Topics Include :-
- The Poloidal becomes a Toroidal Field
- Solar Flares and Solar Prominences
- Helmet Streamers
- Coronal Mass Ejections
- Coronal Holes
- Polar plumes
- Solar-Terrestrial Interactions
The Poloidal becomes a toroidal Field
Solar activity produces a cyclic winding up and relaxation with every maximum and minimum of the 11 year cycle. Lines of force lie along the meridians in the north-south direction between the poles, on and below the photosphere. The magnetic field lines are 'frozen in' the solar material, and in time become distorted by the differential rotation. As the cycle progresses the lines become stretched and wrapped around the sun. By this means the field lines are drawn together into an intense toroidal field (doughnut shaped) parallel to the equator and the field strength greatly enhanced.
The figure shows the threads or rope like magnetic cords. You can see these cords emerge from below the Photoshere in the form of this prominence shown left. If you look carefully you will see it's twists (coils).
Field lines are brought together to form tubes of magnetic flux which becomes twisted by the effects of convection. Bundles of tubes may be wound together in ropes, amplifying further the field strength.
When the field strengths in the ropes become sufficiently great, they float to the surface. Sunspot groups form where kinks in the rope penetrate the photosphere.
The ropes are squeezed together by convection currents, despite their tendency to push apart. The rapid equatorial rotation distorts lines of force and convection causes them to twist around each other to form magnetic cords like rope being woven into strong threads. The enhanced fields first reach maximum strength at lattitudes of about +/- 40 degrees. As a result, sunspot formation tends to occur first at these lattitudes.
At solar maximum the sum of the fields cancel and the poloidal field reverses, allowing the formation of a toroidal field, which itself cancels and reverses at zero field point. The sun then goes through a minimum and the twisted field lines eventually appear straightened out again. The strong polarity at the poles produces regions of open field lines (coronal holes) where the toroidal field is weakest.
Here's another way of putting it [refer to the diagram, left].
How can a strong toroidal field be created from a weak magnetic one?
The poloidal field is initially restricted to the polar regions (a).
The force lines pass through the surface layers of the sun (b) [the geographic North Pole shown is a south magnetic pole].
Because of the differential rotation, field lines are dragged faster near the equator than elsewhere, and stretched, resulting in the appearance of a toroidal field. Diagram (c) is an enlargement of concentrated field lines which run in opposite directions in the two hemispheres.
Note their small inclination to the equator, which explains the lower latitude of leading sunspots, compared with trailing ones. In the next 11 year cycle except that of the sun's rotation, are reversed.
The two diagrams on the right show bipolar region formation (a positive and negative sunspot next to each other, that can have an unseen loop or arch prominence connecting them). The ropes or magnetic cords are said to emerge on the surface due to bouyancy and give rise to sunspots which generally occur in pairs. The leading one has the same polarity as the hemisphere in which it forms; the trailing one has the opposite polarity and is located at the slightly higher latitude. Because of the field gradient towards the poles, the trailing spot's magnetic flux precedes that of the leading spot; the net effect of many spots is a reversal of the polar field.
At the end of the cycle, the new poloidal field produces a toroidal field which begins to cancel the initial one until the field is zero at the solar minimum.
The above diagram is a text book gross oversimplification. The Sun's field is in fact hardly uniform and is very chaotic. Its more like this [left].
Very close to the Sun's surface the magnetic structure is seen to be similar to that of the Earth's atmospheric wind cells, meaning that within the solar disk magnetic north can be opposite to that of a cell above and below. Thus, near to the Sun's surface the magnetic polarity has no resemblance to a dipole magnetic. Most very near magnetic measurements, when taken over a time period, show a very unstable arrangement. Magnetic flux fields are a jumbled mess [left]. As the distance from the Sun increases, a more stable magnetic field emerges. The field is similar to a dipole, however, at the equatorial region the field seems to expand outward. Thus, the dipole geometry does not apply.
