James A. Marusek on solar cycle 24

“As of the end of October, the cumulative number of spotless days (days without sunspots) in the transition into solar cycle 24 now stands at 745. The transitions into Solar Cycles 16-23, referred to as “recent solar cycles” (years 1923 to ~2008), averaged 362 cumulative spotless days (with a range from 227 to 568 spotless days). Since the current transition now exceeds 568 spotless days, it is very clear that the sun has undergone a state change. The solar “Grand Maxima” state that has persisted during most of the 20th century has come to an abrupt end. The “old solar cycles” (SC 10-15, years 1856 to 1923) averaged 797 spotless days, over twice that of the “recent solar cycles”. Those solar cycle minimums ranged from 406 – 1028 spotless days. If this solar minimum ends soon then the upcoming solar cycle may be similar to these “old solar cycles”.

So far the sun continues to be fairly quiet. This solar minimum acts like the Energizer bunny. It just keeps going, and going, and going.

The Average Magnetic Planetary Index (Ap index) is a proxy measurement for the intensity of solar magnetic activity as it alters the geomagnetic field on Earth. It has been referred to as the common yardstick for solar magnetic activity. An Ap index of “4” was the lowest recorded monthly value since measurements began in January 1932.

Back in January 2009, David Archibald predicted the Ap index would hit a low in October 2009 with a value of “3”. Analysis from past solar cycles shows that the Ap index generally reaches its lowest value approximately a year after the solar sunspot minimum. So the question is how well did he do.

The Ap Index for last month, October, was “2” [correction: “3”]. That is really close in my book. The Ap index had been hovering near rock bottom for 11 months now. Beginning in November 2008, there have been 8 monthly readings of “4” along with 3 monthly readings of “5”. But this month the value broke through the glass ceiling and spawned the lowest AP monthly index value in the past 77 years. So with this transition into solar cycle 24, all the AP monthly records have been broken. The lowest single month value, two consecutive month value, three consecutive month value, etc. All of those records have fallen, swept away in this solar state change.

So what does this all mean? Well, the sun’s interplanetary magnetic field has fallen to around 4 nT (nano Tesla) from a typical value of 6 to 8 nT. The solar winds pressure is down to 50 year lows. And the heliospheric current sheet is flattening. All these changes allow high-energy galactic cosmic rays to penetrate deeper into our solar system. In 2009, cosmic ray intensities have increased 19% beyond anything we’ve seen in the past 50 years, when satellite measurements began. Greater numbers of galactic cosmic rays driving deep into our atmosphere cause greater cloud formation (through ionization) which then results in decreasing surface temperature on Earth. This is because low level clouds reflect sunlight back into space. This is why Northern and Southern hemispheres have experienced unusually cold winters during the past couple years. The influence of the sun’s magnetic field is a force to be reckoned with in natural climate change.

The sun exhibits great variability in the strength of each solar cycle. This variability ranges from extremely quiet “Grand Minima” such as the Maunder Minimum to a very active “Grand Maxima” such as the enhanced activity observed during most of the 20th century. A solar Grand Minima is defined as a period when the (smoothed) sunspot number is less than 15 during at least two consecutive decades. The sun spends about 17 percent of the time in a Grand Minima state. In the past, these periods caused great hardship to humanity and significant loss of life.

Solar Grand Minima events correspond to periods of dramatic natural global cooling. The Maunder Minimum (about 1645-1715 A.D.) and Spörer Minimum (about 1420-1570 A.D.) are two examples of recent “Grand Minima” events and each period has been referred to as a Little Ice Age. During the “Grand Minima” galactic cosmic ray fluxes were at least 200% to 300% higher than anything measured to date.

So each morning I turn on my computer and check to see how the sun is doing. Most days I am still greeted with the message “The sun is blank – no sunspots.”

James A. Marusek” From CCNet 3 November


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