Showing papers on "Solar cycle 24 published in 2023"

Prediction for the amplitude and second maximum of Solar Cycle 25 and a comparison of the predictions based on strength of polar magnetic field and low latitude sunspot area

Abstract: The maximum of a solar cycle contain two or more peaks, known as Gnevyshev peaks. Studies of this property of solar cycles may help for better understanding the solar dynamo mechanism. We analysed the 13-month smoothed monthly mean Version-2 international sunspot number (SN) during the period 1874–2017 and found that there exists a good correlation between the amplitude (value of the main and highest peak) and the value of the second maximum (value of the second highest peak) during the maximum of a solar cycle. Using this relationship and the earlier predicted value 86 ± 18 (92 ± 11) of the amplitude of Solar Cycle 25, here we predict a value 73 ± 15 (79 ± 15) for the second maximum of Solar Cycle 25. The ratio of the predicted second maximum to the amplitude is found to be 0.85, almost the same as that of Solar Cycle 24. The least-square cosine fits to the values of the peaks that occurred first and second during the maxima of Solar Cycles 12–24 suggest that in Solar Cycle 25 the second maximum would occur before the main maximum, the same as in Solar Cycle 24. However, these fits suggest ≈106 and ≈119 for the second maximum and the amplitude of Solar Cycle 25, respectively. Earlier, we analysed the combined Greenwich and Debrecen sunspot-group data during 1874–2017 and predicted the amplitude of Solar Cycle 25 from the activity just after the maximum of Solar Cycle 24 in the equatorial latitudes of the Sun’s southern hemisphere. Here from the hindsight of the results we found the earlier prediction is reasonably reliable. We analysed the polar-fields data measured in Wilcox Observatory during Solar Cycles 20–24 and obtained a value 125 ± 7 for the amplitude of Solar Cycle 25. This is slightly larger–whereas the value ≈86 (≈92) predicted from the activity in the equatorial latitudes is slightly smaller–than the observed amplitude of Solar Cycle 24. This difference is discussed briefly.

A Critical Comment on “Can Solar Cycle 25 Be a New Dalton Minimum?”

Abstract: Abstract The sunspot number is the most used solar-activity index to study the behavior of solar activity. In this work, we reproduce the methodology of Coban, Raheem, and Cavus ( Solar Phys . 296 , 156, 2021) using a long short-term memory model with daily data from the American Association of Variable Star Observers (AAVSO) to predict the maximum amplitude of Solar Cycle 25. We have also used that same methodology with daily values from the official sunspot number (Version 2) of the Sunspot Index and Long-term Solar Observations (SILSO). The objective of this work is to analyze if the predictions obtained from that methodology agree with the observed values available for the current Solar Cycle 25. Thus, we conclude that the predictions are not reproducing well the behavior of the Solar Cycle 25 in its rising phase. Moreover, contrary to the previous prediction, no minor peak occurred in February 2022, and we also conclude that it seems unlikely that the combination of the solar-activity level of Solar Cycle 24 and 25 constitutes a new Dalton-type Minimum, such as Coban, Raheem, and Cavus (2021) proposed.

Solar Cycle Precursors and the Outlook for Cycle 25

Abstract: Sunspot Cycle 25 is now over 3 years past the cycle minimum of December 2019. At this point in the cycle, curve-fitting to the activity becomes reliable and now consistently indicates a maximum sunspot number of 135 +/- 10 - slightly larger than Cycle 24's maximum of 116.4, but well below the average of 179. A geomagnetic precursor, the minimum in the aa-index, and the Sun's magnetic precursors, the Sun's polar field strength and its axial dipole moment at the time of minimum, are often used to predict the amplitude of the cycle at (or before) the onset of the cycle. We examine Cycle 25 predictions produced by these precursors. The geomagnetic precursor indicated a Cycle 25 slightly stronger that Cycle 24, with a maximum of 132 +/- 8. The Sun's magnetic precursors indicated that Cycle 25 would be more similar to Cycle 24, with a maximum sunspot number of 120 +/- 10 or 114 +/- 15. Combining the curve-fitting results with the precursor predictions, we conclude that Cycle 25 will have a maximum smoothed sunspot number of 134 +/- 8 with maximum occurring late in the fall of 2024. Models for predicting the Sun's magnetic field ahead of minimum, were generally successful at predicting the polar precursors years in advance. The fact that Sun's magnetic precursors at cycle minimum were successfully predicted years before minimum and that the precursors are consistent with the size of Cycle 25 suggests that we can now reliably predict the solar cycle.