The Alpha EffectTwisting of the magnetic field lines is caused by the effects of the Sun's rotation. This is called the alpha-effect after the Greek letter that looks like a twisted loop. Early models of the Sun's dynamo assumed that the twisting is produced by the effects of the Sun's rotation on very large convective flows that carry heat to the Sun's surface. One problem with this assumption is that the expected twisting is far too much and it produces magnetic cycles that are only a couple years in length. More recent dynamo models assume that the twisting is due to the effect of the Sun's rotation on the rising "tubes" of magnetic field from deep within the Sun. The twist produced by the alpha effect makes sunspot groups that obey Joy's law and also makes the magnetic field reverse from one sunspot cycle to the next (Hale's law).
Strangely, activity in the Corona is somehow independent of, but in phase with the surface magnetic field. Helmet streamers centre on the equator during the solar minimum but light up the entire globe all around during the solar maximum. Therefore the same force that causes the toroidal field in the photosphere causes the whole globe to light up in the corona. Coronal holes shrink and ultimately disappear around solar maximum. The solar wind originating from the streamers (closed field lines) is slow.
The sun starts to form large polar coronal holes very soon after solar maximum. Conversely, when the toroidal field disappears and the poles reverse a poloidal field dominates the photosphere, a strong polarity at the poles produces regions of open field lines (large coronal holes) with a fast solar wind originating from them, while streamers move away from the polar coronal hole areas in the corona and center on the equatorial plane.
Electric Theory suggests that the Photosphere granules are actually ends of electric arcs reaching towards the sun's interior.
The magnetic spiral at the pole. Flux drifts from the equatorial sunspot belt at the perimeter to the negative North Pole of the sun
SunspotsFred Hoyle long ago pointed out; the Sun does not conform to the expected behavior of an internally heated ball of gas, simply radiating its energy into space. Instead, its behavior at every level is complex and baffling. Nowhere is it more mysterious than in a sunspot.
He also pointed out, with the strong gravity and the mere 5,800-degree temperature at the surface, the Sun’s atmosphere should be only a few thousand kilometers thick, according to the “gas laws” astrophysicists typically apply to such bodies. Instead, the atmosphere balloons out to 100,000 kilometers, where it heats up to a million degrees or more. From there, particles accelerate out among the planets in defiance of gravity.
Sunspot viewed in ultraviolet light, taken by the TRACE spacecraft.It is believed that sunspots - which are often accompanied by solar flares and explosions - result when pent-up magnetic fields finally break through the surface. Sunspot numbers vary as the sun rotates and magnetic flux emerges and fragments.
Hale proved in 1908 that sunspots are associated with strong magnetic fields. Hale observed that on one hemisphere the leading parts of these active regions (with respect to the direction of the solar rotation) all have the same polarity, while on the other hemisphere the polarities are oppositely oriented. In subsequent 11-yr sunspot cycles the polarities in the active regions are reversed. This is Hale's polarity law. The Sun therefore exhibits in fact a 22-year magnetic cycle.
Sunspots most often appear in the low latitudes near the solar equator, and they almost never appear below 5 or above 40 degrees north and south latitude.
They are sources of intense magnetic knots that spiral outwards, places where intense magnetic loops hundreds of times stronger than the ambient dipole field poke through the photosphere. They are darker than the surrounding surface because they are cooler: the normal solar surface (photosphere) has a temperature of about 5800 K, whereas sunspots are about 4000 K. The lower temperature is presumably caused by the magnetic fields in sunspots suppressing the convective heat transfer.
Sunspot magnetic fields have a strength of a few thousand gauss, whereas the average photospheric field strength is much less: less than a few gauss (G). For comparison: Earth's magnetic field is about 0.3 G at the equator and 0.6 G at the poles. A typical bar magnetic is about 10,000 G
The mean polar field of the Sun is relatively week (only a few gauss) and it is not organized in active regions. Only about 1% of the total magnetic flux is at the poles, whereas about 70% is concentrated in the area between ca. 30 degrees latitude.
Magnetograms of the Sun show that sunspots are components of magnetic bipolar regions. Field lines leave through one sunspot and re-enter through the other (of opposite polarity). They are formed when magnetic field lines just below the sun's surface are twisted and emerge through the solar photosphere. The twisted magnetic field above sunspots are sites where solar flares are observed to occur.
Active regions are the surface manifestation of the toroidal magnetic field which erupts from the interior of the Sun in the form of loops. The bipolar active regions live a few days to weeks, sometimes a few months, and then disintegrate into progressively smaller magnetic regions and thus gradually dissolve.
