  Flux ropes are twisted magnetic structures, which can be detected by in situ
measurements in the solar wind. However, different properties of detected flux
ropes suggest different types of flux-rope population. As such, are there
different populations of flux ropes? The answer is positive, and is the result
of the analysis of four lists of flux ropes, including magnetic clouds (MCs),
observed at 1 AU. The in situ data for the four lists have been fitted with the
same cylindrical force-free field model, which provides an estimation of the
local flux-rope parameters such as its radius and orientation. Since the
flux-rope distributions have a large dynamic range, we go beyond a simple
histogram analysis by developing a partition technique that uniformly
distributes the statistical fluctuations over the radius range. By doing so, we
find that small flux ropes with radius R<0.1 AU have a steep power-law
distribution in contrast to the larger flux ropes (identified as MCs), which
have a Gaussian-like distribution. Next, from four CME catalogs, we estimate
the expected flux-rope frequency per year at 1 AU. We find that the predicted
numbers are similar to the frequencies of MCs observed in situ. However, we
also find that small flux ropes are at least ten times too abundant to
correspond to CMEs, even to narrow ones. Investigating the different possible
scenarios for the origin of those small flux ropes, we conclude that these
twisted structures can be formed by blowout jets in the low corona or in
coronal streamers.
