A two-step (fast + slow in comparison to the exponential law) behavior of radio-emission fluxes was discovered by the differential method in the phases of growth and decay during an analysis of radio-burst observation data received at IZMIRAN by means of meter-band spectrographs and fixed-frequency radiometers. It was shown that the observed fast mode of flux growth may be connected with the fast mode 3013 MHz of the acceleration of the electrons responsible for synchrotron radiation of the flare in the microwave band.

Проанализированы записи радиоизлучения Солнца, полученные на спектрографе ИЗМИРАН (25–270 МГц) для события солнечной вспышки 12 февраля 2010 г. Отмечено, что в трех больших группах всплесков III типа наблюдалась разнообразная тонкая структура на фоне невысокого континуума. Согласно данным радиогелиографа Нансэ, источники всех трех групп всплесков располагались в одной активной области 11046 и их излучение сопровождалось всплесками в мягком рентгеновском диапазоне (космический аппарат GOES): в 07:21 UT С7.9, в 09:40 UT В9.6 и в 11:25 UT М8.3. После первой группы всплесков наблюдались классические волокна (fiber bursts) в сочетании с обратно дрейфующими волокнами с необычным дугообразным дрейфом. После третьей (самой мощной) группы наблюдались стабильные секундные пульсации и медленно дрейфующие волокна. Мгновенная полоса частот у них на порядок превышала полосу частот классических волокон, а частотный дрейф был в несколько раз меньше. Более сложные волокна наблюдались в самой слабой группе в интервале 09:40:30–09:42:00 UT. Они представляли собой узкополосные ( 0.5 МГц) волокна, периодически повторяющиеся в небольшой полосе частот (5–6 МГц) в течение нескольких секунд. Особенностью данного явления является также присутствие множества хаотически дрейфующих ансамблей волокон, пересекающихся и накладывающихся друг на друга. Предполагается, что появление таких структур может быть связано с существованием множества мелких ударных фронтов за передним краем коронального выброса массы.

Solar radio emission records received at the IZMIRAN spectrograph (25–270 MHz) during the solar flare event of February 12, 2010 are analyzed. Different fine structures were observed in three large groups of type III bursts against a low continuum. According to data from the Nancay radioheliograph, sources of all three groups of bursts were located in one active region, 11046, and their emissions were accompanied by soft X-ray bursts (GOES satellite): C7.9 at 0721 UT, B9.6 at 0940 UT, and M8.3 at 1125 UT. After the first group of bursts, classical fiber bursts were observed in combination with reverse-drift fiber bursts with unusual arc drift. After the third (the most powerful) group, stable second-length pulsations and slow-drift fiber bursts were observed, the instantaneous frequency bands of which were an order of magnitude larger than the frequency band of classical fiber bursts, and the frequency drift was several times lower. More complex fiber bursts were observed in the weakest group in the time range 0940:39–0942:00 UT. They were narrow-band (∼0.5 MHz) fiber bursts, periodically recurring in a narrow frequency band (5–6 MHz) during several seconds. The presence of many chaotically drifting ensembles of fibers, crossing and superimposing on one another, is a feature of this event. It is assumed that occurrence of these structures can be connected with the existence of many small shock fronts behind the leading edge of a coronal mass ejection.

Type III radio bursts are produced near the local electron plasma frequency fp and near its harmonic 2fp by fast electrons ejected from the solar active regions and moving through the corona and solar wind. The coronal bursts have dynamic spectra with frequency rapidly falling with time, the typical duration being about 1–3 s. In the present paper, 37 well-defined coronal type III radio bursts (25–450 MHz) are analyzed. The results obtained substantiate an earlier statement that the dependence of the central frequency of the emission on time can be fitted to a power-law model, f(t) ∝ (t − t0)−α, where α can be as low as 1. In the case of negligible plasma acceleration and conical flow, it means that the electron number density within about 1 solar radius above the photosphere will decrease as r−2, like in the solar wind. For the data set chosen, the index α varies in the range from 0.2 to 7 or bigger, with mean and median values of 1.2 and 0.5, respectively. A surprisingly large fraction of events, 84%, have α ⩽ 1.2. These results provide strong evidence that in the type III source regions the electron number density scales as n(r) ∝ (r − r0)−β, with minimum, mean, and median β = 2α of 0.4, 2.4, and 1.0, respectively. Hence, the typical density profiles are more gently sloping than those given by existing empirical coronal models. Several events are found with a wind-like dependence of burst frequency on time. Smaller power-law indices could result from the effects of non-conical geometry of the plasma flow tubes, deceleration of coronal plasma, and/or the curvature of the magnetic field lines. The last effect is shown to be too weak to explain such low power-law indices. A strong tendency is found for bursts from the same group to have similar power-law indices, thereby favoring the hypothesis that they are usually produced by the same source region.