Solar Hysteresis Pattern and Spectral Components in TEC Time Series (GPS and TIE‐GCM) of the Quadrilaterally Coupled Geomagnetic Conjugate Low‐latitude Stations

Abstract: The current study is a first-of-its-kind in that it compares the Total Electron Content (TEC) of the solar cycle from the Global Positioning System (GPS) and Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) over the geomagnetically conjugate low-latitude stations with the particular scenario of lower atmospheric conditions over land- and sea-locked locations. For this, TEC data for the period 2009-2017 is used from northern hemispheric stations Varanasi (25.31⁰N; 82.97⁰E) and LHAZ (29.65⁰N; 91.10⁰E) and southern hemispheric stations DGAR (7.27⁰S; 72.37⁰E) and COCO Island (12.18⁰S; 96.83⁰E).The solar cycle variation in TEC is identified by two distinct maxima and hysteresis between the ascending and descending phases. The solar cycle trends are modulated by the equatorial ionization anomaly as well as longitudinal biases. The Lomb-Scargle periodogram shows that the improved TIE-GCM version 2.0, which incorporates variable eddy diffusion to provide an accurate simulation of seasonal variability, is largely successful in simulating semi-annual and annual oscillations but still needs to resolve the seasonal anomaly feature, particularly in the case of southern low latitude stations. Terannual (120-day) and 1.4-year (500-day) periodicities in the TEC time series are observed only at EIA region stations, not at off-crest location LHAZ, and are most likely caused by E x B drift. The wavelet coherence analysis reveals that the Quasi Biannual Oscillations (QBO) in the TEC time series (597-, 773-, and 930-day) have a strong physical affinity with the QBO oscillation of F10.7 flux. Results indicate that both solar activity and equatorial electrodynamics significantly influence the QBO oscillation in the TEC. This article is protected by copyright. All rights reserved.

Quasi-periodic Variations of Coronal Mass Ejections with Different Angular Widths

Abstract: Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.

Hale cycle in solar hemispheric radio flux and sunspots: Evidence for a northward-shifted relic field

Abstract: Solar and heliospheric parameters can depict notable differences between the northern and southern hemisphere. Although hemispheric asymmetries of some heliospheric parameters vary systematically with Hale cycle, this is not common for solar parameters. Also, no physical mechanism exists which can explain systematic hemispheric asymmetries. We use a novel method of high heliolatitudes to increase the fraction of one hemisphere in solar 10.7cm radio fluxes and sunspot numbers. We calculate sets of hemispheric high-latitude radio fluxes and sunspot numbers with increasing heliographic latitude during the last 75 years. We also normalise these fluxes by yearly means in order to study their continuous variation. We find that cycle maximum radio fluxes and sunspot numbers in each odd cycle (19, 21, 23) are larger at northern high latitudes, while in all even cycles (18, 20, 22 24) they are larger at southern latitudes. This alternation indicates a new form of Hale cycle variation in solar activity. Hemispheric differences at cycle maxima are 15% for radio flux and 23% for sunspot numbers. The difference is largest during cycle 19 and smallest in cycle 24. Continuous fluxes depict a Hale cycle in both hemispheres, with an opposite phase and amplitude of 5% in north and 4% in south. Hemispheric Hale cycle can be explained if there is a northward directed relic magnetic field, which is shifted northward. In odd cycles, the northern hemisphere is enhanced more than the southern hemisphere and, in even cycles, the northern hemisphere is reduced more than the southern hemisphere. The decrease of asymmetry during the 7 cycles can be explained if the relic shift oscillates at the 210-year Suess/deVries period. Gleissberg cycle consists of one off-equator excursion of the relic. Relic field in the Sun also offers a possibility for century-scale forecasting of solar activity.

Discovery of a relation between the decay rate of the Sun's magnetic dipole and the growth rate of the following sunspot cycle: a new precursor for solar cycle prediction

Abstract: Sunspots have been observed for over four centuries and the magnetic nature of sunspot cycles has been known for about a century: however, some of its underlying physics still remain elusive. It is known that the solar magnetic cycle involves a recycling of magnetic flux between the poloidal and toroidal components of the magnetic field, that manifests as the solar dipole and sunspots, respectively. Here we report the discovery of a new relationship between the rise rate of the sunspot cycle and the decay rate of the solar (axial) dipole moment. We argue that this points to the existence of a causal connection between the aforementioned physical quantities -- providing an extension to the Waldmeier effect: namely, the decay rate of the Sun's dipole moment is related to the rate of rise and eventual amplitude of the following sunspot cycle. We demonstrate how one may take advantage of this new relationship to predict the amplitude and timing of the sunspot cycle. Our analysis indicates solar cycle 25 is going to be a weak-moderate cycle, peaking in \(2024.00_{-0.49}^{+0.68} \).

