Local maximum in the microwave spectrum of solar active regions as a factor in predicting powerful flares

We discuss the results of a study of microwave radiation from three flare-active regions??NOAA 10300, 10930, and 11158??with powerful eruptive events (X-class flares and coronal mass ejections) recorded on July 15, 2002; December 13, 2006; and February 15, 2011, when the regions were in the central part of the disk. There exists evidence of a ??-configuration in the structure of the photospheric magnetic field formed one or two days prior to the eruptive process as a result of the emergence of a new magnetic flux and shifting movements of the sunspots and accompanied by changes in the spectral characteristics of the microwave radiation of the active regions (ARs), which suggests the development of a peculiar radio source. The analysis of these regions continues a series of studies of eruptive events carried out at RATAN-600 in the 1980s?C1990s and gives a reason to conclude that early detections of peculiar sources in the microwave radiation of ARs, which are essentially areas of high energy release in the solar atmosphere, can be used as a factor in predicting powerful eruptive (geoeffective) processes on the Sun.     

Long-period geomagnetic pulsations caused by the solar wind negative pressure impulse on 22 March 1979 (CDAW-6)

An analysis is made of the long-period geomagnetic pulsations as recorded at seven Norilsk meridian stations ( = 162°, latitudinal range: 61°–71°N) following abrupt magnetospheric expansion during the storm of 22 March 1979 caused by a rapid decrease in solar wind density. As with the time interval following an abrupt contraction at the time of sudden storm commencement, there exist two types of pulsations in the pulsation spectra: latitude-independent (T>400 s) and latitude-dependent (T<200 s) pulsations. The first pulsation type is interpreted in terms of forced pulsations associated with magnetopause oscillations. The oscillation period is determined by plasma density in the boundary layer and by the radius of the magnetosphere (T ^1/2R⁴). The latitudinal dependence of the period, amplitude and polarization of the second-type pulsations is in agreement with the resonance mechanism of their origin.     

Evolution of Solar Active Regions Before Large Flares: Overview of the Events of 2010–2017

Geomagnetism and Aeronomy - The paper presents a study of the evolution of the photospheric magnetic field of active regions (ARs) of the Sun in which flares (larger than the M9 class in the...     

Structure and development of the spotless flare on March 16, 1981

The morphological peculiarities of the 1N (N09W22) two-ribbon spotless flare on March 16, 1981, as well as its connection with a magnetic field, have been considered. In contrast to major flares of the active region, this spotless flare is characterized by a large-scale development process, a large distance from the magnetic neutral line, and the absence of the spread of the ribbons. The development of the flare had four periods. At the beginning of each period, a sharp increase in the brightness of the flare was observed along with a simultaneous decrease in the area of the flare ribbons. The areas of the ribbons varied synchronously during all of the periods. However, the situation changed abruptly near the maximum: the area of one of the ribbons increased, whereas the area of the other ribbon decreased. In our opinion, this behavior is a manifestation of real physical processes in the flare source and was a precursor of the beginning of the flare decay. The magnetic field and its topology, as well as the cellular structure of the chromosphere, were primarily responsible for the evolution of the flare. Almost all of the mottles and bright parts of the flare were localized in the immediate vicinity of magnetic hills with field intensities from 80 to 250 G. The main structural elements of the flare have been identified. A phenomenon called the tunnel effect has been revealed: the flare progresses inside a tunnel formed by the system of dark arch structures (filaments). The results indicate that spotless flares apparently constitute a specific class of flare phenomena and the study of them is of great interest for understanding of the origin of solar flares.     

Construction of the light curves for solar flares in the Hα line

The results of an investigation of some factors affecting the construction of the light curves for solar flares in the Hα line are presented. It is determined that the type of the light curve depends on the method of measuring the intensity, the size of the measurement window, and the brightness fluctuations of the quiet chromosphere areas (the reference areas). The light curves constructed on the basis of the flare’s peak intensity show a real picture of the flare development process. A method for the selection of the “reference areas” is suggested.