The Origin of the Dual-Slope Spectrum from Intermediate to Transitional Scale in Equatorial Spread F

F. S. Kuo；S. Y. Chou

Chinese Journal of Physics

39卷6期（2001 / 12 / 01）

577 - 593

英文

Horizontal spectra of equatorial bubble-irregularities generated by numerical simulations are systematically investigated. We found that a bubble with smooth structure grows in the bottom-side ionosphere due to Gravitational Rayleigh-Taylor (GRT) instabilities, and breaks into an irregular structure in the topside ionosphere to form a system of bubble-irregularities. A smooth waveform of the density fluctuations will be obtained from a horizontal cut through the smooth structure of the bubble, while an irregular waveform will be obtained if a horizontal cut through the irregular structure of the bubble is made. The power spectra of the smooth waveform are always steep with spectral index - 3 » - 6, and the spectra of the irregular waveform are shallow with spectral index - 1.5 » - 2. This characteristic is found to be universal, regardless of the scale size of the system of bubble-irregularities. Considering the relative detection-probability, we argue that a satellite passing through the topside ionosphere will most likely encounter irregular waveforms of the primary bubble-irregularities (larger scale) with shallow spectrum, and smooth waveforms of the secondary bubbles (small scale) with steeper spectrum. One example of satellite data of IPEI on board ROCSAT-1 is examined and explained, based on these simulation results.