1. Introduction
Active regions (ARs) are commonly regarded as the area of magnetic field concentrations roughly centered over a sunspot or sunspot group, visible on magnetograms and uniquely enumerated by the National Oceanic and Atmospheric Administration (NOAA). An updated definition was introduced by [1] as ‘…the totality of observable phenomena in a 3D volume represented by the extension of magnetic field from the photosphere to the corona…’ including electromagnetic (EM) emissions and strong twisted magnetic field emergence. Although the AR hallmarks are the loops connecting oppositely magnetic polarities and stretching out into the solar corona, ARs have been also recognized as the origin of diverse solar activity phenomena, including both EM emissions (from small-scale brightenings to solar flares, SFs [2,3]) and plasma motions (from jets to coronal mass ejections, CMEs [4,5]). Although SFs are usually regarded as the detected signatures across the EM spectrum, the underlying process of magnetic reconnection includes major reconfiguration of the magnetic structure in the AR, particle acceleration and mass motions. Large SFs are well known to correlate strongly with CMEs, which are the eruptions of magnetized plasma from the corona towards the heliosphere. Often, during their eruption and propagation, SFs and CMEs form shock waves that are known to accelerate particles. The solar energetic particles [6] consists mostly of protons, electrons and smaller fraction of heavy ions that gyrate along the heliospheric magnetic field lines.
The above agents of solar activity are known to have an impact in the heliosphere, on the planetary magnetospheres and atmospheres, technological devices, both in space and ground based, and are also considered a health risk for humans (
Still, the estimation of the magnetic fields of solar eruptions is impeded by the lack of direct observations in the corona and IP space [16]. With the launch of the Solar Dynamics Observatory (SDO) spacecraft, photospheric magnetic maps (line-of-sight magnetic flux and vector magnetic field data) are provided with 1 arc second spatial resolution and 45 s cadence by the Helioseismic and Magnetic Imager (HMI), [17]. Based on the line-of-sight and and vector magnetograms, there are a number of methods developed for performing magnetic field extrapolations in the corona, starting with potential [16,18] to non-linear force-free solutions [19,20]. The structure of the IP magnetic field (IMF) is often approximated as a spiral, termed the Parker spiral [21], where the 2D shape (ecliptic plane projection) is a function of the solar wind speed. Later modifications, e.g., Fisk-type IMF [22], were also proposed. The propagation and merging of multiple ICMEs can, however, severely disturb the quiet-time, well-ordered IMF spiral [23].
Disturbances in the heliosphere (plasma and magnetic fields) are generated by the interactions and shock formation between fast and slow solar wind streams and by the transport and merging of ICMEs (modeled by, for example,
The geomagnetic disturbances (together with the accompanying atmospheric effects, i.e., the polar lights,
The problem of the correct identification of the ICME magnetic field direction is rooted in the possibility of the overall rotation and deflection of the CMEs during their propagation through the IP space; see the review by [31] and the relevant listed literature. The most probable reasons are considered the longitudinal deflection towards the equator due to (polar) coronal holes, clockwise filament rotation during the rise phase when originating at positive helicity source regions and vice versa, and CME−CME interaction in the heliosphere.
As noted by [31], the amount of CME rotation cannot be observed but is instead estimated based on comparison between the magnetic field orientation of pre-eruptive phenomena (e.g., polarity inversion line (PIL) of the source region or filament observations) and the ejecta at 1 AU (by the fitting of a 3D model to the in situ data).
At the photospheric end, one could evaluate the magnetic field properties of ARs also with the aid of HMI observations and their data products, although many models start from coronal structures [32]. Moreover, the importance of the interaction between the photospheric and heliospheric magnetic fields was shown early on, e.g., [33]. At the other end, i.e., 1 AU/ahead of Earth, one can sample the magnetic fields at a single point in the ICME structure. Caution needs to be applied to interpretations based on the single-point sampling of large ejecta or solar wind structures. By ensuring that a given IP structure leads to a GS, one could focus on the photospheric magnetic field structure of those events and search for tendencies in their properties. We point out that the IP transport is not accounted for by this approach, which is adopted also in the present study.
Thus, the main aim of the presented study is to investigate the parameters of ARs (e.g., the (orientation of) photospheric magnetic fields, current systems and energy density properties) leading to GSs, which we term geoeffective ARs. The significance of this work with respect to the previous research is to investigate in detail the link between the available magnetic field parameters and the parameters of GSs, SFs, and CMEs.
2. Data and Event Sample
For this study, we use all Space-weather HMI Active Region Patch (SHARP) products [34] that provide estimations of magnetic fields and fluxes, currents, helicity, and twist. The parameters are based on data from the SDO/HMI instrument. The database provides information about multiple parameters, calculated with a 12 min cadence, based on the automatic recognition of ARs,
The 16 SHARP parameters used in our study are as follows:
USFLUX: Total unsigned flux [Mx];
MEANGAM: Mean inclination angle, [degrees];
MEANGBT: Mean value of the total field gradient [G/Mm];
MEANGBZ: Mean value of the vertical field gradient [G/Mm];
MEANGBH: Mean value of the horizontal field gradient [G/Mm];
MEANJZD: Mean vertical current density [mA/m2];
TOTUSJZ: Total unsigned vertical current [A];
MEANALP: Mean twist parameter, [1/Mm];
MEANJZH: Mean current helicity [G2/m];
TOTUSJH: Total unsigned current helicity [G2/m];
ABSNJZH: Absolute value of the net current helicity [G2/m];
SAVNCPP: Sum of the absolute value of the net currents [A];
MEANPOT: Mean photospheric excess magnetic energy density [Ergs/cm3];
TOTPOT: Total photospheric magnetic energy density [Ergs/cm3];
MEANSHR: Mean shear angle for Btotal [degrees];
RVALUE: Unsigned flux, R [35] [Mx].
The details are described in [34].
