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T.h. Zurbuchen - One of the best experts on this subject based on the ideXlab platform.
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composition of quasi stationary Solar Wind flows from ulysses Solar Wind ion composition spectrometer
Journal of Geophysical Research, 2000Co-Authors: Nathan A. Schwadron, George Gloeckler, L.a. Fisk, R Von Steiger, J Geiss, S Hefti, B Wilken, R R Wimmerschweingruber, T.h. ZurbuchenAbstract:Using improved, self-consistent analysis techniques, we determine the average Solar Wind charge state and elemental composition of nearly 40 ion species of He, C, N, O, Ne, Mg, Si, S, and Fe observed with the Solar Wind Ion Composition Spectrometer on Ulysses. We compare results obtained during selected time periods, including both slow Solar Wind and fast streams, concentrating on the quasi-stationary flows away from recurrent or intermittent disturbances such as corotating interaction regions or coronal mass ejections. In the fast streams the charge state distributions are consistent with a single freezing-in temperature for each element, whereas in the slow Wind these distributions appear to be composed of contributions from a range of temperatures. The elemental composition shows the well-known first ionization potential (FIP) bias of the Solar Wind composition with respect to the photosphere. However, it appears that our average enrichment factor of low-FIP elements in the slow Wind, not quite a factor of 3, is smaller than that in previous compilations. In fast streams the FIP bias is found to be yet smaller but still significantly above 1, clearly indicating that the FIP fractionation effect is also active beneath coronal holes from where the fast Wind originates. This imposes basic requirements upon FIP fractionation models, which should reproduce the stronger and more variable low-FIP bias in the slow Wind and a weaker (and perhaps conceptually different) low-FIP bias in fast streams. Taken together, these results firmly establish the fundamental difference between the two quasi-stationary Solar Wind types.
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On the Slow Solar Wind
Space Science Reviews, 1998Co-Authors: L.a. Fisk, Nathan A. Schwadron, T.h. ZurbuchenAbstract:A theory for the origin of the slow Solar Wind is described. Recent papers have demonstrated that magnetic flux moves across coronal holes as a result of the interplay between the differential rotation of the photosphere and the non-radial expansion of the Solar Wind in more rigidly rotating coronal holes. This flux will be deposited at low latitudes and should reconnect with closed magnetic loops, thereby releasing material from the loops to form the slow Solar Wind. It is pointed out that this mechanism provides a natural explanation for the charge states of elements observed in the slow Solar Wind, and for the presence of the First-Ionization Potential, or FIP, effect in the slow Wind and its absence in fast Wind. Comments are also provided on the role that the ACE mission should have in understanding the slow Solar Wind.
Hans-jörg Fahr - One of the best experts on this subject based on the ideXlab platform.
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The role of Solar Wind electrons at the Solar Wind termination shock
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: S. V. Chalov, Hans-jörg FahrAbstract:Voyager 2 plasma observations have recently revealed that, as predicted by theory, there exists a Solar Wind termination shock at 87 au. However, it is evidently different from classical expectations, for instance revealing the downstream Solar Wind protons still to be in a supersonic mode. In this paper we show that in order to explain the non-classical structure and facts of this shock, one has to start from a multi-fluid magnetohydrodynamic (MHD) approach describing the shock transition. Different from our earlier attempt, here we consider Solar Wind electrons as an additional extra fluid and allow for preferential heating of electrons compared to thermal Solar Wind protons at the shock. As we can then show, with this enlargement of the MHD theory by a separate electron fluid we are able to describe observed features of the Solar Wind termination shock. We arrive at the conclusion that the downstream Solar Wind thermal plasma is energetically dominated by the pressure of quasi-mass-less electrons.
