Dawn storms are among the brightest events in the Jovian aurorae. Up to
now, they had only been observed from Earth-based observatories, only
showing the Sun-facing side of the planet. Here we show for the first
time global views of the phenomenon, from its initiation to its end and
from the nightside of the aurora onto the dayside. Based on Juno's first
20 orbits, some patterns now emerge. Small short-lived spots are often
seen for a couple of hours before the main emission starts to brighten
and evolve from a straight arc to a more irregular one in the midnight
sector. As the whole feature rotates dawn-ward, the arc then separates
into two arcs with a central initially void region that is progressively
filled with emissions. A gap in longitude then often forms before the
whole feature dims. Finally, it transforms into an equatorward-moving
patch of auroral emissions associated with plasma injection signatures.
Some dawn storms remain weak and never fully develop. We also found
cases of successive dawn storms within a few hours. Dawn storm thus
share many fundamental features with the auroral signatures of the
substorms at Earth. These findings demonstrate that, whatever their
sources, mass and energy do not always circulate smoothly in planetary
magnetospheres. Instead they often accumulate until the magnetospheres
reconfigure and generate substorm-like responses in the planetary
aurorae, although the temporal and spatial scales are different for
different planets.