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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