Carrington Rotation Research Articles

Asymmetric Latitudinal Gradients of Galactic Cosmic Rays at Low and High Cutoff Rigidities in Two Negative Solar Magnetic Cycles: Solar Cycles 21/22 and 23/24

The south–north asymmetry of the Galactic cosmic-ray (GCR) density [ $n$ ] denoted as $\delta n_{\text{S-N}}/n$ with respect to the heliospheric current sheet (HCS), observed by neutron monitors at low (≈ 1 GV) and high (≈ 13 and ≈ 17 GV) cutoff rigidities [ $P_{\text{c}}$ ], is investigated in two negative solar magnetic polarities when the dominant polar field is toward the northern hemisphere of the Sun. Using a new simple correction method for secular changes due to solar activity for the $\delta n_{\text{S-N}}/n$ reveals that it is inversely rigidity dependent. Annual values of the corrected $\delta n_{\text{S-N}}/n$ are close to zero in both solar magnetic cycles and exhibit substantial deviations due to their temporal 27-day variations. After corrections for Earth’s excursions in helio-latitude for the north–south (NS) differences of HCS tilt angle [ $\alpha$ ] as $\Delta\alpha_{ \text{N-S}}^{\text{E}}$ , the number of 27.3-day Carrington rotations that possess correspondences between the corrected $\delta n _{\text{S-N}}/n$ and $\Delta\alpha_{\text{N-S}}^{\text{E}}$ in both solar cycles (SCs) is significantly increased. Correlations of the two parameters are considerably increased in both SCs, particularly for SC 21/22. The asymmetric or unidirectional latitudinal gradients [ $G _{\perp}$ ] derived from the consistencies between corrected $\delta n_{\text{S-N}}/n$ and $\Delta\alpha_{\text{N-S}}^{ \text{E}}$ for the low and high $P_{\text{c}}$ in the SC 21/22 are 1.38% AU−1 and 0.69% AU−1, respectively, which are a few times larger than of SC 23/24. This suggests that asymmetric cosmic-ray modulation by the asymmetric HCS is more pronounced in SC 21/22 than in SC 23/24. Although the corrections also provide results that are fairly consistent with the drift model for the symmetric or bidirectional latitudinal gradient [ $G_{z}$ ], the effects of the SN asymmetric modulation of the GCR density are important as well. It is found that $G_{\perp}$ , $G_{z}$ , and SN asymmetric GCR modulation by NS asymmetric solar-wind speed are also inversely dependent on rigidity. The interplay between SN asymmetric modulation of the GCR density by the asymmetries in HCS and solar-wind speed, together with the effects of diffusion, are discussed for both of the negative solar magnetic cycles.

Scaling laws of quiet-Sun coronal loops

We study a series of relations between physical parameters in coronal loops of the quiet Sun reconstructed by combining tomographic techniques and modeling of the coronal magnetic field. We use differential emission measure tomography (DEMT) to determine the three-dimensional distribution of the electron density and temperature in the corona, and we model the magnetic field with a potential-field source-surface (PFSS) extrapolation of a synoptic magnetogram. By tracing the DEMT products along the extrapolated magnetic field lines, we obtain loop-averaged electron density and temperature. Also, loop-integrated energy-related quantities are computed for each closed magnetic field line. We apply the procedure to Carrington rotation 2082, during the activity minimum between Solar Cycles 23 and 24, using data from the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory (STEREO) spacecraft. We find a scaling law between the loop-average density N and loop length L,Nm∼L-0.35, but we do not find a significant relation between loop-average temperature and loop length. We confirm though the previously found result that loop-average temperatures at the equatorial latitudes are lower than at higher latitudes. We associate this behavior with the presence at the equatorial latitudes of loops with decreasing temperatures along their length (“down” loops), which are in general colder than loops with increasing temperatures (“up” loops). We also discuss the role of “down” loops in the obtained scaling laws of heating flux versus loop length for different heliographic latitudes. We find that the obtained scalings for quiet-Sun loops do not generally agree with those found in the case of AR loops from previous observational and theoretical studies. We suggest that to better understand the relations found, it is necessary to forward model the reconstructed loops using hydrodynamic codes working under the physical conditions of the quiet-Sun corona.

