Average Temporal Profiles of Solar Flare Microwave Emission: Morphology and Application

Variations in spectro--optical characteristics of tropospheric water cluster aerosol forced by solar emissions

Multi-frequency Observations of Solar Microwave bursts recorded during solar maximum period 1980–81 are analysed and compared with x-ray data for staying the nature of microwave emissions from active regions. Most of the microwave burst spectra showed that the spectral index below the peak frequency is always less than 2

Multi–frequency Observations of Solar Microwave bursts recorded during solar maximum period 1980–81 are analysed and compared with x–ray data for studying the nature of microwave emissions from active regions. Most of the microwave burst spectra showed that the spectral index below the peak frequency is always less than 2.The magneto-ionic conditions of the burst sources and the electron energies as obtained from these multi-frequency observations of the bursts showed that the centimetric and x-ray observations are satisfactorily explained, if the emitting regions are dense, hot and compact associated with strong magnetic fields of a few hundred gauss, suggesting that the thermal gyroresonance process is the most likely emission mechanism involved in the emission of microwave and x-ray radiations from the active regions of sun.

Aims. We interpret long-periodic (minutes) modulations detected in solar microwave emission during flaring events as signatures of large-scale transverse oscillations of coronal loops. Methods. Our data analysis method is based methodologically on a sliding-window Fourier transform combined with the VignerWille technique. We analyze three different events where TRACE detected post-flare oscillating loops (on Mar. 23, 2000; Sep. 15, 2001; Sep. 07, 2001) Results. For the transverse large-scale oscillatory motion of a loop, a properly located observer, in addition to the modulation caused by the emission diagram pattern motion at the main frequency of the loop oscillation, may detect a modulation at twice the frequency, produced by the varying magnetic field during each inclination of the loop. Our main result consists in identification of these “modulation pairs” in the dynamic spectra of solar microwave emission and their association with the observed oscillating coronal loops.

The spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) of active regions with a complex magnetic field configuration before powerful flares, as well as the fine structure of active sources of ultraviolet (UV) emission based on AIA/SDO data, are studied. It is shown that there is unsteady behavior of microwave sources, along with the ignition of a system of crossed UV loops (X-structures). A class-M X-ray flare occurs after several hours at the site of ignition of the intersecting UV loops. The similar behavior observed in microwave and ultraviolet emission in the five active regions studied by us likely serves as a sign of a preflare situation in the active region on the Sun.

This paper presents the multiwavelength analysis of a 13 s quasi-periodic pulsation (QPP) observed in hard X-ray (12–300 keV) and microwave (4.9–34 GHz) emissions during a C-class flare that occurred on 2015 September 21. Atmospheric Image Assembly (AIA) 304 and 171 Å images show an emerging loop/flux tube (L1) moving radially outward, which interacts with the preexisting structures within the active region (AR). The QPP was observed during the expansion of and rising motion of L1. The Nobeyama Radioheliograph microwave images in 17/34 GHz channels reveal a single radio source that was co-spatial with a neighboring loop (L2). In addition, using AIA 304 Å images, we detected intensity oscillations in the legs of L2 with a period of about 26 s. A similar oscillation period was observed in the GOES soft X-ray flux derivative. This oscillation period seems to increase with time. We suggest that the observed QPP is most likely generated by the interaction between L2 and L3 observed in the AIA hot channels (131 and 94 Å). The merging speed of loops L2 and L3 was ∼35 km s−1. L1 was destroyed possibly by its interaction with preexisting structures in the AR, and produced a cool jet with the speed of ∼106–118 km s−1 associated with a narrow CME (∼770 km s−1). Another mechanism of the QPP in terms of a sausage oscillation of the loop (L2) is also possible.

We have analyzed data on solar protons, neutrons, electrons, gamma‐ray, optical and microwave emissions for the 1990 May 24 solar flare. Taking into account high energy neutron and gamma‐ray observations, we have suggested two neutron injections occurred during the flare. These two injections are called f‐ (first) and s‐ (second). Two components of interacting protons correspondingly existed to produce these neutrons at the Sun. The flare gave also a rise to solar cosmic ray event, which was detected by the neutron monitor network and GOES satellites. Two components of protons were observed in the interplanetary medium (p‐ (prompt) and d‐ (delayed) components). A possible spectrum of the s‐component of interacting protons coincided with injection spectrum of p‐component of interplanetary protons. For this reason, s‐ and p‐ components of protons may be considered as different portions of a single population of accelerated particles in the solar corona. The net result is that three proton components (f‐, p/...