As the aim of our analyses is to investigate the magnetic properties of geo-effective ARs, we start with a pre-selection of all GSs in SC24 (2009–2019). In order to improve the statistics, we extend the event list by including GSs with a Dst index below −50 nT in the current SC as well. Weaker than this threshold, GSs are not driven by fast solar wind structures [36] and thus are not considered SW effective. Moreover, the solar origin driver of weak GSs is very difficult to identify.
We use the Dst values as reported in the final and provisional Kyoto lists by mid-2023,
Then, we continue with the identification of the CME-associated SF, using the information provided in the Geostationary Operational Environmental Satellite (GOES) reports
The SF class is defined as the peak value of the soft X-ray (SXR) flux, in Wm−2, with the so-called X-class being the most energetic eruptive phenomena, with SXR flux above 10−4 Wm−2, whereas the M, C, B, A-classes are 10 times smaller than the previous. At the day of SF occurrence, we also check the NOAA reports and collect the solar region (SR) types based on the so-called -- (or Mount Wilson sunspot magnetic) classification,
The results from Table 1 show a wide distribution of the Dst index, with mean (median) values of −86 (−72) nT, respectively. The values are very similar compared to the overall distribution of GSs in the last two SCs [37], reporting −86 (−69) nT. The CMEs identified as the GS-origin have values for the projected speed of ∼750 (620) km s−1, and are predominantly halo, with 51/64 cases with 360 degrees for the AW. The CMEs in our list are much slower than those reported by [37], ∼1000 (870) km s−1. In contrast, the CME-related SFs in Table 1 have larger mean/median SXR flux of M6.9 (M1.6) compared to M1.5 (M1.4) in [37].
The resulted SR types are as follows: 6 , 16 , 1 , 15 , 19 , and 7 cases had no reported SR type. We note that the used identification for limb events is partially reliable, as the classification changes from one day to the next. In our list, eight events have a reported longitude larger than 80 degrees. In addition, since the reports are conducted at midday, they give more accurate information for the previous day. This is why we also collect the SR reports on the day following the SF. Any changes in the SR type are listed in parentheses in Table 1. The updated SR results are mostly consistent, providing 5 , 15 , 1 , 13 , 25 , and 5 cases had no reported type.
3. Results
3.1. Timing Estimation
The temporal evolution of the SHARP parameters is explored for all events in our list, Table 1, with an example shown in Figure 1 for the event on 1 August 2010. Daily overviews are generated for all events. The flare timings are over-plotted with different colors, for the start (green), peak (red) and end (blue) times, respectively. Some of the parameters have redundant trends, though we decided to keep all 16 SHARP parameters while performing the correlation analysis.
By inspecting the temporal behavior of all events in the sample (not provided), we notice no consistent trends in the daily trends and especially around the time of the SF. Moreover, the change of the different SHARP parameters is usually within a rather narrow range.
Several time markers can be considered while selecting a representative value of each SHARP parameter, namely, the following:
An exact value taken just prior to the SF start;
Averaged value during the rise phase of the SF (onset-to-peak);
Averaged value during the entire SF duration (onset-to-end);
Averaged value during the decline phase of the SF (peak-to-end).
The statistical correlations were performed using all four values of the SHARP parameters, leading to consistent results (explicitly shown at
3.2. Correlations
The results are organized in terms of linear (Pearson) and non-linear (rank or Spearman) correlation coefficients. The event size (n) is the same (64) for all pairs and one could easily calculate the standard error for a given correlation coefficient (r), as , proposed by [41]. For the two extreme cases, we obtain 0.01 ± 0.13 and 0.99 ± 0.01, which demonstrates the statistical validity of the obtained correlations.
The matrix of the Spearman correlations is shown in Figure 2 for the entire sample, whereas the Pearson correlations are organized in Appendix A, Figure A1. By comparing the two matrices, one can deduce that overall, the values for the Spearman correlations are larger compared to the Pearson ones, however, not statistically significant. The larger values are shown in darker color with the exact value present in the respective cell. The lowest correlation coefficients are obtained between the SHARP parameters and the Dst index of the GSs (first column in both matrices). The correlations with the SF class are stronger than those obtained with the CME speed and AW. The flare rise time and duration do not correlate with the SHARP parameters.
The total unsigned magnetic flux (USFLUX) has the strongest correlation coefficients (well above 0.8–0.9) with the other summed values, namely, for the current, current density and energy density. Also, USFLUX correlates strongly with the net current helicity, net currents, R-value, and SF class.
In contrast, all components of the field gradients are well inter-correlated but are poorly related to the other SHARP and solar parameters, with the exception of the horizontal gradient (MEANGBH) responding well to the mean shear angle (MEANSHR), the other components of the field gradient, and the inclination angle (MEANGAM). Interestingly, the components of the field gradient do not correlate well with the remaining SHARP and solar parameters. Similarly, the mean twist parameter (MEANAPL) correlates well only with the mean current helicity (MEANJZH).
The inclination angle (MEANGAM), however, has large correlation coefficients with the shear angle (MEANSHR), the excess energy density (MEANPOT), and the horizontal gradient (MEANGBH). The remaining SHARP parameters from the list (total/net current, current helicities and magnetic energy densities) show strong inter-correlations.
In addition, we present the correlation matrices for two sub-sets, namely, for the strong (with Dst index ≤ −100 nT) and weak GSs (with Dst index from ≤−50 to −100 nT). The results are shown in Figure 3 for the Spearman correlations and in Figure A2 for the Pearson correlations. The correlation matrices are optimized for the sub-set of parameters with moderate-to-strong correlations. The strong GSs are associated with halo CMEs only; thus, the AW parameter will be dropped. Apart from the flare rise and duration, we drop also MEANGBT, MEANGBZ, MEANJZD, MEANALP, MEANJZH. The matrices with the complete set of parameters are available online,
3.3. Scatter Plots
The distribution (linear scatter plots) of the SHARP parameters vs. the Dst index are explicitly shown in Figure 4, except for the R-value due to a lack of correlation in that case (close to 0). Overall, the points tend to cluster at lower values of the Dst (i.e., upper part of the scatter plots).
