Period Of Solar Activity Research Articles

Genetic mechanism of multi-scale sedimentary cycles and their impacts on shale-oil distribution in Permian Lucaogou Formation, Jimusar Sag, Junggar Basin

Complex lithofacies of Lucaogou Formation in Jimusar Sag promote strong heterogeneity of oil distribution in fine grained sedimentary rocks. It is of great significance to define the formation mechanism of fine-grained sedimentary rocks for favorable reservoir prediction and exploration target selection in Jimusar Sag. Based on detailed petrographic characterization, in-situ geochemical parameter testing, and high-resolution cycle analysis, sedimentary cycles on the micron to meter scales were successfully identified in Lucaogou Formation from Jimusar Sag. Precession-forced paleo-environmental evolution mainly induces the deposition of meter-scale sedimentary cycles. In the period of low precession, the paleo-environment is cold and dry, the lake level falls. Silt-grained particles advance toward the center of the lake basin carried by gravity current, thus siliciclastic sediments are mainly deposited. In the period of high precession, the climate is warm and humid, the lake level rises. The inputs of siliciclastic sediments are limited and the temperature increases, which are conductive to the carbonate deposition. On this basis, high-frequency paleo-environmental evolution caused by solar activity (70–110yr cycle) further induces the formation of sedimentary cycles on micron-centimeter scale. When the precession is low, the rise and fall of lake level controlled by solar activity is contribute to the deposition of tuff-rich lamina and silt-grained felsic lamina, respectively. The period of high precession is under the background of overall high lake-level, the rise and fall of lake level, along with fall and rise of temperature, controlled by solar activity finally induce the deposition of tuff-rich lamina and carbonate lamina, respectively. The development of multi-scale sedimentary cycles controlled by Milankovitch cycle and solar activity cycle have important implications for shale oil enrichment. The fine-grained sediments deposited during the period of low precession and intense solar activity dominate feldspar dissolution pores and intergranular pores, which are favorable for shale oil enrichment.

Sunspot activity influences tree growth: Molecular evidence and ecological implications.

Solar activity has a significant influence on Earth's climate and may drive many biological processes. Here, we measured growth in 11 tree species distributed along an ≈600-km latitudinal gradient in South-Central Chile, recording the width of their growth-rings among periods of maximum (highest number of sunspots) and minimum (lowest number of sunspots) solar activity. In one of these species, Quillaja saponaria, we experimentally assessed three ecophysiological traits (CO2 fixation through photosynthesis [Amax], growth and leaf production) as well as the expression of five genes related to cell wall elongation and expansion following exposure to high and low levels of UV-B radiation, simulating scenarios of maximum and minimum solar activity, respectively. We found lower tree growth during the periods of maximum solar activity, with this trend being more evident at lower latitudes, where UV-B radiation is higher. Exposure of Q.saponaria to higher levels of UV-B affected the ecophysiological parameters, revealing a decrease in Amax, growth and leaf production. In addition, higher levels of UV-B led to repression in four of the five genes studied. Our results may help foresee environmental scenarios for different plant species associated with solar activity.

Analysis of temporal and spatial variation characteristics of midlatitude summer nighttime anomaly in low and middle solar activity period

