SIDC Weekly Bulletin

Issued: 2019 Sep 23 1654 UTC

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[SIDC Weekly bulletin] on Solar and Geomagnetic activity
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WEEK 977 from 2019 Sep 16
SOLAR ACTIVITY
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The Solar disk was spotless and Solar X-ray flux remained below B class levels throughout the week.

A filament located near N30E05 was seen erupting in SDO/AIA 304 images on September 16 after 6:00UT. It was associated with a very narrow and slow CME towards the West as seen by STEREO A COR2. Corresponding SoHO/LASCO C2 and C3 coronagraph images show a slow and East directed CME. Based on these
observations it was judged that the ejecta were sufficiently East of the Sun-Earth line.

An equatorial negative polarity coronal hole crossed the central meridian on September 20.

Another filament stretching from the central meridian towards the Eastern limb, and located South of the mentioned coronal hole, was seen to erupt in SDO/AIA 304 imagery from around 21:00UT on September 19. Corresponding STEREO/COR2 coronagraph data indicated a narrow and slow (300 km/s) CME, while SoHO/LASCO data did not show any clear signs of any (partial) halo CME. It was anticipated that possible effects from this slow CME would not be noticeable within the anticipated High speed stream from the coronal hole and no specific arrival forecast was made.

Proton levels were at background values throughout the week.
GEOMAGNETIC ACTIVITY
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Solar wind was generally on decline with speed gradually decaying from around 450 km/s to around 300 km/s with two slight and brief increases against this trend around late September 17, and early September 21. Bz did not see any deep negative excursions. The magnetic field phi angle started the week in the negative sector, was then since late September 17 in the positive sector for most of the week before switching back into the negative sector just before the end of the week.

Geomagnetic conditions were generally quiet to unsettled with some active periods occurring at the start of the week when Solar wind speed was still slightly elevated.
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DAILY INDICES
DATE RC EISN 10CM Ak BKG M X
2019 Sep 16 000 000 069 014 A3.7 0 0
2019 Sep 17 000 000 068 011 A3.5 0 0
2019 Sep 18 000 000 066 008 A3.7 0 0
2019 Sep 19 000 000 067 004 A3.6 0 0
2019 Sep 20 /// 000 067 003 A3.4 0 0
2019 Sep 21 /// 000 068 006 A3.7 0 0
2019 Sep 22 /// 000 068 004 A3.5 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
NONE

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Website http://www.sidc.be.

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