A statistical evaluation of ballistic backmapping for the slow solar wind: The interplay of solar wind acceleration and corotation

Abstract Mapping solar wind plasma back to its source is often achieved using the ‘two-step ballistic backmapping’ method. Solar observations are mapped through heliosphere edge of a PFSS model, by assuming constant speed, radial, flow. Tracing field lines model gives location at 1 R⊙ The heliospheric mapping component hinges upon argument that two known sources error, stemming from acceleration and non-radial flow, effectively cancel. This assumption has not been tested statistically. In this study, we evaluate portion two-step backmapping, in addition models with explicit radial acceleration, azimuthal velocity, vφ, derived angular momentum conservation. We estimate longitudinal offsets, Δφ, between 326 Earth-observed crossings current sheet (HCS), corresponding 2.5 models. While detailed can be optimised produce Δφ good average agreement HCS crossing data, performs almost as well, although all residuals have sizeable standard deviation σ ∼ 16○. conclude proposed error cancellation likely contributes performance mapping. However, interplanetary height effective corotation both smaller than previously assumed. Our results further suggest early Parker Probe large vφ around 36 do represent overall wind, due requirement for it balanced increased acceleration.