Mark Andrew Popecki

Particle acceleration and sources in the November 1997 solar energetic particle events

We report studies of two large solar energetic particle (SEP) events on Nov. 4 and 6, 1997 that were observed using advanced energetic particle detectors on the ACE and the Wind spacecraft. Both events showed enriched Fe/O, and had a ∼1 MeV/n ³He/4He ratio = 2.1 × 10−3, 4 times the coronal value. The Nov. 6 event had exceptionally hard spectra, with much higher intensities of high energy (10s of MeV) particles than the Nov. 4 event, yet below 1 MeV/n the intensities in the Nov. 6 event were lower than for Nov. 4. Strong, complex temporal variations observed for ∼120 keV Fe/O contrasted with only gradual changes of this ratio at ∼25 MeV/n. A spectral break was observed in the Nov. 6 event, wherein below a few MeV/n the spectra became harder. Taken together, these observations point to different seed and acceleration mechanisms dominating at low and high energies in these events.

Energy Dependence of the Ionic Charge State Distribution During the November 1997 Solar Energetic Particle Event

3 Abstract. Ionic charge state distributions for a variety of species, such as C, O, Ne, Mg, Si and Fe were obtained with the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) on ACE for the strongest of a series of energetic particle events after the November 4 and 7, 1997, flares. The capabilities of SEPICA allow a much more detailed analysis of the charge dis- tributions than previous instrumentation. Over the energy range from ≈ 0.2 to 1 MeV/Nuc a trend is observed that shows charge states increasing with energy, in particular for Mg, Si and Fe. In addition, for Fe a mixed charge state distribution with a distinct peak at lower charge states (10 - 14) is ob- served simultaneously with a tail reaching to charge states up to ≈ 20. This may be an indication of a mixture of different energetic particle populations. 1

FAST observations of preferentially accelerated He+ in association with auroral electromagnetic ion cyclotron waves

The TEAMS instrument on the FAST satellite has detected events in which He+ ions are resonantly accelerated perpendicular to the magnetic field to energies of several keV. The events occur in association with electromagnetic ion cyclotron (EMIC) waves and conic distributions of up to a few hundred eV in H+ and a few keV in O+. Concentrations of He+ can be significantly elevated during the events. Our interpretation is that the He+ ions are accelerated through a cyclotron resonance with the waves. This acceleration is similar to a proposed mechanism for selective ion acceleration in impulsive solar flares.

Transverse ion acceleration mechanisms in the aurora at solar minimum: occurrence distributions

Abstract We present a statistical study of 714 ion conic events detected by the Fast Auroral Snapshot Explorer (FAST) from September 1996 to February 1997. Ninety-nine percent of the events found are associated with either broad-band extremely low frequency (BBELF) emissions or electromagnetic ion cyclotron (EMIC) waves. Lower hybrid waves are much less important in transverse ion acceleration above 2000 km. The BBELF events are more numerous, comprising some 84% of ion conic events identified, and occur at all local times, with a peak near noon and a minimum near dusk. The EMIC events are concentrated in the dusk to midnight sector and are more likely to occur at lower latitudes compared to the BBELF events. The occurrence rate of EMIC conics has an apparent local minimum at 2000–2500 km, while the BBELF conic occurrence rate varies only slowly between 2000 km and the FAST apogee of 4200 km. The occurrence rate of EMIC conics is more strongly correlated with K p than the BBELF conic occurrence rate. These results are consistent with previous studies of ion conics at lower altitudes. The correlation of both BBELF and EMIC ion conics with phenomena that are associated with parallel electric fields suggests that parallel electric fields play a significant role in transverse ion heating in the aurora.

Species dependent energies in upward directed ion beams over auroral arcs as observed with FAST TEAMS

Upward flowing field-aligned ion beams over auroral arcs have been observed with the 3-dimensional ion mass spectrograph TEAMS on FAST. We have performed a statistical study on a sample of 77 ion beams from the auroral campaign in early 1997. All observed beams contain substantial amounts of H+, He+ and O+. A clear ordering of the total energies according to mass is found, with H+ having the lowest and O+ the highest energy. The composition varies significantly from beam to beam, with O+/H+ ratios ranging from ≈ 0.1 to 10. No variation of the energy ratio between species is observed as a function of relative abundance. These results are discussed in the light of earlier observations of higher energies for O+ in statistical studies of beams during solar minimum and attempts to explain this behavior in terms of beam instabilities.

