Evidence of whistler-mediated reconnection in the near-Earth space and the characteristics of the associated wave activities

*X. H. Deng[1] ,Hiroshi Matsumoto [1],Hirotsugu Kojima [1]
Toshifumi Mukai [2]
Radio Science Center for Space and Atmosphere, Kyoto University[1]
Institute of Space and Astronautical Science[2]

Magnetic reconnection plays a crucial role in the dynamics of the magnetosphere plasmas by providing a mechanism for the fast release of stored magnetic energy. Traditional picture of reconnection has been unable to explain satisfactorily the short timescales. The qadratic dispersion property of whistlers is the key to understand the result that the reconnection rate is independent of the mechanism, which breaks the frozen-in flux condition. This theory needs to be confronted with observational evidence. Here we report the first in situ observational evidences both at the dayside magnetopause and in the magnetotail. The results show good agreement with the theoretical prediction.

Magnetic reconnection plays a crucial role in the dynamics of the magnetosphere, solar corona and laboratory plasmas by providing a mechanism for the fast release of stored magnetic energy. Traditional picture of reconnection has been unable to explain satisfactorily the short timescales associated with the energy release. Recently, there has been a significant breakthrough in our theoretical understanding of the physical processes of magnetic reconnection in collisionless plasma. The crucial conclusion of the Geospace Environmental Modeling Reconnection Challenge Project is that the Hall effect is the critical factor in collisionless magnetic re-connection. The quadratic dispersion property of whistlers is the key to understand the result that the reconnection rate is independent of the mechanism, which breaks the frozen-in flux condition. This theory needs to be confronted with observational evidence. Here we report the first in situ observational evidences both at the dayside magnetopause and in the magnetotail. The results show good agreement with the theoretical prediction. The structure of the reconnection layer and the characteristics of wave activities associated with re-connection have been also investigated. By surveying the data of GEOTAIL we have revealed a strong inherent correlation between reconnection and the great enhancement of wave activities. Our study clearly shows that waves and wave-particle interaction associated with magnetic reconnection are very important, they can server as an effective additional diagnostic tool or evidence for magnetic reconnection, more importantly it provides significant clue to details of reconnection process itself. More detailed mea-surements, especially of electron and ion flows in the reconnection region are urgently required and the problems, such as the nature of the turbulence, which instability has the major and crucial role in triggering reconnection and how the particles are accelerated need further exploration.