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Besides their causal connection with long and short-term magnetic variability, solar bipolar magnetic regions are our chief source of insight into the location, size, and properties of large-scale toroidal magnetic structures in the solar…

Solar and Stellar Astrophysics · Physics 2022-03-23 A. Munoz-Jaramillo , B. Navarrete , L. E. Campusano

There is no list of bipolar active regions (ARs) with reverse polarity (anti-Hale regions), although statistical investigations of such ARs (bearing the imprint of deep subphotospheric processes) are important for understanding solar-cycle…

Solar and Stellar Astrophysics · Physics 2020-12-09 A. Zhukova , A. Khlystova , V. Abramenko , D. Sokoloff

We present a systematic study of sunspot physical parameters using full disk magnetograms from MDI/SoHO and HMI/SDO. Our aim is to use uniform datasets and analysis procedures to characterize the sunspots, paying particular attention to the…

Solar and Stellar Astrophysics · Physics 2018-11-14 Jing Li

Solar active regions (ARs) determine solar polar fields and cause solar cycle variability within the framework of the Babcock-Leighton (BL) dynamo. The contribution of an AR to the polar field is measured by its dipole field, which results…

Solar and Stellar Astrophysics · Physics 2025-06-03 Ruihui Wang , Jie Jiang , Yukun Luo

We describe the defining observations of the solar cycle that provide constraints for the dynamo processes operating within the Sun. Specifically, we report on the following topics: historical sunspot numbers and revisions; active region…

Solar and Stellar Astrophysics · Physics 2023-09-29 Aimee Norton , Rachel Howe , Lisa Upton , Ilya Usoskin

The 11-year cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-97 solar minimum, most solar activity emerged in…

Astrophysics · Physics 2009-10-31 E. E. Benevolenskaya , J. T. Hoeksema , A. G. Kosovichev , P. H. Scherrer

The systematic variation of solar active region (AR) properties with their magnetic flux has been the subject of numerous studies but the proposed scaling laws still vary rather widely. A correct representation of these laws and the…

Solar and Stellar Astrophysics · Physics 2026-04-24 Guilherme A. L. Nogueira , Robertus Erdelyi , Ruihui Wang , Kristof Petrovay

The flux of energetic particles originating from the Sun fluctuates during the solar cycles. It depends on the number and properties of Active Regions (ARs) present in a single day and associated solar activities, such as solar flares and…

Through meticulous daily observation of the Sun's large-scale magnetic field the Wilcox Solar Observatory (WSO) has catalogued two magnetic (Hale) cycles of solar activity. Those two (~22-year long) Hale cycles have yielded four…

Solar and Stellar Astrophysics · Physics 2022-09-15 Scott W. McIntosh , Phillip H. Scherrer , Leif Svalgaard , Robert J. Leamon

The magnetic flux that is generated by dynamo inside the Sun emerges in the form of bipolar magnetic regions. We have analyzed the whole set of solar magnetograms obtained with the SOHO/MDI instrument in 1995-2011, and automatically…

Solar and Stellar Astrophysics · Physics 2015-06-03 J. O. Stenflo , A. G. Kosovichev

Data for 3046 solar active regions (ARs) observed since May 12, 1996 to December 27, 2021 were utilized to explore how the magnetic fluxes from ARs of different complexity follow the solar cycle. Magnetograms from the Michelson Doppler…

Solar and Stellar Astrophysics · Physics 2022-12-15 Valentina I. Abramenko , Regina A. Suleymanova , Anastasija V. Zhukova

Recent studies indicate that a small number of rogue solar active regions (ARs) may have a significant impact on the end-of-cycle polar field and the long-term behavior of solar activity. The impact of individual ARs can be qualified based…

Solar and Stellar Astrophysics · Physics 2024-05-13 Ruihui Wang , Jie Jiang , Yukun Luo

It is known that the tilt angles of active regions increase with their latitude (Joy's law). It has never been checked before, however, whether the average tilt angles change from one cycle to another. Flux transport models show the…

Solar and Stellar Astrophysics · Physics 2015-05-18 Maria Dasi-Espuig , Sami K. Solanki , Natasha A. Krivova , Robert H. Cameron , Tania Peñuela

Recent work has revealed an phenomenological picture of the how the $\sim$11-year sunspot cycle of Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal…

Solar and Stellar Astrophysics · Physics 2015-06-23 Scott W. McIntosh , Robert J. Leamon

Studying the hemispheric distribution of active regions (ARs) with different magnetic morphology may clarify the features of the dynamo process that is hidden under the photospheric level. The magnetic flux data for 3047 ARs from the CrAO…

Solar and Stellar Astrophysics · Physics 2024-07-10 A. Zhukova

Context: Solar active regions (ARs) are key manifestations of the Sun's magnetic activity, displaying diverse spatial and temporal characteristics. Their formation and evolution play a crucial role in understanding the solar dynamo and…

Solar and Stellar Astrophysics · Physics 2025-08-06 M. Švanda , J. Jurčák , M. Schmassmann

We believe the Babcock--Leighton process of poloidal field generation to be the main source of irregularity in the solar cycle. The random nature of this process may make the poloidal field in one hemisphere stronger than that in the other…

Astrophysics · Physics 2009-02-09 Ashish Goel , Arnab Rai Choudhuri

Hemispheric irregularities of solar magnetic activity is a well-observed phenomenon -- the origin of which has been studied through numerical simulations and data-analysis techniques. In this work we explore possible causes generating…

Solar and Stellar Astrophysics · Physics 2019-12-18 Prantika Bhowmik

It has recently been discovered that the time phases (time-varying delays) of the irregular periodicities observed in the Sunspot series, consisting of the approximate 27-day latitude-averaged plasma rotation and approximate 11-yr magnetic…

Solar and Stellar Astrophysics · Physics 2026-02-24 William A. Gardner , Antonio Napolitano

The historical reconstruction of the Sun's surface magnetic field remains a persistent challenge, limiting our ability to investigate the long-term global properties of the Sun, including the evolution of the large-scale magnetic field,…

Solar and Stellar Astrophysics · Physics 2025-11-25 Bibhuti Kumar Jha , Lisa A. Upton , Greg Kopp , Odele Coddington
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