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Daily bulletin on solar and geomagnetic activity from the SIDC

Emesso: 2017 Sep 05 1230 UTC

SIDC Forecast

Brillamenti solari

M-class flares expected (probability >=50%)

Geomagnetism

Major (ISES: Severe) magstorm expected (A>=100 or K>=7)

Protoni solari

Proton event in progress (>10 MeV)

	10cm flux	Ap
05 Sep 2017	160	015
06 Sep 2017	150	091
07 Sep 2017	140	075

Bulletin

Solar activity was at high levels with Catania group 46 (NOAA active region 2673) producing several (10) M class flares. The strongest flare was an M5.5 flare peaking at 20:33UT. This region continued to grow and develop in complexity. It contains strong mixed polarity field and further M class flares are expected from this region with also a potential for an X class flare. Associated to the M5.5 flare a full halo CME is visible in SoHO LASCO C2 images. The images show a first ejection front from 19:00 UT onwards which is predominantly directed towards the South West. From 20:36UT an additional front is first visible in the South but it expands to a full halo CME afterwards. These are probably two separate eruptions but both are related to the activity in Catania group 46 (NOAA Active region 2673). The second eruption can be related to the dimming seen to the East of the region ahead of the M5.5 flare. Analysis of the coronagraph data indicates that the projected speed of the first ejection measures between 500 and 1000 km/s while the projected speed of the second faster ejection is close to 1500km/s. Based on the drag based model, arrival of the associated CME shock front can be expected around UT noon September 6. As a result of the M5.5 flare and the associated CME initiation, the >10MeV proton flux levels started rising from around 23:00UT passing the event threshold level of 10pfu at 00:40UT. A maximum of just over 100 pfu was reached around 7:20UT, after which a slow recovery seemed to have set in. However, just recently levels increased over 100 pfu again. The higher energy (>50 Mev) proton fluxes have shown little or no increase. If further strong activity persists in Catania group 46, further and renewed increases in proton flux levels are possible.

Solar wind conditions somewhat unexpectedly became increased again. Yesterday afternoon, total magnetic field climbed to values of up to 9nT with Bz variable but seeing peaks down to -7nT. After midnight, total field recovered to nominal values below 4nT. Solar wind speed showed a steady increase towards peak values of over 600 km/s around 1:20UT, before declining slowly to current values of around 530 km/s. The slow decline is expected to continue until tomorrow September 6 UT noon, when a shock related to yesterdays CME is expected to arrive, with Solar wind speed expected to reach 800km/s. Geomagnetic conditions were quiet to active (local K Dourbes 1-4) with even an isolated minor storming episode (NOAA Kp reached 5 for the 0-3UT period) in response to the enhanced solar wind conditions. Initially unsettled conditions are expected until the arrival of yesterdays CME, tomorrow September 6 UT noon, which is expected to cause some geomagnetic storming. Storm levels may reach major or possibly severe levels.

Today's estimated international sunspot number (ISN): 129, based on 14 stations.

Solar indices for 04 Sep 2017

Wolf number Catania	125
10cm solar flux	183
AK Chambon La Forêt	034
AK Wingst	019
Estimated Ap	021
Estimated international sunspot number	121 - Based on 26 stations

Noticeable events summary

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

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