Dst Index Research Articles

Properties of Forbush Decreases with AMS-02 Daily Proton Flux Data

A Forbush decrease (FD) is a sudden reduction of Galactic Cosmic Rays (GCRs) that is usually caused by intense solar wind transients, such as Interplanetary Coronal Mass Ejections (ICMEs) and Corotating Interaction Regions (CIRs). Using daily proton fluxes measured by AMS-02 between 2011 May and 2019 October, we identified 142 FD events with an automatic systematic analysis method. The properties of 47 FDs caused by ICMEs and of 54 FDs caused by CIRs were analyzed. We found that the rigidity dependence of the GCR flux decrease is generally better described by an exponential function for both ICME and CIR FDs. We also found that the FD Amplitude of ICME FDs has a moderate correlation with the minimum Dst index and a number of solar wind parameters, such as maximum temperature, pressure, and magnetic field. For CIR FD events, neither FD Amplitude nor Maximum Affected Rigidity had a significant correlation with solar wind parameters.

Solar events and solar wind conditions associated with intense geomagnetic storms

Intense magnetic storms pose a systemic threat to the electric power grid. In this study we examined the solar/interplanetary causes of such storms, their peak theoretical and observed intensities, and their occurrence frequency. Using coronal mass ejection (CME) and solar wind data, we selected the 18 intense magnetic storms from 1996 to 2021 with disturbance storm time (Dst) index of less than – 200 nT and analyzed solar events and solar wind conditions associated with them. Approximately 83% of the CMEs associated with the storms were full halo type and more than 83% of the flares associated with the storms were located within 30 degrees in longitude of solar central meridian. The integrated dawn-to-dusk electric field in the solar wind (Ey) showed a good correlation with |min. Dst| of the storms and the peak Ey (Eyp) and the peak southward interplanetary magnetic field showed next good correlations with |min. Dst|. We obtained the Eyp of 236 mV/m for |min. Dst| of 2500 nT of the expected upper limit of Earth’s magnetosphere using the empirical equations from the correlations between |min. Dst| and solar wind parameters and showed that this value of Ey is possible according to the past observations. The Eyp of 54 mV/m for the 13 March 1989 storm and that of 165/79 mV/m for the Carrington storm (|min. Dst|= 1760/850 nT) were also obtained. The analysis using the complimentary cumulative distribution function suggested the probabilities of Ey of 100, 200, 250, and 340 mV/m over the next 100 years to be 0.563, 0.110, 0.060 and 0.026, respectively.Graphical

Variations of Signal Strength during Solar Bursts: A Probable Coronal and Surface Effects of the Sun

Variations of signal strengths during solar bursts recorded at Kalyani corresponding to two different frequencies, 406.7 MHz and 100 MHz are reported. The amplitude of the signals received at 406.7 MHz is found larger and that the flares analyzed are mostly of M-type. The signal strengths of the coronal effect at such times were very high compared to the surface effect of the Sun. The signal level of surface effect of the Sun at the peak activity varies in amplitude from 0.06 volts to 0.1 volt while those related to solar corona vary in between 7.0 to 7.2 volts. Both the solar wind velocity and proton density are found to increase in the dates of severe bursts and there are sudden disturbances in the arrival direction of solar wind particles. Also the geomagnetic indices are enhanced at the time of solar bursts when the DST index reduces rapidly.

Multi‐Hour‐Ahead Dst Index Prediction Using Multi‐Fidelity Boosted Neural Networks

AbstractThe Disturbance storm time (Dst) index has been widely used as a proxy for the ring current intensity, and therefore as a measure of geomagnetic activity. It is derived by measurements from four ground magnetometers in the geomagnetic equatorial region. We present a new model for predicting Dst with a lead time between 1 and 6 hr. The model is first developed using a Gated Recurrent Unit (GRU) network that is trained using solar wind parameters. The uncertainty of the Dst model is then estimated by using the Accurate and Reliable Uncertainty Estimate method (Camporeale & Carè, 2021, https://doi.org/10.1615/int.j.uncertaintyquantification.2021034623). Finally, a multi‐fidelity boosting method is developed in order to enhance the accuracy of the model and reduce its associated uncertainty. It is shown that the developed model can predict Dst 6 hr ahead with a root‐mean‐square‐error of 13.54 nT. This is significantly better than a persistence model or a single GRU model.

