ON POLAR MAGNETIC FIELD REVERSAL AND SURFACE FLUX TRANSPORT DURING SOLAR CYCLE 24

Context. The choice of free parameters in surface flux transport (SFT) models describing the evolution of the large-scale poloidal magnetic field of the Sun is critical for the correct reproduction of the polar magnetic flux built up during a solar cycle, which is known to be a good predictor of the amplitude of the upcoming cycle. Aims. For an informed choice of parameters it is important to understand the effects of and interplay among the various parameters and to optimize the models for the polar magnetic field. Methods. Here we present the results of a large-scale systematic study of the parameter space in an SFT model where the source term representing the net effect of tilted flux emergence was chosen to represent a typical, average solar cycle as described by observations. Results. Comparing the results with observational constraints on the spatiotemporal variation of the polar magnetic field, as seen in magnetograms for the last four solar cycles, we mark allowed and excluded regions in the 3D parameter space defined by the flow amplitude u0, the magnetic diffusivity η and the decay time scale τ, for three different assumed meridional flow profiles. Conclusions. Without a significant decay term in the SFT equation (i.e., for τ > 10 yr) the global dipole moment reverses too late in the cycle for all flow profiles and parameters, providing independent supporting evidence for the need of a decay term, even in the case of identical cycles. An allowed domain is found to exist for τ values in the 5–10 yr range for all flow profiles considered. Generally higher values of η (500–800 km2 s−1) are preferred though some solutions with lower η are still allowed.

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SUN’S POLAR MAGNETIC FIELD REVERSALS IN SOLAR CYCLE 24

Odessa Astronomical Publications ◽

10.18524/1810-4215.2015.28.71123 ◽

2015 ◽

Vol 28 (2) ◽

pp. 272-273

Author(s):

M. I. Pishkalo ◽

U. M. Leiko

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Polar Magnetic Field ◽

Solar Cycle 24 ◽

Cycle 24

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Solar cycle 24: An unusual polar field reversal

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832981 ◽

2018 ◽

Vol 618 ◽

pp. A148 ◽

Cited By ~ 11

Author(s):

P. Janardhan ◽

K. Fujiki ◽

M. Ingale ◽

S. K. Bisoi ◽

D. Rout

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Field Strength ◽

Polar Field ◽

Line Of Sight ◽

Zero Field ◽

Field Reversal ◽

Reversal Process ◽

Solar Cycle 24 ◽

Cycle 24

Context. It is well known that the polarity of the Sun’s magnetic field reverses or flips around the maximum of each 11 year solar cycle. This is commonly known as polar field reversal and plays a key role in deciding the polar field strength at the end of a cycle, which is crucial for the prediction of the upcoming cycle. Aims. We aim to investigate solar polar fields during cycle 24, using measurements of solar magnetic fields in the latitude range 55°–90° and 78°–90°, to report a prolonged and unusual hemispheric asymmetry in the polar field reversal pattern in solar cycle 24. Methods. This study was carried out using medium resolution line-of-sight synoptic magnetograms from the magnetic database of the National Solar Observatory at Kitt Peak (NSO/KP), USA for the period between February 1975 and October 2017, covering solar cycles 21–24 and high-resolution line-of-sight synoptic magnetograms from the Michaelson Doppler Imager instrument onboard the Solar Heliospheric Observatory. Synoptic magnetograms using radial measurements from the Heliospheric Magnetic Imager instrument onboard the Solar Dynamics Observatory, covering solar cycle 23 and 24, were also used. Results. We show that the southern solar hemisphere unambiguously reversed polarity in mid-2013 while the reversal in the field in the northern solar hemisphere started as early as June 2012, was followed by a sustained period of near-zero field strength lasting until the end of 2014, after which the field began to show a clear rise from its near-zero value. While this study compliments a similar study carried out using microwave brightness measurements which claimed that the field reversal process in cycle 24 was completed by the end of 2015, our results show that the field reversal in cycle 24 was completed earlier that is, in late 2014. Signatures of this unusual field reversal pattern were also clearly identifiable in the solar wind, using our observations of interplanetary scintillation at 327 MHz which supported our magnetic field observations and confirmed that the field reversal process was completed at the end of 2014.

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Polar Magnetic Field Reversals of the Sun in Maunder Minimum

International Astronomical Union Colloquium ◽

10.1017/s0252921100064472 ◽

2000 ◽

Vol 179 ◽

pp. 193-196

Author(s):

V. I. Makarov ◽

A. G. Tlatov

Keyword(s):

Magnetic Field ◽

Maunder Minimum ◽

The Sun ◽

Annual Rings ◽

Field Reversal ◽

Polar Magnetic Field ◽

Pine Trees ◽

Using Data ◽

Magnetic Field Reversal

AbstractA possible scenario of polar magnetic field reversal of the Sun during the Maunder Minimum (1645–1715) is discussed using data of magnetic field reversals of the Sun for 1880–1991 and the14Ccontent variations in the bi-annual rings of the pine-trees in 1600–1730 yrs.

