Statistical analysis of shocklets in the earth\u27s foreshock region observed by Geotail

In the foreshock region of the earth\u27s magnetosphere, the so-called \u27shocklets\u27, large amplitude ultra-low frequency magnetohydrodynamic (MHD) waves, are often observed. One of the eminent features of these waves is that they are composed of two distinct parts; relatively low frequency, almost linearly polarized wave, and high frequency, elliptically to circularly polarized discrete wave packets. We make statistical analysis of these shocklets, using magnetic field data obtained by Geotail spacecraft. We discuss distribution of such fundamental parameters as the wave propagation direction, compressibility, ellipticity of the discrete wave packets, and correlations among them. Based on the results, we examine whether these waves can be naturally produced via nonlinear evolution of finite amplitude dispersive Alfven waves