267 research outputs found
Iron charge state distributions as an indicator of hot ICMEs: Possible sources and temporal and spatial variations during solar maximum
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95224/1/jgra17034.pd
Kinetic properties of heavy solar wind ions from UlyssesâSWICS
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95282/1/grl20935.pd
Are highâlatitude forwardâreverse shock pairs driven by CME overexpansion?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95129/1/jgra18211.pd
Ion Charge States in Halo CMEs: What can we Learn about the Explosion?
We describe a new modeling approach to develop a more quantitative
understanding of the charge state distributions of the ions of various elements
detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced
Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution
based on observations of CMEs propagating in the plane of the sky and on
theoretical models, we integrate time dependent equations for the ionization
balance of various elements to compare with ACE data. We find that plasma in
the CME ``core'' typically requires further heating following filament
eruption, with thermal energy input similar to the kinetic energy input. This
extra heating is presumably the result of post eruptive reconnection. Plasma
corresponding to the CME ``cavity'' is usually not further ionized, since
whether heated or not, the low density gives freeze-in close the the Sun. The
current analysis is limited by ambiguities in the underlying model CME
evolution. Such methods are likely to reach their full potential when applied
to data to be acquired by STEREO when at optimum separation. CME evolution
observed with one spacecraft may be used to interpret CME charge states
detected by the other.Comment: 20 pages, accepted by Ap
Variations in solar wind fractionation as seen by ACE/SWICS over a solar cycle and the implications for Genesis Mission results
We use ACE/SWICS elemental composition data to compare the variations in
solar wind fractionation as measured by SWICS during the last solar maximum
(1999-2001), the solar minimum (2006-2009) and the period in which the Genesis
spacecraft was collecting solar wind (late 2001 - early 2004). We differentiate
our analysis in terms of solar wind regimes (i.e. originating from interstream
or coronal hole flows, or coronal mass ejecta). Abundances are normalized to
the low-FIP ion magnesium to uncover correlations that are not apparent when
normalizing to high-FIP ions. We find that relative to magnesium, the other
low-FIP elements are measurably fractionated, but the degree of fractionation
does not vary significantly over the solar cycle. For the high-FIP ions,
variation in fractionation over the solar cycle is significant: greatest for
Ne/Mg and C/Mg, less so for O/Mg, and the least for He/Mg. When abundance
ratios are examined as a function of solar wind speed, we find a strong
correlation, with the remarkable observation that the degree of fractionation
follows a mass-dependent trend. We discuss the implications for correcting the
Genesis sample return results to photospheric abundances.Comment: Accepted for publication in Ap
Response of a delta-doped charge-coupled device to low energy protons and nitrogen ions
We present the results of a study of the response of a delta-doped charge-coupled device (CCD) exposed to ions with energies less than 10âkeV10keV. The study of ions in the solar wind, the majority having energies in the 1â5âkeV1â5keV range, has proven to be vital in understanding the solar atmosphere and the near Earth space environment. Delta-doped CCD technology has essentially removed the dead layer of the silicon detector. Using the delta-doped detector, we are able to detect H+H+ and N+N+ ions with energies ranging from 1âtoâ10âkeV1to10keV in the laboratory. This is a remarkable improvement in the low energy detection threshold over conventional solid-state detectors, such as those used in space sensors, one example being the solar wind ion composition spectrometer (SWICS) on the Advanced Composition Explorer spacecraft, which can only detect ions with energies greater than 30âkeV30keV because of the solid-state detectorâs minimum energy threshold. Because this threshold is much higher than the average energy of the solar wind ions, the SWICS instrument employs a bulky high voltage postacceleration stage that accelerates ions above the 30âkeV30keV detection threshold. This stage is massive, exposes the instrument to hazardous high voltages, and is therefore problematic both in terms of price and its impact on spacecraft resources. Adaptation of delta-doping technology in future space missions may be successful in reducing the need for heavy postacceleration stages allowing for miniaturization of space-borne ion detectors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87896/2/053301_1.pd
The solar wind composition throughout the solar cycle: A continuum of dynamic states
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95110/1/grl15245.pd
Reply to comment by P. Riley and J. T. Gosling on âAre highâlatitude forwardâreverse shock pairs driven by overexpansion?â
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95455/1/jgra18795.pd
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