetopausefor thoseperiods when the EISCAT tosheathmagnetic field was southwardand duskward at the 'POLAR' radar experimentfield of view was nearthe cusp. time,and flux transferevents (Fl•s) were observedat the Variousobservational and operationalconstraints and prob- ISEE location. At the same time, the EISCAT radar observed lemslimited the number of joint operationintervals to roughly ionosphericflow bursts of upto 1 km s-1. Thepeak of each five. Of these,FTEs wereclearly seen at themagnetopause in burstfollowed an FTE observationat ISEE by a few minutes. one interval, 0800- !000 UT on 1 December, 1986. Neither The bursts, each lasting ten or fifteen minutes, were groundactivity nor FTEs were seenon the otheroccasions. comprisedof farsta westwardthen a polewardflow. An all; Here we examineobservations of FTEs at the magnetopause skycamera at Ny •lesundobserved dayside auroral breakup andrelated ionospheric and dayside auroral phenonomena as formsduring or shortly after the flow bursts,moving seennear the cusp footpoint by theEISCAT radar and all-sky westwardthen poleward. While these flow burstsand camerasand photometers in Svalbard. associateddayside auroral forms have been previously reportedin associationwith southwardiMF orientations,this Observations is the first observation of a direct link to FTEs at the magnetopause.On this occasion,the lower limit on the For thiscampaign the EISCAT radarused the 'Polar' beam- inferredpotential associated with the FTEs is roughly10 kV. swingingtechnique for obtainingtwo-dimensional ionospheric Their inferred east-westextent in the ionosphereranges flow vectorsin theneighborhood of thedayside cusp north of between700 and 1000km, correspondingto a 3 - 5 RE local TromsO.The technique has been described in detailby Lock- timeextent at theaverage magnetopause. woodet al. [1989]. The basiccycle time is 5 minutes. ISEE 2 was inboundin the early post-noonsector in the Introduction northernhemisphere and crossed the magnetopauseat about 0925 UT at a positionof (8.43, 3.29, 5.08) RE GSM. The It iswidely believed that magnetic reconnection occurs at the left panelof Figure1 showsthe ISEE trajectoryprojected on daysidemagnetopause in both a quasi-steadyand transient theY-Z GSM planefor a 30-minuteperiod after ISEE crossed form,the latterproducing "flux transferevents" or FTEs. themagnetopause. Also shown are three traces of theTsyga- Steady-statereconnecfion leads to globalmagnetospheric and nenko[ 1987]model magnetic field lineswhich pass through ionosphericconvection, but the precise effect of transientre- thetrajectory, and the Y-Z projectionsof theobserved field connectionis lessclear. Nevertheless,impulsive or transient orientationwithin the magnetosphere on thispass. The fight reconnectionat the magnetopauseought to producesome panelshows the geographicplacement of the centerof the manifestationin the magnetosphereand ionosphere.Bol- EISCATradar 'POLAR' range gates 1through 5,the Ny Ale- shakovaand Troitskaya[1982], GlaBmeieret al. [!984], sundall-sky camera field of view,the meridian scanned by the Lanzerottiet al. [1987]and Goertz et al. [1985],all searched photometersand the ISEE footpointsfrom 0940 to 1000UT. forground signatures of FTEs with ambiguous results. The centerof the EISCAT field of view is at roughly75.0% 13.0ø geographic,some 270 krnwest of theISEE footpoint. Figure2 showsan overviewof the !SEE 2 magneticfield Copyright 1990 by the American Geophysical Union. dataand the inferred electric potentials across the radar field of Paper number 90GL02045 view associatedwith the flows for the period0800 to 1000 0094-8276/90/90GL-02045503.00 UT on 1 December 1986. The field data are running 12 s 2241 2242 Elphicet al.: SimultaneousGround/Space FTE Observations "• 40I ISEE2 1Dec.1986 0 ca-40 • 40.:- • 40 10 Fig. 1. (Left) View from the sunof the trajectoryof ISEE 2 in GSM coordinateswith observedmagnetospheric field vectors o N •'•'•'• - mojor557'7nm events just insidethe magnetopausebetween 0930 and 1000UT on 1 • 0 • , oefineObyo.s.c.