Abstract
Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmosphere, causing rapid fluctuations in the power of radio signals used in telecommunication and GPS navigation, thus playing a crucial role in space weather impacts. Complex structuring and self-organization of equatorial plasma depletions involving bifurcation, connection, disconnection and reconnection are the signatures of nonlinear evolution of interchange instability and secondary instabilities, responsible for the generation of coherent structures and turbulence in the ionosphere. The aims of this paper are three-fold: (1) to report the first optical imaging of reconnection of equatorial plasma depletions in the South Atlantic Magnetic Anomaly, (2) to investigate the optical imaging of equatorial ionospheric intermittent turbulence, and (3) to compare nonlinear characteristics of optical imaging of equatorial plasma depletions for two different altitudes at same times. We show that the degree of spatiotemporal complexity of ionospheric intermittent turbulence can be quantified by nonlinear studies of optical images, confirming the duality of amplitude-phase synchronization in multiscale interactions. By decomposing the analyses into North-South and East-West directions we show that the degree of non-Gaussianity, intermittency and multifractality is stronger in the North-South direction, confirming the anisotropic nature of the interchange instability. In particular, by using simultaneous observation of multi-spectral all-sky emissions from two different heights we show that the degree of non-Gaussianity and intermittency in the bottomside F-region ionosphere is stronger than the peak F-region ionosphere. Our results are confirmed by two sets of observations on the nights of 28 September 2002 and 9 November 2002.
Highlights
Equatorial plasma depletions (EPDs) related to density irregularities often occur in the nighttime ionosphere at low- and mid-latitudes
This primary instability often leads to the formation of large-scale EPDs that can rise to high altitudes in the topside F-region
We apply the aforementioned tools to distinguish the nature of ionospheric turbulence, after the onset of EPD reconnection, using simultaneous multi-spectral optical imaging at two different heights by comparing for the sake of clarity in Fig. 8 the total power spectral density, and the probability density function for the spatial scale 60 km, kurtosis and phase coherent index of the N-S emission intensity of OI 630.0 nm (21:48:08 LT) and OI 777.4 nm (21:46:04 LT) emissions taken from Figs 6 and 7
Summary
Equatorial plasma depletions (EPDs) related to density irregularities often occur in the nighttime ionosphere at low- and mid-latitudes. We apply the aforementioned tools to distinguish the nature of ionospheric turbulence, after the onset of EPD reconnection, using simultaneous multi-spectral optical imaging at two different heights by comparing for the sake of clarity in Fig. 8 the total power spectral density, and the probability density function for the spatial scale 60 km, kurtosis and phase coherent index of the N-S emission intensity of OI 630.0 nm (21:48:08 LT) and OI 777.4 nm (21:46:04 LT) emissions taken from Figs 6 and 7 The value of the normalized variance computed by Eq (1) for the power spectrum of Fig. 10a for OI 630.0 nm (OI 777.4 nm) emission is 0.341 (0.180), very close to the value of 0.342 (0.181) obtained by computing the normalized variance of the emission intensity of the linearized images of Fig. 9b,d
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