Escape of O+ through the distant tail plasma sheet

[1] In February 2007, the STEREO-B spacecraft encountered the magnetosheath, plasma sheet and plasma sheet boundary layer from about 200 R E to 300 R E downtail. This time period was during solar minimum, and there was no storm activity during this month. Using data from the PLASTIC instrument, we find that even during quiet times, O + is a constant feature of the deep magnetotail, with an O + density of about 15% of the O + density in the near-earth plasma sheet for similar conditions. The tailward flux of the O + is similar to the flux of O + beams that have been observed in the lobe/mantle region of the deep tail. The total outflow rate of the O + down the plasma sheet is 1.1 × 10 24 ions/s, which is 10% of the total outflow rate of 1 × 10 25 ions/s, and of the same order as the estimated loss from dayside transport.

PLASMOID RELEASES IN THE HELIOSPHERIC CURRENT SHEET AND ASSOCIATED CORONAL HOLE BOUNDARY LAYER EVOLUTION

As the heliospheric current sheet (HCS) is corotating past STEREO-B, near-Earth spacecraft ACE, Wind and Cluster, and STEREO-A over more than three days between 2008 January 10 and 14, we observe various sections of (near-pressure-balanced) flux-rope- and magnetic-island-type plasmoids in the associated heliospheric plasma sheet (HPS). The plasmoids can qualify as slow interplanetary coronal mass ejections and are relatively low proton beta (<0.5) structures, with small length scales (an order of magnitude lower than typical magnetic cloud values) and low magnetic field strengths (2-8 nT). One of them, in particular, detected at STEREO-B, corresponds to the first reported evidence of a detached plasmoid in the HPS. The in situ signatures near Earth are associated with a long-decay X-ray flare and a slow small-scale streamer ejecta, observed remotely with white-light coronagraphs aboard STEREO-B and SOHO and tracked by triangulation. Before the arrival of the HPS, a coronal hole boundary layer (CHBL) is detected in situ. The multi-spacecraft observations indicate a CHBL stream corotating with the HCS but with a decreasing speed distribution suggestive of a localized or transient nature. While we may reasonably assume that an interaction between ejecta and CHBL provides the source of momentum for the slow ejectas acceleration, the outstanding composition properties of the CHBL near Earth provide here circumstantial evidence that this interaction or possibly an earlier one, taking place during streamer swelling when the ejecta rises slowly, results in additional mixing processes.

FAST/TEAMS observations of charge exchange signatures in ions mirroring at low altitudes

Using the TEAMS instrument on FAST, we have observed a case in which signatures of the inner edge of the plasma sheet are clearly observed in the energy spectra of ions mirroring at the FAST altitude. That inner edge is dominated by He+. We show that this is the natural composition expected from charge exchange as the ions drift in from the plasma sheet.

Equator‐S observations of He+ energization by EMIC waves in the dawnside equatorial magnetosphere

gyrofrequency (Pc1 frequency range). These events wereobserved during quiet magnetospheric conditions at the inner edgeof the plasmasheet. At this boundary 10 to 40 keV protons, whichconvect on open drift paths, exhibit a pronounced pitch angleanisotropy providing the free energy for the enhancement of thePc1 emissions. I

Evidence of a Two-Temperature Source Region in the 3He-Rich Solar Energetic Particle Event of 2000 May 1

Using instruments on the ACE and Wind spacecraft, we investigate the temporal evolution, spectra, and ionization states of solar energetic particle (SEP) Fe in the impulsive event of 2000 May 1. Proton and electron intensities and anisotropies were used to help constrain the characteristics of the interplanetary propagation, taking into account focusing, pitch-angle scattering, adiabatic deceleration, and convection. We find that the event was nearly scatter-free, with an interplanetary scattering mean free path larger than 1 AU. The Fe spectrum spectral form is consistent with stochastic acceleration, but the observed increase of the ionization state of Fe between 200-600 keV nucleon-1 is larger than can be explained using a single temperature source even after including the effect of adiabatic deceleration in the solar wind. A two-temperature source region is required to fit the observed range of Fe charge states, with the bulk (>80%) of the particles coming from a T ~ 106 K region, and the remainder from a region with T ~ 1.6 × 107 K.