Solar Activity Research Articles

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.

Orbital and suborbital climate cycles recorded in terrestrial strata from the late Paleocene-early Eocene in the Subei Basin, East China

Interannual-to millennial-scale climate cycles have been recognized in ancient sedimentary strata and may be closely associated with solar activity. However, the physical driving mechanisms of such cycles remain a mystery. To better understand the nature and evolution of suborbital cycles in ice-free conditions, we performed a quantitative analysis of high-resolution phosphorus (P), gray-scale values, and iron (Fe) data obtained from a core deposited in a mid-latitude lake (Funing Formation of the Subei Basin) during the Late Paleocene-Early Eocene. Time series analysis reveals evidence for ∼88-yr and ∼ 11-yr solar activity cycles in the gray value data, and ∼ 20-kyr precession cycles, ∼10-kyr half-precession cycles, and ∼ 2-kyr solar activity cycles in the Fe data. The data indicate that paleoclimate changes in the Subei Basin at this time were driven by both orbital and suborbital cycles. Amplitude modulation analysis suggests that ∼20-kyr precession modulated the amplitude of the observed 2-kyr cycles. It is inferred that the Earth's climate is driven not only by eccentricity-modulated precession cycle, but also by precession-modulated millennial cycles.

Consistency of climatic changes at different time scales in Central England and Greenland

Characteristic variations in the Greenland isotope temperature data over the last 1000 years and in the meteorological temperature measurements collected from Central England during the past four centuries have been analyzed. We take advantage of the continuous wavelet transform to analyze the simultaneous occurrence of temperature variations of different time scales. We assess the extent to which these phenomena can be compared when examining two different northern hemisphere locations at different time scales. Among the long-term variations, we focus on the cooling at the turn of the 18th century, which occurred slightly later in Greenland than in central England, and the warming observed at present. On the short time scale, the range under study is limited to times of the order of 5-10 years. It has been found that it is on these scales that temperature variations in the two locations are relatively consistent, with a cross-correlation coefficient as high as 0.6 for timescales of the order of 9 years. The main solar activity cycle also falls within the interval of significant correlations. It is shown that despite the absence of direct correlation between temperature and solar activity, the time dependence of the wavelet cross-correlation coefficient of the two temperature series on the scale of 11 years reproduces the long-term variations of solar activity.

Temperature distribution in the crevasse-drainage systems of the Antarctic glaciers: A case study of the Perunika Glacier

Discovered only about 200 years ago, Antarctica is the poorest and most isolated ecosystem on Earth. Its thinner atmosphere, due to the centrifugal forces of Earth’s rotation, the ozone hole, and stronger solar radiation, creates a natural laboratory that provides information about the state and trajectory of Earth’s climate condition. This study aimed to determine the depth of heat penetration from the surface of the glacier into the crevasses in the ablation zone and establish the zone of constant temperatures in the glacier. It explored the relationship between the air temperature at the glacier surface and the temperature distribution in the crevasses, including the temperature gradient at different levels and the direction of the airflow. We used autonomous data loggers for measuring and recording temperature and relative humidity. The measured depth reached 18 m in the central part of the glacier and 9 m in the periphery. An ultrasonic anemometer was installed in the deepest crevasse in to the center of the glacier to determine the size and direction of air flows. Meteorological parameters such as air temperature, humidity, atmospheric pressure, and solar radiation were measured on-site using autonomous sensors and recording devices mounted on installations on the glacier surface and at depth using alpine techniques. The results show a temperature gradient through 3-meter layers, a relatively clear boundary of the constant temperature zone, and a significant infiltration of cold air through the crevices driven by turbulent wind processes. Additionally, a weak negative correlation was found between solar activity and temperatures in the crevasses. It appears that as solar activity increases, the temperature decreases. There are also weak but consistently positive correlations with air movement both upward and downward. The temperature becomes constant with the increase of the depth until a zone of constant temperatures is determined and the temperature variance becomes insignificant. This zone varies in different crevаsses, meaning it is influenced by the specific characteristics of each crevasse location. At shallow depths, temperature is influenced by external temperature, but with the depth increasing this influence decreases. On windy days, the zone of constant temperature expands. During higher solar activity, air circulation accelerates—both upward and downward. The relationship between solar activity and climatic processes in glacier drainage systems adds new insights to solar-terrestrial physics.

