Archive for the ‘Solar physics’ Category


It’s not known exactly what factors govern this constant minimum, but this is an interesting finding as Phys.org reports.

Using more than a half-century of observations, Japanese astronomers have discovered that the microwaves coming from the sun at the minimums of the past five solar cycles have been the same each time, despite large differences in the maximums of the cycles.

In Japan, continuous four-frequency solar microwave observations (1, 2, 3.75 and 9.4 GHz) began in 1957 at the Toyokawa Branch of the Research Institute of Atmospherics, Nagoya University. In 1994, the telescopes were relocated to NAOJ Nobeyama Campus, where they have continued observations up to the present.

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Solar flare [credit: NASA]


Even though the current solar cycle (SC 24) is well-known for its relatively low level of sunspots, it can still produce surprisingly powerful bursts of ‘counter-intuitive’ activity, causing solar scientists to put their thinking caps on.

A series of rapid-fire solar flares is providing the first chance to test a new theory of why the sun releases its biggest outbursts when its activity is ramping down, says Science News.

Migrating bands of magnetism that meet at the sun’s equator may cause the biggest flares, even as the sun is going to sleep. A single complex sunspot called Active Region 2673 emitted seven bright flares — powerful bursts of radiation triggered by magnetic activity — from September 4 to September 10.

Four were X-class solar flares, the most intense kind.

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Sunspots [image credit: NASA]


One of the authors of the research says: “The results of our study show us that we have identified the governing parameters in our model”. Both climate and exoplanet research could benefit from the findings.

The Sun shines from the heavens, seemingly calm and unvarying. In fact, it doesn’t always shine with uniform brightness, but shows dimmings and brightenings, reports Phys.org.

Two phenomena alone are responsible for these fluctuations: the magnetic fields on the visible surface and gigantic plasma currents, bubbling up from the star’s interior.

A team headed by the Max Planck Institute for Solar System Research in Göttingen reports this result in today’s issue of Nature Astronomy. For the first time, the scientists have managed to reconstruct fluctuations in brightness on all time scales observed to date – from minutes up to decades.

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Something new for solar theorists to ponder. Of course the surface itself doesn’t have a uniform rotation speed – at the equator it rotates faster than it does at the poles. ‘The idea that the solar core could be rotating more rapidly than the surface has been considered for more than 20 years, but has never before been measured’.

The sun’s core rotates nearly four times faster than the sun’s surface, according to new findings by an international team of astronomers. Scientists had assumed the core was rotating like a merry-go-round at about the same speed as the surface, says Phys.org.

“The most likely explanation is that this core rotation is left over from the period when the sun formed, some 4.6 billion years ago,” said Roger Ulrich, a UCLA professor emeritus of astronomy, who has studied the sun’s interior for more than 40 years and co-author of the study that was published today in the journal Astronomy and Astrophysics.

“It’s a surprise, and exciting to think we might have uncovered a relic of what the sun was like when it first formed.”

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Credit: NASA


Extreme ultraviolet radiation (EUV) is perhaps an aspect of solar activity that gets less attention than it should. The authors make the interesting point in their introduction to the research article that ‘Although the total solar irradiance at Earth varies very little, the relative variance in the EUV is as large as the mean irradiance. This EUV light interacts with Earth’s thermosphere and stratosphere and may affect climate in a “top-down” process in regions such as northern Europe’.

A pair of researchers with Aberystwyth University in the U.K. has used data from NASA’s Solar Dynamics Observatory to learn more about how the sun’s corona behaves over differing stages of its 11-year cycle, reports Bob Yirka at phys.org.

In their paper published on the open access site Science Advances, Huw Morgan and Youra Taroyan describe attributes of the sun they observed over time and what they discovered about the “quiet corona” and its possible impact on us back here on Earth.

