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Yesterday I saw online a lot of people seeing auroras both in the North and in the South of the globe. Unfortunately, I wasn't one of these people, and this got me curious about how much we can predict solar activity and the appearance of auroras on Earth. For example, I know we can make accurate predictions of eclipses, and weather forecasts on Earth are very common (within limitations).

In short, can we predict the appearance of auroras on Earth? If so, how good are these predictions?

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    $\begingroup$ Somewhat possible, because auroras maps to solar wind activity, but it's not trivial so seems that auroras can be forecasted now just for $\pm 3$ days. $\endgroup$
    – Agnius Vasiliauskas
    Commented May 11 at 19:53
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    $\begingroup$ @AgniusVasiliauskas I am curious how forecasting past events works (the "-3" part of $\pm3$ you cited). Wouldn't it just be looking at past records? $\endgroup$
    – Kyle Kanos
    Commented May 11 at 20:23
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    $\begingroup$ aurorawatch.lancs.ac.uk $\endgroup$
    – ProfRob
    Commented May 11 at 20:29
  • $\begingroup$ @KyleKanos With $\pm 3$ I meant that it may even be less than 3 days, maybe just 2. Agree, I should wrote $2~ \text {days} \pm 1 \text {day}$. $\endgroup$
    – Agnius Vasiliauskas
    Commented May 11 at 21:04
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    $\begingroup$ Yes, see swpc.noaa.gov $\endgroup$
    – honeste_vivere
    Commented May 13 at 13:18

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Approximately yes, as follows.

Ham radio guys monitor solar activity closely because of the effects that it has on radio communications on earth. In this context, large numbers of sunspots are well-correlated with favorable conditions on earth for long-distance radio contacts- and the connecting mechanism is that large numbers of sunspots are correlated with the occurrence of mass ejections of charged particles from the sun. Those charged particles energize the layers of the atmosphere responsible for deflecting radio beams back to earth, thereby allowing them to carom back and forth between the earth's surface and the ionosphere and thereby circle the globe.

So you can estimate the prevalence of intense auroral activity with sunspot count.

That said, we are now at the maximum in the current 11-year sunspot cycle, which makes the coronal mass ejection responsible for last night's aurora an usual event, and demonstrates the utility of predicting auroras on the basis of sunspot count.

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    $\begingroup$ Probably a typo, but we are currently at the maximum of the sunspot cycle, which makes sunspots, solar events, coronal mass ejections, and corresponding auroras on Earth a quite usual event. $\endgroup$
    – Martin
    Commented May 13 at 1:36
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    $\begingroup$ OMG the article on wkikpedia says the peak happened in 2013 and we are now at minimum!!! will correct immediately. -NN $\endgroup$
    – niels nielsen
    Commented May 13 at 2:45
  • $\begingroup$ @nielsnielsen I think there was indeed a peak in 2013, but the solar cycle is about 11 years long, so we should be at a peak again $\endgroup$
    – Níckolas Alves
    Commented May 13 at 3:41
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One way to estimate the likelyhood of auroras is to look at the cosmic radiation on Earth. There are plenty of neutron monitors worldwide which count the number of cosmic particles and provide near-real time data on nmdb.eu.

enter image description here

At the start of last weekend, we saw the number cosmic particles going down ~15%. This was caused by a solar plasma cloud ejected from the sun which, once near Earth, shields away galactic particles with its magnetic fields. The corresponding drop of the count rate on Earth is called "Forbush Decrease", which usually restores during 1-3 days while the plasma cloud passes the Earth.

Since the plasma is causing auroras on Earth, we can often see strong and low-latitude auroras during these solar events.

This time, we are experiencing an extraordinary plasma cloud from the sun. The drop has not been significantly restored for more than 48 hours. This shows that the plasma cloud might be huge and is still present in the vicinity of Earth. This time, it takes extremely long for the cloud to pass by. A truely unusual event!

As you can watch the neutron monitor data live, you can make a good guess from the data whether auroras could be expected. Since the count rates are still extremely low, it would take several more days for it to fully restore. Hence, we will probably see auroras in the next nights, too. Good luck!

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