Late Pleistocene to Holocene alluvial deposits of the Inaouène Valley and their paleoenvironmental significance (north Morocco)

This study investigates the paleoenvironmental changes and fluvial dynamics in the Inaouène River Valley of central northern Morocco over the last 22,000 years. Through comprehensive field study and radiocarbon dating of Upper Pleistocene and Holocene alluvial deposits, the research identifies six main alluvial units reflecting distinct phases of fluvial activity and environmental conditions. These phases include coarse gravel aggradation between ∼22 and 15 cal kaBP, indicating a braided channel system, followed by multiple fine-dominated alluviation phases occurring at ∼13, ∼10, ∼6–5, ∼3, ∼0.7–0.3, and ∼0.1-0 cal kaBP. The trunk channel evolved from a low-sinuosity wandering style in the Early-Middle Holocene to a high-sinuosity pattern in the Late Holocene. Periods of landscape stability, evidenced by soil formation, were dated around 0.3 and 0.8 cal kaBP, with additional episodes estimated just after ∼12 cal kaBP and around 3.8 cal kaBP. Notably, the study also uncovered evidence of significant human intervention during the Middle Holocene.A comparison with other archives enabled us to reconstruct late Pleistocene and Holocene palaeoenvironmental conditions on both regional and supraregional scales, linking specific stages of floodplain development to prevalent influencing factors. Emphasizing the fluvial system response, we present a cause-effect model that focuses on long-lasting climatic phases (e.g., Last Glacial Maximum, MIS2-MIS1 transition, African Humid Period) as well as sub-millennial to centennial Rapid Climate Changes, North Atlantic cooling events, and solar activity minima. Human intervention played a key role in the Inaouène's evolution during the Middle Holocene, as evidenced by clear anthropogenic markers found in the associated deposits. These findings not only contribute to our understanding of the area's geomorphological history but also highlight its significant archaeological potential, opening new avenues for interdisciplinary research in this understudied region.The study offers new insights into central northern Morocco's late Quaternary alluvial geochronology and paleoenvironmental evolution, aligning with regional findings and contributing to a broader understanding of climate-driven landscape changes and human-environment interactions across North Africa and the Mediterranean.

Dependence of the main ionospheric trough position on local time, longitude and geomagnetic activity in the southern winter hemisphere

Based on the meticulous identification of ionization troughs, performed earlier from the CHAMP satellite data, twoadditional issueswereresolved: (1) the longitudinal effect characteristics in the position of the main ionospheric trough (MIT) were corrected, and (2) for the first time,the dependence of theMITposition on geomagnetic activity was determined foralllocaltime hours. A large dataset from the CHAMP satellite in the southern winter hemisphere under high solar activity was utilized. According to the refined data the amplitude of the longitudinal effect in the MITposition changes from ∼ 3° to ∼ 5° in the course of the day. The shape of the longitudinal effectvarieswith local time, however, the MIT in the eastern hemisphere isconsistentlylocated at higher latitudes than in the western hemisphere. The main reason for the longitudinal effect is the dependence of the equatorward boundary of auroral diffuse precipitation on the tilt angle of the Earth’s dipole. The dependence on geomagnetic activitywas determined as a linear regression ΛT = Λ0 − aKp, where Λ is the geomagnetic latitude, and the Kp indexisconsidered for the previous6 h. The latitude Λ0 and coefficient a exhibited pronounced dependence on local time, with Λ0 increasing and a decreasing when moving from night to day. Because the amplitude of the longitudinal effect decreases with increasing magnetic activity, the value of a alsodependson longitude. Consequently, coefficienta wasdetermined separatelyforthe eastern and western hemispheres. Theaveragevaluesof a vary from 1.3 − 1.4° during the day to 1.8 − 1.9° at night. Thedifference between theeastern and western hemispheres is ∼ 0.3°.

