Sol (Sun) and its phenomena

http://www.spaceweather.com/ said:

HELIOSPHERIC CURRENT SHEET: Today, April 7th, Earth is expected to cross through a fold in the heliospheric current sheet. The crossing could trigger unsettled conditions in our planet's magnetic field. NOAA forecasters estimate a 50% chance of minor geomagnetic storms. Aurora alerts: text or voice
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The heliospheric current sheet separates regions of the solar wind where the magnetic field points toward or away from the Sun. The complex field structure in the photosphere simplifies with increasing height in the corona until a single line separates the two polarities at about 2.5 solar radii. That line is drawn out by the radially accelerating solar wind to form a surface similar to the one shown in this idealized picture. The surface is curved because the underlying magnetic pattern rotates every 27 days with the Sun.
It would take about 3 weeks for material near the current sheet traveling at 400 km/s in the solar wind to reach the orbit of Jupiter, as depicted here. In reality the surface becomes increasingly distorted because of variations in the solar wind speed along the surface and other dynamic effects operating in the interplanetary medium.

The shape of the current sheet usually evolves slowly - over months - as the large-scale pattern of the Sun's field changes in response to the emergence and decay of solar active regions. Coronal mass ejections often disrupt the background pattern temporarily, but sometimes the changes are permanent.

During most of the solar cycle the source of the heliospheric current sheet resembles a slightly tilted dipole with varying degrees of quadrupole distortion. Near solar maximum the polar dipole decays, leaving a much more complicated structure. This picture shows the heliospheric current sheet as it might appear during the rising phase of the cycle, when the dipole and quadrupole components are balanced; at this point the neutral line at the base of the sheet resembles the seam on a baseball.

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http://www.plasma-universe.com/Heliospheric_current_sheet said:

Heliospheric current sheet

Heliospheric current sheet, the largest structure in the heliosphere.
The Heliospheric current sheet (HCS) is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south[/b]. This field extends from the Sun's equatorial plane throughout the entire Solar System and is the largest structure in the heliosphere.[1] The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (Solar Wind).[2] (see also Unipolar generator). A small electrical current flows within the sheet, about 10-10 amps/m2. The thickness of the current sheet is about 10,000km.

The underlying magnetic field is called the interplanetary magnetic field, which has an associated interplanetary electric field [3], and the resulting electric current forms part of the heliospheric current circuit.[4] The Heliospheric current sheet is also sometimes called the Interplanetary Current Sheet and Heliospheric neutral sheet.

Ballerina's skirt shape
As the Sun rotates, its magnetic field twists into a Parker spiral,[5] a form of an Archimedean spiral, named after its discovery by Eugene Parker. As the spiraling magnetic sheets changes polarity, it warps into a wavy spiral shape that has been likened to a ballerina's skirt.[6][7] Further dynamics have suggested that "The Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward"

Magnetic field
The heliospheric current sheet rotates along with the Sun once every 27 days, during which time the peaks and troughs of the skirt pass through the Earth's magnetosphere, interacting with it. Near the surface of the Sun, the magnetic field produced by the radial electric current in the sheet is of the order of 5x10-6T.[4]

The magnetic field at the surface of the Sun is about 10-4 tesla. If the form of the field were a magnetic dipole, the strength would decrease with the cube of the distance, resulting in about 10-11 tesla at the Earth's orbit. The heliospheric current sheet results in higher order multipole components so that the actual magnetic field at the Earth due to the Sun is 100 times greater.

Electric current
The electric current in the heliospheric current sheet has a radially component, the circuit being closed by currents aligned with the Sun's magnetic field in the solar polar regions. The total current in the circuit is on the order of 3×109 amperes.[4] As a comparison with other astrophysical electric currents, the Birkeland currents that supply the Earth's aurora are about a thousand times weaker at a million amperes. The maximum current density in the sheet is on the order of 10-10 A/m2 (10-4 amps/km2).

It has been noted that:
"It is remarkable that the radial component of the spiral structure implies a current the continually flows towards the Sun. The charge accumulating from this process must be removed elsewhere. This occurs most simply via line currents that originate over the Sun's poles"[9]

Interplanetary electric field
The interplanetary electric field (IEF) extends throughout the interplanetary current sheet, and is generally orientated north-south. The separation of the field is relatively small, but its extent is the same as the heliospheric current sheet which extends throughout the plasmasphere.

