SIDC Weekly Bulletin

:Issued: 2023 Mar 20 1745 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 1159 from 2023 Mar 13
SOLAR ACTIVITY
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Over the past week the solar flaring activity was at low levels.  There
were fifteen numbered active regions on the visible disk. They all had
relatively simple alpha or beta magnetic field configuration and produced
23 C-class flares and 1 M-class flare. The largest flare over a week was a
M1.1 flare, peaking at 15:07 UTC on March 17, associated with NOAA AR3254.
The second largest flare was an impulsive C9.4 flare at 07:10 UTC on March
18, produced by NOAA active region 3256. This event was also associated
with Type IV radio emission.

Two small equatorial coronal holes of positive polarity were visible in the
week. The first one transited the central meridian on March 11 and the
second one on March 16. 

A filament eruption in the southeastern quadrant was observed on March 12
around 17:45UTC. The associated CME appeared in SoHO/LASCO C2 coronagraph
data from 19:00UTC onwards. The CME was directed to the south and the bulk
of the CME was not expected to be Earth directed. However, a glancing blow
of the shock was predicted to impact Earth on March 15. Indeed, shock was
observed in the solar wind early on March 15, that might be associated to
the CME. 
A full halo CME was seen in LASCO C2 imagery from 03:36 UTC on March 13.
This was determined to be a back-sided event and was not expected to arrive
to Earth. However, the greater than 10 MeV proton flux levels have been
elevated related to this event, reaching minor radiation storm levels.
A filament eruption occurred in the northern hemisphere near disc center at
around 09:50UTC on March 13. The associated CME, that appears in SoHO/LASCO
C2 coronagraph data from 10:48UTC onwards, was directed to the north-west.
The bulk of this eruptions was estimated to miss Earth, but there was a
chance for a glancing blow early on March 16. However, this was not
observed in the in-situ solar wind data. Another filament eruption in the
southwestern quadrant was observed on March 17 from around 09:20UTC. The
associated CME appears in SoHO/LASCO C2 coronagraph data from 10:23UTC
onwards. The CME was directed to the south-west and the bulk of the CME was
not expected to be Earth directed, but there was a chance, that a glancing
blow of the shock may impact Earth late on on March 19.

The greater than 10 MeV proton flux was at nominal levels at the start of
the week and got elevated on March 13 following backsided full halo CME,
crossing the 10pfu event threshold around 07:45UTC on March 13. The greater
than 10 MeV proton flux has reached the maximum value of 22pfu at around
04:25UTC on March 15 and returned to near the nominal levels from around
16:00UTC on March 15. The greater than 2 MeV electron flux was below the
1000 pfu threshold throughout the week. The 24h electron fluence was at
normal levels throughout the week.
GEOMAGNETIC ACTIVITY
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The solar wind parameters have been indicative of slow solar wind
conditions at the start of the week. The solar wind speed showed a
gradually decreasing trend, decreasing from 380 km/s to values around 320
km/s. The orientation of the magnetic field was predominantly in the
negative sector (field directed towards the Sun) with a variable
north-south component Bz ranging between 0 to 6 nT. A high-speed stream
from a positive polarity equatorial coronal hole began to influence the
Earth from March 14. The solar wind conditions became slightly disturbed
with the total interplanetary magnetic field rose to 15 nT at around
04:30UTC on March 14. The north-south component of the magnetic field was
variable, ranging between -11 to 13 nT.  The solar wind velocity followed
an increasing trend, rising from 320 km/s to 410 km/s. The orientation of
the magnetic field showed a switch from the negative (field towards the
Sun) to positive sector (field away from the Sun). On March 15, around
03:39UTC a shock was observed with solar wind speed jumping from 410 km/s
to 550 km/s and the total interplanetary magnetic field jumping from 8 nT
to 24 nT. The shock might be associated to the CME that left the Sun on
19:00UTC, March 12. Towards the end of the week, the solar wind speed
gradually decreased to values near 420 km/s.

The geomagnetic conditions were at quiet to unsettled levels at the start
of the week, increasing to active on March 14 – March 16 due to the ICME
and high speed steam influences with isolated moderate storm period
globally (NOAA- Kp = 6-) and minor storm period locally (K Bel = 5) at
around 03:00 UTC and 21:00 UTC on March 15. Conditions then returned to
quiet to unsettled levels for the rest of the week.
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DAILY INDICES
DATE           RC   EISN  10CM   Ak   BKG    M   X
2023 Mar 13   101    104   143   003   B5.6   0   0   
2023 Mar 14   122    111   139   018   B5.9   0   0   
2023 Mar 15   135    106   136   028   B5.6   0   0   
2023 Mar 16   110    096   135   007   B6.1   0   0   
2023 Mar 17   110    071   134   007   B8.4   1   0   
2023 Mar 18   ///    044   140   010   B8.7   0   0   
2023 Mar 19   ///    074   143   014   B9.5   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 
17  1504  1507 1511 S22W65 M1.0 SN       12/3247      

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