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The multifluid character of the Solar Wind termination shock explaining the downstream supersonic Solar Wind ion flow
2010Co-Authors: S. V. Chalov, Hans-jörg FahrAbstract:The Voyager‐2 observations at the recent crossing of the Solar Wind termination shock show that the downstream thermal protons still move with supersonic speed. Obviously it is due to their inefficient shock‐heating and that the surpathermal ions absorb most of the upstream kinetic Solar Wind energy. In this paper we present a three‐fluid approach of the Solar Wind plasma consisting of a thermal, a suprathermal and a high‐energetic fluid. Within a consistent set of conservation equations for this three‐fluid plasma we derive solutions for the observed properties of the upstream precursor and downstream plasma, assuming that the conservation of the magnetic moment of suprathermal ions in the jump conditions is fulfilled.
R M Skoug - One of the best experts on this subject based on the ideXlab platform.
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extremely high speed Solar Wind 29 30 october 2003
Journal of Geophysical Research, 2004Co-Authors: R M Skoug, J. T. Gosling, D J Mccomas, J.t. Steinberg, C W Smith, N F Ness, L F BurlagaAbstract:[1] On 29-30 October 2003 the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft measured Solar Wind speeds in excess of 1850 km/s, some of the highest speeds ever directly measured in the Solar Wind. These speeds were observed following two large coronal mass ejection (CME) driven shocks. Surprisingly, despite the unusually high speeds, many of the other Solar Wind parameters were not particularly unusual in comparison with other large transient events. The magnetic field reached -68 nT, a large but not unprecedented value. The proton temperatures were significantly higher than typical for a CME in the Solar Wind at 1 AU (>10 7 K), but the proton densities were moderate, leading to low to moderate proton beta. The Solar Wind dynamic pressure was not unusual for large events but, when coupled with the large negative B z , was sufficient to cause intense geomagnetic disturbances.
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ulysses second orbit remarkably different Solar Wind
Space Science Reviews, 2001Co-Authors: D J Mccomas, J. T. Gosling, R Goldstein, R M SkougAbstract:By the time of the 34th ESLAB symposium, dedicated to the memory of John Simpson, Ulysses had nearly reached its peak southerly latitude in its second polar orbit. The global Solar Wind structure observed thus far in Ulysses’ second orbit is remarkably different from that observed over its first orbit. In particular, Ulysses observed highly irregular Solar Wind with less periodic stream interaction regions, much more frequent coronal mass ejections. and only a single, short interval of fast Solar Wind. Ulysses also observed the slowest Solar Wind seen thus far in its ten-year journey (~270 km s−1). The complicated Solar Wind structure undoubtedly arises from the more complex coronal structure found around Solar activity maximum, when the large polar coronal holes have disappeared and coronal streamers, small-scale corona] holes, and frequent CMEs are found at all heliolatitudes.
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Solar Wind observations over ulysses first full polar orbit
Journal of Geophysical Research, 2000Co-Authors: D J Mccomas, J. T. Gosling, B L Barraclough, H O Funsten, E Santiagomunoz, R M Skoug, B E Goldstein, M Neugebauer, P Riley, A BaloghAbstract:This study examines Solar Wind plasma and magnetic field observations from Ulysses' first full polar orbit in order to characterize the high-latitude Solar Wind under conditions of decreasing and low Solar activity. By comparing observations taken over nearly all heliolatitudes and two different intervals covering the same radial distances, we are able to separate the radial and latitudinal variations in the Solar Wind. We find that once the radial gradients are removed, none of the high-latitude Solar Wind parameters show much latitudinal variation, indicating that the Solar Wind emanating from the polar coronal holes is extremely uniform. In addition, by examining nearly 6 years of data starting in the declining phase of the last Solar cycle and extending through the most recent Solar minimum, we are able to address hemispheric asymmetries in the observations. We find that these asymmetries are most likely driven by differences in the Solar Wind source over the Solar cycle and indicate that more energy goes into the polar Solar Wind during the declining phase of the Solar cycle than around minimum. Because the mass flux is larger in the declining phase while the speeds are very similar, we conclude that this energy is introduced at an altitude below the Solar Wind acceleration critical point. Finally, we provide details of the statistics of over 20 Solar Wind parameters so that upcoming observations from Ulysses' second polar orbit, during much more active times on the Sun, can be readily compared to the quieter first orbit results.
