Generation of ULF waves in the polar cusp region by velocity shear-driven kinetic Alfvén modes |
| |
| Authors: | G S Lakhina |
| |
| Institution: | (1) Courant Institute of Mathematical Sciences, New York University, New York, N.Y., USA;(2) Present address: Indian Institute of Geomagnetism, Colaba, Bombay, India |
| |
| Abstract: | The velocity shear of ion beams observed in the polar cusp region can drive the kinetic Alfvén modes unstable. A hot ion beam can excite both a resonant kinetic Alfvén wave instability and a nonresonant coupled Alfvén ion-acoustic wave instability. For the case of a cold ion beam only the latter instability is excited. For the altitude range of 5–7R
e
, velocity shearS 0.04–1.0 is needed to excite the kinetic Alfvén wave instabilities. HereS=(dV
B
/
cB
dx), whereV
b
is the streaming velocity,and
cB
is the gyrofrequency of the bean ions. The excited modes have frequencies, in the satellite frame of reference, in the ULF frequency range. The noise generated by the velocity shear-driven Alfvén modes is electromagnetic in nature. These modes have a substantial component of parallel electric fields and, therefore, they can play an important role in the ionosphere-magnetosphere coupling process occurring in the polar cusp region. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