Similar sets of scatter plots are prepared for the correlations with the SF class and CME speed, available as supplementary materials and also online,
While inspecting Figure 4 for MEANGBT, MEANGBZ, MEANJZD, MEANAPL, and ABSNJZH, one notices notable outliers. In order to quantify the effect of the outliers (usually at very large values of the selected SHARP parameter), we calculate the Spearman correlation coefficients and their uncertainty after their removal:
Dst vs. MEANGBT: ();
Dst vs. MEANGBZ: ();
Dst vs. MEANJZD: ();
Dst vs. MEANAPL: ();
Dst vs. ABSNJZH: (),
4. Discussion
Based on the obtained correlations, several of the SHARP parameters are not very promising markers of statistical associations and could well be dropped in larger studies in order to save resources, namely, the components of the field gradient (MEANGBT, MEANGBZ, and MEANGBH), the vertical current density, twist, and current helicity (MEANJZD, MEANAPL and MEANJZH, respectively). In contrast, the parameters for the total flux, current, current helicity, magnetic energy density, and shear angle show moderate-to-strong correlations also with the SF class and the CME parameters but not with the Dst index.
The low correlations between the SHARP parameters and the Dst index of the GSs can be interpreted twofold. On one side, the lack of correlation can be explained as a lack of causation between the AR magnetic field properties and the resultant Dst index of the GSs. Namely, the AR generates the eruption only, and under suitable coronal conditions, the resultant CME can escape into the IP space. Thus, an ejecta is geoeffective when a combination of suitable conditions are present in the heliosphere (and unrelated to the distribution of the surface magnetic fields): specific direction of propagation (i.e., Earth-directed/halo CMEs) with strong southward-directed magnetic fields. Finally, the early precursors of geo-effective eruptions need to be sought in the correct identification of the magnetic properties of the ejecta and/or its tracking its orientation through the heliosphere.
The majority of the ARs in our list are classified as the type (∼40% or 25/64), and (14/64), which is evidence of their magnetic field complexity. This is consistent with the trends of complex magnetic configurations leading to solar eruptive events [42,43]. Also, complex ARs (like ) have more than one PIL, and the main direction of the magnetic field of the ejecta will depend on at which PIL the flare/CME is originating.
Thus, an alternative interpretation of our findings can be put forward, namely, the correlation is lost due to the subsequent rotation or deflection of the eruptions in the solar corona [44,45] and/or in the heliosphere, at least for some of the cases. These effects would mask any trends of the underlying magnetic structure of the parent ARs. Namely, some of the GSs may originate from initially unfavorable magnetic field conditions and, vice versa, initially southward magnetic field configurations can be lost in the IP space.
The small event size in our case (64 ARs with SHARP data and accompanied GSs) is also insufficient to highlight the trends, if any. Moreover, our analysis is based on photospheric magnetic fields with no subsequent tracking of the resultant ICMEs. In this way, the conditions in the IP space turn out to be a crucial factor for the geomagnetic potential of the IP ejecta, whereas the AR configuration can be explored for solar eruption forecasting.
In order to differentiate between the two scenarios, one needs to deduce the magnetic field configurations of CMEs in the corona and IP space, which is the missing piece of information between the remotely observed photospheric and in situ detected magnetic fields. With the lack of multiple spacecraft from the sun to Earth, the improvement in CME modeling seems to be the only solution at present [26].
Alternatively, we expect closer association between the SHARP parameters and SFs because there is some direct causal connection (i.e., large flares are only possible if there is large amount of free energy and if the AR is highly non-potential). This is why previous studies have focused on the properties of SFs (e.g., confinement or not [46,47]).
In summary, there are many uncertainties involved in the relationship between the SHARP parameters of the ARs and the geomagnetic effect of the CMEs they produce: most important are the changes close to the Sun (like CME deflection/rotation) and in the IP space (change in ICME speed due to interaction with ambient solar wind flow, erosion of the ICME magnetic field due to interaction with IMF, etc.). These aspects deserve further investigation. When a comprehensive list of (I)CME deflections is available, the above analyses could be performed using such event groups. In this way, the effect of (I)CME deflection/rotation on the correlations between AR properties and the geomagnetic impact (Dst) can be quantitatively tested.
5. Conclusions
This study focuses on the exploration of the statistical relationship between a set of magnetic field parameters of ARs (from SDO/HMI SHARP database) with the properties of solar eruptions and GSs. A search for the parent ARs of GSs during SC24 leads to a final list of 64 events. The main findings from the statistical analyses can be summarized as follows:
The mean (median) value of the Dst index of our sample of GSs is −86 (−72) nT, which is similar to the respective value over the last two SCs −86 (−69) nT [37].
The GS-associated CMEs are slower with the mean (median) projected speed of ∼750 (620) km s−1, compared to the ∼1000 (870) km s−1 values reported by [37] over SC23+24.
The GS-associated SFs have larger mean SXR flux of M6.9 compared to M1.5 reported by [37] over SC23+24, although the median value is nearly the same.
Selected SHARP (MEANGBT, MEANGBZ, MEANJZD, MEANALP, and MEANJZH) and solar (flare rise and duration) parameters show weak or negative statistical correlations with the other SHARP or solar parameters, apart from a few strong inter-correlations.
The remaining SHARP parameters (USFLUX, MEANGAM, MEANGBH, TOTUSJZ, TOTUSJH, ABSNJZH, SAVNCPP, MEANPOT, TOTPOT, and MEANSHR) show moderate-to-strong correlations with the SF class (but not to the rise and duration times) and to a degree also with the CME speed and AW, whereas no correlation is found with the Dst index of the GSs. The latter correlation trend is improved slightly when considering strong GSs (with Dst ≤ −100 nT).
The weak correlations with the GSs are not improved after the removal of outliers from the event samples.
In the current analyses, we started with the list of GSs and deduced their solar origin, in terms of CMEs, SFs, and ARs. The opposite direction, starting with a comprehensive list of ARs, summarizing their SHARP parameters and exploring the resultant GSs, goes beyond the scope of this work.