• December,1986. Also shownpassing through the trajectory arethree model magnetic field linesfrom Tsyganenko[1987]. (Right) Geographiclocations of the EISCAT radar field of 0800 •30 0840 0900 0930 0940 1000 view, showingrange gates ! through5, andthe field of view UT of theNy Jdesundall-sky-camera installation (large circle). Fig. 2. Combinedtime seriesplot of the ISEE 2 magnetic Location of the persistentcusp/cleft arc is shownby the field observationsin boundary normal coordinatesand hatchedregion. The footpointsof ISEE 2 field linesbetween inferredelectric potential across the EISCAT field of viewfor 0930 (northern-mostpoint) and 1000 UT (southern-most the interval 0800 to 1000 UT on December 1, 1986. point) are shownby the thick traceto the eastof the EISCAT Horizontal bars at the bottom of the figure denotedayside fieldof view and the Ny •lesund magnetic meridian. auroralbreakup events as seen at Ny •!esund. averagesevery 4 s in boundarynormal coordinates. The L aratingthe two beamdirections there, but normalizedto a 200 andM componentsare in the nominal magnetopauseplane km separationfor comparisonwith (I)Ns. Thesevalues are whilethe N componentis normalto thatplane. The normalis essentiallylower limits on thepotentials since the plasma flow calculated assuming the magnetopauseis a tangential may haveextended over a muchbroader region than just the discontinuity.The resultingL andN unit vectorsare (-0.442, radarfield of view. Maxima in CI)Nsare 3 kV at 0832 UT, 10 0.019, 0.897) and (0.891, 0.131, 0.436) in GSM kV at 0850 UT, 10 kV at 0907 UT and 11 kV at 0924 UT. coordinates.The inferrednormal is about7 ø off the average Maxima in (I)Ewfollow thosein (I)Nsby roughly2 minutes, magnetopausenormal direction at the ISEE 2 location. butare smaller in magnitude.After thethird (I•s peakthe po- Minimumvariance analysis yields a similarnormal direction. tentialsnever drop back to theirearlier low levels.The begin- The databegin with ISEE 2 inboundin the magnetosheath. ningsof a fifth (I)Nsexcursion is seenbefore the dataend at After 0806 UT the magnetosheathfield was strongly 0934 UT. duskward(~ 40 nT) and southward.Using the canonical10- In Figure 3 we focuson the !SEE 2 BL and BN components nT peak-to-peakminimum BN amplitudeand 1-minutemini- togetherwith the northwardand eastwardflow components mum duration identification criteria, the first FTE occurs at from the first four rangegates from 0815 to 0945 UT. The 0845 UT (earlier BN activity around0820 UT doesnot meet highestflow speedsare seenat the poleward-mostlatitudes theacceptance criteria). Another• is observedat 0904 UT. (rangegate 4), but very similarflow behavioris also seenat Thereafter,a long seriesof BN excursionsare seen;those thelower-latitude range gates. There is a westwardswing in passingthe selection criteria occur at 0911, 0914, 0926, 0931, thelow speed(< 400 m s-1) flowsjust before0830 UT. A 0937 and 0950 UT. In the midst of this interval,at 0917 UT, strongwestward flow burstjust before 0840 UT is seenonly a BL spike is seen [Farrugia et al., 1988; Farrugia, 1989]. at gate4; thelower latitude positions reflect the enhanced flow The magnetopauseis crossedat 0925 UT, with a partial at about0844 UT. The flow persistsin a westwardsense crossinglater near 0936 UT. until0851 UT, thenswings northward. The nextwestward The bottompanel of Figure 2 showsthe north-southand flow burst begins just before 0900 UT and turns more east-westpotential drops calculated from the-VxB electric northwardby 0907 UT. This flow persistsuntil the next field integratedover the radar field of view. For (!)NSthe westward flow intensification at 0918 - 0922 UT. north-southelectric field is integratedover the 200 km spanof Horizontalbars at thebottom of Figure2 denoteauroral thefirst four rangegates. cI)]•w is derivedfrom the east-west breakupevents seen by theNy •lesund557.7 nm all-sky- electricfield at range gate four integrated over the 285 lcm sep- camerato the northand eastof the EISCAT range. These Elphicet ai.: SimultaneousGround/Space FTE Observations 2243 80 , , 630 photometerscons 557'7nm o.s.c.imoges N 60 ISEE N• E•1--- BL - Dec 1 1986 - 20 _ 0 (nT) 09:05- • -20 60 j• 09:11:21 40 BN 2o 09:10 0 - • -20 09:14:21 400 •'EISCAT / [ ' ..:. ' _ 09:15 VNorth 0 ,, ,,. Gate 1 (m/s)-,oo - ,,,-.,, .... Gate2 09:16:21 o "...,,•C..x ........ - .... Gate3 ß "x, "..\ . , Gate 4 09:20 . VEast -.oo ß 09:18:21 -1200 i i i 90 0 - 90 Zenith•.ngle (deg.) I ,, I 08:30 09:00 09:30 UT Fig.4. (Left)Meridian scans of the630 nm emissions over Ny ]tlesundbetween roughly 0903 and 0925 UT. Notethe Fig.3. Timeseries of theISEE BL andBN components and appearanceof
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