Determination of the Coronal and Interplanetary Magnetic-Field Strength and Radial Profiles from the Large-Scale Photospheric Magnetic Fields

TL;DR

This paper introduces a new model for estimating the Sun's magnetic field at various distances and solar cycle phases, based on large-scale photospheric magnetic observations, and validates it against in-situ measurements.

Contribution

The paper presents a novel model linking photospheric magnetic fields to coronal and interplanetary magnetic fields, showing good agreement with direct measurements across different solar cycle phases.

Findings

Model predictions align well with in-situ measurements.

Magnetic field strength decreased from Solar Cycle 21 to 24.

Correlation between modeled and observed magnetic fields is high.

Abstract

A new model has been proposed for magnetic field determination at different distances from the Sun during different solar cycle phases. The model depends on the observed large-scale non-polar photospheric magnetic fields and that measured at polar regions from 55N to 90N and from 55S to 90S,which are the visible manifestations of cyclic changes in the toroidal and poloidal components of the global magnetic field of the Sun. The modeled magnetic field is determined as the superposition of the non-polar and the polar photospheric magnetic field cycle variations. The agreement between the model predictions and magnetic fields derived from direct, in-situ, measurements at different distances from the Sun, obtained by different methods, and at different solar activity phases is quite satisfactory. From a comparison of the magnetic fields as observed and as calculated from the model at 1 AU, it should be concluded that the model magnetic-field variations adequately explains the major features of the IMF Bx component cycle evolution at the Earth's orbit. The model CR-averaged magnetic fields correlate with CR-averaged IMF Bx component at the Earth's orbit with a coefficient of 0.688, and for seven CR-averaged data the correlation reaches 0.808. The model magnetic-field radial profiles were compared with that of the already existing models. In addition, the decrease in the non-polar and polar photospheric magnetic fields has been revealed. Both magnetic fields during solar cycle maxima and that during minima phases decreased from Cycle 21 to Cycle 24. It means that both the toroidal and poloidal components and therefore, the solar global magnetic field decreased from Cycle 21 to Cycle 24.