Open AccessInterplanetary sources of magnetic storms: A statistical study
Author(s) -
Vennerstroem S.
Publication year - 2001
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001ja000004
Subject(s) - solar wind , ecliptic , coronal mass ejection , interplanetary magnetic field , physics , interplanetary medium , interplanetary spaceflight , storm , heliospheric current sheet , dipole model of the earth's magnetic field , geomagnetic storm , atmospheric sciences , magnetic field , geophysics , environmental science , meteorology , quantum mechanics
Magnetic storms are mainly caused by the occurrence of intense southward magnetic fields in the interplanetary medium. These fields can be formed directly either by ejection of magnetic structures from the Sun or by stream interaction processes during solar wind propagation. In the present study we examine 30 years of satellite measurement of the solar wind during magnetic storms, with the aim of estimating the relative importance of these two processes. We use the solar wind proton temperature relative to the temperature expected from the empirical relation to the solar wind speed T p / T exp , together with the speed gradient, and the interplanetary magnetic field azimuth in the ecliptic, in order to distinguish between the two processes statistically. We find that compression due to stream interaction is at least as important as the direct effect of ejection of intense fields, and probably more so. Only around 20–25% of major and large storm hours and 10–15% of medium and small storm hours are directly associated with a solar wind meeting the criteria T p / T exp < 0.5, a criteria which previously has been found to be a good indicator of ejected material. More than 50% of the storm hours are caused by a solar wind having an enhanced proton temperature relative to what is expected on the basis of the observed speed and having clear traces of gardenhose orientation of the magnetic field in the ecliptic plane.