Nonlinear Evolution of Thermal Self-Focusing Instability in Ionospheric Modifications at High Latitudes: Aspect Angle Dependence

Details Nonlinear Evolution of Thermal Self-Focusing Instability in Ionospheric Modifications at High Latitudes: Aspect Angle Dependence Nonlinear Evolution of Thermal Self-Focusing Instability in Ionospheric Modifications at High Latitudes: Aspect Angle Dependence

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsa31a0343g&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SA31A-0343

Physics

2400 Ionosphere (6929), 2403 Active Experiments, 2439 Ionospheric Irregularities, 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934)

Scientific paper

A simulation study with the 2D numerical model for the nonlinear evolution of the thermal self-focusing instability (SFI) at high latitudes to examine the dependence of the nonlinear effects on the direction of the heater beam is presented. The strongest heating effects, large electron temperature increases of about 300 %, have been observed in the field-aligned direction in the heating experiment using the EISCAT incoherent scatter radar [ Rietveld et al., 2003] at high latitudes near Tromsø. The simulation results demonstrate that due to a local heating of the F region anisotropic plasma, field-aligned density depletions with a strong enhancement of the electron temperature inside the depletions/striations are developed. The electron temperature increases more than 200 % when the incident beam is near the magnetic zenith, which has been observed in the electron heating by the EISCAT radar. We show that during the nonlinear evolution of the thermal SFI, the bunch-scale structures aligned along the magnetic field are formed, the reflection point of the ordinary wave is shifted upward, and the electron concentration is decreased due to the negative density perturbations inside of striations. The spectral characteristics of the simulated density fluctuation spectra are similar to those observed in the midlatitude experiments at the SURA HF facility [ Tereshchenko et al., 2004]. In the high latitude simulations as well as in the midlatitude simulations by Gondarenko et al. [2005], the spectral slopes become steeper when the heater beam recedes from the magnetic zenith. Rietveld et al. (2003) JGR, 108, 1141; Tereshchenko et al. (2004) Phys. Lett. A, 325, 381; Gondarenko et al. (2005) JGR - in press.

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