  We quantify the spatiotemporal evolution of the substorm ionospheric current
system utilizing the SuperMAG 100+ magnetometers.We construct dynamical
directed networks from this data for the first time. If the canonical
cross-correlation between vector magnetic field perturbations observed at two
magnetometer stations exceeds a threshold, they form a network connection. The
time lag at which canonical cross-correlation is maximal determines the
direction of propagation or expansion of the structure captured by the network
connection. If spatial correlation reflects ionospheric current patterns,
network properties can test different models for the evolving substorm current
system.We select 86 isolated substorms based on nightside ground station
coverage. We find, and obtain the timings for, a consistent picture in which
the classic substorm current wedge forms. A current system is seen premidnight
following the substorm current wedge westward expansion. Later, there is a
weaker signal of eastward expansion. Finally, there is evidence of
substorm-enhanced convection.