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Ilya Usoskin has kindly sent me the data for the new group sunspot number series he and his colleagues have published. I’ve done a rough and ready plot below. Excel file here in case you have problems wit the links below.

group-sunspot

Group sunspot number average value. Missing values given as zero

T. Willamo1, I. G. Usoskin2,3 and G. A. Kovaltsov4

1 Department of Physics, University of Helsinki, 00014 Helsinki, Finland
2 Space Climate Research Unit, University of Oulu, 90014 Oulu, Finland
e-mail: Ilya.Usoskin@oulu.fi
3 Sodankylä Geophysical Observatory, University of Oulu, 90014 Oulu, Finland
4 Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia

Received: 4 October 2016
Accepted: 6 March 2017

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One thing the Sun has in common with the planets is rotation. ‘Rossby waves, also known as planetary waves, are a natural phenomenon in the atmosphere and oceans of planets that largely owe their properties to rotation of the planet.’ – Wikipedia. New evidence shows these type of waves also exist on the Sun.

Our sun is a chaotic place, simmering with magnetic energy and constantly spewing out particles. Sometimes the sun releases solar flares and coronal mass ejections — huge eruptions of charged particles — which contribute to space weather and can interfere with satellites and telecommunications on Earth.

While it has long been hard to predict such events, new research has uncovered a mechanism that may help forecasting these explosions, reports ScienceDaily. The research finds a phenomenon similar to a common weather system seen on our own planet. Weather on Earth reacts to the influence of jet streams, which blow air in narrow currents around the globe. These atmospheric currents are a type of Rossby wave, movements driven by the planet’s rotation.

Using comprehensive imaging of the entire sun with data from the NASA heliophysics Solar Terrestrial Relations Observatory — STEREO — and Solar Dynamics Observatory — SDO — scientists have now found proof of Rossby waves on the sun.
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Quiet sun [image credit: NASA]


Solar variation influencing climate is suddenly plausible, say researchers. Who knew? Well, nearly everyone except climate modellers. Although they still mutter about human influence, the reality of the solar slowdown is starting to bite it seems. If as they suggest ‘A weaker sun could reduce temperatures by half a degree’ what might they expect from a ‘stronger sun’?

For the first time, model calculations show a plausible way that fluctuations in solar activity could have a tangible impact on the climate, reports Phys.org.

Studies funded by the Swiss National Science Foundation expect human-induced global warming to tail off slightly over the next few decades. A weaker sun could reduce temperatures by half a degree.
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Solar activity [image credit: NASA]

Solar activity [image credit: NASA]


A tough question on the face of it, but the researchers claim to have unearthed a ‘new type of solar event’ based on evidence from one tree (according to this report).
H/T oldmanK

Nagoya, Japan – An international team led by researchers at Nagoya University, along with US and Swiss colleagues, has identified a new type of solar event and dated it to the year 5480 BC; they did this by measuring carbon-14 levels in tree rings, which reflect the effects of cosmic radiation on the atmosphere at the time, as Scienmag reports.

They have also proposed causes of this event, thereby extending knowledge of how the sun behaves. When the activity of the sun changes, it has direct effects on the earth.

For example, when the sun is relatively inactive, the amount of a type of carbon called carbon-14 increases in the earth’s atmosphere. Because carbon in the air is absorbed by trees, carbon-14 levels in tree rings actually reflect solar activity and unusual solar events in the past.

The team took advantage of such a phenomenon by analyzing a specimen from a bristlecone pine tree, a species that can live for thousands of years, to look back deep into the history of the sun.
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Credit: Imperial College London

Credit: Imperial College London


A small team of researchers with the University of Hawaii, Ponta Grossa State University in Brazil and Stanford University has found what they believe is the reason that the surface of the sun rotates more slowly than its core, reports Phys.org.

In their paper published in the journal Physical Review Letters, the team explains how they used a new technique to measure the speed of the sun’s rotation at different depths and what it revealed about the speed of the sun’s outer 70km deep skin.

Scientists have known for some time that the surface of the sun spins more slowly than its interior but have no good explanation for it. In this new effort, the researchers were able to take a better look at what was occurring and by doing so discovered what they believe is the source of the slowdown.
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Petrified log at Petrified Forest National Park, AZ [image credit: Jon Sullivan / Wikipedia]

Petrified log at Petrified Forest National Park, AZ
[image credit: Jon Sullivan / Wikipedia]


They seem to base their estimates of the past solar cycle length on a study of only 79 years’ worth of data which is almost certainly too short for high accuracy, but the results are interesting nevertheless.

A pair of German researchers has found evidence in ancient tree rings of a solar sunspot cycle millions of years ago similar to the one observed in more modern times, reports Phys.org.

