SIDC Weekly Bulletin

Issued: 2020 Aug 03 2333 UTC
Product: documentation at www.sidc.be/products/bul
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SIDC Weekly bulletin on Solar and Geomagnetic activity #
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WEEK 1022 from 2020 Jul 27
SOLAR ACTIVITY
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The solar activity was mostly quiet over the past week. There were three unipolar active regions observed on the solar disc. The first active region was sunspot group Catania 37/NOAA-AR 2767, classified as Alpha/Hsx, which emerged on the disc last week on July 22nd. The second active region, NOAA-AR 2768, classified most of the time as Alpha/Axx, rotated from the north-east limb and became visible on the disc on July 27th. The third active region, NOAA-AR 2769, classified as Alpha/Axx, which became visible from the Earth on Aug 1st also rotated on the disc from the north-east limb at the same latitude as NOAA-AR 2768. All three active regions remained stable and did not produce any significant flaring activity. There was a single B-class flare and the X-ray flux remained below C-class flare level during the entire week.

Throughout the week three Coronal Mass Ejections (CMEs) were released by the Sun, respectively on July 28th, July 29th and July 31st. The CME from July 31st was related to a prominence eruption. All CMEs originated from the east-limb, yet none of them was observed to have Earth-directed component and there was no foreseen impact on Earth.

Over the past week the greater than 10 MeV proton flux remained at background levels and the greater than 2 MeV electron flux was oscillating between nominal and Moderate levels, remaining well under events alert threshold.
GEOMAGNETIC ACTIVITY
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The solar wind conditions (based on DSCOVR and ACE data) were at slightly elevated levels at the beginning of the week under the influence of a High speed stream (HSS) coming from a negative polarity coronal hole (CH 63), which had crossed the central meridian on July 23rd. The solar wind speed on July 27th until midday of July 28th was in the range of 360 km/s to 440 km/s. On July 29th, the solar wind parameters relaxed back to nominal conditions typical for pristine slow solar wind with solar wind velocity smoothly decreasing from 390km/s to 320 km/s. At the end of the week on Aug 2nd a corotating interaction region (CIR) arrived at Earth as a precursor of the HSS originating from a recurrent positive polarity coronal hole (CH 64), which resided in the northern hemisphere since the beginning of the week and crossed the central meridian on July 30th. The CIR was first registered approximately at 04:30 UTC and continued to influence the solar wind parameters throughout the r!
est of the day, causing enhancements in the density, temperature, velocity and magnetic field. The magnitude of the interplanetary magnetic field reached 12 nT at 11:50 UTC with a minimum Bz component of -10 nT and solar wind speed of 374 km/s (as reported by DSCOVR). Moderate-amplitude Bz fluctuations were observed throughout Aug 2nd with solar wind speed increasing to 520 km/s.

The geomagnetic conditions were mostly quiet throughout the week. A small rarefaction wave was observed around 18:00 UTC on July 29th, which caused a short two-hour period of locally unsettled conditions with K Dourbes index equal to 3. The global geomagnetic condition remained quiet with a maximum value of the Kp NOAA index equal to 2. At the end of the week on Aug 2nd in response to the CIR impact and the arrival of the HSS associated with CH 64, long periods of unsettled geomagnetic condition were observed with Kp NOAA and K Dourbes indices equal to 3.
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DAILY INDICES
DATE RC EISN 10CM Ak BKG M X
2020 Jul 27 /// /// 071 004 A3.2 0 0
2020 Jul 28 /// /// 072 006 A3.1 0 0
2020 Jul 29 /// /// 073 006 A2.4 0 0
2020 Jul 30 /// /// 073 004 A2.5 0 0
2020 Jul 31 /// /// 072 006 A2.8 0 0
2020 Aug 01 /// 019 072 005 A3.3 0 0
2020 Aug 02 /// 017 073 012 A3.4 0 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
NONE

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