Sunspot numbers and spotless days around solar minimum

This study examines the relationship between solar activity (Sunspot Number) (SSN) and geomagnetic indices (Kp and Ap) using time-series decomposition, distribution analysis, and correlation analysis. The results show an inverse relationship between Kp, Ap, and SSN up to 1990, followed by a strong positive correlation thereafter. Distribution analysis indicates that SSN is dominated by low-frequency components, whereas Kp and Ap capture both long-term trends and shorter-term variations, such as the ~ 27-day solar rotation cycle. Correlation analysis reveals weak overall correlations but strong trend correlations, particularly during the 12:00–15:00 UT interval for Kp and Ap with SSN.

Abstract The Sun exhibits an 11 yr cyclic variation, maintained by dynamo action in the solar interior. Mean-field flux transport dynamo models have successfully reproduced most of the features observed in solar cycles, while the model includes many free parameters, such as the speed of the meridional flow and the amplitude of the poloidal field generation. Inferring these free parameters is on demand because they correspond to the solar interior condition. We suggest a novel method for inferring the free parameters using a genetic algorithm. At each generation, we evaluate the fitness of our simulation against the observational data and optimize the parameters. We apply our method to the observed solar cycle data from 1723 to 2024 and successfully reproduce the observations from both qualitative and quantitative perspectives. We expect our method to be applicable to sunspot numbers, even those obtained from isotope data and historical documents, in the future, to better understand past solar interior dynamics.

The present study used the solar radio flux (F10.7 cm) and the sunspot number (SSN) created throughout five years, beginning in December 2019 and ending in December 2023, for the solar cycle 25. The number of sunspots and the solar radio flux were measured monthly using data from the WDC-SILSO, Royal Observatory of Belgium, Brussels. A five-year link between the two variables was constructed, marking the start of the solar cycle 25 (2019 to 2023) years. Understanding their relationship and the degree to which they impact solar activity, which affects terrestrial and space technology, is also important. For sunspots, the highest value reached (127.6) in 2023, while the lowest value (1.8) was attained in 2019. With time, the value increased like the number of spots, rising and falling until it achieved its maximum value over the course of the five years (159.1 radio flux number) in 2023. Both serve as markers for rising and falling solar activity levels. Through statistical analysis and graphs for each of them that depict the pattern of solar activity for that time period, this study demonstrated the strong, persistent association between the number of sunspots and solar radio flux. Additionally, helpfully, the rising phases of the solar cycles 24 and 25 were compared over the same period, including the first five years. This forecasts what the 25th cycle's supplemental chart will look like for the next five years.

Problems of modern climate change and assessment of their consequences IPCC (2021-2023) according to the latest assessment reports, there is an increase in dangerous weather phenomena that cause significant social and economic damage in various regions of the Earth. In this article, various climatic factors affecting the state of dust storm formation associated with modern climate change were studied. It was established that the longest (72 hours) duration of dust storms at the Aral Sea station in the southern region of Kazakhstan in the period from 2005 to 2022 was recorded in May 2018. The values of meteoparameters at that time, that is, its dependence on weather conditions, quantitative indicators of solar activity (Wolf number), bioclimatic indicators, as well as the conditions of macrocirculation formation, were considered, and it turned out that there was an important correlation relationship between the number of days when dust storms were most observed and the Wolf number (r=1.00), Wangenheim-GIRs circulation forms, including the e Form (r=0.49), El- Niño indices (r=0.47 as a result of the analysis, it was determined that the prolonged Obser ation of dust storms was associated with the north-western cold front.

