# How does the aurora brightness depend on the distance from the poles?

I checked a few sites about aurora: http://www.aurora-service.eu/aurora-school/all-about-the-kp-index/ https://www.swpc.noaa.gov/products/aurora-30-minute-forecast https://www.swpc.noaa.gov/products/3-day-forecast The 30 min forecast gives the probability of visible aurora on a grid, while the 3 day forecast gives only maximum Kp index. It is not clear what is the relationship between the brightness of the aurora and these values. For example if there is high probability for a certain coord in our grid, then does that mean that we will have a bright aurora with a good chance too, or does that mean that we will have a faint aurora, but we can be certain it will be there? The same is true for the Kp, they write that the higher the Kp the further we can see aurora from the poles, but they don't tell us if closer to the poles the brightness will raise with the Kp or it just stays the same. They don't tell anything about whether they calculated the daytime, moon phases, weather into the probability of visible aurora values or not (probably not). It looks really weird from scientific perspective that space agencies are using this kind of values without clear definition and units. Can anybody clarify what these values mean and what is the relationship between them? It would be nice to forecast both the brightness and the probability of the aurora with some sort of distribution for a certain coord, but maybe I ask too much...

• Looks like even scientists don't know what the Kp index means: sciencedirect.com/science/article/abs/pii/0032063363900746 Commented Dec 31, 2019 at 17:19
• I think citing a paper from the 60s is a bit misleading to use as evidence that scientists do not understand what a Kp index means. This is especially true since space plasma physics is only ~50 years old... Commented Jan 1, 2020 at 16:56
• @honeste_vivere You are right, I forgot to check the year. Commented Jan 1, 2020 at 18:50
• @honeste_vivere Thanks! I think I'll use the probability grid then and don't try to calculate the brightness. I guess only NOAA has the data to do that. Commented Jan 1, 2020 at 18:52
• There should be available Kp and AE indices through OMNIWeb via NASA's SPDF services. Commented Jan 1, 2020 at 20:42