Solar Activity Research Articles

Differential Responses of Total Ozone Content to Solar Activity Parameters at Two Saudi Arabian Locations

This study examines the correlations between Total Ozone Content (TOC) at two locations in Saudi Arabia—Abha and Jeddah—and various solar activity indicators (sunspot numbers, solar radio flux) and cosmic rays, using data spanning from 1979 to 2023. The research employs correlation analyses and spectral techniques, such as Fast Fourier Transform and wavelet analysis, to explore these relationships.The results reveal significant non-zero correlations between changes in TOC at both Saudi sites and the studied solar activity indicators and cosmic rays, with these correlations varying in strength and significance across different solar cycles and seasons.Spectral analysis suggests the presence of several periodicities in the TOC data from both sites, including cycles of 3.9 years, 2.63 years, 1.65 years, 1.1-1.2 years, 325 days (∼0.88 years), 285-293 days (∼0.78-0.80 years), 273 days (∼0.75 years), 249-232 days (∼0.68 years), and 202-188 days (∼0.52 years). Notable shared periodicities between TOC and solar activity and cosmic rays data include ∼ 2.6 years, 3.8-3.9 years, 1.56 years, 325 days, 273 days, and 166 days.The findings from both correlation and spectral analyses suggest a potential connection between variations in TOC and solar activity at the specific locations studied. This aligns with previous research indicating that increased UV radiation during periods of high solar activity enhances ozone production, particularly at lower latitudes, and that increased magnetic activity reduces the influx of cosmic rays into the heliosphere, impacting atmospheric ionization.

Mediaeval Korean aurora and flood records and Solar activity cycle of ∼200 yr

Mediaeval Korean aurora and flood records and Solar activity cycle of ∼200 yr

Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica

A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction L as a proxy of the spectral index. Here we analyze L from four Antarctic NMs from 2015 March to 2023 September. We have calibrated L from the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015–2019 from the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97–16.6 GV for AMS-02 data, with uncertainty of 0.018 in the daily spectral index as inferred from L. In addition to the 11 yr solar activity cycle, a wavelet analysis confirms a 27 day periodicity in the GCR flux and spectral index corresponding to solar rotation, especially near sunspot minimum, while the flux occasionally exhibits a strong harmonic at 13.5 days. The magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic-ray spectral variations over the long-term future.

Properties of Solar Wind Current Sheets in the Martian Space Environment

Transient current sheets (CSs) are common magnetic structures in the solar wind that can significantly disturb the planetary space environment and cause space weather phenomena. This study focuses on their properties in the Martian space environment and investigates their transformations caused by the Martian bow shock. Based on 14 months of data from the Mars Atmosphere and Volatile Evolution mission during similar solar activity, 786 CSs with directional changes greater than 90° and magnetic field depression were automatically identified, including 256 events in the upstream solar wind and 530 events in the Martian magnetosheath. After crossing the bow shock, the duration and thickness of the CSs decrease, while their current density and occurrence rate significantly increase. In the Martian magnetosheath, CSs located on the dayside exhibit stronger current density, a relatively lower occurrence rate, and a smaller Bx/BT than CSs located on the nightside. From the dayside to the nightside, the predominant magnetic field component of CSs changes to Bx due to the draping process. Moreover, a clear dawn–dusk asymmetry in CS properties emerges from the foreshock to the downstream region of the Martian bow shock. Our results reveal the properties and evolution of solar wind CSs in the Martian space environment.

Trends in Ionospheric Solar Activity Indices

Trends in Ionospheric Solar Activity Indices

The Solar FUV-UV Spectra Measurement Experiment in the Near Space by High Altitude Balloon

An experiment measuring the solar far-ultraviolet-ultraviolet (FUV-UV) irradiance with spectral resolution better than 0.1 nm in the wavelength range from 170 to 400 nm was carried out by the “HongHu-6” high-altitude balloon that flew to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer to near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength range between 150 and 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. Solar UV irradiance in the wavelength range 210 – 400 nm is absorbed by the upper atmosphere as a function of wavelength, and energy is deposited vertically in the lower regions of the near space. This experiment historically provides measurement data to fill a gap in the wavelength shorter than 280 nm in the lower regions of the near space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the “HongHu-6” balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, provide information on the SUVS instrument preflight calibration, and present the first results from the flight data.