The closer association between the SHARP parameters and the geoeffective SFs obtained in the present study has been previously reported but for the research topic of confined vs. eruptive SFs [48], and thus for a different event sample. Alternative (to SHARP) photospheric magnetic field parameters for flare eruption are also proposed [49]. Nevertheless, the SHARP parameters seem to be more promising for exploring the photospheric link to SFs and/or CMEs, despite the large scatter present. The semi-automatic numerical procedures developed in this work (
Conceptualization, R.M.; methodology, all; software, M.N.; validation, M.N., R.M. and A.V.; formal analysis, all; writing—original draft preparation, R.M.; writing—review and editing, all; visualization, M.N.; project administration, R.M. and W.P.; funding acquisition, R.M. and W.P. All authors have read and agreed to the published version of the manuscript.
Not applicable.
Not applicable.
Data used in this study are available at:
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
The following abbreviations are used in this manuscript:
AR | active region |
AW | angular width |
CDAW | Coordinated Data Analysis Workshop |
CME | coronal mass ejection |
Dst | disturbance storm time |
EM | electromagnetic |
GOES | Geostationary Operational Environmental Satellite |
GS | geomagnetic storm |
HMI | Helioseismic and Magnetic Imager |
ICME | interplanetary coronal mass ejection |
IMF | interplanetary magnetic field |
IP | interplanetary |
PIL | polarity inversion line |
LASCO | Large Angle and Spectrometric COronagraph |
NOAA | National Oceanic and Atmospheric Administration |
SC | solar cycle |
SDO | Solar Dynamics Observatory |
SEE | solar energetic electron |
SEP | solar energetic proton |
SF | solar flare |
SHARP | Space-weather HMI Active Region Patch |
SN | sunspot number |
SOHO | Solar and Heliospheric Observatory |
SR | sunspot region |
SXR | soft X-ray |
SW | space weather |
UT | universal time |
Footnotes
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Figure 1. Temporal evolution of the SHARP parameters for the event on 1 August 2010.
Figure 3. Spearman correlation coefficients between the SW and SHARP parameters for the sub-sample of strong (on the left) and weak (right) GSs.
Figure 4. Scatter plots between the Dst index and the SHARP parameters (for the used abbreviations, see text).
Event list based on GSs detected since 2009 with an identified solar origin. Dst index is in nT; time in UT; SF class, timing (onset, peak and end times), location and AR are from the GOES reports; CME information is from the CDAW database; speed in km s−1; d: double; h: hour; m: multiple; u: uncertain; v: visual. SR types are given at the day of the SF/CME and in the case of any changes on the following day, the type is shown in parentheses.
No. | GS | SR | CME | SF | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
yyyy-mm-dd | h | Dst | Type | Day/Onset | Speed | AW | Onset/Peak/End | Class | Location | AR | |
1 | 2010-08-04 | 2 | −74 | | 01/13:42 | 850 | 360 | 07:55/08:26/09:35 | C3.2 | N20E36 | 11092 |
2 | 2011-03-11 | 6 | −83 | | 07/20:00 u | 2125 | 360 | 19:43/20:12/20:58 | M3.7 | N31W53 | 11164 |
3 | 2011-08-06 | 4 | −115 | 04/04:12 | 1315 | 360 | 03:41/03:57/04:04 | M9.3 | N19W36 | 11261 | |
4 | 2011-09-10 | 5 | −75 | 06/23:06 u | 575 | 360 | 22:12/22:20/22:24 | X2.1 | N14W18 | 11283 | |
5 | 2011-09-26 | 24 | −118 | 24/12:48 | 1915 | 360 | 12:33/13:20/14:10 | M7.1 | N10E56 | 11302 | |
6 | 2011-09-28 | 7 | −68 | 24/19:36 u | 972 | 360 | 19:09/19:21/19:41 | M3.0 | N12E42 | 11302 | |
7 | 2011-10-25 | 2 | −147 | 22/10:24 | 1005 | 360 | 10:00/11:10/13:09 | M1.3 | N25W77 | 11314 | |
8 | 2012-01-23 | 6 | −71 | | 19/14:36 | 1120 | 360 | 13:44/16:05/17:50 | M3.2 | N32E22 | 11402 |
9 | 2012-01-25 | 11 | −75 | | 23/04:00 | 2175 | 360 | 03:38/03:59/04:34 | M8.7 | N28W21 | 11402 |
10 | 2012-02-27 | 20 | −57 | 25/15:12 u | 1039 | 97 | 14:20/15:00/15:15 | B5.9 | N09E68 v | 11424 | |
11 | 2012-03-04 | 2 | −50 | no | 02/18:00 u | 710 | 206 | 17:29/17:46/18:07 | M3.3 | N16E83 | 11429 |
12 | 2012-03-07 | 10 | −88 | 04/11:00 d | 1306 | 360 | 10:29/10:52/12:16 | M2.0 | N19E61 | 11429 | |
