Characteristics of High-Energy (90 MeV) SolarProton Events in the Rising Phase of Solar Cycle23 Observed by SOHO/ERNE

Abstract This study aims to comprehend solar and interplanetary (IP) phenomena generating solar energetic particle (SEP) events with proton energies exceeding 90MeV and identify the locations and commencement times of proton acceleration during such events. Forty energetic proton events, with intensities surpassing 10\((^{-3})\) cm\((^{-2})\) sr\((^{-1})\) MeV\((^{-1})\) at \(({\sim })\) 94MeV, were meticulously selected from observations by the {\it Energetic and Relativistic Nuclei and Electrons} (ERNE) instrument onboard the {\it Solar and Heliospheric Observatory} (SOHO) during solar cycle 23. Using the fixed path length method (1.2AU) and velocity dispersion analysis (VDA), we estimated particle injection times, cross validating results with the height of radio type II/IV burst emission and comparing them with flare and coronal mass ejection (CME) characteristics. All analyzed proton events were associated with CMEs and 27 of the proton events were associated with on-the-disk soft x--ray flares. Of the 13 other events, six did not have a GOES flare reported but in eleven events evidence exist of behind the limb flaring. Only two events were void of any flare signatures. Radio type II/IV burst emission association was also significant. Of the non associated two events, only one was completely void of radio emission and one showed metric continuum and tilted type III burst lane emission. Most of the first protons were injected when the CME leading edges were below 5R\((_{\odot})\), and most of the protons reached their maximum intensity while the CMEs were above 10R\((_{\odot})\). The maximum proton intensities were achieved much earlier than the possible passage of an interplanetary shock near Earth, suggesting that the majority of high energy protons at 90 MeV were accelerated as a result of earlier processes. In roughly half of the events the CME front was above the estimated type II burst location. We suggest that in these cases the type II bursts may be related to CME interaction processes and shocks at the CME flanks.