Temporal variation of atmospheric electric field in comparison with solar terrestrial activities during the 24th solar cycle

Solar activities play an important role in the variation of the Atmospheric Electric Field (AEF), and affect the Global Electric Circuit (GEC). The relationship between the variation of the AEF and solar activities is focused in the present study. It includes the variation in the AEF with respect to sunspot numbers, direct and indirect radiations, and solar flares during the decline phase of solar cycle 24 from 2015–2019 for Islamabad (ISL) observatory in detail, and partially for Muzaffarabad (MZF) observatory. A few of them had good relationship with the atmospheric electric field. The solar eclipse effect on the atmospheric electric field for the Muzaffarabad station is also presented in this work. A significant increase was observed during the eclipse period which led to decrease in electrical conductivity of atmospheric electric field as compared to alternate days for the same period.

Conditions for the occurrence of intense fluxes of energetic electrons at L<1.2 associated with solar activity and solar wind parameters

We present the results of a statistical study of transient enhancements of electrons with energies >30 keV at low drift shells in the quasi-trapped region (forbidden zone) at the geomagnetic equator. Using data from low-altitude NOAA/POES and MetOp satellites, we have compiled a catalog of events with forbidden energetic electron (FEE) enhancements for the period from 1998 to 2023. Statistical analysis of FEE events has revealed solar-cyclic, as well as seasonal and diurnal variations in the occurrence of FEE enhancements. We have examined the correlation of the annual frequency of FEE events with solar activity, solar wind parameters, and geomagnetic activity. Strong correlations have been found with the F10.7 index of solar activity (radio emission flux) as well as with the Alfvén Mach number (solar wind parameter). An interpretation of the obtained results is proposed which is based on the mechanism of electrical drift and radial transport of electrons from Earth’s inner radiation belt to the quasi-trapped region (L<1.2). The key factor for the operation of the mechanism is the effective penetration of the electric field to low latitudes when a significant difference in the conductivity of the high-latitude ionosphere occurs in the illuminated and unilluminated sectors of local time under conditions of weakening auroral activity.

Long-term geomagnetic activities and stratospheric winter temperature

In this research, impact of long term solar forcing on stratospheric winter temperature is checked. The 11- year sunspot activity and geomagnetic indices (AE, Kp, Dst) are used as an indicator for solar forcing, as geomagnetic activity indices show good correlation with solar variability. To understand the impact of solar forcing through high latitude, stratospheric winter (November to March) time North Polar Region (60N–90N) temperature anomalies are considered. The findings showed that temperature changes in the stratosphere are significantly correlated with solar activity, as evidenced by a significant positive correlation between the 11-year moving mean of stratospheric (10 hPa) temperature anomalies and sunspot number. Approximately from 1970 to 2000, the North Polar Region saw positive anomalous stratospheric winter temperatures. During the same time, the geomagnetic activity also showed a substantial increase. The year-to-year correlation between stratospheric pole temperature and geomagnetic activity is significant (about 0.5). The Empirical Mode Decomposition analysis reveals a highly significant correlation (around 0.9) between the long-term component of stratospheric winter temperature (IMF-4) and the long-term component of geomagnetic activity (IMF-3 and IMF-4). One of the reasons for the increase in lower stratospheric temperature is an increase in ozone concentration during the same period when geomagnetic activity is higher. Empirical orthogonal function (EOF) and correlation analysis of stratospheric winter temperature with large-scale circulation patterns are also carried out. The spatial correlation is checked for stratospheric winter temperature at North Pole and lower atmospheric levels (250 hPa and 850 hPa) followed by pre-monsoon and monsoon season. This study includes statistical analysis, however, also highlights the necessity of in-depth dynamical analysis to improve our understanding of how solar activity impacts Earth's atmospheric layers, which may be helpful in predicting the weather and climate.

