Magnetic bubbles and kinetic Alfvén waves in the high‐latitude magnetopause boundary

We present a detailed analysis of magnetic bubbles observed by the Polar satellite in the high‐latitude magnetopause boundary. The bubbles which represent holes or strong depressions (up to 98%) of the ambient magnetic field are filled with heated solar wind plasma elements and observed in the vicinity of strong magnetopause currents and possibly near the reconnection site. We analyze the wave modes in the frequency range 0‐30 Hz at the magnetopause (bubble) layer and conclude that the broadband waves in this frequency range represent most likely spatial turbulence of kinetic Alfvén waves (KAW), Doppler‐shifted to higher frequencies (in the satellite frame) by convective plasma flows. We present also results of a numerical simulation which indicate that the bubbles are produced by a tearing mode reconnection process and the KAW fluctuations are related to the Hall instability created by macroscopic pressure and magnetic field gradients. The observed spatial spectrum of KAW extends from several ion gyroradii (∼ 500 km) down to the electron inertial length (∼ 5 km).