Prediction of ionospheric TEC during the occurrence of earthquakes in Indonesia using ARMA and CoK models

Predicting ionospheric Total Electron Content (TEC) variations associated with seismic activity is crucial for mitigating potential disruptions in communication networks, particularly during earthquakes. This research investigates applying two modelling techniques, Autoregressive Moving Average (ARMA) and Cokriging (CoK) based models to forecast ionospheric TEC changes linked to seismic events in Indonesia. The study focuses on two significant earthquakes: the December 2004 Sumatra earthquake and the August 2012 Sulawesi earthquake. GPS TEC data from a BAKO station near Indonesia and solar and geomagnetic data were utilized to assess the causes of TEC variations. The December 2004 Sumatra earthquake, registering a magnitude of 9.1–9.3, exhibited notable TEC variations 5 days before the event. Analysis revealed that the TEC variations were weakly linked to solar and geomagnetic activities. Both ARMA and CoK models were employed to predict TEC variations during the Earthquakes. The ARMA model demonstrated a maximum TEC prediction of 50.92 TECU and a Root Mean Square Error (RMSE) value of 6.15, while the CoK model predicted a maximum TEC of 50.68 TECU with an RMSE value of 6.14. The August 2012 Sulawesi earthquake having a magnitude of 6.6, revealed TEC anomalies 6 days before the event. For both the Sumatra and Sulawesi earthquakes, the GPS TEC variations showed weak associations with solar and geomagnetic activities but stronger correlations with the earthquake-induced electric field for the considered two stations. The ARMA model predicted a maximum TEC of 54.43 TECU with an RMSE of 3.05, while the CoK model predicted a maximum TEC of 52.90 TECU with an RMSE of 7.35. Evaluation metrics including RMSE, Mean Absolute Deviation (MAD), Relative Error, and Normalized RMSE (NRMSE) were employed to assess the accuracy and reliability of the prediction models. The results indicated that while both models captured the general trend in TEC variations, nuances emerged in their responses to seismic events. The ARMA model demonstrated heightened sensitivity to seismic disturbances, particularly evident on the day of the earthquake, whereas the CoK model exhibited more consistent performance across pre- and post-earthquake periods.

Study on MHD Pulses, Waves, and Instability in Trigging multiple renewables noise on various spectral information scales

Major concepts covered in this research include: State of being free vibration and method start changing; MHD waveguides like the magnetic properties dorsal fin, radicular groups, and radicular streaming sites; processes for frequency supplied in imperativeness overflows throughout sub hurricanes and solar activity; the possibility of Heat diffusion resonant frequencies along empty field lines; potential motorists of MHD waves; diagnostic tools of plasma screens with MHD waves; the collaboration of MHD waves mostly with positive ions limits (ionosphere and chromosphere). This review is directed largely at experts in the subjects of magnetosphere material science and solar theoretical physics, while it does delve into the intricacies of the surround investigation fields to those who are concerned. Though there are several noise contributors, aerodynamics is the most significant. When it concerns to aerodynamics noise, the distal end of blades of wind turbines is where the majority of the action occurs. A subject of this research is on blade tip noise caused by wind generators, and an evaluation and comparison of the many methods being used and researched to minimize this difficulty is the paper's primary focus. Subjective assessment outcomes are also compared to quantifiable measurements. Several methods are proposed, and the risks and benefits are compared. Among the most intriguing instances of plasma in reality that we're able to examine close quarters are really the Solar energy, Atmosphere's geomagnetic, and stratosphere. Were very could be used to model such plasmas effectively in principle (MHD). In MHD, the statistics and dynamics of liquids that conduct electricity are hypothetically characterized.

