The solar magnetic field and the solar wind: Existence of preferred longitudes

Direct measurements of the solar wind speed and the radial component of the interplanetary magnetic field acquired over more than three solar cycles are used to search for signatures of a persistent dependence of solar wind properties on olar longitude. Two methods of analysis are used. One finds the rotation period that maximizes theamplitude of longitudinal variations of both interplanetary andnear-Earth data mapped to the Sun. The other is based on power spectra of near-Earth and near-Venus data. The two methods give the same r sult. Preferred-longitude effects are found for a synodic solar rotation period of27.03 +0.02 days. Such high precision s attained by using several hundred thousand hourly averages of the solar wind speed and magnetic field. The 27.03-day periodicity is dominant o ly over long periods of time; other periodicities ar often more prominent for shorter intervals such as a single solar cycle or less. The 27.03-day signal isstronger and more consistent in the magnetic f eld than in the solar wind speed and is stronger fo intervals of high and eclining solar activity han for intervals of low or rising activity. On average, solar magnetic field lines in the ecliptic plane point outward on one side of the Sun and inward on the other, reversing direction approximately very 11 years while maintaining thesame phase. The data re consistent with a model in which the solar magnetic dipole returns tothe same longitude after each reversal.