PRESTO ALERT

Fast warning for important solar events with implications for the space environment.
Source SIDC (RWC-Belgium)
Frequency ASAP, when needed
Format Plain text
Mail header PRESTO ALERT
SIDC code presto

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Latest issue

:Issued: 2016 Jul 20 0714 UTC
:Product: documentation at http://www.sidc.be/products/presto
#--------------------------------------------------------------------#
# FAST WARNING 'PRESTO' MESSAGE  from the SIDC (RWC-Belgium)         #
#--------------------------------------------------------------------#
A shock in the solar wind speed was observed on 19 July at 23:05UT, with a
jump from about 320 km/s to 450 km/s. Particle density was enhanced and
ranged between 20 and 70 p/cc until about 01UT. Bz varied initially between
-12 and + 12nT, then briefly dipped to -28 nT at  00:22UT before turning
strongly northward (+34 nT) between 00:45 and 01:15UT. The timing of the
strong negative Bz dip coincided with a change in the phi angle from away
to towards the Sun (an expected sector boundary crossing). Since 02UT,
solar wind has been increasing to about 550 km/s, with Bz varying between
mostly -6 and +6 nT.

Minor geomagnetic storming has been observed in the Kp index during the
21-24UT, 00-03UT and 03-06UT intervals. At Dourbes, minor storming was
observed from 01-04UT. Dst is currently only at -28 nT. There remains a
chance on further minor storming episodes.

The source of the disturbance is currently thought to be the much earlier
than expected (a full day ahead) arrival of a complex series of faint CMEs
that departed the Sun around noon on 17 July. However, this would require
true speeds nearly double than those determined from the initial
coronagraphic imagery. Hence, interaction with the high speed stream from
nearby negative coronal hole(s) can be considered.
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