Solar cycle-related variation in solar differential rotation and meridional flow in solar cycle 24

Imada, Shinsuke; Matoba, Kengo; Fujiyama, Masashi; Iijima, Haruhisa

doi:10.1186/s40623-020-01314-y

Cited by 14 publications

(5 citation statements)

References 38 publications

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“…As shown in Fig. 8, solar cycle 24, mainly analyzed in this study, had low solar activity (Iijima et al 2017;Imada et al 2020) and did not produce any large-scale events that exceeded the X10 class. Furthermore, no flare events with EUV late phase, which is the second peak of the Fe XV and Fe XVI line emission, were found in this statistical study.…”

Section: Discussion and Summarymentioning

confidence: 69%

Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares

Nishimoto

Watanabe

Jin

et al. 2023

Earth Planets Space

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The X-rays and extreme ultraviolet (EUV) emitted during solar flares can rapidly change the physical composition of Earth’s ionosphere, causing space weather phenomena. It is important to develop an accurate understanding of solar flare emission spectra to understand how it affects the ionosphere. We reproduced the entire solar flare emission spectrum using an empirical model and physics-based model, and input it into the Earth’s atmospheric model, GAIA to calculate the total electron content (TEC) enhancement due to solar flare emission. We compared the statistics of nine solar flare events and calculated the TEC enhancements with the corresponding observed data. The model used in this study was able to estimate the TEC enhancement due to solar flare emission with a correlation coefficient greater than 0.9. The results of this study indicate that the TEC enhancement due to solar flare emission is determined by soft X-ray and EUV emission with wavelengths shorter than 35 nm. The TEC enhancement is found to be largely due to the change in the soft X-ray emission and EUV line emissions with wavelengths, such as Fe XVII 10.08 nm, Fe XIX 10.85 nm and He II 30.38 nm. Graphical Abstract

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Section: Discussion and Summarymentioning

confidence: 69%

Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares

Nishimoto

Watanabe

Jin

et al. 2023

Earth Planets Space

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“…Near the base of the tachocline where the turbulent viscosity is low, the related time constant can facilitate the 22-year oscillation. Solar cycle signatures are observed in the zonal and meridional flow velocities of the Sun (Imada et al [31]) in support of the wave momentum source that is proposed to generate the atmospheric oscillation. A zonal flow oscillation can generate the eastward-westward electric current oscillation to produce the northward-southward solar cycle variation of the dynamo magnetic field illustrated in Figure 7.…”

Section: Discussionmentioning

confidence: 90%

Proposed Wave Momentum Source for Generating the 22-Year Solar Cycle

Mayr¹

2023

IJAA

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For the 22-year solar cycle oscillation there is no external time dependent source. A nonlinear oscillation, the solar cycle must be generated internally, and Babcock-Leighton models apply an artificial nonlinear source term that can simulate the observations-which leaves open the question of the actual source mechanism for the solar cycle. Addressing this question, we propose to take guidance from the wave mechanism that generates the 2-year Quasi-biennial Oscillation (QBO) in the Earth atmosphere. Upward propagating gravity waves, eastward and westward, deposit momentum to generate the observed zonal wind oscillation. On the Sun, helioseismology has provided a thorough understanding of the acoustic p-waves, which propagate down into the convective envelope guided by the increasing temperature and related propagation velocity. Near the tachocline with low turbulent viscosity, the waves propagating eastward and westward can produce an axisymmetric 22-year oscillation of the zonal flow velocities that can generate the magnetic solar dynamo. Following the Earth model, waves in opposite directions can generate in the Sun wind and magnetic field oscillations in opposite directions, the proposition of a potential solar cycle mechanism.

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“…On the other hand, magnetic elements with a strong (weak) magnetic field show a lower (higher) meridional circulation velocity. Imada et al (2020) found that the average meridional flow profile peaked at ≈ 15 m s −1 at 45 • . During the declining phase of the cycle, the meridional flow at the middle latitude (30 • ) accelerated from 10 to 17 m s −1 in both hemispheres.…”

Section: Discussionmentioning

confidence: 97%

Variation of Chromospheric Features as a Function of Latitude and Time Using Ca-K Spectroheliograms for Solar Cycles 15 – 23: Implications for Meridional Flow

et al. 2021

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We have analyzed the Ca-K images obtained at Kodaikanal Observatory as a function of latitude and time for the period of 1913 -2004 covering Solar Cycles 15 to 23. We have classified the chromospheric activity into plage, Enhanced Network (EN), Active Network (AN), and Quiet Network (QN) areas to differentiate between large strong active and small weak active regions. The strong active regions represent toroidal and weak active regions poloidal component of the magnetic field. We find that plage areas mostly up to 50 • latitude belt vary with about 11-year solar cycle. We also find that a weak activity represented by EN, AN and QN varies with about 11-year with significant amplitude up to about 50 • latitude in both hemispheres. The amplitude of the variation is minimum around 50 • latitude and again increases by a small amount in the polar region. In addition, the plots of plages, EN, AN and QN as functions of time indicate the maximum of activity at different latitude occur at different epoch. To determine the phase difference for the different latitude belts, we have computed the cross-correlation coefficients of other latitude belts with the 35 • latitude belt. We find that the activity shifts from mid-latitude belts towards equatorial belts at high speed at the beginning of a solar cycle and at lower speed as the cycle progresses. The speed of the shift varies between ≈ 19 and 3 m s −1 considering all the data for the observed period. This speed can be linked with the speed of meridional flows, believed to occur between convection zone and the surface of the Sun.

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Solar cycle-related variation in solar differential rotation and meridional flow in solar cycle 24

Cited by 14 publications

References 38 publications

Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares

Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares

Proposed Wave Momentum Source for Generating the 22-Year Solar Cycle

Variation of Chromospheric Features as a Function of Latitude and Time Using Ca-K Spectroheliograms for Solar Cycles 15 – 23: Implications for Meridional Flow

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