  Using multipoint Magnetospheric Multiscale (MMS) observations in an unusual
string-of-pearls configuration, we examine in detail observations of the
reformation of a fast magnetosonic shock observed on the upstream edge of a
foreshock transient structure upstream of Earth's bow shock. The four MMS
spacecraft were separated by several hundred km, comparable to suprathermal ion
gyro-radius scales or several ion inertial lengths. At least half of the shock
reformation cycle was observed, with a new shock ramp rising up out of the
"foot" region of the original shock ramp. Using the multipoint observations, we
convert the observed time-series data into distance along the shock normal in
the shock's rest frame. That conversion allows for a unique study of the
relative spatial scales of the shock's various features, including the shock's
growth rate, and how they evolve during the reformation cycle. Analysis
indicates that: the growth rate increases during reformation, electron-scale
physics play an important role in the shock reformation, and energy conversion
processes also undergo the same cyclical periodicity as reformation. Strong,
thin electron-kinetic-scale current sheets and large-amplitude electrostatic
and electromagnetic waves are reported. Results highlight the critical
cross-scale coupling between electron-kinetic- and ion-kinetic-scale processes
and details of the nature of nonstationarity, shock-front reformation at
collisionless, fast magnetosonic shocks.