Peter Bochsler - One of the best experts on this subject based on the ideXlab platform.
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isotopic mass fractionation of Solar Wind evidence from fast and slow Solar Wind collected by the genesis mission
The Astrophysical Journal, 2012Co-Authors: Peter Bochsler, M Neugebauer, V S Heber, H Baur, K D Mckeegan, D B Reisenfeld, R Wieler, R C WiensAbstract:NASA's Genesis space mission returned samples of Solar Wind collected over ~2.3 years. We present elemental and isotopic compositions of He, Ne, and Ar analyzed in diamond-like carbon targets from the slow and fast Solar Wind collectors to investigate isotopic fractionation processes during Solar Wind formation. The Solar Wind provides information on the isotopic composition for most volatile elements for the Solar atmosphere, the bulk Sun and hence, on the Solar nebula from which it formed 4.6 Ga ago. Our data reveal a heavy isotope depletion in the slow Solar Wind compared to the fast Wind composition by 63.1 ± 2.1‰ for He, 4.2 ± 0.5‰ amu–1 for Ne and 2.6 ± 0.5‰ amu–1 for Ar. The three Ne isotopes suggest that isotopic fractionation processes between fast and slow Solar Wind are mass dependent. The He/H ratios of the collected slow and fast Solar Wind samples are 0.0344 and 0.0406, respectively. The inefficient Coulomb drag model reproduces the measured isotopic fractionation between fast and slow Wind. Therefore, we apply this model to infer the photospheric isotopic composition of He, Ne, and Ar from our Solar Wind data. We also compare the isotopic composition of oxygen and nitrogen measured in the Solar Wind with values of early Solar system condensates, probably representing Solar nebula composition. We interpret the differences between these samples as being due to isotopic fractionation during Solar Wind formation. For both elements, the magnitude and sign of the observed differences are in good agreement with the values predicted by the inefficient Coulomb drag model.
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Minor ions in the Solar Wind
The Astronomy and Astrophysics Review, 2007Co-Authors: Peter BochslerAbstract:Ions heavier than ^4He are treated as “minors” in the Solar Wind. This is justified for many applications since minor ions have no significant influence on the dynamics of the interplanetary plasma. However, minor ions carry information on many aspects of the formation, on the acceleration and on the transfer of Solar plasma from the corona into the interplanetary space. This review concentrates on various aspects of minor ions as diagnostic tracers. The elemental abundance patterns of the Solar Wind are shaped in the chromosphere and in the lower transition region by processes, which are not fully understood at this moment. Despite this lack of detailed understanding, observed abundance patterns have been classified and are now commonly used to characterize the sources, and to trace back Solar-Wind flows to their origins in the Solar atmosphere. Furthermore, the Solar Wind is the most important source of information for Solar isotopic abundances and for Solar abundances of volatile elements. In order to fully exploit this information, a comprehensive understanding of elemental and isotopic fractionation processes is required. We provide observational clues to distinguish different processes at work.
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Solar Wind helium isotopic composition from SWICS/ULYSSES
Space Science Reviews, 1995Co-Authors: R. Bodmer, Peter Bochsler, R Von Steiger, J Geiss, G. GloecklerAbstract:This is the first study of the isotopic composition of Solar Wind helium with the SWICS time-of flight mass spectrometer. Although the design of SWICS is not optimized to measure^3He abundances precisely,^4He/^3He flux ratios can be deduced from the data. The long term ratio is 2290±200, which agrees with the results obtained with the ICI magnetic mass spectrometer on ISEE-3 and with the Apollo SWC foil experiments. The ULYSSES spacecraft follows a trajectory which is ideal for the study of different Solar Wind types. During one year, from mid-1992 to mid-1993, it was in a range of heliographic latitudes where a recurrent fast stream from the southern polar coronal hole was observed every Solar rotation. Solar Wind bulk velocities ranged from 350 km/s to 950 km/s which would, in principle allow us to identify velocity-correlated compositional variations. Our investigation of Solar Wind helium, however, shows an isotopic ratio which does not depend on the Solar Wind speed.
