SIDC Weekly Bulletin

Review of past solar and geomagnetic activity.
Source SIDC (RWC-Belgium)
Frequency Weekly
Format Plain text
Mail header SIDC Weekly Bulletin
SIDC code bul

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:Issued: 2025 Apr 21 1221 UTC
:Product: documentation at http://www.sidc.be/products/bul
#--------------------------------------------------------------------#
# SIDC Weekly bulletin on Solar and Geomagnetic activity             #
#--------------------------------------------------------------------#
WEEK 1268 from 2025 Apr 14

Solar Active Regions (ARs) and flares
---------------
Solar flaring activity was high in the beginning of the week, with five
M-class flares recorded on April 13-14 and moderate to low for the rest of
the week. In total, eight M-class flares were recorded. The strongest
flares were an M4.2 flare (SIDC Flare 4126) peaking at 06:50 UTC on April
14, associated with SIDC Sunspot Group 469 (NOAA Active Region 4055) and an
M4.4 flare (SIDC Flare 4156) from beyond the east limb, peaking at 23:50
UTC on April 18. There was a total of eleven active regions on the visible
disk during the week. The most complex one at the beginning of the week was
SIDC Sunspot Group 469 (NOAA Active Region 4055, magnetic type
beta-gamma-delta). Later during the week, SIDC Sunspot Groups 450, 473 and
474 (NOAA Active Regions 4060, 4062 and 4064) evolved to magnetic type
beta-gamma during different periods of the week, with SIDC Sunspot Group
450 having a magnetic type beta-delta on April 18.

Coronal mass ejections
---------------------
Few Coronal Mass Ejections (CMEs) were detected during the week, but were
either events near the west or east limb or backsided and had no impact on
Earth. The most important one was a wide CME observed in LASCO/C2 and
LASCO/C3 coronagraph imagery, lifting off around 00:00 UTC on April 19. It
was most likely associated with the M4.4 flare (SIDC Flare 4156) that
peaked at 23:50 UTC on April 18. A few filament eruptions were observed in
SDO/AIA 304 data during the week, but either no associated CME was observed
in the available coronagraph imagery, or it was not Earth-directed.

Coronal Holes
---------------------
Three coronal holes have crossed the central meridian during the last week.
The first (SIDC Coronal Hole 105) was an equatorial, negative polarity
coronal hole that crossed the central meridian on April 15. The second was
a southern, mid-latitude, negative polarity coronal hole (SIDC Coronal Hole
104) that started to cross the central meridian on April 17. The third was
an equatorial, positive polarity coronal hole (returning SIDC Coronal Hole
82) that crossed the central meridian on April 19.

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

Electron fluxes at GEO
---------------------
The greater than 2 MeV electron flux as measured by GOES 16 and GOES 18 was
above the threshold at different times during the week, following a diurnal
variation. The 24-hour electron fluence was at nominal levels throughout
the week.

Solar wind
---------------------
The solar wind conditions were enhanced at the beginning of the week, under
the waning influence of a high-speed stream from the elongated, negative
polarity coronal hole (SIDC Coronal Hole 87) that first crossed the central
meridian on April 07. A shock was detected in the solar wind data (DSCOVR)
at 16:35 UTC on April 15. The interplanetary magnetic field jumped from 6
nT to 17 nT and briefly reached values up to 23 nT. The Bz component jumped
from -4 nT to -11 nT. The solar wind speed jumped from 400 km/s to around
480 km/s and then increased up to 515 km/s. The solar wind density at the
shock jumped from 5.6 ppcc to around 24.4 ppcc. The shock was most likely
related to the expected interplanetary Coronal Mass Ejection (ICME)
arrivals, associated with the CMEs that lifted off around 23:00 UTC on
April 12 and the partial halo CME that lifted off around 08:30 UTC on April
13. A gradual return to the slow solar wind regime followed. The solar wind
conditions (ACE and DSCOVR) were enhanced again on April 20, likely due to
the arrival of a high-speed stream from the southern, positive polarity
coronal hole (SIDC Coronal Hole 104).

Geomagnetism
---------------------
Geomagnetic conditions globally reached severe storm levels (NOAA Kp 8- )
in the UTC evening of April 16. Geomagnetic conditions locally reached
moderate storm levels (K BEL 6) during the same period. The geomagnetic
storms were most likely the result of the arrivals of the interplanetary
Coronal Mass Ejections (ICMEs), associated with the CMEs that lifted off
around 23:00 UTC on April 12 and the partial halo CME that lifted off
around 08:30 UTC on April 13. Mostly unsettled to active levels, with
isolated minor storm intervals (NOAA Kp 3 to 5, K BEL 3 to 5) were observed
during the rest of the week.

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DAILY INDICES
DATE           RC   EISN  10CM   Ak   BKG    M   X
2025 Apr 14   ///    080   152   025   C1.8   2   0   
2025 Apr 15   ///    069   153   030   C1.4   2   0   
2025 Apr 16   ///    089   148   067   C1.0   0   0   
2025 Apr 17   ///    100   151   011   B8.7   0   0   
2025 Apr 18   142    115   156   018   C1.0   1   0   
2025 Apr 19   ///    112   157   022   C1.0   0   0   
2025 Apr 20   ///    125   156   014   C1.0   1   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 
14  0600  0605 0611 ////// M1.4          26/4055      

14  0636  0650 0658 N06W82 M4.2 SF       26/4055      

15  1004  1020 1028 ////// M1.5          ///////      

15  1757  1813 1827 ////// M1.3          ///////      

18  2308  2350 0015 ////// M4.4          ///////      II/1 

20  1137  1211 1259 ////// M1.0          ///4068      

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Details

This report is sent once a week, typically on a monday.
The weekly bulletin gives an overview of solar and geomagnetic activity of the past week and includes a noticeable solar events list.
Check the ISES code book for information on ISES codes.