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Prediction of declining solar activity trends during solar cycles 25 and 26 and indication of other solar minimum
摘要： Study of variations in solar activity parameters has its importance in understanding the underlying mechanisms of space weather phenomena and space climate variability. We have used the already observed data of solar parameters viz. sunspot numbers, F10.7 cm index and Lyman alpha index recorded for last seventy years (1947–2017). We have applied the Hodrick Prescott ?ltering method to bifurcate each time series into cyclic and trend parts. The cyclic part of each time series was used to analyse the persistence while the trend part was used to obtain the input data for the study of future predictions. Further, the cyclic component of each parameter was analysed by using the rescaled range analysis and the value of Hurst exponent was obtained for sunspot numbers, F10.7 cm index and Lyman alpha index as 0.90, 0.93 and 0.96 respectively. By using the simplex projection analysis on the values of amplitude and phase of the trend component of each time series, we have reconstructed the future time series representing solar cycles 25 and 26. When extrapolated further in time, the reconstructed series provided the maximum values of sunspot numbers as 89 ± 9 and 78 ± 7; maximum values of F10.7 cm index were 124 ± 11 and 118 ± 9 and Lyman alpha index were 4.61 ± 0.08 and 4.41 ± 0.08 respectively for solar cycles 25 and 26. In our analysis we have found that the solar cycle 25 will start in the year 2021 (January) and will last till 2031 (February) with its maxima in year 2024 (February) while the solar cycle 26 will start in the year 2031 (March) with its maxima in 2036 (June) and will last till the year 2041 (February). We have also compared the activities of solar cycles 5 and 6 (Dalton minima periods) to solar cycles 25 and 26 and have observed that the other solar minimum is underway.
关键词： Rescale range analysis,Sunspot numbers,Solar activity,solar minimum,Hurst exponent,Simplex projection analysis
更新于2025-09-23 15:22:29
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Triggering Mechanism and Material Transfer of a Failed Solar Filament Eruption
摘要： Solar ?lament eruptions are often associated with solar ?ares and coronal mass ejections, which have the greatest impact on space weather. However, the ?ne structures and the trigger mechanisms of solar ?laments are still unclear. To address these issues, we studied a failed solar active-region ?lament eruption associated with a C-class ?are by using high-resolution Hα images from the New Vacuum Solar Telescope, supplemented by EUV observations from the Solar Dynamics Observatory. Before the ?lament eruption, a small bipolar magnetic ?eld emerged below the ?lament. Then magnetic reconnection between the ?lament and the emerging bipolar magnetic ?eld triggered the ?lament eruption. During the ?lament eruption, the untwisting motion of the ?lament can be clearly traced by the eruptive threads. Moreover, the footpoints of the eruptive threads are determined by tracing the descending ?lament material. Note that the twisted structure of the ?lament and the right part of the eruptive ?lament threads cannot be seen before the ?lament eruption. These eruptive threads in the right part of the ?lament are found to be rooting in the weak negative polarities near the main negative sunspot. Moreover, a new ?lament formed in the ?lament channel due to material injection from the eruptive ?lament. The above observations and the potential ?eld extrapolations are inclined to support the idea that the ?lament materials were transferred into the overlying magnetic loops and the nearby ?lament channel by magnetic reconnection. These observations improve our understanding of the complexity of ?lament eruptions.
关键词： Solar activity,Solar magnetic ?elds,Solar magnetic reconnection,Sunspots,Solar active region magnetic ?elds,Solar ?lament eruptions,Solar active region ?laments,Solar ?ares,Solar physics,Solar atmosphere
更新于2025-09-23 15:19:57
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Quasi ~500-year Cycle Signals in Solar Activity
摘要： Direct observations of solar activity are available for the past four century, so some proxies reflecting solar activity such as 14C, 10Be and geomagnetic variations are used to reconstruct solar activity in the past. In this present paper, the authors use rectified wavelet power transform and time-averaged wavelet power spectrum to investigate long-term fluctuations of the reconstructed solar activity series. Results show obvious a quasi ~500-year cycle exists in the past solar activity. Three reconstructed solar activity series from 14C variations confirm the periodic signals.
