Comparing Two Intervals of Exceptionally Strong Solar Rotation Recurrence of Galactic Cosmic Rays

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: Phase Relationship Between Coronal Rotation and Solar Activitymentioning

confidence: 99%

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

Zhang

Monthly Notices of the Royal Astronomical Society

et al. 2019

“…Solar minima are periods of low activity when modulation is weak and GCR intensities are the highest, while during solar maxima modulation is strong and GCR intensities are at their lowest levels. Gil & Mursula (2018) compared the two exceptionally strong recurrences of GCR intensities during two solar periods of 2007-2008 and 2014-2015 using neutron monitor data, solar wind data, and coronal extreme ultraviolet images. They found that in the most recent period there was a coronal hole in the southern hemisphere about 3-4 days before each decrease in the CR intensity.…”

Section: Introductionmentioning

confidence: 99%

Galactic Cosmic Rays Modulation in the Vicinity of Corotating Interaction Regions: Observations During the Last Two Solar Minima

Ghanbari

Florinski

Guo

et al. 2019

ApJ

Corotating interaction regions (CIRs) are responsible for short-term recurrent cosmic-ray modulation, prominent near solar minima. Using the OMNI data sets for two periods of low solar activity near the beginning and end of solar cycle 24, superposed epoch analysis was performed on the solar wind plasma features for 53 and 43 events during periods 2007-2008 and 2017-2018, respectively. Turbulent properties of the solar wind were studied using the variance method for each CIR. Power spectra have been constructed for overlapped subintervals in the vicinity of stream interfaces (SIs). Using measured correlation lengths and turbulent energies, parallel and perpendicular diffusion mean free paths for cosmic-ray ions have been inferred based on two distinct theoretical formulations. For the two periods with opposite solar polarities, our results show that unlike solar wind speed, magnetic field strength, flow pressure, and proton density are relatively higher during the latest period. Increased turbulent energy and reduced parallel transport coefficients of energetic particles at the SIs are observed. The diffusion coefficients follow the same trends during both periods. The perpendicular diffusion starts increasing nearly a day before SIs and is higher in the fast wind. Superposed epoch analysis is performed on the >120 MeV proton count rate obtained from the CRIS instrument on board the ACE spacecraft for the same events. The recorded proton rates have peaks half a day before a SI and reach their minimum more than a day after a SI and have a high anticorrelation with the perpendicular diffusion coefficient.

“…In our calculations we follow Torrence & Webster (1999) using tools given by Jevrejeva et al (2003) and Grinsted et al (2004). Comparing solar minimum 23/24 and 24/25 it is clear that in all of the studied parameters the 27-days variation was prevalent in both time intervals, although was more incessantly visible during the former one (compare, e.g., Modzelewska & Alania 2013;Gil & Mursula 2018;Jian et al 2019). The relationships in time-frequency domain around solar rotation period between GCR and other studied time series were analyzed using the cross wavelet transform (XWT).…”

Section: Periodic Gcr Variations and Heliospheric Parametersmentioning

confidence: 99%

Recurrence of galactic cosmic-ray intensity and anisotropy in solar minima 23/24 and 24/25 observed by ACE/CRIS, STEREO, SOHO/EPHIN and neutron monitors

Modzelewska

Gil

2021

A&A

Self Cite

Aims. We studied the 27-day variations of galactic cosmic rays (GCRs) based on neutron monitor (NM), ACE/CRIS, STEREO, and SOHO/EPHIN measurements in the solar minima 23/24 and 24/25, which are characterized by the opposite polarities of solar magnetic cycle. We used the opportunity to reanalyze the polarity dependence of the amplitudes of the recurrent GCR variations in 2007–2009 for the negative A < 0 solar magnetic polarity and to compared it with the clear periodic variations related to solar rotation in 2017–2019 for positive A > 0. Methods. We used the Fourier analysis method to study the periodicity in the GCR fluxes. Because the GCR recurrence is a consequence of solar rotation, we analyzed not only GCR fluxes, but also solar and heliospheric parameters to examine the relations of the 27-day GCR variations and heliospheric as well as solar wind parameters. Results. We find that the polarity dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy for NMs data is kept for the last two solar minima: 23/24 (2007–2009) and 24/25 (2017–2019), with greater amplitudes in the positive A > 0 solar magnetic polarity. ACE/CRIS, SOHO/EPHIN, and STEREO measurements are not governed by this principle of greater amplitudes in the positive A > 0 polarity. The GCR recurrence caused by the solar rotation for low-energy (< 1 GeV) cosmic rays is more sensitive to the enhanced diffusion effects, resulting in the same level in 27-day amplitudes for the positive and negative polarities. In contrast, the high-energy (> 1 GeV) cosmic rays that are registered by NMs are more sensitive to the large-scale drift effect, which leads to the 22-year Hale cycle in the 27-day GCR variation, with the larger amplitudes in the A > 0 polarity than in A < 0.