Modeling the Global Distribution of Solar Wind Parameters on the Source Surface Using Multiple Observations and the Artificial Neural Network Technique

The global distribution of magnetic field and other plasma parameters on the source surface, which we set at 2.5 solar radii, is important for coronal and heliospheric modeling. In this article, we introduce a new data-driven self-consistent method to obtain the global distribution of different parameters. The magnetic and polarized brightness ( $pB$ ) observations are used to derive the magnetic field and electron density on the source surface, respectively. Then, an artificial neural network (ANN) machine learning technique is applied to establish an empirical relation among the solar wind velocity, the magnetic field properties, and the electron density. The ANN is trained with global observational data, and is validated to be more reliable than the Wang–Sheeley–Arge (WSA) model for reconstructing the solar wind velocity, especially at high latitudes. The plasma temperature distribution is derived by solving a simplified one-dimensional (1D) magnetohydrodynamic (MHD) equation system on the source surface. Using the method in this study we can obtain the global distribution for all the parameters self-consistently based on magnetic and polarized brightness observations. The modeling results of four Carrington rotations from different solar cycle phases are presented to validate the method.

Does Adding Solar Wind Poynting Flux Improve the Optimum Solar Wind‐Magnetosphere Coupling Function?

AbstractWe study the contribution of the solar wind Poynting flux to the total power input into the magnetosphere. The dominant power delivered by the solar wind is the kinetic energy flux of the particles, which is larger than Ssw by a factor of order , where MA is the Alfvén Mach number. The currents flowing in the bow shock and magnetosheath and the electric field of the solar wind give regions where , which are sources of Poynting flux, generated from the kinetic energy flux. For southward interplanetary magnetic field, is duskward and the currents in the high‐latitude tail magnetopause are also sources of Poynting flux. We show transfer of kinetic energy into the magnetosphere is less efficient than direct entry of by a factor MA. Because MA is typically of order 10, this means that although the power density in the solar wind due to is typically only 1%, it is responsible for of order 10% of the energy input to the magnetosphere. To investigate the effect of this, we add a term to the solar wind‐magnetosphere energy coupling function that allows for and that increases the correlation with the geomagnetic am index for 1995–2017 (inclusive) from 0.908 to 0.924 for 1‐day averages and from 0.978 to 0.979 for annual means. The increase for means on daily or smaller timescales is a small improvement but is significant (at over the 3σ level), whereas the improvement for annual or Carrington rotation means is not significant.

Effect of the non-uniform solar chromospheric Lyα radiation on determining the coronal H I outflow velocity

We derived maps of the solar wind outflow velocity of coronal neutral hydrogen atoms at solar minimum in the altitude range 1.5–4.0 R⊙. We applied the Doppler dimming technique to coronagraphic observations in the UV H I Lyα line at 121.6 nm. The technique exploits the intensity reduction in the coronal line with increasing velocities of the outflowing plasma to determine the solar wind velocity by iterative modelling. The Lyα line intensity is sensitive to the wind outflow velocity and also depends on the physical properties of coronal particles and underlying chromospheric emission. Measurements of irradiance by the chromospheric Lyα radiation in the corona are required for a rigorous application of the Doppler dimming technique, but they are not provided by past and current instrumentations. A correlation function between the H I 121.6 nm and He II 30.4 nm line intensities was used to construct Carrington rotation maps of the non-uniform solar chromospheric Lyα radiation and thus to compute the Lyα line irradiance throughout the outer corona. Approximations concerning the temperature of the scattering H I atoms and exciting solar disc radiation were also adopted to significantly reduce the computational time and obtain a faster procedure for a quick-look data analysis of future coronagraphic observations. The effect of the chromospheric Lyα brightness distribution on the resulting H I outflow velocities was quantified. In particular, we found that the usual uniform-disc approximation systematically leads to an overestimated velocity in the polar and mid-latitude coronal regions up to a maximum of about 50−60 km s−1 closer to the Sun. This difference decreases at higher altitudes, where an increasingly larger chromospheric portion, including both brighter and darker disc features, contributes to illuminate the solar corona, and the non-uniform radiation condition progressively approaches the uniform-disc approximation.