Double Superposed Epoch Analysis of Geomagnetic Storms and Corresponding Solar Wind and IMF in Solar Cycles 23 and 24

Abstract: The weakest solar cycle 24 (SC24, 2010–2019) in 100 years was 1/3rd less active compared to the previous solar cycle 23 (SC23, 1996–2009). We identify 135 and 61 ICME (interplanetary coronal mass ejection) driven clear geomagnetic storms (DstMin ≤ −50 nT) in SC23 and SC24, respectively, giving a reduction of 55% storms in SC24, and present the double superposed epoch analysis (DSEA) of the storms/activities in SC23 and SC24 using the Dst, symmetric H (SymH), Kp and AE indices. The DSEA method for the corresponding solar wind velocity V, north-south component of the interplanetary magnetic field (IMF Bz) and the product VBz are also presented. Compared to SC23, the maximum storm/activity intensity in SC24 reduces by 52%, 12%, and 45% at low, mid and high latitudes and the corresponding maxima in -VBz, V, and -Bz reduce by 39%, 17%, and 38%, respectively. The epoch average storm/activity intensity reduces by 27%, 11%, and 4% at low, mid and high latitudes and average maxima in -VBz, V, and -Bz reduce by 24%, 14%, and 13%, respectively. The results seem to reveal that the average reduction in the main driver -VBz (∼24%) might have caused nearly the same and equal average storm/activity intensity reductions in all latitudes (∼25%), though the irregular nature of the AE index makes the reduction very small (4%) at high latitudes, and small (∼11%) at mid latitudes mainly due to the small (0–9) quasi logarithmic scale of the Kp index.

Evaluation of total electron content derived from the spaceborne receivers of GRACE/GRACE-FO missions

Abstract: The Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission GRACE-FO are gravity satellites jointly developed by the National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR), which are composed of two satellites. Such tandem satellite missions provide us with a good opportunity to evaluate the ionospheric total electron content (TEC) derived from their onboard global positioning system (GPS) receivers. In addition, the K-band ranging system (KBR) between two satellites provides also the in-situ electron density (Ne) at the satellite orbits, which can help further to evaluate the reliability of TEC. By combing the observations from GRACE and GRACE-FO, 20 years of data (from 2002 to 2022) have been accumulated to analyze the solar cycle dependence of TEC and Ne at the topside ionosphere. Our results show that the TEC from the tandem satellites is generally the same, but slight differences can still be found, showing solar cycle and local time dependences. In addition, we found that the TEC differences between the tandem satellites of GRACE are somehow smaller than that of GRACE-FO, and the consistency between the TEC and inter-satellite electron density results of GRACE is also better.

Solar Flux Effects on the Variations of Equatorial Electrojet (EEJ) and Counter-Electrojet (CEJ) Current across the Different Longitudinal Sectors during Low and High Solar Activity

Abstract: This study examined the effect of solar flux (F10.7) and sunspots number (R) on the daily variation of equatorial electrojet (EEJ) and morning/afternoon counter electrojet (MCEJ/ACEJ) in the ionospheric E region across the eight longitudinal sectors during quiet days from January 2008 to December 2013. In particular, we focus on both minimum and maximum solar cycle of 24. For this purpose, we have collected a 6-year ground-based magnetic data from multiple stations to investigate EEJ/CEJ climatology in the Peruvian, Brazilian, West & East African, Indian, Southeast Asian, Philippine, and Pacific sectors with the corresponding F10.7 and R data from satellites simultaneously. Our results reveal that the variations of monthly mean EEJ intensities were consistent with the variations of solar flux and sunspot number patterns of a cycle, further indicating that there is a significant seasonal and longitudinal dependence. During the high solar cycle period, F10.7 and R have shown a strong peak around equinoctial months, consequently, the strong daytime EEJs occurred in the Peruvian and Southeast Asian sectors followed by the Philippine regions throughout the years investigated. In those sectors, the correlation between the day Maxima EEJ and F10.7 strengths have a positive value during periods of high solar activity, and they have relatively higher values than the other sectors. A predominance of MCEJ occurrences is observed in the Brazilian (TTB), East African (AAE), and Peruvian (HUA) sectors. We have also observed the CEJ dependence on solar flux with an anti-correlation between ACEJ events and F10.7 are observed especially during a high solar cycle period.

