- 3343 - SUNSPOTS - what have we learned? Until they understand the Sun much better, solar researchers still won’t be able to definitively connect the dots between climate on terra firma and the absence or abundance of sunspots on our nearest star.
--------------------- 3343 - SUNSPOTS - what have we learned?
- Solar observers have been trying to make sense of our yellow dwarf star’s increasingly puzzling sunspot cycles.
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- The Sun is supposed to follow 11-year cycles of minimum and maximum activity that should trace set patterns like clockwork, give or take weaker and stronger sunspot patterns, flares, and periods of coronal mass ejections.
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- But solar cycle 24 (2008), which began in 2008, and the predictions for cycle 25 (2020), which commenced in 2020, have strange behavior.
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- The sunspot maximum of cycle 24 (2008), began almost a year late, looks to be the smallest in 100 years and the third in a trend of diminishing activity within sunspot cycles. 2020, last years cycle 25 (2020) likely could be smaller than cycle 24 (2008).
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- The leading solar polar magnetic field indicator in use for solar cycle 25 (2020) shows that the next cycle will be similar to the current 2021 cycle This indicator has been accurate for the last four cycles.
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- Astronomers cannot accurately forecast the level of solar activity much past the next maximum. The internal process that recycles and amplifies the magnetic field still is not well understood.
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- This year’s 2021 peculiar solar behavior raises questions for astronomers. Does the previous cycle hint at what the Sun has in store in the future? What can we expect for the next two or three solar cycles? Is Earth destined for a colder climate rather than a warmer climate?
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- cycle 24 (2008) was one of the weakest sunspot and magnetic activity cycles in more than a century. cycle 24 (2008) and probably cycle 25 (2020) could be part of a suggested 100-year cycle that appears in the solar sunspot record known as the “Gleissberg Cycle“.
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- Analysis of trends and magnetic field strengths does indicate that the upcoming sunspot minimum will be very low, and cycle 25 (2020) will also be about the same or even at lower activity than the current one.
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- Without a predictive theory for the physical process that generates the Sun’s magnetic fields, it isn’t clear what we might expect for the next few cycles. The subsurface flow fields would seem to indicate that cycle 25 (2020) will be even weaker than the current cycle, with fewer than 100 spots.
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- Cycles tend to grow bigger and bigger over five to six cycles and then become smaller and smaller over the following five to six cycles. The Sun is currently in a phase of declining activity.
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- What causes solar cycles? Solar cycles hinge on the creation of the Sun’s magnetic fields. These fields are triggered by the star’s internal differential rotation, the rotation of the solar atmosphere at different speeds, latitudes, and depths. The Sun spins more slowly at the poles than at its equator. Twisting or turning these magnetic fields within the Sun’s photosphere (visible surface) may, in turn, play a role in generating sunspots.
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- Astronomers believe solar magnetic fields are generated by dynamic flows of electrically conducting plasma in the Sun’s interior. This, in turn, generates electric currents that create the Sun’s active dynamo, responsible for generating magnetic fields.
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- Changes in differential rotation can weaken the solar dynamo. If the dynamo is weakened enough, it can spiral into what is known as a “Grand Minimum“. The best known of these was the so-called Maunder Minimum, a 70-year period of diminished solar activity from 1645 to 1715. During this time, observers often recorded no sunspots for years.
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- These days, the Sun is active, but unusual in its lack of sunspots. What could be causing this? cycle 24 (2008) resembles cycles 14 and 15 at the start of the 20th century. What drove the preceding series of strong cycles that we refer to as the Modern Maximum, which is generally thought to have begun with cycle 15 in 1914?
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- Throughout most of the 19th century, the number of sunspots tended to be a bit low. But from 1930 to 1990, the Sun seemed a bit more active than usual. The Sun’s current behavior is hardly unprecedented. The early part of the 20th century saw many weak cycles.
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- How are such sunspot cycles created? The cycle arises when the energy of the Sun’s internal plasma flows gets converted into magnetic energy. The Sun’s polar (north-south) magnetic fields, in turn, are built over the course of a cycle by the poleward transport of the magnetic field that emerges at the surface in active sunspot regions.
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- These north-south magnetic fields thread through the Sun’s convection zone, where differential rotation shears them out. This means the outer layers rotate faster at the equator and slower at the poles. These sheared fields become oriented east to west and become so strong that they emerge through the surface in active regions but with east-west polarities opposite to that of the previous cycle.
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- The strength of a cycle is determined by the strength of the Sun’s polar fields at the start of the 11-year solar cycle. The strength of these polar fields is determined by the strength and number of active regions that erupted during the previous cycle.
