The interior of the Sun holds the key to predicting the strength of each solar cycle. Internal magnetic fields are twisted up and wrapped around the Sun due to the Sun's differential rotation. These fields are thought to be what gives rise to the formation of sunspots and related space weather activity.
05 March 2005 | The latest research results by Drs. Leif Svalgaard, Yohsuke Kamide at the Solar-Terrestrial Environment Laboratory, Nagoya University (Japan) and Edward W. Cliver at the Space Vehicles Directorate, Air Force Research Laboratory, Hanscom Air Force Base (Massachusetts) suggest that the Sun may be less active during the next solar cycle than it has been during the last 100 years.
These results are based upon one of the most successful solar cycle prediction methods in existence. The "Precursor Method" is capable of predicting the magnitude of the next solar maximum up to about 7 years before the solar maximum occurs. This is possible by examining the strength of the magnetic fields that congregate in the polar regions of the Sun a few years before the solar minimum of each solar cycle and relating the strength of those fields to the observed sunspot numbers during the next solar maximum. The polar magnetic fields provide the "seed" magnetic flux necessary to drive the sunspot activity during the next solar cycle.
The most recent findings by Dr. Svalgaard et al. are based on only the first of three years of data during the current decline of solar cycle 23. At least two more years of data (through the solar minimum) are required to provide a more accurate prediction. Nevertheless, sufficient data is now available to make an initial reasonable prediction. They predict that the next solar maximum (the time during which the proliferation of sunspots is greatest) will be associated with a sunspot number of only 75, with an error of ± 8. If this prediction holds true, the next solar cycle (cycle 24) will peak around the year 2011 with a sunspot number that is lower than any previous solar cycle since cycle 14 when the observed sunspot number peaked at a value of only 64 in 1906.
What is the significance of this prediction, assuming it holds true? Sunspots are a source of eruptive phenomena such as solar flares. Energetic coronal mass ejections are also related to the occurence of solar flares. And coronal mass ejections can produce hazardous space weather conditions to spacecraft, aircraft and power grids. One would think that a lower sunspot number would be good news for these industries. Overall average space weather effects may indeed be a bit milder. But these industries are more adversely affected by the few extreme solar outbursts that occur during the solar cycle than they are during the less volatile "average" conditions observed during the solar cycle. Svalgaard et al. are quick to point out that some of the most intense space weather storms have occurred during solar cycles having low sunspot numbers. For example, two of the eight most intense geomagnetic storms during the last ~150 years occurred during solar cycle 14, while three of the five strongest energetic proton events at greater than 30 MeV since 1859 occurred during solar cycle 13 when the peak sunspot number plateaued at only 88. The scientists note that the next solar cycle could prove to be an excellent test-bed for a number of models and theories concerning the solar cycle and solar activity.
A direct measure of the strength of the solar polar fields will be possible during 2007-2008 when the Ulysses space probe will make another pass over the solar poles. Dr. Svalgaard and his colleagues fully expect the strength of the polar fields measured during these polar passes will be significantly smaller than the strength of the fields that were observed during the polar passes of 1994 and 1995 during the minimum phase of the last solar cycle. This would help validate their prediction of a much smaller solar maximum during the next solar cycle than has been observed in recent memory.
This research was published in the Geophysical Research Letters, volume 32 on 11 January 2005 (L01104, doi:10.1029/2004GL021664, 2005) by the American Geophysical Union.
Leif Svalgaard, Edward W. Cliver, and Yohsuke Kamide (2005), Sunspot cycle 24: Smallest cycle in 100 years?, Geophys. Res. Lett., 32, L01104, doi:10.1029/2004GL021664, 2005.
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