Formation and Evolutionary Changes of Coronal Holes in the Growth Phase of Cycle 23

Abstract

The regularities in the formation of coronal holes in the growth phase of cycle 23 are studied. The period from January 1, 1997, to March 1, 2000 (Carrington rotations 1918–2059), is considered in detail. The evolution of the global magnetic field of the Sun from a zonal to a sectorial structure of the field distribution is analyzed. The zonal structure is shown to be quasi-stable. The sum of zonal harmonics dominates until Carrington rotation 1941, although a stable four-sector structure of the global magnetic field is formed in rotation 1932. In Carrington rotations 1941–1950, the contribution of the zonal and sectorial components becomes approximately equal, and, starting with Carrington rotation 1950, the sectorial structure of the global magnetic field is dominant. The sectorial structure undergoes sharp changes, from four-sector at the beginning of the growth of sector harmonics (Carrington rotation 1926) to two-sector, then back to four-sector, and then again to the two-sector structure. Coronal holes unambiguously trace all evolutionary changes in the global magnetic field. The structure of the polarity of the global magnetic field uniquely determines the zones of photospheric magnetic fields in which coronal holes form.