Viewing archive of Wednesday, 28 July 2021

Daily bulletin on solar and geomagnetic activity from the SIDC

Issued: 2021 Jul 28 1235 UTC

SIDC Forecast

Solar flares

Quiet conditions (<50% probability of C-class flares)

Geomagnetism

Active conditions expected (A>=20 or K=4)

Solar protons

Quiet

	10cm flux	Ap
28 Jul 2021	080	017
29 Jul 2021	080	007
30 Jul 2021	080	004

Bulletin

The solar activity has been quiet over the past 24 hours, with the X-ray flux below C-level. The two sunspot groups (Catania sunspot group 22 / NOAA AR-2846, and Catania sunspot group 23 / NOAA AR-2847) have produced few B-class flares. A new bipolar sunspot groups (Catania sunspot group 24) has emerged close to the central meridian at altitude -04 degrees and did not produce any significant flare. The solar activity is expected to remain at low levels over the next 24 hours with a small chances of C-class flare.

A large coronal dimming was observed on July 28 from 08:03 UTC to 09:33 UTC in the north-west quadrant (near latitude 34 degrees and longitude 13 degrees). Further investigation on this event will be provided as data comes in. The true speed of the coronal mass ejection observed in SOHO/LASCO-C2 coronagraphe images on July 27 at 03:24 UTC with a projected speed of 388 km/s has been re-evaluated to about 600 km/s with a new arrival time estimated on July 30 mid days. Only minor to no effect is expected on the solar wind conditions and geomagnetic activity.

The greater than 10 MeV proton flux was at nominal levels over the past 24 hours and is expected to remain so for the next 24 hours. The greater than 2 MeV electron flux was below the 1000 pfu threshold in the past 24 hours. The greater than 2 MeV electron flux may slightly increase during the next 24 hours due to the arrival of the high-speed streams. The 24h electron fluence was at normal levels in the last 24 hours and may also slightly increase for the next 24 hours.

The solar wind parameters (as observed by ACE and DSCOVR) show the arrival of the expected high-speed streams associated with the positive polarity northern polar coronal hole, that crossed the central meridian on July 24. The solar wind speed increased from 304 km/s to the values now around 505 km/s. The interplanetary magnetic field magnitude became enhanced and reached up to 17 nT, the Bz components fluctuated between -11 nT and 13 nT. The enhanced solar wind conditions are expected to persist for the next few days. The solar wind may also be temporarily enhanced later on July 28 due to an additional effect of a possible glancing blow from the eastward coronal mass ejection driven by the C4.3 flare on July 24.

The geomagnetic conditions became active with the expected arrival of the high-speed streams (NOAA-Kp and K-Dourbes = 4). The conditions are expected to remain unsettled with possible short periods of active conditions.

Today's estimated international sunspot number (ISN): 006, based on 18 stations.

Solar indices for 27 Jul 2021

Wolf number Catania	029
10cm solar flux	080
AK Chambon La Forêt	020
AK Wingst	006
Estimated Ap	006
Estimated international sunspot number	017 - Based on 26 stations

Noticeable events summary

Provided by the Solar Influences Data analysis Center© - SIDC - Processed by SpaceWeatherLive

All times in UTC

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