Условия появления интенсивных потоков энергичных электронов на L<1.2, связанные с солнечной активностью и параметрами солнечного ветра

We present the results of a statistical study of transient enhancements of electrons with energies >30 keV at low drift shells in the quasi-trapped region (forbidden zone) at the geomagnetic equator. Using data from low-altitude NOAA/POES and MetOp satellites, we have compiled a catalog of events with forbidden energetic electron (FEE) enhancements for the period from 1998 to 2023. Statistical analysis of FEE events has revealed solar-cyclic, as well as seasonal and diurnal variations in the occurrence of FEE enhancements. We have examined the correlation of the annual frequency of FEE events with solar activity, solar wind parameters, and geomagnetic activity. Strong correlations have been found with the F10.7 index of solar activity (radio emission flux) as well as with the Alfvén Mach number (solar wind parameter). An interpretation of the obtained results is proposed which is based on the mechanism of electrical drift and radial transport of electrons from Earth’s inner radiation belt to the quasi-trapped region (L<1.2). The key factor for the operation of the mechanism is the effective penetration of the electric field to low latitudes when a significant difference in the conductivity of the high-latitude ionosphere occurs in the illuminated and unilluminated sectors of local time under conditions of weakening auroral activity.

Automated High-Precision Recognition of Solar Filaments Based on an Improved U2-Net

Solar filaments are a significant solar activity phenomenon, typically observed in full-disk solar observations in the H-alpha band. They are closely associated with the magnetic fields of solar active regions, solar flare eruptions, and coronal mass ejections. With the increasing volume of observational data, the automated high-precision recognition of solar filaments using deep learning is crucial. In this study, we processed full-disk H-alpha solar images captured by the Chinese H-alpha Solar Explorer in 2023 to generate labels for solar filaments. The preprocessing steps included limb-darkening removal, grayscale transformation, K-means clustering, particle erosion, multiple closing operations, and hole filling. The dataset containing solar filament labels is constructed for deep learning. We developed the Attention U2-Net neural network for deep learning on the solar dataset by introducing an attention mechanism into U2-Net. In the results, Attention U2-Net achieved an average Accuracy of 0.9987, an average Precision of 0.8221, an average Recall of 0.8469, an average IoU of 0.7139, and an average F1-score of 0.8323 on the solar filament test set, showing significant improvements compared to other U-net variants.

Unveiling the impact of cosmic rays and solar activities on climate through optimized boost algorithms

This investigation explores the enhancement of climate anomaly predictions by incorporating Solar Sunspot Number (SSN) and Cosmic Ray (CR) data into climate models. Leveraging XGBoost and CatBoost regression methodologies enhanced by Atom Search Optimization (ASO) and Nuclear Reaction Optimization (NRO) for predictive analysis. Utilizing a dataset spanning from 1965 to 2020, comprising 672 data points per climate parameter, the study delves into the dynamics between CR flux, SSN variability, and climate parameters. The models aimed to forecast variations in total precipitation anomaly (TPA), total cloud cover anomaly (TCCA), and sea surface temperature anomaly (SSTA) based on decadal solar cycle activities and CR data. Our findings reveal the significant impact of integrating SSN and CR data into environmental prediction models for TCCA, TPA, and SSTA, employing CatBoost and XGBoost machine learning (ML) algorithms. Performance evaluation, centered on root mean square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and Nash-Sutcliffe efficiency (NSE), illuminated the efficacy of ASO and NRO in model optimization, particularly under scenarios with and without SSN/CR data inclusion. The analytical outcomes underscore the enhanced prediction accuracy for TCCA, TPA, and SSTA when incorporating SSN and CR data, with ASO generally outperforming NRO in optimizing model parameters. Our regression models, optimized using ASO and NRO, showed a marked improvement in SSTA forecasts, with an increase in the R2 value from 0.73 to 0.76 when SSN/CR data were not included. The CatBoost was superior the XGBoost models with results of four error metrics. These results underscore the critical role of solar activity data and optimized algorithms in enhancing the accuracy and reliability of climate modeling. This study underscores the utility of advanced ML techniques and the importance of strategic variable selection in environmental modeling, offering new insights into the complex interactions between solar activity, CR, and climate dynamics.

Space radiation measured during first-ever commercial suborbital mission on Virgin Galactic SpaceShipTwo Unity on 29 June 2023

