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I am taking a class on the space environment and I have a few questions about the solar wind. A number of sources list the composition as (approximately) 4% He$^{++}$ and 96% H$^{+}$. What exactly does this mean? Does it mean by mass or by number of ions?

Also, when discussing proton flux due to the solar wind at Earth: What exactly is included in the flux numbers quoted (e.g., one source I have says 2e12 m$^{-2}$s$^{-1}$). Is that the flux due to only the H$^{+}$ and excluding the He$^{++}$ and other minor constituents? Or, are they including all the protons from the other ions as well?

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  • $\begingroup$ Just to clarify, it's by number density, not strictly number. $\endgroup$
    – honeste_vivere
    Jan 17 '17 at 15:51
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That's by number-- you get a lot more helium than that by mass. Also, when they talk about proton flux, they just count the bare protons, not protons embedded in larger ions like helium. Those are the kinds of things that should be made clear, but end up being common assumed conventions.

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