Aurora Alert! There is a very good chance of the aurora appearing this week, and it may be around for a few days too.
**Update March 15 AM: Bt is now 9 and the Bz -6 so the conditions are OK for a fairly weak aurora to appear **
The reason being an elongated “coronal hole” is now facing the earth allowing the solar wind to escape the sun. Given its elongated shape and location in the centre of the solar disk, it could very well result in a couple of days, or longer, of auroras here on earth.
How definite is this?
Of course, there is no actual guarantee as lots of other things also need to go right (clear skies this week will of course be important!) but given the relative quiet on the aurora front over the last year or more, this week is certainly looking good and it will be well worth keeping an eye on the gauges.
Gauges, what gauges?
The gauge to watch is the Bt and Bz. Spaceweather always has this information displayed in the left hand column, under the planetary K-index, and under the heading “Interplanetary Magnetic Field”. Without going into the details too much, basically what we want for an aurora to appear is a Bz that is strongly negative eg -10 ~ -20.
The Bt determines this in that the value of the Bz (either positive or negative) can not be greater than the value of the Bt. So if the Bt hits 10~20+ then there is a real chance of an aurora appearing – so long as that Bz value goes negative. If on the other hand the Bt value is around 4 or 5, there is no real chance of anything happening.
Click here for some photos of the aurora which appeared in October 2015 due to a coronal hole.