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997 – 2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200 – 300 kHz for slow-drifting fibers in type II bursts, and 700 – 1000 kHz for fast-drifting fibers in type II + IV (continuum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable frequency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejections (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actually observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14 – 8 MHz were seen as the direct expansion of similar fine structure (as fibers or “herringbone” structure) in the decametric range observed with the Nançay and IZMIRAN spectrographs.

The main data on observations of the Sun, interplanetary medium, and magnetosphere, obtained mainly by home researchers during the stroncyest magnetic storm of November 20, 2003 (Dst = -472 nT), are presented in the work. This period corresponds to the next earthward turning of the active side of the Sun that generated the series of the strongest solar flares (including flares of class > X17) and the magnetic storm with Dst = -401 nT from the end of October to the beginning of November 2003. Although the number and power of the flares were much smaller during the period under study, the magnetic storm was the second strongest for the entire period of observation of the Dst index and was apparently caused by the interaction of frequently occurred coronal mass ejections in the interplanetary space, as a result of which the region of interaction compressed and the southern IMF component increased to less than -45 nT.

The extreme solar activity of October–November 2003 was recorded at IZMIRAN with digital radiospectrographs at 25–270 MHz and fixed-frequency radiometers at 169, 204 and 3000 MHz. An outstanding metre-wavelength noise storm took place during the fist passage of the grandiose evolving active complex across the disc which testifies to permanent electron acceleration over the complex with energy of up to tens of kiloelectronvolts. Against this background, intense metric and microwave radio bursts were recorded in association with several outstanding flare and huge coronal mass ejection (CME) events. The dynamic spectra of these events display multiband and sometimes fine-structure type II bursts, initiated by coronal shocks, and various continuum emissions. In some cases, a corresponding microwave burst at 3000 MHz includes not only an impulsive component coinciding with a flare maximum but also a predominating delayed long-duration component with a smooth time profile. The latter component is thought to be linked with a post-eruptive energy release and particle acceleration when the magnetic field, strongly disturbed by a CME, relaxes to a new quasi-equilibrium configuration via reconnection in high coronal levels.

We present new observational data on the phenomena of extremely high activity on the Sun and in the heliosphere that took place in October–November 2003. A large variety of solar and heliospheric parameters give evidence that the interval under consideration is unique over the entire observation time. Based on these data, comparing them with similar situations in the past and using available theoretical concepts, we discuss possible cause-and-effect connections between the processes observed. The paper includes the first results and conclusions derived by the collaboration “Solar Extreme Events-2003” organized in Russia for detailed investigations of these events. As a result of our consideration, it is beyond question that the physical causes of solar and heliospheric phenomena in October–November 2003 are not exclusively local and do not belong only to the active regions and solar atmosphere above them. The energy reservoirs and driving forces of these processes have a more global nature. In general, they are hidden from an observer, since ultimately their sources lie in the subphotospheric layers of the Sun, where changes that are fast and difficult to predict can sometimes take place (and indeed they do). Solar flares can serve as sufficiently good tracers of these sudden changes and reconstructions on the Sun, although one can still find other diagnostic indicators among the parameters of magnetic fields, motions of matter, and emission characteristics.