D J Mccomas - One of the best experts on this subject based on the ideXlab platform.
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extremely high speed Solar Wind 29 30 october 2003
Journal of Geophysical Research, 2004Co-Authors: R M Skoug, J. T. Gosling, D J Mccomas, J.t. Steinberg, C W Smith, N F Ness, L F BurlagaAbstract:[1] On 29-30 October 2003 the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft measured Solar Wind speeds in excess of 1850 km/s, some of the highest speeds ever directly measured in the Solar Wind. These speeds were observed following two large coronal mass ejection (CME) driven shocks. Surprisingly, despite the unusually high speeds, many of the other Solar Wind parameters were not particularly unusual in comparison with other large transient events. The magnetic field reached -68 nT, a large but not unprecedented value. The proton temperatures were significantly higher than typical for a CME in the Solar Wind at 1 AU (>10 7 K), but the proton densities were moderate, leading to low to moderate proton beta. The Solar Wind dynamic pressure was not unusual for large events but, when coupled with the large negative B z , was sufficient to cause intense geomagnetic disturbances.
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ulysses second orbit remarkably different Solar Wind
Space Science Reviews, 2001Co-Authors: D J Mccomas, J. T. Gosling, R Goldstein, R M SkougAbstract:By the time of the 34th ESLAB symposium, dedicated to the memory of John Simpson, Ulysses had nearly reached its peak southerly latitude in its second polar orbit. The global Solar Wind structure observed thus far in Ulysses’ second orbit is remarkably different from that observed over its first orbit. In particular, Ulysses observed highly irregular Solar Wind with less periodic stream interaction regions, much more frequent coronal mass ejections. and only a single, short interval of fast Solar Wind. Ulysses also observed the slowest Solar Wind seen thus far in its ten-year journey (~270 km s−1). The complicated Solar Wind structure undoubtedly arises from the more complex coronal structure found around Solar activity maximum, when the large polar coronal holes have disappeared and coronal streamers, small-scale corona] holes, and frequent CMEs are found at all heliolatitudes.
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Solar Wind observations over ulysses first full polar orbit
Journal of Geophysical Research, 2000Co-Authors: D J Mccomas, J. T. Gosling, B L Barraclough, H O Funsten, E Santiagomunoz, R M Skoug, B E Goldstein, M Neugebauer, P Riley, A BaloghAbstract:This study examines Solar Wind plasma and magnetic field observations from Ulysses' first full polar orbit in order to characterize the high-latitude Solar Wind under conditions of decreasing and low Solar activity. By comparing observations taken over nearly all heliolatitudes and two different intervals covering the same radial distances, we are able to separate the radial and latitudinal variations in the Solar Wind. We find that once the radial gradients are removed, none of the high-latitude Solar Wind parameters show much latitudinal variation, indicating that the Solar Wind emanating from the polar coronal holes is extremely uniform. In addition, by examining nearly 6 years of data starting in the declining phase of the last Solar cycle and extending through the most recent Solar minimum, we are able to address hemispheric asymmetries in the observations. We find that these asymmetries are most likely driven by differences in the Solar Wind source over the Solar cycle and indicate that more energy goes into the polar Solar Wind during the declining phase of the Solar cycle than around minimum. Because the mass flux is larger in the declining phase while the speeds are very similar, we conclude that this energy is introduced at an altitude below the Solar Wind acceleration critical point. Finally, we provide details of the statistics of over 20 Solar Wind parameters so that upcoming observations from Ulysses' second polar orbit, during much more active times on the Sun, can be readily compared to the quieter first orbit results.
