23rd Solar Cycle Research Articles

Comparison of Two Methods for Calculating Magnetic Helicity in the Solar Corona

Duo to the large magnetic Reynolds number, the magnetic helicity originating from the solar interior can be carried away through the photosphere into the corona. However, the relationship between the accumulated magnetic helicity flux through the photosphere and the magnetic helicity in the corona is still unclear. By selecting 36 newly emerging active regions in the 23rd solar cycle, we apply optical flow methods to derive the accumulated magnetic helicity through the photosphere (H m p ) by using the sequential longitudinal magnetograms, we use nonlinear force-free field extrapolation to obtain the 3D coronal magnetic field, and we adopt finite volume methods to calculate the instantaneous relative magnetic helicity in the corona (H m c ) by using vector magnetograms. It is found that the local correlation tracking (LCT)–based H m p is larger than H m c in 1″, and that the Differential Affine Velocity Estimator–based H m p is more consistent with H m c than the LCT-based H m p . H m p is more consistent with H m c in evaluation from 2″ than from 1″. Moreover, systematically shows consistency with the Hemispheric Helicity Rule (over 55%), no matter which resolution and method are used. These estimations suggest that the consistency of H m c and H m p is partly dependent on the resolution of the magnetograms and the calculation methods.

Solar Supergranular Fractal Dimension Dependence on the Solar Cycle Phase

We study the complexity of the supergranular network through fractal dimension by using the Ca ii K digitized data archive obtained from the Kodaikanal Solar Observatory. The data consist of 326 visually selected supergranular cells spread across the 23rd solar cycle. Only cells that were well-defined were chosen for the analysis and we discuss the potential selection effect thereof, mainly that it favors cells of a smaller size (<20 Mm). Within this sample, we analyzed the fractal dimension of supergranules across the solar cycle and find that it is anticorrelated with the activity level.

A Multiscale Approach to Geomagnetic Storm Morphology Analysis Based on DMA Activity Measures

The article is focused on the approach based on the discrete mathematical analysis conception and continues a series of studies related to the application of the previously developed methodology to geophysical data analysis. The main idea of the study is the modification of earlier conceptions regarding the interpreter’s logic that allows introducing a multiscale approach and performing the time series analysis using the activity measure plots, implying the vertical scale. This approach was used to study the morphology of several intense geomagnetic storms at the final stages of the 23rd and 24th solar activity cycles. Geomagnetic observatory data and interplanetary magnetic field parameters as well as the solar wind flux speed and proton density were analyzed for each of the studied storms using the activity measures. The developed methods, applied to geomagnetic storm morphological analysis, displayed good results in revealing the decreases and increases in various durations and intensities during storms, detecting low-amplitude disturbances, and storm sudden commencement recognition. The results provide an opportunity to analyze any physical data using a unified scale and, in particular, to implement this approach to geomagnetic activity studies.

An Analysis of the Latest Super Geomagnetic Storm of the 23RD Solar Cycle (May 15, 2005, Dst: –247 nT)

An Analysis of the Latest Super Geomagnetic Storm of the 23RD Solar Cycle (May 15, 2005, Dst: –247 nT)

A SOC based avalanche model to study the magnetosphere-ionosphere energy transfer and AE index fluctuations

ABSTRACT Magnetosphere-ionosphere energy transfer and AE fluctuations are studied using a cellular automata model of terrestrial magnetosphere based on the concept of self-organised criticality (SOC). The model is a SOC-driven dissipative dynamical system with both spatial and temporal degrees of freedom. The input parameter to this model is derived from the real-time values of solar wind ion density and flow speed data. Both the direction and intensity of the real-time values of the BZ component of the interplanetary magnetic field (IMF) are the factors controlling the energy injection into the system. The model produces an output series which can be regarded as a mathematical representation of the AE index. The spectral response of the simulated output follows a 1/fβ power law, demonstrates a breakpoint at f0 = 0.050 mHz (5.5 hours) having slopes βA = 2.2–2.4 for f > f0 and βB = 0.9–1.0 for f < f0, the typical characteristics of the natural AE index. The entire 23rd solar cycle had been studied using the model. The parameter KA plays a significant role in the entire process. KA represents the remaining percentage of the released energy from the previous magnetosphere-ionosphere energy transfer, stored in the ionosphere.

