On II December 1994 the Geotail spacecraft encountered an active reconnection diffusion region around the X line in the Earth's magnetotail. Three interesting features were observed. One is quadrdpole pattern of the out-of-plane By magnetic field component during the passage of magnetic islands and the crossing of the neutral sheet, The second is a direction reversal of the electron beams in the vicinity of the separatrix of the magnetic topology of reconnection. The third is a clear plasma flow reversal. By combining the observations of plasma, magnetic field, particles, and waves, this report may provide evidence of multiple X lines collisionless reconnection in the magnetotail at the microscopic level.

rhe role of waves in the dynamics of the Earth's magnetospbere has long been an interesting topic. Here we concentrate on one event when a bell-studied Coronal Mass Ejection struek the Earth on January 10. 1997. as GEOTAIL skimmed along the dayside magnetopetld observed 3-dimensional multiple x-line magnetic rconnec ion. Electrostatic Solitary Waves (ESW) and Amplitude Modulated Electrostatic Waves (AMEW) were detected associated with reconneetion, The ESW had amplitudes up to-2OmV/m. The ESW evolved from two-dimensional structures with smaller amplitudes to one-dimensional structures with larger amplitudes The observation ofESW and AMEW clearly show that the enhanced broadband electrostatic emissions 0ssocialed with reconnection are not random noises btg have coherent structures, The nonlinear coherent structures provide important disstpation in the eleatron diffusion region during magnetic reconnection

Magnetic reconnection has a crucial role in a variety of plasma environments 1-3 in providing a mechanism for the fast release of stored magnetic energy. During reconnection the plasma forms a 'magnetic nozzle', like the nozzle of a hose, and the rate is controlled how fast plasma can flow out of the nozzle. But the traditional picture of reconnection has been unable to explain satisfactorily the short timescales associated with the energy release, because the lfow is mediated by hevavy ions with a alow resultant velocity. Recent theoretical work 4-6 has suggested that the energy release is instead mediated by electrons in waves called 'whistlers', which move much faster for a given perturbation of the magnetic field because of their smaller mass. Moreover, th whistler vlocity and associated plasma velocity both increase as the 'nozzle' becomes marrower. A marrower nozzle therefore no longer reduces the total plasma flow-the outflow is independent of the size of the nozzle. Here we report observations demonstrating that reconnection in the magnetosphere is driven by whistlers, in good agreement with the theoretical predictions.