Abstract. The large solar flare of 14 July 2000 10 UT occurred in an active region near the central meridian. It was accompanied by the eruption of a filament and a rapid halo-type coronal mass ejection (CME). Large particle fluxes were detected up to relativistic energies at 1 AU. In this paper accelerated particles and plasma structures in the corona are traced using radio, X-ray, EUV and visible light observations, together with neutron monitor measurements of relativistic protons at 1 AU. Both the bulk of the radio emission at decimetric and longer waves and the escape of suprathermal electrons and relativistic protons from the Sun were delayed by 10-20 min with respect to the hard X-ray emission. Despite the delay and the association with a flare near the central meridian the neutron monitor time profile was impulsive. We show that the escape of the relativistic protons occurred in time coincident both with a coronal shock wave, which may be the bow shock of the CME, and with radio sources which trace electron acceleration and magnetic field reconfiguration in the western hemisphere. Three observations support the idea that the relativistic protons were accelerated during this reconfiguration, at heights between 0.1 and 1 R above the photosphere, and not in the flaring active region or at the bow shock of the CME: (i) the rise of the neutron monitor count rates is simultaneous with the brightening of a new continuum radio source; (ii) the duration of the continuum emission is similar to the rise time of the neutron monitor count rates; (iii) the radio source is close to the Earth-connected interplanetary magnetic field line.
[1] A flare on 2003 October 28 produced a relativistic particle event at Earth, although the active region AR 10486 was located to the east of the central meridian of the Sun. The paper considers features related to the acceleration at the Sun and the propagation to the Earth of energetic particles in this event, which occurred on a disturbed interplanetary background caused by preceding activity on the Sun and a corotating high-speed solar wind stream. From a study of the onset times of the event at different neutron monitors, we conclude that the earliest arriving solar particles were neutrons. The first relativistic protons arrived a few minutes later. Among relativistic solar protons (RSP), two populations could clearly be distinguished: prompt and delayed ones. The prompt solar protons caused an impulse-like increase at a few neutron monitor stations. The delayed solar protons arrived at Earth 0.5 hours later. Both prompt and delayed relativistic protons arrived at Earth from the antisunward direction. On the other hand, subrelativistic electrons that were traced by their radio emission from meter waves (Nançay Radioheliograph and Decametric Array) to kilometer waves (Wind/WAVES) are accompanied by metric radio emission in the western solar hemisphere, far from the flaring active region. We propose a scenario that reconciles the unusual features of energetic particles at the Earth with the observed structure of the interplanetary magnetic field, which suggests the Earth is at the interface between an interplanetary coronal mass ejection (ICME) and a corotating stream during the event. In this scenario the high-energy protons and electrons are accelerated in the flaring active region, injected into the eastern leg of an ICME loop rooted in the active region, and reach the Earth from the antisunward direction after passing through the summit of the loop. We attribute the promptly escaping subrelativistic electrons to acceleration in the western solar hemisphere and propagation along the nominal Parker spiral.
In order to avoid the disagreements and difficulties now found in the interpretation of quiet-Sun UV observations concerning the chromosphere-corona transition region, 6-and ll-cm maps obtained at cycle maximum with the Nanqay radiotelescope are used in combination with existing measurements of the central brightness temperatures at centimetric wavelengths and with the hydrodynamic conservation equations so as to obtain an equatorial, quiet solar atmosphere model between 10000 K and 300000 K, in the interspicular regions. This model introduces a large ascending velocity in these regions. Some of the consequences of the model concerning the heating and replenishment of the corona are discussed. An explanation of sudden disappearance of quiescent prominences is suggested.
Comparison of maps of the Sun obtained over the period June 29 to July 8, 1982 at 169 MHz with the Nan~ay Radioheliograph and at 73.8, 50, and 30.9 MHz with the Clark Lake Radioheliograph shows that the slowly varying component at meter and decameter wavelengths is not always thermal emission. During the period under study weak noise storm continua were the most frequent sources of slowly varying component at 169 and 73.8 MHz. Most filaments show no radio counterpart on the disk. A streamer has been detected on the disk from 169 to 30.9 MHz with an optimum observability at 50 MHz. The brightest source of the slowly varying component from 73.8 to 30.9 MHz for most of the period was located above an extended coronal hole in a region where a depression was observed at 169 MHz. In favorable cases, electron densities can be derived from the positions of noise storms and radio streamers; these are in agreement with previous K-corona eclipse observations.
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