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[en] A brief review of the recent studies on magnetic reconnection by the Alaskan group will be presented in this paper. The subjects covered include: the multiple X line reconnection (MXR) model for the flux transfer events, the criterion for the transition from the single X line to the multiple X line reconnection, a global simulation of the dayside magnetopause reconnection, a particle simulation of single X line reconnection and multiple X line reconnection, a patchy reconnection mechanism, and a mechanism for the generation of cusp-region hydromagnetic waves. (author). 35 refs.; 5 figs
[en] The possibility that MHD equations spontaneously develop coherent spatial structures flat or elongated is discussed. It is suggested that such stuctures are unstable with respect to reconnecting (tearing type) perturbations. The modifications produced by the occurrence of such phenomena in the usual theory of MHD turbulence are studied. (author). 16 refs.; 3 figs
[en] We present the relationships between the disappearances of two small pores, magnetic cancellations, and magnetic reconnection episodes in the NOAA AR 12778 on 2020 October 26 with high-resolution observations of the New Vacuum Solar Telescope and the Solar Dynamics Observatory. Two emerging positive polarities (P1 and P2) approach a negative polarity (N1) with velocities of 0.26 and 0.42 km s−1, respectively. Then, two small-scale magnetic reconnection episodes occur between a series of magnetic loops that are rooted in these polarities. The reconnection inflow velocities are around 4.0 km s−1 which is faster than the movements of P1 and P2. Compared with the first magnetic reconnection episode, more magnetic free energy is released in the second reconnection episode due to the greater magnetic strength of P2. Subsequently, magnetic cancellation occurs first between P1 and N1, and then between P2 and N1. At the same time, the pores S1 (N1) and S2 (P2) decay and disappear. The area decay rate of the small pore S2 is estimated to be 7.3 Mm2 hr−1, which is larger than previously reported cases. And the flux decay rate of S2 is 5.1 × 1019 Mx hr−1, similar to the results obtained in the larger sunspots. We conclude that the magnetic reconnection episodes may be caused by both the movement of the magnetic polarities and the plasma dynamics themselves. The decay and disappearance of the small pores and the polarities are driven by magnetic reconnection episodes and then flux submergence. We suggest that a magnetic reconnection episode is a more efficient mechanism for the disappearance of solar pores.
[en] In taillike configurations magnetic reconnection necessarily leads to the formation of plasmoids. This paper analyses the dynamical evolution of the developing plasmoids and the influence of magnetic reconnection on the propertie of plasmoids. By two dimensional resistive MHD calculations it is shown that plasmoid properties depend very much on the reconnection process especially when the reconnection rate is large. Thus the early plasmoid formation is dominated by magnetic reconnection. At later times the main plasmoid acceleration is due to pressure forces while the tension of open interplanetary fieldlines is negligible. The comparison of different resistivity and equilibrium modells reveals a definite influence of the microscopic dissipation and the initial state on magnetic reconnection and the resulting evolution of plasmoids. (author). 8 refs.; 6 figs
[en] We revisit the transition from Alfvén resonance to forced magnetic reconnection with a focus on the property of their singularities. As the driven frequency tends to zero, the logarithmic singularity of Alfvén resonance shifts to the power-law singularity of forced reconnection, due to merging of the two resonance layers. The transition criterion depends on either kinetic effects or dissipations that resolve the singularity. As an example, a small but finite resistivity η is introduced to investigate the transition process. The transition threshold is then obtained as the driven frequency reaches a level of ∼O((η/k)1/3)
[en] Controversy has been raised regarding the cause of hysteresis, or bistability, of solutions to the equations that govern the geometry of the reconnection region in Hall magnetohydrodynamic (MHD) systems. This brief communication presents a comparison of the frameworks within which this controversy has arisen and illustrates that the Hall MHD hysteresis originally discovered numerically by Cassak et al. [Phys. Rev. Lett. 95, 235002 (2005)] is a different phenomenon from that recently reported by Zocco et al. [Phys. Plasmas 16, 110703 (2009)] on the basis of analysis and simulations in electron MHD with finite electron inertia. We demonstrate that the analytic prediction of hysteresis in EMHD does not describe or explain the hysteresis originally reported in Hall MHD, which is shown to persist even in the absence of electron inertia.