Monday, June 20, 2011

Solar Activity May Be Lessening In A Dramatic Way.

Coronal mass ejections (CMEs)

June 17-19: No obviously earth directed CMEs were observed.

Coronal holes

Coronal hole history (since late October 2002)Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago
A recurrent coronal hole (CH457) in the southern hemisphere will be Earth facing on June 19-20. A coronal hole (CH458) in the southern hemisphere was Earth facing on June 16.
The above coronal hole map is based on a new method where coronal holes are detected automatically. The method may need some fine tuning, however, it has significant advantages over detecting coronal holes manually. The main improvement is the ability to detect coronal holes at and just beyond the solar limbs. Early results using this method for SDO images over a span of several weeks indicate a good match between coronal holes observed over the visible disk and their extent and position at the east and west limbs. Note that the polar coronal holes are easily detected using the new method, the extent and intensity of both holes are consistent with other data sources.

A graphical comparison of solar cycles 21, 22, 23 and 24

Solar cycle 24 has initially displayed much less activity than recent cycles. Based on statistical models the monthly smoothed sunspot number is likely to peak between 50 and 70 in 2013. Models based on solar polar magnetic field strength indicate the peak could occur as early as in 2012. The comparison with recent cycles is interesting to track the development of cycle 24.  The X axis in the chart is the number of months since the cycle started, while the Y axis is the monthly smoothed sunspot number.
Chart color overview
CycleMonthly smoothed sunspot number
  • Cycle 21 started in June 1976 and lasted 10 years and 3 months.
  • Cycle 22 started in September 1986 and lasted 9 years and 8 months.
  • Cycle 23 started in May 1996 and lasted 12 years and 6 months.
  • Cycle 24 started in December 2008.
Please note that the start dates for each cycle is calculated using the 13-month smoothed monthly mean sunspot number. One advantage of using this statistical (numerical) approach is that the start month of a solar cycle is the same as the month of the solar minimum. It is possible to use other criteria to separate solar minimum and the start of a solar sunspot cycle, however, which criteria to use and how much importance each is given, unfortunately leaves room for individual opinion.
[Solar Terrestrial Activity Report] [Solar Cycles 1-20]

Sunspots Suggest a Drop in Solar Activity

Results from three separate studies indicate that the sun could be less active in its next cycle. While the relationship between solar activity and climate is still a matter of scientific debate, some scientists say this could slow down the warming trend on Earth.
The results of the studies were announced on Tuesday at the annual meeting of the American Astronomical Society’s solar physics division.
“This is highly unusual and unexpected,” Frank Hill, associate director of the National Solar Observatory’s Solar Synoptic Network, told “But the fact that three completely different views of the sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.”
All three studies suggest an upcoming period of less solar activity than the typical 11-year cycle of solar activity would suggest. One indicator was the number and frequency of sunspots, which are caused by intense magnetic forces. Others included the magnetic strength of those sunspots and patterns in a gas stream under the surface of the sun.
Scientists say the sun’s activity will peak in about 2013, reports MSNBC, but that the indicators from the studies point to an extended period of low activity after that.
The sun had a similar period, between 1645 and 1715, that coincided with lower temperatures on Earth. That period on Earth is known as “the Little Ice Age.”

Major drop in solar activity predicted

Three different lines of research indicate that the coming solar maximum could be the last we’ll see for a few decades.
By National Solar Observatory, Sunspot, New Mexico — Published: June 14, 2011
Mobile "jet streams" in the Sun migrate from the poles toward the equator as the solar cycle progresses. At left (solar minimum) the red jet streams are located near the poles. At right (solar maximum) they have migrated close to the equator. The jet streams are associated with the locations where sunspots emerge during the solar cycle, and are thought to play an important role in generating the Sun's magnetic field.
Photo by F. Hill, et al. (GONG/NSO/AURA/NSF)
A missing jet stream, fading spots, and slower activity near the poles say that our Sun is heading for a rest period even as it is acting up for the first time in years, according to scientists at the National Solar Observatory (NSO) and the Air Force Research Laboratory (AFRL).

As the current sunspot cycle, Cycle 24, begins to ramp up toward maximum, independent studies of the solar interior, visible surface, and the corona indicate that the next 11-year solar sunspot cycle, Cycle 25, will be greatly reduced or may not happen at all.

“This is highly unusual and unexpected,” Frank Hill, associate director of the NSO’s Solar Synoptic Network, said of the results. “But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.”

Spot numbers and other solar activity rise and fall about every 11 years, which is half of the Sun’s 22-year magnetic interval, because the Sun’s magnetic poles reverse with each cycle. An immediate question is whether this slowdown presages a second Maunder Minimum, a 70-year period with virtually no sunspots between 1645 and 1715.

Hill is the lead author on one of three papers on these results being presented this week. Using data from the Global Oscillation Network Group (GONG) of six observing stations around the world, the team translates surface pulsations caused by sound reverberating through the Sun into models of the internal structure. One of its discoveries is an east-west zonal wind flow inside the Sun, called the torsional oscillation, which starts at mid-latitudes and migrates toward the equator. The latitude of this wind stream matches the new spot formation in each cycle, and successfully predicted the late onset of the current Cycle 24.

“We expected to see the start of the zonal flow for Cycle 25 by now,” Hill explained, “but we see no sign of it. This indicates that the start of Cycle 25 may be delayed to 2021 or 2022, or may not happen at all.”

In the second paper, Matt Penn and William Livingston see a long-term weakening trend in the strength of sunspots, and predict that by Cycle 25 magnetic fields erupting on the Sun will be so weak that few if any sunspots will be formed. Spots are formed when intense magnetic flux tubes erupt from the interior and keep cooled gas from circulating back to the interior. For typical sunspots, this magnetism has a strength of 2,500 to 3,500 gauss (Earth’s magnetic field is less than 1 gauss at the surface); the field must reach at least 1,500 gauss to form a dark spot.

Using more than 13 years of sunspot data collected at the McMath-Pierce Telescope at Kitt Peak in Arizona, Penn and Livingston observed that the average field strength declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They also observed that spot temperatures have risen exactly as expected for such changes in the magnetic field. If the trend continues, the field strength will drop below the 1,500 gauss threshold and spots will largely disappear as the magnetic field is no longer strong enough to overcome convective forces on the solar surface.

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