Solar science expert Leif Svalgaard of Stanford University, makes a prediction of Solar Cycle 25 size: “Preliminarily it looks like a repeat of Cycle 24, or at least not any smaller.”
Svalgaard uses a technique that is based upon the dipole moment when the preceding Solar Cycle reaches the minimum. He used this technique for his prediction of Solar Cycle 24 sunspot number that turned out to be very close to what actually took place. He predicted Cycle 24 Sunspot numbers would be much smaller than Cycle 23 when at the same time most of the other forecasters were predicting a rerun of Cycle 23.
He made this preliminary prediction of the size of Solar Cycle 25 as part of his posting March posting: “HMI-WSO Polar Fields and Nobeyama 17GHz Emissions.”
The Sun has both a South and a North Polar magnetic field. These fields reverse during every Solar Cycle. When the two Fields cross the Sun’s equator, that approximates the period of maximum solar activity. Then the fields continue to separate as they migrate toward the Sun’s north and south poles respectively. The minimum solar activity, and the start of a new Solar Cycle is approximately described by the maximum dipole, meaning the time of maximum magnetic field separation. From this point the two solar fields begin to move back toward the equator as the new Solar Cycle begins to increase in activity.
The chart below shows North and South Polar Fields.
Chart courtesy of solen.info
Note how Solar Cycle 23 had a smaller spread between the North and South Polar Fields than the spread on Cycles 21 and 22. Svalgaard used this smaller spread to make his forecast of the size of Cycle 24.
Svalgaard shows the dipole value for Solar Cycles 22, 23, and 24 and 25.
Here is how to read the chart. Cycle 22 began in March of 1986, so the placement of the number “22” is located where that Cycle began. The chart below it has the dipole magnetic field reversed that as to allow the reader to make each of the polar fields charts easier to compare. If Svalgaard had not reversed the magnetic field, then the second chart from the top would have a descending line making comparison less obvious. The dipole at the end of Solar Cycle 21 and the start of Solar Cycle 22 was approximately 250 microTesla. That same point for the end of Cycle 22 and the start of Cycle 23 was approximately 200 microTesla. Svalgaard’s forecast of Solar Cycle 24 was based upon that point at the end of Cycle 23 and the beginning of 24 where the dipole was 100 microTesla. Much below the previous Cycles. His new comments indicate that the dipole at the beginning of Solar Cycle will probably be about the size of the previous one, say 100microTesla , so Cycle 25 should not be much different that Cycle 24.
A final chart to give you more prospective showing the familiar Solar Cycle’s activity as defined by the number of Sunspots.