Properties of electric turbulence in the polar cap ionosphere

Geomagnetism and Aeronomy (Impact Factor: 0.49). 04/2010; 50(5):576-587. DOI: 10.1134/S001679321005004X


Small-scale (scales of ∼0.5–256 km) electric fields in the polar cap ionosphere are studied on the basis of measurements of
the Dynamics Explorer 2 (DE-2) low-altitude satellite with a polar orbit. Nineteen DE-2 passes through the high-latitude ionosphere
from the morning side to the evening side are considered when the IMF z component was southward. A rather extensive polar cap, which could be identified using the ɛ-t spectrograms of precipitating particles with auroral energies, was formed during the analyzed events. It is shown that the
logarithmic diagrams (LDs), constructed using the discrete wavelet transform of electric fields in the polar cap, are power
law (μ ∼ s
α). Here, μ is the variance of the detail coefficients of the signal discrete wavelet transform, s is the wavelet scale, and index α characterizes the LD slope. The probability density functions P(δE, s) of the electric field fluctuations δE observed on different scales s are non-Gaussian and have intensified wings. When the probability density functions are renormalized, that is constructed
of δE/s
γ, where γ is the scaling exponent, they lie near a single curve, which indicates that the studied fields are statistically
self-similar. In spite of the fact that the amplitude of electric fluctuations in the polar cap is much smaller than in the
auroral zone, the quantitative characteristics of field scaling in the two regions are similar. Two possible causes of the
observed turbulent structure of the electric field in the polar cap are considered: (1) the structure is transferred from
the solar wind, which is known to have turbulent properties, and (2) the structure is generated by convection velocity shears
in the region of open magnetic field lines. The detected dependence of the characteristic distribution of turbulent electric
fields over the polar cap region on IMF B

and the correlation of the rms amplitudes of δE fluctuations with IMF B

and the solar wind transfer function (B


2 + B


2)1/2sin(θ/2), where θ is the angle between the geomagnetic field and IMF reconnecting on the dayside magnetopause when IMF B

< 0, together with the absence of dependence on the IMF variability are arguments for the second mechanism.

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Available from: B. V. Kozelov, Oct 13, 2015
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    ABSTRACT: We analyze the dependence of the magnitude of the magnetic field, its three components, and the clock angle in the magnetosheath just in front of the magnetopause on the same values in the solar wind before a shock wave using the data of the THEMIS experiment. We take into account the time delay of the solar wind arrival at the subsolar point of the magnetopause. We obtain dependencies of the components of the magnetic field and the clock angle at the magnetopause on the corresponding quantities in the solar wind for different averaging intervals. We point to the events for which the direction of the magnetic field at the magnetopause is highly different from the direction of the magnetic field in the solar wind up to the sign change.
    Geomagnetism and Aeronomy 10/2012; 52(6). DOI:10.1134/S0016793212060084 · 0.49 Impact Factor
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    ABSTRACT: Scaling properties of variable electric fields in the topside ionosphere have been investigated on scales s from similar to 30 m to 2 km by FAST electric field observations with sample rate of 512 s(-1), in sixteen events of the broadband ELF turbulence. It is shown that down to scales of a few hundred meters, the power of turbulent electric fluctuations is a power law, similar to s (alpha). Scaling index alpha derived from the slope of logarithmic diagrams (LD) constructed by the discrete wavelet transform of data can be estimated as alpha = 2.2 +/- 0.3, which is close to alpha estimate earlier reported for scales 1-30 km by electric field observations of the Dynamics Explorer 2 satellite. The behavior of alpha index is analyzed near the scale of the order of electron inertial length lambda(e) = c/omega(0) (omega(0) being the electron plasma frequency). At altitudes considered (700-2500 km), lambda(e) makes 100-900 m. We demonstrate that at scales a parts per thousand currency sign lambda(e), a decrease of LD slope and deviation from the power law are typically observed. As pointed out in the discussion, this feature cannot be identified as a transition to the diffusion range, where dissipation of the turbulence occurs.
    Geomagnetism and Aeronomy 07/2012; 52(4-4):474-481. DOI:10.1134/S0016793212040044 · 0.49 Impact Factor

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