Nonaxisymmetric Component of Solar Activity: the Vector of the Longitudinal Asymmetry

Abstract

The vector representation of sunspots is used to study the nonaxisymmetric features of the solar activity distribution (sunspot data from Greenwich–USAF/NOAA, 1874–2016). Each sunspot is represented by a polar vector with modulus equal to the sunspot area and the phase equal to the sunspot heliolongitude. The vector sum of these individual vectors defines both the magnitude of the longitudinal asymmetry and the dominating longitude of the sunspot distribution. These characteristics are to a large extent free from the influence of a stochastic component and emphasize the nonaxisymmetric component of the solar activity. The longitudinal asymmetry follows the 11-year solar cycle with the amplitude three times lower than the sunspot area maximum. Longitudinal asymmetry is mostly determined by large sunspots: 82% of the longitudinal asymmetry is given by sunspots with area from 100 to 2000 MSH. Longitudinal asymmetries of the northern and southern hemispheres are connected only weakly (correlation coefficient $R = 0.29$ ). The longitudinal distribution displays a maximum at the longitude $\sim 180^{\circ }$ during ascent-maximum and at $\sim 0^{\circ }/360^{\circ }$ during descent-minimum. The active longitude changes with the reversals of polarity of the local (minimum of solar activity) and global magnetic fields (reversal of polar magnetic field).