Kinetic Alfvén waves in the magnetotail during substorms

Kinetic Alfven waves (KAWs) are low-frequency dispersive Alfven waves with a small perpendicular wavelength and long parallel wavelength to the ambient magnetic field direction. KAWs carry the parallel electric field with a large perpendicular wave vector angle to the ambient magnetic field. It is well known that KAWs play a significant role in the mass and energy transport in the magnetosphere during substorms. The substorm is a 1-3 h short time coupling between the solar wind, magnetosphere, and ionosphere. The mass and energy from the solar wind are transport into the magnetosphere, and then, the energy is dissipative in the magnetotail associated with substorm auroral in the high-latitude ionosphere. The unique feature of kinetic Alfven waves is that the accompanied parallel electric field which can accelerate electrons and ions along the ambient magnetic field. On the other hand, the KAWs' large perpendicular electric field can accelerate ions cross the magnetic field and provide large Poynting flux along the magnetic field. The small-scale KAWs can be excited by the surface wave mode conversion on the magnetospheric boundary layer with large density and magnetic field gradient, such as the magnetopause and plasma sheet boundary layer. The finite ion gyroradius effect and electron pressure effect in the high beta plasma, such as in the magnetotail plasma sheet and its boundary layer on KAWs, are both consider in this review paper. Under the different beta value space plasma, the theory dispersion relation and observations on KAWs in the magnetotail during substorms are presented.