ISSN 0016�7932, Geomagnetism and Aeronomy, 2013, Vol. 53, No. 8, pp. 971–976. © Pleiades Publishing, Ltd., 2013.

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INTRODUCTION

The development of extreme events causedresearchers to study situations when comparativelyweak (large and moderate) flare events cause extremeSPEs in the near�Earth space. Twenty�one events withproton fluxes larger than 2 × 103 pfu at a maximum,caused by X ≤ 6 flares, were selected from 42 SPEs(http://www.swpc.noaa.gov/ftpdir/indices/SPE.txt)for the last four solar cycles (1976–2012). The tablepresents a sample of such SPEs, which indicates that19 events occurred in CARs, i.e., in transition structuresbetween active regions (ARs) and activity complexes.The characteristics of flares and coronal mass ejections(CMEs) were taken from (http://www.wdcb.ru/STP/online_data.en.html).

ACTIVE REGION COMPLEXES

A set of two and more sunspot groups (ARs) with acommon magnetic field, in the evolution of which therelation and interaction between individual compo�nents is revealed (Ishkov and Mogilevskii, 1983), isusually called a CAR. Researchers started understand�ing that CARs are a significant individual structure ofsunspot activity when the “Solar Maximum Year1980” program was fulfilled. Several groups ofresearchers (Ioshpa et al., 1981; Korobova, 1981)determined the main characteristics of these com�plexes: sunspot groups in CARs follow one another atclose latitudes within up to 30° along longitude (latitu�dinal CARs) or at the nearest longitudes up to 20° inlatitude (longitudinal CARs); a CAR usually includesfrom two to four ARs, but one sunspot group is pro�

nouncedly larger than the remaining groups; a com�mon magnetic field at a level of ≥100 G is the mostsubstantial CAR characteristic responsible for itsappearance and development; a relatively prolongedinteraction and MHD relation between sunspots andsunspot groups in CARs is the most important featureof this complex. This is observed in sunspot motions,synchronous turning of the largest sunspots (which iscontrolled by the magnetic field sign), “rigid” rotationof CARs as a whole, etc. Figure 1 presents a CAR ofcycle 24: AR11402 (N28, L211; Sp max = 630 mil�lionth of visible hemisphere, m.v.h. ) + AR11401 +AR11405 + AR11407, where a large M8.7/2B flareevent (the second intense SPE in the current solarcycle, which occupied the area of the main compo�nents) occurred on January 23, 2012. A CAR includesan increased number of sympathetic flares, the timesof onsets or maximums of which are in the 0–25m

(more frequently, 0–12m) interval. This time intervalcorresponds to the disturbance propagation velocityvarying from ~5 × 106 to 107 cm/s, which is close to thelocal Alfvén velocity in the photosphere and lowerchromosphere at average magnetic field values in anAR. According to the data of an HXIS device at theSMM space solar observatory, flares in one compo�nent triggered flares in another component in CARs inJune 1980 (Poleto et al., 1993). Moreover, some sym�pathetic flares (especially weak) were homological;i.e., they appeared at certain time intervals in approx�imately the same areas and had close developmentcharacteristics in all radiation ranges. A large flareevent with a 3B optical flare (when two large soft X�raybursts (X5.4 + X1.3) were registered) and with thelargest proton flux in the current solar cycle also

Complex Active Regions as the Main Source of Extremeand Large Solar Proton Events

V. N. IshkovPushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation,

Russian Academy of Sciences, Troitsk, Moscow oblast, 142190 Russiae�mail: ishkov@izmiran.ru

Received June 13, 2013

Abstract—A study of solar proton sources indicated that solar flare events responsible for ≥2000 pfu protonfluxes mostly occur in complex active regions (CARs), i.e., in transition structures between active regions andactivity complexes. Different classes of similar structures and their relation to solar proton events (SPEs) andevolution, depending on the origination conditions, are considered. Arguments in favor of the fact that sun�spot groups with extreme dimensions are CARs are presented. An analysis of the flare activity in a CARresulted in the detection of “physical” boundaries, which separate magnetic structures of the same polarityand are responsible for the independent development of each structure.