Extracting Inner‐Heliosphere Solar Wind Speed Information From Heliospheric Imager Observations

AbstractWe present evidence that variability in the STEREO‐A Heliospheric Imager (HI) data is correlated with in situ solar wind speed estimates from WIND, STEREO‐A, and STEREO‐B. For 2008–2012, we compute the variability in HI differenced images in a plane‐of‐sky shell between 20 to 22.5 solar radii and, for a range of position angles, compare daily means of HI variability and in situ solar wind speed estimates. We show that the HI variability data and in situ solar wind speeds have similar temporal autocorrelation functions. Carrington rotation periodicities are well documented for in situ solar wind speeds, but, to our knowledge, this is the first time they have been presented in statistics computed from HI images. In situ solar wind speeds from STEREO‐A, STEREO‐B, and WIND are all are correlated with the HI variability, with a lag that varies in a manner consistent with the longitudinal separation of the in situ monitor and the HI instrument. Unlike many approaches to processing HI observations, our method requires no manual feature tracking; it is automated, is quick to compute, and does not suffer the subjective biases associated with manual classifications. These results suggest we could possibly estimate solar wind speeds in the low heliosphere directly from HI observations. This motivates further investigation, as this could be a significant asset to the space weather forecasting community; it might provide an independent observational constraint on heliospheric solar wind forecasts, through, for example, data assimilation. Finally, these results are another argument for the potential utility of including a HI on an operational space weather mission.

SPECTRUM: Synthetic Spectral Calculations for Global Space Plasma Modeling

Abstract High-resolution spectroscopy is the most accurate tool for measuring the properties of the solar corona. However, interpreting measured line intensities and line profiles emitted by the optically thin solar corona is complicated by line-of-sight (LOS) integration, which leads to measuring weighted averages of the plasma properties along the LOS. LOS integration effects can be removed by combining CHIANTI spectral emissivities with a 3D global model of the solar corona to calculate the contribution of all structures along the LOS to the measured intensities. In this paper, we describe SPECTRUM, a postprocessing tool that can calculate the emission from the optically thin solar corona by combining 3D magnetohydrodynamic (MHD) space plasma simulation results with the CHIANTI database. Doppler-shifted, nonthermal line broadening due to low-frequency Alfvén waves and anisotropic proton and isotropic electron temperatures can be individually taken into account during calculations. Synthetic spectral calculations can then be used for model validation, for interpretation of solar observations, and for forward modeling purposes. SPECTRUM is implemented within the Space Weather Modeling Framework (SWMF) and is therefore publicly available. In this paper, we describe the SPECTRUM module and show its applications by comparing synthetic spectra using simulation data by the 3D MHD Alfvén Wave Solar Model with observations done by the Hinode/Extreme-ultraviolet Imaging Spectrometer during Carrington rotations 2063 and 2082.

