:Issued: 2026 Apr 28 1328 UTC :Product: documentation at http://www.sidc.be/products/bul #--------------------------------------------------------------------# # SIDC Weekly bulletin on Solar and Geomagnetic activity # #--------------------------------------------------------------------# WEEK 1321 from 2026 Apr 20 Solar Active Regions (ARs) and flares --------------- The Solar flaring activity was at low to high levels throughout the week, with 56 C-class flares, 14 M-class flares and 2 X-class flares. There were 7 sunspot groups observed on the visible solar disk. SIDC SG 624 (NOAA AR 4207), SIDC SG 847 (NOAA AR 4420), 850 (NOAA AR 4423) and 805 (NOAA AR 4425) all produced M-class flares and most of the C-class flares. The largest flare was a X2.5 flare (SIDC Flare 7473) peaking on April 24 at 08:13 UTC, the second-largest flare a X2.4 flare (SIDC Flare 7462) peaking on April 24 at 01:07 UTC both were produced by SIDC SG 624. Coronal mass ejections --------------------- One Coronal Mass Ejections (CMEs) was observed throughout the week with an Earth directed component. This CME was observed LASCO-C2 data around 08:34 UTC on April 24, with an estimated speed of 1269 km/s. This CME is associated with a X2.5 flare (SIDC Flare 7473) peaking on April 24 at 08:13 UTC. It was predicted to arrive on April 26 as a likely glancing blow arrival, but no CME was seen in the solar wind data at that time. A filament located around N21, E05 erupted on April 21st the CME associated with this filament eruption travelled North and missed Earth. Coronal Holes --------------------- Two positive polarity (SIDC CH 156 and 157) and three negative polarity (SIDC CH 147, 142, 149) coronal holes were present on the solar disk in the past week. Returning equatorial SIDC Coronal Hole 157 (equatorial coronal hole extending to the polar south with a positive polarity) started crossing the central meridian on April 21 and SIDC Coronal Hole 157 (equatorial coronal hole with a negative polarity) started crossing the central meridian on April 22. 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, as measured by GOES-18 and GOES-19 fluctuated around the 1000 pfu threshold from the start of the week until April 24 after which it stayed below the threshold for the rest of the period. The 24-hour electron fluence was at moderate levels at the start of the week until April 25 and then stayed at normal level until the end of the week. Solar wind --------------------- At the beginning of the week, the Earth was under the influence of a high-speed stream associated with SIDC Coronal Hole (CH) 147 before going to slow solar wind condition. From April 25 onward the earth came under the influence of high-speed streams from SIDC CH 156 and 157 until the end of the week. The solar wind speed ranged from 351 km/s to 614 km/s and the total interplanetary magnetic field from 1 nT to 14 nT, with the Bz reaching a minimum of -13 nT. The phi-angle was in the negative sector at the start of the week until April 25 when it switched to the positive sector for the rest of the week. Geomagnetism --------------------- The geomagnetic conditions reached minor storm conditions (Kp 5 & K BEL 5) at the start of the week from April 19 to April 21. Then they were quite to unsettled before reaching active conditions (Kp 4 & K BEL 4) from April 24th onward until the end of the week. --------------------------------------------------------------------------- DAILY INDICES DATE RC EISN 10CM Ak BKG M X 2026 Apr 20 044 042 105 030 B3.4 0 0 2026 Apr 21 079 056 112 022 B5.1 0 0 2026 Apr 22 /// 077 116 006 B5.5 0 0 2026 Apr 23 /// 074 128 006 C1.0 5 0 2026 Apr 24 101 104 146 012 C1.4 3 2 2026 Apr 25 /// 129 148 012 B9.4 2 0 2026 Apr 26 /// 128 156 012 C1.0 5 0 --------------------------------------------------------------------------- # 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) --------------------------------------------------------------------------- NOTICEABLE EVENTS SUMMARY DAY BEGIN MAX END LOC XRAY OP 10CM Catania/NOAA RADIO_BURST_TYPES 23 0424 0435 0448 ////// M1.6 82/4419 III/3 23 0450 0459 0508 N18E43 M1.2 1 85/4420 23 0840 0848 0853 N18W62 M4.3 SN 82/4419 VI/1III/3II/2 23 1342 1400 1411 N17W65 M1.7 SF 82/4419 III/3 23 1700 1708 1714 N17W65 M4.9 1N 82/4419 III/2 24 0051 0107 0113 ////// X2.4 82/4419 24 0801 0813 0818 N19W73 X2.5 2B 82/4419 III/3II/3 24 0857 0907 0919 ////// M1.9 ///4223 24 1234 1301 1314 S06E37 M1.7 1F ///4423 24 1754 1815 1830 N18W80 M6.4 1F 82/4419 III/1VI/1 25 0756 0759 0803 S05E27 M1.3 SF 88/4423 25 1422 1430 1432 N07E73 M1.1 SF ///4425 III/2 26 0008 0023 0035 ////// M1.3 ///4425 26 1354 1403 1408 N15W12 M1.4 S ///4420 26 1918 1924 1927 ////// M1.7 ///4420 26 1954 2004 2007 N05E55 M2.2 1N ///4425 26 2251 2257 2302 ////// M6.0 ///4420 III/2II/2 #--------------------------------------------------------------------# # Solar Influences Data analysis Center - RWC Belgium # # Royal Observatory of Belgium # # # # Website http://www.sidc.be. # # E-mail sidc-support@oma.be # # To unsubscribe http://www.sidc.be/registration/unsub.php # # # # Legal notices: # # - Intellectual Property Rights: # # http://www.astro.oma.be/common/internet/en/data-policy-en.pdf # # - Liability Disclaimer: # # http://www.astro.oma.be/common/internet/en/disclaimer-en.pdf # # - Use and processing of your personal information: # # http://www.astro.oma.be/common/internet/en/privacy-policy-en.pdf # #--------------------------------------------------------------------#