V. G. Fainshtein

Height stratification of solar magnetic fields in cycle 23

The radial component Br of magnetic field was calculated in the potential approximation and the synoptic maps of Br for several heights in the Solar atmosphere were constructed based on observations of the photospheric magnetic field made on the old magnetograph at the US Kitt Peak National Observatory and on the new SOLIS magnetograph at the US National Solar Observatory for cycle 23 (the years 1997–2009). Parameters of large-scale structures of magnetic field with positive and negative polarities were determined at seven heights in the Sun’s atmosphere—from the photosphere (H = Ro) to H = 2.5 Ro (Ro is the Solar radius). The processes of polar reversal for polar fields and changing of the sector structure of the field at middle latitudes were observed. Characteristic lifespans and rotations were ascertained. The general picture of variations of the large-scale solar magnetic field during cycle 23 was put forward. Two types of boundaries of large magnetic structures at various heights were identified.

Comparison of the properties of leading and trailing sunspots

The magnetic properties of leading and trailing sunspots were compared based on SDO/HMI and SDO/AIA data with a high spatial resolution for the growth phase and maximum of cycle 24. The properties of the solar atmosphere above sunspots are also discussed independently for both of these sunspot types. It was shown that the contrast in the He II 304 (C304) line above the umbra of leading and single sunspots is on average smaller than such a contrast above the umbra of trailing sunspots and on average weakly depends on the umbra area for both C304 sunspot types. It was established that the minimal angle between the field direction and the normal to the solar surface at the field measurement site is smaller in leading sunspots than in trailing ones (αmin − ls < αmin − fs) in 84% of the considered magnetically connected “leading-trailing” sunspot pairs, and a positive correlation exists between angles αmin − ls and αmin − fs. It was found that the C304 contrast increases with decreasing αmin − ls, fs for leading and trailing sunspots, and the C304 − ls/C304 − fs ratio on average decreases with increasing αmin − ls/αmin − fs ratio. The dependences of the maximal and average magnetic induction values in an umbra on the umbra area were constructed for the first time and compared independently for leading and trailing sunspots. It was concluded that the maximal and average magnetic field values do not vanish when the umbra area decreases to very small values. In all cases the magnetic field in leading and single sunspots is larger than in trailing ones.

Magnetic field dynamics based on SOHO/MDI data in the region of flares related to halo coronal mass ejections

Variations in the photospheric magnetic field in the region of solar flares, related to halo coronal mass ejections (HCMEs) with velocities V > 1500, 1000 < V < 1500, and V < 650 km/s, have been studied based on SOHO/MDI data. Using data with a time resolution of 96 min, it has been indicated that on average the 〈BL〉 and 〈|BL|〉 field characteristics increase nonmonotonically during 1–1.5 days before a flare and decrease during 0.5–1 days after a flare for groups of ejections with V > 1000 km/s for all considered HCME groups. Angle brackets designate averaging of the measured BL magnetic field component and its magnitude |BL| within an area with specified dimensions and the center coincident with the projection onto the region where the flare center field is measured. It has been established that a solar flare related to an HCME originates when the 〈BL〉 and 〈|BL|〉 values are larger than the boundary values in the flare region. Based on 1-min data, it has been found for several HCMEs with V > 1500 km/s that the beginning of powerful flares related to ejections is accompanied by rapid impulsive or stepped variations in 〈BL〉 and 〈|BL|〉 near the center of a flare with a size of approximately 4.5°. It has been established that the HCME velocity positively correlates with the |〈BL〉| value at the flare onset.

Investigation of CME properties using the data of SDO and PROBA2 spacecraft

Formation and motion (at the initial stage) of six limb CMEs detected in the period June 2010 to June 2011 are investigated using the high-resolution data of the PROBA2 and SDO spacecraft combined with the data of SOHO/LASCO coronagraphs. It is demonstrated that several loop-like structures of enhanced brightness originate in the region of CME formation, and they move one after another with, as a rule, different velocities. These loop-like structures in the final analysis form the frontal structure of CME. Time dependences of the velocity and acceleration of the ejection’s front are obtained for all CMEs under consideration. A conclusion is drawn about possible existence of two classes of CMEs depending on their velocity time profiles. Ejections, whose velocity after reaching its maximum sharply drops by a value of more than 100 km/s and then goes over into a regime of slow change, belong to the first class. Another class of CMEs is formed by ejections whose velocity changes slowly immediately after reaching the maximum. It is demonstrated that the CME’s angular dimension increases at the initial stage of ejection motion up to a factor of 3 with a time scale of doubling the angular size value within the limits 3.5–11 min since the moment of the first measurement of this parameter of an ejection. For three CMEs it is shown that at the initial stage of their motion for a certain time interval they are stronger expanded than grow in the longitude direction.

Properties of the magnetic fields of coronal holes with active regions

AbstractWe determine the structure of the magnetic fields of coronal holes (CHs) and investigate its change in connection with the emergence of active regions (ARs) in CHs. Based on our observations in the HeI 1083 nm line performed with the CrAO TST-2 telescope, we have selected CHs of two types: without (15 CHs) and with (28 CHs) ARs. Magnetograms obtained at the Kitt Peak National Solar Observatory have been used to calculate the magnetic fields of the same objects.We have calculated magnetic field characteristics by Rudenko’s method in the potential approximation at several heights in the corona, namely, the average (over the CH area) radial field component 〈Br〉 and its magnitude 〈|Br|/B〉 and the maximum and minimum (over the CH area) values of Br. The distributions of the isolines of these parameters superimposed on the CH images and the field lines of the calculated magnetic field have been constructed with resolutions of 33.4″ and 100.2″ on the solar surface. Analysis of these data has yielded the following results: The field lines originating in CHs without ARs are open or very high loops that are closed outside CHs. The latter occurs in completely or partially closed CHs.The system of open loops is stable, changes little with the birth of ARs, and is completely restored after the disappearance of ARs.ARs emerging inside CHs are bipolar or multipolar magnetic structures. They are formed by closed field lines.The field lines originating in ARs are closed either inside ARs or in the immediate neighborhood of ARs in CHs.There is virtually no connection of ARs inside CHs with external ARs or other places outside CHs.

