  A fundamental property of coronal mass ejections (CMEs) is their radial
expansion, which determines the increase in the CME radial size and the
decrease in the CME magnetic field strength as the CME propagates. CME radial
expansion can be investigated either by using remote observations or by in-situ
measurements based on multiple spacecraft in radial conjunction. However, there
have been only few case studies combining both remote and in-situ observations.
It is therefore unknown if the radial expansion estimated remotely in the
corona is consistent with that estimated locally in the heliosphere. To address
this question, we first select 22 CME events between the years 2010 and 2013,
which were well observed by coronagraphs and by two or three spacecraft in
radial conjunction. We use the graduated cylindrical shell model to estimate
the radial size, radial expansion speed, and a measure of the dimensionless
expansion parameter of CMEs in the corona. The same parameters and two
additional measures of the radial-size increase and magnetic-field-strength
decrease with heliocentric distance of CMEs based on in-situ measurements are
also calculated. For most of the events, the CME radial size estimated by
remote observations is inconsistent with the in-situ estimates. We further
statistically analyze the correlations of these expansion parameters estimated
using remote and in-situ observations, and discuss the potential reasons for
the inconsistencies and their implications for the CME space weather
forecasting.
