Level Of Solar Activity Research Articles

Adaptation of the NeQuick2 model for GNSS wide-area ionospheric delay correction in China and the surrounding areas

As an empirical three-dimensional ionospheric electron density model, NeQuick2 can generally represent the temporal and spatial characterization of ionospheric Total Electron Content (TEC) at a global scale. However, mismodeling errors usually exist between NeQuick2 representation and actual state of short-term ionospheric variation in small scales. In this contribution, an adaptation method is proposed for the NeQuick2 model based on data ingestion with GNSS-derived ionospheric TEC data. The relationship between the background NeQuick2 Slant TEC (STEC) estimations and real STEC measurements can be properly modelled with a ‘scaling factor’ in a highly efficient manner. In order to verify the feasibility and usefulness of the algorithm, validation experiments are carried out with GNSS tracking stations in China and the surrounding areas under different levels of solar activity. The results show that the bias of NeQuick2 corrections after adaptation are mostly within 1.0 TECu, suggesting that the systematic bias of the original NeQuick2 model can be significantly reduced. In comparison with about 50%-70% STEC RMS errors corrected by the original NeQuick2 model, the NeQuick2 model after adaptation can generally correct about 80% − 90% STEC RMS errors, which is also better than the CODE final GIM product as it has smaller residual bias and uses fewer reference stations. Therefore, the proposed algorithm can be satisfactorily applied in wide area GNSS ionospheric corrections.

Solar-Flux Variation in Helium Lines According to SDO/EVE Data in the 24th Cycle and the Forecast for Different Levels of Solar Activity. Lyman Decrements of Hydrogen and Helium Lines

The extreme ultraviolet radiation (EUV radiation) of the Sun is studied. The time series of daily values of the radiation fluxes outside flares in the EUV range are constructed based on the archive of daily Solar Dynamics Observatory/EUV Variability Experiment observations for 2010–2018. The fluxes in the lines of neutral helium He I (58.4 nm and 53.7 nm) and ionized helium He II (30.4 nm and 25.6 nm) are analyzed for the 24th activity cycle. The coefficients of quadratic regressions are calculated in order to restore the fluxes at different phases of the cycle. The decrement variation in the lines of neutral hydrogen and neutral and ionized helium during the 24th cycle and flares are considered.

Exhaustive study of three-time periods of solar activity due to single active regions: sunspot, flare, CME, and geo-effectiveness characteristics

In this paper, we present the multi-wavelength study of a high level of solar activity during which a single active region produced multiple flares/CMEs. According to the sunspot observations, the current solar cycle 24 manifest to be less intense in comparison with the previous recent sunspot cycles. In the course of the current sunspot cycle 24, several small and large sunspot groups have produced various moderate and intense flare/CME events. There are a few active regions with a large number of flaring activities passed across the visible disk of the Sun during 2012-2015. In this study, we consider the three periods 22-29 Oct 2013, 01-08 Nov 2013, and 25 Oct-08-Nov 2014, during which 228 flares have been observed. Considering only active regions near the central part of the disk, 59 CMEs (halo or partial) have been reported among which only 39 events are associated with flares. We conclude that an active region with a larger area, more complex morphology and stronger magnetic field has a comparatively higher possibility of producing extremely fast CMEs (speed $>1500$ km/sec). So that among the 5 X class flares of the reported periods, 3 of them (60%) are associated with a CME. The lift-off time for CME-flare associated events has a +15 to +30 minute time interval range after the occurrence time of associated flares suggesting that the flares produce the CMEs. Additionally, we compiled the geomagnetic storms occurring within 1-5 days after the CME onset. 10% of the 59 CMEs are related to a magnetic storm but all are moderate storms.