13 | 2012-03-09 | 9 | −145 | | 07/00:24 | 2684 | 360 | 00:02/00:24/00:40 | X5.4 | N17E27 | 11429 |
14 | 2012-03-12 | 17 | −64 | | 10/18:00 | 1296 | 360 | 17:15/17:44/18:30 | M8.4 | N17W24 | 11429 |
15 | 2012-03-15 | 21 | −88 | | 13/17:36 | 1884 | 360 | 17:12/17:41/18:25 | M7.9 | N17W66 | 11429 |
16 | 2012-04-13 | 5 | −60 | no | 09/12:36 u | 921 | 360 | 12:12/12:44/13:08 | C3.9 | N20W65 | 11451 |
17 | 2012-06-17 | 14 | −86 | | 14/14:12 u | 987 | 360 | 12:52/14:35/15:56 | M1.9 | S17E06 | 11504 |
18 | 2012-07-09 | 13 | −78 | | 06/23:24 u | 1828 | 360 | 23:01/23:08/23:14 | X1.1 | S13W59 | 11515 |
19 | 2012-07-15 | 17 | −139 | | 12/16:48 | 885 | 360 | 15:37/16:49/17:30 | X1.4 | S15W01 | 11520 |
20 | 2012-09-03 | 11 | −69 | | 31/20:00 u | 1442 | 360 | 19:45/20:43/21:51 | C8.4 | S19E42 | 11562 |
21 | 2012-09-05 | 6 | −64 | | 02/04:00 | 538 | 360 | 01:50/01:58/02:10 | C2.9 | N03W05 | 11560 |
22 | 2012-10-01 | 5 | −122 | | 28/00:12 | 947 | 360 | 23:36/23:57/00:34 | C3.7 | N06W34 | 11577 |
23 | 2012-10-13 | 8 | −90 | no | 09/00:48 u | 692 | 122 | 23:56/01:06/02:01 | C2.0 | S26E86 | 11589 |
24 | 2013-03-01 | 11 | −55 | | 27/04:00 u | 622 | 138 | 03:25/03:32/03:39 | B8.3 | S19W05 | 11682 |
25 | 2013-03-17 | 21 | −132 | | 15/07:12 | 1063 | 360 | 05:46/06:58/08:35 | X1.1 | N11E12 | 11692 |
26 | 2013-03-29 | 17 | −59 | no ( | 23/12:24 u | 663 | 177 | 12:15/12:22/12:27 | B6.8 | N17E87 u | 11704 |
27 | 2013-05-18 | 5 | −61 | | 15/01:48 m | 1366 | 360 | 01:25/01:48/01:58 | X1.2 | N12E64 | 11748 |
28 | 2013-05-19 | 15 | −51 | | 17/09:12 | 1345 | 360 | 08:43/08:57/09:19 | M3.2 | N12E57 | 11748 |
29 | 2013-05-25 | 7 | −59 | | 22/13:26 | 1466 | 360 | 13:08/13:32/14:08 | M5.0 | N14W87 | 11745 |
30 | 2013-07-06 | 19 | −87 | no ( | 03/07:24 u | 807 | 267 | 07:00/07:08/07:18 | M1.5 | S11E82 | 11787 |
31 | 2013-10-02 | 8 | −72 | | 29/22:12 | 1179 | 360 | 21:43/23:39/01:03 | C1.2 | N10W43 | 11850 v |
32 | 2013-10-30 | 24 | −54 | | 28/02:24 | 695 | 360 | 01:41/02:03/02:12 | X1.0 | N04W66 | 11875 |
33 | 2014-02-19 | 9 | −119 | | 16/10:00 | 634 | 360 | 09:20/09:26/09:29 | M1.1 | S11E01 | 11977 |
34 | 2014-02-27 | 24 | −97 | | 25/01:26 | 2147 | 360 | 00:39/00:49/01:03 | X4.9 | S12E82 | 11990 |
35 | 2014-11-10 | 18 | −65 | | 07/18:08 u | 795 | 293 | 16:53/17:26/17:34 | X1.6 | N15E33 | 12205 |
36 | 2014-12-22 | 6 | −71 | | 17/05:00 u | 587 | 360 | 04:25/04:51/05:20 | M8.7 | S20E09 | 12242 |
37 | 2014-12-23 | 23 | −57 | | 19/01:05 u | 1195 | 360 | 21:41/21:58/21:45 | M6.9 | S11E15 | 12242 |
38 | 2014-12-24 | 23 | −53 | | 20/01:26 u | 830 | 257 | 00:11/00:28/00:55 | X1.8 | S21W24 | 12242 |
39 | 2014-12-26 | 2 | −57 | | 21/12:12 u | 669 | 360 | 11:24/12:17/12:57 | M1.0 | S14W25 | 12241 |
40 | 2015-03-17 | 23 | −234 | | 15/01:48 | 719 | 360 | 01:15/02:13/03:20 | C9.1 | S22W25 | 12297 |
41 | 2015-06-23 | 5 | −198 | | 21/02:36 m | 1366 | 360 | 01:02/01:42/02:00 | M2.0 | N12E16 | 12371 |
42 | 2015-06-25 | 17 | −81 | | 22/18:36 d | 1209 | 360 | 17:39/18:23/18:51 | M6.5 | N12W08 | 12371 |
43 | 2015-06-26 | 18 | −51 | | 25/08:36 u | 1627 | 360 | 08:02/08:16/09:05 | M7.9 | N09W42 | 12371 |
44 | 2015-08-16 | 8 | −98 | | 12/14:48 u | 647 | 204 | 14:26/15:26/16:47 | B7.0 | S27W27 | 12399 v |
45 | 2015-08-23 | 9 | −57 | 22/07:12 u | 547 | 360 | 06:39/06:49/06:59 | M1.2 | S15E13 | 12403 | |
46 | 2015-09-20 | 16 | −81 | | 18/05:00 | 823 | 131 | 04:22/06:31/07:20 | C2.6 | S21W10 | 12415 |
47 | 2015-10-18 | 10 | −56 | 14/00:24 u | 770 | 79 | 23:34/23:40/23:44 | B6.4 | S06E76 | 12434 | |
48 | 2015-11-03 | 13 | −51 | 01/12:00 m | 751 | 114 | 12:03/12:06/12:10 | C1.3 | N07E30 | 12443 | |
49 | 2015-11-07 | 7 | −87 | | 04/14:48 | 578 | 360 | 13:31/13:52/14:13 | M3.7 | N09W04 | 12443 |
50 | 2015-11-10 | 14 | −56 | | 09/13:26 u | 1041 | 273 | 12:49/13:12/13:28 | M3.9 | S11E41 | 12449 |
51 | 2015-12-14 | 20 | −55 | | 11/04:36 u | 628 | 84 | 04:22/04:47/05:15 | C1.4 | S15E52 | 12468 |
52 | 2015-12-20 | 23 | −166 | | 16/09:36 | 579 | 360 | 08:34/09:03/09:23 | C6.6 | S13W04 | 12468 |
53 | 2016-02-01 | 9 | −53 | 28/22:12 u | 684 | 71 | 21:48/21:57/22:02 | C3.3 | N09W50 | 12488 | |
54 | 2016-02-16 | 20 | −65 | 11/21:18 u | 719 | 360 | 20:18/21:03/21:28 | C8.9 | N09W08 | 12497 | |