Supervised neural networks for helioseismic ring-diagram inversions

Context. The inversion of ring fit parameters to obtain subsurface flow maps in ring-diagram analysis for eight years of SDO observations is computationally expensive, requiring ∼3200 CPU hours. Aims. In this paper we apply machine-learning techniques to the inversion step of the ring diagram pipeline in order to speed up the calculations. Specifically, we train a predictor for subsurface flows using the mode fit parameters and the previous inversion results to replace future inversion requirements. Methods. We utilize artificial neural networks (ANNs) as a supervised learning method for predicting the flows in 15° ring tiles. We discuss each step of the proposed method to determine the optimal approach. In order to demonstrate that the machine-learning results still contain the subtle signatures key to local helioseismic studies, we use the machine-learning results to study the recently discovered solar equatorial Rossby waves. Results. The ANN is computationally efficient, able to make future flow predictions of an entire Carrington rotation in a matter of seconds, which is much faster than the current ∼31 CPU hours. Initial training of the networks requires ∼3 CPU hours. The trained ANN can achieve a rms error equal to approximately half that reported for the velocity inversions, demonstrating the accuracy of the machine learning (and perhaps the overestimation of the original errors from the ring-diagram pipeline). We find the signature of equatorial Rossby waves in the machine-learning flows covering six years of data, demonstrating that small-amplitude signals are maintained. The recovery of Rossby waves in the machine-learning flow maps can be achieved with only one Carrington rotation (27.275 days) of training data. Conclusions. We show that machine learning can be applied to and perform more efficiently than the current ring-diagram inversion. The computation burden of the machine learning includes 3 CPU hours for initial training, then around 10−4 CPU hours for future predictions.

Forecasting the Ambient Solar Wind with Numerical Models. I. On the Implementation of an Operational Framework

Abstract The ambient solar wind conditions in interplanetary space and in the near-Earth environment are determined by activity on the Sun. Steady solar wind streams modulate the propagation behavior of interplanetary coronal mass ejections and are themselves an important driver of recurrent geomagnetic storm activity. The knowledge of the ambient solar wind flows and fields is thus an essential component of successful space weather forecasting. Here, we present an implementation of an operational framework for operating, validating, and optimizing models of the ambient solar wind flow on the example of Carrington Rotation 2077. We reconstruct the global topology of the coronal magnetic field using the potential field source surface model (PFSS) and the Schatten current sheet model (SCS) and discuss three empirical relationships for specifying the solar wind conditions near the Sun, namely the Wang–Sheeley (WS) model, the distance from the coronal hole boundary model (DCHB), and the Wang–Sheeley–Arge (WSA) model. By adding uncertainty in the latitude about the sub-Earth point, we select an ensemble of initial conditions and map the solutions to Earth by the Heliospheric Upwind eXtrapolation (HUX) model. We assess the forecasting performance from a continuous variable validation and find that the WSA model most accurately predicts the solar wind speed time series (RMSE ≈ 83 km s−1). We note that the process of ensemble forecasting slightly improves the forecasting performance of all solar wind models investigated. We conclude that the implemented framework is well suited for studying the relationship between coronal magnetic fields and the properties of the ambient solar wind flow in the near-Earth environment.

A Variational Approach to Data Assimilation in the Solar Wind

AbstractVariational data assimilation (DA) has enabled huge improvements in the skill of operational weather forecasting. In this study, we use a simple solar‐wind propagation model to develop the first solar‐wind variational DA scheme. This scheme enables solar‐wind observations far from the Sun, such as at 1 AU, to update and improve the inner‐boundary conditions of the solar wind model (at 30 solar radii). In this way, observational information can be used to improve estimates of the near‐Earth solar wind, even when the observations are not directly downstream of the Earth. Using controlled experiments with synthetic observations, we demonstrate this method's potential to improve solar wind forecasts, though the best results are achieved in conjunction with accurate initial estimates of the solar wind. The variational DA scheme is also applied to Solar‐Terrestrial Relations Observatory (STEREO) in situ observations using initial solar wind conditions supplied by a coronal model of the observed photospheric magnetic field. We consider the period October 2010 to October 2011, when the STEREO spacecraft were approximately 80∘ ahead/behind Earth in its orbit. For 12 of 13 Carrington Rotations, assimilation of STEREO data improves the near‐Earth solar wind estimate over the nonassimilated state, with a 18.4% reduction in the root mean square error. The largest gains are made by the DA during times when the steady‐state assumption of the coronal models breaks down. While applying this pure variational approach to complex solar‐wind models is technically challenging, we discuss hybrid DA approaches which are simpler to implement and may retain many of the advantages demonstrated here.