The spatiotemporal variation characteristics of midlatitude summer nighttime anomaly (MSNA) are essential for ionospheric modeling in the MSNA region. Based on GIM TEC, COSMIC NmF2, COSMIC IEC (Integrate Electron Content), and GPS TEC, this paper analyzes the spatiotemporal variation characteristics of MSNA during the low and middle solar activity period. First, we use the fourth-order Fourier function to fit the TEC, NmF2, and IEC. Second, we calculate an MSNA index and give its spatiotemporal distribution during the low and middle solar activity period. Third, on the basis of GIM TEC and GPS TEC, we describe the spatiotemporal distribution of TEC peak moments from October to January (Oct-Jan) and May to August (May-Aug). Our detailed analysis shows the following: (1) MSNA in the Southern Hemisphere is most significant in Oct-Jan. Moreover, MSNA in the Northern Hemisphere is most significant in May-Aug. (2) MSNA mainly occurs in three regions: South America and Antarctica, Western Europe to eastern North America, and Northeast Asia to the Pacific. (3) When solar activity increases, the MSNA region in the Northern Hemisphere becomes smaller, and the MSNA index is unchanged. Moreover, the MSNA region in the Southern Hemisphere is unchanged, but the MSNA index increases. (4) From Oct-Jan, there are some apparent differences between the east and west sides of the MSNA region of the Antarctic Peninsula. The peak moments of TEC in the west region concentrate before midnight (20:00–22:00 LT), and the peak moments of TEC in the east region concentrate after midnight (00:00–08:00 LT). As the level of solar activity increases, the peak moments in the eastern region are significantly shifted to later local time. (5) As the level of solar activity increases, the incidence of MSNA at three GPS stations (OHI300ATA, YSSK00RUS, and BRST00FRA) shows a decreasing trend.

Numerical simulation of stratospheric QBO impact on the planetary waves up to the thermosphere

With the help of numerical simulation, a detailed analysis of the dynamical effect of the stratospheric quasi-biennial oscillation (QBO) of the equatorial zonal wind on the planetary waves (PWs) up to thermospheric heights is carried out for the first time. The 3-dimensional nonlinear mechanistic model of middle and upper atmosphere (MUAM) is used, which is capable of simulating the general atmospheric circulation from the surface up to 300–400 km altitude. The amplitudes of stationary and westward travelling PWs with periods from 4 to 10 days are calculated based on ensembles of model simulations for conditions corresponding to the easterly and westerly QBO phases. Fluxes of wave activity and refractive indices of the atmosphere are calculated to analyze the detailed behavior of the PWs. The important result to emerge is that the stratospheric QBO causes statistically significant changes in the amplitudes of individual wave components up to 25% in the mesosphere-lower thermosphere and 10% changes above 200 km. This change in wave structures should be especially noticeable in the atmosphere during periods of low solar activity, when the direct contribution of solar activity fluctuations is minimized. Propagating from the troposphere to the upper atmosphere, PWs contribute to the propagation of the QBO signal not only from the equatorial region to extratropical latitudes, but also from the stratosphere to the thermosphere. The need for a detailed analysis of large-scale wave disturbances in the upper atmosphere and their relationship with the underlying layers is due, in particular, to their significant impact on satellite navigation and communication systems, which is caused by amplitude and phase fluctuations of the radio signal.

Short-term Adaptive Forecast Model for TEC over equatorial low latitude region

In today's world, satellite navigation is one of the most widely used navigational aids, which is why accurate positioning is of critical importance. The ionosphere's Total Electron Content (TEC) is a significant contributor to the positional error in signal traveling between a satellite and the earth and reduces the system's positional accuracy. The ionosphere adds an excess delay to the radio wave traversing through it, resulting in position estimation error. Since the delay is a function of the ionospheric parameter TEC, estimation of TEC can help in correcting the errors. The challenge in estimating TEC in the equatorial region is that it exhibits a non-deterministic or unpredictable characteristic due to the complex electrodynamics resulting from Equatorial Ionospheric Anomaly (EIA). In addition, space weather phenomena like geomagnetic storms further disturb the ionosphere causing irregular short-term disturbances. This study explores the inherent VTEC pattern during geomagnetic storm conditions, especially during the high solar activity period, and proposes a short-term adaptive segmented regression model to forecast VTEC. The study is undertaken over six years of high solar activity period in the 24th solar cycle. The forecast model uses both linear and polynomial autoregression coefficients of recent past data. The model's performance is evaluated for extreme conditions, including the high solar activity and geomagnetic storms, which are the most challenging scenario for TEC prediction. The accuracy of the predicted output is calculated in terms of RMSE and correlation coefficient. The results were also compared with IRI 2016 model. The proposed short-term prediction model thus aims to help fill the precision required by long-term forecast models by considering near real-time nonlinear dynamics in the ionosphere.