Statistical comparison of time profiles of Forbush decreases associated with coronal mass ejections and streams from coronal holes in solar cycles 23–24

ABSTRACT In this paper, Forbush decrease (FD) profiles are compared for events associated with (i) coronal mass ejections from active regions accompanied by solar flares (AR CMEs), (ii) filament eruptions away from active regions (non-AR CMEs), and (iii) high-speed streams (HSSs) from coronal holes (CHs). FD profiles are described by time parameters that are delayed from an FD onset to the registration of maximum values of cosmic ray (CR) density variations, CR density hourly decrease, CR equatorial anisotropy, solar wind (SW) speed, interplanetary magnetic field (IMF) strength and minimum Dst index. Distributions of these parameters from 1997 to 2020 and within maxima and minima of the last solar cycles (SCs) were compared by statistical methods. The results obtained reveal that statistical properties of the time parameters depend both on the FD source and on the solar activity period. FDs associated with AR CMEs develop even at close values of SW parameters faster than those associated with non-AR CMEs and HSS from CHs. Differences between typical FD profiles for events associated with AR and non-AR CMEs are more significant when the interplanetary disturbance contains a magnetic cloud. The difference between FD profiles for events associated with AR and non-AR CMEs is less distinguishable within maximum SC 24 than within maximum SC 23. For FDs associated with HSS from CHs, the main phase durations and the time delays of maximal SW speed are longer within SC 23–24 minimum, while the time delays of maximal IMF strength differ insignificantly between 23–24 and 24–25 minima.

Extreme Event Statistics in Dst, SYM‐H, and SMR Geomagnetic Indices

AbstractExtreme space weather events are rare, and quantifying their likelihood is challenging, often relying on geomagnetic indices obtained from ground‐based magnetometer observations that span multiple solar cycles. The Dst index ring‐current monitor, derived from an hourly average over four low‐latitude stations, is a benchmark for extreme space weather events, and has been extensively studied statistically. We apply extreme value theory (EVT) to two geomagnetic ring current indices: SYM‐H (derived from 6 stations) and SMR (derived from up to 120 stations). EVT analysis reveals a divergence between the return level found for Dst, and those for SYM‐H and SMR, that increases non‐linearly with return period. For return periods below 10 years, hourly averaged SYM‐H and SMR have return levels similar to Dst, but at return periods of 50 and 100 years, they respectively exceed that of Dst by about 10% and 15% (SYM‐H) and about 7% and 12% (SMR). One minute resolution SYM‐H and SMR return levels progressively exceed that of Dst; their 5, 10, 50, and 100 year return levels exceed that of Dst by about 10%, 12%, 20% and 25% respectively. Our results indicate that consideration should be given to the differences between the indices if selecting one to use as a bench mark in model validation or resilience planning for the wide range of space weather sensitive systems that underpin our society.

Double Superposed Epoch Analysis of Geomagnetic Storms and Corresponding Solar Wind and IMF in Solar Cycles 23 and 24

AbstractThe weakest solar cycle 24 (SC24, 2010–2019) in 100 years was 1/3rd less active compared to the previous solar cycle 23 (SC23, 1996–2009). We identify 135 and 61 ICME (interplanetary coronal mass ejection) driven clear geomagnetic storms (DstMin ≤ −50 nT) in SC23 and SC24, respectively, giving a reduction of 55% storms in SC24, and present the double superposed epoch analysis (DSEA) of the storms/activities in SC23 and SC24 using the Dst, symmetric H (SymH), Kp and AE indices. The DSEA method for the corresponding solar wind velocity V, north‐south component of the interplanetary magnetic field (IMF Bz) and the product VBz are also presented. Compared to SC23, the maximum storm/activity intensity in SC24 reduces by 52%, 12%, and 45% at low, mid and high latitudes and the corresponding maxima in ‐VBz, V, and ‐Bz reduce by 39%, 17%, and 38%, respectively. The epoch average storm/activity intensity reduces by 27%, 11%, and 4% at low, mid and high latitudes and average maxima in ‐VBz, V, and ‐Bz reduce by 24%, 14%, and 13%, respectively. The results seem to reveal that the average reduction in the main driver ‐VBz (∼24%) might have caused nearly the same and equal average storm/activity intensity reductions in all latitudes (∼25%), though the irregular nature of the AE index makes the reduction very small (4%) at high latitudes, and small (∼11%) at mid latitudes mainly due to the small (0–9) quasi logarithmic scale of the Kp index.

