The Split Janus-faced Sun: Magnetic Rhythm and Duality in the Solar Cycle

Abstract

The solar cycle - most notably characterized by its sunspot activity patterns - serves as a cornerstone of heliospheric physics. This research uncovers a fundamental magnetic dichotomy in the Sun's full-disk field, identifying two functionally separate populations: the Strong-Field Group (SG) and Weak-Field Group (WG). The solar cycle exhibits a dual nature, much like Janus, with the SG and WG operating in opposing phases regardless of low or high latitudes. The SG-dominated cycle represents one facet of this duality and is visually prominent at the solar surface. It is well-established that this component synchronizes with the sunspot cycle at low latitudes but operates in anti-phase at high latitudes. In contrast, the WG-driven cycle acts as its hidden counterpart, functioning in opposition to the SG at both high and low latitudes -- a behavior that had not been identified until now. Influenced by these magnetic field groups, this dual nature permeates the entire solar atmosphere, revealing that the full-disk solar activity is globally modulated by the Janus cycle.

Figures (10)

• Figure 1: Top panel: the synoptic magnetogram of Carrington rotation (CR) 1888. Bottom panel: synoptic magnetograms from CRs 1625 to 2007, with the color scale saturated at 100 G. The vertical black lines indicate the minimum epochs of the solar cycles. In the mid- and low-latitude regions, the butterfly pattern is distinctly observed.
• Figure 2: Daily sunspot number (version 2) from 1975 Feb. 19 to 2003 Sept. 25.
• Figure 3: Top Panel: Pearson correlation coefficients between daily magnetic field strength values (from magnetograms) within distinct strength ranges and daily sunspot numbers, calculated separately for low-latitude (red circles) and high-latitude (blue circles) regions. The almost horizontal red and blue dashed lines denote the $95\%$ confidence levels for their respective correlations. Vertical black dashed lines divide the magnetic elements across the solar disk into four field-strength regimes (labeled I, II, III, and IV), corresponding to weak-to-strong magnetic strength ranges. Bottom Panel: Number of data points (red and blue circles) used to compute the correlations in the top panel for low- and high-latitude regions, respectively. Sample sizes may vary due to differences in the frequency of magnetic elements across field-strength regimes (stronger magnetic fields are typically less frequent on the solar surface).
• Figure 4: Schematic diagram of the division (vertical red lines) of the solar magnetic field into four components (Components I to IV). The horizontal red dashed line divides the solar surface into high and low latitudes. Shadow areas indicate approximate divisions. The blue plus sign indicates being in phase with the solar cycle, while the blue minus sign, being in phase with the solar cycle.
• Figure 5: The distribution histogram (upper panel) and the cumulative distribution percentage (lower panel) of magnetic element counts at low latitudes in synoptic magnetograms from Carrington rotations 1625 to 2007. The vertical dashed lines correspond to magnetic field strength values of 5.29 G, 18.37 G, and 80 G, which categorize the magnetic field into four distinct components.