A multi-GPU finite volume solver for magnetohydrodynamics-based solar wind simulations

Magnetohydrodynamic (MHD) simulations in the domain of spherical shell are a crucial and challenging subject in many fields such as geophysics and solar-terrestrial physics, due to the complication of the MHD equations and the specificity of the domain. Besides, due to the real-time requirement, accelerating the heavy computation is proposed in many practical problems, of which the space weather simulation and forecast from the Sun to Earth is a typical case. Considering these factors, we first develop a new, spatially second-order accurate finite volume (FV) solver for three-dimensional (3D) MHD simulations with the multiple time steps strategy, which is based on the six-component grid for spherical shell domain. Then to speed up the simulation, we implement the solver on multiple GPUs with optimizations of CUDA and establish an effective multi-GPU FV solver on the spherical shell domain. A MHD manufactured solution is used to validate the solvers’ spatial accuracy, and to measure their performances. Results show that both solvers have nice scalability, and speedup ratios of 27.7x to 30.06x are obtained on GPUs. Then we utilize them to study the ambient solar wind for Carrington rotation (CR) 2060. The multi-GPU FV solver can not only obtain speedup ratios of about 29.0x, but capture main features of the solar corona and the mapped in-situ solar wind measurements.

An effective matrix-free implicit scheme for the magnetohydrodynamic solar wind simulations

The magnetohydrodynamics (MHD) modeling of the steady solar wind is an essential and important ingredient in numerical space weather study. Numerically solving the MHD equation system is not an easy work due to its complexity by combining the Euler equations of gas dynamics with the Maxwells equations of electromagnetics and the solenoidal constraint. Moreover, the vast physical temporal and spatial scales of the solar wind simulation propose harsh requirements for computational efficiency and memory storage. Considering these factors, we develop an easily implemented finite volume (FV) scheme using the GMRES algorithm with an LU-SGS preconditioner for the three-dimensional (3D) MHD-based simulation. The steady-state solar wind from 1 Rs to 20 Rs during Carrington rotation (CR) 2051 is simulated for the validation of the proposed matrix-free implicit solver. Compared with the explicit solver, the implicit one can effectively enlarge the CFL number to 100 and achieve speedup ratios of 31.27 × and 28.05 × , which reduces the computational time for the steady-state study from several days to only a few hours. The simulation captures main features of the solar corona and the mapped in-situ solar wind measurements. The scheme proposed here provides a promising choice to conduct the 3D MHD simulation of the solar wind background from the Sun to the Earth beyond.

Effect of Magnetic Field Strength on Solar Differential Rotation and Meridional Circulation

Abstract We studied the solar surface flows (differential rotation and meridional circulation) using a magnetic element feature tracking technique by which the surface velocity is obtained using magnetic field data. We used the line-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory from 2010 May 01 to 2017 August 16 (Carrington rotations 2096 to 2193) and tracked the magnetic element features every hour. Using our method, we estimated the differential rotation velocity profile. We found rotation velocities of ∼30 and −170 m s−1 at latitudes of 0° and 60° in the Carrington rotation frame, respectively. Our results are consistent with previous results obtained by other methods, such as direct Doppler, time-distance helioseismology, or cross-correlation analyses. We also estimated the meridional circulation velocity profile and found that it peaked at ∼12 m s−1 at a latitude of 45°, which is also consistent with previous results. The dependence of the surface flow velocity on the magnetic field strength was also studied. In our analysis, the magnetic elements with stronger and weaker magnetic fields largely represent the characteristics of the active region remnants and solar magnetic networks, respectively. We found that magnetic elements with a strong (weak) magnetic field show a faster (slower) rotation speed. On the other hand, magnetic elements with a strong (weak) magnetic field show slower (faster) meridional circulation velocity. These results might be related to the Sun’s internal dynamics.

Bihelical Spectrum of Solar Magnetic Helicity and Its Evolution

Abstract Using a recently developed two-scale formalism to determine the magnetic helicity spectrum, we analyze synoptic vector magnetograms built with data from the Vector Spectromagnetograph instrument on the Synoptic Optical Long-term Investigations of the Sun telescope during 2010 January–2016 July. In contrast to an earlier study using only three Carrington rotations (CRs), our analysis includes 74 synoptic CR maps. We recover here bihelical spectra at different phases of solar cycle 24, where the net magnetic helicity in the majority of the data is consistent with a large-scale dynamo with helical turbulence operating in the Sun. More than 20% of the analyzed maps, however, show violations of the expected sign rule.

