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.

Results of the spectral measurements of ionospheric noise in the meter band are presented. The events lasting several milliseconds (the emission maximum of which drifts upward (in frequency), is reflected (stops), and drifts downward) have been distinguished. Moreover, multiple harmonics are observed. The frequency-time structure of such events have been considered from the viewpoint of registration of the electron beam synchrotron emission harmonics at ionospheric altitudes in the geomagnetic field. The model calculations of the frequency-time structure of ionospheric radio noise bursts drifting in frequency have been performed taking into account the measurement conditions. It has been indicated that the model electron radio noise bursts agree with the measured bursts reflecting from the ionosphere at altitudes of 100–180 km. The model of the monoenergetic beam of electrons precipitating from the radiation belt (L ∼ 2.0–2.8) into the ionosphere has been proposed.

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.

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.

An intense and complex type IV solar radio burst over the time period 1992 0217 08-12 was recorded simultaneously by 3 spectrographs, ARTEMIS (100-500 MHz), OSRA (200-400 MHz) and IZMIRAN (180-270 MHz), and by the Nancay radioheliograph. For approximate to 2 hours, the event exhibited strong pulsations on various time scales and "zebra patterns" with new features: sudden frequency shifts of the whole pattern, splitting of individual zebra stripes into two stripes, structuration of the upper-frequency split stripes into emission dots in phase with approximate to 0.2 s pulsations. Another new and spectacular feature was a approximate to 10 MHz bandwidth emission at the high frequency cut-off of the whole event, oscillating between 350 and 450 MHz in phase with approximate to 3 min pulsations, and itself structured by the approximate to 0.2 s pulsations.Another property observed for the first time was that the circular polarization of zebra patterns changed sign during the event, possibly due to magnetic field reversal at some point of a long-lasting magnetic reconnection process in the upper corona. According to a classical picture, electrons are accelerated in the current sheet and trapped in the magnetic arch. Pulsations are due to MHD waves affecting the whole arch and electron beams as well.We confront two existing theories to these new observational features. The l + w double right arrow t model (Chernov 1976, 1989), based on Langmuir wave - whistler coupling at normal and anomalous Doppler resonance, can account for all the observed fine structures of zebra patterns, and gives a plausible magnetic field of 11 x 10(-4) T in the source. The Winglee & Dulk (1986) model, based on electron-cyclotron maser emission of upper-hybrid waves at double plasma resonance, seems the most adequate to account for the evolving emission line, with its source in the dense current sheet.

The large behind -limb (W 140, 0900 UT) flare on February, 16, 1984 was followed by a complex of radio bursts - type II, III, IV and V bursts.

Basing on radio measurements from different stations the paper presents a compilation of observations and resultinng questions concerning the interpretation of some remarkable features of the solar behind-limb event on 16th February 1984. The event was related to a very strong relativistic particle emission. Attention is paid to the related microwave radiation stimulating a discussion of the discrimination between plasma and gyromagnetic radiation being important for plasma diagnostics. Another outstanding feature is the occurrence of a spectacular multi-band U-shaped type II burst pattern challenging a discussion of possible higher harmonic plasma radiation.

Spectre dynamique des emissions radio entre 1000 et 45 MHz de frequence, enregistrements de sursauts a des frequences fixes et observations d'emissions RX a partir du satellite Prognoz 8, lors de la grande eruption chromospherique du 16 mai 1981