The evolution of ten growth-phase pseudobreakups and subsequent substorms,
identified in northern hemisphere Polar UV images during winter 1998/99, are
compared to the AE index, the unified PC indices, and GOES B-field data.
Comparing substorm onset (auroral breakup) with GOES data, AE and PC indices,
it is found that an exact onset determination from these parameters is in
most cases not possible. The three weakest substorms leave no clear signatures
in the auxiliary parameters. For the other events, the AE increase appears
with a time delay of 5-15 min after onset. The PC indices increase, as
expected, before the AE index. The time span between PC increase and onset
varies widely (-26 - 5 min). A tail dipolarization is seen in GOES data with
a time delay of 2-31 min after onset. The dipolarization delay at
geosynchronous orbit appears due to the GOES displacement from the tail
onset region. Using the mapped GOES distance from the auroral breakup region
as an estimate of GOES displacement from the breakup source region, we find
that the tail dipolarization region expands in average with an azimuthal speed
of 0.22 MLT min-1 and an equatorward speed of 0.09o min-1.
Pseudobreakups leave hardly any signature in AE or PC index data except in
the four strongest substorm cases. In these cases, a bump appears in the PC
indices during the pseudobreakup. A bump in geosynchronous B-field data is
found only in those two cases where GOES is located very close to the
pseudobreakup tail source region.