Russian Space Weather Initiatives (RSWI) support different models for space weather forecastin (http://alpha.npi.msu.su/RSWI/rswi.html). The models give the long-time (months-years) and short-time (days) predictions of the solar activity, heliospheric conditions, and dynamics of the Earth's magnetic field and radiation. Many different parameters measured from the Sun to the Earth's magnetosphere are used as inputs to the space weather models. The paper is devoted to a short overview of these models.

On July 28, 1999 between 08:15 and 10:30 UT a radio event including long-lasting zebra-patterns was recorded in the frequency range 45-550 MHz by the IZMIRAN and Phoenix-2 spectrometers. These emissions were related to a small flare (1B M2.3) in AR 8649. After the event maximum, at 08:55, some unusual fiber-bursts appeared with absorption at both low and high frequency edges of the emission stripe. Additionally, some stripes were observed only in absorption. After 10:19 almost all zebra stripes and fiber bursts showed absorption at the high frequency edge. During that interval zebra-stripes formed some cascades with U-burst like changes of the frequency drift (from negative to positve). In such cases fiber-bursts continuously converted into zebra-stripes testifying the common origin of both structures. The frequency bandwidth of the zebra-patterns is probably defined by the vertical dimensions of new emerging flare loops.

The 14 July 2000 (`Bastille Day') eruptive and geoeffective flare event was observed by the digital IZMIRAN radio spectrograph in the frequency range of 25–270 MHz. This instrument allowed the analysis of various features of the dynamic radio spectrum and their comparison with other observational data, in particular with development of a spectacular EUV post-eruption arcade recorded aboard the Transition Region and Coronal Explorer (TRACE). (1) A compressed multi-hour radio spectrum shows that the event caused a conspicuous weakening of the pre-existing noise storm. This phenomenon was perhaps caused by interaction of a large halo coronal mass ejection (CME), recorded by the the Large Angle and Spectroscopic Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO), with emitting coronal structures. (2) Several type II bands are present at the initial and maximum phases of the flare event. The frequency drifts of the clearest bands correspond to the estimated shock wave speed of 1100–2300 km s−1 that is comparable with the CME speed observed in the sky plane. (3) Significant broadband enhancements of the metric radio emission took place around of 10:24–10:27 UT coinciding with sharp development of the EUV arcade in the northeast direction. It appears to correspond to the intensification of the electron acceleration in a process of post-eruption loop formation. (4) The high-resolution radio spectrum revealed a superposition of numerous type III-like bursts and/or pulsations with a time scale ranging from a few seconds to several tens of seconds. These features can be attributed particularly to successive formation of new loops of the arcade and corresponding temporal fragmentation of the electron acceleration in the course of the post-eruption reconnection. In summary, the analysis demonstrates the correspondence between the multi-scale temporal features of the metric radio emission and such phenomena as the CME and post-eruption EUV arcade. Some spectra, images, and movies illustrating the event are presented also on the accompanying CD-ROM.

The IZMIRAN's solar meter digital radiospectrograph was newly upgraded at the end of 1999. Some outstanding meter solar radio bursts have been registered by this device with enhanced time resolution and frequency range during the first half of 2000. Radiospectra of these events (mainly complicated type II bursts) and accompanying data are analysed.

Usually the gyrosynchrotron emission of microwave bursts from electron populations with a power-law (PL) energy distribution has been considered under the assumption that the spectral index of the distribution is constant over a wide range of energies. Meanwhile, there is strong evidence, in particular from hard X-ray and γ-ray, but also from cm/mm wavelength radio observations, that in many solar flare events the spectrum of the emitting electrons is characterized by a significant hardening at energies above 100–500 keV. We present some examples of calculated microwave burst spectra at cm/mm wavelengths taking into account the above evidence. It is shown that a break in the energy spectrum of the PL electrons can indeed result in a spectral hardening sometimes observed in microwave bursts at frequencies above 10–30 GHz.

A description of the scientific experiment 'SOlar Radio Spectrometer' (SORS) of the CORONAS-I project is given. The goal of the experiment is the investigation of the solar radio emission and plasma wave phenomena in the Earth's ionosphere in the wide frequency band 100 kHz–300 MHz. Results of the SORS observations for a three-month working period are discussed, and proposals for improvement of the SORS equipment for future CORONAS missions are made.