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Time variations of the mean magnetic flux in active regions of different magneto-morphological classes

Anastasiya Zhukova, Valentina Abramenko

TL;DR

The paper investigates how active regions of different magneto-morphological classes (A: regular, B: irregular, U: unipolar) vary in their mean unsigned magnetic flux over solar cycles, testing the involvement of convection-zone turbulence in the solar dynamo. Using 3048 ARs observed from 1996 May 12 to 2021 Dec 27, with magnetograms from MDI/SOHO and HMI/SDO, the authors compute the mean flux per solar rotation for each MMC class and apply a 13-rotation moving average to obtain time profiles. They find that the mean flux of B-class ARs dominates over A-class ARs during most of the active phase (by up to a factor of about $4\times$) and exhibits highly intermittent behavior, while A-class ARs remain roughly quasi-constant around $1.3\times 10^{22}$ Mx in SC23 and $0.8\times 10^{22}$ Mx in SC24. The similarity of A-class and U-class flux profiles supports a common origin in the regular global dynamo, whereas the intermittent B-class flux points to a substantial turbulent component in AR formation; together the findings provide observational evidence for the coexisting action of the mean-field dynamo and convection-zone turbulence during active-region emergence and cycle evolution.

Abstract

Using a recently suggested magneto-morphological classification (MMC, Abramenko, 2021, MNRAS Vol 507) of solar active regions (ARs), we explored 3048 ARs, observed from12 May 1996 to 27 December 2021. Magnetograms were acquired with the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) and with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). ARs were separated between three classes: class A - regular ARs (bipoles which follow the empirical rules compatible with the mean field dynamo theory); class B - irregular ARs (``wrong'' bipoles and multipolars); class U - unipolar sunspots. An aim of the present study is to explore time variations of a typical unsigned magnetic flux of ARs of different classes. The typical flux was acquired as the mean flux over all ARs of a given class observed during one solar rotation. The time profiles of the mean fluxes for different classes were compared. We found that, except for periods of deep solar minima, the mean flux of B-class ARs always dominate that of A-class ARs, and, what is the most important, the time profile of B-class ARs is highly intermittent versus the rather smooth and quazi-constant A-class profile. Intermittency implies a direct involvement of turbulence. We conclude that, through the entire active phase, the Sun is capable of producing regular moderate ARs at a quazi-constant rate along with the production of large and complex irregular ARs in the very intermittent manner. The result is the first observational evidence for the long-standing speculative assumption on the involvement of the convection zone turbulence into the regular global dynamo-process on a stage of the active regions formation.

Time variations of the mean magnetic flux in active regions of different magneto-morphological classes

TL;DR

The paper investigates how active regions of different magneto-morphological classes (A: regular, B: irregular, U: unipolar) vary in their mean unsigned magnetic flux over solar cycles, testing the involvement of convection-zone turbulence in the solar dynamo. Using 3048 ARs observed from 1996 May 12 to 2021 Dec 27, with magnetograms from MDI/SOHO and HMI/SDO, the authors compute the mean flux per solar rotation for each MMC class and apply a 13-rotation moving average to obtain time profiles. They find that the mean flux of B-class ARs dominates over A-class ARs during most of the active phase (by up to a factor of about ) and exhibits highly intermittent behavior, while A-class ARs remain roughly quasi-constant around Mx in SC23 and Mx in SC24. The similarity of A-class and U-class flux profiles supports a common origin in the regular global dynamo, whereas the intermittent B-class flux points to a substantial turbulent component in AR formation; together the findings provide observational evidence for the coexisting action of the mean-field dynamo and convection-zone turbulence during active-region emergence and cycle evolution.

Abstract

Using a recently suggested magneto-morphological classification (MMC, Abramenko, 2021, MNRAS Vol 507) of solar active regions (ARs), we explored 3048 ARs, observed from12 May 1996 to 27 December 2021. Magnetograms were acquired with the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) and with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). ARs were separated between three classes: class A - regular ARs (bipoles which follow the empirical rules compatible with the mean field dynamo theory); class B - irregular ARs (``wrong'' bipoles and multipolars); class U - unipolar sunspots. An aim of the present study is to explore time variations of a typical unsigned magnetic flux of ARs of different classes. The typical flux was acquired as the mean flux over all ARs of a given class observed during one solar rotation. The time profiles of the mean fluxes for different classes were compared. We found that, except for periods of deep solar minima, the mean flux of B-class ARs always dominate that of A-class ARs, and, what is the most important, the time profile of B-class ARs is highly intermittent versus the rather smooth and quazi-constant A-class profile. Intermittency implies a direct involvement of turbulence. We conclude that, through the entire active phase, the Sun is capable of producing regular moderate ARs at a quazi-constant rate along with the production of large and complex irregular ARs in the very intermittent manner. The result is the first observational evidence for the long-standing speculative assumption on the involvement of the convection zone turbulence into the regular global dynamo-process on a stage of the active regions formation.
Paper Structure (5 sections, 3 figures, 2 tables)

This paper contains 5 sections, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data and method
  3. Temporal variations of the mean flux in regular and irregular ARs
  4. Temporal variations of the mean flux in regular ARs and unipolar spots
  5. Concluding remarks

Figures (3)

  • Figure 1: A sketch of the magneto-morphological classification. Sketch c1 represents violation of Hale polarity law, c2 - violation of Joy's law, c3 - violation of a rule of the leading spot's dominance. Sketches d1 and d2 represent various schemes of a distortion and fragmentation of a single flux tube. Sketch e represents a simultaneous appearance of several intertwined flux tubes. Sunspot polarities are shown for even cycles.
  • Figure 2: Time variations of the mean magnetic flux for A-class (blue) and B-class (red) ARs. For convenience, the total area of sunspots (in MSH) by USAF NOAA SRS illustrates the cycle progress (top frame).
  • Figure 3: Time variations of the mean magnetic flux for A-class (blue) and U-class (unipolar sunspots, green) ARs. Notations are the same as in Figure \ref{['fig2']}.