DOI: 10.1134/S0016793213080070

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Sample of SPEs with proton fluxes >2 × 103 pfu caused by <X6 flares (www.wdcb.ru/stp/online_data.en.html)

Y/M/D Fmax* Spacecraft Fl D/to Importance Coordinates CME/V AR Geoeffec�tiveness

Sunspot formation

activity structure

2001/11/06/0215

3.17 × 104 GOES 04/1603 X1/3B N06W18 H/1810 9684 S4 AR

2000/07/15/1230

2.40 × 104 GOES 14/1003 X5.7/3B N22W07 H/1674 9077 S4 CAR

2001/11/24/0555

1.89 × 104 GOES 22/>2209 M9/2N S15W34 H/1437 9704 S4 CAR?

2000/11/09/1555

1.48 × 104 GOES 08/2242 M7.4/3F N10W77 pH/1738 9213 S4 CAR

1992/10/31/0710

1.37 × 104 M 30/1659 X1.7/2B S22W61 7321 S4 CAR

2001/09/25/2235

1.29 × 104 GOES 24/0932 X2/2B S16E23 H/2402 9632 S4 CAR

1989/08/13/0710

9.20 × 103 M 12/1427 X2.6/2B S16W37 pH/ 5629 S3 CAR

1989/12/01/1343

7.30 × 103 GOES 30/1229 X2.6/2N N26W59 5800 S3 CAR

1994/02/21/0900

6.98 × 103 M, GOES 20/0104 M4/3B N09W02 7671 S3 CAR

2012/03/07/1540

6.53 × 103 GOES 07/0002 X5.4/3B N17E27 H/2684 11429 S3 CAR

2012/01/24/1530

6.31 × 103 GOES 23/0256 M8.7/2B N28W21 H/2175 11402 S3 CAR

2005/01/17/1750

5.04 × 103 GOES 16/2225 X2.6/3B* N14W08 H/2861 10720 S3 CAR

1992/05/09/2100

4.55 × 103 M, GOES 08/1512 M7.4/2N S25E07 7154 S3 CAR

2005/05/15/0240

3.14 × 103 GOES 13/1613 M8.0/2B N12E12 H/1689 10759 S3 CAR

1992/10/31/0710

2.70 × 103 GOES 30/1659 X1.7/2N S26W63 7321 S3 CAR

2002/04/21/2320

2.52 × 103 GOES 21/0043 X1.5/1F S14W84 H/2393 9906 S3 CAR

2001/10/02/0810

2.36 × 103 GOES 01/0441 M9.1/ sl8w89 H/1405 9628 S3 CAR

1991/07/08/0645

2.30 × 103 GOES 07/0223 X1.9/3B N28E00 6703 S3 CAR

2004/07/26/2250

2.21 × 103 GOES 25/1419 M1.1/1F N08W33 H/1333 10652 S3 CAR

1978/09/24/0400

2.2 × 103 M, IMP 23/0941 XI /3B N35W50 1294 S3 CAR

1981/10/13/2247

2.0 × 103 M, IMP 07/2308 X3.1/2B S18E31 3390 S3 CAR

Fmax, the flux at a maximum (pfu); (M) METEOR, (CME/V) the CME type and propagation velocity in km/s.

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COMPLEX ACTIVE REGIONS AS THE MAIN SOURCE OF EXTREME 973

occurred on March 7, 2012, in CAR AR11429(N18L301, Sp max = 1270 m.v.h.) + AR11430. In thiscase, these flares occurred in both components of lon�gitudinal CARs at an hourly interval (Fig. 2).

