Abstract The magnetic structure of the extended solar corona varies with the changing photospheric field during the solar cycle. A simple potential model of the corona using solar surface observations from 1976 to the present shows how the large-scale coronal field evolves over more than a solar activity cycle. These predictions match well with large stable structures inferred from measurements of coronal electron density and the interplanetary magnetic field (IMF), though dynamic changes are poorly modeled. The Sun's polar field was about 25% stronger at solar minimum in 1986 than in 1976; the heliospheric current sheet was also flatter. In Cycle 21 the coronal and photospheric large-scale long-lived field patterns rotated every 26.9 days in the northern hemisphere; the southern field rotated every 28 days. Similar periods have been present in the IMF and in the occurrence of solar flares during the last several solar cycles. Improved understanding will require more comprehensive physical models, more accurate and continuous photospheric field observations, and more complete coronal data at all heights and latitudes with which to compare and test the models. Important observations with improved accuracy and better spatial and temporal resolution will be provided by instruments on future space missions.
Large-scale solar and heliospheric magnetic fields
Advances in Space Research ; 11 , 1 ; 15-24
1991-01-01
10 pages
Article (Journal)
Electronic Resource
English
Large-scale solar and heliospheric magnetic fields
NTRS | 1991
|Solar and heliospheric space missions
Online Contents | 2015
|Solar and heliospheric space missions
Elsevier | 2014
|