IC 10 is a dwarf galaxy in Cassiopeia, located at a distance of 660 kpc, and hosts a young stellar population, a large number of Wolf–Rayet stars, and a large number of massive stars in general. Utilizing a series of 11 Chandra observations (spanning 2003–2021, with a total exposure of 235.1 ks), 375 point sources of X-ray emission were detected. Similar studies have been conducted earlier in the central region of IC 10. Here, we consider all regions covered by Chandra-ACIS. By comparing our catalog of X-ray sources with a published optical catalog, we found that 146 sources have optical counterparts. We also created a list of 60 blue supergiant (SG) candidates with X-ray binary (XRB) companions by using an optical color–magnitude selection criterion to isolate the blue SGs. Blue SG-XRBs form a major class of progenitors of double-degenerate binaries. Hence, their numbers are an important factor in modeling the rate of gravitational-wave sources. Identifying the nature of individual sources is necessary as it paves the way toward a comprehensive census of XRBs in IC 10, thus enabling meaningful comparisons with other Local Group galaxies exhibiting starbursts, such as the Magellanic Clouds.

Abstract From 2002 to 2025, the Hubble Space Telescope’s Advanced Camera for Surveys has suffered in the harsh radiation environment above the protection of the Earth’s atmosphere. We track the degradation of its image quality, as Solar protons and galactic cosmic rays have damaged its photosensitive charge-coupled device (CCD) imaging sensors. The rate of damage in low Earth orbit is modulated by $18.5^{+4.5}_{-0.5}$ per cent during an 11 year Solar cycle, peaking $430^{+11}_{-5}$ days after Solar minimum as recorded in the number of sunspots. The type of damage is consistent with defects in the silicon lattice that have all stabilised into one of three configurations. We also present the open-source Algorithm for Charge Transfer Inefficiency correction (ArCTIc) v7, available from https://github.com/jkeger/arctic. This models the (instantaneous or gradual) capture of photoelectrons into lattice defects, and their release after (a discrete set or continuum of) characteristic time delays, which creates spurious trailing in an image. Calibrated using the trailing of hot pixels, and applied during post-processing of astronomical images, ArCTIc can correct 99.5 % of Charge Transfer Inefficiency trailing averaged over the camera’s lifetime, and 99.9 % of trailing in the worst-affected recent data.

Abstract The low‐Earth orbit Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) instruments, spanning 1995–2023, have spatiotemporal patterns within their metadata that are consistent with the South Atlantic Anomaly (SAA). While the SAA had a known influence on these instruments, this study details new variability and impacts. A large volume of radiation‐triggered events can cause the First‐In First‐Out (FIFO) buffer overflow to occur, which temporarily “blinded” LIS and OTD. Patterns of FIFO and the instrument status flags displayed an evolving intensity and areal extent of SAA interference, affecting climatological view‐time records. The interference had a strong relationship to the sunspot number with Pearson correlation values of −0.50 and −0.48 ( p < 0.0001 for both) for the view‐time anomaly and FIFO occurrence, respectively, over the entire record. For the LIS instruments, the size of the affected region was zero in their early respective records then peaked at millions of square kilometers during solar minimum. LIS on the Tropical Rainfall Measuring Mission (TRMM, TLIS) observed a seasonal cycle with the worst interference during the JJA season and least during DJF. All three instruments found a westward drift of the SAA, at 0.54° y −1 , 0.22° y −1 , and 0.70° y −1 for TLIS, OTD, and International Space Station LIS (ILIS), respectively. However, while both LIS instruments noted a northward drift, OTD had a southward drift. The influence of external factors including the thermosphere, properties of the radiation, orbital characteristics, and hardware degradation remain to be examined to describe the implications for the SAA itself.