The preliminary result of orbital atmosphere detector on board spherical satellite

<p indent="0mm">The spherical satellite is Chinese first spherical small satellite, integrating atmospheric composition, atmospheric density detection and precision orbit determination. The payload is the Orbital Atmosphere Detector, which was launched into near circular polar orbit with the orbit altitude of <sc>520 km</sc> and inclination angle of 97.4° on 14 October, 2021. The scientific objectives, operating principle and the ground calibration results of the Orbital Atmosphere Detector are presented in this paper. The preliminary <italic>in-situ</italic> observed results are analyzed and discussed. The observed mass densities are strongly correlated with <italic>F</italic>10.7 and <italic>Kp</italic>. The peak-to-valley ratio of observed mass densities during the quiet period of solar and geomagnetic activity on 3 November 2021 was 3.02; the peak of observed mass density increased from 2.8×10⁻¹³ to 8.0×<sc>10⁻¹³ kg/m³</sc> during the strong geomagnetic storm event on 4 November, 2021, an increase of 2.857 times compared to the MSIS00 model of 1.316 times. The observed data show that the increase in atmospheric density started at the South Pole and spread to the middle and low latitudes, while the MSIS00 model only show a weak symmetrically increase between the northern and southern hemispheres during the storm. The observed results show that the observed data objectively reflect the spatial and temporal distribution of thermosphere density during the quiet period and the geomagnetic storm event, and thermosphere atmospheric model correction can be implemented based on the large amount of observed data.

Performance Evaluation of Modified IRI2016 and Its Application to the 24 hr Ahead Forecast foF2 Mapping Over China

AbstractIn this paper, we have modified the International Reference Ionosphere model 2016 (IRI2016) with the Global Navigation Satellite System total electron content data observation in China by adjusting the ionospheric index (IG12) for given location and time. The capability of the modified IRI2016 to reproduce the F2 layer critical frequency foF2 is validated for high/low solar activity conditions and disturbed geomagnetic conditions for the time period 2014–2017 over low‐latitude ionosonde station located at Sanya in China. The analysis shows that the modified IRI2016 better reproduced the variability of the observed foF2 versus time and seasons. Also, the modified IRI2016 foF2 prediction exhibits lower root mean square error and higher correlation coefficients (R) over different solar activity periods, and significantly reduces the average percentage deviations (△foF2(%)) under enhanced geomagnetic activity periods. Subsequently, the 24 hr ahead forecast foF2 map over China constructed by the combination of the modified IRI2016 and the eXtreme Gradient Boosting algorithm is presented for the first time. The promising performance of the modified IRI2016 indicates that this combination method may be an effective way to predict the ionospheric parameters, though further validations are needed in the future work.

Solar Cycle Variability in Coronal Holes and Their Effects on Solar Wind Sources

AbstractVarious upstream spacecraft have now observed the solar wind conditions affecting the Earth since the 1970s, covering over four solar activity cycles. These measurements provide a long term picture of the related patterns in large scale incident plasma and magnetic field parameters of interest for both interpreting cycles in geospace effects, and understanding how the Sun controls our space environment. This paper focuses on the latter, in part to provide context at the start of the new solar cycle 25, and toward establishing connections between the 1 AU ecliptic solar wind behavior and the unprecedented near‐Sun measurements of heliospheric features on Parker Solar Probe and Solar Orbiter. Magnetograph data‐based potential field source surface models provide a basic picture of how the solar wind sources, including those that give rise to corotating high speed streams in the ecliptic, have changed since the beginning of the record of regular solar wind measurements. In particular, they suggest the contributions from low to mid latitude coronal holes dominate the observed cycles (21–24), especially the weaker cycles (23 and 24), impacting upstream measurement interpretations, modeling, and forecasting considerations. For example, recurring features are affected by differential rotation of the Sun's surface field, which through its effects on the corona, can produce solar wind streams reappearing at ∼25–30 days intervals instead of at the canonical 27.3 days Carrington rotation rate. In addition, the conditions that lead to the corotating stream structure that can dominate periods of low solar activity are seen to be more complicated than suggested by the simple concepts of early studies. The overall results illustrate where in the cycles well‐defined, long‐lived large scale structures can be expected, and the advantages of synoptic displays of 1 AU solar wind parameters for anticipating timings of recurring features.

