A night of the shy aurora

/ 2017-12-05

Yesterday, we posted that a G2 (moderate) geomagnetic storm watch was in place for 04-05 December. This storm watch was issued by the National Oceanic and Atmospheric Agency who are responsible for space weather forecasts in the US, and was the result of a recurrent coronal hole. This coronal hole was the source of a high speed stream of solar wind that gave us UK aurora sightings back at the start of November. With a G2 storm, we expect that aurora may be visible from across swathes of the northern UK – local conditions permitting.

Local conditions

This is always a problem for the UK. Even the best aurora display can be scuppered by bad weather and a bright moon. Both of which we had last night. Cloud covered much of the north of the UK and we were only one night past a “super moon”. But all was not lost, some clear patches were to be found – especially on the north East coast.

Where was the aurora seen from?

Unfortunately, last night wasn’t quite what we’d hoped for. Activity levels did not reach G2 storm levels, though they did reach G1 (minor). More on that below. We issued a yellow alert at 7:30pm last night from our Crooktree magnetometer (and even a little earlier from our Shetland magnetometer) and this slightly elevated level was recorded for the next few hours. With a yellow alert, we expect that aurora might be visible on camera from Scotland and perhaps the north of England.

Saltburn, north Yorkshire, England, UK

Stirling, Scotland, UK

Wooler, north Northumberland, England, UK

Whitley Bay (near Newcastle-upon-Tyne), England, UK

What happened to the G2?

A bit of bad timing unfortunately! As the graphs below show the solar wind just didn’t want to “play ball”. During the early evening we had a period of southward (negative) Bz but the solar wind speed was fairly low. When the solar wind speed started to increase (as a a result of that coronal hole), Bz flips positive. Not good! It then remains positive until around midnight – by which time the UK has started moving away from the brightest part of the aurora.

Solar wind/IMF data for 04-05 Dec 2017 from DSCOVR satellite. NOAA/NASA

So how about tonight?

Conditions at the moment are very good. Bz is mostly southward (though is flipping between northward and southward) and the solar wind speed is up. Aurora is very likely to be seen from our friends in the southern hemisphere (depending upon local conditions). If Bz can stay southward and the solar wind speed remains high until this evening, then we have a good shot at seeing the aurora here in the UK. The British Geological Survey, for example, are predicting active conditions for the next day or two:

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