Abstract The rapid development of low‐Earth orbit (LEO) satellites brings increased attention to spacecraft collisions, space debris, orbital decay, and satellite reentry. Neutral density and associated drag force on the satellite orbits elevate space risks, significantly determined by space weather disturbances, particularly geomagnetic storms. On 3 September 2024, the Australian Binar‐2, 3, and 4 satellites were deployed, but their actual lifetimes were only around 2 months, much shorter than designed, only 20% that of the nearly identical Binar 1 satellite launched in 2022. For the first time, we analyze the premature reentries of the Binar‐2, 3, and 4 satellites to unveil the severe space weather impact on their lifetimes, especially the influence of accuracy of medium‐ and long‐term space weather prediction on satellite lifetime designs. Our findings reveal that the premature reentries of Binar‐2, 3, and 4 satellites were caused by enhanced neutral density due to much higher solar and geomagnetic activities than predicted. The actual satellite lifetimes align well with estimations based on observed space parameters, whereas large deviations occur when using predicted parameters. The widely used predictions for medium‐ and long‐term space weather underestimated the F10.7 index and sunspot numbers during Solar Cycle 25 (SC25), especially during the peak time, leading to discrepancies in the designed satellite lifetimes. Our results illustrate the importance of medium‐to long‐term space weather forecasting for the lifespan of LEO satellites.

Abstract The study of solar active regions (ARs) is of central importance to a range of fundamental science, as well as the practical applications of space weather. AR emergence and life cycles are two areas of particular interest, yet the lack of consistent full-Sun observations has made long-term studies of ARs difficult. Here, we present results from a study to identify and characterize long-lived active regions (LLARs), defined as those which were observed during at least two consecutive Carrington rotations and that did not undergo significant successive flux emergence once the decay phase began. Such ARs accounted for 13% of all NOAA-identified ARs between 2011 and 2019, and their distribution closely follows the annual sunspot number. This implies that LLARs are produced by the same basic driving processes as regular ARs. LLAR areas tend to be significantly larger and contain more magnetic flux compared to other ARs, but the two categories have similar magnetic complexity distributions. The most striking result, however, is that LLARs are 3–6 times more likely than other ARs to be the source of a solar flare of GOES class C or greater. This highlights the importance of studying what makes a LLAR and how to identify them at emergence with a view toward improved space weather forecasting. The further implications of these findings for AR heating spatial and temporal patterns will be explored in an upcoming study.

Simplex Projection Predictions of the Remainder of Solar Cycle 25 and the Next Solar Cycle 26 Based on the Monthly Mean Sunspot Numbers

Background:In a previous study, we reported associations between space weather [galactic cosmic rays (GCRs)] and solar and geomagnetic activities (SGAs)] with shorter telomere length in a cohort of elderly men in Massachusetts. Here, we investigated the impact of space weather on epigenetic aging in the same cohort.Methods:We analyzed 1,487 blood DNA methylation measures from 771 older men in the Normative Aging Study (1999–2013). Daily space weather indicators were obtained from NASA including sunspot number (SSN) and interplanetary magnetic field as solar activity parameters, Kp-index as a geomagnetic parameter, and neutron monitors and modeled cosmic ray-induced ionization as measures of GCRs. The 30-day moving average of each parameter was prespecified as the exposure window. Four epigenetic age acceleration metrics, including HorvathAgeAccel, HannumAgeAccel, PhenoAgeAccel, and GrimAgeAccel, were derived, and exploratory epigenome-wide association study (EWAS) and pathway enrichment analyses were conducted.Results:GCRs were associated with accelerated epigenetic aging, whereas SGAs were associated with slower aging. Each interquartile range increase in SSN corresponded to a 0.61-year lower HorvathAgeAccel and 0.50-year lower PhenoAgeAccel, while higher neutron counts were associated with 0.32-year greater HorvathAgeAccel and 0.29-year greater HannumAgeAccel. EWAS identified hundreds of CpGs associated with GCRs (predominantly lower methylation) and thousands with SGAs (predominantly higher methylation), enriched in genome maintenance pathways such as P53 signaling, DNA repair, and inflammatory response, consistent with astronaut studies showing activation of similar stress and repair pathways.Conclusion:Short-term space weather fluctuations were associated with distinct epigenetic aging patterns in blood, suggesting that, as observed in astronauts, terrestrial populations may likewise show biological sensitivity to space weather variability.

