Product: Forecast Discussion Issued: 2021 Dec 23 0030 UTC Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center Solar Activity .24 hr Summary... Solar activity reached moderate levels with an isolated M-class flare. There were nine sunspot groups present on the visible disk. The main highlights were: NOAA/SWPC Region 2918 (N20E52, Cro/beta) was assigned to a newly emerged group that was magnetically simple and inactive. Region 2907 (S21W50, Eai/beta-gamma) continued to decay in some areas and grow in others. The region produced occasional C-class flares, to include a C8/1n at 22/1808 UTC. Region 2908 (S20W39, Dai/beta-gamma) consolidated in areas and gained some mixed polarity spots. The region remained unstable and was the source of optical flares and C-class activity; to include an M1/1n at 22/0706 UTC. Region 2909 (S21W26, Hsx/alpha) changed little and was mostly stable. No clearly discernible, new Earth-directed CMEs were observed in available coronagraph imagery, to include in association with the M1 flare today. However, there did appear to possibly be a very faint, slow signature with a southwest vector, so analysis of this event continues. Analysis of yesterday's (21 Dec) C4 flare associated, faint CME continues. However, initial indications are there could be an Earth-directed component. Final analysis and modelling of this event are pending. .Forecast... Low solar activity levels are expected, with a chance for M-class flares (R1-R2; Minor-Moderate radio blackouts) and a slight chance of X-class (R3; Strong radio blackout) 23-25 Dec. Energetic Particle .24 hr Summary... The greater than 2 MeV electron flux reached high levels with a peak of 1,190 pfu at 22/1715 UTC. The greater than 10 MeV proton flux maintained background levels. .Forecast... The greater than 2 MeV electron flux is expected to reach high levels again on 23 Dec in response to CH HSS influences. Possible glancing blow CME arrival (from 20 Dec) is anticipated to decrease levels back to normal to moderate on 24 Dec and remain at those levels on 25 Dec. The greater than 10 MeV proton flux is expected to continue at background 23-25 Dec, with a slight chance of an S1 (Minor) radiation storm due to the favorable position and flare probabilities of Regions 2907, 2908, and 2909. Solar Wind .24 hr Summary... Solar wind parameters were indicative of continued CH HSS influences. Total IMF strength was fairly steady at mainly 4-5 nT, while the Bz component varied orientations with a few periods of prolonged southward direction. Solar wind speed was steady at 575 km/s and the phi angle was negative. .Forecast... The CH HSS regime shows no signs of waning, so elevated speeds are expected to continue into 23 Dec. Conditions are likely to become more disturbed and enhanced later in the day as glancing blow CME (from the 20 Dec event) may arrive at Earth. CME influences are likely to continue into 24 Dec and wane on 25 Dec. Early model results indicate a possible weak, glancing blow arrival of the 22 Dec CME as early as late on 25 Dec. Geospace .24 hr Summary... The geomagnetic field was quiet to unsettled in varied response to CH HSS effects. .Forecast... The geomagnetic field is expected to be quiet to unsettled most of 23 Dec as CH HSS influences continue. However, possible glancing blow CME arrival (from 20 Dec) would likely escalate conditions to active levels, with a chance for G1 (Minor) storm levels. Any CME influences would likely continue into 24 Dec, leading to unsettled to active conditions, with a likely isolated period of G1 storm levels as the CME passage continues. Responses are expected to decline and return to quiet to unsettled conditions on 25 Dec. Another escalation of geomagnetic response is possible late on 25 Dec due to the proximity of another approaching CME (of 21 Dec) and associated effects.
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