PRESTO ALERT

:Issued: 2012 May 21 2231 UTC
:Product: documentation at http://www.sidc.be/products/presto
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# FAST WARNING 'PRESTO' MESSAGE  from the SIDC (RWC-Belgium)         #
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An interplanetary shock wave was detected by ACE at 18:45 UT on May 21.
The solar wind speed jumped from 330 km/s to 410 km/s. However, the
corresponding jump of the interplanetary magnetic field (IMF) magnitude
was weak (from 2 to 4 nT), and the IMF magnitude rose only up to 7 nT in
the post-shock solar wind flow. This resulted only in active geomagnetic
conditions (K = 4 reported by Dourbes and NOAA).
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