Spatial distribution of solar flares in 23rd solar cycle

H-alpha flares accompanied by the X-radiation f ?? 10^?6 wm^?2 in power are examined; 2331 flares were registered during the first half of the 23rd solar cycle (1997?C2000). The specific power of the X-radiation of the flares monotonically doubles from the minimum to the maximum of the sunspot. An increase in the number of flares in each solar rotation is nonmonotonic and disproportional to the relative number of sunspots. Several longitudinal intervals with increased flare activity can be distinguished in the entire time interval of five to ten rotations. The longitudinal distributions of flares and boundaries of the sector structures of a large-scale magnetic field differ considerably. This confirms the existence of two types of zero lines; the first type is determined by active regions, and the second one is determined by large-scale structures with weak magnetic fields. The flares concentrate near Hale??s zero lines of the first type.     

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.     

Relationship between coronal holes and boundaries of structures of the large-scale magnetic fields

By means of comparison of the positions of 665 observed coronal holes (CHs) and the structures of the magnetic field at different heights, it was shown that 43% of the observed CHs are not associated with unipolar regions of the background field at the photosphere. With height increasing from 1 to 2.5 solar radii, the structure of the magnetic field varies in 57% of all CHs. In 16% of the cases, variations of the structure can be observed at heights as small as 2500–10 000 km. Comparison of the positions of CHs with the longitudinal distribution of long-lived +/− and −/+ boundaries of the large-scale structure of the magnetic field at all the heights was carried out. It was shown that CHs adjoin or intersect with the Hale boundaries half as often as with those having the opposite distribution of the fields at both sides of the boundary. These results attest to a closer connection between the CHs and the photospheric and subphotospheric fields than with coronal fields. The magnetic fields of coronal structures can shield the coronal holes, thus creating “closed” CHs with a limited output of high-speed solar wind streams.     

Comparison of the magnetic properties of leading and following spots and the overlying ultraviolet emission

SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α _min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α _min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α _min and 〈α〉 decrease with growth in the maximum magnetic field B _max in both leading and following spots. The presence of a positive correlation between B _max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C ₃₀₄. Spots satisfying certain conditions display a positive correlation between C _304?L and 〈α _L 〉 for the leading (L) spots, and between C _304?L /C _304?F and l _L /l _F , where l _L (l _F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.     

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.     

AN INVESTIGATION OF SOLAR FACTORS GOVERNING CORONAL MASS EJECTION CHARACTERISTICS

This paper deals with the influence of the distance of the apparent axes of coronal mass ejections (CMEs) from a neutral line (NL) on the source surface and of coronal hole (CH) boundaries upon apparent characteristics of CMEs: e.g., the structure, the velocity of individual features, and the width.(a) It is found that the chance of measuring a CME velocity of ascent appears to decrease with increasing distance from a neutral line or coronal hole.(b) The apparent velocity of a CME appears to depend on the distance of its core from a neutral line or coronal hole boundary. CME speeds for events within 15 deg of a surface neutral line are significantly higher than those apparently much farther from surface neutral lines.(c) CME spans tend to be wider when they are more closely associated with surface neutral lines. It is shown that the contribution of CMEs in the neighbourhood of the NL (the heliomagnetic latitude of the CME apparent axis L < 15 deg) decreases with increasing length of the chain of coronal streamers separating the CH of like polarity of the magnetic field and depends on the character of the relationship between CMEs and other forms of activity. The study revealed a concentration of the apparent axes of CMEs toward zero lines of the photospheric magnetic field from the J. M. Wilcox Solar Observatory at Stanford.     

An investigation of the large-scale magnetic field variations in the corona prior to and after CME eruptions

The magnetic field changes in the corona at the site of coronal mass ejections (CMEs) have been investigated using the potential field-source surface model. It is shown that a CME is accompanied by the opening of closed field lines that formed the streamer's helmet base prior to the onset of a coronal disturbance. Two to three days after the appearance of the CME, the field configuration at the location of the coronal ejection reverts approximately to the state pre-existing before the generation of the CME. The appearance of small transient open magnetic tubes has been found after eruption of the coronal mass. These magnetic tubes seem to be the analogs for transient coronal holes.Taking into account the results of calculations of the field changes in the neighbourhood of the CME occurrence site, we have suggested a possible mechanism governing the spatio-temporal correlation between some flares and CMEs. Also, a possible mechanism has been proposed for field reconfiguration in the corona, leading to loss of the equilibrium of the magnetic configuration and to the subsequent generation of a CME in the region of coronal streamer chains separating coronal holes with same-polarity magnetic field.     

The existence of long-lived rays of the coronal streamer belt – Radial density and velocity distributions of the solar wind flowing in them

A technique is proposed for separating the rays of the streamer belt with quasi-stationary and non-stationary solar wind (SW) flows. It is shown that the lifetime of rays with a quasi-stationary SW can exceed 20 days. A new method has been developed for measuring the relative density distribution of a quasi-stationary slow SW flowing along the streamer belt's ray of increased brightness, based on the LASCO/SOHO data. It is shown that the density n for such SW flows varies with the radius R according to the relationship nR ^–, where =₁3.3–3.9 within 4 R ₀ R 6 R ₀ (here R ₀ is the solar radius), and decreases gradually further away. It is also shown that the V(R)-profiles in some rays of the streamer belt differ little from each other, although the value of the mass flow density, j _E, at the Earth's orbit in them can vary more than by a factor of 4. This distinguishes in a crucial respect a slow SW in the streamer belt's rays from a fast SW originating in coronal holes, for which j _Econstant and the dependences V(R) in different fast flows can differ greatly.     

Some properties of the latitude brightness distributions in the K and F coronae according to SOHO/LASCO data

We have obtained continuous latitude distributions of the K and F corona brightnesses at various distances for the first time, using both the Hayes—Vourlidas—Howard method and our own recently proposed, simple technique for separating the emission of the K and F coronas. Data from the LASCO C2 and C3 coronagraphs are analyzed. Variations of the angular size of the brightness distribution of the F corona with latitude and distance are estimated, as well as the ratio of the maximum F-corona brightness to the F-corona brightness at the pole. The variations in the F-corona brightness at large distances (R = 25 R _⊙, where R _⊙ is the solar radius) are studied on various time scales—a month, a year, and 11 years (the solar cycle). The latitude distribution of the F-corona brightness varies most appreciably over a year, and only weakly over one solar revolution and one solar-activity cycle (as considered on a fixed day of the year).