Auroral oval reconstruction for historical geomagnetic storms in the 18th and 19th century

AbstractThe investigation of extreme space weather events can yield important information about the solar activity. Here, we present the reconstruction of the auroral oval position and size based on Bayesian inference for nine historical geomagnetic storms between 1716 and 1882, including the Carrington event in 1859, by using ground‐based observations, which enables us to derive the Kp index for historical events for the first time. The results for the latter show a very high level of geomagnetic disturbance (8.2 Kp 8.7, −929 nT Dst −1327 nT). Furthermore, we were able to derive the position of the pole in corrected geomagnetic coordinates, where especially the longitude is in good agreement with the position derived from the gufm1 model (Jackson et al., 2000). For the eight other historical storms, the Kp and Dst indices have been calculated here for the first time. In all cases, a very high Kp index was derived. The only exception is the geomagnetic storm from March 1716, which is, with a Kp index of , comparable with the St. Patrick's Day storm in 2015.

Global Ionospheric TEC Forecasting for Geomagnetic Storm Time Using a Deep Learning‐Based Multi‐Model Ensemble Method

AbstractIn recent years, deep learning has been extensively used for ionospheric total electron content (TEC) prediction, and many models can yield promising prediction results, particularly under quiet conditions. Owing to the ionosphere's intricate and dramatic changes during geomagnetic storms, the high‐reliable prediction of the storm‐time ionospheric TEC remains a challenging problem. In this study, we developed a new deep learning‐based multi‐model ensemble method (DLMEM) to forecast geomagnetic storm‐time ionospheric TEC that combines the Random Forest (RF) model, the Extreme Gradient Boosting (XGBoost) algorithm, and the Gated Recurrent Unit (GRU) network with the attention mechanism. Seven features in 170 geomagnetic storm events, including the three components Bx, By and Bz of interplanetary magnetic field (IMF), the Kp and Dst indices of geomagnetic activity data, the F10.7 index of solar activity data and global TEC data, were used for modeling. The test set results showed that the DLMEM model can reduce the root mean square errors (RMSE) by an average of 43.6% in comparison to our previously presented model Ion‐LSTM, especially during the recovery period of geomagnetic storms. Furthermore, compared to Ion‐LSTM, the RMSE values of the low‐, middle‐ and high‐latitude single‐station forecast TEC can be greatly decreased by 33%, 53% and 59%, respectively. It was shown that the new model allows for more precise short‐term global ionospheric forecasting during geomagnetic storms, enabling real‐time monitoring of ionospheric changes.

A Novel Ionospheric Disturbance Index to Evaluate the Global Effect on BeiDou Navigation Satellite System Signal Caused by the Moderate Geomagnetic Storm on May 12, 2021.

In this paper, we propose a new method to quantitatively evaluate the quality of the carrier phase observation signals of the BeiDou Navigation Satellite System (BDS) during weak and moderate geomagnetic storms. We take a moderate geomagnetic storm that occurred on 12 May 2021 during the 25th solar cycle as an example. The results show that the newly defined PAS (Percentage of Affected Satellites) index shows significant anomaly changes during the moderate geomagnetic storm. Its variation trend has good correlations with the geomagnetic storm Kp index and Dst index. The anomaly stations are mainly distributed in the equatorial region and auroral region in the northern and southern hemispheres. The proposed PAS index has a good indication for both BDS2 and BDS3 satellites. We further validated this index by calculating the Precise Point Position (PPP) positioning error. We found that the anomaly period of PAS has strong consistency with the abnormal period of PPP positioning accuracy. This study could provide methodological support for the evaluation of the signal quality and analysis of positioning accuracy for the BeiDou satellite navigation system under different space weather conditions.

