All about the Kp index

Everything you need to know about the Kp number system
and viewing auroras at lower latitudes

 

The most important thing to know about aurora watching is the kp index. It is a scale of numbers between 0 – 9 known as the planetary index. Using this scale, it is easy to determine what kp number you need to have a chance of seeing auroras where you are. So look on the map, have a look which line and which corresponding kp number are on top of or just above your location. Remember this number, it will never change (well the magnetic poles are moving slowly each year so you may need to review it again in about 20 years).
Now when you check the aurora forecast page, you will know what kp number to look out for to be in with a chance of auroras where you live.

How the numbers work

The kp number system is just a scale of geomagnetic activity. It is not a plot map where you can definitely say auroras will be visible. But experience tells us where auroras are visible and at what point of the kp scale they were visible at. So we can plot a map and say for example, this place usually gets auroras when Kp6 level is met. And so on and so forth. But it is not exact. So we would recommend if the maps says you need kp6, then go out when it is Kp5, because you might get lucky.
The kp numbers start at 0 and as the geomagnetic (aurora) strength increases, so too does the kp number. So kp 0 being a very weak or none existent aurora, right through to 9 being a major geomagnetic storm with auroras likely in France and even Northern Spain.

Geomagnetic Storms

Geomagnetic storms are labelled G1 to G5. It is a period when there is strong to very strong geomagnetic activity due to a lot of build up in Earth’s magnetotail which causes magnetic reconnection and snap back to occur, this accelerates a lot of particles back towards earth (a natural particle accelerator if you will) which can spark really awesome northern/southern lights displays. As aurora chasers, geomagnetic storms are what we are always hoping for. Here is a table which converts the G into Kp.
G1 = Kp5
G2 = Kp6
G3 = Kp7
G4 = Kp8
G5 = Kp9

http://www.aurora-service.eu/aurora-school/all-about-the-kp-index/