The number of sunspots gradually decreases until they disappear at solar minimum approximately five years after the maximun. What actually happens during this decay process is unknown, but it seems that the field disappears underneath the surface.
In the course of the 11-yr cycle this process of development and decay of active regions takes place at progressively lower latitudes, which shows up as the apparent migration of sunspots towards the equator in the butterfly diagram. It thus seems that it is the toroidal field which moves towards the equator and which reverses direction every 11 yr.
During the decay of active regions the leading parts are mainly spread (by surface diffusion) towards the equator and the trailing parts mainly towards the poles. Most of these regions gradually disappear.
A number of following parts, however, does not disappear but forms so-called unipolar magnetic regions which migrate poleward. These unipolar regions have a polarity which is opposite to the polarity of the existing polar field. This causes a reversal of the polar field, which takes place some years after the reversal of the toroidal field and not at both poles simultaneously.
In this image a dark-cored filament looks like a glowing snake with a dark stripe painted along its back. The 'head' of the snake is a complicated feature where the stripe splits up among many bright points. The canal-like structures in the penumbra of sunspots could be described as a pattern of cracks.
It is important to understand a sunspot because it gives a glimpse below the bright photosphere. It is cooler down there by thousands of degrees! The sunspot center should be much hotter and brighter than its surroundings. And the penumbral filaments bear no resemblance to convection in a hot gas, with or without magnetic fields.
Strong magnetic fields are measured at the sunspot center, but magnetic fields are only produced by electric currents. Electric discharges in plasma take the form of long thin filaments. Just like a neon tube, it is the discharge that causes the gases to glow. The penumbral filaments were observed to split near their 'footpoints' in the dark umbra and to move around. It is typical behavior of plasma filaments and can be observed in novelty plasma balls.
An electric discharge offers a simple explanation for why the penumbral filaments have dark cores. In an electric universe all bodies may receive electric current from the environment in a cosmic charging process associated with the development of a galaxy. And because electrical phenomena are scalable over at least 14 orders of magnitude, we may look to electric discharge phenomena in other atmospheres to gain insights into what may be happening in the Sun's atmosphere.
An artificial tornado of fire shows the bright edges to the vortex near the base.We might equate the penumbral filaments with giant lightning bolts, but the features do not match well. A lightning flash lasts for 0.2 seconds and covers a distance of about 10 km. The penumbral filaments last for at least one hour and are of the order of 1000 km long. If we could scale a lightning bolt 100 times we might have a flash that lasted between 20 and 200 seconds and was 1000 km long. The lifetime is too short. Also, measurements of scars on lightning conductors show that the lightning channel is only about 5 mm wide. Scaling that by 100 times would have solar lightning channels far below the limit of telescopic resolution.
But a tornado lasts for minutes and can have a diameter of the order of one kilometre. Scale those figures up 100 times and we match penumbral filaments very well. And if the circulating cylinder of plasma is radiating heat and light, as we see on the Sun, then the solar 'tornado' will appear, side on, to have a dark core.
Tornadoes are associated with severe electrical storms. They are the result of rapidly rotating electric charge. Electrons are the current carriers in a tornado. The difference is that the electrons are moving at many metres per second in the tornado while they take several hours to move one metre in copper wire. The result is that powerful electromagnetic forces are in control of the tornado. The result has been called a 'charged sheath vortex.'
The shape of the vortex is constrained to be long and thin with a circular cross-section. This true shape of the vortex is usually hidden in tornadoes because of the obscuring dust and clouds. The vortex itself will only be visible if it has sufficient electrical energy to ionise atoms in the atmosphere. That is the case on the Sun. And some people who have survived the experience of being 'run over' by a tornado have reported an electrical glow in the inner wall of the tornado.
It is thought that a tornado is a means for mechanical energy in the storm to be converted somehow to electrical power, which is then transmitted very effectively to ground by the electrical conduit of the charged sheath vortex inside the tornado. Electrical power from space is partially dissipated in the mechanical energy of the encircling winds. The tornadic winds are driven by the charge sheath vortex.
