Structure of the magnetopause at the ion gyroscale: mass and momentum transfer S. Savin (1), E. Amata (2), M. Andre (3), M. Dunlop (4), Y. Khotyaintsev (3), J. Buechner (5), J. Blecki (6), J.L. Rauch (7) (1) Russia IKI, Moscow, (2) IFSI, Roma, Italy, (3) IRFU, Uppsala, Sweden, (4) RAL, UK, (5) MPSP, Germany, (6) SRC, Warsaw, Poland, (7) LPCE, Orleans, France; Conclusions A study of the magnetopause (MP) fine structure from the Cluster and Interball data highlights the fundamental role of the finite-gyroradius effects, surface charges and accelerated plasma jets. In the MP boundary layers the accelerated jets provide non- local flow balance via the small-scale electric fields, supported at the MP substructures by parallel electron currents, and via the respective rotation of magnetic field. The complicated MP shape suggests its systematic velocity departure from the local normal towards the average one. The electric fields in the magnetosheath (MSH) frame accelerate the MSH plasma along MP downstream so that the plasma excess is removed close to the moving MP. The electric bursts provide effective collisions for ceasing of the MSH normal flows just in front of MP, the collisions result in the ion heating. Over outer cusp the MSH flows interact with a high-beta boundary layer through reflected waves, visible as sunward bursts in Poynting flux. The waves have 3- wave phase coupling with both enhanced MSH waves and local Alfvenic fluctuations. The most prominent local impulsive momentum loss via accelerated plasma jets qualitatively differs from bow shock or reconnection processes. Its input into the total MSH mass balance reaches 1/3. Kinetic energy of the jets can substantially exceed the magnetic energy at the high-latitude MP, which should result in the MP deformation and driven reconnection. A kind of wave-particle interaction is operating at transient small-scale current sheets with surface charges. At scales of ion gyroradius it infers Hall dynamics, so that electric fields of the surface charges serve as a mechanism for momentum coupling through the current sheets and lead to acceleration/ deceleration of ions with large (relative to the sheet width) gyroradius. Work was supported by INTAS grant Non-stationary plasma jets in MSH: from MHD towads gyroscale Cascade-like properties of the turbulence Accelera- tion of MSH plasma tailward by extra normal electric field and rotated magnetic field MP current sheet structure at gyroscale (~100 km, circled) Energy densities: Wkin- ion kinetic, Wb- magnetic, and ion flux nVi ; GDCF- gasdynamic model Averaged in space, the jets carry the momentum difference between measured and predicted by GDCF ion fluxes Ion distribution function and cuts of distributions of differential ion flux (Vpar- along magnetic field) at MP MP structure at gyroscale: pile-up of low-energy ions and acceleration by perpendicular electric field of the ions with gyroradius > MP width Cuts of distributions of omni-directional ions at 4-second resolution from Cluster 1 (left) and Cluster 3 (right) near MP Cuts of distributions of anti-sunward flowing ions inside & outside (black) MP; blue (red) lines – outer ions, accelerated by 300 (200) V potential at MP Left: partial ion densities and Ex electric field (green,Cluster 1). Middle (from top): magnetic field, clock angle & Ex electric field from 4 Clusters; light blue lines mark MP current sheets Top: Ion density (blue), partial density for energies > 300 eV (black) and that of > 1 keV (violet). Bottom: partial ion flux, dashed lines – z-component, full lines – y, lines with blue dashes – x; color–coding like at the top. From top: GSE electric field (E*10) in MSH frame (V= -45, -90, -150 km/s); magnetic field and ion velocity (dashed lines; shifted by -100 units); GSE Poynting flux (in mW/m 2 ), P2001_N_B (green) along average MVA normal, P2001_N_E - along electric field direction of maximum variance, shifted by -300 units; electric drift-velocity Model magnetic field lines and direction of different vectors for Cluster on February 13, Top: XZ GSE plane; Insert A: a cartoon for MP deformation. Bottom: YZ GSE plane; Insert B: Scheme for conservation of nV i (thick arrows) by ions with gyroradius > MP width. ‘Jumping’ from MSH (violet, over plane) with magnetic field (thin arrows) ~ parallel to nV i, into cusp (blue) the ions ~ conserve momentum and start to rotate; the magnetic field for high  is transported by the ions; i.e. in cusp frame an electric field is generated to fit the plasma cross-field drift Comparison of E x and Hall term inside MP: green line shows the Hall-term X-projection, the black one – E x ; in the middle of the TCS one can see that the that the spike in [j x B] x /  0 en ~ E x (a): WHISPER electric field spectrogr am with color- coded intensity (scale at the right side); (b): electric field E`x in the MSH frame Cluster orbit on Ferruary 13, 2001 Middle- and fine- scale MP structure: magnetic field rotation and cross-field acceleration (left); ion gyroscale current sheet (TCS) originated from Hall effect Correlation of positive E` x spikes (in the frame, moving with MSH bulk velocity, bottom) and plasma waves (20-60 kHz, top) conforms to instability of parallel electron currents, neutralizing charge separation due to inertial drift (cf. Genot, et al., Ann. Geophys., 22, , 2004) and interaction of ions of keV with the gyroscale electric structures. The latter infers for such ions effective collisions with loosing of eV per ‘collision’, i.e. their deceleration in the MP normal direction. These ions are accelerated downstream along MP by the inertial (polarization) drift in the quasi DC perpendicular electric field. The lower-energy ions are accelerated downstream by both DC & spiky electric fields (in the case of the detected rotation of magnetic field just outside MP) The charged Thin Current Sheets (TCS) serve to support selfconsistently the transverse Hall current, separating two plasmas at ion gyroscales (i.e. without any 'anomalous' resistivity or a 'diffusion region'). It does not necessarily imply 'classic' reconnection with parallel electric field, while reconnection should include the ion- scale layers. In other words, a charged TCS just because of its ion-gyroradius width becomes partially transparent for the larger-energy ions and respective magnetic flux without any change of the field topology (which could be superimposed or not). Transport of momentum across the layers is also provided by ions with larger gyroradius without any magnetic field annihilation. The momentum transfer (Stasiewicz, Space Sci. Rev., 65, 221, 1994) in terms of gyro- viscosity in the case of anti-parallel fields, predicts a forcing of the boundary Earthward without a macro- reconnection. Over the cusp and especially at the boundary of 'plasma balls‘, the gyro-stress rises due to |B| minimum and the acceleration of the flow around MP towards the tail; thus, the MP inward motion due to this effect should have a maximum at the sunward edge of the cusp for the IMF B z < 0 in our case. In spite of sampling of the MP outside the maximum gyro-viscosity effect, the data demonstrate clear momentum transfer across the MP, especially in its component, parallel to MP. In the structured plasma jets ion kinetic energy density (W kin ) and plasma flux (nV i ) can highly exceed that of solar wind (SW) and the flux in MSH, predicted by models. It is in surprising contrast to a MHD bow shock behavior. Closer to MP, nV i tends to approach to the SW value, the jets look to constitute a substantial sink of the flow, which plays a major role into the mass balance near MP. A jet with dynamic pressure over that of magnetic field (W b ) should deform MP and – via secondary reconnection of the deformed fields – provide an input into mass and momentum transfer across MP Momentum transfer by ion gyroscale effect POSTER C181 IAGA A