Collective Study of Polar Crown Filaments in the Past Four Solar Cycles

Abstract Polar crown filaments (PCFs) form above the magnetic polarity inversion line, which separates the unipolar polar fields and the nearest dispersed fields from the trailing part of active regions with opposite polarity. The statistical properties of PCFs are correlated with the solar cycle. Therefore, the study of PCFs plays an important role in understanding the variations of the solar cycle, especially the prolonged cycle 23 and the current “abnormal” solar cycle 24. In this Letter, we investigate PCFs using full-disk Hα data from 1973 to early 2018, recorded by Kanzelhöhe Solar Observatory and Big Bear Solar Observatory, in digital form from 1997 to 2018 and in 35 mm film (digitized) from 1973 to 1996. PCFs are identified manually because their segmented shape and close-to-limb location were not handled well by automatical detections in several previous studies. Our results show that the PCFs start to move poleward at the beginning of each solar cycle. When the PCFs approach to the maximum latitude, the polar field strength reduces to zero followed by a reversal. The migration rates are about 0.°4 to 0.°7 per Carrington rotation, with a clear N–S asymmetric pattern. In cycles 21 and 23, the PCFs in the northern hemisphere migrate faster than those in the southern hemisphere. However, in the “abnormal” cycle 24, the southern PCFs migrate faster, which is consistent with other observations of magnetic fields and radio emission. In addition, there are more days in cycle 23 and 24 without PCFs than in the previous cycles.

Coherent changes of solar and ionospheric activity during long-lived coronal mega-hole from Carrington rotation CR2165 to CR2188

Correlations of solar and ionospheric activity are investigated during the long-lived coronal mega-hole (CMH) for 24 solar rotations at the decline phase of SC24 from June, 2015, to March, 2017. Pch index (Luo et al., 2008) which is a function of the intensity in the central area developed for forecasting of daily solar wind speed (Vsw) is used as characteristic of efficiency of CMH. The solar activity indices Pch, SSN2, F10.7, Lyman-α, MgII, Vsw, and the ionospheric indices – global electron content GEC and global noon TECgn index averaged from data of 288 IGS observatories are analyzed. Sporadic disturbances in solar and ionospheric data are smoothed by the time-weighted exponential accumulation of their history with the persistence factor τ (0 ≤τ < 1) for the preceding 27 days. Growing coronal hole power Pch(τ) during the CMH life is observed while all other solar and ionospheric indices are decreasing at the decreasing phase of SC24. The solar wind speed near the Earth is diminishing from CR2165 to CR2174 but growing afterwards. Delayed correlation of solar wind speed Vsw(τ) with Pch(τ) shows lag (delay) of Vsw(τ) by 4 days relative Pch(τ) index while the ionospheric data don't show any delay. Examination of relations of the ionosphere activity with the solar and ionospheric global indices is made with noon measurements of the foF2 critical frequency and total electron content TEC at eight observatories (4 from the northern hemisphere and 4 from the southern hemisphere). The best linear correlation of foF2(τ) and TEC(τ) at selected sites is obtained with GEC(τ) and TECgn(τ) indices (the correlation coefficient ρ from 0.7 to 0.9 in the most cases) so that TECgn(τ) and GEC(τ) global indices could serve as potential candidates for driving the ionospheric model in the real time regime.

