Coronal hole faces Earth

Thursday, 3 May 2018 - 16:04 UTC

Coronal hole faces Earth

We've been in a very quiet space weather period for a while now but we have finally something interesting to report about! A transequatorial coronal hole is facing our planet today and sending a high speed solar wind stream towards us!

This coronal hole has been around for a while now and the last time it faced Earth, the solar wind stream flowing from this coronal hole caused active geomagnetic conditions which stands for a Kp of 4.

What should we expect this time around? To give us a clue on what to expect, we took a look at the solar wind data from STEREO Ahead. STEREO Ahead is a satellite monitoring the far side and it was inside the solar wind stream from this coronal hole around 27 April. The interplanetary magnetic field strength at STEREO Ahead increased briefly past 20nT and the north-south direction of the IMF (Bz) also peaked near -20nT for a short period. This was during the onset phase of the stream which we call a co-rotating interaction region where bunched up solar wind particles ahead of the solar wind stream arrives. The high speed solar wind stream reached solar wind speeds of over 600km/s a day later on 28 April.

Very decent numbers indeed that would've sparked nice aurora here on Earth. If we translate these numbers to a Kp-value we think minor G1 geomagnetic storm conditions are possible (Kp=5) when the solar wind stream arrives which will likely be this Sunday, 6 May. High latitude sky watchers at northern hemisphere locations might struggle with the short nights but if you are at a location where it still gets dark enough you might enjoy some nice aurora this Sunday. Southern hemisphere sky watchers are enjoying the longer nights right now so if the weather cooperates this will be a nice opportunity for sky watchers in Tasmania and southern New Zealand! Good luck!

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Current data suggest that it is not possible to see aurora now at middle latitudes
The density of the solar wind is moderate (22.75 p/cm3)

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