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Source-region characteristics of anemone active regions in the ascending phase of solar cycle 24

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038927 ◽

2020 ◽

Vol 642 ◽

pp. A233

Author(s):

R. Sharma ◽

C. Cid

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Minimum Distance ◽

Source Region ◽

Coronal Holes ◽

Active Regions ◽

Yearly Average ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Rise Phase

Context. Active regions in close proximity to coronal holes, also known as anemone regions, are the best candidates for studying the interaction between closed and open magnetic field topologies at the Sun. Statistical investigation of their source-region characteristics can provide vital clues regarding their possible association with energetic events, relevant from space weather perspectives. Aims. The main goal of our study is to understand the distinct properties of flaring and non-flaring anemone active regions and their host coronal holes, by examining spatial and magnetic field distributions during the rise phase of the solar cycle, in the years 2011–2014. Methods. Anemone regions were identified from the minimum-distance threshold, estimated using the data available in the online catalogs for on-disk active regions and coronal holes. Along with the source-region area and magnetic field characteristics, associated filament and flare cases were also located. Regions with and without flare events were further selected for a detailed statistical examination to understand the major properties of the energetic events, both eruptive and confined, at the anemone-type active regions. Results. Identified anemone regions showed weak asymmetry in their spatial distribution over the solar disk, with yearly average independent from mean sunspot number trend, during the rise phase of solar cycle 24. With the progression in solar cycle, the area and minimum-distance parameters indicated a decreasing trend in their magnitudes, while the magnetic field characteristics indicated an increase in their estimated magnitudes. More than half of the regions in our database had an association with a filament structure, and nearly a third were linked with a magnetic reconnection (flare) event. Anemone regions with and without flares had clear distinctions in their source-region characteristics evident from the distribution of their properties and density analysis. The key differences included larger area and magnetic field magnitudes for flaring anemone regions, along with smaller distances between the centers of the active region and its host coronal hole.

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Hemispheric injection of magnetic helicity by surface flux transport

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936475 ◽

2019 ◽

Vol 631 ◽

pp. A138 ◽

Cited By ~ 3

Author(s):

G. Hawkes ◽

A. R. Yeates

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Solar Rotation ◽

Surface Flux ◽

Magnetic Helicity ◽

Solar Cycles ◽

Flux Transport ◽

Transport Models ◽

Radial Magnetic Field ◽

Helicity Injection

Aims. We estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700–2009). Methods. We determine the radial magnetic field evolution using two separate surface flux transport models: one driven by magnetogram inputs and another by statistical active region insertion guided by the sunspot number record. The injection of relative magnetic helicity is then computed from this radial magnetic field together with the known electric field in the flux transport models. Results. Neglecting flux emergence, solar rotation is the dominant contributor to the helicity injection. At high latitudes, the injection is always negative/positive in the northern/southern hemisphere, while at low latitudes the injection tends to have the opposite sign when integrated over the full solar cycle. The overall helicity injection in a given solar cycle depends on the balance between these two contributions. This net injected helicity correlates well with the end-of-cycle axial dipole moment.

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On the Dynamics of the Largest Active Region of the Solar Cycle 24

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317008924 ◽

2017 ◽

Vol 13 (S335) ◽

pp. 32-35

Author(s):

Ranadeep Sarkar ◽

Nandita Srivastava ◽

Sajal Kumar Dhara

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Active Region ◽

Comparative Study ◽

Lorentz Force ◽

Sunspot Group ◽

Solar Dynamics Observatory ◽

Solar Cycle 24 ◽

Solar Dynamics ◽

Cycle 24

AbstractWe have studied the dynamics of the solar active region (AR) NOAA 12192 using full-disc continuum images and the vector magnetograms observed by the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO). AR 12192 is the largest region of the solar cycle 24. It underwent a noticeable growth and produced 6 X-class, 22 M-class and 53 C-class flares during its disc passage. But the most peculiar fact of this AR is that it was associated with only one CME in spite of producing several X-class flares. In this work, we present the area evolution of this giant sunspot group during the first three rotations when it appeared as AR 12172, AR 12192 and AR 12209, respectively. We have also attempted to make a comparative study of the flare-related photospheric magnetic field and Lorentz force changes for both the eruptive and non-eruptive flares produced by AR 12192.

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Study of Geomagnetic Storms, Interplanetary Magnetic Field and Solar Wind

Journal of Mountain Research ◽

10.51220/jmr.v19i1.6 ◽

2019 ◽

Vol 14 (1) ◽

Author(s):

Chandrasekhar Bhoj ◽

Lalan Prasad

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Cycle ◽

Interplanetary Magnetic Field ◽

Correlation Coefficient ◽

Geomagnetic Storms ◽

Solar Cycle 24 ◽

Time Periods ◽

Cycle 24 ◽

The Imf

The aim of this paper is to investigate the association of the geomagnetic storms with the IMF for solar cycle 24. Result of the present analysis shows that IMF is geoeffective parameter but its impact varies in accordance with different time periods. The correlation coefficient between Dst and IMF found to be -0.6 for solar cycle 24.

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Study of Geomagnetic Storms, Interplanetary Magnetic Field and Solar Wind

Journal of Mountain Research ◽

10.51220/jmr.v14i1.6 ◽

2019 ◽

Vol 14 (1) ◽

Author(s):

Chandrasekhar Bhoj ◽

Lalan Prasad

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Cycle ◽

Interplanetary Magnetic Field ◽

Correlation Coefficient ◽

Geomagnetic Storms ◽

Solar Cycle 24 ◽

Time Periods ◽

Cycle 24 ◽

The Imf

The aim of this paper is to investigate the association of the geomagnetic storms with the IMF for solar cycle 24. Result of the present analysis shows that IMF is geoeffective parameter but its impact varies in accordance with different time periods. The correlation coefficient between Dst and IMF found to be -0.6 for solar cycle 24

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