The Earth and other planets receive electrical power from space in the same way as the Sun. We receive far less than does the Sun, which seems to be covered with tornadic charge sheath vortexes. The solar tornadoes are seen most clearly at the edge of sunspots in the form of penumbral filaments. The strong solenoidal magnetic field created by each vortex gives rise to the observed filamentary magnetic field in the penumbra.
Dust devil comparisonMartian dust devils are tornadoes that dwarf their earthly counterpart. It shows that clouds are not required to generate them. They are an atmospheric electric discharge phenomenon. Ralph Juergens noted the possible identity of solar granules with 'anode tufts'. Anode tufts are small, bright, secondary plasmas that form above an anode that is otherwise too small to handle the current flow into it. Langmuir reported the tufts as small bright spheres moving above the anode surface. It seems possible that in the stratified atmosphere of the Sun those bright discharges rather take the distinct form of the charge sheath vortex.
Left: Sun's photosphere as it normally appears, covered with granules, with sunspot showing dark umbra in the center surrounded by the lighter penumbra, composed of rope-vortices rising explosively from beneath the surface.The granules are bright because the gases inside the charge sheath vortex have been heated by compression and radiation from the walls of the vortex. Those hot gases fountain out of the tops of the vortexes to form the granules. Also, lightning in some form will deliver power to the top of the granule, creating unresolved bright spots. Above the granules the ions recombine with electrons to form neutral gas, which absorbs light.
Right: Few thousand kms into the chromosphere are ropes of the same sunspot penumbra extendingThe gas would be constrained to flow down between the granules, its motion modified by collisions with ions moving under electromagnetic influences. This may create the dark 'canals', which have the branched pattern of electric discharges. There would be a powerful influence from the strong electric fields of the plasma sheaths (double-layers) of the anode tufts. Varying levels of lightning activity above each granule could explain the observed variation in brightness of solar granules. It is noteworthy that large faint granules have never been seen. They would not be expected on this model.
outward into a surrounding maze of filaments, constrained by the complex magnetic fields.
Solar plasmoid (seen from above the pole) imaged in ultra-violet light using data from the SOHO spacecraft.In the electrical model, the Sun receives electrical energy from interstellar space in the form of a glow discharge. Plasma experiments show that some energy will be stored in a donut shaped 'plasmoid' above the Sun's equator. The energy is released sporadically from the plasmoid to the mid-latitudes of the Sun. In laboratory experiments, a torus forms above the equator of a positively charged sphere. Discharges then fly between the torus and the mid to low latitudes of the sphere. In the electric model, the Sun is the positively charged focal point of an electric field. The Sun is surrounded by an equatorial torus (right). In experiments that produce the equatorial torus, the observed discharging to the positively charged sphere migrates latitudinally as the power input varies. The higher power produces maximum activity near the equator. The same thing occurs on the Sun in the latitudinal migration of sunspots in relation to the total energetic output of the Sun. The global tornado storm is pushed aside by more powerful charge sheath vortexes that deliver electrical energy from the plasmoid to much lower levels. The resulting holes in the tornado level, or photosphere, are what we call sunspots. Rather than being a site where energy flow has been restricted, a sunspot is a site where it is enhanced. That explains why 'they are launch pads for complex expulsions of plasma that race through the solar system.' The giant electrical tornadoes that form sunspots accelerate particles in their powerful electromagnetic fields, generating UV light and x-rays instead of visible light. However, because temperature is a measure of random motion, the field-directed motion of the particles within the sunspot vortex appears 'cool.'
This model can explain why sunspots of the same magnetic polarity are strangely attracted toward each other instead of being repelled. The sunspots are receiving electric current flowing in parallel rotating streams, which results in their being mutually attracted over long distances and repelled at short distances. That also explains why sunspots often seem to maintain their identity even if they come close enough to merge. There is also other evidence that suggests the presence of electric currents aligned with the magnetic field in a sunspot.
Granulation has been observed in the umbra, or dark centers of sunspots, by overexposing sunspot images. The umbral granules are more closely packed than photospheric granules. That is to be expected on this model because the current in the large charge sheath vortex forming the sunspot is being delivered to denser atmosphere at lower depths. A larger fraction of umbrae than observed so far could have faint or small-scale filamentary structure. The nature of a charge sheath vortex is to tend to compress material inside and lengthen the tube in both directions. Since it is also acting as a conduit for electrical energy, it seems that the moving bright dots are small-scale filamentary lightning emanating from the lower ends of the penumbral filament vortex.