The paper presents the variations of space radiation (primary and secondary galactic cosmic rays (GCR) absorbed dose rate in silicon and flux) measured during the first-ever commercial suborbital flight of the Virgin Galactic (VG) SpaceShipTwo Unity on 29 June 2023. A Portable Dosimeter-Spectrometer Liulin-CNR-VG is used. It is developed in the Space Research and Technology Institute, Bulgarian Academy of Sciences (SRTI-BAS) under a scientific contract with National Research Council of Italy (CNR), Italy. Liulin-CNR-VG size is 63х54 × 23 mm. Its weight is 0.092 kg. During the first part of the SpaceShipTwo flight, up to 14.4 km, the dose rate rises from 0.058 μGy h-1 up to 2.5 μGy h-1. Above the altitude of 30 km, the dose rate falls to 2.2 μGy h-1, while the dose to flux ratio increases to values about 1.0 nGy cm2 particle-1. The latter confirms the outcomes of previous balloon experiments, i.e. the change of the composition of the radiation field of the GCR and secondary radiation source from predominantly light particles as electrons, pions and muons towards heavier particles as protons and neutrons. On the descending part of the flight, one maximum in the flux and dose rate curves is obtained as Regener-Pfotzer maximum (R-PM). The flux calculated by the moving avervage is equal to 1.2 cm-2 s-1 and the dose rate is equal to 2.9 μGy h-1 at an altitude of 13 km. These values are well in line with those expected in conditions of relatively high solar activity, such as during the flight. The dose rates measured by Liulin-CNR-VG are in good agreement with other Liulin data, such as those recorded during balloon flights in 2005 and 2015 and civil aviation flights. The calculated total equivalent dose rate during the VG SpaceShipTwo flight is 7.46 μSv for 1.22 h. This reveals that there is a very small radiation risk for the pilots and astronauts flying at the VG SpaceShipTwo up to 85.1 1 km altitude.

Exploring the time variability of the solar wind using LOFAR pulsar data

High-precision pulsar timing is highly dependent on the precise and accurate modelling of any effects that can potentially impact the data. In particular, effects that contain stochastic elements contribute to some level of corruption and complexity in the analysis of pulsar-timing data. It has been shown that commonly used solar wind models do not accurately account for variability in the amplitude of the solar wind on both short and long timescales. In this study, we test and validate a new, cutting-edge solar wind modelling method included in the enterprise software suite (widely used for pulsar noise analysis) through extended simulations. We use it to investigate temporal variability in LOFAR data. Our model testing scheme in itself provides an invaluable asset for pulsar timing array (PTA) experiments. Since, improperly accounting for the solar wind signature in pulsar data can induce false-positive signals, it is of fundamental importance to include in any such investigations. We employed a Bayesian approach utilising a continuously varying Gaussian process to model the solar wind. It uses a spherical approximation that modulates the electron density. This method, which we refer to as a solar wind Gaussian process (SWGP), has been integrated into existing noise analysis software, specifically enterprise . Our Validation of this model was performed through simulations. We then conduct noise analysis on eight pulsars from the LOFAR dataset, with most pulsars having a time span of $ 11$ years encompassing one full solar activity cycle. Furthermore, we derived the electron densities from the dispersion measure values obtained by the SWGP model. Our analysis reveals a strong correlation between the electron density at 1 AU and the ecliptic latitude (ELAT) of the pulsar. Pulsars with $|ELAT|< 3^ circ $ exhibit significantly higher average electron densities. Furthermore, we observed distinct temporal patterns in the electron densities in different pulsars. In particular, pulsars within $|ELAT|< 3^ circ $ exhibit similar temporal variations, while the electron densities of those outside this range correlate with the solar activity cycle. Notably, some pulsars exhibit sensitivity to the solar wind up to $45^ circ $ away from the Sun in LOFAR data. The continuous variability in electron density offered in this model represents a substantial improvement over previous models, that assume a single value for piece-wise bins of time. This advancement holds promise for solar wind modelling in future International Pulsar Timing Array (IPTA) data combinations.

Short-term solar eruptive activity prediction models based on machine learning approaches: A review

Short-term solar eruptive activity prediction models based on machine learning approaches: A review

Decay time estimate for LEO spacecraft

The growing concerns posed by orbital debris represent a serious threat to the future of space operations in low Earth orbit. With the goal of limiting the formation of new debris, space agencies are proposing international guidelines that satellites should be able to deorbiting within 25 years of the end of their operational life. Orbital decay is typically caused by atmospheric drag, so estimating the decay time of a satellite subject to drag is critical to assessing whether the guidelines are met. However, such estimate is a very challenging task because of the difficulty of accurately modeling atmospheric properties and because of the coupling of orbital dynamics with spacecraft attitude. In this paper, a simplified algorithm based on the King-Hele formulation is proposed to rapidly estimate the decay time of an orbiting satellite without imposing any assumptions on the spacecraft’s nominal size, mass, geometry or attitude. The algorithm accounts for the effect of solar activity level variations on atmospheric properties and drag coefficient through an iterative procedure and can be applied to any object in orbit. Numerical tests show that the predictions in terms of decay times are very accurate for satellites that are quite different in size and geometry, including the presence of an aerodynamic drag augmentation system such as a drag sail.

