A small but interesting southern hemisphere coronal hole is facing our planet today.
While this coronal hole is fairly small, a quick look at the solar wind data from STEREO Ahead shows us some surprising numbers. The solar wind stream from this coronal hole arrived at STEREO Ahead late on 20 August and pushed the total strength of the interplanetary magnetic field (Bt) to almost 20nT. Even the Bz briefly dipped as low as -15nT. Impressive for such a small coronal hole. This was caused by the Co-rotating Interaction Region (CIR) which forms ahead of the high speed solar wind stream. The high speed solar wind stream itself reached a speed of about 600km/s on 21 August. Respectable numbers and that is good news for high latitude sky watchers here on Earth. It is expected that this coronal hole solar wind stream arrives at Earth on Tuesday, 27 August. Active geomagnetic conditions (Kp4) seem very much possible with these numbers either late on 27 August or on 28 August.
Sharp eyes see that another coronal hole is starting to rotate into view behind this coronal hole. That coronal hole should face Earth next week. The coronal hole solar wind stream from this second coronal hole arrived today at STEREO Ahead and also show us some promising numbers but more on that next week. All in all, we are in for a double coronal hole solar wind stream arrival next week. Interesting developments for high latitude sky watchers to keep an eye on.
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