Solar coronal rotation according to soft X-ray solar radiation during the 22nd, 23rd, and 24th solar cycles

Using the developed method of combining numerous scattered time series of the same type of measurements into a single weighted average series, according to the data of the GOES series satellites, a single series of daily data was synthesized during the 22nd, 23rd and 24th solar cycles (1986 – 2019 years). The flare and background components were distinguished from this data series, which were investigated by means the method of constructing a composite spectral periodogram for the presence of quasiperiodic oscillations at various solar cycles. Some of these found quasiperiods may be explained by both synodic and sidereal rotation of the Sun, while others coincide with the average lifetime of the solar atmosphere active formations such as the sunspot groups and the facular plages. Special attention was paid to the study of the change over time the revealed quasiperiodic values over the course of solar cycles by calculating the sample normalized spectral density of the analyzed data in a sliding time window with a value of up to two years. Based on the revealed quasiperiodic value changes presented on the dynamic diagrams, it can be concluded that the differential rotation of the solar corona is unstable and manifests itself only at certain stages of the development and existence of solar activity cycles.

Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA Mission

Abstract We present a study of the solar-cycle variations of &gt;80 MeV proton flux intensities in the lower edge of the inner radiation belt, based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission. The analyzed data sample covers an ∼8 yr interval from 2006 July to 2014 September, thus spanning from the decaying phase of the 23rd solar cycle to the maximum of the 24th cycle. We explored the intensity temporal variations as a function of drift shell and proton energy, also providing an explicit investigation of the solar modulation effects at different equatorial pitch angles. PAMELA observations offer new important constraints for the modeling of low-altitude particle radiation environment at the highest trapping energies.

Comparative Analysis of Fractal Properties of Solar Faculae

Present study is aimed at investigating the solar faculae area from 1990 to 2007 which partially covered the22nd and 23rd solar cycle. Rescaled Range Analysis (RRA) and Detrended Fluctuation Analysis (DFA) have beenadopted to evaluate the behaviour of nonlinear dynamics of solar faculae area. Results show that the value of Hurstexponent for solar faculae area from RRA and DFA is negatively correlated. It means it is non-persistent and longrange correlated. Obtained result is inaccurate so the only solution is to transform the data into stationary data by takingdifferencing. RRA is applied on residuals and RRA to evaluate the fractal property of the time series. Solar faculae areainvestigated in this study is fractal in nature and predictable ass well. Moreover, the time series of solar faculae area isnon-linear as established by the Brock – Dechert – Scheinkman (BDS) test results

Comparative Analysis of Fractal Properties of Solar Faculae

Present study is aimed at investigating the solar faculae area from 1990 to 2007 which partially covered the 22nd and 23rd solar cycle. Rescaled Range Analysis (RRA) and Detrended Fluctuation Analysis (DFA) have been adopted to evaluate the behaviour of nonlinear dynamics of solar faculae area. Results show that the value of Hurst exponent for solar faculae area from RRA and DFA is negatively correlated. It means it is non-persistent and long-range correlated. Obtained result is inaccurate so the only solution is to transform the data into stationary data by taking differencing. RRA is applied on residuals and RRA to evaluate the fractal property of the time series. Solar faculae area investigated in this study is fractal in nature and predictable ass well. Moreover, the time series of solar faculae area is non-linear as established by the Brock – Dechert – Scheinkman (BDS) test results.

Solar activity cycles recorded in long-term data on tritium activity concentration in precipitation at Zagreb, Croatia

It has been expected that the solar cycle may have an influence on the production rate of cosmogenic tritium. However, prevailing anthropogenic bomb tritium in precipitation in the second half of the 20th century prevented such studies. We analyzed long-term data (1976–2020) of tritium activity concentration in precipitation at Zagreb, Croatia, by various statistical methods looking for the solar cycle periodicity. Frequency and Wavelet analyses were performed on the whole data set, while sinusoidal fitting was performed on data since 1996, when bomb tritium is negligible. All methods resulted in two distinct periods. The shorter 1-year period corresponds to the annual variation of tritium in precipitation typical for the Northern Hemisphere stations. The longer period of 10.21 yr, ≈11 yr and 12.17 yr was obtained by frequency analysis, wavelet analysis and sinusoidal fitting, respectively. These values are close to the solar cycle with 11 yr period on the average (ranging from 9 yr to 13.6 yr). Additionally, we compared the maxima in the smoothed monthly sunspot number in the 23rd and 24th solar cycles and the minima in tritium activity concentration in precipitation. A delay of about 30 months between them was observed and plausibly explained by the residence time of cosmogenic tritium in the stratosphere before entering the troposphere.

