09:00 to 09:30 G Hornig ([Bochum])The topology of three-dimensional reconnection The process of magnetic reconnection in the absence of neutral points is analysed with respect to the topology of the magnetic field. It is shown that the domain of magnetic flux undergoing reconnection comprises regions of different reconnective behaviour. There are regions where the process generates only a certain type of slippage of plasma with respect to the field lines, as well as regions where the magnetic field is reconnected in a way similar to the classical two-dimensional reconnection. It is shown that this behaviour is consistent with the small but non-vanishing production of magnetic helicity in this case. An interpretation of the rate of reconnection for the different regions gives further insights into the complex process of three-dimensional reconnection. INI 1 09:30 to 10:00 JD Gibbon ([Imperial College])Singularities in 3D-Euler \& MHD INI 1 10:00 to 10:15 D Pontin ([St Andrews])Kinematic 3D reconnection at nulls INI 1 10:15 to 10:30 J McLaughlin ([St Andrews])MHD wave propagation in the neighbourhood of 2D null point The nature of fast magnetoacoustic and Alfvén waves is investigated in a zero beta plasma. This gives an indication of wave propagation in the low beta solar corona. It is found that for a two-dimensional null point, the fast wave is attracted to that point and the front of the wave slows down as it approaches the null point, causing the current density to accumulate there and rise rapidly. Ohmic dissipation will extract the energy in the wave at this point. This illustrates that null points play an important role in the rapid dissipation of fast magnetoacoustic waves and suggests the location where wave heating will occur in the corona. The Alfvén wave behaves in a different manner in that the wave energy is dissipated along the separatrices. For Alfvén waves that are decoupled from fast waves, the value of the plasma beta is unimportant. However, the phenomenon of dissipating the majority of the wave energy at a specific place is a feature of both wave types. Related Links http://www.edpsciences.org/papers/aa/full/2004/24/aa0900/aa0900.html - 'Astronomy & Astrophysics' e-journal INI 1 10:30 to 10:45 G Abel (British Antarctic Survey)Fractal reconnection at the Earth's magnetopause \& associated ionospheric convection Large scale properties of reconnection structures on the magnetopause can be explained successfully by simple models incorporating laminar magnetosheath flow with antiparallel reconnection. However, such models are inconsistent with the highly turbulent nature of the magnetosheath flow adjacent to the magnetopause. This presentation proposes a fractal reconnection model that resolves this contradiction by replacing the laminar magnetosheath flow with a turbulent flow which has realistic levels of fluctuation. The resultant fractal reconnection structures preserve the large scale behaviour of simpler models, consistent with ground based observations, but have small scale fluctuations consistent with those observed in situ by spacecraft. We also present observations of evidence for scale-free fluctuations in ionospheric convection associated with dayside reconnection. This scale free behaviour may well arise as a consequence of the fractal reconnection model proposed. INI 1 11:30 to 12:00 PL Pritchett ([UCLA])Overview of collisionless reconnection theory Particle-in-cell simulations in 3D are used to explore the physics of collisionless magnetic reconnection. The presence of a moderate guide field does not alter significantly the reconnection rate but does drastically change the detailed dynamics of the reconnection region. Away from the neutral line an electron beam feature (produced by a finite parallel electric field) produces turbulence in the ion plasma frequency range; the region near the X line, however, remains quiet with respect to wave turbulence. Futher issues affecting reconnection such as the roles of external driving and the normal magnetic field component will be considered. INI 1 12:00 to 12:30 M Hesse ([NASA, Goddard])The physics of the reconnection diffusion region We present an analysis based on particle-in-cell simulations and kinetic theory of the electron dissipation region in component merging. Specifically, we will derive scaling laws of the electron demagnetization scale based on electron nongyrotropy effects, which continue to play the dominant role even in the presence of a guide field. We will compare our results to those of other recent and on-going investigations, and derive a general expression of the reconnection electric field for guide-field magnetic reconnection. The role of electron heat flux will be discussed explicitly. INI 1 12:45 to 13:00 J Huba ([Washington])Hall magnetic reconnection in 2D \& 3D Numerical results of two and three dimensional magnetic reconnection in the Hall limit (L < c/wpi where c/wpi ion inertial length) are presented. Two dimensional Hall magnetohydrodynamic (MHD) simulations are used to determine the magnetic reconnection rate in the Hall limit. The simulations are run until a steady state is achieved for four initial current sheet thicknesses: L = 1,5,10, and 20 c/wpi It is found that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. Specifically, the Hall reconnection rate is weakly dependent on the initial current layer width and is ~ 0.1 V_A0B_0 where V_A0 and B_0 are the Alfven velocity and magnetic field strength