Dispersive Alfven Waves Radiated by a Reconnection Diffusion Region Dispersive Alfven Waves Radiated by the Reconnection Diffusion Region

Details Dispersive Alfven Waves Radiated by a Reconnection Diffusion Region Dispersive Alfven Waves Radiated by the Reconnection Diffusion Region Dispersive Alfven Waves Radiated by a Reconnection Diffusion Region Dispersive Alfven Waves Radiated by the Reconnection Diffusion Region

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm24b..07s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM24B-07

Physics

[2487] Ionosphere / Wave Propagation, [2704] Magnetospheric Physics / Auroral Phenomena, [2723] Magnetospheric Physics / Magnetic Reconnection, [2772] Magnetospheric Physics / Plasma Waves And Instabilities

Scientific paper

We have studied the waves radiated by the reconnection diffusion region, depending on the half width (w) of the diffusion region. For the half widths comparable to the electron skin depth (de) the radiation of whistler mode dominates. On the other hand, for wider current sheets approaching the ion skin depth, the dispersive Alfven waves become important. The dispersive Alfven waves (DAWs) consists of the inertial Alfven waves (IAWs) and kinetic Alfven waves (KAWS) depending on the plasma beta, the ratio of plasma thermal and the magnetic field energy densities. For low beta less than the ratio of the electron to ion mass, the electron inertia determines their dispersive behavior and such waves are called inertial Alfven waves (IAWs). For larger beta, the ion thermal behavior determines the dispersive properties of the kinetic Alfven waves (KAWs). It turns out that the radiation of IAWs are limited to extremely small angles from the magnetic fields in an electron-ion plasma, and such waves do not yield fast reconnection when their radiation opens the reconnection exhaust angle. But IAWs have large cone angles in pair (electron-positron) plasmas and can be effective in mediating fast reconnection. In electron-ion plasmas with sufficiently large beta, kinetic Alfven waves radiated from the diffusion region are effective in opening the exhaust. We will discuss the method of analytical calculations relating the group-velocity cone angles of the KAWs to (i)the reconnection exhaust cone angle, (ii) the inflow velocity into the diffusion region and hence (iii) the reconnection rate. The wave number and frequency spectral features of the KAWs facilitating the reconnection will be discussed. The group velocity essentially gives the wave radiation pattern of the diffusion region, which acts like an antenna. The radiation pattern limits the conical structure of the exhaust, even though the exhaust might include other linear and nonlinear features.The KAWs radiated from the reconnection diffusion region in the distant part of the magnetosphere may propgate down to the ionosphere, affecting the ionosphere-magnetosphere coupling.

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