Reverse flow events and small‐scale effects in the cusp ionosphere

Abstract

We report in situ measurements of plasma irregularities associated with a reverse flow event (RFE) in the cusp F region ionosphere. The Investigation of Cusp Irregularities 3 (ICI‐3) sounding rocket, while flying through a RFE, encountered several regions with density irregularities down to meter scales. We address in detail the region with the most intense small‐scale fluctuations in both the density and in the AC electric field, which were observed on the equatorward edge of a flow shear, and coincided with a double‐humped jet of fast flow. Due to its long‐wavelength and low‐frequency character, the Kelvin‐Helmholtz instability (KHI) alone cannot be the source of the observed irregularities. Using ICI‐3 data as inputs, we perform a numerical stability analysis of the inhomogeneous energy‐density‐driven instability (IEDDI) and demonstrate that it can excite electrostatic ion cyclotron waves in a wide range of wave numbers and frequencies for the electric field configuration observed in that region, which can give rise to the observed small‐scale turbulence. The IEDDI can seed as a secondary process on steepened vortices created by a primary KHI. Such an interplay between macroprocesses and microprocesses could be an important mechanism for ion heating in relation to RFEs.

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

“…9°N, 11.9°E, geographic coordinates; 76.4°N, 110.2°E Corrected Geomagnetic Coordinates coordinates) at 07:21.31 UT on 3 December 2011. In this study, we use probes 2, 4, and 5 to derive the electron density (see Figure 1 in Spicher et al, 2016). The payload instruments included a low energy particle spectrometer (LEP), AC and DC electric field, and nine Langmuir probes.…”

“…The payload instruments included a low energy particle spectrometer (LEP), AC and DC electric field, and nine Langmuir probes. For more details about the payload, see Spicher et al (2016). In this study, we use probes 2, 4, and 5 to derive the electron density (see Figure 1 in Spicher et al, 2016).…”

“…Though there were no clear steep density gradients, the electron density was significantly fluctuated. This To present the electron density fluctuations at different scales, we show in Figure 5d a spectrogram of the electron density as a function of time (UT) and frequency (Hz) (Spicher et al, 2016). The density fluctuations are derived by calculating the RMS of the detrended Ne at certain window (1 km and 100 m and 10 m), where Ne is detrended by removing its moving average values.…”

“…The density fluctuations are derived by calculating the RMS of the detrended Ne at certain window (1 km and 100 m and 10 m), where Ne is detrended by removing its moving average values. The interval at 350-365 s shows enhanced PSD down to 10 3 Hz (corresponding to a 1-m spatial scale) and was studied in detail by Spicher et al (2016). Note that in Figure 5c, Ne is in unit of 10 11 m −3 , while ΔNe is in the unit of 10 10 m −3 .…”

“…The ICI-3 data was published in Spicher et al (2016). The payload services and the launch operations were funded through the Norwegian Space Centre.…”