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Enhancements of suprathermal particles observed at 1AU often can be related to Corotating Interaction Regions (CIRs). The compression regions associated with CIRs and their driven shocks which typically form at a few AU distance to the Sun can efficiently accelerate particles. If accelerated at the trailing edge of a CIR these particles can travel sunward along the ambient magnetic field and thus enhanced fluxes can be observed even if the acceleration region has passed over the spacecraft. We have analysed a CIR that has been observed at L1 by ACE/SWICS and SOHO/CELIAS/STOF on days 207 and 208 in 2003. The combination of SWICS and STOF data allowed us to study suprathermal Helium ranging from its onset at solar wind bulk energies up to 330 keV/nuc. Here we present our results for the temporal evolution of the flux, energy spectra and the He+/He++ ratio. In particular we present observational evidence for a turnover of the energy spectra at lower energies after the CIR passage which has been theoretically predicted but never been observed so far.

Supra-thermal neutral atoms such as H and He have been detected with the particle instrument CELIAS/HSTOF onboard SOHO since 1996. While the observed energetic neutral hydrogen (ENH) fluxes are well distinct from background ion fluxes, the helium (ENHe) fluxes have to be corrected for the local He ion and alpha particle fluxes in the same energy region. The latter ion background originates from well known sources such as solar particle events or co-rotating interaction regions and the ion particle flux and spectrum is a function of time. The resulting H/He ratio in the supra-thermal energy region is lower than expected from the anomalous cosmic ray abundances. Heavier neutral particles are not identified in the CELIAS/HSTOF dataset. We will discuss the neutral energetic flux measurements in view of the H/He ratio and potential source regions from the heliosheath region and beyond.

The observations of magnetic field fluctuations and suprathermal ion spectra upstream of interplanetary shocks driven by coronal mass ejections (CMEs) give information on two time scales: (1) the eddy turn‐over time scale i.e. the non‐linear cascading time scale of solar wind turbulence, and (2) the growth time scale for waves amplified by energetic protons accelerated at the shock. These two time scales scale differently with wave number. From an analysis of data from the ACE magnetometer and the suprathermal particle sensor SOHO/STOF we derive the solar‐wind eddy turn‐over time.

The observations on magnetic field fluctuations and suprathermal ion spectra near the shocks driven by the coronal mass ejections during the time periods of the Bastille Day 2000 event and the Halloween 2003 events are summarized.

Since the launch of the Solar and Heliospheric Observatory (SOHO) on Dec. 2, 1995, the Suprathermal Time‐Of‐Flight (STOF) energetic particle sensor of the Charge, Element and Isotope Analysis System (CELIAS) has observed gradual and impulsive solar particle events from solar activity cycle minimum to maximum. The instrument CELIAS/STOF has the capability of detecting energetic ions and determine the mass, energy and charge of each particle. We report on the measurements of the detected energetic particle events from 1996 to 2001, i.e. the velocity dispersion of energetic He ions in the energy/charge range between 30 and 800 keV/nuc. For energetic particle events we analyse the velocity dispersion of the suprathermal He and O ions (78 and 43 events, resp.) and estimate the onset time of the solar event and set limits on the propagation length along the connecting magnetic field line.

We report on measurements of the He charge states as observed in recurring energetic particle events during the recent solar minimum in 1996. The time-of-flight mass spectrometer CELIAS/STOF on board the SOHO satellite has the capability of detecting energetic ions between 35 and 630 keV/q and determine the mass, energy and charge of each particle. Typically we observe a He+/He2+ ratio of 0.16 to 0.31 in the range of 25 to 150 keV/nuc. We discuss the implications of these observations on the existing models of particle acceleration in corotating interaction regions (CIRs), i.e. the location of the acceleration process of corotating particle events as observed near 1 AU.

We have observed the 1S‐2S transition of atomic hydrogen with a resolution of 5 parts in 1011 by means of Doppler‐free two photon spectroscopy in an atomic beam. The significantly asymmetric line shape is strongly affected by the relativistic Doppler effect. The new high resolution can be used for improved measurements of the Rydberg constant, the 1S Lamb shift, and the isotope shift of hydrogen and deuterium.