Winter 2008 Issue

Cycle 24 Begins!

Has sunspot Cycle 24 finally begun? Here KH6/K6MIO follows up on his article in the Fall 2007 issue of CQ VHF with a report on what seems to be the positive indicator that the new cycle has begun.

By Jim Kennedy, KH6/K6MIO

An NSO solar magnetogram from December 18, 2007 shows the magnetic pair 30N-145. Note its position in the dateline in figure 1. (Credit: NSO/AURA/NSF)

Six-meter devotees have anxiously been awaiting the peak years of solar Cycle 24 and the return of good ionospheric DX conditions. In December 2007 and January 2008 we saw the first solid indications that Cycle 24 is beginning to rev up.

At the end of one cycle and the beginning of the next cycle, there is a period of time when the two cycles overlap. Magnetically active regions and associated sunspots from both cycles are seen on the sun at the same time.

Sunspots always appear as pairs in active regions. Powerful dipolar magnetic fields connect the leading and following spot in each pair, giving the pair a characteristic magnetic polarity. In one of the sun’s (north/south) hemispheres, the field will point outward from the leading spot and inward to the following spot, and in the other hemisphere it will be exactly the opposite—inward to the leading spot and outward from the following spot.

These characteristics make it possible to readily tell the difference between the old-cycle and new-cycle regions:

1. Old-cycle spots are near the equator, with their spot-pair polarities opposite in the Northern and Southern Hemispheres.

2. New-cycle spots are near 30° north and south latitudes, with north and south polarities that are reversed from that of old-cycle pairs.

The beginning of each new cycle is indicated by the sustained appearance of these 30° latitude, reversed-polarity magnetic active regions, often with spot pairs or groups.
There was a brief appearance of a small reversed-polarity spot pair near 30° south in July 2006, but it vanished almost immediately. It was a fluke; nothing further was seen for 17 months.

That changed on December 11, 2007, when an already-formed reversed-polarity active region pair rotated over the limb into view. While no actual sunspots formed, the magnetic structure was clear. The system grew in size for a few days and then began to diminish and rotated out of view on the 23rd. Then, on January 2, 2008, another reversed-polarity magnetic region (981) emerged and produced a small sunspot group. This was a second, distinct region and not a recurrence of the December group (see figure 1).

Since Northern Hemisphere activity has preceded that of the Southern Hemisphere for the last few cycles, and now two reversed-polarity northern groups have been seen, this is a good indication that Cycle 24 is finally arriving.

At this writing (early January), the Ri sunspot index has been very low (<12) since June 2007. It appears that solar minimum is very near, but may not have occurred yet. This would seem to eliminate all but three of the professional Cycle 24 predictions discussed in my previous article1, as the others called for much earlier minimum dates.
 

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