SIDC Weekly Bulletin

:Issued: 2026 Apr 20 1451 UTC
:Product: documentation at http://www.sidc.be/products/bul
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# SIDC Weekly bulletin on Solar and Geomagnetic activity             #
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WEEK 1320 from 2026 Apr 13

Solar Active Regions (ARs) and flares
---------------
There were 7 sunspot groups visible during the week, from SIDC Sunspot
Group 825 ( NOAA 4419) to SIDC Sunspot Group 846 (NOAA 4418). The most
complex of these groups was SIDC 825 (NOAA 4319), that reached a beta gamma
magnetic field configuration. Only C-class flaring was observed during the
week, with 8 C-class flares detected.

Coronal mass ejections
---------------------
No clear Earth directed CMEs were observed during the week. A wide CME
(angular width about 90 degrees) was seen erupting towards the SW at 18:00
UTC on 13 April, this CME is backsided. A filament located around S20E20
erupted early on 15 April, leading to a CME seen by LASCO C2 at 09:00 UT on
15 April. A second CME from a similar filament eruption erupted on 18
April, seen by LASCO C2 at 09:00 UT on 18 April.

Coronal Holes
---------------------
At the beginning of the week there were two mid-latitude positive polarity
coronal holes (SIDC Coronal Holes 154 and 158) in the western hemisphere,
and one (159) crossing the central meridian on April 13, also with positive
polarity. A large equatorial coronal hole with negative polarity (SIDC
Coronal Hole 147) was observed traversing the central meridian on April 14.

Proton flux levels
---------------------
The greater than 10 MeV proton flux remained below the 10 pfu threshold
throughout the week.

Electron fluxes at GEO
---------------------
The greater than 2 MeV electron flux measured by GOES 18 and 19 was
fluctuating around the threshold most of the week. It went clearly below it
on 18 April and stayed so for two days.

Solar wind
---------------------
The solar wind at the Earth was slow until April 18, when the high speed
stream from SIDC Coronal Hole 147 arrived. The solar wind speed then rose
to close to 600 km/s with interplanetary magnetic field up to 18 nT and Bz
down to -14 nT.  At the end of the week, the Earth was still within this
fast solar wind stream, but gradually transitioning into a slow solar wind
regime.

Geomagnetism
---------------------
The geomagnetic conditions in the week were quiet until the arrival of the
high speed stream from SIDC Coronal Hole 147. On April 18 and 19 Kp rose to
6- (moderate storm levels) and K_Bel up to 5 (minor storm levels).

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DAILY INDICES
DATE           RC   EISN  10CM   Ak   BKG    M   X
2026 Apr 13   ///    058   099   004   B2.6   0   0   
2026 Apr 14   076    061   101   003   B2.8   0   0   
2026 Apr 15   ///    053   105   008   B3.0   0   0   
2026 Apr 16   ///    054   108   003   B3.6   0   0   
2026 Apr 17   ///    053   107   006   B3.4   0   0   
2026 Apr 18   ///    046   106   035   B3.0   0   0   
2026 Apr 19   ///    040   105   018   B3.1   0   0   
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# RC   : Sunspot index (Wolf Number) from Catania Observatory (Italy)
# EISN : Estimated International Sunspot Number
# 10cm : 10.7 cm  radioflux (DRAO, Canada)
# Ak   : Ak Index Wingst (Germany)
# BKG  : Background GOES X-ray level (NOAA, USA)
# M,X  : Number of X-ray flares in M and X class, see below (NOAA, USA)
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NOTICEABLE EVENTS SUMMARY
DAY BEGIN MAX  END  LOC    XRAY OP  10CM Catania/NOAA RADIO_BURST_TYPES 
NONE
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