TY - JOUR IS - 24 N1 - Copyright 2005 by the American Geophysical Union TI - Ion sound wave packets at the quasiperpendicular shock front AV - public VL - 32 Y1 - 2005/12/28/ JF - Geophysical Research Letters A1 - Balikhin, M A1 - Walker, S A1 - Treumann, R A1 - Alleyne, H A1 - Krasnoselskikh, V A1 - Gedalin, M A1 - Andre, M A1 - Dunlop, M A1 - Fazakerley, A N2 - Electric field measurements from a single spacecraft have been used to study ion-sound turbulence observed within the Earth's bow shock. The observed frequency of the ion-sound waves can be both lower and higher than the local electron cyclotron frequency depending upon the direction of wave propagation in the plasma rest frame. The ion-sound waves observed upstream of the ramp can not be generated either by an instability related to the gradient in the electron temperature or an electric current within the ramp. A comparison of wave vectors for distinctive wave packets indicate that non-stationary, short scale current layers formed in the processes of the ramp evolution might be the source of the free energy for such waves. ID - discovery162799 UR - http://dx.doi.org/10.1029/2005GL024660 PB - American Geophysical Union SN - 0094-8276 ER -