Distinctive response of thermospheric cooling to ICME and CIR-driven geomagnetic storms

The temporal response of thermospheric CO2 and NO cooling emissions is investigated during ICME and CIR-driven geomagnetic storms by using data from the SABER instrument onboard the TIMED, GRACE, and DMSP satellites. The superposed epoch analysis reveals that the cooling emissions experience a strong enhancement and quick recovery to pre-event value within 3–4 days during CME storms. Whereas, it shows slower recovery that lasts for more than 6–7 days during CIR-driven storms. We performed detailed study of NO cooling emission owing to the fact that the production of NO depends on the external energy input. The different response of thermospheric NO cooling during CME and CIR storms can be attributed to differences in precipitation of particle (electron and ion) fluxes. A strong correlation with a positive timelag is observed between NO cooling emission and Dst index, coupling functions and particle flux. Further, the correlation between NO cooling flux and particle flux displays a distinct and stronger correlation during CIR storms as compared to CME. This study also shows that the Newell coupling function (normalized cross-correlation, r = 0.90 for CME and r = 0.92 for CIR) and the Akasofu parameter (r = 0.92 for CME, r = 0.76 for CIR) are better correlated with NO cooling flux, respectively, during CIR- and ICME-driven storms.

CORRELATIVE STUDY OF SOLAR TRANSIENT PARAMETERS ASSOCIATED WITH DST INDEX FOR SOLAR CYCLE 23 AND 24

Geomagnetic storms and solar coronal mass ejections (CMEs) have been shown to be associated since the discovery of CMEs in solar activity (Yurchyshyn et al., 2004). An intense geomagnetic storm can either be stemmed from a CME, or from a coronal hole. However, a great geomagnetic storm can only be sourced from a CME (Le et al., 2012). The aim of this paper is to study the relation between the coronal mass ejections (CMEs), and their associated solar flares and correlate this with the Disturbance storm time (Dst) index. We have studied the count rate of soft X-rays class of X, M and C type through a histogram type plot for studying the number of X-rays of different class observed during solar cycle 23 and 24. We have also studied the angular width, speed of coronal mass ejections (CMEs) and disturbance storm time (Dst) index of solar cycle 23 and 24 for the whole cycle (Pant et al., 2021).

Characteristics of Solar Wind and Geomagnetic Conditions of Extreme Geomagnetically Induced Currents at the Vykhodnoy Station (2012–2018)

We investigated 140 events with the largest geomagnetically induced currents (GIC) recorded at the Vykhodnoy station (65 MLat) in 2012–2018. The significant differences between the parameters of the solar wind and geomagnetic indices from typical values are shown. Distinctive increases in solar wind velocity and dynamic pressure, decreases of IMF Bz are found. The Kp, AE, AL, Dst indices, as well as the Dst rate of growth Dst/dt are significantly shifted from the usual values. The relationship with interplanetary shocks in the solar wind is also analyzed.

The Relationship of Magnetospheric Parameters with Cosmic-Ray Cutoff Rigidities Depending on Latitude

We have studied the features of the latitudinal behavior of geomagnetic thresholds of cosmic rays R, as well as their sensitivity to the interplanetary medium and magnetospheric parameters during three phases of the magnetic storm on September 7–8, 2017, in the initial, main, and recovery phases. For this purpose, values of R were calculated in two different ways—by the method of spectrographic global survey (Rsgs) and by the method of tracing the trajectories of cosmic-ray (CR) particles in the model magnetic field (Ref). The maximum lowering of thresholds is observed at the storm maximum (Dst = –142 nT), reaching the values of ΔRsgs = –0.52 GV and ΔRef = –0.66 GV. The curve of ΔRsgs variations, depending on the observation station (latitude) cutoff rigidity, assumes a classical form with a maximum dropping the thresholds at midlatitudinal stations. ΔR correlates most strongly with the Dst index, which indicates that the ring current plays a main part in the dependence of variations of CR cutoff rigidities. The significant influence of solar-wind velocity V and interplanetary magnetic field (IMF) parameters on ΔRsgs and ΔRef is also seen. In the main phase, ΔRef depends on B and Bz of the IMF, and ΔRsgs depends on B and By. For ΔRsgs, the correlation with electromagnetic parameters varies, depending on the observation station, in a regular manner. There is no such tendency for ΔRef.

