Properties of electric turbulence in the polar cap ionosphere

Small-scale (scales of similar to 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 E >-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 (mu similar to s (alpha)). Here, mu is the variance of the detail coefficients of the signal discrete wavelet transform, s is the wavelet scale, and index alpha characterizes the LD slope. The probability density functions P(delta E, s) of the electric field fluctuations delta E observed on different scales s are non-Gaussian and have intensified wings. When the probability density functions are renormalized, that is constructed of delta E/s (gamma), where gamma 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 (y) and the correlation of the rms amplitudes of delta E fluctuations with IMF B (z) and the solar wind transfer function (B (y) (2) + B (z) (2))(1/2)sin(theta/2), where theta is the angle between the geomagnetic field and IMF reconnecting on the dayside magnetopause when IMF B (z) < 0, together with the absence of dependence on the IMF variability are arguments for the second mechanism.