Correlation between the parameters of coronal mass ejections and features of their propagation in the corona with the large-scale structure of the solar magnetic field

Correlation between the parameters of coronal mass ejections (CMEs) that are detected on the LASCO coronographs and are associated with eruptive prominences and the distances of CME axes from the coronal streamer belt has been analyzed. The deviations of CME trajectories from the radial direction have been investigated.

Method for determining the parameters of full halo coronal mass ejections

A method for determining the parameters of halo-type coronal mass ejections (full halo CMEs)—direction of motion, angular size, CME velocity along the Sun-Earth axis, etc.—has been proposed and tested. The method is based on the found empirical dependence between the angular sizes of CMEs located near the sky plane and angular sizes of associated eruptive prominences or post-eruptive arcades as well as on the relationships between the halo CME parameters derived in a simple geometrical CME model. Using this method and the SOHO/LASCO C3 and SOHO/EIT data, the parameters of 33 full halo CMEs have been determined. It is concluded that (1) the trajectories of all considered full halo CMEs deviate with recession of the CME front to RF > (2–5)R0 toward the Sun-Earth axis; (2) the majority of full halo CMEs recorded by LASCO C3 coronagraphs have relatively large angular sizes, 2α > 60°.

Magnetic field variations accompanying the filament eruption and the flare related to coronal mass ejections

Field variations in the region of eruptive event of June 7, 2011, associated with the filament eruption (FE), flare, and coronal mass ejection are studied based on vector measurements of the photospheric magnetic field with the SDO/HMI instrument. Variations of the module (B), the radial (Br) and transverse (Bt) components of the magnetic induction, and the inclination angle (α) of field lines to the radial direction from the center of the Sun are analyzed. It is shown that the strongest changes of the field before the event were located near the base of the southeastern leg of the eruptive filament; after the beginning of the event, they were located in the CME flare region. It is suggested that the FE is associated with two episodes of strong and rapid field variations: before the beginning of the slow filament rise and before its sudden acceleration. For the first time, variations of the inclination angles of the field lines over time in different parts of the eruptive event are studied in detail. It was found that the inclination angles of the field lines decrease in the vicinity of its channel during the slow rise of the filament, and the inclination angles of the field lines increase sharply after the beginning of the flare in the flare region in the vicinity of the neutral line.

On the occurrence and the motion of fast impulsive coronal mass ejections associated with powerful flares and unassociated with eruptive filaments

The formation and initial stage of the motion of several rapid, impulsive coronal mass ejections of the “halo” type (HCME) associated with flares of M and X class, but unassociated with the eruption of solar filaments, was studied using GOES-12/SXI, SOHO/EIT, and SDO/AIA data. The HCMEs considered can be divided into three groups according to the features of their formation: (i) some HCMEs arise due to an imbalance of single emission looped structures observed in the 195 Å channel of an EIT instrument for several hours before the first recording of mass ejection in the field of view of an SXI X-ray telescope, and after the eruption, these loops become structural elements of HCMEs; (ii) HCMEs can be formed as a result of an imbalance of several loops in the process of combining these loops into a single structure; and (iii) HCME formation begins with the upward motion of the group of coronal loops observed using the AIA data first in the “hot” 131 Å channel, a few minutes later in the “cold” 211 Å channel, later in the 193 Å channel, and, finally, in the 171 Å channel. The action of moving looped structures on the overlying regions of the corona leads to the formation and the motion of the frontal structure of HCMEs with increased brightness. In this case, these eruptive loops do not become structural elements of HCMEs. All investigated HCMEs began their translational motion before the occurrence of the associated flares. According to the results of studying the kinematics of the considered HCMEs we concluded that there are two types of coronal mass ejections differing according to the time profile of the velocity, which is determined by the area and the magnetic configuration of the active region where the mass ejection was formed. It is shown that HCMEs occurring at different times in the same active region have the same type of velocity profile.

Height stratification and polar reversal of the Sun’s magnetic fields in cycles 21–23

Using calculations of the magnetic field in the solar atmosphere in the potential approximation, it is shown that, (1) as distance R from the Sun’s center grows, the area of the positive magnetic field (S+field) in 10-deg latitude zones tends to 100% (0%) in the neighborhood of the solar minimum. At the distance R = 2.5R⊙(R⊙ is the solar radius), these values of the positive field are observed during ≈(12–55) Carrington rotations (CRs) for solar minima between neighboring cycles; (2) polar magnetic field reversals can occur repeatedly. Note that a polar reversal at large heights ends by 6–16 Carrington rotations earlier than on the Sun’s surface. On the Sun’s surface, a field polar reversal begins earlier at lower latitudes than at high ones; (3) for each longitude at different Rs and separately for each solar hemisphere the radial component of the field was averaged on synoptic maps in the 0°–40° latitude range. It is established that the TR rotation periods of the boundaries between the sectors (areas of longitudes with the same sign of the averaged field) can be shorter than, longer than, and equal to Carrington solar rotation period TCR. It turned out that boundaries with TR < TCR are observed at all heights, while boundaries with TR > TCR are observed at relatively small heights.