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

“…Such a stability suggests that the charge state composition measured during the 1994-1996 pass may be very similar to the one corresponding to the SUMER observations so that the Ulysses measurements can be combined to the SUMER observations despite the fact that the former took place earlier. Thus, we will restrict our comparison to the data taken in 1994-1996. Measurements from the 1994-1996 pass were published by Ko et al (1997), von Steiger et al (2000, and Gloeckler & Geiss (2007). The differences between these studies consist mainly of the time interval that each of them considered, whether they discriminated between the south and north polar wind or not, and what elements they studied.…”

“…The differences between these studies consist mainly of the time interval that each of them considered, whether they discriminated between the south and north polar wind or not, and what elements they studied. Ko et al (1997) averaged a 100 day set of data taken from day 170 to 270 in 1994, during the Ulysses pass over the south pole, and measured the charge state Ko et al 1997); those for the north pole were averaged from day 182 of 1995 to day 121 of 1996, and represent the data set closest in time to the SUMER observations. The south pole composition was slightly but significantly shifted toward higher charge states than the north pole one.…”

“…Using those data requires the ability to predict the charge state evolution of the solar wind plasma as it leaves the Sun. For example, Ko et al (1997) developed empirical models of the density, velocity, and temperature evolution of the wind plasma in the solar corona trying to reproduce Ulysses charge state ratios. However, studying the evolution of charge state ratios in the solar wind, Esser et al (1998) found that insitu measurements of charge state ratios could not be used as direct indicators of the temperature of the solar corona; they also attempted to reproduce measured values using different empirical models and found that several different scenarios were compatible with measurements.…”

“…This technique capitalizes on the ability to calculate the evolution of the charge state composition of the wind plasma using the plasma bulk velocity v, electron density n e , and electron temperature T e in the same way as Ko et al (1997) and Esser et al (1998). While predicted frozen-in charge states can be directly compared to in-situ measurements as done by these authors, the charge state values close to the Sun are combined with the CHIANTI spectral code (Dere et al 1997;Landi et al 2013) to calculate line intensities close to the Sun, to be compared with spectroscopic observations, similarly to what Poletto et al (2002) did for the O vi doublet.…”

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

“…For instance, Ko et al (1997) obtained a temperature of ≈1.5 MK at 1.4 R . Attempts to reconcile the observations with their interpretations were made by assuming differential flows between ions of the same element (Esser and Edgar 2001), but recent studies conclude that non-Maxwellian electron velocity distributions with an enhanced supra-thermal tail are required in the inner corona to account for the observed charge distributions in the solar wind (Chen et al 2003).…”