Excitation of banded whistler waves in the magnetosphere

Linear kinetic dispersion analysis and a two-dimensional electromagnetic particle-in-cell simulation are performed to demonstrate a possible excitation mechanism of banded whistler waves in the magnetosphere outside of the plasma-pause. Whistler waves in the lower and the upper bands can be generated simultaneously by the whistler anisotropy instability driven by two bi-Maxwellian electron components with T(perpendicular to)/T(parallel to) > 1 at different T(parallel to), independently, where parallel to and perpendicular to denote directions relative to the background geomagnetic field. Given omega(e)/Omega(e), the ratio of the electron plasma frequency to the electron cyclotron frequency, T(parallel to) of each electron component determines the properties of the excited waves. For the typical magnetospheric condition of 1 < omega(e)/Omega(e) < 5 in regions associated with strong chorus emissions, the present study suggests that upper-band waves can be excited by anisotropic electrons below similar to 1 keV, while lower-band waves are excited by anisotropic electrons above similar to 10 keV. The resultant lower-band waves are generally field-aligned and substantially electromagnetic. However, the excited upperband waves generally propagate obliquely to the background geomagnetic field with quasi-electrostatic fluctuating electric fields. Citation: Liu, K., S. P. Gary, and D. Winske (2011), Excitation of banded whistler waves in the magnetosphere, Geophys. Res. Lett., 38, L14108, doi:10.1029/2011GL048375.