Direct evidence of double‐slope power spectra in the high‐latitude ionospheric plasma

Abstract

We report direct observations of the double‐slope power spectra for plasma irregularities in the F layer of the polar ionosphere. The investigation of cusp irregularities ICI‐2 sounding rocket, which was launched into the polar cusp ionosphere, intersected enhanced plasma density regions with decameter‐scale irregularities. Density measurements at unprecedented high resolution with multi‐Needle Langmuir Probes allowed for a detailed study of the plasma irregularities down to kinetic scales. Spectral analysis reveals double‐slope power spectra for regions of enhanced fluctuations associated mainly with density gradients, with the steepening of the spectra occurring close to the oxygen gyrofrequency. These findings are further supported with the first results from the ICI‐3 rocket, which flew through regions with strong precipitation and velocity shears. Previously, double‐slope spectra have been observed in the equatorial ionosphere. The present work gives a direct evidence that the double‐slope power spectra can be common in the high‐latitude ionosphere.

Simultaneous Rocket and Scintillation Observations of Plasma Irregularities Associated With a Reversed Flow Event in the Cusp Ionosphere

“…Since, the scintillations on the ground are due to the scattering of the GPS signals by the ionospheric irregularities and the interference when the radio waves propagate away from the irregular phase screen (Rino, 1979). Spicher et al (2014) reported that the electron density at high latitudes often shows double-slope power spectra. If we assume that the RFE was stationary in magnetic latitude during its lifetime, which was the situation for the current event, we can convert the data from a temporal scale to a spatial scale.…”

“…The pierce point of GPS PRN30 moved southward at a speed of~66 m/s. Figure 3 of Spicher et al (2014). By using 1 km/s (the speed of the ICI-3 rocket), this spatial scale corresponds to a frequency range of 3-30 Hz in the low frequency part of the ICI-3 electron density power spectra.…”

“…The frequency range of 0.2-2 Hz in the GPS data corresponds to 330-33 m in a spatial scale. However, Spicher et al (2014) presented the spectral slopes of the electron density data in 2-s intervals, while we use 4-s intervals. The black lines of Figures 8d-8e are linear fits to the low frequency part of the power spectra.…”

Plasma turbulence and coherent structures in the polar cap observed by the ICI‐2 sounding rocket

“…Such dual‐slope spectra indicate the presence of two different physical regimes, one where low‐frequency processes are dominating and another one where kinetic effects might be important. The double‐slope spectra in the high‐latitude F layer ionosphere had not been observed prior to Spicher et al [] presumably due to insufficient resolution in the previous experiments.…”

“…Using sounding rocket data, Spicher et al [] presented direct evidence of a steepening of the spectra at high frequencies in the polar regions, with the spectral knee close to the O + gyrofrequency. Such dual‐slope spectra indicate the presence of two different physical regimes, one where low‐frequency processes are dominating and another one where kinetic effects might be important.…”