Astrophysicists have surmised that the sunspots are the result of focused magnetic fields interfering with heat transport, or convection. Standard models offer no explanation for the eleven-year sunspot cycle. Though a connection to the period of Jupiter is possible, the remote gravitational effects of Jupiter on the Sun cannot compare to the energetic events associated with the sunspot cycle.
The sunspot cycle is associated with the Sun’s magnetic field. It is difficult to conjure a magnetic field from inside a hot ball of conducting plasma, particularly when the solar magnetic field shows amazing complexity and often rapid variability.
The Sun has a generally dipole magnetic field that switches polarity with the sunspot cycle. Unlike a dipole magnet, in which the field is twice as strong at the poles as at the equator, the Sun has very evenly distributed field strength. This oddity can be explained only if the Sun is the recipient of electric currents flowing radially into it. These magnetic field-aligned currents adjust the contours of the magnetic field by their natural tendency to space themselves evenly over an anode surface. An internal dynamo will not produce this magnetic field pattern.
The Sun’s interplanetary magnetic field increases in strength with sunspot number. Electrically, the relationship is essential, since the interplanetary magnetic field is generated by the current flow to and from the Sun. As the power increases, sunspot numbers rise (reflecting current input) and the magnetic field strengthens.
In the electrical model the sunspot cycle is induced by fluctuations in the DC power supply from the local arm of our galaxy, as the varying current density and magnetic fields of huge Birkeland current filaments slowly rotate past our solar system. The solar magnetic field reversals may be a result of simple ‘transformer’ action.
Important Consequences of the Electric Star Model for the Sun
1. A star is formed electromagnetically, not gravitationally, and is powered thereafter electrically (by Eddington's "subtle radiation").
2. Near the Sun, galactic transmission lines are in the form of 0.3 parsecs wide rotating Birkeland filaments (based on those detected at the center of the Milky Way). Their motion relative to the Sun will produce a slowly varying magnetic field and current density, this causing a solar activity cycle. To that extent, all stars are variable, and location is vital.
3. An electric star has an internal radial electric field. But because plasma is an outstanding conductor it cannot sustain a high electric field. So plasma self-organizes to form a protective sheath or 'double layer' across which most of the electric field is concentrated and in which most of the electrical energy is stored. It is the release of that internal stored energy that causes CME's, nova outbursts, polar jets, and the birth of stellar companions.
4. In a ball of plasma like the Sun the radial electric field will tend to be concentrated in shells or double layers above and beneath the photosphere. A double layer exists above the solar photosphere, in the chromosphere.
5. The photosphere and chromosphere together act like a pnp transistor, modulating the current flow in the solar wind. It has an effective negative feedback influence to steady the energy radiated by the photosphere so that astrophysicists can talk of a 'solar constant,' while the Sun's other external electrical activity (UV light and x-rays) is much more variable. Because the photosphere is an electrical plasma discharge phenomenon it also expands or contracts to adjust to its electrical environment. That explains why the Sun 'rings' like an electric bell.
6. Double layers may break down with an explosive release of electrical energy. A nova outburst is a result of the breakdown of an internal stellar DL. Billions of volts could exist across a typical solar flare double layer.
7. A star is a resonant electrical load in a galactic circuit and naturally shows periodic behavior. Superimposed is the non-linear behavior of plasma discharges. Two stars close together can induce cataclysmic variability or pulsar behavior through such plasma discharges.
8. The model to apply to a star is that of a homopolar electric motor. It explains why the equator of the Sun rotates the fastest when it should be slowed by mass loss to the solar wind. (The same model applies to spiral galaxies and explains why outer stars orbit more rapidly than expected. The spiral arms of the galaxy and the spiral structure of the solar 'wind' then have a connection).
9. The current that powers the Sun can be viewed as flowing in along the wavy polar magnetic field lines, then from the poles toward the equator. That current flow manifests as huge sub-photospheric flows of gas. In the mid-latitudes the circuit is completed as the current flows outward in a current sheet called the solar wind.