In their paper published in the journal Geology, Ludwig Luthardt and Ronny Rößler describe how they gathered an assortment of petrified tree samples from a region in Germany and used them to count sunspot cycles.

Scientists know that the sun undergoes a sunspot cycle of approximately 11 years—some spots appear, grow cooler and then slowly move toward the equator and eventually disappear—the changes to the sun spots cause changes to the brightness level of the sun—as the level waxes and wanes, plants here on Earth respond, growing more or less in a given year—this can be seen in the width of tree rings.

In this new effort, the researchers gathered petrified tree samples from a region of Germany that was covered by lava during a volcanic eruption approximately 290 million years ago (during the Permian period), offering a historical record of sun activity.
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Credit: cherishthescientist.net

Credit: cherishthescientist.net


We’ve ignored the early history and jumped in further on in this Space.com article about sunspots and the solar cycle. The astrophysicist author wonders if it will take another 400 years to figure out why the solar cycle (the period between magnetic reversals) is around 11 years on average. Maybe a few Talkshop posts could be helpful, dare we say?

What the heck was going on to cause these spots? In the early 1900s, a few key observations pointed astronomers and physicists in the right direction. For one, sunspot activity seemed to cycle every 11 years, from lots of sunspots to just a few-sunspots and back to lots of sunspots.

The cycle was even apparent during the weird “Maunder Minimum,” when there was very little activity in the 1600s (the term was coined much later). 

Then there’s the temperature. Sunspots look dark, but that’s only in comparison to the blazing solar surface around them; they’re cooler than the rest of the sun, but still ragingly hot in their own right.

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Tim writes,

Gerry Pease has just sent us this link to his arXiv astro-ph.SR paper, co-authored with Greg Glenn, entitled Long Term Sunspot Cycle Phase Coherence with Periodic Phase Disruptions. It details previously unrecognized sunspot cycle phase coherence data, sunspot cycle magnitude correlations, and planetary resonances that could have been very useful in the past to  astrophysicists attempting to predict sunspot cycles, if only they had not ignored the possibility of planetary causation:
https://arxiv.org/ftp/arxiv/papers/1610/1610.03553.pdf

-Gerry Pease

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Where to find Proxima Centauri [credit: Wikipedia]

Where to find Proxima Centauri [credit: Wikipedia]


Co-author Jeremy Drake said: “The existence of a cycle in Proxima Centauri shows that we don’t understand how stars’ magnetic fields are generated as well as we thought we did.” Let the head-scratching begin.

Observations confirm that the closest star to our solar system has a regular magnetic cycle similar to our Sun, reports Sky & Telescope.

With the recent discovery of a potentially habitable planet around Proxima Centauri, astronomers have been studying this star with renewed fervor. Part of their attention focuses on the star’s behavior. M dwarfs are notorious for their flares, and such stellar tantrums could be deadly for budding life on nearby planets.

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Solar flare erupting from a sunspot [image credit: space.com]

Solar flare erupting from a sunspot [image credit: space.com]


Researchers have unearthed a cause-and-effect conundrum for solar physicists, involving solar flares. Phys.org reports.

Solar physicists have long viewed the rotation of sunspots as a primary generator of solar flares – the sudden, powerful blasts of electromagnetic radiation and charged particles that burst into space during explosions on the sun’s surface. Their turning motion causes energy to build up that is released in the form of flares.

But a team of NJIT scientists now claims that flares in turn have a powerful impact on sunspots, the visible concentrations of magnetic fields on the sun’s surface, or photosphere. In a paper published in Nature Communications this week, the researchers argue that flares cause sunspots to rotate at much faster speeds than are usually observed before they erupt.

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Variation in solar activity during a recent sunspot cycle [credit: Wikipedia]

Variation in solar activity during a recent sunspot cycle [credit: Wikipedia]


Here we are told that ‘Researchers…are putting forward a new theory’ which may be amusing to Talkshop regulars and others who have been discussing and investigating such matters for years, but – better late than never for the rest of the science world!

The Sun’s activity is determined by the Sun’s magnetic field. Two combined effects are responsible for the latter: The omega and the alpha effect. Exactly where and how the alpha effect originates is currently unknown.

