Short-Term Variations in the Equatorial Rotation Rate of Sunspot Groups

Zhang

Monthly Notices of the Royal Astronomical Society

et al. 2019

Temporal variation of the solar coronal rotation appears to be very complex and its relevances to the eleven-year solar activity cycle are still unclear. Using the modified coronal index for the time interval from 1939 January 1 to 2019 May 31, the systematic regularities of the solar coronal rotation are investigated. Our main findings are as follows: (1) from a global point of view, the synodic coronal rotation period with a value of 27.5 days is the only significant period at the periodic scales shorter than 64 days; (2) the coronal rotation period exhibit an obviously decreasing trend during the considered time interval, implying the solar corona accelerates its global rotation rate in the long run; (3) there exist significant periods of 3.25, 6.13, 9.53, and 11.13 years in the period length of the coronal rotation, providing an evidence that the coronal rotation should be connected with the quasi-biennial oscillation, the eleven-year solar cycle, and the 22-year Hale cycle (or the magnetic activity reversal); and (4) the phase relationship between the coronal rotation period and the solar magnetic activity is not only time-dependent but also frequency-dependent. For a small range around the 11-year cycle band, there is a systematic trend in the phase, and the small mismatch in this band brings out the phase to drift. The possible mechanism for the above analysis results is discussed.

Section: Periodicity In the Plcr Time Seriessupporting

confidence: 66%

Systematic regularity of solar coronal rotation during the time interval 1939–2019

Zhang

Monthly Notices of the Royal Astronomical Society

et al. 2019

“…So there could be some variation in the spin angular momentum of the Sun.) The solar rotation varies on many timescales (see Schröter, 1985;Snodgrass, 1992;Komm and Javaraiah, 2002;Antia, 2002;Ulrich, 2005a, 2005b;Brajša, Ruždjak, and Wöhl, 2006;Javaraiah, 2013;Javaraiah and Bertello, 2016). Javaraiah (2005) foun that significant (at the 99.5% confidence level) positive (before around 1945) and negative (after around 1945) correlations exist between the Sun's orbital torque and the solar equatorial rotation rate determined from sunspot group data during the period 1879 -2004.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

“…A best linear fit to the values of amplitudes (164.5, 158.5, 120.8, 81.9, 30 -50) and times of Cycles 21 -25 (predicted values are used for Cycle 25) suggests 7 -23 for the amplitude of Cycle 26, which is expected to begin close to the epoch 2030. Planetary configurations may cause modulations in the emerging magnetic flux (Javaraiah, 2005;Javaraiah and Bertello, 2016). It should be noted that no alignment of the major planets is exactly repeated (Jose, 1965).…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

“…The reason could be that Cycle 24 proceeds at different speeds in the northern and southern hemispheres. The southern hemisphere sunspot peak of Cycle 24 occurred in April 2014 and was about 30% stronger than the northern hemisphere peak, which occurred in September 2011 (Hathaway, 2015;Javaraiah, 2016;Deng et al, 2016, and references therein), but the polar fields had a similar strength in both the northern and southern hemispheres at the end of Cycle 23. Therefore, the polar fields may be going through different dynamo processes in the northern and southern hemispheres, which produces two different seeds.…”

Section: Introductionmentioning

confidence: 90%

See 1 more Smart Citation

Will Solar Cycles 25 and 26 Be Weaker than Cycle 24?

Javaraiah¹

2017

Sol Phys

Self Cite

The study of variations in solar activity is important for understanding the underlying mechanism of solar activity and for predicting the level of activity in view of the activity impact on space weather and global climate. Here we have used the amplitudes (the peak values of the 13-month smoothed international sunspot number) of Solar Cycles 1 -24 to predict the relative amplitudes of the solar cycles during the rising phase of the upcoming Gleissberg cycle. We fitted a cosine function to the amplitudes and times of the solar cycles after subtracting a linear fit of the amplitudes. The best cosine fit shows overall properties (periods, maxima, minima, etc.) of Gleissberg cycles, but with large uncertainties. We obtain a pattern of the rising phase of the upcoming Gleissberg cycle, but there is considerable ambiguity. Using the epochs of violations of the Gnevyshev-Ohl rule (G-O rule) and the 'tentative inverse G-O rule' of solar cycles during the period 1610 -2015, and also using the epochs where the orbital angular momentum of the Sun is steeply decreased during the period 1600 -2099, we infer that Solar Cycle 25 will be weaker than Cycle 24. Cycles 25 and 26 will have almost same strength, and their epochs are at the minimum between the current and upcoming Gleissberg cycles. In addition, Cycle 27 is expected to be stronger than Cycle 26 and weaker than Cycle 28, and Cycle 29 is expected to be stronger than both Cycles 28 and 30. The maximum of Cycle 29 is expected to represent the next Gleissberg maximum. Our analysis also suggests a much lower value (30 -40) for the maximum amplitude of the upcoming Cycle 25.

“…The period lengths of the solar rotation ascertained by different authors using different solar activity indices all have a general downward trend (Heristchi & Mouradian 2009;Chandra & Vats 2011;Xu et al 2020). Furthermore, these rotation periods have specific characteristics, such as the periodic behavior of the rotation period (Javaraiah & Gokhale 1995;Chandra & Vats 2011) and the cross-correlation between the rotation period and the solar activity (Javaraiah & Gokhale 1995;Chandra & Vats 2011;Javaraiah & Bertello 2016;Deng et al 2020). However, the previous studies of temporal variation of the solar rotation focused on the photosphere, chromosphere, and corona.…”

Section: Introductionmentioning

confidence: 98%

Temporal Variation of the Rotation in the Solar Transition Region

Zhang

et al. 2023

ApJL

The temporal variations of solar rotation in the photosphere, chromosphere, and corona have been widely investigated, whereas the rotation of the solar transition region is rarely studied. Here, we perform a primary study about the long-term variation of the rotation in the transition region using Lyα irradiance from 1947 February 14 to 2023 February 20. Correlation techniques are used, and the main results are as follows. (1) The sidereal rotation period of the solar transition region varies between 22.24 and 31.49 days, and the mean sidereal rotation period is 25.50 days for the studied time interval 1947–2022. (2) The rotation period of the transition region exhibits a clear downward trend during 1947–2022, which might be caused by the reduced heliospheric pressure and the weaker solar global magnetic fields. (3) Significant periodic signal of the quasi-Schwabe cycle is found in the rotation periods of the transition region. (4) The cross-correlation between the rotation periods of the solar transition region and sunspot activity corroborates a strong correlation with the Schwabe cycle. Possible mechanisms responsible for these results are discussed.