55 | 2017-04-22 | 17 | −51 | no ( | 18/19:48 | 926 | 360 | 19:21/20:10/20:49 | C5.5 | N14E77 | 12651 |
56 | 2017-07-16 | 16 | −72 | | 14/01:26 | 1200 | 360 | 01:07/02:09/03:24 | M2.4 | S06W29 | 12665 |
57 | 2017-09-08 | 2 | −122 | | 06/12:24 | 1571 | 360 | 11:53/12:02/12:10 | X9.3 | S08W33 | 12673 |
58 | 2021-05-12 | 15 | −61 | 09/12:00 | 266 | 284 | 13:38/13:58/14:09 | C4.0 | N15E51 | 12822 | |
59 | 2021-10-12 | 15 | −65 | | 09/07:12 | 712 | 360 | 06:19/06:38/06:53 | M1.6 | N17E09 | 12882 |
60 | 2022-02-03 | 11 | −66 | | 29/23:36 | 530 | 360 | 22:32/23:32/00:32 | M1.1 | N17E11 v | 12936 v |
61 | 2022-02-10 | 20 | −60 | | 06/14:00 | 334 | 360 | 12:52/13:41/14:41 | C3.1 | S20W07 | 12939 |
62 | 2022-04-14 | 22 | −81 | no | 11/05:48 | 940 | 360 | 04:59/05:21/05:58 | C1.6 | S18E11 | 12987 v |
63 | 2023-02-27 | 13 | −132 | | 25/19:24 | 1170 | 360 | 20:03/20:30/21:29 | M3.7 | N23W43 | 13229 v |
64 | 2023-04-24 | 7 | −213 | | 21/18:12 | 1284 | 360 | 17:44/18:12/18:44 | M1.7 | S22W11 | 13283 u |
Supplementary Materials
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References
1. van Driel-Gesztelyi, L.; Green, L.M. Evolution of Active Regions. Living Rev. Sol. Phys.; 2015; 12, 1. [DOI: https://dx.doi.org/10.1007/lrsp-2015-1]
2. Fletcher, L.; Dennis, B.R.; Hudson, H.S.; Krucker, S.; Phillips, K.; Veronig, A.; Battaglia, M.; Bone, L.; Caspi, A.; Chen, Q. et al. An Observational Overview of Solar Flares. Space Sci. Rev.; 2011; 159, pp. 19-106. [DOI: https://dx.doi.org/10.1007/s11214-010-9701-8]
3. Benz, A.O. Flare Observations. Living Rev. Sol. Phys.; 2017; 14, 2. [DOI: https://dx.doi.org/10.1007/s41116-016-0004-3]
4. Webb, D.F.; Howard, T.A. Coronal Mass Ejections: Observations. Living Rev. Sol. Phys.; 2012; 9, 3. [DOI: https://dx.doi.org/10.12942/lrsp-2012-3]
5. Green, L.M.; Török, T.; Vršnak, B.; Manchester, W.; Veronig, A. The Origin, Early Evolution and Predictability of Solar Eruptions. Space Sci. Rev.; 2018; 214, 46. [DOI: https://dx.doi.org/10.1007/s11214-017-0462-5]
6. Klein, K.L.; Dalla, S. Acceleration and Propagation of Solar Energetic Particles. Space Sci. Rev.; 2017; 212, pp. 1107-1136. [DOI: https://dx.doi.org/10.1007/s11214-017-0382-4]
7. Pulkkinen, T. Space Weather: Terrestrial Perspective. Living Rev. Sol. Phys.; 2007; 4, 1. [DOI: https://dx.doi.org/10.12942/lrsp-2007-1]
8. Koskinen, H.E.J.; Baker, D.N.; Balogh, A.; Gombosi, T.; Veronig, A.; von Steiger, R. Achievements and Challenges in the Science of Space Weather. Space Sci. Rev.; 2017; 212, pp. 1137-1157. [DOI: https://dx.doi.org/10.1007/s11214-017-0390-4]
9. Temmer, M. Space weather: The solar perspective. Living Rev. Sol. Phys.; 2021; 18, 4. [DOI: https://dx.doi.org/10.1007/s41116-021-00030-3]
10. Miteva, R.; Samwel, S.W.; Tkatchova, S. Space Weather Effects on Satellites. Astronomy; 2023; 2, pp. 165-179. [DOI: https://dx.doi.org/10.3390/astronomy2030012]
11. Kolarski, A.; Veselinović, N.; Srećković, V.A.; Mijić, Z.; Savić, M.; Dragić, A. Impacts of Extreme Space Weather Events on September 6th, 2017 on Ionosphere and Primary Cosmic Rays. Remote Sens.; 2023; 15, 1403. [DOI: https://dx.doi.org/10.3390/rs15051403]
12. Kilpua, E.; Koskinen, H.E.J.; Pulkkinen, T.I. Coronal mass ejections and their sheath regions in interplanetary space. Living Rev. Sol. Phys.; 2017; 14, 5. [DOI: https://dx.doi.org/10.1007/s41116-017-0009-6] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/31997985]
13. Semkova, J.; Koleva, R.; Benghin, V.; Dachev, T.; Matviichuk, Y.; Tomov, B.; Krastev, K.; Maltchev, S.; Dimitrov, P.; Mitrofanov, I. et al. Charged particles radiation measurements with Liulin-MO dosimeter of FREND instrument aboard ExoMars Trace Gas Orbiter during the transit and in high elliptic Mars orbit. Icarus; 2018; 303, pp. 53-66. [DOI: https://dx.doi.org/10.1016/j.icarus.2017.12.034]
14. Hands, A.D.P.; Ryden, K.A.; Meredith, N.P.; Glauert, S.A.; Horne, R.B. Radiation Effects on Satellites During Extreme Space Weather Events. Space Weather; 2018; 16, pp. 1216-1226. [DOI: https://dx.doi.org/10.1029/2018SW001913]
15. Miteva, R.; Samwel, S.W.; Costa-Duarte, M.V.; Malandraki, O.E. Solar cycle dependence of Wind/EPACT protons, solar flares and coronal mass ejections. Sun Geosph.; 2017; 12, pp. 11-19.