Characteristics of Different Groups of Flare-CME in the Minimum to Rising Phase of Solar Cycle 24

Abstract: Coronal Mass Ejections are significant solar events that involve intense explosions of magnetic fields and mass particles out from the corona. As the hot plasma are brought by the solar wind into the Earth’s magnetosphere, geomagnetic storm is generated and causing malfunctions in telecommunication and power systems. This study is aimed to investigate the distribution of flare-CMEs characteristics which occurred at the beginning phase of solar cycle 24, from Dec. 2008 until Dec. 2013. In the analysis, all events are classified according to their class of flares associated with the CMEs. The CMEs that are accompanied by A, B, and C flares are categorized as low group flare-CME, while CMEs with M and X flares are placed under high group flare-CME. Afterwards, they are analyzed to observe the distribution of their main CME properties; velocity, acceleration and angular width. At the end of the study, we found that velocity and angular width are the two properties that have high influential for high and low groups, with R value of 0.36 and 0.67, respectively. Most of high group flare-CMEs showed up in 360° as well as low group flare-CMEs if the associated minor flares lasted longer than 30 min. Furthermore, the speed range of 360° high and low class flare-CME cannot be defined from the results since all of them propagated at fluctuating velocity. Hence, it is believed that full halo CMEs have no velocity boundary as they can travel from 500 km/s and go beyond 2500 km/s.

Prediction of even and odd sunspot cycles: implications for cycles 25 and 2

Abstract: Prediction of sunspots has been an everlasting interest in the space science community since the discovery of the sunspot cycle. The sunspot number is an indirect indicator of many different solar phenomena, e.g., total and spectral solar radiation, coronal mass ejections, solar flares and magnetic active regions. Its cyclic variation can even be used as a pacemaker to time different aspects of solar activity, solar wind and resulting geomagnetic variations. Therefore, there is considerable practical interest in predicting the evolution of future sunspot cycle(s). This is especially true in today’s technological society where space hazards pose a significant threat, e.g., to satellites, communications and electric grids on ground have been recognized. Another interest to predicting sunspots arises from the relatively recently recognized influences of variable solar radiation and solar wind activity on Earth’s climate system.There are a variety of methods developed for predicting sunspots ranging from statistical methods to intensive physical simulations. Some of the most successful, yet relatively simple, methods are based on finding precursors that serve as indicators for the strength of the coming solar cycle. These methods are often based on statistics of all past solar cycles. However, most of these methods do not typically take into account the 22-year Hale cycle of solar magnetism, which is well known in different solar and geomagnetic phenomena.Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well described by a simple parameterized mathematical expression. We find that the parameters describing even sunspot cycles can be predicted quite accurately using the sunspot number 41 months prior to sunspot minimum as a precursor. The parameters of the odd cycles can be best predicted with geomagnetic maximum geomagnetic aa index close to fall equinox within a 3-year window preceding the sunspot minimum. Cross-validated hindcasts indicate that our method has a very good prediction accuracy. For the coming sunspot cycle 25 we predict an amplitude of 171 +/- 23 and the end of the cycle in September 2029 +/- 1.9 years. We are also able to make a rough prediction for cycle 26 based on the predicted cycle 25. While the uncertainty for the cycle amplitude is large we estimate that the cycle 26 will likely be stronger than cycle 25. These results suggest an increasing trend in solar activity for the next two decades.

Variation of Small Scale Magnetic Fields Over a Century using Ca-K Images as Proxy

Abstract: A combined uniform and long-time series of Ca-K images from the Kodaikanal Observatory (KO), Mount Wilson Observatory (MWO), and Mauna Loa Solar Observatory (MLSO) were used to identify and study the Ca-K small-scale features and their solar cycle variations over a century. The small scale features are classified into three distinct categories: enhanced network (EN), active network (AN), and quiet network (QN). All these features show that their areas vary according to the 11-year solar cycle. The relative amplitude of the Ca-K network variations agree with that of the sunspot cycle. The total area of these small-scale features varies from about 5% during the minimum phase of the solar cycle to about 20% during its maximum phase. Considering the average intensity and the amplitude of their area variations, we find that the total contribution of EN, AN and QN to the irradiance variation of the Sun is about 3%.