Variability of Earth’s ionospheric outflow in response to the dynamic terrestrial exosphere

The most abundant neutral constituent in the exospheric region (i.e., beyond ≈ 500 km altitude) is the atomic hydrogen (H); however, its density distributions predicted by physics-based models have been challenged by satellite-based observations of its far ultraviolet emissions. This discrepancy may impact magnetospheric ions’ densities and velocities since numerous chemistry and ion-neutral coupling interactions rely sensitively on the underlying neutral hydrogen population. The Polar Wind Outflow Model a first-principled model for relevant ion species in the high-latitude ionosphere, is employed to investigate the role of neutral H on the ionospheric outflow. Specifically, variability in the outflow of ionospheric H+, He+, N+, and O+ as a response to systematic enhancement and depletion of H number densities were simulated. The altitude-dependent ion density and energy partition profiles vary with neutral H density, solar activities, and ion species. These findings suggest that the exosphere plays a crucial role in controlling the production and loss of ions through ionospheric chemistry, as well as the energy contributions by altering ion-neutral-electron collisions and the ambipolar electric field to the high-latitude ionospheric outflow. As a result, the escape rates of the ionospheric outflow are directly associated with exospheric distributions. This work potentially helps understand the dominant mechanisms of atmospheric escape, particularly during a hydrogen-rich early Earth’s and exoplanet’s atmosphere, which is known to play a significant role in understanding the evolution of Earth’s atmosphere.

The origin of interplanetary switchbacks in reconnection at chromospheric network boundaries

There is renewed interest in heliospheric physics following the recent exploration of the pristine solar wind by the Parker Solar Probe. Magnetic switchback structures are frequently observed in the inner heliosphere, but there are open questions about their origin. Many researchers are investigating the statistical properties of switchbacks and their relationships with wave modes, stream types and solar activity, but the sources of switchbacks remain elusive. Here we report that interplanetary switchbacks originate from magnetic reconnection on the Sun that occurs at chromospheric network boundaries and launch solar jet flows. We link in situ interplanetary measurements and remote-sensing solar observations to establish a connection between interplanetary switchbacks and their solar source region, featuring solar jets, chromospheric network boundaries and photospheric magnetic field evolution. Our findings suggest that joint observations of switchbacks and solar jets provide a better estimate of the contribution of magnetic reconnection to coronal heating and solar wind acceleration.

A Spatial Reconstruction Method of Ionospheric foF2 Based on High Accuracy Surface Modeling Theory

The ionospheric F2 critical frequency (foF2) is one of the most crucial application parameters in high-frequency communication, detection, and electronic warfare. To improve the accuracy of spatial reconstruction of the ionospheric foF2, we propose a high-accuracy surface (HAS) modeling method. This method converts difficult-to-solve differential equations into more manageable algebraic equations using direct difference approximation, significantly reducing algorithm complexity and computational load while exhibiting excellent convergence properties. We used seven stations in Brisbane, Canberra, Darwin, Hobart, Learmonth, Perth, and Townsville, with one station as a validation station and six as training stations (e.g., Brisbane as a validation station and the other stations—Canberra, Darwin, Hobart, Learmonth, Perth, and Townsville—as training stations). The training stations and the HAS method were used to train and reconstruct the validation stations at different solar activity periods, seasons, and local times. The predicted values of the validation stations were compared with the measured values, and the proposed method was analyzed and validated. The reconstruction results show the following. (1) The relative root mean square errors (RRMSEs) of HAS method prediction in different solar activity epochs were 13.67%, 7.74%, and 9.19%, respectively, which are 13.57%, 7.41%, and 6.41% higher than the prediction accuracy of the Kriging method, respectively. (2) In the four seasons, the RRMSEs of the HAS method prediction are 9.27%, 13.1%, 8.81%, and 8.09%, respectively, which are 10.83%, 11.73%, 4.25%, and 12.00% higher than the prediction accuracy of the Kriging method. (c) During the daytime and nighttime, the RRMSEs of HAS method prediction were 9.23% and 11.17%, which were 5.92% and 11.99% higher than the prediction accuracy of the Kriging method, respectively. (d) Under the validation dataset, the average predictive RRMSE of the HAS method was 10.29%, and the average predictive RRMSE of the IRI prediction model was 12.35%, with a 2.06% improvement in the predictive accuracy of the HAS method. In general, the prediction effect of the HAS method was better than that of the Kriging method, thus verifying the effectiveness and reliability of the proposed method. In summary, the proposed reconstruction method is of great significance for improving usable frequency prediction and enhancing communication performance.