Impact of Solar Activity on the Environment in March 2022

Data from 64 stations of the global ionosonde network were used to estimate the correlation coefficient between the critical frequency of the ionosphere and its total electron content TEC during periods of high solar activity in March 2022. This coefficient in the vast majority of cases exceeded the value of 0.9, which indicates the interchangeability of these parameters in assessing the state of the environment. This assessment using the TEC parameter revealed a global positive ionization perturbation with a deviation of 30 to 100% from the month median at the end of the month, which can affect the operation of various space technological systems.

Effect of the Non‐Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

AbstractThe annual mean (Sq0), annual (Sq1), and semiannual (Sq2) components of the monthly averaged daily amplitude of the geomagnetic Y component during quiet period over several solar cycles at 25 mid‐low latitudes observatories were separated by means of Fourier analysis. No obvious distinction is found for the morphology of the spatial distribution of these Sq(Y) components during solar quiet and active periods, except that they are more intense in high solar activity. We found that the longitudinal variations in the Southern Hemisphere were primarily attributed to the differences in the annual component (Sq1), which is stronger at the Eurasia and Australia anomaly zones than at the South Atlantic Ocean anomaly (SAA) zones. The positive correlation between Sq0 and geomagnetic vertical component Z suggests that the convection electric fields in the dynamo region play a key role in controlling the annual mean (Sq0). On the other hand, the Sq1 exhibits a positive correlation with geomagnetic horizontal component H, implying the interhemispheric field‐aligned currents (IHFACs) may contribute to difference of the annual variation amplitude at the different observatories. Sq2 is most prominent in the SAA region while rather weak at other positive anomaly zones (in total field), which indicates there is a negative correlation between the total field anomaly and the semiannual variations.

Peculiarities of the Heliospheric State and the Solar-Wind/Magnetosphere Coupling in the Era of Weakened Solar Activity

Based on the data of the solar wind (SW) measurements of the OMNI database for the period 1976–2019, we investigate the behavior of SW types, as well as plasma and interplanetary magnetic field (IMF) parameters, for 21–24 solar cycles (SCs). Our analysis shows that with the beginning of the period of low solar activity (SC 23), the number of all types of disturbed events in the interplanetary medium decreased, but the proportion of magnetic storms initiated by CIR increased. In addition, a change in the nature of SW interaction with the magnetosphere could occur due to a decrease in the density, temperature, and IMF of solar wind.

Exploring the variability of the venusian thermosphere with the IPSL Venus GCM

Recent simulations of the Institut Pierre-Simon Laplace (IPSL) Venus Global Climate Model (VGCM) developed at the Laboratoire de Météorologie Dynamique (LMD) were performed with a model top raised from ∼10−5 (∼150 km) to ∼10−8 Pa (180–250 km; upper boundary). The parameterizations of non-LTE CO2 near infrared heating rates and of non-orographic gravity waves were improved. In addition, a tuning of atomic oxygen production was introduced to improve related effects (heating and cooling) and resulting thermospheric number densities. This work focusses on validating the modelled thermospheric structure using data from the Pioneer Venus, Magellan and Venus Express missions which cover similar and complementary (equator and pole) regions at different periods of solar activity, typically above altitudes of 130 km. This version of the IPSL VGCM shows good agreement with the diurnal evolution of the exospheric temperature at the equator reconstructed from the atomic oxygen scale height of the Pioneer Venus Orbiter Neutral Mass Spectrometer data. The model is also able to reproduce the sensitivity of the exospheric temperature and species density to the EUV flux of the solar high activity period (from 180 to 230 solar flux unit; s.f.u). However, to fit with the PV-ONMS density observations, it was necessary to increase the photodissociation of CO2 into CO and O above 135 km by a factor of 10. Indeed, our study points to the importance of an additional source of oxygen and carbon monoxide production above 130 km other than CO2 photolysis to explain the vertical profiles of CO and O number density in the thermosphere. Moreover, the presence of a GW drag at altitudes above 140 km has a significant impact on the nightside temperature value and its distribution.