Statistical Study of the Correlation between Solar Energetic Particles and Properties of Active Regions

Abstract: The flux of energetic particles originating from the Sun fluctuates during the solar cycles. It depends on the number and properties of Active Regions (ARs) present in a single day and associated solar activities, such as solar flares and coronal mass ejections (CMEs). Observational records of the Space Weather Prediction Center (SWPC NOAA) enable the creation of time-indexed databases containing information about ARs and particle flux enhancements, most widely known as Solar Energetic Particle events (SEPs). In this work, we utilize the data available for Solar Cycles 21-24, and the initial phase of Cycle 25 to perform a statistical analysis of the correlation between SEPs and properties of ARs inferred from the McIntosh and Hale classifications. We find that the complexity of the magnetic field, longitudinal location, area, and penumbra type of the largest sunspot of ARs are most correlated with the production of SEPs. It is found that most SEPs ($\approx$60\%, or 108 out of 181 considered events) were generated from an AR classified with the 'k' McIntosh subclass as the second component, and these ARs are more likely to produce SEPs if they fall in a Hale class containing $\delta$ component. The resulting database containing information about SEP events and ARs is publicly available and can be used for the development of Machine Learning (ML) models to predict the occurrence of SEPs.

The 25 solar cycle become higher than the predicted model

Abstract: What was this model talking about? That the 24 and 25 solar cycles will be almost similar in their strength. 1.8 years have passed since the beginning of the 25th cycle (September 2020). And already the events of the last 3-4 months of the growth phase, especially March 2022, force us to overestimate previously made forecasts for the 25th cycle. According to the website http://spaceweather.com/ for 05.04.2022, “in March 2022 alone, 146 solar flares occurred, including 1 X-class flare and 13 M- class flares.” The flare formula for this March, according to the Brussels Observatory, was 193/11/1 (C/M/X class flares). In addition, the Wolf number obtained in Brussels in March had a value of W78.4, which is more than for the same period in cycle 24 (March 2011 W56.2). The flare formula for March 2011 is 186/21/1. A comparison of the Wolf Numbers for the 2011 and 2022 gives reason to conclude that cycle 25 becomes higher than the predicted model.

Extreme Geomagnetic Disturbances (GMDs) Observed in Eastern Arctic Canada: Occurrence Characteristics and Solar Cycle Dependence

Abstract: Extreme (≥ 20 nT/s) geomagnetic disturbances (GMDs, also denoted as MPEs - magnetic perturbation events) – impulsive nighttime disturbances with time scale ~5-10 min, have sufficient amplitude to cause bursts of geomagnetically induced currents (GICs) that can damage technical infrastructure. In this study we present occurrence statistics for extreme GMD events from five stations in the MACCS and AUTUMNX magnetometer arrays in Arctic Canada at magnetic latitudes ranging from 65° to 75°. We report all large (≥ 6 nT/s) and extreme GMDs from these stations from 2011 through 2022 to analyze variations of GMD activity over a full solar cycle and compare them to those found in three earlier studies. GMD activity between 2011 and 2022 did not closely follow the sunspot cycle, but instead was lowest during its rising phase and maximum (2011-2014) and highest during the early declining phase (2015-2017). Most of these GMDs, especially the most extreme, were associated with high-speed solar wind streams (Vsw > 600 km/s) and steady solar wind pressure. All extreme GMDs occurred within 80 min after substorm onsets, but few within 5 min. Multistation data often revealed a poleward progression of GMDs, consistent with a tailward retreat of the magnetotail reconnection region. These observations indicate that extreme GIC hazard conditions can occur for a variety of solar wind drivers and geomagnetic conditions, not only for fast-coronal mass ejection driven storms.

