Shape and dynamics of the terrestrial magnetopause:

1. Shape and dynamics of the terrestrial magnetopause: CLUSTER and THEMIS multi-spacecraft observations Oleksiy Agapitov1,2, Evgeny Panov3,4 and Uli Auster5 agapit@univ.kiev.ua 1National Taras Shevchenko University of Kyiv, Kyiv, Ukraine; 2 Space Research Institute NASU and NSAU, Kyiv, Ukraine; 3Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, 4Space Research Institute of RAS, Moscow, Russia 5Institut für Geophysik und extraterrestrische Physik, Braunschweig, Germany. Abstract Terrestrial magnetopause is a current sheet between two plasmas, which are frozen in the solar and the Earth's magnetic fields. Changing solar wind parameters and the Earth' rotation bring the magnetopause in motion and make it subject to different fluid and plasma instabilities. This makes the magnetopause a highly dynamical object. First multi-spacecraft CLUSTER and THEMIS missions provide a unique opportunity to reconstruct the magnetopause shape and dynamics at all latitudes. In this poster we present the results of shape and motion analysis of several magnetopause crossings using both four spacecraft CLUSTER data and brand-new five spacecraft THEMIS data with the help of various single- and multi-spacecraft analyses. THEMIS Observation of a Wavy Magnetopause Analysis Techniques Modern multi-spacecraft observations by CLUSTER & THEMIS provide us advanced opportunities. Especially important would be to apply multi-point analyses for the investigation of the Earth‘s magnetopause in order to resolve the spatio-temporal variations.The results of these investigations can help to understand the dynamics and topology of the magnetopause.For our shape and motion analyses we used the minimum variance of magnetic field technique [1] in order to obtain the magnetopause normal, De Hoffman-Teller technique [2] for the identification of the velocity of the magnetopause flapping, as well as the Faraday residue technique [3], the Timing technique [4] and the Discontinuity Analyzer [5], when appropriate, in order to prove the found magnetopause normal and velocity. [1] Sonnerup, B. U. O. and Scheible, M. (1998). Minimum and maximum variance analysis. in Analysis Methods for Multi-Spacecraft Data, ISSI SR-001, edited by G. Paschmann and P. W. Daly, p. 1850, ESA Publ. Div., Noordwijk, Netherlands. [2] Khrabrov, V. A. and Sonnerup, B.U.Ö. (1998). DeHoffmann-Teller analysis. in Analysis Methods for Multi-Spacecraft Data, ISSI SR-001, edited by G. Paschmann and P. W. Daly, p. 1850, ESA Publ. Div., Noordwijk, Netherlands. [3] Khrabrov, V. A. and Sonnerup, B.U.Ö. (1998). Orientation and motion of current layers: Minimization of the Faraday residue. Geophys. Res. Lett., 25, p. 2373-2376. [4] Russell, C. T., Mellott, M. M., Smith, E. J., King, J. H., Jun. 1983. Multiple spacecraft observations of interplanetary shocks: four spacecraft determination of shock normals. J. Geophys. Res. 88, 4739-4748. [5] Dunlop, M.W., Balogh, A., Glassmeier, K.-H.(2002) Four-point CLUSTER application of magnetic field analysis tools: the discontinuity analyzer. J. Geophys. Res. 107, 24-1 A B C D E a), b), c) - Proton concentration, proton bulk velocity and magnetic field magnitude respectively WIND measurements d) – ACE magnetic field magnitude. The disturbance connected to MP surface observation is marked with gray. a), b), c), d) - magnetic field GSE components and magnitude from THEMIS s/c (‘a’ – black, ‘b’ – blue, ‘c’ – dark green, ‘d’ – light green and ‘e’ – red) Positions of the WIND and ACE in the solar wind 20/05/2007 and schematic propagation of the solar wind disturbance with time of observation Analysis of the MP crossings from 15:30 to 15:58. The global disturbance at 15:38 is observed. The front of positive MP perturbation moves tail ward with velocity about 160 km/sec (normal velocity is 130.2 km/sec from timing technique). The backward MP surface moving follows in 10 minutes and also propagate tailward with the same velocity (Vn = -125.0 km/sec from timing). At 15:49, 15:51, 15:53 the train of positive MP surface disturbances are observed. They can be associated with wave train on MP surface. Amplitudes are about hundreds km. Periodic structure in the solar wind proton bulk velocity can be the source of such perturbation. The schematic reconstruction of event in the down figures. Same format as previous figure CLUSTER Observation of a Planar Magnetopause BL, [nT] BM, [nT] THEMIS Observation of an Indented Magnetopause BN, [nT] A B C D E L, M and N components of the magnetic field measured by the four CLUSTER spacecraft during the magnetopause crossing on April 5, 2001 around 6:24 UT (left), relative position of the four spacecraft and magnetopause normal directions (middle), and deviation of the magnetopause normals from each other (right). The magnetopause normals are along the minimum variance directions of the magnetic field. They deviate from each other less then 10 degrees. This demonstrates that the magnetopause was nearly planar. The magnetopause velocities, estimated using the single-spacecraft deHoffmann-Teller and Minimum Faraday Residue analyses were between 56 and 71 km/s. They correspond well to the result of the multi-spacecraft Timing analysis – 53 km/s. This velocity knowledge provided us the magnetopause thickness estimate of about 630 km. From this, in turn, we have yelled the magnetopause current density estimate of the order of 100 nA/m2 Another sample of the magnetic field data collected by the five THEMIS spacecraft during the magnetopause crossing on May 20, 2007 around 11:17 UT (left) revealed that the magnetopause can be indented. The size of the indentation is about one Earth‘s radius. With the help of the Timing analysis and Minimum Faraday residue technique we gained the velocities of the walls of this indentation. This revealed that the whole structure did not change its size from spacecraft two spacecraft and it is moving along the magnetopause surface with the velocity about 160 km/s Possibly it connects with solar wind disturbance observed by WIND and ACE (right figure. Format of right figures is the same as of previous.). CLUSTER Observation of a Disturbed Magnetopause BL, [nT] Observations of MP surface flapping and indentation at 2007-05-30 BM, [nT] A B C D E BN, [nT] A similar analysis of the magnetic field measured by the four CLUSTER spacecraft during the magnetopause crossing on April 5, 2001 around 2:13 UT (left), revealed that while the magnetopause normal directions from the black, red and blue data were nearly coplanar, the magnetopause normal from the green data deviated about 15 degrees from the others (right). This demonstrates that in the position of the green spacecraft the magnetopause surface was locally disturbed (middle). The magnetopause velocity from the green data, estimated using the single-spacecraft deHoffmann-Teller and Minimum Faraday Residue analyses was about 150 km/s. This value significantly exceeds the magnetopause velocities obtained in the same way from the other spacecraft data (between 20 and 50 km/s). The non-planarity makes the usage of the Timing technique inappropriate and results in an huge uncertainty in the magnetopause thickness estimate (between 300 and 2000 km). X, Y and Z components of the magnetic field in the GSE frame of references, as well as the total magnetic field, measured by the five THEMIS spacecraft during the magnetopause crossing on May 30, 2007 from 23:00 to 23:30 UT (left). The magnetopause normals obtained with the help of the minimum variance of the magnetic field are near-parallel suggesting that the magnetopause was planar on the scales of the spacecraft separations. The magnetopause velocities, however, were opposite from crossing to crossing proving that it was flapping back and forth with the velocities between 15 and 40 km/s . The estimated magnetopause thickness was in the range between 300 and 800 km. The obtained, this way, magnetopause current density estimate is up to 100 nA/m2 CLUSTERObservation of a Bended Magnetopause Conclusions In this study we have applied conventional single-spacecraft and modern mutli-spacecraft analyses to several magnetopause crossings by both CLUSTER and THEMIS fleets. These analyses allowed us to disclose a variety of local magnetopause shapes and motion characteristics on the scales of the spacecraft separations. In particular, the high-latitude CLUSTER data analysis has revealed case-studies of 1) a plain, 2) a disturbed and 3) a bended magnetopause surface. For these crossings we have also derived that the magnetopause was moving at a velocity between 14 and 150 km/s, had the thickness between 300 and 2200 km and the current density between 5 and 150 nA/m2. The low-latitude THEMIS data analyses of the magnetopause crossings near the sub-Solar point have helped us to find 4) a magnetopause flapping back and forth with the amplitude about 1 Re, 5) an indented magnetopause with the curvature radius of about 1 Re, and 6) a wave propagating along the magnetopause surface with the propagation speed about 160 km/s and the amplitude about several thousands km. We speculate that these different shapes and motional behaviors of the magnetopause were caused by specific solar wind conditions. Outlook. Simultaneous observation of THEMIS and CLUSTER systems will provide the possibility to identify the direct source of MP surface disturbances in the solar wind. Acknowledgments: We thank the CSDSweb and NASA SSC services for providing the WIND and ACE data. We highly appreciate the CLUSTER Active Archive and THEMIS teams for the opportunity to use the spacecraft data. We also acknowledge the Committee on Space Research and the LOC of the "Solar-Terrestrial Interactions: Instrumentation and Techniques" workshop for doing the first step towards this work. BL, [nT] BM, [nT] BN, [nT] The magnetopause shape analysis using the magnetic field measured by the four CLUSTER spacecraft during the magnetopause crossing on April 5, 2001 around 12:26 UT (left) revealed that while the four magnetopause normals hugely deviated from each other (between 10 and 60 degrees), they, nevertheless, were all in the same plane (middle and right). This shows that the magnetopause was bended. This result is in agreement with the results of the Discontinuity Analyzer technique. The magnetopause velocities, estimated using the single-spacecraft deHoffmann-Teller and Minimum Faraday Residue analyses were between 50 and 75 km/s.