Solar modulation of cosmic proton and helium with AMS-02

We investigate the solar modulation effect with the long-time cosmic ray (CR) proton and helium spectra measured by AMS-02 on the timescale of a Bartels rotation (27 days) between May 2011 and May 2017. The time covers the negative heliospheric magnetic field polarity cycle, the polarity reversal period, and the positive polarity cycle. The precise AMS-02 data provide an excellent opportunity to improve the understanding of the time-dependent solar modulation effect. In this work, a two-dimensional solar modulation model is used to compute the propagation of cosmic rays in the heliosphere. The CR propagation equation is numerically solved by the public code solarprop. We find that the drift effect is suppressed during the high solar activity period for a long time but nearly recovered in the first half of 2017. The time-dependent rigidity dependence of the mean free path is critical to reproduce the observations during the polarity reversal period. We also confirm that protons and helium have the same diffusive mean free path. The future monthly AMS-02 and PAMELA data will further confirm the vital assumption about the universal mean free path for all species. The monthly antiproton data will be crucial to break the degeneracy between the diffusion and drift effect and determine the level of drift effect during different epochs.

Relationship between sunspot number and seasonal rainfall over Kerala using wavelet analysis

In this work, we investigate the periodicities of rainfall over Kerala, India, and sunspot number (1871–2016) and their possible association. Fourier and wavelet transform were performed on the rainfall and sunspot number time series to determine dominant periods. Both the data were considered on an annual scale, as well as on a seasonal scale by grouping into winter, pre-monsoon, monsoon, and post-monsoon seasons. Fourier analysis showed short periods between 2–12 years for all the seasonal rainfall and a prominent 10.7-year period for sunspot number. Further, the wavelet spectrum of rainfall over Kerala showed the most significant periodicities around 2–10 years but with intermittent character and 8–12 years for sunspot number. The periodicity of sunspot number and rainfall estimated by Fourier analysis was in agreement with wavelet analysis. Wavelet analysis gave common spectral powers with varying significance for winter and monsoon seasons around 2–3 years. Common features in the wavelet power of the two time series were visible at 8–12 years with varying significance, suggesting a relationship between them. The cross-wavelet transform, employed to study the temporal relationship, indicated high cross-power around 8–12 years, during all the seasons. The relationship between sunspot number and rainfall over Kerala during varying levels of solar activity was examined using wavelet coherence. Results showed higher coherence during the high solar activity period than during low solar activity, mainly during winter, monsoon, and post-monsoon seasons. Coherence studies were also performed to check whether the influence of solar activity on rainfall completely diminished after the onset of global warming. Results showed persistence of solar influence in different seasons during the whole period of study.