Coronal Elemental Abundance: New Results from Soft X-Ray Spectroscopy of the Sun

Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionisation potential (FIP) of the element. We estimate FIP bias from direct measurements of elemental abundances from soft X-ray spectra using data from multiple space missions covering a range of solar activity levels. This comprehensive analysis shows clear evidence for a decrease in FIP bias around maximum intensity of the X-ray flare with coronal abundances briefly tending to photospheric values and a slow recovery as the flare decays. The departure from coronal abundances are larger for the low FIP elements Ca, Fe and Si than for S which have a mid FIP value. These changes in the degree of fractionation might provide inputs to model wave propagation through the chromosphere during flares.

Climatological study of the ion temperature in the ionosphere as recorded by Millstone Hill incoherent scatter radar and comparison with the IRI model

Ion temperature data recorded by Millstone Hill incoherent scatter radar (42.61° N, 288.51° E) over four full solar cycles (from 1970 to 2018) are analyzed to depict its climatological behavior in the range of altitudes between 100 and 550 km. The ion temperature dependencies on altitude, local time, month of the year, and solar activity level are studied through a climatological analysis based on binning and boxplot representation of statistical values. Binned observations of ion temperature are compared with International Reference Ionosphere (IRI) modeled values (IRI-2016 version). This comparison reveals several shortcomings in the IRI modeling of the ion temperature at ionosphere altitudes, in particular for the altitudinal, diurnal, seasonal, and solar activity description. The main finding of this study is that the overall IRI overestimation of the ion temperature can be probably ascribed to the long-term ionosphere cooling. Moreover, the study suggests that the IRI ion temperature model needs to implement the seasonal and solar activity dependence, and introduce a more refined diurnal description to allow multiple diurnal maxima seen in observations. The IRI ion temperature anchor point at 430 km is investigated in more detail to show how also a better description of the altitude dependence is desirable for modeling purposes. Some hints and clues are finally given to improve the IRI ion temperature model.

Prediction of Solar Flares and Background Fluxes of X-Ray Radiation According to Synoptic Ground-Based Observations Using Machine-Learning Models

The paper presents machine-learning models for predicting powerful solar flares and background X-ray fluxes in the range of 1–8 A. To predict solar flares for the next day, information was used on the current level of solar activity obtained from ground-based synoptic observations, such as characteristics of sunspots and radio fluxes at wavelengths of 10.7 and 5 cm, as well as the level of the background flux and the number of solar flares of the current day obtained from the GOES satellite. To predict the background fluxes of X-ray radiation, only data from ground-based telescopes were used. The high efficiency of the forecast for the next day is shown. The neural network was trained on data available since 2002.

On the Use of Naked-eye Sunspot Observations during the Maunder Minimum

Abstract Naked-eye sunspot observations (NESOs) have been recorded for the past two millennia, approximately. These kinds of records were made around the world, mainly in Asian civilizations, and they are compiled in several catalogs. In this work, we analyze solar activity on days of the 19th century when NESOs were recorded. We found that only more than five sunspot groups were recorded in 39% of days corresponding to these NESO events. Furthermore, regarding the largest groups observed on days when NESOs were reported, we show that the uncorrected areas of these groups were below 200 millionths of solar disk (msd) in 3.2% of total cases, while it is 12.9% for areas between 200 and 499 msd. Thus, NESO records do not necessarily imply high solar activity and big sunspot groups. Therefore, these results contradict the interpretations of recent works that, using the same NESO set, suggest the solar activity level during the Maunder Minimum is still an open question. NESO records support the Maunder Minimum as a very low solar activity period.

A Methodology for Estimation of Hourly‐Monthly Stochastic Trend Characteristics of Midlatitude Ionosphere