CAR AND LARGE PROTON EVENTS

The table indicates that 90% of all considered SPEsoccurred precisely in CARs. This means that consid�

erable proton fluxes escape when magnetic fields havespecial configurations, which are mostly implementedin CARs and only sometimes in ARs. Such a magneticfield configuration is also responsible for the forma�tion of a halo (when data are available) and, some�times, a partial halo in CMEs, the propagation veloc�ity of which is very high and extreme (>2000 km/s) infive cases. One of the two exceptional cases was regis�tered on November 4, 2001, when a proton flare event

SDO/HMI Quick–Look Magnetogram: 2012�01�22 0915:00 SDO/AIA 304 2012�01�23 0342:34 UT

Fig. 1. Image of a CAR on January 2012: four ARs in a common magnetic field (left); the large proton flare of January 23, whichentrapped both main CAR components (λ = 304 Å, SDO) (right). The images shown in Figs. 1 and 2 are taken from the SDOwebsite: http://sdo.gsfc.nasa.gov/assets/img/browse/2012/.

SDO/AIA 304 2012�03�07 0059:57 UT

Fig. 2. SPE of March 7, 2012, in the He II 304 Å line (SDO), which entrapped both main CAR components.

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20011030 20011102 20011102

20011102 20011102 20011102

(a)

(b)

(c)

(d)

(e)

(f)

S

NN

S

Fig. 3. Development of AR9684 from October 30 to November 2, 2001. The main structures and rotation direction of the sunspotgroup as a whole are marked with arrows. Images (d), (e), and (f) were obtained in the Ha 195 A lines and in the soft X�ray rangefrom (Zhang Guiquing, 2003).

with an extreme proton flux occurred in a single sun�spot group. AR9684 (N06L136, Sp max = 550 m.v.h.)crossed the eastern limb on October 27, 2001, and wasdivided into two unequal parts by a clearly defined fil�ament. A large leading sunspot of polarity N was fol�lowed by smaller sunspots of opposite polarity. OnOctober 30–November 3, a sunspot group (Fig. 3)rather rapidly turned counterclockwise by 25° withoutsignificant flares (Zhang Guiqing, 2003). This groupproduced both flare events only when a new magneticflux emerged on November 3–4.

CAR AND VERY LARGE SUNSPOT GROUPS

The studies of CARs made it possible to analyzevery large sunspot groups. As a rule, it is rather difficult todistinguish group components in such sunspot groups;however, one of the widest ARs for the last five solarcycles—AR 5395 (N34L257, Sp max = 3600 m.v.h.)—which occurred in March 1989, offered such anopportunity. This region crossed the eastern limb dur�ing a powerful flare period, continued developing dur�ing this period, and generated powerful flares duringalmost the entire transit across the visible solar disk.This cannot be explained by the flare energy releaseconcepts, according to which flares of significant

importance occur in limited time intervals. This inter�val depends on the power and emergence velocity of anew magnetic flux and is 55 ± 30 h (not more than16% of the AR transit time), when the entire energy ofthe newly emerged magnetic flux is implemented (Ish�kov, 1989). Figure 4 schematically presents the devel�opment of the given sunspot group, which can be rep�resented as a succession of sunspot groups thatappeared within an AR, i.e., a CAR. The most pro�longed and powerful flare events occurred on the visi�ble solar disk in a CAR (structures I and II): The flare ofimportance X >12/3B March 6 lasted longer than 6h,the flare of importance X4.5/3B March 10 was observedduring more than 7.5h, and the X4 level of the latter flareremained unchanged during 45 min. On March 10,structure III was formed at the sunspot group center;this structure rapidly extended the sunspot group from14° on March 10 to 20° on March 13. Structure IV(from March 14) extended the group to 23°. A flareactive CAR in January 2005 can be the second similarexample: AR10720 (N09L177, Sp max = 1630 m.v.h.),originated near the eastern limb on January 10–11. Ananalysis of photospheric images and magnetic fieldmap indicate that three fast successive emergences ofbipolar structures (ARs), which produced three periodsof the flares energy realization, are clearly defined inthis AR. The first magnetic flux was responsible for the

