scholarly journals Solar cycle 24: An unusual polar field reversal

2018 ◽  
Vol 618 ◽  
pp. A148 ◽  
Author(s):  
P. Janardhan ◽  
K. Fujiki ◽  
M. Ingale ◽  
S. K. Bisoi ◽  
D. Rout

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.

2020 ◽  
Vol 642 ◽  
pp. A233
Author(s):  
R. Sharma ◽  
C. Cid

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.


2017 ◽  
Vol 13 (S335) ◽  
pp. 32-35
Author(s):  
Ranadeep Sarkar ◽  
Nandita Srivastava ◽  
Sajal Kumar Dhara

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.


2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Chandrasekhar Bhoj ◽  
Lalan Prasad

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.


2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Chandrasekhar Bhoj ◽  
Lalan Prasad

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


2010 ◽  
Vol 28 (2) ◽  
pp. 417-425 ◽  
Author(s):  
A. Yoshida ◽  
H. Yamagishi

Abstract. It is shown that the monthly smoothed sunspot number (SSN) or its rate of decrease during the final years of a solar cycle is correlated with the amplitude of the succeeding cycle. Based on this relationship, the amplitude of solar cycle 24 is predicted to be 84.5±23.9, assuming that the monthly smoothed SSN reached its minimum in December 2008. It is further shown that the monthly SSN in the three-year period from 2006 through 2008 is well correlated with the monthly average of the intensity of the interplanetary magnetic field (IMF). This correlation indicates that the SSN in the final years of a solar cycle is a good proxy for the IMF, which is understood to reflect the magnetic field in the corona of the sun, and the IMF is expected to be smallest at the solar minimum. We believe that this finding illuminates a physical meaning underlying the well-known precursor method for forecasting the amplitude of the next solar cycle using the aa index at the solar minimum or its average value in the decaying phase of the solar cycle (e.g. Ohl, 1966), since it is known that the geomagnetic disturbance depends strongly on the intensity of the IMF. That is, the old empirical method is considered to be based on the fact that the intensity of the coronal magnetic field decreases in the late phase of a solar cycle in parallel with the SSN. It seems that the precursor method proposed by Schatten et al. (1978) and Svalgaard et al. (2005), which uses the intensity of the polar magnetic field of the sun several years before a solar minimum, is also based on the same physical phenomenon, but seen from a different angle.


2016 ◽  
Vol 818 (2) ◽  
pp. 147 ◽  
Author(s):  
L. F. Burlaga ◽  
N. F. Ness ◽  
J. D. Richardson ◽  
R. B. Decker ◽  
S. M. Krimigis

2018 ◽  
Vol 867 (2) ◽  
pp. 129 ◽  
Author(s):  
Qing Chang ◽  
Xiaojun Xu ◽  
Tielong Zhang ◽  
Lihui Chai ◽  
Yong Wei ◽  
...  

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