The faintest solar coronal hard X-rays observed with FOXSI

Context. Solar nanoflares are small impulsive events releasing magnetic energy in the corona. If nanoflares follow the same physics as their larger counterparts, they should emit hard X-rays (HXRs) but with a rather faint intensity. A copious and continuous presence of nanoflares would result in a sustained HXR emission. These nanoflares could deliver enormous amounts of energy into the solar corona, possibly accounting for its high temperatures. To date, there has not been any direct observation of such persistent HXRs from the quiescent Sun. However, the quiet-Sun HXR emission was constrained in 2010 using almost 12 days of quiescent solar off-pointing observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). These observations set 2σ upper limits at 3.4 × 10−2 photons s−1 cm−2 keV−1 and 9.5 × 10−4 photons s−1 cm−2 keV−1 for the 3–6 keV and 6–12 keV energy ranges, respectively. Aims. Observing faint HXR emission is challenging because it demands high sensitivity and dynamic range instruments. The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment excels in these two attributes when compared with RHESSI. FOXSI completed its second and third successful flights (FOXSI-2 and -3) on December 11, 2014, and September 7, 2018, respectively. This paper aims to constrain the quiet-Sun emission in the 5–10 keV energy range using FOXSI-2 and -3 observations. Methods. To fully characterize the sensitivity of FOXSI, we assessed ghost ray backgrounds generated by sources outside of the field of view via a ray-tracing algorithm. We used a Bayesian approach to provide upper thresholds of quiet-Sun HXR emission and probability distributions for the expected flux when a quiet-Sun HXR source is assumed to exist. Results. We found a FOXSI-2 upper limit of 4.5 × 10−2 photons s−1 cm−2 keV−1 with a 2σ confidence level in the 5–10 keV energy range. This limit is the first-ever quiet-Sun upper threshold in HXR reported using ∼1 min observations during a period of high solar activity. RHESSI was unable to measure the quiet-Sun emission during active times due to its limited dynamic range. During the FOXSI-3 flight, the Sun exhibited a fairly quiet configuration, displaying only one aged nonflaring active region. Using the entire ∼6.5 min of FOXSI-3 data, we report a 2σ upper limit of ∼10−4 photons s−1 cm−2 keV−1 for the 5–10 keV energy range. Conclusions. The FOXSI-3 upper limits on quiet-Sun emission are similar to that previously reported, but FOXSI-3 achieved these results with only 5 min of observations or about 1/2600 less time than RHESSI. A possible future spacecraft using hard X-ray focusing optics like those in the FOXSI concept would allow enough observation time to constrain the current HXR quiet-Sun limits further, or perhaps even make direct detections. This is the first report of quiet-Sun HXR limits from FOXSI and the first science paper using FOXSI-3 observations.

Развитие ретинопатии недоношенных в зависимости от солнечной активности и срока гестации. Прогнозирование и анализ клинических исходов

Purpose. To analyze the prevalence of retinopathy of prematurity (ROP) depending on the gestational age and solar activity; to predict the outcome of ROP in children born in different solar activity seasons. Material and methods. 229 case histories of premature infants born at children's hospital, Tambov within 2017–2019 were analyzed. They were divided into two groups: group I – children with retinopathy of prematurity (1, 2 and 3 degree), mean gestational age – 27.1 ± 2.3 weeks; mean birth weight 1008 ± 390 g and group II – premature infants without any retinopathy (pre retinopathy), mean gestational age 30.3 ± 2.12 weeks, mean gestational age 1614 ± 380 g. Also, all children were divided according to the birthday terms and periods of solar activity: winter, spring, summer, autumn. The disease outcome was taken into account in the children with ROP: children undergone laser coagulation (LC) and spontaneous regression. Results. The study revealed a strong direct relationship between the outcome of ROP and gestational age and seasonal solar activity. There were received the differences between ROP outcomes in children born in the period of increased and decreased insolation. Conclusion. The significant correlations were received: the greater the gestational age and birth weight is, the less likely the need for LC. A mathematical model for predicting the outcome of ROP was developed. Keywords: retinopathy of prematurity, solar activity, gestational age, screening, preventive measures, prediction.

Occurrence of Ionospheric irregularities over Brazil and Africa during the 2019 Antarctic minor sudden stratospheric warming

The influence of sudden stratospheric warming (SSW) on the ionosphere and ionospheric irregularities has been studied extensively over the years. However, majority of these investigations have been conducted using warming events originating from the northern hemisphere. Only a few studies have been done on ionospheric variations due to the Antarctic SSW events and to the best of our knowledge, there have not been any studies on southern hemisphere SSW and the occurrence of ionospheric irregularities. In this study, the occurrence of ionospheric irregularities during the 2019 minor Southern hemisphere (SH)/Antarctic SSW is investigated. The event occurs in a relatively calm solar and geomagnetic activity period which makes it possible to identify the effects of SSW on the occurrence of irregularities. Three ionosondes located in different latitudinal regions in Brazil as well as a network of ground-based GPS receiver stations located in both Brazil and Africa were used for this undertaking. Complimentary data from the same ionosonde stations using the same months from 2017 and 2018 were also used. On average more Spread-F was observed in 2019 than in 2017 or 2018 at all stations. ROT observations showed more occurrence in the Brazil sectors followed by West Africa and thenEast Africa. It was observed that the occurrence frequency decreased between 8% and 46 % from the pre-SSW phase to ascending/peak phases and from 2018 to 2019 for the peak phase.