Analysis of the Occurrence of the First Most Intense Geomagnetic Storm (G4) to Hit the Earth in Solar Cycle 25; A Multiple-Step Geomagnetic Storm

A study of the occurrence of the first intense Geomagnetic storm (G4) to hit the Earth since the start of the Solar Cycle 25 is carried out. This study analyzed the Geomagnetic Storm that occurred between the 28th of October and the 7th of November 2021. The values of the Disturbance storm time (Dst) index of the storm reach -115 nT (G4) which occurred on the 4th of November at 1300UT. The storm is the first intense magnetic storm that occurred in the solar cycle 25. It is also a multiple-step storm with moderate two-step storm occurrence which occurred on the 5th and 6th of November at 1500UT and 0600UT respectively towards the recovery phase after the intense storm. The interplanetary magnetic field (IMF) Bz (nT) during these storm events decreases. Our analysis shows that the rise in solar wind speed, temperature and the enhancement of pressure plays a significant role in the occurrence of the first intense Geomagnetic storm of Solar Cycle 25.

Development of Forbush Decreases Associated with Coronal Ejections from Active Regions and non-Active Regions

In this paper, we study the development of Forbush decreases associated with coronal mass ejectionsfrom active regions accompanied by solar flares and filament eruptions from non-active regions usingthe database of Forbush effects and interplanetary disturbances created at IZMIRAN. We compared thedevelopment of two types of Forbush decreases during solar cycles 23–24, the maxima of these cycles, andthe minimum between them. Using statistical methods, we studied the distributions of time intervals from thebeginning of the Forbush decrease to registration: the minimum cosmic ray density, the maximum hourlydecrease in density, the maximum cosmic ray anisotropy, the maximum solar wind velocity, the maximumstrength of the interplanetary magnetic field, and the minimum of the Dst index. The difference in the developmentof two types of Forbush decreases was compared when the interplanetary disturbance contains ordoes not contain a magnetic cloud near the Earth. The results showed that flare-associated events developfaster than filament-associated events, even at close values of the solar wind parameters. The difference in thedevelopment of two types of Forbush decreases is more noticeable in the case of the presence of a magneticcloud near the Earth’s orbit. The largest difference between the time parameters in the two types of events isobserved for the time of registration of the maximum intensity of the interplanetary magnetic field. The mainphase of the two types of Forbush decreases is the same at the solar cycle 23 maximum and longer for filament-associated events at the cycle 24 maximum and 23–24 minimum. Considering all time parameters, thedifference in the development of the two types of Forbush decreases is more noticeable at the maximum ofcycle 23 and at the minimum of cycle 23–24 than at the maximum of cycle 24

A New GNSS TEC Neural Network Prediction Algorithm With the Data Fusion of Physical Observation

This work models and predicts anomalous jumps in GNSS total electron content (TEC) caused by geomagnetic disturbance or solar radiation by introducing F10.7 and regional Dst indices, which are used to characterize solar radiation and geomagnetic disturbance status, respectively. We then introduced long-distance constraint stations to restrain ionospheric variations during high solar activity, which reduced the influence of unmodelled factors on prediction accuracy. In our experimental work, Global Ionosphere Map (GIM) TEC data from 11 stations located at different latitudes were used for comparison during maximum (2014) and minimum (2018) of solar cycle 24. Sample data for >27 days were used for learning, and then ionospheric changes for the whole year were predicted using the sliding window method. The results showed that, the standard deviation for the global ionospheric prediction products could be guaranteed to be within 2 TECU. The proximity station constraint method proposed in this paper and the Dst high-order polynomial correction method during geomagnetic disturbance control the prediction error within -4.4 TECU, while the change of adjacent days is -51.4 TECU in 2014. The new algorithm reduced the TEC jump effect in predictions, and the prediction of ionospheric products provided by this algorithm can meet the basic requirements of ionospheric delay correction in high-precision positioning.

