Engineering topics

vonSteiger, R.

Publications and source records attributed to vonSteiger, R..

3 records

NASA NTRS2008

Fe, O, and C Charge States Associated with Quiescent Versus Active Current Sheets in the Solar Wind

Ulysses MAG data were used to locate the heliospheric current sheet in data from 1991 through 2006. The purpose was to characterize typical charge states for Fe, O, and C in the vicinity of the current sheet and provide insight into the physical sources for these charge states in the corona. A study of He/H around the current sheets has led to a clear distinction between quiescent current sheets at times of low solar activity and active current sheets associated with magnetic clouds (and, presumably, ICMES). It has been shown that high ionization state Fe is produced in the corona in current sheets associated with CMEs through spectroscopic observations of the corona and through in situ detection at Ulysses. Here we show that the ionization state of Fe is typically only enhanced around active current sheets while the ionization states of O and C are commonly enhanced around both quiescent and active current sheets. This is consistent with UV coronal spectroscopy, which has shown that reconnection in current sheets behind CMEs leads to high temperatures not typically seen above quiet streamers.

Suess, S. T.↗

NASA NTRS1995

Solar wind ion composition and charge states

The solar wind, a highly tenuous plasma streaming from the Sun into interplanetary space at supersonic speed, is roughly composed of 95% hydrogen and 5% helium by number. All other, heavy elements contribute less than 0.1% by number and thus are truly test particles Nevertheless, these particles provide valuable information not present in the main components. We first discuss the importance of the heavy ions as tracers for processes in the solar atmosphere. Specifically, their relative abundances are found to be different in the solar wind as compared to the photosphere. This fractionation, which is best organized as a function of the first ionization time (FIT) of the elements under solar surface conditions, provides information on the structure of the chromosphere. where it is imparted on the partially ionized material by an atom-ion separation mechanism. Moreover, the charge states of the heavy ions can be used to infer the coronal temperature, since they are frozen-in near the altitude where the expansion time scale overcomes the ionization/recombination time scales. Next, we review the published values of ion abundances in the solar wind, concentrating on the recent results of the SWICS instrument on Ulysses. About 8 elements and more than 20 charge states can be routinely analyzed by this sensor. There is clear evidence that both the composition and the charge state distribution is significantly different in the fast solar wind from the south polar coronal hole, traversed by Ulysses in 1993/94, as compared to the solar wind normally encountered near the ecliptic plane. The fractionation between low- and high-FIT elements is reduced, and the charge states indicate a lower, more uniform coronal temperature in the hole. Finally, we discuss these results in the framework of existing theoretical models of the chromosphere and corona, attempting to identify differences between the low- and high-latitude regions of the solar atmosphere.

vonSteiger, R.↗

NASA NTRS1995

Composition of transient events in the solar wind: Ulysses/SWICS observations

The Ulysses mission covers an extensive data base which includes an in-ecliptic phase (Oct 1990 - Feb 1992), a southern hemisphere polar pass (with a southernmost point of 80 deg S heliographic latitude reached in Sept 1994). and a south to north transit passing through the ecliptic plane (March 1995). The Solar Wind Ion Composition Spectrometer measures solar wind ion composition, including charge state composition. for all types of solar wind flows. In-ecliptic measurements of the charge states of solar wind heavy ions in transient-related solar wind. such as solar wind associated with coronal mass c ejections (CMEs), typically indicate hotter than normal coronal temperatures. This distinction is not as prevalent for higher latitude observations. In this paper, we present temporal and latitudinal variations in the charge state composition of Oxygen, Silicon, and Iron for several transient-related solar wind events.

Galvin, A. B.↗