Open AccessSolar origin of the 26‐day periodicity observed by Ulysses
Author(s) -
Bai T.,
Hoeksema J. T.,
Weber M.,
Acton L. W.
Publication year - 1997
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 - 10.1029/96ja03844
Subject(s) - interplanetary magnetic field , physics , longitude , astronomy , interplanetary spaceflight , southern hemisphere , solar wind , coronal hole , latitude , solar rotation , coronal mass ejection , astrophysics , solar physics , magnetic field , quantum mechanics
The Ulysses spacecraft discovered that the interplanetary magnetic sector structure went through a major restructuring in mid‐1992. The observed recurrence period changed from about 25.4 days to about 26.2 days. Another interesting discovery is that the solar wind speed, energetic particle fluxes, and interplanetary magnetic field all varied quasiperiodically with a similar 26.2‐day period during Ulysses' midlatitude passage south of the ecliptic in 1992–1993. In order to find the solar origins of these interplanetary phenomena, we compared Ulysses observations with relevant solar data. According to our study the global pattern of the open magnetic field lines originating in the photosphere changed drastically in June 1992, and this resulted in a major restructuring of the interplanetary sector structure. After that time the magnetic field pattern in the midlatitude and high‐latitude zones of the southern hemisphere was dominated by two large unipolar regions (covering the entire longitude interval) that rotated with a synodic period of about 28.5 days until mid‐1993. Because the heliographic longitude of the spacecraft remained the same while it approached the Sun, the 26.2‐day period seen by Ulysses is equivalent to the terrestrial synodic period of 28.5 days. By analyzing soft X ray data observed by the Yohkoh satellite we confirm the existence of a stable lobe protruding from the polar coronal hole. This protrusion persisted from 1992 until the end of the study in mid‐1995.