Combining remote and in situ observations of coronal mass ejections to better constrain magnetic cloud reconstruction

Abstract

Determination of the nonradial extent of magnetic clouds (MCs) is vital for two key reasons. First, it affects the amount of “drag” a fast MC experiences and therefore controls the travel time from the Sun to 1‐AU, a critical parameter for space‐weather prediction. Second, it is vital to estimating the flux content of MCs, which in turn is important for understanding both the formation and eruption of the magnetic flux rope and for determining the role of coronal mass ejections in the heliospheric flux budget and the evolution of heliospheric flux over the solar cycle. In this study, it is demonstrated that the cross‐sectional elongation of MCs is poorly constrained by in situ observations of the magnetic field alone. A method for combining remote and in situ observations of ejecta to better determine MC cross‐sectional elongation is then outlined and applied to a previously studied event which occurred during the SOHO‐Ulysses quadrature of late 1996. The new technique reveals an axial magnetic flux content ∼4 times higher than that inferred by a force‐free flux rope model fit to the same in situ observations of the magnetic cloud. This event also shows evidence of axial distortion by the structured ambient solar wind.