Modeling and Forecasting Ionospheric foF2 Variation Based on CNN-BiLSTM-TPA during Low- and High-Solar Activity Years

The transmission of high-frequency signals over long distances depends on the ionosphere’s reflective properties, with the selection of operating frequencies being closely tied to variations in the ionosphere. The accurate prediction of ionospheric critical frequency foF2 and other parameters in low latitudes is of great significance for understanding ionospheric changes in high-frequency communications. Currently, deep learning algorithms demonstrate significant advantages in capturing characteristics of the ionosphere. In this paper, a state-of-the-art hybrid neural network is utilized in conjunction with a temporal pattern attention mechanism for predicting variations in the foF2 parameter during high- and low-solar activity years. Convolutional neural networks (CNNs) and bidirectional long short-term memory (BiLSTM), which is capable of extracting spatiotemporal features of ionospheric variations, are incorporated into a hybrid neural network. The foF2 data used for training and testing come from three observatories in Brisbane (27°53′S, 152°92′E), Darwin (12°45′S, 130°95′E) and Townsville (19°63′S, 146°85′E) in 2000, 2008, 2009 and 2014 (the peak or trough years of solar activity in solar cycles 23 and 24), using the advanced Australian Digital Ionospheric Sounder. The results show that the proposed model accurately captures the changes in ionospheric foF2 characteristics and outperforms International Reference Ionosphere 2020 (IRI-2020) and BiLSTM ionospheric prediction models.

The Response of Stratospheric Gravity Waves to the 11-Year Solar Cycle

Atmospheric gravity waves are one of the important dynamic processes in near space and are widely present in the atmosphere. They play a crucial role in the transfer of energy and momentum between different regions of the atmosphere. The Sun, as the ultimate source of gravity wave energy, significantly influences the intensity of gravity wave disturbances through its activity variations. This paper utilizes data from the Global Navigation Satellite System Occultation Sounder (GNOS) onboard the Fengyun-3C (FY-3C) satellite to invert global stratospheric gravity wave disturbances. It provides the global stratospheric gravity wave distribution from 2015 to 2023, nearly covering one solar activity cycle, and focuses on analyzing the response of gravity waves at different latitudes, altitudes, and wavelengths to the solar activity cycle. We found that short-wavelength gravity waves respond more noticeably to solar activity compared to long-wavelength gravity waves. Through analyzing the intensity of stratospheric gravity wave disturbances across different latitude bands, we found that in high-latitude regions, stratospheric gravity wave disturbances are most sensitive and respond most quickly to variations in solar activity. Furthermore, the Southern Hemisphere exhibits a stronger response to the current year’s solar activity changes compared to the Northern Hemisphere. In the mid-latitude and equatorial regions, the response to changes in solar activity intensity is delayed. The correlation gradually strengthens with this lag, reaching a very strong level after a 2-year lag. Additionally, the correlation between the Southern Hemisphere and solar activity is generally higher than that of the Northern Hemisphere.

Tailored accelerometer calibration by POD for thermospheric density retrieval with GRACE and GRACE-FO

