  Magnetic clouds (MCs) are transient structures containing large-scale
magnetic flux ropes from solar eruptions. The twist of magnetic field lines
around the rope axis reveals information about flux rope formation processes
and geoeffectivity. During propagation, MC flux ropes may erode via
reconnection with the ambient solar wind. Any erosion reduces the magnetic flux
and helicity of the ropes, and changes their cross-sectional twist profiles.
This study relates twist profiles in MC flux ropes observed at 1 AU to the
amount of erosion undergone by the MCs in interplanetary space. The twist
profiles of two well-identified MC flux ropes associated with the clear
appearance of post eruption arcades in the solar corona are analysed. To infer
the amount of erosion, the magnetic flux content of the ropes in the solar
atmosphere is estimated, and compared to estimates at 1 AU. The first MC shows
a monotonically decreasing twist from the axis to periphery, while the second
displays high twist at the axis, rising twist near the edges, and lower twist
in between. The first MC displays a larger reduction in magnetic flux between
the Sun and 1 AU, suggesting more erosion, than that seen in the second MC. In
the second cloud, rising twist at the rope edges may have been due to an
envelope of overlying coronal field lines with relatively high twist, formed by
reconnection beneath the erupting flux rope in the low corona. This high-twist
envelope remained almost intact from the Sun to 1 AU due to the low erosion
levels. In contrast, the high-twist envelope of the first cloud may have been
entirely peeled away via erosion by the time it reaches 1 AU.