Local-time, seasonal and solar cycle variation of Nitric Oxide radiative emission over Indian longitude sector

• Localtime,seasonal & solar cycle variations of NO emission are studied over Indian longitude. • Maximum volume emission rate(VER), dobule the nighttime mean, is observed at 13 LT. • Peak altitude of NOVER descends downward by 18 km from midnight to noon. • Peak VER & intensity show a winter maximum and a summer minimum. We study the local-time, seasonal and solar cycle variations of Nitric Oxide (NO) infrared radiative emission, as observed by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the NASA’s Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite, over Indian longitude sector. It covers nineteen (January 2002-December 2020) years of NO radiative emission data in the altitude region of 100–155 km. The NO volume emission rate (VER) shows a strong local-time variation with maximum and minimum, respectively, during local-noon and local-midnight. The peak altitude of NO VER decreases by about 18 km from the midnight to the lowest altitude of 117 km at noon. The mean NO VER also undergoes a significant change between the day and night. The mean daytime NO VER is more than double the night-time counterpart. The seasonal variation of peak NO VER shows a maximum during the month of December and a minimum during March. The peak altitude is maximum during September and minimum during June unlike the peak NO VER. The lowest peak altitude, maximum VER and maximum intensity are observed during winter. The relative change in NO VER between the winter and the summer seasons, peaks around 116 km, increases with altitude above 108 km. The long-term trend of NO VER/intensity shows a clear solar cycle variation with higher values during the higher solar activity periods. The NO intensity exhibits a strong correlation with sunspot number (SSN), F10.7 solar index and Lyman- α during both 23rd and 24th solar cycles, although the peak VER does not coincide with the peak SSN.

Research on Solar Proton Event in the 23rd Solar Cycle Using the Machine Learning Methods

Solar Proton Event (SPE) can pose crucial risks to the spacecraft. It is meaningful to analyze and build the relationships between SPE and the associated Coronal Mass Ejection (CME) and solar flares. In this study, the SPE in the 23rd solar cycle is investigated by using machine learning methods. Datasets were constructed based on CME and the solar proton events lists from 1997 to 2006 from the CDA web database. Apriori algorithm are used to survey the correlations between SPEs and the characteristics of flares and CME. The results show that X class flares, full halo CME, high speed (greater than 1000 km·s^-1) CME, and western flares are the four characteristics that most likely to be associated with SPE. The corresponding probabilities are 0.366, 0.355, 0.30 and 0.155. The SPE probabilities at the condition of more than one (CME or flare) features occurring simultaneously were exhibited as well. Using the over sampled CME and flares features, five SPE prediction models are built through five different supervised machine learning algorithms, thus Logistic Regression, Support Vector Classification, <italic>K</italic>-nearest neighbor, Random Forest and Gradient Boosting Decision Tree. The models all present pretty good prediction accuracy (>0.94), precision (>0.96) and recall rate (>0.91).

Analysis of Relationship Between Ionospheric and Solar Parameters Using Graphical Models

AbstractFor the investigation of time variations of critical frequency (foF2), solar radiation flux at 10.7 cm wavelength (F10.7 index) and geomagnetic activity index Kp, we use conditional independence graphical models which describe and transparently represent the structure of relationships in the time series. We employ multivariate statistic methods applied to daily observational data obtained from midlatitude ionosondes within the period 1994–2009 (23rd Solar Cycle). It is demonstrated that conditional independence graphical models represent a robust method of multivariate statistical analysis, useful for finding a relation between one of the main ionospheric parameters and space weather conditions. This method appears to be more appropriate than correlation analysis between foF2 and the main geomagnetic and solar indices, especially for long‐term data for which the model characteristics may change or time series can be interrupted. We compare the results obtained by the graphical models method with cross‐correlation analysis. We found that the method is suitable for the analysis of the dependence between foF2 values and time‐shifted F10.7 time series. In particular, we clearly identified +0 day shift in all cases, and +1‐, +2–3‐, and +4–5‐day shifts in European, American, and East Asia sector, respectively. The conditional independence graphs method can be applied even in the case when classical parametric methods are not convenient.

