SIDC Weekly Bulletin

:Issued: 2020 Aug 03 2333 UTC
:Product: documentation at http://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 rest 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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