A New View of the Coupling of the Sun and the Heliosphere

Zurbuchen, T. H.

doi:10.1146/annurev.astro.45.010807.154030

Cited by 120 publications

(74 citation statements)

References 184 publications

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“…(a) As shown clearly by the Ulysses measurements, the high-latitude fast wind exhibits near constant speed (McComas et al 2008) and composition von Steiger et al 1995;Zurbuchen 2007). Its observed variability consists primarily of Alfvénic fluctuations that may be due entirely to the expected dynamics induced by the small-scale photospheric evolution described above.…”

Section: Introductionmentioning

confidence: 89%

The Structure and Dynamics of the Corona—Heliosphere Connection

et al. 2011

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Determining the source at the Sun of the slow solar wind is one of the major unsolved problems in solar and heliospheric physics. First, we review the existing theories for the slow wind and argue that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A new theory in which the slow wind originates from the continuous opening and closing of narrow open field corridors, the S-Web model, is described. Support for the S-Web model is derived from MHD solutions for the quasisteady corona and wind during the time of the August 1, 2008 eclipse. Additionally, we perform fully dynamic numerical simulations of the corona and heliosphere in order to test the S-Web model as well as the interchange model proposed by Fisk and co-workers. We discuss the implications of our simulations for the competing theories and for understanding the corona -heliosphere connection, in general.

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Section: Introductionmentioning

confidence: 89%

The Structure and Dynamics of the Corona—Heliosphere Connection

et al. 2011

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“…These deviations were most pronounced in He/O where the solar wind He is reduced by over 35%, and also with a small fractionation effect affecting all elements according to their first ionization potential (FIP), that is, elements with increasing FIP are suppressed relative to their photospheric composition. This fractionation process is much enhanced in streamer-associated slow wind (references in von Steiger et al [2000] and Zurbuchen [2007]). Furthermore, the variability of any given compositional quantity is also increased in slow wind relative to wind associated with PCHs.…”

Section: Elemental Abundances Of C O Si and Fementioning

confidence: 99%

“…The polar pass in 1994, marked S94 in Figure 1, led to the first detailed observations of solar wind originating from polar coronal holes (PCHs), which are the source of more than two thirds of the heliosphere near solar minimum [von Steiger, 1996]. Besides its high speed and unique dynamic signatures [Bame et al, 1977], PCHassociated solar winds also exhibit compositional signatures in their heavy-ion components, which distinguish them from other, generally slower and more variable solar wind streams that are associated with streamers and tend to dominate the space environment near the ecliptic plane [Geiss et al, 1995;Zurbuchen, 2007]. The ionization charge states of heavy elements indicate a substantially lower temperature of the solar wind source region, especially for C and O, whose ionization state is defined within the first 1.5 R s above the photosphere [Bürgi and Geiss, 1986]; the elemental composition of heavy ions is nearly photospheric, in contrast to streamer-associated wind, which is enriched in elements with a first ionization potential (FIP) <10 eV [von Steiger et al, 1997].…”

Section: Introductionmentioning

confidence: 99%

Polar coronal holes during the past solar cycle: Ulysses observations

Steiger

Zurbuchen

2011

J. Geophys. Res.

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[1] During its nearly 19-year mission, Ulysses pioneered novel measurements of the three-dimensional heliosphere and particularly in situ observations of high-latitude solar wind from polar coronal holes (PCHs). Winds from PCHs exhibit constant elemental abundances to within the limits of the measurements, indicative of the fact that such winds truly provide a ground state of solar wind composition. However, these solar wind streams show long-term variability in the composition of ionic charge states frozen into the low corona. The C and O freeze-in temperatures measured in high-latitude solar wind have decreased ∼10% as compared to the previous solar minimum and are now around 0.87 and 1.01 MK, respectively. The ionization states of Si and Fe also exhibit a substantial cooling with a reduction of 0.4 and 0.5 charge states, respectively. We show that these observations are indicative of an overall decrease of coronal temperature, forming a trend toward cooler PCH temperature persisting for over 14 years. We support these observations with a detailed and comprehensive description of the data analysis processes relevant for Ulysses SWICS and similar instruments.Citation: von Steiger, R., and T. H. Zurbuchen (2011), Polar coronal holes during the past solar cycle: Ulysses observations,

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“…An impressive amount of data has been collected over the last few decades to understand the origin, heating, and acceleration of the solar wind. The WIND, ACE, and Ulysses spacecraft have provided us with insitu measurements of the dynamic, magnetic, compositional, and ionization properties of the solar wind plasma almost continuously for the last 20 yr, as a function of time both near the Earth and elsewhere in the heliosphere (Zurbuchen 2007). Furthermore, remote sensing observations of the wind source regions on the Sun have allowed us to determine the physical properties of the plasmas in candidate regions of the solar atmosphere where the solar wind is thought to originate.…”

Section: Introductionmentioning

confidence: 99%

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

Landi

Oran

Lepri

et al. 2014

ApJ

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We test three theoretical models of the fast solar wind with a set of remote sensing observations and in-situ measurements taken during the minimum of solar cycle 23. First, the model electron density and temperature are compared to SOHO/SUMER spectroscopic measurements. Second, the model electron density, temperature, and wind speed are used to predict the charge state evolution of the wind plasma from the source regions to the freeze-in point. Frozen-in charge states are compared with Ulysses/SWICS measurements at 1 AU, while charge states close to the Sun are combined with the CHIANTI spectral code to calculate the intensities of selected spectral lines, to be compared with SOHO/SUMER observations in the north polar coronal hole. We find that none of the theoretical models are able to completely reproduce all observations; namely, all of them underestimate the charge state distribution of the solar wind everywhere, although the levels of disagreement vary from model to model. We discuss possible causes of the disagreement, namely, uncertainties in the calculation of the charge state evolution and of line intensities, in the atomic data, and in the assumptions on the wind plasma conditions. Last, we discuss the scenario where the wind is accelerated from a region located in the solar corona rather than in the chromosphere as assumed in the three theoretical models, and find that a wind originating from the corona is in much closer agreement with observations.

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A New View of the Coupling of the Sun and the Heliosphere

Cited by 120 publications

References 184 publications

The Structure and Dynamics of the Corona—Heliosphere Connection

The Structure and Dynamics of the Corona—Heliosphere Connection

Polar coronal holes during the past solar cycle: Ulysses observations

Charge State Evolution in the Solar Wind. Iii. Model Comparison With Observations

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