Correlation length of large-scale solar wind velocity fluctuations measured tangent to the Earth's orbit: First results from Stereo

Abstract. Observations by Ulysses during its second out-of-ecliptic orbit have shown that near the solar activity maximum the solar wind appears as a highly variable flow at all heliolatitudes. In the present study Ulysses data from polar latitudes are compared to contemporary ACE data in the ecliptic plane to search for the presence of latitudinal effects in the large-scale structure of the solar wind velocity. The investigated period roughly covers the Sun's magnetic polarity reversal. The Ulysses-ACE comparison is performed through a multi-scale statistical analysis of the velocity fluctuations at scales from 1 to 64 days. The results indicate that, from a statistical point of view, the character of the wind velocity structure does not appear to change remarkably with latitude. It is likely that this result is characteristic of the particular phase of the solar magnetic cycle.

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Effect of large-scale inhomogeneity of solar wind velocity on distribution of directions of interplanetary magnetic field vector

Solnechno-Zemnaya Fizika ◽

10.12737/szf-53201905 ◽

2019 ◽

Vol 5 (3) ◽

pp. 50-63

Author(s):

Дмитрий Ерофеев ◽

Dmitry Erofeev

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Angular Distribution ◽

Solar Cycle ◽

Interplanetary Magnetic Field ◽

Wind Velocity ◽

High Speed ◽

Large Scale ◽

Solar Wind Velocity ◽

Statistical Characteristics

Using data with hourly resolution obtained in near-Earth heliosphere in 1965–2014, we have calculated statistical characteristics of the angles describing the direction of the interplanetary magnetic field (IMF): root-mean-square deviations of azimuthal and elevation angles, asymmetries of their distributions, and coefficient of correlation of the angles. It has been shown that the above characteristics varied in the course of solar cycle, and some of them changed their signs when solar polar magnetic field reversed. The results obtained from the experimental data analysis were compared with a model describing transport of large-scale disturbances of IMF lines by the inhomogeneous solar wind. The comparison has shown that the variations in the angular distribution of IMF in the course of solar cycle probably occur due to the appearance of the large-scale latitudinal gradient of solar wind velocity during solar minima. In addition, the angular distribution of IMF has been found to be substantially affected by the longitudinal velocity gradient in trailing parts of high-speed streams and short-term local-scale variations in velocity gradients.

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Effect of large-scale inhomogeneity of solar wind velocity on distribution of directions of interplanetary magnetic field vector

Solar-Terrestrial Physics ◽

10.12737/stp-53201905 ◽

2019 ◽

Vol 5 (3) ◽

pp. 42-53

Author(s):

Дмитрий Ерофеев ◽

Dmitry Erofeev

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Angular Distribution ◽

Solar Cycle ◽

Interplanetary Magnetic Field ◽

Wind Velocity ◽

High Speed ◽

Large Scale ◽

Solar Wind Velocity ◽

Statistical Characteristics

Using data with hourly resolution obtained in near-Earth heliosphere in 1965–2014, we have calculated statistical characteristics of the angles describing the direction of the interplanetary magnetic field (IMF): root-mean-square deviations of azimuthal and elevation angles, asymmetries of their distributions, and coefficient of correlation of the angles. It has been shown that the above characteristics varied in the course of solar cycle, and some of them changed their signs when solar polar magnetic field reversed. The results obtained from the experimental data analysis were compared with a model describing transport of large-scale disturbances of IMF lines by the inhomogeneous solar wind. The comparison has shown that the variations in the angular distribution of IMF in the course of solar cycle probably occur due to the appearance of the large-scale latitudinal gradient of solar wind velocity during solar minima. In addition, the angular distribution of IMF has been found to be substantially affected by the longitudinal velocity gradient in trailing parts of high-speed streams and short-term local-scale variations in velocity gradients.

Download Full-text