On the Probable Change of the Status of the Current Unusual Failure of 11-Year Solar Cyclicity from Local to Global

The anomalous increase in the area of the 23rd solar cycle detected by galactic cosmic rays (GCRs) was a precursor of failure of the 11-year cyclicity: in accordance with the author’s hypothesis about the invariant of the 22-year cycle, an increase in the area of the 23rd cycle was followed by a decrease in the area (energy intensity) of the next 24th cycle. A decrease in energy intensity is accompanied by a decrease (relative variation) in the luminosity of the Sun, which in the 24th cycle has decreased to the level of the average value of the three previous cycles, i.e., almost twice. If the invariant of the 22-year cycle is preserved, the restoration of the 11-year cyclicity in the 25th cycle should be expected. If the invariant of the 22-year cycle is violated, the level of the GCR radiation background at the maximum of the forthcoming 25th cycle (from 2024 to 2025) should not be lower than the background radiation level at the maximum of the 24th cycle (2014). In this case, the state of the 23rd–24th–25th cycle unusual failure will change from local to global.

From Hector Mine M7.1 to Ridgecrest M7.1 Earthquake. A Look from a 20-Year Perspective

The paper provides a comparative analysis of precursory phenomena in the ionosphere and atmosphere for two strong earthquakes of the same magnitude M7.1 that happened in the same region (North-East from Los Angeles) within a time span of 20 years, the Hector Mine and Ridgecrest earthquakes. Regardless of the similarity of their location (South-Eastern California, near 160 km one from another), there was one essential difference: the Hector Mine earthquake happened during geomagnetically disturbed conditions (essential in the sense of ionospheric precursors identification). In contrast, the quiet geomagnetic conditions characterized the period around the time of the Ridgecrest earthquake. The Hector mine earthquake happened in the middle of the rising phase of the 23-rd solar cycle characterized by high solar activity, while the Ridgecrest earthquake happened by the very end of the 24th cycle under very low solar activity conditions. We provide a comprehensive multi-factor analysis, determine the precursory period for both earthquakes and demonstrate the close similarity of ionospheric precursors. Unlike the majority of papers dealing with earthquake precursor identification based on the “abnormality” of observed time-series mainly determined by amplitude difference between “normal” (usually climatic) behavior and “abnormal” behavior with amplitudes exceeding some pre-established threshold, we used the technique of cognitive recognition of the precursors based on the physical mechanisms of their generation and the morphology of their behavior during the precursory period. These permits to uniquely identify precursors even in conditions of disturbed environment as it was around the time of the Hector Mine earthquake. We demonstrate the close similarity of precursors’ development for both events. The leading time of precursor appearance for the same region and similar magnitude was identical. For the Hector Mine it was 11 October 1999—5 days in advance—and for 2019 Ridgecrest it was 28 June—7 days before the mainshock and five days before the strongest foreshock.

Fractality of an MHD shell model for turbulent plasma driven by solar wind data: A review

The Gledzer-Yamada-Ohkitani MHD shell model is used to describe dissipative events that take place in magnetized plasmas. In this review we summarize a series of works aimed to characterize the fractal features of the GOY shell model using various choices of the forcing terms, as an attempt to model the behavior of the Earth's magnetosphere driven by the solar wind. Usually, stochasticity in the shell model is included by using the solution of a Langevin equation in its forcing terms. We compare that method with cases where solar wind data spanning the full 23rd solar cycle is used to build the forcing terms of the shell model. Correlations are found between the fractal dimension of the forcing and the energy dissipation rate obtained from the shell model description. This shows that the GOY shell model is able to respond to statistical variations on the driving. Also, it shows that the fractal dimension, although it is a very simple measure of complexity, is able to capture variations both in the driving terms and in the output, along the solar cycle. These results are consistent with analogous studies of fractality for geomagnetic indexes such as Dst or SYM-H.

Research on Solar Proton Event in the 23rd Solar Cycle Using the Machine Learning Methods

在耀斑伴随日冕物质抛射（CME）事件编目数据的基础上，进行太阳质子事件（SPE）匹配，构建研究数据集.利用Apriori算法挖掘SPE与耀斑级别、耀斑发生日面位置以及CME角宽度和速度的关联关系.结果表明：X级耀斑、全晕CME、高速（>1000km&#183;^-1） CME和日面西半球耀斑是最可能伴随质子事件的4种特征，其诱发质子事件概率依次为0.366，0.355，0.30，0.155.角宽度低于120&#176;或速度低于400km&#183;^-1的CME产生质子事件的概率为0.高速CME产生质子事件的概率是低速（400～1000km&#183;^-1） CME的8.6倍，X级耀斑产生质子事件的概率是M级耀斑的6.2倍，日面西部耀斑产生质子事件的概率是日面东部耀斑概率的3.9倍，全晕CME产生太阳质子事件的概率是非全晕（120&#176;～360&#176;） CME的3.8倍.对太阳质子事件样本进行过采样处理，利用随机森林等5种典型有监督学习算法，构建了基于第23太阳活动周耀斑和CME特征的质子事件预测模型.结果表明，该预报模型的质子事件预测准确率、精确率和召回率均控制在91%以上.

