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Product: Daily Forecast of Geomagnetic Activity
Issued: 2025 September 21 06:50UTC
Prepared by the Athens Space Weather Forecasting Center
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I. Solar activity
--Current Status
Solar Flux (10.7cm) measured on 20.09.2025 at 23:00 UTC was 166 sfu.
The background X-Ray flux is at the class C1.6 level.
No obviously Earth directed CMEs were observed in available LASCO imagery on September 17-19.
A coronal hole (CH1317) at northern hemisphere will become Earth facing on September 19-21.

II. Solar Energetic Particle Events
Protons fluxes are quiet.
The greater than 2 MeV electron flux at geosynchronous orbit maintained at minor storm levels.

III. Interplanetary and Geomagnetic conditions
The solar wind speed measured by ACE satellite reached the max value 362 Km/s on September 21 at 07:50 UT during the last 24 hours.
The solar wind speed from STEREO A was detected 400 Km/s during the last 24 hours.
The vertical component of IMF Bz reached the max value -2 nT on September 21 at 03:30 UT during the last 24 hours.
The geomagnetic field was at quiet levels during the last 24 hours.
The Kp index now is at quiet levels with Kp=1.

IV. 3-day Geomagnetic Activity Forecast
The geomagnetic field is expected to be at quiet to active levels on September 21, at quiet to minor storm (G1) levels on September 22 due to the effect of the coronal hole high speed stream and at quiet to unsettled levels on September 23.

Date	Ap index forecast	Geomagnetic Activity level	
21.09.2025	12	Quiet to Active	
22.09.2025	20	Quiet to Minor storm (G1)	
23.09.2025	10	Quiet to Unsettled	

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Athens Space Weather Forecasting Center
Physics Department, National & Kapodistrian University of Athens
Athens Neutron Monitor Station A.NE.MO.S
Tel.: +30 210 727 6901
email: spaceweather@phys.uoa.gr
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