The interplanetary electric field is caused by ions leaving the Sun, initially flowing along and parallel to the Sun's magnetic field. But as the ions move further outwards, the azimuthal component of the Sun's magnetic field becomes more influential, and protons are deflected to the south and electrons to the north, resulting in an electric field that compensates the magnetic forces.[10]

Solar wind
"The Solar Wind consists of a hot plasma -- an electrically neutral mixture of electrons and ions (principally protons with some heavier atomic nuclei) at roughly 100,000°K. Its source is the Sun's atmosphere, or corona, and it is continually present in interplanetary space. The gas flows radially outwards at a typical speed of 450km per second to at least 70 AU and probably much further. The average speed of the flowing gas is remarkably independent of its distance from the Sun".[11]

Solar wind acceleration
"The speed of the solar wind away from Sun increases as the distance from the Sun increases. The wind accelerates rapidly in the first few tens of Ro, and accelerates only slowly after this."[12]

History
The heliospheric current sheet was discovered by John M. Wilcox and Norman F. Ness, who published their finding in 1965 [13].

The image above is a painting by NASA artist, Werner Heil. It was developed by Prof. John Wilcox as a tool for visualizing the surface that separates the two magnetic polarity regions produced by the Sun in the solar system. His concept was that a "baseball seam" shape located near the Sun separates the two magnetic hemispheres of the interplanetary medium; the shape was determined by the large-scale magnetic field at the Sun. That geometrical shape is carried radially outward by the solar wind. As the Sun, and the magnetic field configuration it generates, continue to rotate underneath the structure, the resulting surface becomes the one you see in the painting.[14]

Hannes Alfvén and Per Carlqvist speculate[15] on the existence of a galactic current sheet, a counterpart of the heliospheric current sheet, with an estimated galactic current of 1017 - 1019 Amps, that might flow in the plane of symmetry of the galaxy.

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http://strangesounds.org/2016/04/the-suns-magnetic-field-hypnotizing-video-poleshift.html said:

The sun’s magnetic field is just too hypnotizing just before it shifts
By Strange Sounds - Apr 11, 2016

Something big is about to happen on the sun. The sun’s magnetic field is about to flip. And this change will have ripple effects throughout the solar system.

The sun’s magnetic field changes polarity approximately every 11 years. It happens at the peak of each solar cycle as the sun’s inner magnetic dynamo re-organizes itself. The coming reversal will mark the midpoint of Solar Cycle 24. Half of “solar max” will be behind us, with half yet to come.

A reversal of the sun’s magnetic field is, literally, a big event. The domain of the sun’s magnetic influence (also known as the “heliosphere”) extends billions of kilometers beyond Pluto. Changes to the field’s polarity ripple all the way out to the Voyager probes, on the doorstep of interstellar space.

When solar physicists talk about solar field reversals, their conversation often centers on the “current sheet.” The current sheet is a sprawling surface jutting outward from the sun’s equator where the sun’s slowly rotating magnetic field induces an electrical current. The current itself is small, only one ten-billionth of an amp per square meter (0.0000000001 amps/m2), but there’s a lot of it: the amperage flows through a region 10,000 km thick and billions of kilometers wide. Electrically speaking, the entire heliosphere is organized around this enormous sheet.

During field reversals, the current sheet becomes very wavy. (Heliospheric current sheet, it is explained at the video)

Cosmic rays are also affected. These are high-energy particles accelerated to nearly light speed by supernova explosions and other violent events in the galaxy. Cosmic rays are a danger to astronauts and space probes, and some researchers say they might affect the cloudiness and climate of Earth.

The current sheet acts as a barrier to cosmic rays, deflecting them as they attempt to penetrate the inner solar system. A wavy, crinkly sheet acts as a better shield against these energetic particles from deep space.

As the field reversal approaches, data from Wilcox show that the sun’s two hemispheres are out of synch.

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http://www.spaceweather.com/ said:

SOLAR SECTOR BOUNDARY CROSSING (UPDATED): On April 29th or 30th, Earth will cross a fold in the heliospheric current sheet--a vast wavy structure in interplanetary space separating regions of opposite magnetic polarity. This is called a "solar sector boundary crossing," and it could trigger geomagnetic activity around Earth's poles. NOAA forecasters estimate a 60% chance of G1-class geomagnetic storms on April 29th.

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Archaea said:

The patterns in the first video kind of reminded me of the patterns formed by cymatics.

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http://www.spaceweather.com/ said:

SOLAR SECTOR BOUNDARY CROSSING: Late on May 25th, Earth will cross a fold in the heliospheric current sheet and enter a region of space filled with negative polarity magnetic fields. Such fields can open a crack in Earth's magnetosphere, allowing solar wind to pour in and fuel geomagnetic disturbances. According to NOAA forecasters, the odds of a G1-class storm is 20% to 30%. Aurora alerts: text, voice.