10. The transfer of charge to the solar wind takes place through the photosphere. It occurs in the form of a tightly packed global tornadic electrical discharge. The importance of the tornadic form for us is that it is slower than lightning, being under the tight control of powerful electromagnetic forces, and less bright than lightning. The intense, equally spaced solenoidal magnetic fields of the photospheric tornadoes gives rise to the surprisingly evenly spaced magnetic field lines of the Sun.
11. Encircling the Sun''s equator is a ring current forming a doughnut-shaped plasmoid. It is visible in UV light and is a source of stored electromagnetic energy. Occasionally the plasmoid discharges directly to lower levels of the Sun, punching a hole, that we call a sunspot, through the photosphere. A sunspot group can be compared to regional lightning on Earth. Electric discharges in a plasma naturally drive such rotation. Sunspots of the same magnetic polarity are drawn toward each other. Two parallel electric current filaments following the magnetic field lines are naturally drawn together.
12. Sometimes the slow discharge that forms a sunspot may trigger a stellar lightning flash, resulting in a more sudden and powerful release of stored electrical energy. An x-ray flash is the signature of such lightning. That arc may result in a CME. The corona often dims as power is withdrawn from the solar plasmoid.
13. The conventional thermonuclear story of stellar evolution is incorrect so we do not know the age of the Sun, or its character in the past or future. The inexplicable and drastic global climate changes on Earth in the past may have found an answer in the variable nature of stars.
Our Sun, like all stars, is a variable star. We must learn to live with the uncertainty of a star that is a product of its environment. We can expect our Sun to change when it enters regions of interstellar space where there is more or less dust, which alters the plasma characteristics.
Data from Ulysses show that the solar wind originates in holes in the sun's corona, and the speed of the solar wind varies inversely with coronal temperature. The standard model of the solar wind has it "boiling off" the Sun so that you would expect a direct correlation between coronal temperature and solar wind speed. That is precisely the opposite of what the Ulysses spacecraft saw. In the electric model of the Sun, where the solar electric field is strong in the coronal holes, protons of the solar wind are being strongly accelerated away from the Sun. Their random motion becomes less significant in a process called de-thermalization. Outside the coronal holes, where the coronal electric field is weaker, the protons move more aimlessly. As a result they suffer more collisions and move more randomly. The degree of random movement of particles directly equates to temperature. So the solar wind is fastest where the corona appears coolest and the solar wind is slowest where the corona appears hottest — as Ulysses found.
The Maunder MinimumThe time period 1645-1715 corresponding to the Maunder minimum in sunspot number occurred during an extended time period of severe winters and overall cold weather in Western Europe, which is sometimes referred to in the climatic literature as the "little ice age".
During this unusually frigid period, lakes and rivers froze all across Europe, and the Arctic Sea ice extended further south than it has since that time. Auroral sightings have been reported as far back as 500 BC, but are truly reliable only for the last 400 years or so.
These data indicate that prolonged epochs of low auroral activity, similar to the Maunder minimum, have occurred at earlier epochs, in particular in 1420 - 1500 (the so-called Spörer minimum) and 1290 - 1340 (the Wolf minimum). There is evidence that the Earth has seen six such periods of solar inactivity in the last 5000 years.
The abundance of 10Be and 14C, as determined respectively from polar ice cores and tree rings, shows pronounced increases around the times of the Maunder, Spörer and Wolf minima. A significant drop of the 14C abundance in 1100 - 1250 AD, possibly associated with a period of abnormally high solar activity, roughly coincides with a period of warming in Medieval Europe, and of generalized drought in North America, as evidenced by the demises of the Anassazi culture in the second half of the 13th century.
Right: White and black correspond respectively to positive and negative magnetic polarities (i.e., normal magnetic field component pointing toward and away from the observer). The white lines trace the paths of magnetic neutral lines. Most regions of strong magnetic fields are grouped in pairs of opposite polarities.
Solar Flares and Solar Prominences
Hale's "spectroheliograph, " invented in 1892 and viewing the Sun in narrow color bands, allowed a completely new range of phenomena to be observed. Many were associated with sunspots, e.g. bright clouds or "plages" (that coincide with photospheric faculae [bright patches in the photosphere] and often surrounding large sunspot groups) in the chromosphere, seen in the light emitted by glowing hydrogen, and observations of the inner corona were made possible.