AbstractSpatiotemporal variability of ionosphere poses a major challenge in characterization of observable parameters, critical frequency of F2 layer (foF2), maximum ionization height (hmF2), total electron content (TEC), and slab thickness. The nature of the multiscale space‐time variability of ionosphere can be modeled as a random field. In this study, as a first step in random field modeling of the trend, hourly‐monthly parametric probability density functions (PPDF) of foF2, hmF2, slab thickness, and TEC are obtained using IONOLAB‐PDF method for three midlatitude stations (namely, Juliusruh, Pruhonice, and Rome) for low, moderate, and high solar activity years of 2009, 2012, and 2014, respectively. foF2 and hmF2 are obtained from ionosondes. TEC is estimated from dual‐frequency Global Positioning System (GPS) receivers. It is observed that hourly‐monthly PPDFs of all ionospheric parameters at the three midlatitude stations can best be represented by lognormal and Weibull distributions. The estimates of mean and standard deviations of hourly‐monthly PPDFs indicate that the spatiotemporal stochastic trend variation of the midlatitude ionosphere differs in terms of foF2 and GPS‐TEC. The hourly‐monthly PPDF of foF2 represents all major anomalies as well as seasonal and hourly trends, whereas those of GPS‐TEC is highly dependent on solar activity level and latitude. The general statistical trend of hmF2 is anticorrelated with foF2 as expected. The mean of hourly‐monthly PPDF of slab thickness is around 400 km in 2012 and 2014 for all stations between 0200 UT and 1600 UT.

They do change after all: 25 yr of GONG data reveal variation of p-mode energy supply rates

ABSTRACT It has been shown over and over again that the parameters of solar p modes vary through the solar activity cycle: frequencies, amplitudes, lifetimes, energies. However, so far, the rates at which energy is supplied to the p modes have not been detected to be sensitive to the level of magnetic activity. We set out to re-inspect their temporal behaviour over the course of the last two Schwabe cycles. For this, we use Global Oscillation Network Group (GONG) p-mode parameter tables. We analyse the energy supply rates for modes of harmonic degrees l = 0–150 and average over the azimuthal orders and, subsequently, over modes in different parameter ranges. This averaging greatly helps in reducing the noise in the data. We find that energy supply rates are anticorrelated with the level of solar activity, for which we use the F10.7 index as a proxy. Modes of different mode frequency and harmonic degrees show varying strengths of anticorrelation with the F10.7 index, reaching as low as r = −0.82 for low frequency modes with l = 101–150. In this first dedicated study of solar p-mode energy supply rates in GONG data, we find that they do indeed vary through the solar cycle. Earlier investigations with data from other instruments were hindered by being limited to low harmonic degrees or by the data sets being too short. We provide tables of time-averaged energy supply rates for individual modes as well as for averages over disjunct frequency bins.

Effective Solar Activity Index for the Median of the Critical Frequency of the F2 Layer

Abstract—By comparing the moving 12-month averaged values of the F107 solar radiation flux at a wavelength of 10.7 cm and ionospheric solar activity index T, we established the effective solar activity index TF, which is defined as a second-degree polynomial from F107 with coefficients independent of time; it is intended for use in problems of forecasting the median of the critical frequency of the F2 layer, foF2, using well-known ionospheric models instead of T and F107 indices or international sunspot numbers Ri. TF is applicable for any solar activity level and the entire F107 measurement period. By definition, TF is independent of geomagnetic activity. The T index may depend on geomagnetic activity due to the dependence of the median of foF2 on this activity. It was found that the moving 12-month averaged index of geomagnetic activity Ap12 and the difference ΔT = T – TF decreased over time in 1954–2019, but for ΔT, this trend was likely qualitative. As a result, a linear dependence of ΔT on Ap12 is virtually absent for this interval: their correlation coefficient was less than 0.1.

Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond

William Cranch Bond, director of the Harvard College Observatory in mid-19th century, carried out detailed sunspot observations during the period 1847-1849. We highlight Bond was the observer with the highest daily number of sunspot groups observed in Solar Cycle 9 recording 18 groups on 26 December 1848 according to the current sunspot group database. However, we have detected significant mistakes in these counts due to the use of sunspot position tables instead of solar drawings. Therefore, we have revisited the sunspot observations made by Bond, establishing a new group counting. Our new counts of the sunspot groups from Bond's drawings indicate that solar activity was previously overestimated. Moreover, after this new counting, Bond would not be the astronomer who recorded the highest daily group number for Solar Cycle 9 but Schmidt with 16 groups on 14 February 1849. We have also indicated the new highest annual group numbers recorded by any observer for the period 1847-1849 in order to correct those values applied in the "brightest star" method, which is used as a rough indicator of the solar activity level. Furthermore, a comparison between Bond's sunspot records and the sunspot observations made by Schwabe and Wolf is shown. We conclude that the statistics of Wolf and Bond are similar regarding to the group count. Additionally, Schwabe was able to observe smaller groups than Bond.