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While the cause of coronal holes remains a mystery, they “correlate to areas on the sun where magnetic fields soar up and away, without looping back down to the surface, as they do elsewhere.”

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On May 23rd, an enormous swarm of sprites flickered and danced across the top of a thunderstorm in Oklahoma. Almost 400 miles away in New Mexico, amateur astronomer Thomas Ashcraft trained his cameras on the display. He captured the sprites--and something more:

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"Note the dendritic upward spray in the midst of the sprite cluster," points out Ashcraft. "That is a possible 'pop-through gigantic jet'--a rare event."

Ashcraft has posted a video of the event with VLF-ELF radio emissions he recorded as a soundtrack. Turn up the volume: "The deep bass sound of the lightning stroke sounds like a distant shotgun blast in the night," he says.

What is a pop-through gigantic jet? Lightning scientist Oscar van der Velde of the Technical University of Catalonia explains: "A cluster of sprites can actually warp Earth's ionosphere, bringing it down from its usual altitude of 90 km to only 40 km." This sets the stage for the jet.

"The sprite cluster triggers an upward-directed discharge which in the past received fancy names as 'troll' or 'palm tree'," says van der Velde. "A satellite-based study by Taiwanese researchers in 2012 found them similar to gigantic jets--large isolated discharges reaching from the thundercloud toward the ionosphere. In case of a 'pop-through gigantic jet,' the lowering of the ionosphere is not uniform and the jet may then reach higher than the bottom tendrils of the sprite."

Although sprites have been seen for at least a century, most scientists did not believe they existed until after 1989 when sprites were photographed by cameras onboard the space shuttle. Now "sprite chasers" routinely photograph sprites--and more!--from their own homes. "They are easily detected by certain cameras," says van der Velde, "and if a storm is in the mood, you may record one every few minutes."

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https://spaceweather.com/ said:

AURORA SURPRISE: No sunspots. No solar flares. No gust of solar wind. In short, there was no reason to expect an outburst of auroras on Feb. 17th. Then this happened

Solar minimum is here - but even now strangely beautiful auroras are dancing around the poles. Deep inside the Arctic Circle, the expert guides of Aurora Holidays in Utsjoki, Finland, can help you chase them. Book now! ​ COSMIC RAYS ARE PEAKING: Once again, cosmic rays percolating through Earth's atmosphere are within a percentage point of the Space Age maximum. This is a symptom of Solar Minimum. When the sun's magnetic field weakens, it allows deep space radiation to enter the solar system. The current Solar Minimum is very deep, and consequently cosmic rays fluxes are very high. You can track the numbers right here on Spaceweather.com.​ STARLINK BUZZES PUERTO RICO: SpaceX successfully launched another batch of 60 Starlink satellites on Feb. 17th. Just hours after the Falcon 9 rocket blasted off from Cape Canaveral, the newly released satellites flew over Puerto Rico where a meteor camera captured them flying single-file across the sky:​ ​ The camera is operated by the Astronomical Society of the Caribbean (Sociedad de Astronomia del Caribe), the largest astronomy group on the Island. "A couple of flashes are visible ahead of the main group of satellites, perhaps from parts or a pair of Starlink satellites ahead of the others," notes the Society.​ This latest launch brings the total number of Starlink satellites in orbit to 300--a number that could grow to 42,000 by the time the Starlink project is complete. The good news is, Starlink could bring internet access to every corner of the world. The bad news is, Starlink poses a serious threat to astronomical research according to a recent study by the International Astronomical Union. See for yourself. Starlink flyby predictions are available from Calsky and Heavens Above. (Got pictures? Submit them here.) Realtime Spaceweather Photo Gallery Free: Spaceweather.com Newsletter​ AURORA SURPRISE: No sunspots. No solar flares. No gust of solar wind. In short, there was no reason to expect an outburst of auroras on Feb. 17th. Then this happened:​ ​ "Surprise auroras strike big!" exclaims Alexander Kuznetsov, who photographed the display from Kilpisjärvi, Finland. "At one point they went pink and moved very fast! I also saw a fast corona unfolding above me, reminding me of an angel."​ "When I first went outside, I was not expecting much because the solar wind speed was relatively low, so I did not take my snowshoes," he says. "Then the show began. Currently, there is over a meter of snow in Kilpisjärvi, so I had to crawl through some snowy terrain to get to the best viewing spot." Where did these auroras come from? A crack opened in Earth's magnetic field (that is, "BsubZ tilted south"). Solar wind poured in to fuel the display--no solar storm required. ​

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Laura said:

I changed the title of this thread to make it more generally about the sun.

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