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[1] We present the first modeling of solar energetic particle (SEP) events inside corotating compression regions. We consider gradual compressions in the interplanetary magnetic field brought on by interaction of the solar wind streams of different speed. The compression model is similar to that previously suggested for the acceleration of lowenergy particles associated with corotating interaction regions (CIRs). In the framework of focused transport, we perform Monte Carlo simulations of the SEP propagation, adiabatic deceleration and reacceleration. A trap-like structure of the interplanetary magnetic field modifies the SEP intensity-time profiles, energy spectra, and anisotropy. Particle diffusion and adiabatic deceleration are typically reduced. For this reason, at a corotating vantage point the SEP event development after the intensity maximum is slower than would be expected based on the modeling in the standard, Archimedean spiral field. At the noncorotating spacecraft the magnetic tube convection past the observer becomes more important. The numerical model forms a basis on which to interpret SEP observations made by present and future spacecrafts at the longitude-dependent speed of solar wind. In particular, the modeling results are similar to the patterns observed with the ERNE particle telescope on board SOHO in August 1996. In the proton anisotropy data, we find a signature of the magnetic mirror associated with the CIR. A relation is established between the spectra observed at 1 AU and the SEP injection spectrum near the Sun.

Abstract. A solar energetic particle (SEP) event was observed on 1999 May 9 by the Energetic and Relativistic Nuclei and Electron instrument (ERNE) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft in association with a coronal mass ejection (CME) and X-ray flare at the western limb. Near flare onset the active region coronal loop structure was seen to erupt and simultaneous blue and red shift velocities of the hot plasma were recorded by the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument onboard SOHO. We observe for the first time three periods of the SEP injection in a single event: (i) the first, extremely-hard spectrum injection triggered by the passage of the flare initiated coronal (shock) wave; (ii) a moderately-hard spectrum phase starting about half a hour later, proceeding and ceasing concurrently with metric continuum radio burst; (iii) a prolonged soft spectrum injection dominating in the late phase of the event, after about 1.5 h from the first proton production. The CME bow shock acceleration provides a straightforward explanation of the final spectral redressing, whereas the first acceleration seems triggered by the flare. These observations lead us to conclude that the 1999 May 9 SEP event was caused by a combination of coronal and interplanetary acceleration processes contributing with varying importance at different stages of the solar eruption associated with both flare and CME. Comparison with other events suggests that it is a common property of mixed SEP events.

Abstract. The energetic particle telescope ERNE onboard SOHO registered a continuous particle flux enhancement during August 7-18, 1996. The particle event was limited in the low energy range from 1.6 to 8 MeV during the first week of the event. It originated from a corotating interaction region (CIR). At 1630 UT on August 13, an additional new flux of energetic particles emerged with maximum energies above 50 MeV. The southwest directed coronal mass ejection (CME) is the most probable source of the high energy particles. Our spectral analysis revealed a two-component structure with a hard Bessel-type spectrum (c•T -0.02) of the CME-injected particles and a soft power law spectrum (index s -4.0) of CIR particles from 1630 UT till 1000 UT on August 14. In the following 3 hours the intensities above 3 MeV decreased more than 10-fold. During the plateau-type intensity maximum phase the intensities remained almost isotropic in the wide ERNE/HED view cone. We claim that the reason for the drop was that the direct connection to the CME was lost but the connection to the CIR was still maintained. The flux of > 12 MeV protons still prevailing in interplanetary space had probably been injected earlier by the CME-associated event in its very early phase in the solar atmosphere, and trapped there between the CIR and the Sun. The spectrum of these protons was of power form and very hard, s • 1.9. During August 15, the high-energy part hardened further, s • 1.1. At the same time, the intensities increased, leading to a second intensity maximum during the first half of August 16. Finally, on August 18, a disconnection from the CIR took place in all energy channels. IntroductionIn 1996, only five periods of energetic particle enhancements above 13 MeV were registered by the Energetic and Relativistic Nuclei and Electrons (ERNE) experiment (a description of the instrument is given by Torsti et al. [1995]) onboard the Solar and Heliospheric Observatory (SOHO). Exceptionally low energetic particle fluxes were observed in events in 1996 as compared to fluxes during two previous solar minimum periods in 1976 and 1986 [Torsti et al., 1997]. During quiet times in 1996, as manifested in the exceptionally low activity of particle acceleration, a uniquely undisturbed interplanetary environment was provided for the study of particle events of solar and interplanetary origin. In addition, the large geometric factor of the ERNE High Energy Detector (HED), about 10 times larger than in particle sensors flown in the 1970s and 1980s, is a new tool to study the appearance and variation of minor particle fluxes in more detail than was possible earlier.Among the particle events in 1996 which started on July 9 and 12, August 13, November 26, and December 24, the August event was the most special. The ERNE high-energy proton channels (13-50 MeV) did not rise above the background until 6 days after the onset of flux enhancement in the lowenergy channels, 1.6-6 MeV. In this range, the intensities remained above the background level during the long p...

Abstract. Two Earth-directed coronal mass ejections (CMEs), which were most e ective in energetic ($1± 50 MeV) particle acceleration during the ®rst 18 months since the Solar and Heliospheric Observatory (SOHO) launch, occurred on April 7 and May 12, 1997. In the analysis of these events we have deconvoluted the injection spectrum of energetic protons by using the method described by Anttila et al. In order to apply the method developed earlier for data of a rotating satellite (Geostationary Operational Environmental Satellites, GOES), we ®rst had to develop a method to calculate the omnidirectional energetic particle intensities from the observations of Energetic and Relativistic Nuclei and Electrons (ERNE), which is an energetic particle detector onboard the three-axis stabilized SOHO spacecraft. The omnidirectional intensities are calculated by ®tting an exponential pitch angle distribution from directional information of energetic protons observed by ERNE. The results of the analysis show that, compared to a much faster and more intensive CMEs observed during the previous solar maximum, the acceleration e ciency decreases fast when the shock propagates outward from the Sun. The particles injected at distances <0.5 AU from the Sun dominate the particle¯ux during the whole period, when the shock propagates to the site of the spacecraft. The main portion of particles injected by the shock during its propagation further outward from the Sun are trapped around the shock, and are seen as an intensity increase at the time of the shock passage.