Climatology Characteristics of Ionospheric Irregularities Described with GNSS ROTI

At equatorial and high latitudes, the intense ionospheric irregularities and plasma density gradients can seriously affect the performances of radio communication and satellite-based navigation systems; that represents a challenging topic for the scientific and engineering communities and operational use of communication and navigation services. The GNSS-based ROTI (rate of TEC index) is one of the most widely used indices to monitor the occurrence and intensity of ionospheric irregularities. In this paper, we examined the long-term performance of the ROTI in terms of finding the climatological characteristics of TEC fluctuations. We considered the different scale temporal signatures and checked the general sensitivity to the solar and geomagnetic activity. We retrieved and analyzed long-term time-series of ROTI values for two chains of GNSS stations located in European and North-American regions. This analysis covers three full years of the 24th solar cycle, which represent different levels of solar activity and include periods of intense geomagnetic storms. The ionospheric irregularities’ geographical distribution, as derived from ROTI, shows a reasonable consistency to be found within the poleward/equatorward boundaries of the auroral oval specified by empirical models. During magnetic midnight and quiet-time conditions, the equatorward boundary of the ROTI-derived ionospheric irregularity zone was observed at 65–70° of north magnetic latitude, while for local noon conditions this boundary was more poleward at 75–85 magnetic latitude. The ionospheric irregularities of low-to-moderate intensity were found to occur within the auroral oval at all levels of geomagnetic activity and seasons. At moderate and high levels of solar activity, the intensities of ionospheric irregularities are larger during local winter conditions than for the local summer and polar day conditions. We found that ROTI displays a selective latitudinal sensitivity to the auroral electrojet activity—the strongest dependence (correlation R > 0.6–0.8) was observed within a narrow latitudinal range of 55–70°N magnetic latitude, which corresponded to a band of the largest ROTI values within the auroral oval zone expanded equatorward during geomagnetic disturbances.

Average Ionospheric Middle and Low Latitudes Nighttime Zonal Currents Deduced From CHAMP

AbstractBy utilizing magnetic field measurements collected by CHAMP during the years 2001–2009, average characteristics of nighttime ionospheric zonal currents at middle and low latitudes are investigated. We provide for the first time the detailed dependencies of these currents on location, local time, season, and the level of solar activity. The main results obtained are (1) the nighttime zonal ionospheric currents at F‐region altitude, derived from the vertical magnetic component, exhibit on average height‐integrated current densities up to 10 mA/m. The amplitude varies quasi‐linearly with F10.7 flux level. (2) During equinoxes symmetric current systems at F‐region altitude are found in the two hemispheres. After sunset, eastward currents dominate at low latitudes, fading away toward midnight. After midnight regions of eastward currents are observed at midlatitude. During solstice seasons, eastward currents are enhanced in the summer hemisphere; westward currents are stronger in local winter. (3) Longitudinal variations of F‐region currents show clear wave‐1 patterns. This is related to the effect of the stationary planetary wave‐1 and the diurnal nonmigrating tide, D0. This dominant tidal signal, enhancing eastward currents over the Pacific region, appears at middle and low latitudes and during all seasons. (4) At the magnetic equator, signs of the equatorial electrojet (EEJ) are evident after 02:30 MLT. Intensity of westward currents in the narrow band increases toward sunrise. Longitudinal variations of the EEJ show a similar wave‐1 pattern as F‐region currents. Here the westward current density is enhanced over Africa/India. The EEJ wave‐1 modulation is strongest around June solstice.

