:Issued: 2026 Apr 03 2029 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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A solar wind shock was detected at Earth on 03 April around 15:05 UTC. This was
followed by a strong enhancement of solar wind parameters and the onset of
geomagnetic storm conditions. 
Solar wind speed increased abruptly from about 600 km/s to approximately 850 km/s.
The interplanetary magnetic field (IMF) was enhanced, with the total field (Bt)
increasing from about 5 nT to approximately 14 nT. The IMF Bz component showed
sustained southward values down to approximately -11 nT. This disturbance occurs
during the ongoing influence of a high-speed solar wind stream (HSS) originating from
SIDC Coronal Hole 149 (the equatorial coronal hole with negative polarity that
crossed the central meridian on 30 March).
These observations are consistent with the arrival of the interplanetary coronal mass
ejection (SIDC CME 645), associated with a filament eruption on 01 April around 23:00
UTC near N28W25. Despite the main propagation direction being towards the northwest,
the wide extent of the CME-driven shock enabled its arrival at Earth. Solar wind
conditions are expected to remain enhanced over the next 24 hours, with continued
high-speed stream influence, the ICME passage, and fluctuating IMF conditions.
Geomagnetic conditions reached major storm levels. The global NOAA Kp index reached
major storm levels (Kp 7), while the local K index (Belgium) reached 6 (moderate
storm levels). The elevated geomagnetic activity is driven by the combined effects of
the ICME impact and the preconditioning of the solar wind by the high-speed stream,
together with sustained southward IMF. Further active to moderate storm conditions
are expected in the coming hours, depending on the evolution of the IMF, in
particular the Bz orientation.
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# Solar Influences Data analysis Center - RWC Belgium                #
# Royal Observatory of Belgium                                       #
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