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites as insitu measurements along the orbit. One main challenge therein is the estimation of physical accelerometer calibration parameters, meaning that these parameters should not absorb other effects and model deficiencies in the Precise Orbit Determination (POD) process. The accelerometers of all geodetic satellites like GRACE and GRACE-FO are affected by time dependent bias and scale factors. Therefore a calibration of the data is indispensable.A dynamic POD based physical accelerometer calibration is developed for the complete GRACE and GRACE-FO missions. We investigate different parametrization strategies and utilize different observation data, as the accurate inter-satellite ranging additionally to GPS orbit data. For the estimation parameters we distinguish between offset and scale, furthermore, cross-track and radial directions are significantly less sensitive than along-track and require a different evaluation. For the offset, constant and time dependent parameters are investigated. Furthermore, a continuous offset calibration over arc boundaries is implemented and tested. The sensitivity of the scale factor is lower, although, in contrast to the offset, it increases with higher total accelerations. This means that it needs to be estimated over longer time periods. We investigate periods between three hours and one month as well as results from Gravity Field Recovery (GFR). Monthly scale factors give valuable results, at least for x-axis and when the Solar activity is not very low. Nevertheless, we also estimate weighted constant scale factors from the monthly results and use these in a subsequent POD, giving more realistic offset results for most periods and cross-track and radial directions.From the used background models in the POD, Earth’s gravitational model has a noticeable influence on the estimated calibration parameters, especially the scale factors. We utilized several different models. Results with monthly ITSG solutions are distinctly better than the ones with the time dependent GOCO06s model.We show that the validation with usual metrics, like post-fit POD residuals, is not able to reflect the quality of the different estimated calibration parameters. For a quantitative validation we introduce an approach based on the modeled non-gravitational accelerations. Therefore, the uncertainty of the models is evaluated first. The influence of main error sources in the models is assessed and propagated to the results.We compare our scale parameters to available references and the complete calibration to TU Delft’s latest results. Finally we show the effect of different calibration options on the retrieved density.The estimated calibration parameters and non-gravitational accelerations for the whole GRACE and GRACE-FO missions are available on our data server www.zarm.uni-bremen.de/zarm_daten.

Assessment of IRI2020 model accuracy in predicting ionospheric parameters: Insights from multiple ionosonde stations

This research assesses the performance of the IRI2020 model in forecasting the ionospheric critical frequency of the F2 layer (foF2) and Maximum Usable Frequency (MUF) of the ionosphere from 2020 to 2023 across multiple ionosonde stations. The primary objective is to analyse the characteristics of foF2 and MUF across various longitudinal sectors during the solar minimum to ascending phase of solar cycle 25 and to evaluate the IRI2020 model’s performance in replicating observed data. Additionally, the study explores the influence of various space weather parameters on the variability of these ionospheric parameters. The findings reveal that the IRI2020 model overestimates the daily mean values of both foF2 and MUF(3000)F2 across the stations over the three years. While exhibiting good performance in capturing the pattern of hourly predictions, the model tends to overestimate foF2 more than MUF(3000)F2, with better predictions observed for MUF(3000)F2. However, hourly estimations display a mix of underestimation and overestimation, predominantly overestimating values. Correlations ranged from 0.58 to 0.92 for foF2 and 0.72 to 0.91 for MUF(3000)F2, showing variability across stations. As solar activity increases, seasonal variations become more evident, especially in stations located in the northern hemisphere.In contrast, stations in the southern hemisphere exhibit less pronounced seasonal variations, suggesting a notable hemispheric asymmetry. Although the IRI2020 better captured the general trend of foF2 and MUF(3000)F2 in our investigation, the percentage deviation for MUF(3000)F2 ranges from 1 % to 15.1 %, which can result in a significant range reduction for practical applications like HF communications. Stations closer to the geomagnetic equatorial line exhibit stronger seasonal asymmetry and higher deviations. Some key space weather parameters, including sunspot number R, F10.7 and R/F10.7 ratio, were found to significantly influence ionospheric variability, with sunspot number R and R/F10.7 showing a stronger correlation with foF2 and MUF(3000)F2. These suggest that the variability of the solar active region parameters primarily controls ionospheric foF2 and MUF(3000)F2.