16. Altschuler, M.D.; Newkirk, G. Magnetic Fields and the Structure of the Solar Corona. I: Methods of Calculating Coronal Fields. Sol. Phys.; 1969; 9, pp. 131-149. [DOI: https://dx.doi.org/10.1007/BF00145734]
17. Scherrer, P.H.; Schou, J.; Bush, R.I.; Kosovichev, A.G.; Bogart, R.S.; Hoeksema, J.T.; Liu, Y.; Duvall, T.L.; Zhao, J.; Title, A.M. et al. The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO). Sol. Phys.; 2012; 275, pp. 207-227. [DOI: https://dx.doi.org/10.1007/s11207-011-9834-2]
18. Contopoulos, I. The Force-Free Electrodynamics Method for the Extrapolation of Coronal Magnetic Fields from Vector Magnetograms. Sol. Phys.; 2013; 282, pp. 419-426. [DOI: https://dx.doi.org/10.1007/s11207-012-0154-y]
19. Wiegelmann, T.; Thalmann, J.K.; Inhester, B.; Tadesse, T.; Sun, X.; Hoeksema, J.T. How Should One Optimize Nonlinear Force-Free Coronal Magnetic Field Extrapolations from SDO/HMI Vector Magnetograms?. Sol. Phys.; 2012; 281, pp. 37-51. [DOI: https://dx.doi.org/10.1007/s11207-012-9966-z]
20. Jarolim, R.; Thalmann, J.K.; Veronig, A.M.; Podladchikova, T. Probing the solar coronal magnetic field with physics-informed neural networks. Nat. Astron.; 2023; 7, pp. 1171-1179. [DOI: https://dx.doi.org/10.1038/s41550-023-02030-9]
21. Parker, E.N. Dynamics of the Interplanetary Gas and Magnetic Fields. Astrophys. J.; 1958; 128, 664. [DOI: https://dx.doi.org/10.1086/146579]
22. Fisk, L.A.; Zurbuchen, T.H.; Schwadron, N.A. On the Coronal Magnetic Field: Consequences of Large-Scale Motions. Astrophys. J.; 1999; 521, pp. 868-877. [DOI: https://dx.doi.org/10.1086/307556]
23. Owens, M.J.; Forsyth, R.J. The Heliospheric Magnetic Field. Living Rev. Sol. Phys.; 2013; 10, 5. [DOI: https://dx.doi.org/10.12942/lrsp-2013-5]
24. Kilpua, E.K.J.; Balogh, A.; von Steiger, R.; Liu, Y.D. Geoeffective Properties of Solar Transients and Stream Interaction Regions. Space Sci. Rev.; 2017; 212, pp. 1271-1314. [DOI: https://dx.doi.org/10.1007/s11214-017-0411-3]
25. Regnault, F.; Strugarek, A.; Janvier, M.; Auchère, F.; Lugaz, N.; Al-Haddad, N. Eruption and propagation of twisted flux ropes from the base of the solar corona to 1 au. Astron. Astrophys.; 2023; 670, A14. [DOI: https://dx.doi.org/10.1051/0004-6361/202244483]
26. Sarkar, R.; Pomoell, J.; Kilpua, E.; Asvestari, E.; Wijsen, N.; Maharana, A.; Poedts, S. Studying the Spheromak Rotation in Data-constrained Coronal Mass Ejection Modeling with EUHFORIA and Assessing Its Effect on the Bz Prediction. Astrophys. J.; 2024; 270, 18. [DOI: https://dx.doi.org/10.3847/1538-4365/ad0df4]
27. Akasofu, S.I. A Historical Review of the Geomagnetic Storm-Producing Plasma Flows from the Sun. Space Sci. Rev.; 2011; 164, pp. 85-132. [DOI: https://dx.doi.org/10.1007/s11214-011-9856-y]
28. Gonzalez, W.D.; Joselyn, J.A.; Kamide, Y.; Kroehl, H.W.; Rostoker, G.; Tsurutani, B.T.; Vasyliunas, V.M. What is a geomagnetic storm?. J. Geophys. Res.; 1994; 99, pp. 5771-5792. [DOI: https://dx.doi.org/10.1029/93JA02867]
29. Lassen, K.; Sharber, J.R.; Winningham, J.D. The development of auroral and geomagnetic substorm activity after a southward turning of the interplanetary magnetic field following several hours of magnetic calm. J. Geophys. Res.; 1977; 82, 5031. [DOI: https://dx.doi.org/10.1029/JA082i032p05031]
30. Kay, C.; Gopalswamy, N. The Effects of Uncertainty in Initial CME Input Parameters on Deflection, Rotation, Bz, and Arrival Time Predictions. J. Geophys. Res. (Space Phys.); 2018; 123, pp. 7220-7240. [DOI: https://dx.doi.org/10.1029/2018JA025780]
31. Manchester, W.; Kilpua, E.K.J.; Liu, Y.D.; Lugaz, N.; Riley, P.; Török, T.; Vršnak, B. The Physical Processes of CME/ICME Evolution. Space Sci. Rev.; 2017; 212, pp. 1159-1219. [DOI: https://dx.doi.org/10.1007/s11214-017-0394-0]
32. Zhou, Z.; Jiang, C.; Liu, R.; Wang, Y.; Liu, L.; Cui, J. The Rotation of Magnetic Flux Ropes Formed during Solar Eruption. Astrophys. J.; 2022; 927, L14. [DOI: https://dx.doi.org/10.3847/2041-8213/ac5740]
33. Schrijver, C.J.; De Rosa, M.L. Photospheric and heliospheric magnetic fields. Sol. Phys.; 2003; 212, pp. 165-200. [DOI: https://dx.doi.org/10.1023/A:1022908504100]
34. Bobra, M.G.; Sun, X.; Hoeksema, J.T.; Turmon, M.; Liu, Y.; Hayashi, K.; Barnes, G.; Leka, K.D. The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs - Space-Weather HMI Active Region Patches. Sol. Phys.; 2014; 289, pp. 3549-3578. [DOI: https://dx.doi.org/10.1007/s11207-014-0529-3]
35. Schrijver, C.J. A Characteristic Magnetic Field Pattern Associated with All Major Solar Flares and Its Use in Flare Forecasting. Astrophys. J.; 2007; 655, pp. L117-L120. [DOI: https://dx.doi.org/10.1086/511857]
