The First Signs of Solar Cycle 25

On 20-Dec-2016 a USET observer saw a small patch of magnetic field in the southern hemisphere of the Sun. The outward magnetic field (white in the magnetograms) was behind the inward field (black patches). This patch is circled in blue in the HMI magnetogram. This high-latitude region (23°S) did not follow the pattern of magnetic field seen in Solar Cycle 24. George Hale noticed that sunspots tended to have a definite pattern of their magnetic field. One hemisphere has the patch of inward field leading the outward. The other hemisphere has the opposite pattern. During the next sunspot cycle the hemispheres reverse patterns.

The arrows in the magnetogram point to magnetic fields that follow Hale’s law for Solar Cycle 24. The blue arrows point to areas that show the pattern for the northern hemisphere and the single red arrow the southern. Even the broad areas of magnetic field in the northern hemisphere follow this pattern.

The magnetic field in the patch of magnetic field in the blue circle has the black leading the white — a sign that it is related to Solar Cycle 25, especially because it is at higher latitudes than most of the sunspots seen around this time. This is another pattern in sunspots. They tend to appear at higher latitudes early in a cycle and appear at ever-lower latitudes as the cycle progresses.

So, this little patch of magnetic field has two reasons to be the “First Sunspot of Solar Cycle 25.” It only needs to be seen as a sunspot and assigned an Active Region number.

The first observer notified other members of USET and one of them went and looked at the Sun. There was a small sunspot where the patch of magnetic field was seen. It was assigned the number AR 12620. It is the small black dot above the label in the orange HMI continuum image. Only one of the four other patches of magnetic field in the magnetogram was also visible as a sunspot (AR 12619). Looks like we have a winner!

Why mention this now? Because Sam Freeland saw another high-latitude (31°S), reversed-polarity patch of magnetic field in the southern hemisphere on 8-Apr-2018 (top panel of picture, the brightest area is the corona above the magnetic patch in an AIA 193 Å collage). This time the patch appeared and faded without forming a sunspot and did not receive an active region number. But Freeland saw a small flare at 12:57 UTC on 9-Apr-2018. This A2.5 flare may also be visible as a small blip in the GOES 14 X-ray flux (bottom panel, arrow points at blip).

Each Solar Cycle overlaps with the ones before and after. We study this overlap in our quest to understand the solar magnetic field and the dynamo that creates it. Our modern data, especially the full-disk magnetograms, makes looking for these overlapping regions a little easier.

As solar minimum draws near, we will see fewer sunspots but more and more of them will have the properties that put them into Solar Cycle 25. Eventually, solar minimum will be reached and after that sunspots associated with Solar Cycle 25 will become the majority. That should happen in 2020.

It is good to see that solar activity will continue to fascinate us in Solar Cycle 25.