Latitudinal Dependence of Variations in the Frequencies of Solar Oscillations Above the Acoustic Cut-Off

At high frequencies beyond the acoustic cut-off, a peak-like structure is visible in the solar power spectrum. Known as the pseudo-modes, their frequencies have been shown to vary in anti-phase with solar magnetic activity. In this work, we determined temporal variations in these frequencies across the solar disc, with the aim of identifying any potential latitudinal dependence of pseudo-mode frequency shifts. We utilised nearly 22 years of spatially resolved GONG data for all azimuthal orders, m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\ extit{m}$\\end{document}, for harmonic degrees 0≤l≤200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$0\\leq l\\leq 200$\\end{document}, and determined shifts using the resampled periodogram method. Periodogram realisations were created from overlapping, successive 216 day-long segments in time, and cropped to 5600 – 6800 μHz. Cross-correlation functions were then repeatedly generated between these realisations to identify any variation in frequency and the uncertainty. We categorised each mode by its latitudinal sensitivity and used this categorisation to produce average frequency shifts for different latitude bands (15∘ and 5∘ in size) which were compared to magnetic proxies, the F10.7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$F_{\\mathrm{10.7}}$\\end{document} index and GONG synoptic maps. Morphological differences in the pseudo-mode shifts between different latitudes were found, which were most pronounced during the rise to solar maximum where shifts reach their minimum values. At all latitudes, shift behaviour was strongly in anti-correlation with the activity proxy. Additionally, periodicities shorter than the 11-year cycle were observed. Wavelet analysis was used to identify a periodicity of four years at all latitudes.

Is There a Synchronizing Influence of Planets on Solar and Stellar Cyclic Activity?

Is There a Synchronizing Influence of Planets on Solar and Stellar Cyclic Activity?

Implications of Solar Wind Disturbances on Forbush Decrease

This study investigated the role of solar wind disturbances on variations in cosmic ray intensity. To conduct the study, use was made of the data on cosmic rays from the SOPO, CLMX, and MOSC neutron stations, as well as solar wind speed data from 2000 to 2005. The source Forbush decrease (FD) dates were generated from onset journal publications, specifically the FD list of Dumbovi ́c et al., (2011). The manual method of FD selection was used to identify FDs. The FD dates, computed magnitudes, and solar wind speed data were recorded and presented. From the study, FDs were generated, some of which were of the same date as those in the source table, while others were not observed in the source table. FDs not observed in the source table were generated and catalogued by this research. It was also observed that the magnitude of FDs generally depends on the coordinates of the observing neutron stations. A strong correlation with a value of cc = 0.93 was observed between FDs of SOPO and MOSC stations, followed by FDs of CLMX and MOSC stations of value cc = 0.89, and lastly, FDs of SOPO and CLMX stations of value cc = 0.74. This implies that observed FDs from neutron stations are coordinate-dependent. The correlation between FD magnitudes and solar activities shows that solar wind had a high and significant correlation with FD magnitude to the tune of cc = 0.54. Based on the findings, the study concludes that solar wind disturbances play a crucial role in causing a sharp decrease in the intensity of cosmic rays known as Forbush decrease.

Effect of solar wind disturbances on small-amplitude simultaneous Forbush events during solar cycle 23

The transient and rapid reduction in galactic cosmic ray (GCR) flux intensity, commonly referred to as Forbush decrease (FD), is widely used as a mediator variable in searching for solar-terrestrial weather linkages. Whereas literature in the field is replete with high-amplitude (FD(%) ⩾3) FD-based analyses, the empirical connections between low-amplitude (FD(%) ⩽3) events and Sun-Earth variables are seldom tested. It is recently observed that the dearth of such studies might be due to the daunting task of accurate detection/precise timing of FDs and other transient astrophysical events. Using a sensitive version of the FD detection algorithm, we selected 264, 267, and 206 low amplitude (FD(%) ⩽3) FDs from the daily GCR data of Hermanus (HRMS), Newark (NWRK) and Oulu (OULU) neutron monitor stations respectively during solar cycle 23. A total of 80 simultaneous small-amplitude FDs were identified from the three stations with a simple coincident computer code. Statistically significant correlations at 95% confidence level exist between the planetary K-index (Kp), disturbance storm time index (Dst), planetary A-index (Ap), and the corresponding simultaneous small-amplitude FDs at OULU station, but not found in HRMS and NWRK data. These significant links between the weak FDs and the geomagnetic indices (Kp, Dst, and Ap) at OULU station suggest that the parameters (Kp, Dst, and Ap) are likely connected with some common solar activities.