All posts by Charles Baldridge

Charles Baldridge a data scientist with a passion for studying space weather and chasing the northern lights. He has been lucky enough to see aurora in person on multiple occasions in his hometown of Burlington Vermont.

How to Identify a Solar Cycle 25 Active Region

Northern Lights Now – Late 2019 and early 2020 mark the depths of the solar minimum and the transition from solar cycle 24 (SC24) to solar cycle 25 (SC25). During the transition, solar scientists watch active regions and identify them as part of the new cycle or the old cycle. Aurora hunters and space weather enthusiasts can follow along and track the progression of the solar cycle as there are more and more new cycle active regions.

Is this active region part of the new solar cycle?

Active regions that are part of the new solar cycle appear closer to the Solar North or South Poles – at higher latitudes – and they have reversed magnetic orientation from the ARs in the previous solar cycle.

Over the course of the cycle active regions appear progressively closer to the equator. At the turn of the solar cycle, new cycle ARs start appearing far from the equator. This can be seen in the Solar Cycle Butterfly Diagram from NASA below. Note the solar cycles are numbered on the lower graph, while the upper graph shows the latitude of the Sunspots at that time.

Butterfly diagram shows latitude of sunspots over the last 10 solar cycles
Butterfly diagram shows latitude of sunspots over the last 10 solar cycles

At the solar maximum of each solar cycle, the Sun’s polarity flips. At solar minimum, the orientation of active regions also reverses. For ARs, the flip means that the western most (leading) part of a active region in the new cycle will have the opposite polarity of the leading edge of ARs from the old cycle. That sounds complicated, so here is an example (click to zoom):

ARs from SC24 and SC25 compared to show the reversed polarity
ARs from SC24 and SC25 compared to show the reversed polarity

The example above shows two recent ARs from the current transition period. On the left is an HMI magnetogram image of AR 12723 from SC24 on Oct 30, 2018. On the right is an example from SC25, AR 12753 from around Christmas 2019. Notice that on the left image, blue and green indicating positive polarity are on to the West (right, leading) of the region while negative polarity represented as Red and Yellow are to the East. In the right image, Active Region 12753 from Christmas 2019 is from SC25. The polarity is reversed with yellow and red leading the way on the western flank of the active region. Also note that AR12753 is at a high latitude centered around 34 degrees south, while AR12723 is close to the solar equator.

In summary, Active regions can be identified as part of the new cycle if they meet these two criteria:

  • The AR should appear at a high latitude (closer to the pole), generally around 30 degrees.
  • It should have the reverse polarity from the previous solar cycle.

Happy Hunting!

Solar Cycle 25 Underway, First Activity Reported

Northern Light Now – The long absence of large solar flare activity may come to an end soon as solar cycle 25 active regions start to appear. The last C-class flare occurred on May 15, 2019 from active region 12741. In the 7 months since, there have been only 19 active regions numbered as the Sun has been in the depths of the cyclic solar minimum. For aurora hunters, the only source of activity has been from an occasional filament eruption and High Speed Streams originating at Coronal Holes. However, over the last several months there are indications that the next solar cycle is picking up and activity will return over the next year. Aurora hunters should start looking forward to the next season.

The Solar Cycle lasts about 11 years. During each cycle, activity increases for about five and a half years. The monthly count of active regions and sunspots visible on the Sun increases until Solar maximum. At maximum, the Sun’s polarity flips and activity slowly tapers back into solar minimum over the remaining five and a half years in the cycle. Currently, the Sun is in the least active part of this cycle and as a result there have been fewer and weaker aurora displays over the last year.

Chart Shows Active regions by month with solar minimum highlighted
Chart Shows Active regions by month with solar minimum highlighted

Solar Cycle 24 (SC24) started in January of 2008 and peaked in July of 2013 and is ending now. At peak, there were nearly 300 active regions numbered in 2013. There were only 22 new active regions numbered in 2019. There is normally an overlap between the end of one solar cycle and the beginning of the next. Of those 22 active regions numbered in 2019, only 17 actually belong to SC24, the other 5 are part of Solar Cycle 25.

When Will Solar Activity Increase?

By the start of the next northern hemisphere aurora season! Aurora hunters can expect the 6 to 9 months ahead to continue to have very low solar activity. During the minimum between SC23 and SC24 there were about 30 months with fewer than seven active regions numbered. In the current minimum, the last month with more than seven active regions identified was September of 2017 – or 27 months ago. This is an arbitrary threshold, but can prove useful when making an estimate. Projecting out and assuming the same length of solar minimum, May or June should be the first month with 7 newly numbered active regions of Solar Cycle 25.

While there won’t be much activity from CMEs originating at active regions, it will certainly be possible that there will be activity from coronal holes. Attentive space weather fans will have noticed over the last couple years that Coronal Holes are the primary driver behind aurora activity during solar minimum. It is possible there will also be activity from filament eruptions (link to what happened today). Overall, the frequency of storms should be about the same over the last 6 months as it will be over the next 6 months – that is to say, not much.

The frequency and magnetic complexity of SC25 regions will continue to increase. With each new region, the likelihood of the next C-class flare increases. Seasoned aurora hunters know that long duration C, M and X class flares are one of the keys to a good northern lights display. Of course, a more complex AR could develop at any time and produce an strong flare, it is just far less likely during solar minimum. So keep watching the data and keep watching the active regions.

Happy Hunting