Study of Neptune dayside magnetosheath fluctuations during Voyager-2 flyby

Abstract

Turbulence in the outer planetary magnetospheres has been relatively less studied than in the Earth’s magnetosphere, especially for the ice giants which have been visited only by the Voyager-2 spacecraft so far. The aim of this work is to study the turbulence in Neptune’s dayside magnetosheath. Voyager-2 magnetometer 3-s averaged magnetic field data were analyzed with several data analysis techniques. It was found that most of the magnetosheath magnetic field is aligned in the BT direction. The BR-component spectrum showed the predominance of short-period (5minutes) oscillations, while the BT- and BN- components showed the occurrence of longer-period (20–50minutes) oscillations. The Fourier spectrum of the magnetic field showed a breakpoint near 0.00165Hz. The lower frequency portion showed index (absolute values) smaller than 1.0. The higher frequency portion showed a much steeper spectrum, with power law values varying from about 2.0 to 2.4. The statistical kurtosis parameters for BR and BN are higher than 3 in almost all scales, while the BT component (main field direction) has a more Gaussian or sub-Gaussian behavior, specially in scales higher than 20minutes. The kurtosis is very high at the low frequency spectral power of 40minutes for the BN-component, indicating asymmetric or non-Gaussian magnetic field distribution in the magnetosheath. The multifractal spectrum is well spread in the magnetosheath revealing a rich and dynamic activity in this region. Overall, the Neptune’s magnetosheath is found to have a strong turbulence activity that is comparable to that of other planetary magnetosheaths.