Engineering topics

Zurbuchen, Thomas H

Publications and source records attributed to Zurbuchen, Thomas H.

2 records

DOE OSTI2012

TWO-PLASMA MODEL FOR LOW CHARGE STATE INTERPLANETARY CORONAL MASS EJECTION OBSERVATIONS

Recent ACE/SWICS observations have revealed that {approx}5% of all in situ observed interplanetary coronal mass ejections include time periods with very low charge state ions found to be associated with prominence eruptions. It was also shown that these low charge state ions are often observed concurrently with very high charge state ions. But, the physical process leading to these mixed charge states is not known and could be caused by either the mixing of plasmas of different temperatures or by non-local freeze-in effects as discussed by Gruesbeck. We provide a detailed and multi-stage analysis that excludes this latter option. We therefore conclude that time periods of very low charge states are the heliospheric remnants of plasmas born in prominences. We further conclude that the contemporaneously observed low and very high charge states are an indication of mixing of plasmas of different temperatures along magnetic field lines, suggesting that silicon and iron are depleted over carbon and oxygen in the cold, prominence-associated plasma. This represents the first experimental determination of elemental composition of prominence-associated plasma.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

ACE/SWICS OBSERVATIONS OF HEAVY ION DROPOUTS WITHIN THE SOLAR WIND

We present the first in situ observations of heavy ion dropouts within the slow solar wind, observed for select elements ranging from helium to iron. For iron, these dropouts manifest themselves as depletions of the Fe/H ratio by factors up to {approx}25. The events often exhibit mass-dependent fractionation and are contained in slow, unsteady wind found within a few days from known stream interfaces. We propose that such dropouts are evidence of gravitational settling within large coronal loops, which later undergo interchange reconnection and become source regions of slow, unsteady wind. Previously, spectroscopic studies by Raymond et al. in 1997 (and later Feldman et al. in 1999) have yielded strong evidence for gravitational settling within these loops. However, their expected in situ signature plasma with heavy elements fractionated by mass was not observed prior to this study. Using data from the SWICS instrument on board the Advanced Composition Explorer (ACE), we investigate the composition of the solar wind within these dropouts and explore long term trends over most of a solar cycle.

79 ASTRONOMY AND ASTROPHYSICS↗