Summary and Forecast

Solar Summary

(last updated 20 Sep 2026 23:30 UT)

Activity 20 Sep: R0 Flares: none. Observed 10.7 cm flux/Equivalent Sunspot Number for 20 Sep: 101/49

Solar Forecast

(last updated 20 Sep 2026 23:30 UT)

21 Sep 22 Sep 23 Sep Activity R0, chance of R1 R0, chance of R1 R0, chance of R1 Fadeouts None expected None expected None expected 10.7cm/SSN 105/54 105/54 100/48 COMMENT: Solar flare activity was at the R0 level on 20-Sep, with a C3.7 flare from Active Region (AR) 4534 (N07W04, beta-gamma-delta) being the largest observed. This region is the most magnetically complex of four numbered and one unnumbered active sunspot regions currently on the visible solar disk. AR 4534 has shown significant growth since appearing on the disk, but remains small overall. AR 4532 (S05W50, beta) has exhibited some mild growth over the same period, and also remains small. Recently numbered AR 4535 has begun to rotate onto the front side of the solar disk at N11E75, and currently appears to exhibit an alpha magnetic classification. An unnumbered region has appeared at N03E15, showing some growth over the past UT day, and exhibiting a beta magnetic classification. The remaining region, AR 4533 (S12E64, alpha) has remained stable since rotating onto the front side of the disk. Solar flare activity is forecast at the R0 level, with a chance of R1 over 21-23 Sep, due to the recent growth of AR 4534, as well as recent eastern-limb flare activity likely originating from AR 4535. Solar radiation storm conditions were at the S0 level on 20-Sep, with the solar proton flux consistent with background levels. S0 solar radiation storm conditions are forecast over 21-23 Sep. No Earth-directed coronal mass ejections (CMEs) were observed over the past UT day. A low-velocity, north-directed CME was visible in SOHO/LASCO from 19/2200UT. This event was observed to originate on the far side of the solar surface, and is not geoeffective. The solar wind environment trended towards ambient conditions over 20-Sep, with the solar wind speed declining from 400-425 km/s early in the UT day to be currently at 355-365 km/s. The interplanetary magnetic field strength (IMF, Bt) was stable over the UT day, peaking at 5 nT. The north-south component (Bz) ranged between -4 and +3 nT over the same period. The solar wind speed is expected to remain at background levels over 21-22 Sep, before rising late on 22-Sep as the Earth begins to connect with a coronal hole high speed wind stream. The solar wind speed will continue to rise on 23-Sep due to this high speed wind stream.

Solar Activity levels are explained in the SWS Solar Terrestrial Glossary.