Recurring coronal holes and their rotation rates during the solar cycles 22–24

Coronal holes (CHs) play a significant role in making the Earth geo-magnetically active during the declining and minimum phases of the solar cycle. In this study, we analysed the evolutionary characteristics of the Recurring CHs from the year 1992 to 2016. The extended minimum of Solar Cycle 23 shows unusual characteristics in the number of persistent coronal holes in the mid- and low-latitude regions of the Sun. Carrington rotation maps of He 10830 A and EUV 195 A observations are used to identify the Coronal holes. The latitude distribution of the RCHs shows that most of them are appeared between $\pm 20^{\circ }$ latitudes. In this period, more number of recurring coronal holes appeared in and around $100^{\circ }$ and $200^{\circ }$ Carrington longitudes. The large sized coronal holes lived for shorter period and they appeared close to the equator. From the area distribution over the latitude considered, it shows that more number of recurring coronal holes with area $<10^{21}~\mbox{cm}^{2}$ appeared in the southern latitude close to the equator. The rotation rates calculated from the RCHs appeared between $\pm 60^{\circ }$ latitude shows rigid body characteristics. The derived rotational profiles of the coronal holes show that they have anchored to a depth well below the tachocline of the interior, and compares well with the helioseismology results.

Responses of Solar Irradiance and the Ionosphere to an Intense Activity Region

AbstractSolar rotation (SR) variation dominates solar extremely ultraviolet (EUV) changes on the timescale of days. The F10.7 index is usually used as an indicator for solar EUV. The SR variation of F10.7 significantly enhanced during the 2008th–2009th Carrington rotations (CRs) owing to an intense active region; F10.7 increased about 180 units during that SR period. That was the most prominent SR variation of F10.7 during solar cycle 23. In this paper, global electron content (GEC) is used to investigate ionospheric response to that strong variation of solar irradiance indicated by F10.7. The variation of GEC with F10.7 was anomalous (GEC‐F10.7 slope significantly decreased) during the 2008th–2009th CRs; however, GEC versus EUV variation during that period was consistent with that during adjacent time intervals when using Solar Heliospheric Observatory/Solar EUV Monitor 26–34 nm EUV measurements. The reason is that F10.7 response to that intense active region was much stronger than EUV response; thus, the EUV‐F10.7 slope decreased. We confirmed decreased EUV‐F10.7 slope during the 2008th–2009th CRs for different wavelengths within 27–120 nm using Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Solar EUV Experiment high spectral resolution EUV measurements. And on the basis of Solar Heliospheric Observatory/Solar EUV Monitor EUV measurements during solar cycle 23, we further presented that EUV‐F10.7 slope statistically tends to decrease when the SR variation of F10.7 significantly enhances. Moreover, we found that ionospheric time lag effect to EUV is exaggerated when using F10.7, owing to the time lag effect of EUV to F10.7.

Correction to: Long- and Mid-Term Variations of the Soft X-ray Flare Character in Solar Cycles

Correction to: Solar Phys We found an important error in the text of our article. On page 6, the second sentence of Section 3.2 “We studied the variations in soft X-ray flare characteristics in more detail by averaging them within the running windows of ± one Carrington rotation with a step of two rotations.” should instead read “We studied the variations in soft X-ray flare characteristics in more detail by averaging them within the running windows of ± 2.5 Carrington rotations with a step of two rotations.” We regret the inconvenience. The online version of the original article can be found at https://doi.org/10.1007/s11207-017-1169-1

Coronal mass ejections as a new indicator of the active Sun

AbstractCoronal mass ejections (CMEs) have become one of the key indicators of solar activity, especially in terms of the consequences of the transient events in the heliosphere. Although CMEs are closely related to the sunspot number (SSN), they are also related to other closed magnetic regions on the Sun such as quiescent filament regions. This makes CMEs a better indicator of solar activity. While sunspots mainly represent the toroidal component of solar magnetism, quiescent filaments (and hence CMEs associated with them) connect the toroidal and poloidal components via the rush-to-the-pole (RTTP) phenomenon. Taking the end of RTTP in each hemisphere as an indicator of solar polarity reversal, it is shown that the north-south reversal asymmetry has a quasi-periodicity of 3-5 solar cycles. Focusing on the geospace consequences of CMEs, it is shown that the maximum CME speeds averaged over Carrington rotation period show good correlation with geomagnetic activity indices such as Dst and aa.