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) are putting forward a new theory for this in the journal Solar Physics. Their calculations suggest that tidal forces from Venus, the Earth and Jupiter can directly influence the Sun’s activity.

Many questions regarding the Sun’s magnetic field are still unanswered. “As with the Earth, we are dealing with a dynamo. Through self-excitation, a magnetic field is created from virtually nothing, whereby the complex movement of the conductive plasma serves as an energy source,” says the physicist Dr. Frank Stefani from HZDR.

The Sun’s so-called alpha-omega dynamo is subject to a regular cycle. Approximately every eleven years the polarity of the Sun’s magnetic field is reversed, with solar activity peaking with the same frequency.

This manifests itself in an increase in sunspots — dark patches on the Sun’s surface which originate from strongly concentrated magnetic fields. “Interestingly, every 11.07 years, the Sun and the planets Venus, the Earth and Jupiter are aligned. We asked ourselves: Is it a coincidence that the solar cycle corresponds with the cycle of the conjunction or the opposition of the three planets?” ponders Stefani.

Although this question is by no means new, up to now scientists could not identify a plausible physical mechanism for how the very weak tidal effects of Venus, the Earth and Jupiter could influence the Sun’s dynamo.
Talkshop comment: Unless they came across some of Ian Wilson’s research perhaps?

Strengthening through resonance
“If you only just give a swing small pushes, it will swing higher with time,” as Frank Stefani explains the principle of resonance. He and his team discovered in recent calculations that the alpha effect is prone to oscillations under certain conditions. “The impulse for this alpha-oscillation requires almost no energy. The planetary tides could act as sufficient pace setters for this.”

The so-called Tayler instability plays a crucial role for the resonance of the Sun’s dynamo. It always arises when a strong enough current flows through a conductive liquid or a plasma. Above a certain strength, the interaction of the current with its own magnetic field generates a flow — in the case of the colossal Sun, a turbulent one.

It is generally understood that the solar dynamo relies on the interaction of two induction mechanisms. Largely undisputed is the omega effect, which originates in the tachocline. This is the name of a narrow band between the Sun’s inner radiative zone and the outer areas in which convection takes place, where heat is transported using the movement of the hot plasma. In the tachocline, various, differentially rotating areas converge. This differential rotation generates the so-called toroidal magnetic field in the form of two “life belts” situated north and south of the solar equator.

[Talkshop note: see link below for further details]

Full report: Are planets setting the sun’s pace? — ScienceDaily

A solar cycle 24 prediction chart [credit:NASA]

A solar cycle 24 prediction chart [credit:NASA]


What follows are extracts, omitting a few of the more technical aspects which can be viewed in the GWPF’s full article here. Possible ‘colder climates’ get a mention.

Sten Odenwald of NASA Heliophysics Education Consortium writes:
Forecasters are already starting to make predictions for what might be in store as our sun winds down its current sunspot cycle in a few years. Are we in for a very intense cycle of solar activity, or the beginning of a century-long absence of sunspots and a rise in colder climates?

Ever since Samuel Schwabe discovered the 11-year ebb and flow of sunspots on the sun in 1843, predicting when the next sunspot cycle will appear, and how strong it will be, has been a cottage industry among scientists and non-scientists alike.

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Tim writes,

A new paper of considerable interest at the Talkshop…

Image

Properties of sunspot cycles and hemispheric wings since the 19th century
Raisa Leussu, Ilya G. Usoskin, Rainer Arlt and Kalevi Mursula
http://dx.doi.org/10.1051/0004-6361/201628335
Open access with registration.

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Tim writes,

Image

Figure 1, plot from http://www.swpc.noaa.gov/communities/space-weather-enthusiasts

Earthquake at 01:36 UT

Once again the spectre of space weather correlation with earthquakes turns up.

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Solar radio and extreme UV during current cycle

Posted: August 6, 2016 by tchannon in Solar physics

Tim wrote,

From A& A (Astronomy and Astrophysics) this month is a paper where some readers will take a shine.

Image

Comparison of solar radio and extreme ultraviolet synoptic limb charts during the present solar maximum
A. J. Oliveira e Silva, C. L. Selhorst, P. J. A. Simões and C. G. Giménez de Castro
A&A, 592 (2016) A91
DOI: http://dx.doi.org/10.1051/0004-6361/201527792
(free access with registration)

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