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- As stars age, their rotation slows via a process known as magnetic braking. The Sun has already entered into a new, unpredicted, long-term, more quiescent phase of its evolution.
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- This relatively quiet phase would play out over several hundred million years. The Sun’s short-term cycles will eventually disappear.
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- From studying stars of similar age and spectral type to our Sun, his team has concluded that for the most part, these solar analogs appear to have coronal X-ray and chromospheric activity and cycles similar to our Sun.
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- There are indications that the Sun is in a transitional phase of its magnetic dynamo activity, but [one] that is apt to last many millions of years. Models for the Sun’s convection zone dynamics coupled with the Sun’s current rotation rate tend to produce slower-rotating equators and faster-rotating poles.
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- A predictive theory for the nature and evolution of magnetic activity in the Sun and stars is incomplete. It‘s not yet clear how these weak cycles will affect climate.
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- The recent recalibration of the sunspot number makes it even clearer that the Sun’s effect on climate is minimal and limited to the 0.1 percent variation in the Sun’s luminosity (radiative output). This gives a small 0.1 degree centigrade change in global temperature far too small to produce a ‘Little Ice Age.’
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- But does the lack of sunspots affect climate at all? The only way he could see solar activity affecting global climate is via its effects on Earth’s upper atmosphere. During the solar cycle, the Sun’s luminosity varies by only 0.2 percent.
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- Solar X-ray intensity can vary by a factor of six to eight times while solar output in the far ultraviolet spectrum can vary by 20 percent over any given solar cycle. So if high-energy solar emissions affect Earth’s thermosphere and stratosphere via some unknown amplified feedback mechanism, this could affect the energy dynamics of Earth’s lower atmosphere, even to the extent of altering planetary circulation and inducing a small change in global temperatures.
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- What more can we do to figure this all out? State-of-the-art computing power is enabling more realistic solarlike physical parameters in computer simulations. The European Space Agency’s Solar Orbiter should lead to more accurate sunspot cycle forecasts.
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- Space missions such as Solar Orbiter, NASA’s Solar Probe Plus (launch in 2018), and ISRO’s Aditya-L1 mission (India’s first mission to study the Sun by 2020) are expected to contribute to this understanding.
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- What we really need is an expansion of observational work dedicated to recording the long-term and short-term nature of activity in a sample of stars that closely resemble the Sun. Then we need a complementary sample of stars that is different from our Sun in the key parameters that theorists need to test their models of the Sun’s magnetic field generation and evolution.
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- This would help researchers understand the relative importance of certain physical parameters such as solar rotation, convection zone depth, the Sun’s effective temperature, and its age or evolutionary status.
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- The Sun’s convection zone ranges from about 124,000 miles in depth up to the photosphere, where photons are created. We need more modeling work on the dynamics of the Sun’s convection zone and the effects of the Sun’s rotation on those dynamics. Solar Orbiter will reveal the details of the Sun’s subsurface convection zone dynamics.
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- Climate physicists and climate modelers have concluded that the impact of solar variations on global temperature change in the past few decades is far less than that due to anthropogenic factors ( man created).
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- Until they understand the Sun much better, solar researchers still won’t be able to definitively connect the dots between climate on terra firma and the absence or abundance of sunspots on our nearest star.
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- Here are some observations that were collected:
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- The year 2013 is called the Sunspot Maximum because in this year, the sun produces
more sunspots and solar storms than any other time in its 11-year cycle.
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- The year 2009 was called Sunspot Minimum with the fewest number of sunspots
counted during each month. For each month in 2009, the average number of sunspots
counted was 2, 1, 1, 1, 3, 3, 4, 0, 4, 5, 4, 11. Sunspots counted for the first 4 months of 2013, the average monthly numbers are 63, 39, 58, 72.
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- The average number of sunspots counted in 2009 rounded to the nearest integer (2+1+1+1+3+3+4+0+4+5+4+11)/12 = 39/12 = 3.25
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- The average number of sunspots counted in 2013 rounded to the nearest
integer? (63+39+58+72)/4 = 58 sunspots
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-------------------------------- January………63
-------------------------------- February……..39
-------------------------------- March…………58
-------------------------------- April…………..72
-------------------------------- May……………63
-------------------------------- June……………74
-------------------------------- July……………..68
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- The average for the first seven months is then (63+39+58+72+63+74+68)/7 = 62.4 . We get 62 sunspots.
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- November 16, 2021 SUNSPOTS - what have we learned? 3343
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--------------------- --- Friday, November 19, 2021 ---------------------------
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