Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves

Details Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves

2007-05-07

arxiv.org/abs/0705.0877v1

Astronomy and Astrophysics

Astrophysics

21 pages, 11 figures. J. Geophys. Res. 2007 (accepted)

Scientific paper

We calculate growth rates and corresponding gains for RX and LO mode radiation associated with the cyclotron maser instability for parameterized horseshoe electron velocity distributions. The velocity distribution function was modeled to closely fit the electron distribution functions observed in the auroral cavity. We systematically varied the model parameters as well as the propagation direction to study the dependence of growth rates on model parameters. The growth rate depends strongly on loss cone opening angle, which must be less than $90^{o}$ for significant CMI growth. The growth rate is sharply peaked for perpendicular radiation ($k_{\parallel} = 0$), with a full-width at half-maximum $1.7^{o}$, in good agreement with observed k-vector orientations and numerical simulations. The fractional bandwidth varied between 10$^{-4}$ and 10$^{-2}$, depending most strongly on propagation direction. This range encompasses nearly all observed fractional AKR burst bandwidths. We find excellent agreement between the computed RX mode emergent intensities and observed AKR intensities assuming convective growth length $L_c\approx$20-40 km and group speed 0.15$c$. The only computed LO mode growth rates compatible observed LO mode radiation levels occurred for number densities more than 100 times the average energetic electron densities measured in auroral cavities. This implies that LO mode radiation is not produced directly by the CMI mechanism but more likely results from mode conversion of RX mode radiation. We find that perturbation of the model velocity distribution by large ion solitary waves (ion holes) can enhance the growth rate by a factor of 2-4. This will result in a gain enhancement more than 40 dB depending on the convective growth length within the structure. Similar enhancements may be caused by EMIC waves.

Affiliated with

Also associated with

No associations

Rating

Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-598461