in the upstream region. Moreover, this rate appears to be independent of the scale length on which the electron frozen-in' condition is broken (as long as it is < c/wpi). The 3D reconnection process is initiated with a magnetic field perturbation localized along the current channel in a reversed field plasma configuration. The perturbation induces a magnetic wave structure that propagates opposite to the current, and leads to the asymmetric thinning of the plasma layer, strong plasma flows in the direction of the current, and rapid magnetic reconnection. The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. The results are applied to reconnection processes in space. INI 1 14:30 to 15:00 F Pegoraro ([Pisa])The role of the Kelvin-Helmholtz instability in magnetic reconnection Magnetic topology plays an important role in the global dynamics of high temperature plasmas. Within the ideal MHD plasma description, two plasma elements that are initially connected by a magnetic field line remain connected at any subsequent time. This condition introduces a topological linking between plasma elements that is preserved during the ideal plasma evolution. Magnetic linking constraints the plasma dynamics by making configurations with lower magnetic energy, but different topological linking, inaccessible. Magnetic field line reconnection partially removes these constrains by allowing the field lines to decouple locally from the plasma motion and to reknit in a different net of connections. In collisionless magnetic field line reconnection the decoupling between the magnetic field and the plasma motion occurs because of the current limitation due to the finite electron inertia (in the fluid limit) or to thermal effects (in the kinetic plasma description). However, in the absence of dissipation, the plasma response both in the fluid and in the kinetic electron treatment admits generalized linking conditions that in a two-dimensional configuration are preserved during the process of magnetic reconnection in the form of Lagrangian invariants. Here we compare the analytical and numerical results obtained recently [1,2] in the study of the nonlinear development of magnetic reconnection in the fluid and in the drift-kinetic limits of the electron response and establish a clear link between these two regimes by showing that the (two) fluid Lagrangian invariants and the (infinite number of) drift-kinetic Lagrangian invariants evolve in time in an analogous fashion: in both cases the growth and saturation of the magnetic island is accompanied by their spatial mixing in the reconnection plane. In particular we show that in the cold electron fluid limit the pattern of current layers formed within the magnetic island in the nonlinear phase of the reconnection process is subject to the onset of a secondary instability of the Kelvin Helmholtz type which leads to a turbulent redistribution of the current layers and to the development of long lived fluid vortices inside the magnetic island. [1] E. Cafaro, et al., Phys. Rev. Lett, 80, 4430 (1998); D. Grasso, et al., Phys. Rev.Lett., 86, 5051 (2001); D. Del Sarto, et al., Phys. Rev. Lett., 91, 235001 (2003). [2] T. Liseikina, et al., Phys. Plasmas, in press (2004). INI 1 15:00 to 15:30 BK Shimavoggi ([Central Florida])Critical exponents and universality in fully developed turbulence Electron-inertia effects on the magnetic reconnection induced by perturbing the boundaries of a slab of plasma with a magnetic neutral surface inside are considered. Cases with the boundaries perturbed at rates slow or fast compared with the hydromagnetic evolution rate are considered separately. When the boundaries are perturbed at a rate slow compared with the hydromagnetic evolution rate and fast compared with the resistive evolution rate a current sheet forms at the magnetic neutral surface which then disappears via exponential damping and diffusion and reconnection takes place. On the other hand, when the boundaries are perturbed at a rate fast compared with the hydromagnetic evolution rate, there is no time for the current sheet formation and reconnection to take place [1]. References: [1] N. Al-Salti and B. K. Shivamoggi: Phys. Plasmas, vol.10, p. 4271, (2003). INI 1 16:00 to 16:15 C Watt ([Alberta])Parameter study of ion acoustic resistivity in collisionless plasmas In order for magnetic reconnection to proceed, there must be some mechanism which can violate the ideal MHD condition in the diffusion region and allow plasma to diffuse across the magnetic field. One of the candidates for breaking the ideal MHD condition is resistivity or anomalous transport due to wave-particle interactions between unstable waves and the ambient plasma. We propose that in the presence of strong currents, ion-acoustic waves will be driven unstable and can provide significant values of resistivity. We present results from a parameter study of the resistivity due to this instability, concentrating on similar ion and electron temperature ratios. This parameter regime is difficult to study analytically, and so we use self-consistent Vlasov simulations to study the plasma response to the ion-acoustic instability. Our results show that the resistivity is very strongly dependent on the current present to drive the waves unstable. INI 1 16:15 to 16:30 P Petkaki (British Antarctic Survey)Nonlinear evolution of the ion-acoustic instability INI 1 16:30 to 17:00 A Bhattacharjee ([New Hampshire])Impulsive reconnection dynamics INI 1