Context. The origin of coronal type II radio bursts and the nature of their band splitting are still not fully understood, though a number of scenarios have been proposed to explain them. This is largely due to the lack of detailed spatially resolved observations of type II burst sources and of their relations to magnetoplasma structure dynamics in parental active regions. Aims. To make progress in solving this problem on the basis of one extremely well observed solar eruptive event.Methods. The relative dynamics of multithermal eruptive plasmas, observed in detail by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, and of harmonic type II burst sources, observed by the Nançay Radioheliograph at ten frequencies from 445 to 151 MHz, was studied for the 3 November 2010 event arising from an active region behind the east solar limb. Special attention was given to the band splitting of the burst. Analysis was supplemented by investigation of coronal hard X-ray (HXR) sources observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager. Results. We found that the flare impulsive phase was accompanied by the formation of a double coronal HXR source, whose upper part coincided with the hot (T ≈ 10 MK) eruptive plasma blob. The leading edge (LE) of the eruptive plasmas (T ≈ 1−2 MK) moved upward from the flare region with a speed of v ≈ 900−1400 km s −1 . The type II burst source initially appeared just above the LE apex and moved with the same speed and in the same direction. After ≈20 s, it started to move about twice as fast, but still in the same direction. At any given moment, the low-frequency component (LFC) source of the splitted type II burst was situated above the highfrequency component (HFC) source, which in turn was situated above the LE. We also found that at a given frequency the HFC source was located slightly closer to the photosphere than the LFC source. Conclusions. Based on the set of established observational facts, we conclude that the shock wave, which could be responsible for the observed type II radio burst, was initially driven by the multi-temperature eruptive plasmas, but later transformed to a freely propagating blast shock wave. The preferable interpretation of the type II burst splitting is that its LFC was emitted from the upstream region of the shock, whereas the HFC was emitted from the downstream region. The shock wave in this case could be subcritical.

Dynamics of hot chromospheric plasma of solar flares is a key to understanding of mechanisms of flare energy release and particle acceleration. A moderate M1.0 class flare of 12 June, 2014 (SOL2014-06-12T21:12) was simultaneously observed by NASA's Interface Region Imaging Spectrograph (IRIS), other spacecraft, and also by New Solar Telescope (NST) at the BBSO. This paper presents the first part of our investigation focused on analysis of the IRIS data. Our analysis of the IRIS data in different spectral lines reveals strong redshifted jet-like flow with the speed of ∼100 km/s of the chromospheric material before the flare. Strong nonthermal emission of the C II k 1334.5Å line, formed in the chromosphere-corona transition region, is observed at the beginning of the impulsive phase in several small (with a size of ∼1 arcsec) points. It is also found that the C II k line is redshifted across the flaring region before, during and after the impulsive phase. A peak of integrated emission of the hot (1.1 · 10 7 K) plasma in the Fe XXI 1354.1Å line is detected approximately 5 minutes after the integrated emission peak of the lower temperature C II k. A strong blueshift of the Fe XXI line across the flaring region corresponds to evaporation flows of the hot chromospheric plasma with a speed of 50 km/s. Additional analysis of the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data supports the idea that the upper chromospheric dynamics observed by IRIS has features of "gentle" evaporation driven by heating of the solar chromosphere by accelerated electrons and by a heat flux from the flare energy release site.

Solar radio emission features a large number of fine structures demonstrating great variability in frequency and time. We present spatially resolved spectral radio observations of type IIIb bursts in the 30 − 80 MHz range made by the Low Frequency Array (LOFAR). The bursts show well-defined fine frequency structuring called "stria" bursts. The spatial characteristics of the stria sources are determined by the propagation effects of radio waves; their movement and expansion speeds are in the range of (0.1−0.6)c. Analysis of the dynamic spectra reveals that both the spectral bandwidth and the frequency drift rate of the striae increase with an increase of their central frequency; the striae bandwidths are in the range of ∼ (20 − 100) kHz and the striae drift rates vary from zero to ∼ 0.3 MHz s −1 . The observed spectral characteristics of the stria bursts are consistent with the model involving modulation of the type III burst emission mechanism by small-amplitude fluctuations of the plasma density along the electron beam path. We estimate that the relative amplitude of the density fluctuations is of ∆n/n ∼ 10 −3 , their characteristic length scale is less than 1000 km, and the characteristic propagation speed is in the range of 400 − 800 km s −1 . These parameters indicate that the observed fine spectral structures could be produced by propagating magnetohydrodynamic waves.