Donald V. Reames

Energetic particles from impulsive solar flares

Observations of solar energetic particles from impulsive flares are reviewed. Consideration is given to observations of electron events, He-3 rich events, and heavy-nuclei-rich events. It is found that these observations can be unified into a description of the particles from impulsive flares. The observations are compared with observations of gamma-ray line in impulsive flares and particles in flares and compared with particles in space. A model for accelerating the unique particle abundances of energetic particles is proposed. 101 refs.

A COMPARATIVE STUDY OF ION CHARACTERISTICS IN THE LARGE GRADUAL SOLAR ENERGETIC PARTICLE EVENTS OF 2002 APRIL 21 AND 2002 AUGUST 24

Solar energetic particles (SEPs) provide an opportunity to study in detail the processes of particle acceleration and transport that are ubiquitous in astrophysical plasmas. Tylka et al. focused on the problem of SEP spectral and compositional variability at energies above a few tens of MeV per nucleon. They motivated their study with two large, gradual SEP events, 2002 April 21 and 2002 August 24, which have similar fast coronal mass ejections (CMEs) and flares but nevertheless illustrate the extremes of high-energy behavior. In this paper, we present additional detailed comparisons between the ion characteristics of these events. These results should be helpful in developing and testing new SEP models, which are currently under development.

Solar energetic particles and space weather

The solar energetic particles (SEPs) of consequence to space weather are accelerated at shock waves driven out from the Sun by fast coronal mass ejections (CMEs). In the large events, these great shocks fill half of the heliosphere. SEP intensity profiles change appearance with longitude. Events with significant intensities of >10 MeV protons occur at an average rate of ∼13 yr−1 near solar maximum and several events with high intensities of >100 MeV protons occur each decade. As particles stream out along magnetic field lines from a shock near the Sun, they generate waves that scatter subsequent particles. At high intensities, wave growth throttles the flow below the “streaming limit.” However, if the shock maintains its strength, particle intensities can rise above this limit to a peak when the shock itself passes over the observer creating a ‘delayed’ radiation hazard, even for protons with energies up to ∼1 GeV. The streaming limit makes us blind to the intensities at the oncoming shock, however, heavi...

Solar energetic particles: Shock acceleration and transport through self-amplified waves

This article reviews our work on the powerful influence of self-amplified Alfven waves on the interplanetary (IP) transport and shock acceleration of solar energetic particles (SEPs). In large gradual events, a huge number of shock-accelerated protons stream through the IPmediumand amplify ambient Alfven waves by orders of magnitude. Nonlinear models that take account of selfamplified waves semi-quantitatively explain many intriguing SEP observations at 1 AU: (a) upper limits to early SEP intensities, (b) flat intensity energy spectra up to ~ 30 MeV/amu before shock arrival, and (c) complex temporal, energy, and event-to-event variations of elemental abundances. Streaming limit complicates estimation of the number and energy of SEPs accelerated in a solar event but provides a safety window for astronauts to seek shelter before a potential hazardous intensity rise at shock passage. Self-amplified waves help bootstrap shock acceleration and the high near-shock SEP intensity predicted at ≤ 20r⊙. is relevant ...

POsitron Electron Magnet Spectrometer (POEMS) for the Eos Mission

The POsitron Electron Magnet Spectrometer (POEMS) has been selected to enter definition phase study for flight on one of the Earth Observing System (Eos) polar platforms. Following launch, which could comes as early as 1997, POEMS will measure the critical positron and electron components of the cosmic radiation and utilize this information to trace processes occurring within our geospace environment, in solar flares, in the solar wind, and elsewhere in the galaxy. In addition, POEMS will measure heavier charged particles to complement the electron/positron measurements. With POEMS data we will investigate the origin (primary or secondary) of galactic positrons, study the charge sign dependence of solar modulation over a large fraction of a solar magnetic cycle, measure positron and neutral particle emission from solar flares, and monitor the temporal variations of the charged intensities and energy spectra in the Eos orbit. Two orthogonal charged particle telescopes are used, each terminating in a shared...