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COMPLEX ACTIVE REGIONS AS THE MAIN SOURCE OF EXTREME 975

generation of the sunspot group itself, its rapid expansionup to 1080 m.v.h. (by a factor of 2.5) on January 12–13,and implementation of four large flares on January14–15 (two of them were proton flares). The secondstructure started emerging north of the first structureand increased the sunspot group area to 1630 m.v.h. byJanuary 16. The magnetic configuration became sothat large proton fluxes emerged and the next two pro�ton flares on January 17 (X3.8/2B) and January 20(X7.1/3B) were responsible for the origination of theS3 SPE. Unfortunately, such an analysis cannot beperformed very frequently in a complex compactregion and on a real time basis. However, this analysiscan be useful, and we can predict the development ofsuch ARs and their flare activity with increasing accu�racy of processing images and high�resolution magne�tograms (SDO) in real time.

PHYSICAL BOUNDARIES ON THE SUN

A study of flare sunspot groups in June 1982,August 1983, and October 1979 indicated that thesestructures are CARs since the components are locatedclose to one another and the magnetic field is commonfor these groups. However, when the CAR compo�nents originate, they contact with magnetic fields of

the same sign and rather rapidly (three to five days)diverge; one of these components decays in this case.Such a situation is only possible if magnetic fluxes thatgenerated such structures were formed in independentadjacent contacting unipolar structures of the samesign, the physical boundaries between which result ina complete spatial independence of flare phenomenain individual components: the flare ribbon emissiondoes not penetrate into the adjacent structure evenwhen the most powerful flare events develop in onestructure (e.g., the X9/3B proton flare of July 12,1982) (Ishkov and Linke, 1990; Golovko, 1985).These boundaries completely isolate one of the CARcomponents, and the repulsion forces result in therapid degradation of one component. A study of thephysical boundaries indicated that they are substantialoutside ARs too as the boundaries between the mag�netic unipolar structures of the same polarity in thegeneral solar magnetic field. These boundaries areresponsible for the origination and existence of regionswith open magnetic fields, i.e., coronal holes, sincethe unipolar structure upper parts start diverging,forming coronal holes (CHs), at 20000–60000 kmaltitudes of the solar atmosphere where magneticrepulsion forces can overcome environmental resis�tance.

II

II

I

III

IV

S

N25

AR5395 N34L257 FKC3600

I

III

IV

S

S

SS

S

SN7

N

N

N

N

N36

512

SS23

N20

24

N22

N

N

5

S

1st stage of evolution – before March, 7 – the structure I + II: X/2 + M/7

2nd stage of evolution – March, 7–12 – formation of the structure III: X/4 + M/173rd stage of evolution – March, 12–15 – formation of the structure IV: X/2 + M/84th stage of evolution – March, 16–20 – evolution of the structure IV: X/3 + M/10

Fig. 4. Schematic AR5395 development, which can be divided into four intervals of emergence of large ARs. The group type forMarch 14 (north at the top and west on the right). During the transit across the visible solar disk, a sunspot group was formed fromstructures I and II. From March 10, structure III is formed at the sunspot group center. Structure IV started forming from March 14.Each emergence of new magnetic fluxes (ARs) resulted in its own series of significant flares during a period about of 40h.

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CONCLUSIONS

A study of large SPEs caused by not extreme solarflares indicated that these events mainly occurred inCARs. This indicates that such proton fluxes canescape only at magnetic field configurations that arepresent in CARs and are rarely implemented in ARs.Extremely large sunspot groups are CARs, succes�sively emerging in a limited space. A study of the CARevolution made it possible to reveal that physicalboundaries exist between magnetic structures of thesame sign. Such boundaries in CARs result in a com�plete spatial independence of active phenomena,including flare ones. Outside ARs, such boundariesresult in the formation of CHs.

REFERENCES

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Ioshpa, B.A., Ishkov, V.N., Mogilevskii, E.I., et al., inEvolyutsiya kompleksa aktivnykh oblastei NR 16862–64v mae 1980 g., “God solnechnogo maksimuma” (Evolu�

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Translated by Yu. Safronov