Stormtime Ring Current Heating of the Ionosphere and Plasmasphere

AbstractThe energy deposition from ring current ions into the high density “cold” plasma of the ionosphere and plasmasphere is analyzed, based on a Comprehensive Inner Magnetosphere‐Ionosphere simulation of the 2015 October 7 storm. In addition, the Naval Research Laboratory Sami3 is Also a Model of the Ionosphere ionosphere/plasmasphere code is used to simulate the effect of Coulomb‐collision heating of plasmasphere and ionosphere electrons by ring current ions. We find that, during stormtime peaks in the Dst index, energy is deposited at altitudes as low as 100 km. Heating along the entirety of any given field line, both in the ionosphere and plasmasphere, contributes to increased temperatures in the ionosphere F layer and inner magnetosphere and to subsequent cold O+ outflows. However, relative to the heating of the plasmasphere, the direct heating of the ionosphere by ring current ions produces only small effects. Qualitative model‐data agreement on the N+/O+ density ratio is consistent with the hypothesis that these outflows are driven by thermal forcing.

Geomagnetic storm forecasting from solar coronal holes

ABSTRACT Coronal holes (CHs) are the source of high-speed streams (HSSs) in the solar wind, whose interaction with the slow solar wind creates corotating interaction regions (CIRs) in the heliosphere. Whenever the CIRs hit the Earth, they can cause geomagnetic storms. We develop a method to predict the strength of CIR/HSS-driven geomagnetic storms directly from solar observations using the CH areas and associated magnetic field polarity. First, we build a data set comprising the properties of CHs on the Sun, the associated HSSs, CIRs, and orientation of the interplanetary magnetic field (IMF) at L1, and the strength of the associated geomagnetic storms by the geomagnetic indices Dst and Kp. Then, we predict the Dst and Kp indices using a Gaussian process model, which accounts for the annual variation of the orientation of Earth’s magnetic field axis. We demonstrate that the polarity of the IMF at L1 associated with CIRs is preserved in around 83 per cent of cases when compared to the polarity of their CH sources. Testing our model over the period 2010–2020, we obtained a correlation coefficient between the predicted and observed Dst index of R = 0.63/0.73, and Kp index of R = 0.65/0.67, for HSSs having a polarity towards/away from the Sun. These findings demonstrate the possibility of predicting CIR/HSS-driven geomagnetic storms directly from solar observations and extending the forecasting lead time up to several days, which is relevant for enhancing space weather predictions.

Atmospheric Effects of Magnetosheath Jets

We report effects in the upper high-latitude atmosphere related to the interaction of fast magnetosheath plasma streams, so-called jets, with the dayside magnetopause. The jets were observed by THEMIS mission in the dayside magnetosphere during a quiet day on 12 July 2009. It was found that the jet interaction was accompanied by strong localized compression and penetration of suprathermal magnetosheath plasma inside the dayside magnetosphere. The compression caused prominent magnetic variations with amplitudes up to 100 nT observed by ground-based magnetic networks SuperMAG and CARISMA. The magnetic variations were also visible in the geomagnetic Dst and AE indices. The jets also resulted in intense precipitation of the suprathermal ions with energies < 10 keV and energetic electrons with energies > 30 keV observed by low-altitude NOAA/POES satellites in a wide longitudinal range. The precipitations produced enhancements of ionization with an amplitude of ~1 TECU (~30% in relative units) and intensification of the ionospheric E and F1 layers as observed in the FORMOSAT-3/COSMIC misson. The enhanced ionization in the upper atmosphere might affect radio communication and navigation in the high-latitude regions. These results also provide new insight into the contribution of magnetospheric forcing to day-to-day ionospheric variability.