关键词： solar activity,wavelet transform,long-term cycle
更新于2025-09-09 09:28:46
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The natural oscillations in stratospheric ozone observed by the GROMOS microwave radiometer at the NDACC station Bern
摘要： A multilinear parametric regression analysis was performed to assess the seasonal and inter-annual variations of stratospheric ozone profiles from the GROMOS (GROund-based Millimeter-wave Ozone Spectrometer) microwave radiometer at Bern, Switzerland (46.95?N, 7.44?E, 577 m). GROMOS takes part in the Network for the Detection of Atmospheric Composition Change (NDACC). The study covers the stratosphere from 50 to 0.5 hPa (from 21 to 53 km) and extends over the period from January 1997 to January 2015. The natural variability was fitted during the regression analysis through the annual and semi-annual oscillations (AO, SAO), the quasi-biennial oscillation (QBO), the El Ni?o–Southern Oscillation (ENSO) and the solar activity cycle. Seasonal ozone variations mainly appear as an annual cycle in the middle and upper stratosphere and a semi-annual cycle in the upper stratosphere. Regarding the inter-annual variations, they are primarily present in the lower and middle stratosphere. In the lower and middle stratosphere ozone variations are controlled predominantly by transport processes, due to the long lifetime of ozone whereas in the upper stratosphere its lifetime is relatively short and ozone is controlled mainly by photochemistry. The present study shows agreement in the observed naturally induced ozone signatures with other studies. Further, we present an overview of the possible causes of the effects observed in stratospheric ozone due to natural oscillations at a northern mid-latitude station. For instance regarding the SAO, we find that polar winter stratopause warmings contribute to the strength of this oscillation since these temperature enhancements lead to a reduction in upper stratospheric ozone. We have detected a strong peak amplitude of about 5% for the solar cycle in lower stratospheric ozone for our 1.5 cycles of solar activity. Though the 11-year ozone oscillation above Bern is in phase with the solar cycle, we suppose that the strong amplitude is partly due to meteorological disturbances and associated ozone anomalies in the Northern hemisphere. Further, our observational study gave the result that ozone above Bern is anti-correlated to the ENSO phenomenon in the lower stratosphere and correlated in the middle stratosphere.
关键词： solar activity cycle,annual oscillation,Switzerland,stratospheric ozone,NDACC,GROMOS,El Ni?o–Southern Oscillation,Bern,semi-annual oscillation,quasi-biennial oscillation,natural oscillations
更新于2025-09-09 09:28:46
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Cyclic Variations in the Solar Radiation Fluxes at the Beginning of the 21st Century
摘要： The solar activity in the current, that is, the 24th, sunspot cycle is analyzed. Cyclic variations in the sunspot number (SSN) and radiation fluxes in various spectral ranges have been estimated in comparison with the general level of the solar radiation, which is traditionally determined by the radio emission flux F10.7 at a wavelength of 10.7 cm (2.8 GHz). The comparative analysis of the variations in the solar constant and solar indices in the UV range, which are important for modeling the state of the Earth’s atmosphere, in the weak 24th cycle and strong 22nd and 23rd cycles has shown relative differences in the amplitudes of variations from the minimum to the maximum of the cycle. The influence of the hysteresis effect between the activity indices and F10.7 in the 24th cycle, which is taken into account here, makes it possible to refine the forecast of the UV indices and solar constant depending on the quadratic regression coefficients that associate the solar indices with F10.7 depending on the phase of the cycle.
关键词： solar activity,cycles of solar activity,activity indexes
更新于2025-09-04 15:30:14
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Photometric magnetic-activity metrics tested with the Sun: application to <i>Kepler</i> M dwarfs
摘要： The Kepler mission has been providing high-quality photometric data leading to many breakthroughs in the exoplanet search and in stellar physics. Stellar magnetic activity results from the interaction between rotation, convection, and magnetic field. Constraining these processes is important if we want to better understand stellar magnetic activity. Using the Sun, we want to test a magnetic activity index based on the analysis of the photometric response and then apply it to a sample of M dwarfs observed by Kepler. We estimate a global stellar magnetic activity index by measuring the standard deviation of the whole time series, Sph. Because stellar variability can be related to convection, pulsations or magnetism, we need to ensure that this index mostly takes into account magnetic effects. We define another stellar magnetic activity index as the average of the standard deviation of shorter subseries which lengths are determined by the rotation period of the star. This way we can ensure that the measured photometric variability is related to starspots crossing the visible stellar disc. This new index combined with a time-frequency analysis based on the Morlet wavelets allows us to determine the existence of magnetic activity cycles. We measure magnetic indexes for the Sun and for 34 M dwarfs observed by Kepler. As expected, we obtain that the sample of M dwarfs studied in this work is much more active than the Sun. Moreover, we find a small correlation between the rotation period and the magnetic index. Finally, by combining a time-frequency analysis with phase diagrams, we discover the presence of long-lived features suggesting the existence of active longitudes on the surface of these stars.
关键词： M dwarfs,Solar activity,Stellar activity,Asteroseismology
更新于2025-09-04 15:30:14
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Forecasting Solar Activity with Computational Intelligence Models
摘要： It is vital to accurately predict solar activity, in order to decrease the plausible damage of electronic equipment in the event of a large high-intensity solar eruption. Recently, we have proposed BELFIS (Brain Emotional Learning-based Fuzzy Inference System) as a tool for the forecasting of chaotic systems. The structure of BELFIS is designed based on the neural structure of fear conditioning. The function of BELFIS is implemented by assigning adaptive networks to the components of the BELFIS structure. This paper especially focuses on performance evaluation of BELFIS as a predictor by forecasting solar cycles 16 to 24. The performance of BELFIS is compared with other computational models used for this purpose, and in particular with adaptive neuro-fuzzy inference system (ANFIS).
关键词： Adaptive Neuro-Fuzzy Inference System,Solar Activity Forecasting,Computational Intelligence Models,Brain Emotional Learning-based Fuzzy Inference System,Solar cycles
更新于2025-09-04 15:30:14