Characterizing Ionospheric Effect on GNSS Radio Occultation Atmospheric Bending Angle

AbstractGlobal Navigation Satellite System (GNSS) atmospheric radio occultation (RO) has been an active remote sensing method to explore the Earth's atmosphere recently. The RO products especially atmospheric bending angles have been widely used for climate study. However, the residual ionospheric error (RIE) still exists to a certain extent after the widely used linear combination in bending angle calculation. In this study, we analyzed both CHAMP and COSMIC data and did full 3‐D ray tracing to characterize RIE. It is found that the order of RIE is around ±0.1 μrad and has an obvious dependency on a variety of factors including altitude, latitude, local time, season, and solar activity level. The amplitude and complexity of RIE generally increase with altitude. It is closely related to the strength of the E layer and the asymmetry between LEO side and GNSS side. Along magnetic latitude direction, the RIE shows a pronounced feature of two peaks and three troughs. From both the simulated and observed RIE, we can identify clearly the ionospheric seasonal variation features, such as the semiannual variation, the equinox asymmetry and the annual anomaly. A spherical asymmetry factor was also defined to quantify the correlation between ionospheric spherical asymmetry degree and RIE. The study provides a comprehensive understanding of RIE, which could contribute to the correction of RIE in the future.

Sunspot Observations by Barnaba Oriani (1778 – 1779)

We present the sunspot observations made by Barnaba Oriani in 1778 and 1779 at the Brera Observatory (Milan, Italy). We have computed the number of sunspot groups and individual sunspots and extracted the positions of all individual sunspots recorded by Oriani. It must be highlighted that the observations made by Oriani in 1779 are not included in the current sunspot-group number database. The observations made in 1778 were already included, but we have found important deficiencies in these values that underestimated the true level of solar activity. The highest daily number of groups recorded by Oriani was 12 (24 August 1778). Only Horrebow in Solar Cycle 2 observed a higher daily number of groups (up to 16 groups in 1769) in the second half of the 18th century. We have compared the sunspot observations made by Oriani and Staudacher for the common dates. In general, Oriani observed a few more groups than Staudacher, while Staudacher recorded more individual sunspots than Oriani. Furthermore, the sunspot positions recorded by both observers are similar, but some significant differences can be found. Finally, we want to highlight that the sunspot records made in the 18th century will help us to understand better the behavior of the long-term solar activity. Therefore, we need to improve the observational coverage of the sunspot records carried out in that century.

Strong Interrelation between the Short-Term Variability in the Ionosphere, Upper Mesosphere, and Winter Polar Stratosphere

We perform a joint analysis of short-period (up to several hours) variability in parameters of the ionosphere, the mesosphere, and the stratosphere at mid-latitude, subauroral, and high-latitude points for a long time interval. The study is based on the ionospheric total electron content (TEC) measurements and data on the OH rotational temperature at the mesopause height. We reveal similar seasonal variations in the dynamics of the short-term variability level, both in the ionosphere and the mesosphere. Maximum variability is observed during winter months and it exceeds the values in summer period up to 5–6 times. The revealed dynamics has no explicit relation to the levels of geomagnetic and solar activities. We suggest that the instabilities in the high-velocity stratospheric subauroral winter jet stream may be a source of the recorded variability seasonal variations in the ionosphere and the mesosphere. We propose a new index to estimate a short-term variability in the stratosphere. The index is shown to experience similar regular seasonal variations with a maximum during winter months. We show a clear correlation between the mesosphere/ionosphere variability indices values and the stratosphere disturbance index. The correlation is shown to be higher for the mesosphere variability index as compared with that in the ionosphere, and at the high-latitude point located closer to the jet stream. The obtained results indicate a strong interrelation between the short-period variability in the ionosphere, in the upper mesosphere, and in the subauroral stratosphere. The results contribute to elucidating the basic mechanisms for a vertical coupling between different atmospheric layers.