Graph-enabled spatio-temporal transformer for ionospheric prediction

The ionosphere, crucial for satellite navigation and radio communication, is highly sensitive to solar and geomagnetic activities. Traditional ionospheric prediction models often struggle to capture its complexities. This paper introduces a Graph-Enabled Spatio-temporal transformer (GEST) model, designed to predict the Total electron content (TEC) in the ionosphere with higher accuracy. The GEST model innovatively integrates six dynamic space weather parameters, including the Kp index, and refines grid distances and weights in the Global ionospheric maps (GIM). Leveraging the efficiency of the Transformer architecture in processing spatio-temporal data, the GEST model adapts to varying ionospheric conditions and provides superior precision. Our evaluations, based on data from the Center for orbit determination in Europe (CODE), demonstrate that the GEST model significantly outperforms traditional methods and other intelligent algorithms such as conv-LSTM. It shows marked improvements in Mean absolute error (MAE), Root mean square error (RMSE), Pearson correlation coefficient (CC), and Mean absolute percentage error (MAPE), particularly during periods of intense solar and geomagnetic activity. These advancements highlight the GEST model’s substantial contributions to the field of ionospheric prediction technology, offering a robust tool for enhancing the reliability of satellite-based systems.

Heterogeneity of the East Asian rainfall influenced by solar-forced western Pacific subtropical high

The existence and causes of the recently observed rainfall heterogeneity over monsoonal east Asia in historical periods remain unclear. Here we show that such rainfall heterogeneity has been present at least in the last millennium, with decadal to centennial precipitation variations over southeast Asia and north China being broadly synchronous, while central to southwest China’s variations are generally out-of-phase with those in southeast Asia and north China. We propose that the western Pacific subtropical high, which reduces decadal to centennial precipitation over central to southwest China due to its anticyclonic feature, could be responsible for the observed rainfall heterogeneity over subtropical East Asia. Further analyses suggest that intensified decadal to centennial solar activity can lead to enhanced and northward and westward extension of the western Pacific subtropical high, resulting in tripolar rainfall heterogenous patterns over monsoonal East Asia.

Schwabe Solar Cycle in 1000–1700: Variations in the Length and Amplitude

One of the most significant features of solar activity is its variability over a wide range of periods, with the dominance of the 11-year cycle or the Schwabe cycle. In this work, a wavelet analysis of data on solar activity in 1000–1700 was carried out, obtained using the number of auroras, taking into account the contribution of the geomagnetic field. The obtained results demonstrate the stable presence of an 11-year cycle during the entire time interval of 1000–1700 A. D. It was found that in 1000–1350 there was a systematic increase in the length of the Schwabe cycle, after which its decline was traced. At the same time, the length of the solar cycle increases during the grand minima of Oort (13 years), Wolf (14 years) and Spörer (14–15 years). It was found that the correlation between the amplitude and the length of the solar cycle was maintained throughout the entire period of time 1000–1700, but its sign changed. In addition, it was obtained that the correlation between the amplitude of the cycle and the length of the previous cycle is stronger than the correlation between the amplitude and length of the same cycle. This result is similar to that previously known for instrumental series. However, we have shown that this pattern persists over a much longer time interval, and it does not depend on the sign of the correlation. The paper also provides indications of the existence of a variation with a period of 30–40 years in solar activity in 1000–1550.

Forecast of Modulation of Cosmic Rays with Rigidity of 10 GV in the 25th Solar Activity Cycle

Based on a forecast of solar activity parameters and the model developed by the authors for modulation of Galactic cosmic rays, we forecasted cosmic ray variations in the 25th solar activity cycle. The cosmic ray flux forecast is based on correlation with the number of sunspots (single-parameter model) or with a set of solar (mainly magnetic) parameters (multiparameter model). The forecast for the number of sunspots was taken from published data; the forecast for other solar parameters was done in the study. It is shown that variations in cosmic rays over three years of the current 25th cycle, in general, do not contradict the forecasts and indicate that the 25th solar activity cycle is expected to be slightly more active compared to the 24th.