  Magnetic clouds (MCs) are large-scale interplanetary transient structures in
the heliosphere that travel from the Sun into the interplanetary medium. The
internal magnetic field lines inside the MCs are twisted, forming a flux rope
(FR). This magnetic field structuring is determined by its initial solar
configuration, by the processes involved during its eruption from the Sun, and
by the dynamical evolution during its interaction with the ambient solar wind.
One of the most important properties of the magnetic structure inside MCs is
the twist of the field lines forming the FR (the number of turns per unit
length). The detailed internal distribution of twist is under debate mainly
because the magnetic field (B) in MCs is observed only along the spacecraft
trajectory, and thus it is necessary to complete observations with theoretical
assumptions. Estimating the twist from the study of a single event is difficult
because the field fluctuations significantly increase the noise of the observed
B time series and thus the bias of the deduced twist. The superposed epoch
applied to MCs has proven to be a powerful technique, permitting the extraction
of their common features, and removing the peculiarity of individual cases. We
apply a superposed epoch technique to analyse the magnetic components in the
local FR frame of a significant sample of moderately asymmetric MCs observed at
1 au. From the superposed profile of B components in the FR frame, we determine
the typical twist distribution in MCs. The twist is nearly uniform in the FR
core (central half part), and it increases moderately, up to a factor two,
towards the MC boundaries. This profile is close to the Lundquist field model
limited to the FR core where the axial field component is above about one-third
of its central value.