The First AGILE Solar Flare Catalog

Abstract: We report the Astro-rivelatore Gamma a Immagini LEggero (AGILE) observations of solar flares, detected by the onboard anticoincidence system in the 80–200 keV energy range, from 2007 May 1 to 2022 August 31. In more than 15 yr, AGILE detected 5003 X-ray, minute-lasting transients, compatible with a solar origin. A cross-correlation of these transients with the Geostationary Operational Environmental Satellites (GOES) official solar flare database allowed us to associate an intensity class (i.e., B, C, M, or X) to 3572 of them, for which we investigated the main temporal and intensity parameters. The AGILE data clearly revealed the solar activity covering the last stages of the 23rd cycle, the whole 24th cycle, and the beginning of the current 25th cycle. In order to compare our results with other space missions operating in the high-energy range, we also analyzed the public lists of solar flares reported by RHESSI and Fermi Gamma-ray Burst Monitor. This catalog reports 1424 events not contained in the GOES official data set, which, after statistical comparisons, are compatible with low-intensity, short-duration solar flares. Besides providing a further data set of solar flares detected in the hard X-ray range, this study allowed to point out two main features: a longer persistence of the decay phase in the high-energy regime, with respect to the soft X-rays, and a tendency of the flare maximum to be reached earlier in the soft X-rays with respect to the hard X-rays. Both these aspects support a two-phase acceleration mechanism of electrons in the solar atmosphere.

A Hybrid CNN-LSTM Model for Predicting Solar Cycle 25

Abstract: The solar cycle is linked to the number of sunspots and follows the fluctuations of the Sun’s magnetic field. It can have powerful global impacts on the Earth. Thus, predicting the timing and amplitude of the peak of the incoming solar cycle 25 is of great importance. This study uses a hybrid deep learning convolutional neural network (CNN) - long short-term memory (LSTM) model and the observed 13-month smoothed sunspot numbers to predict Solar Cycle 25. Here it is shown for the first time that the MinMax normalization method substantially reduces the error of the CNN-LSTM model’s solar cycle predictions compared to the Standard Deviation normalization method. The results also suggest that it is best to use four historical solar cycles to predict the future solar cycle. The predicted Solar Cycle 25 has a 13-month smoothed peak amplitude similar to that of Solar Cycle 24. The predicted Solar Cycle 25 peak spans a relatively long period of time between approximately August 2023 and July 2024.

What do halo CMEs tell us about solar cycle 25?

Abstract: It is known that the weak state of the heliosphere due to diminished solar activity in cycle 24 back-reacted on coronal mass ejections (CMEs) to make them appear wider for a given speed. One of the consequences of the weak state of the heliosphere is that more CMEs appear as halo CMEs (HCMEs), and halos are formed at shorter heliocentric distances. Current predictions for the strength of solar cycle (SC) 25 range from half to twice the strength of SC 24. We compare the HCME occurrence rate and other properties during the rise phase of cycles 23, 24, and 25 to weigh in on the strength of SC 25. We find that HCME and solar wind properties in SC 25 are intermediate between SCs 23 and 24, but closer to SC 24. The HCME occurrence rate, normalized to the sunspot number, is higher in SCs 24 and 25 than in SC 23. The solar wind total pressure in SC 25 is ~35% smaller than that in SC 23. Furthermore, the occurrence rates of high-energy solar energetic particle events and intense geomagnetic storms are well below the corresponding values in SC 23, but similar to those in SC 24. We conclude that cycle 25 is likely to be similar to or slightly stronger than cycle 24, in agreement with polar-field precursor methods for cycle 25 prediction

Charting the solar cycle variation of the climate of space weather and its impacts

Abstract: Sunspot records reveal that whilst the sun has an approximately 11 year cycle of activity, no two cycles are of the same duration. Since this activity is a direct driver of space weather at earth, this presents an operational challenge to quantifying space weather risk. We recently showed [1,2] that the Hilbert transform of the sunspot record can be used to map the variable cycle length onto a regular 'clock' where each cycle has the same duration in Hilbert analytic phase.  Extreme geomagnetic storms rarely occur within the quiet part of the cycle which is a fixed interval of analytic phase on the clock; there is a clear active-quiet switch-off and quiet-active switch-on of activity. Some of the most extreme geomagnetic storms have occurred just at the switch-on time, rather than at solar maximum, so that determining when this will occur could provide guidance on planning and preparedness which necessarily must balance resilience against cost. Here [3] we show how the times of the switch-on/off can be determined directly from the sunspot time-series, without requiring a Hilbert transform.  We propose a method- charting- that can be used to combine observations, and both historical and current reports of societal impacts, to improve our understanding of space weather risk.[1] S. C. Chapman, S. W. McIntosh, R. J. Leamon, N. W. Watkins, Quantifying the solar cycle modulation of extreme space weather, Geophysical Research Letters, (2020) doi:10.1029/2020GL087795[2] S. C. Chapman, S. W. McIntosh, R. J. Leamon, N. W. Watkins, The Sun's magnetic (Hale) cycle and 27 day recurrences in the aa geomagnetic index. Ap. J. (2021) doi: 10.3847/1538-4357/ac069e[3] S. C. Chapman, Charting the Solar Cycle, Front. Astron. Space Sci. - Space Physics, in press (2022) doi: 10.3389/fspas.2022.103709

