Wednesday, 25 September 2019 - 17:16 UTC
A familiar coronal hole is facing our planet today. You might remember this transequatorial coronal hole because it faced our planet at the end of August and caused moderate G2 geomagnetic storm conditions on 31 August and minor G1 geomagnetic storm conditions on 1 and 2 September.
We do see that the coronal hole changed in shape quite dramatically during its trip around the far side of the Sun. It still covers an impressive area but it lost its T-shape. It does however now connect all the way up to the northern hemisphere polar coronal hole. Does that mean we should again expect moderate storm conditions? Perhaps... lets look at the data from STEREO Ahead to see what we should expect:
The NOAA SWPC has already issued a minor G1 geomagnetic storm watch in place for this Friday, 27 September which is very reasonable. We do expect this coronal hole solar wind stream to arrive during the second half of 27 September. STEREO Ahead shows a very decent magnetic field strength (Bt) at the onset of the solar wind stream near 20nT with a maximum southward deflection just below -10nT and solar wind speeds up to 700km/s during the peak of the high speed stream. This is not a guarantee that we see similar numbers at Earth but it gives us a great indication what to expect.
Based on the data presented to us by STEREO Ahead we conclude that minor G1 geomagnetic storm conditions are likely on 27 and 28 September, possibly on 29 September as well. Moderate G2 geomagnetic storm conditions cant be excluded for a short period on the 27th or 28th but don't be too surprised if we top out at minor G1 geomagnetic storm conditions. Keep your eyes on the sky this weekend and of course on your phone to see all the SpaceWeatherLive geomagnetic storm alerts pop up on your phone... providing you have our app installed of course! Haven't done that yet? What are you waiting for? Head over to your Android or Apple app store and download it now. Good luck!
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