Formation and evolution of coronal holes during the rising phase of cycle 23

TL;DR

This study investigates the formation and evolution of coronal holes during the rising phase of solar cycle 23, revealing their relationship with the global magnetic field's structure and polarity changes.

Contribution

It provides a detailed analysis of the correlation between coronal hole formation and the evolving global magnetic field structure during cycle 23.

Findings

Coronal holes trace changes in the global magnetic field structure.

The global magnetic field transitioned from zonal to sectorial dominance.

Coronal hole formation is linked to the polarity zones of the magnetic field.

Abstract

Regularities of formation of coronal holes (CH) at the rising phase of cycle 23 are investigated. The period from 01.01.1997 to 01.03.2000 (Carrington rotations (CRs) 1918-2059) is considered in detail. The evolution of the global magnetic field (GMF) of the Sun from the zonal to the sectorial structure is analyzed. It is shown that the zonal structure is quasi-stable. The sum of zonal harmonics dominated up to CR 1941, although a stable four-sector structure of GMF was formed in 1932. In CRs 1941-1950 the contribution of the zonal and sectorial components becomes approximately equal and from CR 1950 the sectorial structure of GMF was dominated. Sectorial structure of GMF undergoing sharp changes from four-sector, at the beginning of growth of the sectorial harmonics (CR 1926), to the two-sector structure, then back to four-sector and then again to the two-sector structure. CHs clearly trace all evolutionary changes in the GMF. The structure of the polarity of the GMF uniquely determines the zones of photospheric magnetic fields where the CHs are formed.