On the basis of our multiwavelength observations made with the one-dimensional RATAN-600 radio telescope, we study the inversion of the circular polarization in the solar microwave emission at different frequencies. The inversion is detected in the emission of flare-producing active regions (FPARs) at various stages of their development, starting from the pre-flare stage. During the latest 23rd solar cycle maximum, numerous FPARs revealed spectral inhomogeneities in their polarized microwave radiation (Bogod and Tokhchukova, 2003, Astron. Lett.29, 263). Here, we discuss a particular case of such inhomogeneities, the frequency-dependent double inversion of the sign of circular polarization, which probably reflects some essential processes in FPARs. We consider several mechanisms for the double inversion: linear interaction of waves in the region of a quasitransverse magnetic field, the propagation of waves through a region of zero magnetic field, the scattering of radio waves on waves of high-frequency plasma turbulence, the influence of the current fibrils on the propagation of the radio emission, and the magnetic “dips,” in which the direction of magnetic field lines changes the sign relative to the observer. All of them have shortcomings, but the last mechanism explains the observations the best.

Some features of the solar microwave emission and their connection with geomagnetic activity

Dynamic spectra of low-frequency (LF) modulation of microwave emission during solar flares are obtained. Observation data for five radio bursts at frequency 37 GHz recorded by a 14-m Metsaahovi observatory (Finland) radiotelescope in the period from 1990 to 1993 were used. Frequency modulation of the radio emission intensity with the average period 296±37 (1σ) s, which is close to the period of well-known photospheric oscillations, was observed. Possible mechanisms of photospheric oscillation influence on the regions of radio burst generation are discussed.

Auroral kilometric radiation, Jupiter's decametric and Saturn's kilometric radio emissions, solar microwave spike bursts and microwave emissions from some flare stars have all been attributed to the electron cyclotron maser instability. The maser instability is usually assumed to involve the generation of magnetoionic waves. We investigate the modifications to the magneto ionic wave modes due to finite Larmor radius (FLR) corrections arising from a 'warm' background electron plasma with a Maxwellian distribution. We then consider the effects of these modifications on maser emission at frequencies near the fundamental of the electron cyclotron frequency fl e. The FLR effects are found to be small; the maximum temporal growth rate generally differs by ~ 10% from that for emission occurring in the magnetoionic modes. Small shifts occur in the frequencies and propagation angles corresponding to the maximum growth rates.

In a companion paper, we have presented so-called Spatio-Spectral Maximum Entropy Method (SSMEM) particularly designed for Fourier-Transform imaging over a wide spectral range. The SSMEM allows simultaneous acquisition of both spectral and spatial information and we consider it most suitable for imaging spectroscopy of solar microwave emission. In this paper, we run the SSMEM for a realistic model of solar microwave radiation and a model array resembling the Owens Valley Solar Array in order to identify and resolve possible issues in the application of the SSMEM to solar microwave imaging spectroscopy. We mainly concern ourselves with issues as to how the frequency dependent noise in the data and frequency-dependent variations of source size and background flux will affect the result of imaging spectroscopy under the SSMEM. We also test the capability of the SSMEM against other conventional techniques, CLEAN and MEM.

The connection between Coronal Mass Ejections (CME) and radio burst has been discovered especially at lower frequencies (< 2 GHz). The aim of the study is to investigate possible connection between CMEs and variability of radio brightenings at 37 GHz (8 mm) within the time frame of four days. The millimetre radio observations have been made on RT-14 radio telescope at Metsähovi Radio Observatory of Aalto University, Finland. In addition, 11.2 GHz (2.7 cm) total solar flux information is included in the analysis. The radio observations were made between March 2011 and September 2017, totally including 24 events. The results demonstrate that in most of the cases the radio brightening intensity achieves its maximum before CME occurs. Time of 11.2 GHz intensity appearance matches with time of CME appearance with difference of two to three hours. However, in most cases a maximum of 11.2 GHz intensity appears before CMEs. The study investigates a possibility of predicting CME appearance based on milli- and centimetre radio observations. The study also proposes a scenario connection between CMEs and solar microwave events.

We consider the phenomena observed in the microwave radiation emitted by the Sun during a two-hour period, which precedes the time when the coronagraph records coronal mass ejections. The data of 24-h patrol observations of centimeter- and decimeter-wave radiation in 1998 and 2003 are used, as well as the data about individual events in January 2005 and December 2006. Temporal characteristics of the phenomena and the spectral composition of sporadic components of the solar microwave radiation are analyzed. The statistical relation between the characteristics of sporadic radio waves, which are observed within the above-mentioned interval, and the parameters of coronal mass ejections have been found.

We present the preliminary results of the flare analysis. The event took place on 3rd June 2021, at 01:36 UT. It was observed in microwaves by Siberian Radioheliograph (SRH) within the 3-6 GHz, Broadband Microwave Spectropolarimeter (BBMS) and in meter radio range by e-Callisto spectrograph network. We found several of the type III bursts and the type-J burst in the meter radio range. At the same time, only the one burst was detected in the averaged time profiles of microwaves emission. This one corresponds to the strongest type III radio burst. Using the images by SRH, we defined the two sources and analysis of the time profiles of them separately. This approach allowed us finding the microwave bursts associated with the radio bursts, which were not distinguished in averaged time profiles. The delays between microwave and meter radio emission obtained from observations were compared with the results of preliminary analysis of dynamic spectra in radio meter range.