题目：Imbalanced Alfvénic turbulence from MHD to ion kinetic scales in the solar wind

　　报告人：Y. Voitenko, Solar-Terrestrial Center of Excellence, BIRA-IASB, Brussels, Belgium

　　摘要：Because of spatially inhomogeneous sources, Alfvénic turbulence in space is usually imbalanced: amplitudes of waves propagating parallel and anti-parallel to the mean magnetic field are unequal. Collisions between counter-propagating Alfvén waves have been commonly accepted as a fundamental process governing the turbulence. I show that this is not true at ion kinetic scales where the turbulence is controlled by the collisions among co-propagating dispersive Alfvén waves (co-collisions) rather than among counter-propagating ones (counter-collisions). The co-collisions dominate beyond the spectral break scale that is significantly larger than the ion gyroradius. A new quasi-inertial range of turbulence arises between the spectral break and ion gyroradius, where the co-collisions generate steepest non-universal spectra. The spectral indexes vary around >-3 (>-4) in the strong (weak) turbulence, such that steeper spectra follow larger imbalances. Our theoretical predictions are compatible with steep variable spectra observed recently at ion kinetic scales in the solar wind.

　　报告时间：2016年8月17日（星期三）10：00-11：00

　　报告地点：紫台办公大楼317 会议室

欢迎大家积极参加！

　　                                                 紫金山天文台学术委员会