Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

摘要

The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies ω_r < Ω_e, propagating downward in the direction of the Earth's magnetic field, has been analysed in the auroral region at ω_e/Ω_e < 1 where ω_e is the plasma frequency and Ω_e is the gyrofrequency. The FEBs with low to high energy (E_b) but with low temperature (T_(||b)) have no effect on these waves. The FEBs with E_b < 1 keV and T_(||b) ( > 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T_(||b) which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T_(||b). The FEBs with less E_b (giving drift velocity) reduce growth rate more than the beams with larger E_b. The inhibition of growth rate increases with the increase in the ratio ω_e/Ω_e indicating that the beams are more effective at higher altitudes.