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.
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):
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.
Northern Lights Now – There is a good chance for aurora activity later this week as twin CMEs were launch from a flare and a filament eruption launched at the interaction point of a pair of active regions on the Sun’s surface. The activity was nearly centered in the Earth strike-zone, the region that solar activity is most likely two impact Earth. The CMEs should arrive in quick succession on Wednesday and Thursday. SWPC has posted a two day long G1 geomagnetic storm watch, and noted “a chance for G2 (Moderate) conditions.” This means if the storms are oriented correctly, activity levels could reach KP=5 or higher.
Long acting Active Regions
Space forecasters have been watching the active regions responsible for the watch since April 11 during the last solar rotation. Between April 11 and April 18 AR 2738 maintained a stable beta orientation and minimal flaring as it traversed the disk. Just as 2738 was rotating off the Western limb, AR 2739 was developed and was numbered slightly to the East. These two active regions persisted and launched eruptions as they tracked across the far side of the Sun between April 19 and May 3.
One April 30, LASCO captured the signature of a large CME off NE limb from the region that had been AR 2738. This was an indication that there was a chance the region had held together and that it might continue flaring as it rotated into view. On May 3, AR 2740 (old 2738) was renumbered as it came into view on the East Limb. AR 2941 (old AR 2739) was numbered on May 6.
Northern Lights Now – It’s looking like the weekend of March 23-24, 2019 will be good for Aurora hunters! A C4 flare on the Sun launched March 20th sent CME directly towards Earth. As it arrives, aurora conditions should become active. In response, SWPC has issued a G2 geomagnetic storm watch.
This story will be updated, come back soon.
Here’s a timelapse showing the Solar Storm erupting off the surface of the Sun from SDO. You will see it at roughly 11:30 coming from the active region further to the west (rightmost).
You can find the most up-to-date forecast for geomagnetic activity on the NLN 3-day forecast page. As of the time of the initial post, activity is predicted to increase the second half of March 23 and continue into the 24th.