Journal cover Journal topic
Annales Geophysicae An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 1.621 IF 1.621
  • IF 5-year value: 1.614 IF 5-year 1.614
  • CiteScore value: 1.61 CiteScore 1.61
  • SNIP value: 0.900 SNIP 0.900
  • SJR value: 0.910 SJR 0.910
  • IPP value: 1.58 IPP 1.58
  • h5-index value: 24 h5-index 24
  • Scimago H index value: 80 Scimago H index 80
Volume 22, issue 2
Ann. Geophys., 22, 689-696, 2004
https://doi.org/10.5194/angeo-22-689-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 689-696, 2004
https://doi.org/10.5194/angeo-22-689-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  01 Jan 2004

01 Jan 2004

Compressive fluctuations in high-latitude solar wind

B. Bavassano1, E. Pietropaolo2, and R. Bruno1 B. Bavassano et al.
  • 1Istituto di Fisica dello Spazio Interplanetario (C.N.R.), Roma, Italy
  • 2Dipartimento di Fisica, Università di L’Aquila, L’Aquila, Italy

Abstract. Solar wind compressive fluctuations at MHD scales have been extensively studied in the past using data from spacecraft on the ecliptic plane. In the present study, based on plasma and magnetic field measurements by Ulysses, a statistical analysis of the compressive fluctuations observed in the high-latitude solar wind is performed. Data are from the first out-of-ecliptic orbit of Ulysses, when the Sun's activity is low and the high-latitude heliosphere is characterized by the presence of a fast and relatively steady solar wind, the polar wind. Our analysis is based on the computation of hourly-scale correlation coefficients for several pairs of solar wind parameters such as velocity, density, temperature, magnetic field magnitude, and plasma pressures (thermal, magnetic, and total). The behaviour of the fluctuations in terms of their amplitude has been examined, too, and comparisons with the predictions of existing models have been performed. The results support the view that the compressive fluctuations in the polar solar wind are mainly a superposition of MHD compressive modes and of pressure-balanced structures. Nearly-incompressible effects do not seem to play a relevant role. In conclusion, our results about compressive fluctuations in the polar wind do not appear as a break with respect to previous low-latitude observations. However, our study clearly indicates that in a homogeneous environment, as the polar wind, the pressure-balanced fluctuations tend to play a major role.

Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma) – Space plasma physics (turbulence)

Publications Copernicus
Download
Citation
Share