IDENTIFICATION OF MIRROR WAVES BY THE PHASE DIFFERENCE BETWEEN PERTURBED MAGNETIC-FIELD AND PLASMAS

A new approach is proposed to identify mirror waves based on the 90 de grees phase difference between the magnetic field and plasma fluctuati ons. Magnetosheath observations, the linear MHD theory, and one-dimens ional hybrid simulations support that the 90 degrees phase difference is a special character for mirror waves. This phase difference is inde pendent of Doppler shift which means that our result remains the same in both the satellite (laboratory) and the plasma frames of reference. Therefore it is useful to distinguish mirror waves from slow waves wh ich also have an anticorrelation (i.e., 180 degrees out of phase) rela tionship between magnetic field strength and plasma density fluctuatio ns. The time evolution in the later stage shows that the dominant pert urbed components are the magnetic field fluctuation along the backgrou nd magnetic field B-0 and the velocity fluctuation perpendicular to B- 0 and the wave vector k. A higher coherence and a stable 90 degrees ph ase difference between these two dominant components are found as time increases. The coherence between this velocity component and the plas ma density is also high with a 90 degrees phase difference. A tendency is found that the longer wavelengths are progressively generated when mirror waves grow in simulation.