Evaluation of NeQuick2 Model over Mid-Latitudes of Northern Hemisphere

NeQuick2 is a three-dimensional ionospheric electron density empirical model that uses numerical integration to calculate the total electron content along any line-of-sight (LOS). As one of the most commonly used three-dimensional ionospheric models, it is necessary to objectively evaluate the accuracy and stability of NeQuick2 over a long period, especially over the mid-latitudes of the northern hemisphere where most of the ground-based GNSS stations are distributed. Therefore, different methods are used in this study to evaluate the accuracy of the NeQuick2 model from 2008 to 2021, including comparison with the International Global Navigation Satellite System Global Ionosphere Maps (IGSG), Jason2 Vertical Electron content (VTEC), and self-consistent evaluation. The comparison with IGSG shows that the standard deviation (STD) value is about 2.59 TECU. The accuracy of the IGSG and NeQuick2 model over ocean regions shows that the bias of IGSG is more significant than that of the NeQuick2 model. The mean STD value is 2.09 TECU for IGSG, and the corresponding value is 3.18 TECU for the NeQuick2 model, which is about 50% worse than IGSG. The dSTEC assessment results indicate that the variation in bias for IGSG is more stable than that of the NeQuick2 model. The mean STD value is 0.86 and 1.52 TECU for IGSG and NeQuick2 model, respectively. The conclusion could be made that NeQuick2 model represents the average ionosphere electron content and its accuracy fluctuates with solar conditions. Compared with the IGSG, the NeQuick2 model always underestimates TEC value, especially in low solar activity periods and compared with Jason2, the TEC values obtained by NeQuick2 model are overestimated, but the degree of overestimation is smaller than that of IGSG.

Solar variability between 650 CE and 1900 - Novel insights from a global compilation of new and existing high-resolution 14C records

This study investigates solar variability between 650 CE and 1900 based on new and published 14C records with a time resolution of two years or higher. The new high-resolution 14C data presented here are derived from Danish oak and span the period 1058–1250 CE. We determine the durations of past solar minima and periods with moderate solar activity from the solar modulation potential calculated using a carbon-box model with the high-resolution 14C records as input. The observed intervals of solar minima and intermittent periods with moderate activity levels suggest that a Maunder-type minimum occurred in 656–707 CE. We tentatively propose to name this minimum the Horrebow Minimum after Christian Horrebow, an early Danish astronomer who studied the occurrence of sunspots and was the first to propose that they follow a cyclic behaviour. Changes in amplitude and cycle length of the 11-year solar cycle are investigated by bandpass filtering 23 individual 14C records. The filtered 14C data indicate that the length of the 11-year solar cycle may be prolonged before the onset of the Oort, Maunder, and Spörer minima. The amplitude of the 11-year solar cycle associated with solar minima and periods with moderate solar activity between 650 CE and 1900 is estimated to 1.1‰. A two-sample Kolmogorov-Smirnov goodness-of-fit test indicates that there is no significant difference between the amplitude distribution of 11-year solar cycles during solar minima and periods of moderate solar activity. A review of the high-resolution 14C records encompassing the near-Earth supernova events that occurred in 1006 CE, 1054, 1181, 1572, and 1604 suggests that these events were not accompanied by distinct changes in the 14C production rate. Nonetheless, an unusual increase of c. 10‰ in Δ14C between 1048 CE and 1055 is observed and discussed.

Climatology of global, hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.