Abstract The International Sunspot Number ( Ri ) provides a long-term measure of solar activity. This study compares Ri with sunspot numbers independently derived from Solar and Heliospheric Observatory/Michelson Doppler Imager and Solar Dynamics Observatory/Helioseismic and Magnetic Imager continuum imagery, United States Air Force/National Oceanic and Atmospheric Administration Solar Region Summary reports, and the author’s own white-light observations from 1996 to 2025. Scaling factors ( k ) were determined for each dataset, and monthly values were compared over Solar Cycles 23–25. The results show excellent agreement between Ri and all the independent datasets, with no evidence of the discrepancy reported by L. Svalgaard during 2014–2015. These findings support the consistency of Ri and highlight the reliability of satellite-based sunspot number derivation.

Abstract A new daily composite of the solar flare index (SFI) and the hemispherically‐resolved versions (hSFI) are presented for 1937 to 2024. The data set confirms that the northern hemisphere (NH) dominated solar flare activity during Solar Cycles 17 to 21, but that the southern hemisphere has dominated from Solar Cycle 22 to present. That said, the highest SFI value occurred in the NH during the recent superstorm of May 2024. In sunspot activity, the “Gnevyshev‐Ohl rule” shows that the sum of sunspot numbers during even‐numbered cycles is related to those of adjacent odd‐numbered cycles. A similar rule appears to apply to SFI. The “Gnevyshev gap” phenomenon where solar maximum activity sometimes has two peaks separated by up to 1–2 years of a gap is confirmed for SFI. Although our data set represents the longest continuous daily data set for solar flare activity to‐date, it is known that stronger solar flare events occurred before 1937. Therefore, a brief discussion of earlier solar flare events in the historical record is also provided for context. The statistics of the SFI and hSFI series are compared to other solar and geomagnetic activity indices, including the May and October 2024 solar storms. Statistical analysis of past geomagnetic storms confirms they are more frequent during active cycles and less frequent during solar minima. Strong geomagnetic storms are also more likely to occur during the positive phase of a 1.7 year's quasi‐biennial oscillation in solar activity. The likelihood of low‐magnetic latitude aurorae seems to have a 30 year periodicity component.

Abstract The occurrence of extreme space weather events, and, in particular, severe geomagnetic storms, while rare, can result in disproportionately large societal consequences. Accurate estimates of their likelihood over the timescale of a solar cycle or longer can provide crucial and actionable information for policymakers. In this study, we refine several previous estimates for the probability of extreme geomagnetic storms. In particular, we extend the analysis to show how the probability varies from one cycle to the next. We find that the probability of an extreme event varies by more than two orders of magnitude from the weakest to the strongest cycles observed over the last years. With the most recent sunspot number data suggesting that Cycle 25 is approximately larger than Cycle 24, and comparable to Cycle 20, we estimate that the probability of a Carrington‐level event ( nT) over the next decade will be % ( 95% CI) for a power‐law distribution and % ( 95% CI) for a log‐normal distribution, notably less than the value obtained using data spanning the entire interval over which we have measurements (% ( 95% CI) and % ( 95% CI), respectively).

This study shows the correlation of 705 interplanetary (IP) type II radio bursts detected during the solar cycle (SC) 23, 24, and ascending phase of SC 25 with sunspot number (SSN) and number of flares by class. The results show that 675 (96%) of these bursts were associated with coronal mass ejections (CMEs), while the remaining 30 (4%) were not associated with CMEs. The total number of IP type II bursts was caused by B-class (5), C-class (138), M-class (275), and X-class (124) solar flares, and among them, M- class (51%) flares dominated. We examined the relationship between IP type II bursts and SSN during the ascending phase of all three SCs and found a high correlation between them (correlation coefficients 0.91, 0.98, 0.99, respectively). We found the correlation of the number of IP type II bursts with the number of C, M, and X solar flares, and found that M-class flares showed a strong correlation with IP type II bursts (correlation coefficients 0.76, 0.93, and 0.72, respectively).

