Abstract
During its ongoing mission, the Cluster II constellation has provided
the first small-scale multipoint measurements of the space environment,
and dramatically advanced scientific understanding in numerous regimes.
One such region is the Earth’s inner magnetospheric ring current, which
could now be computed using the curl of the magnetic field over a
spacecraft tetrahedron instead of via plasma moments. While this
produced the first 3D current estimates, it also produced different
results from prior ring current studies with differing magnitudes and
correlations with storm indices/local times. In this analysis, we
revisit Cluster ring current data via curlometry, and conduct additional
quantitative sensitivity simulations using actual spacecraft position
data. During the orbits that observed ring current structure,
tetrahedron shape and linearity assumptions can create large errors up
to 100% of physical current magnitude in curlometer output that
contradict accepted estimated quality parameters. These false currents
are directly related to the structure of the current environment, and
cannot be distinguished from the actual currents without additional
limiting assumptions. The trustworthiness of curlometer output in the
ring current is therefore dependent on the linearity of the magnetic
structure relative to the tetrahedron orientation, which requires
additional characterization. The Cluster curlometer output in the ring
current is then explored in light of these new uncertainties, with the
computed current magnitude and direction both potentially impacted by
the production of false currents.