36. Kane, R.P. How good is the relationship of solar and interplanetary plasma parameters with geomagnetic storms?. J. Geophys. Res. (Space Phys.); 2005; 110, A02213. [DOI: https://dx.doi.org/10.1029/2004JA010799]
37. Miteva, R.; Samwel, S.W. Catalog of Geomagnetic Storms with Dst Index ≤ -50 nT and Their Solar and Interplanetary Origin (1996–2019). Atmosphere; 2023; 14, 1744. [DOI: https://dx.doi.org/10.3390/atmos14121744]
38. Cane, H.V.; Richardson, I.G. Interplanetary coronal mass ejections in the near-Earth solar wind during 1996–2002. J. Geophys. Res. (Space Phys.); 2003; 108, 1156. [DOI: https://dx.doi.org/10.1029/2002JA009817]
39. Richardson, I.G.; Cane, H.V. Near-Earth Interplanetary Coronal Mass Ejections During Solar Cycle 23 (1996–2009): Catalog and Summary of Properties. Sol. Phys.; 2010; 264, pp. 189-237. [DOI: https://dx.doi.org/10.1007/s11207-010-9568-6]
40. Gopalswamy, N.; Yashiro, S.; Michalek, G.; Stenborg, G.; Vourlidas, A.; Freeland, S.; Howard, R. The SOHO/LASCO CME Catalog. Earth Moon Planets; 2009; 104, pp. 295-313. [DOI: https://dx.doi.org/10.1007/s11038-008-9282-7]
41. Guerra, J.A.; Park, S.H.; Gallagher, P.T.; Kontogiannis, I.; Georgoulis, M.K.; Bloomfield, D.S. Active Region Photospheric Magnetic Properties Derived from Line-of-Sight and Radial Fields. Sol. Phys.; 2018; 293, 9. [DOI: https://dx.doi.org/10.1007/s11207-017-1231-z]
42. Gao, P.X. Association of X-class flares with sunspot groups of various classes in Cycles 22 and 23. Mon. Not. R. Astron. Soc.; 2019; 484, pp. 5692-5701. [DOI: https://dx.doi.org/10.1093/mnras/stz362]
43. Miteva, R.; Samwel, S.W. M-Class Solar Flares in Solar Cycles 23 and 24: Properties and Space Weather Relevance. Universe; 2022; 8, 39. [DOI: https://dx.doi.org/10.3390/universe8010039]
44. Wang, R.; Liu, Y.D.; Dai, X.; Yang, Z.; Huang, C.; Hu, H. The Role of Active Region Coronal Magnetic Field in Determining Coronal Mass Ejection Propagation Direction. Astrophys. J.; 2015; 814, 80. [DOI: https://dx.doi.org/10.1088/0004-637X/814/1/80]
45. Wang, J.; Hoeksema, J.T.; Liu, S. The Deflection of Coronal Mass Ejections by the Ambient Coronal Magnetic Field Configuration. J. Geophys. Res. (Space Phys.); 2020; 125, e27530. [DOI: https://dx.doi.org/10.1029/2019JA027530]
46. Li, T.; Liu, L.; Hou, Y.; Zhang, J. Two Types of Confined Solar Flares. Astrophys. J.; 2019; 881, 151. [DOI: https://dx.doi.org/10.3847/1538-4357/ab3121]
47. Gupta, M.; Thalmann, J.K.; Veronig, A.M. Stability of the coronal magnetic field around large confined and eruptive solar flares. Astron. Astrophys.; 2024; 686, A115. [DOI: https://dx.doi.org/10.1051/0004-6361/202346212]
48. Chen, Y.; Manchester, W.B.; Hero, A.O.; Toth, G.; DuFumier, B.; Zhou, T.; Wang, X.; Zhu, H.; Sun, Z.; Gombosi, T.I. Identifying Solar Flare Precursors Using Time Series of SDO/HMI Images and SHARP Parameters. Space Weather; 2019; 17, pp. 1404-1426. [DOI: https://dx.doi.org/10.1029/2019SW002214]
49. Lin, P.H.; Kusano, K.; Shiota, D.; Inoue, S.; Leka, K.D.; Mizuno, Y. A New Parameter of the Photospheric Magnetic Field to Distinguish Eruptive-flare Producing Solar Active Regions. Astrophys. J.; 2020; 894, 20. [DOI: https://dx.doi.org/10.3847/1538-4357/ab822c]
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Abstract
Geomagnetic storms (GSs) are major disturbances in the terrestrial atmosphere caused by the reconnection process between the incoming plasma ejecta in the solar wind and the planetary magnetosphere. The strongest GSs can lead to auroral displays even at lower latitudes, and cause both satellite and ground-based infrastructure malfunctions. The early recognition of geoeffective events based on specific features on the solar photosphere is crucial for the development of early warning systems. In this study, we explore 16 magnetic field parameters provided by the Space-weather HMI Active Region Patch (SHARP) database from the SDO/HMI instrument. The analysis includes 64 active regions that produced strong GS during solar cycle (SC) 24 and the ongoing SC25. We present the statistical results between the SHARP and solar parameters, in terms of Pearson and Spearman correlation coefficients, and discuss their space weather potential.
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1 Institute of Astronomy and National Astronomical Observatory (IANAO), Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
2 Astronomy & Astrophysics Section, Dublin Institute for Advanced Studies, Dunsink Observatory, D15 XR2R Dublin, Ireland;
3 Institute of Physics, Kanzelhöhe Observatory for Solar and Environmental Research, University of Graz, 8010 Graz, Austria;