The first observation of a flare was in 1859. A fast-moving plasma cloud ejected from the Sun. A huge magnetic storm happened 17 hours later. The solar wind takes 4-5 days to cover the same distance. If a typical big flare spreads over 10,000 km in 10 minutes, it must propagate quite rapidly. Some of its features begin much more abruptly, e.g. the associated x-rays, can rise in just a few seconds. This suggests that the energy source is not the heat of the Sun, which spreads and changes rather gradually, but the intense magnetic fields of sunspots. Flares and Prominences are found along the neutral line boundaries (white lines in image above). Solar flares are a brightening of the chromosphere near a sunspot group. They are believed to be associated with the emergence of magnetic flux through the photosphere and are linked to the solar cycle. The energy source of solar flares is believed to be the reconfiguration and dissipation of magnetic fields via reconnection.
Flares are thought to be caused by sudden magnetic field changes in areas where the sun's magnetic field is concentrated. Solar flares are accompanied by the release of gas, electrons, visible light, ultraviolet light and X-rays. During such events, the X-ray brightness of a flaring active region often exceeds the total X-ray brightness of the rest of the Sun.
A flare reaches maximum brightness in a few minutes and declines more slowly, ranging from 10 minututes to several hours (20 minutes is typical).
Occasionally, cooler clouds of gases high up in the chromosphere will rise and orient themselves along the magnetic lines from sunspot pairs. These arches of gas are called prominences.
Prominences may erupt following flare outbursts, usually as a growing arch whose centre expands rapidly and disappears, while its ends remain rooted in the chromosphere below.
Filaments tend to form along the boundaries between regions of positive and negative normal magnetic fields (the white lines in the above figure). Filaments and prominences are one and the same. The flow of material is usually downwards in both quiescent and loop (arch) prominences. In loop prominences coronal material descends from above, flowing down thru both feet of the arch. Arch prominences connect regions of opposite polarity in developing sunspot groups and so cross the neutral line, unlike quiescent prominences that run along them.
Twists are visible in this giant prominenceThe lifetime of a prominence is controlled by the rate of condensation of coronal material and the rate of flow along the magnetic field line into the chromosphere. Depletion of material and local magnetic field changes can terminate it.
Prominences can last two to three months and can extend 30,000 miles (50,000 km) or more above the sun's surface. Upon reaching this height above the surface, they can erupt for a few minutes to hours and send large amounts of material racing through the corona and outward into space at 600 miles per second or 1,000 km/s; these eruptions are called coronal mass ejections.
Lightning in astronomyAt any given time there are several million electrical discharges in the photospheric region, each about 1,000-2,000 km long and lasting 10 min, causing the average temperature of the solar 'surface' to rise to 6,000 K. The flow of positive ions in the electromagnetically compressed discharge channels persists for a time after the charge is consumed and the hot gas ascends and extends above the extinct arcs, forming the white patches of granulation.
Most of the particles are recycled, as in terrestrial meteorology, but some are ejected to greater heights, aided by radiation pressure, carrying charge with them and building up electrical energy in the corona. The resulting discharges are generally more sporadic and violent, such as long prominences, and these are observed to have the same velocity of propagation as terrestrial lightning, attracting other prominences like currents in parallel conductors.
The electrical and magnetic influence of these powerful discharges destroy some areas of the photospheric discharges, forming sunspots, in which the magnetic field pattern is the resultant of the surrounding photospheric discharges and that of the flare above. It is unnecessary therefore to assume that magnetic fields are produced by some unknown process inside the Sun, especially as the generally held view, that the magnetic field is always vertical in the umbra of sunspots, has been disproved by observations.
Helmet streamers are large cap-like coronal structures with long pointed peaks that usually overlie sunspots and active regions. We often find a prominence or filament lying at the base of these structures.
The changes in the surface magnetic field distribution through the solar cycle, as evidenced by the evolving numbers and spatial distributions of sunspots and prominences are also reflected in the corona. The latitudinal distribution of helmet streamers illustrates the response of the corona to changes in the surface magnetic field, and can be seen to vary in phase with the sunspot distribution during that time interval.
Streamers and mass ejections are observed all the way to the poles at solar maximum, and at any given time in the cycle streamers extend to higher latitudes than sunspots and active regions. These are indications that the large-scale structure of the corona evolves independently from the evolution of active regions.