The First AGILE Solar Flare Catalog

Abstract: We report the Astrorivelatore Gamma ad Immagini LEggero (AGILE) observations of solar flares, detected by the on board anticoincidence system in the 80-200 keV energy range, from 2007 May 1st to 2022 August 31st. In more than 15 yr, AGILE detected 5003 X-ray, minute-lasting transients, compatible with a solar origin. A cross-correlation of these transients with the Geostationary Operational Environmental Satellites (GOES) official solar flare database allowed to associate an intensity class (i.e., B, C, M, or X) to 3572 of them, for which we investigated the main temporal and intensity parameters. The AGILE data clearly revealed the solar activity covering the last stages of the 23rd cycle, the whole 24th cycle, and the beginning of the current 25th cycle. In order to compare our results with other space missions operating in the high-energy range, we also analyzed the public lists of solar flares reported by RHESSI and Fermi Gamma-ray Burst Monitor. This catalog reports 1424 events not contained in the GOES official dataset, which, after statistical comparisons, are compatible with low-intensity, short-duration solar flares. Besides providing a further dataset of solar flares detected in the hard X-ray range, this study allowed to point out two main features: a longer persistence of the decay phase in the high-energy regime, with respect to the soft X-rays, and a tendency of the flare maximum to be reached earlier in the soft X-rays with respect to the hard X-rays. Both these aspects support a two-phase acceleration mechanism of electrons in the solar atmosphere.

Variation of small scale magnetic fields over a century using Ca-K images as proxy

Abstract: A combined uniform and long-time series of Ca-K images from the Kodaikanal Observatory (KO), Mount Wilson Observatory (MWO), and Mauna Loa Solar Observatory (MLSO) were used to identify and study the Ca-K small-scale features and their solar cycle variations over a century. The small scale features are classified into three distinct categories: enhanced network (EN), active network (AN), and quiet network (QN). All these features show that their areas vary according to the 11-year solar cycle. The relative amplitude of the Ca-K network variations agree with that of the sunspot cycle. The total area of these small-scale features varies from about 5% during the minimum phase of the solar cycle to about 20% during its maximum phase. Considering the average intensity and the amplitude of their area variations, we find that the total contribution of EN, AN and QN to the irradiance variation of the Sun is about 3%.

Solar Cycle 25 Prediction Using N-BEATS

Abstract: Solar activities lead to Sun variation with an 11 yr periodicity. The periodic variation affects space weather and heliophysics research. So it is important to accurately predict solar cycle variations. In this paper, we predicted the ongoing Solar Cycle 25 using neural basis expansion analysis for the interpretable time series deep learning method. 13 months of smoothed monthly total sunspot numbers taken by sunspot Index and Long-term Solar Observations are selected to train and evaluate our model. We used root mean square error (RMSE) and mean absolute time lag (MATL) to evaluate our model performance. RMSE and MATL measure the difference between our predicted values and the actual values along the Y- and X-axis, respectively. The RMSE value is 26.62 ± 1.56 and the MATL value is 1.34 ± 0.35, demonstrating that our model is able to better predict sunspot number variation. Finally, we predicted the variation of the sunspot numbers for Solar Cycle 25 using the model. The sunspot number of Solar Cycle 25 will peak around 2024 February with an amplitude of 133.9 ± 7.2. This means that Solar Cycle 25 will be slightly more intense than Solar Cycle 24.