Long -Term Relations of Cosmic ray Intensity with Sunspot Numbers and Geomagnetic Activity Parameters During the Period of 2013-2024

Abstract Coronal mass ejections (CMEs), as crucial drivers of space weather, necessitate a comprehensive understanding of their initiation and evolution in the solar corona in order to better predict their propagation. Solar Cycle 24 exhibited lower sunspot numbers compared to Solar Cycle 23, along with a decrease in the heliospheric magnetic pressure. Consequently, a higher frequency of weak CMEs was observed during Solar Cycle 24. Forecasting CMEs is vital, and various methods, primarily involving the study of the global magnetic parameters using data sets like Space-weather Helioseismic and Magnetic Imager Active Region Patches, have been employed in earlier works. In this study, we perform numerical simulations of CMEs within a magnetohydrodynamics framework using Message Passing Interface–Adaptive Mesh Refinement Versatile Advection Code in 2.5D. By employing the breakout model for CME initiation, we introduce a multipolar magnetic field configuration within a background bipolar magnetic field, inducing shear to trigger the CME eruption. Our investigation focuses on understanding the impact of the background global magnetic field on CME eruptions. Furthermore, we analyze the evolution of various global magnetic parameters in distinct scenarios (failed eruption, single eruption, and multiple eruptions) resulting from varying amounts of helicity injection in the form of shear at the base of the magnetic arcade system. Our findings reveal that an increase in the strength of the background poloidal magnetic field constrains CME eruptions. Furthermore, we establish that the growth rate of absolute net current helicity is the crucial factor that determines the likelihood of CME eruptions.

Abstract We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of I Zw 18, a nearby dwarf galaxy with a metallicity of ∼3% solar. Its proximity enables a detailed study of highly ionized gas that can be interpreted in the context of newly discovered high-redshift dwarf galaxies. We derive aperture spectra centered on 11 regions of interest; the spectra show very low extinction, A V ≲ 0.1, consistent with optical determinations. The gas is highly ionized; we have detected 10 fine-structure lines, including [O iv] 25.9 μm with an ionization potential (IP) of ∼55 eV, and [Ne v] 14.3 μm with an IP of ∼97 eV. The ionization state of I Zw 18 falls at the extreme upper end of all of the line ratios we analyzed, but not coincident with galaxies containing an accreting massive black hole (active galactic nucleus). Comparison of the line ratios with state-of-the-art photoionization and shock models suggests that the high-ionization state in I Zw 18 is not due to shocks. Rather, it can be attributed to metal-poor stellar populations with a self-consistent contribution of X-ray binaries or ultra-luminous X-ray sources. It could also be partially due to a small number of hot low-metallicity Wolf−Rayet stars ionizing the gas; a small fraction (a few percent) of the ionization could come from an intermediate-mass black hole. Our spectroscopy also revealed four 14 μm continuum sources, ≳30–100 pc in diameter, three of which were not previously identified. Their properties are consistent with H ii regions ionized by young star clusters.

Abstract Geomagnetic storms produce global variations in the geomagnetic field that are measured at magnetic observatories. Roughly one half of magnetic storms are preceded by sudden increases in the horizontal component of the magnetic field world‐wide. These increases, called storm sudden commencements (SSC), produce geomagnetically induced currents and cause other space weather disturbances whose study is paramount due to the technological dependence of our society. SSC event lists date back to 1868 and provide invaluable information about interplanetary conditions over centennial time scales. Since 1975, the Service of Rapid Magnetic Variations has been responsible for the maintenance and consistency of the SSC list. Here we will review the significant changes in the definition and methods of SSC detection that have been introduced over time and will analyze and discuss whether those changes have affected the homogeneity of the SSC series. Alerted by the greatly reduced number of SSCs in solar cycle 24, we have reanalyzed SSC occurrence in the period 2006–2017. As a result, we found a 26% increase in the number of SSCs, which motivates a change in the adopted SSC definition but leaves the SSC level exceptionally low during this period. We completed the study by examining the relation and dependency of SSCs with solar sunspot numbers and the temporal variation of the horizontal magnetic field.