Correlation Analysis between Magnetic Storms and Solar Extreme Ultraviolet Radiation during the 23rd Solar Cycle

统计第23个太阳活动周内中等及以上强度（<i>Dst</i>_min<-50nT）的磁暴事件，线性拟合分析磁暴主相D<i>Dst</i>_min和达到D<i>Dst</i>_min前一个表征太阳极紫外辐射强度的<i>F</i>_10.7之间的相关性.结果表明：随着太阳极紫外辐射增强，D<i>Dst</i>_min<-50nT的磁暴出现的总数增多，在弱、中等和强太阳极紫外辐射条件下，其数量分别为56，84和85；随着太阳极紫外辐射增强，强磁暴（-200nT ≤ <i>Dst</i>_min<-100nT）和大磁暴（<i>Dst</i>_min<-200nT）发生的数量和相对发生率呈增长趋势，尤其是大磁暴数目（1，4，12）和相对发生率（1.79%，4.76%，14.12%）明显呈增长趋势；大磁暴（|<i>Dst</i>_min|）与太阳极紫外辐射（<i>F</i>_10.7）之间存在中度正相关关系，其相关系数为0.532，并且主要体现在大磁暴（|<i>Dst</i>_min|）与强太阳极紫外辐射（<i>F</i>_10.7）之间的中度正相关性，其相关系数为0.582.大磁暴与强太阳极紫外辐射之间的相关性可为空间天气预报提供参考依据.

The Statistical Analysis of Characteristics of Coronal Mass Ejection During the Descending Phase of Solar Cycle 23 and 24

The characteristics of CMEs we studied are angular width, linear speed, and acceleration for all categories of CMEs such as narrow (W ≤20°), intermediate (20°&lt; W&lt;200°), wide (W ≥ 200°) and linear speed &lt;500 km/s during the descending phase of solar cycle 23 and 24 and compared them. We have found that there are 1951 narrow CMEs during solar cycle 23 that is 1.9 times greater than in solar cycle 24 (1047). On the other side, the number of intermediate CMEs during solar cycle 24 (1571) is 1.14 times more than solar cycle 23 (1162). We observed no noticeable difference between the number of wide CMEs of solar cycle 23 (29) and 24 (36). The angular width of CMEs during the descending phase of solar cycle 23 and solar cycle 24, predominately distributed around 100-600. The fascinating result is that the angular width distributions for the descending phase of solar cycles are approximately identical. On comparing the results of linear speed of both solar cycle, we can say that, (i) 93.7% (1729) and 87.7% (908) of narrow CMEs, (ii) 97% (1328) and 94% (1479) of intermediate CMEs and (iii) 44% (13) and 42% (15) of wide CMEs have speed of &lt;500 km s-1, respectively. Mostly the fractions of narrow and intermediate CMEs decline sharply at the speeds greater than 500 km s-1. The maximum speed observed during the 23rd cycle is 1994 km/s (wide CME) and the 24th cycle is 3163 km/s (wide CME) respectively. It was noticed that the speed of the 24th solar cycle CME is higher than the 23rd solar cycle CME. The major fraction of CMEs has acceleration in the range of -20 to 20 km s-2, all types of CMEs. The narrow and intermediate CMEs mostly show acceleration while wide CMEs show deceleration.

Analytical Study of Severe and Great Geomagnetic Storms

Severe and Great Geomagnetic storms are considered to be those which have Dst less than -200nT. The investigation years are January 1996 to December 2006, which refers to 23rd solar cycle. During this period, 18 Geomagnetic storms are observed. When there are maximum number of sunspots present at the solar disk, highest number of these Geomagnetic storms are observed, which is quite obvious. The Coronal Mass Ejections responsible for these storms depict latitudinal as well as longitudinal bias showing more inclination towards northern hemisphere and western region of the solar disk. These Coronal Mass Ejections are confined between 25 of the equator.