Transmission Lines in Poland and Space Weather Effects

We analyze the solar influence of space weather events on Polish energy infrastructure via geomagnetic disturbances. We consider two time intervals of very different levels of solar activity (SA) in the course of the solar activity cycle 24: 2010—an early rising phase of SA, near the solar minimum and 2014—solar maximum. From the total number of electrical grid failures, we extract almost five thousand failures in 2010 and more than ten thousand in 2014, which could be related to space weather effects. We analyze data of failures having unidentified causes, failures coupled with the aging of transmission network elements and electronic devices, which appeared during the time intervals of enhanced geomagnetic activity. We show that around the times of increasing geomagnetic activity level, the amount of transmission lines failures in the groups mentioned above grows, but mostly with some delay. It might be connected to some cumulative effect due to the result of transient states and their propagation in the distribution network. Although we do not exclude that the other factors may play a role, the solar-originating disturbances strengthen these effects.

Ionospheric Precursors of Magnetic Storms. 2. Analysis of Slough Station Data

The behavior of the critical frequency of the F2 layer, foF 2, during the 3 days preceding a magnetic storm is analyzed. A total of 254 storms in 1976–2010 were considered, and 1353 events (deviations of foF2 from quiet conditions) were found: 996 and 357 deviations had a positive and negative signs, respectively. It is found that the indicated deviations demonstrate a clearly pronounced and statistically significant dependence on the magnetic storm intensity (the minimal value of the Dst index), on the solar activity level (the F10.7 index), and on the season. The probability of the occurrence of the indicated deviations has clearly pronounced maxima 4–6, 12–13, and 18–20 h prior to the moment of the storm onset (SO). Moreover, the occurrence of the indicated deviations is most probable when the SO moment occurs at 0800–1000 and 1900–2100 LT. The results indicate that the found deviations are not occasional fluctuations in foF2 (Q disturbances) but are related to the subsequent magnetic storm, i.e., they are its precursors.

Вовлеченность генов гипоталамо-гипофизарно-надпочечниковой системы в формирование индивидуальных различий в уровне стрессовой неустойчивости

Целью настоящего исследования являлась оценка вклада 10 полиморфных локусов генов глюкокортикоидного (NR3C1) и минералокортикоидного (NR3C2) рецепторов, а также ген-средовых (G×E) взаимодействий в формирование межиндивидуальных различий в индивидуальных психологических свойствах у 1215 психически здоровых индивидов. Множественный регрессионный анализ выявил, что пренатальный уровень солнечной активности оказывал модулирующий эффект на ассоциацию функциональных полиморфных локусов rs56149945 (N363S) с показателями по шкале «настойчивость» (β = 1,21; р = 0,001) и rs41423247 в гене NR3C1 с индивидуальными различиями в уровне эмоциональной неустойчивости (β = -2,72; р = 0,005). The present study aimed to assess the main effects of ten polymorphisms of glucocorticoid (NR3C1) and mineralocorticoid receptor (NR3C2) genes together with gene-by-environment interactions on individual differences in personality traits in 1215 mentally healthy individuals aged 17-25 years. Multiple linear regression analysis demonstrated that prenatal solar activity level modulated the association of rs56149945 (N363S) with Persistence (β = 1.21; Р = 0.001) and rs41423247 in NR3C1 gene with emotional resistance to stress (β = -2.72; Р = 0.005).

Effects of solar activity on ionospheric current system in the Southeast Asia region

The equatorial ionospheric current system is composed of equatorial electrojet (EEJ) and solar quiet (Sq) that flow in the eastward direction. That being mentioned, this study looked into the changes in ionospheric currents stemming from geomagnetic storm disturbances at different levels of solar activity during solar cycle 24. This analysis was performed by employing an EEJ index known as EUEL, which is calculated from northward geomagnetic component data measured using ground-based magnetometer at five different latitudes across the Southeast Asia region. Based on the outcomes, the impacts of geomagnetic storm on EEJ currents were observed at 1200 LT and 1100 LT, respectively, during high and low solar activity levels. Time delay was associated with changes in EEJ peak time at varied activity levels. This case study reveals that EEJ value at peak time of high solar activity decreased significantly during the main phase of geomagnetic storm.