Comprehensive analysis of the ionospheric response to the largest geomagnetic storms from solar cycle 24 over Europe

Abstract: A multi-instrumental analysis of the meridional ionospheric response is presented over Europe during the two largest ICME-driven geomagnetic storms of solar cycle #24 maximum. Data from 5 European digisonde stations, ground-based Global Navigation Satellite System, Total Electron Content (GNSS TEC), the ratio of the TEC difference (rTEC), as well as Swarm and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite observations have been used for the investigation of selected intervals (11–17 November, 2012, and 16–25 March, 2015). The storm evolution is monitored by digisonde foF2 critical frequency (related to the maximum electron density of F2-layer) and GNSS TEC data. Moreover, Global Ultraviolet Imager (GUVI) measurements from the TIMED satellite are used to investigate the changes in the thermospheric O/N2 ratio. Our main focus was on the main phase of the geomagnetic storms, when during the nighttime hours extremely depleted plasma was detected. The extreme depletion is observed in foF2, TEC and rTEC, which is found to be directly connected to the equatorward motion of the midlatitude ionospheric trough (MIT) on the nightside. We demonstrate a method (beside the existing ones) which allows the monitoring of the storm-time evolution of the disturbances (e.g., MIT, SAPS, SED) in the thermosphere-ionosphere-plasmasphere system by the combined analysis of the worldwide digisonde system data (with the drift measurements and the ionospheric layer parameters with 5–15 min cadence), with rTEC and GNSS TEC data, and with the satellite data like Swarm, TIMED/GUVI.

An Overview of Solar Radio Type II Bursts through analysis of associated solar and near Earth space weather features during Ascending phase of SC 25

Abstract: Abstract. Type II solar radio bursts are the signatures of particle acceleration caused by shock waves in the solar atmosphere and interplanetary space. Being electromagnetic radiation that travel at the speed of light, they can serve as ground observed data to provide early notice of incoming solar storm disturbances. An observational overview of 31 Type II bursts which occurred in the period between May 2021 to December 2022 is made. We analyzed associated parameters such as bandwidth, drift rates, starting frequency to evaluate their dynamical parameters such as the shock and Alfvén speeds to estimate the Alfvén Mach number as well as the coronal magnetic field strength using Rankine-Hugoniot relation. We also evaluated accompanying space weather implication in terms of ionospheric total electron content (TEC) enhancement. At heliocentric distance ∼ 1−2 R⊙, the shock and the Alfvén speeds are in the range 504–1301 km s−1 and 368–837 km s−1, respectively. The Alfvén Mach number is of the order of 1.2 ≤ MA ≤ 1.8 at the same heliocentric distance, and the magnetic field strength shows excellent consistency and could be fit with a single power-law distribution of the type B(r) = 6.56 r −3.92 G. The study finds that 15/31 type II radio bursts are associated with some aspects of space weather such as radio blackouts and/or polar cap absorption events, that are the signature of solar proton enhancement and solar energetic particle events. Observed and analyzed Type II events correlated well with observed ionospheric storm indicated by the TEC enhancement. The findings from this study indicate that through analysis of type II SRBs observed from the ground and their physical features characteristics, it is possible to monitor the current progress of solar cycle 25 and predict the intensity of associated space weather phenomena.

Forecasting Solar Cycle 25 with Physical Model-Validated Recurrent Neural Networks

Abstract: Abstract The Sun’s activity, which is associated with the solar magnetic cycle, creates a dynamic environment in space known as space weather. Severe space weather can disrupt space-based and Earth-based technologies. Slow decadal-scale variations on solar-cycle timescales are important for radiative forcing of the Earth’s atmosphere and impact satellite lifetimes and atmospheric dynamics. Predicting the solar magnetic cycle is therefore of critical importance for humanity. In this context, a novel development is the application of machine-learning algorithms for solar-cycle forecasting. Diverse approaches have been developed for this purpose; however, with no consensus across different techniques and physics-based approaches. Here, we first explore the performance of four different machine-learning algorithms – all of them belonging to a class called Recurrent Neural Networks (RNNs) – in predicting simulated sunspot cycles based on a widely studied, stochastically forced, nonlinear time-delay solar dynamo model. We conclude that the algorithm Echo State Network (ESN) performs the best, but predictability is limited to only one future sunspot cycle, in agreement with recent physical insights. Subsequently, we train the ESN algorithm and a modified version of it (MESN) with solar-cycle observations to forecast Cycles 22 – 25. We obtain accurate hindcasts for Solar Cycles 22 – 24. For Solar Cycle 25 the ESN algorithm forecasts a peak amplitude of 131 ± 14 sunspots around July 2024 and indicates a cycle length of approximately 10 years. The MESN forecasts a peak of 137 ± 2 sunspots around April 2024, with the same cycle length. Qualitatively, both forecasts indicate that Cycle 25 will be slightly stronger than Cycle 24 but weaker than Cycle 23. Our novel approach bridges physical model-based forecasts with machine-learning-based approaches, achieving consistency across these diverse techniques.