Carbon Ionization Stages as a Diagnostic of the Solar Wind

Abstract

Oxygen charge states measured by in situ instrumentation have long been used as a powerful diagnostic of the solar corona and to discriminate between different solar wind regimes, both because they freeze in very close to the Sun, and because the oxygen element abundance is comparatively high, allowing for statistically relevant measures. Like oxygen, carbon is also rather abundant and freezes in very close to the Sun. Here, we show an analysis of carbon and oxygen ionic charge states. First, through auditory and Fourier analysis of in situ measurements of solar wind ion composition by ACE/SWICS we show that some carbon ion ratios are very sensitive to solar wind type, even more sensitive than the commonly used oxygen ion ratios. Then we study the evolution of the ionization states of carbon and oxygen by means of a freeze-in code, and find that carbon ions, commonly found in the solar wind, freeze in at comparable coronal distances, while oxygen ions evolve over a much larger range of coronal distances. Finally, we show that carbon and oxygen ion abundance ratios have similar sensitivity to the electron plasma temperature, but the carbon ratios are more robust against atomic physics uncertainties and a better indicator of the temperature of the solar wind source regions.

Sources of Solar Wind at Solar Minimum: Constraints from Composition Data

“…Clearly, the ordering of ionization temperature and elemental abundance is robust over nearly an entire solar cycle. Here, we use the C 6+ /C 5+ ratio to remain consistent with previously published values, but notice that we recently identified C 6+ /C 4+ as a very suitable temperature proxy for favorable statistical properties and because of the fact that both ionic charge states freeze in at approximately the same location near the Sun (Landi et al 2012). Throughout this paper, we are using the average charge state of carbon.…”

“…Such constraints can be developed in a qualitative sense (i.e., Geiss et al 1995;or von Steiger and Zurbuchen 2011), or they can be done quantitatively (Ko et al 1997;Laming and Lepri 2007;Gruesbeck et al 2011). Landi et al (2012) recently discussed the challenges of qualitative measures, the socalled freeze-in temperatures, as a diagnostic for electron temperatures in the low corona. Although it is possible to calculate freeze-in temperatures from any charge-state ratio of a given element under the assumption of thermal equilibrium, these freeze-in temperatures are substantially different from the local temperatures near the freeze-in point.…”

“…Although it is possible to calculate freeze-in temperatures from any charge-state ratio of a given element under the assumption of thermal equilibrium, these freeze-in temperatures are substantially different from the local temperatures near the freeze-in point. This is caused by non-local effects dominating the freeze-in process (i.e., the ionic charge distribution at a given near-solar distance r 0 is dependent on the thermal properties over a large range of distances r < r 0 ), especially when the ionization and recombination scales of two ions in a given ion ratio exhibit differences (Landi et al 2012). Such non-local effects were shown to be particularly important for O 7+ /O 6+ ratios, but they are less important for C 6+ /C 4+ .…”

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

“…The L12 diagnostic technique relies on the calculation of the evolution of the charge states of an element at all positions along the trajectory of the solar wind, from the wind source region in the solar atmosphere to the freeze-in point. This calculation is carried out using the Michigan Ionization Code (MIC; Landi et al 2012a), which requires three different types of input:…”

A Proton-Cyclotron Wave Storm Generated by Unstable Proton Distribution Functions in the Solar Wind

“…Audification has been used in many different studies in space plasma physics, particularly in the study of ionospheric and magnetospheric processes where several different phenomena have names derived from their audio properties, such as "whistler waves" (Barkhausen 1919(Barkhausen , 1930, "lion roars" (Smith et al 1969), and "hiss." Audification was also used to identify ring particle impacts on the Voyager 2 spacecraft as it passed Saturn (Scarf et al 1982), and features of solar wind time series that were overlooked in a visual analysis have been detected using audification (Alexander et al 2011(Alexander et al , 2014Landi et al 2012). Audification allows us to survey the entire magnetic field data set for the year 2008 in a relatively short time and qualitatively compare the duration, amplitude, and clarity of events found easily.…”