Since coronal activity occurs in phase with sunspot activity, the cause of these must be linked; and that solar flares are confined to active regions, they can not be the cause o coronal manifestations of solar activity (such as coronal mass ejections). A butterfly-like diagram for the observed latitudes of solar flares coincides with the sunspot butterfly diagram. This supports the notion that the larger-scale coronal manifestations of solar activity (such as coronal mass ejections) are not directly related to flares and other smaller-scale phenomenon confined to active region latitudes.
Left: This diagram compares how sun activity (above) effects coronal streamer (below) behaviour throughout the solar cycle. The above image on the right shows no activity (ie. it is at solar minimum), while the streamers (blue image below on the right) are absent at the pole, but staddled around the equatorial plane. The reverse happens at solar maximum (second from left)At solar minimum the corona is reduced to a belt of streamers symmetrically straddling the solar equator. They no longer surround the disc and do not appear over the poles. They dont extend radially away, but bend toward the equatorial plane.
Helmet streamers are formed by a network of magnetic loops that connect the sunspots in active regions and help suspend the prominence material above the solar surface. The closed magnetic field lines trap the electrically charged coronal gases to form these relatively dense structures.
The base of streamers consists of nested loops of magnetic field lines, anchored at both ends below the photosphere on either sides of a magnetic neutral line. Beyond a certain height these magnetic loops are forced opened and stretched radially outward by the solar wind, producing the prototypal ``spiky helmet'' appearance of streamers.
As a helmet streamer first swells in the initial stages of the ejection, a dark cavity comes into view, within which an erupting prominence can be seen. The prominence material is blown outward along with the original streamer material. Comparison of images taken before and after a coronal mass ejection often reveal the disappearance of a filament (prominence) originally located along the magnetic neutral line straddled by the disrupted helmet streamer. Not all filaments disappear this way, and not all mass ejections are accompanied by erupting prominences.
The relatively faint X-ray emission believed to be associated with the dissipation of magnetic energy, occur as magnetic field lines blow open by the mass ejection [Elecric Universe Model state that its impossible for magnetic field lines to blow open because they always exist as a closed loop], reconnect and close up again over the ejection site, eventually leading to the formation of a new helmet streamer
Coronal Mass Ejections
While helmet streamers are long-lived, their demise often occurs abruptly through one of the larger-scale and perhaps most spectacular manifestation of solar activity: coronal mass ejections. A CME is the eruption of plasma from the Sun's outer atmosphere, or corona. The build up and interaction of magnetic loops, which can stretch over, under, and around each other, seems to supply the energy to heat the corona and produce the violent explosion of a CME.
Eventually, some of the overlying magnetic loops merge and cancel each other, cutting a hole in the magnetic net and allowing the CME to escape at high speed. If a CME erupts on the side of the Sun facing Earth, and if our orbit intersects the path of that cloud, the results can be spectacular and sometimes hazardous.
In the larger coronal mass ejections up to 1013 kg of coronal material may be ejected outward at speeds as high as 1000 kilometers per second (average values are closer to ~ 1012 kg and 400 km s-1). Observations show that the expanding coronal material can be still accelerating a few solar radii away from the Sun, and often moving at velocities in excess of the gravitational escape speed, suggesting that the acceleration process is primarily magnetic in origin.
Coronal mass ejections occur at all latitudes, suggesting that they are not directly related to intense localized heating events such as flares, as the latter are restricted to low latitude active regions. In fact few coronal mass ejections are observed to be preceded by large flares or intense activity.
The 1989 (at early Maximum) coronal mass ejection was one of the most powerful recorded. Approximately 2 X 1013 kg of material were ejected with peak velocities of nearly 2000 km/s, blowing a hole nearly 100 degrees wide through the solar corona.
A Coronal HoleCoronal holes are the very dark regions shown in X-ray images usually located above the solar poles, but sometimes may extend down to lower latitudes. They can be seen as regions devoid of helmet streamers or other bright coronal structures.
The fact that coronal holes look dark indicates lower gas densities than in bright structures such as helmet streamers. Coronal holes look dark in X-ray images in part because of the lesser densities, but also because less heating occurs there. This suggest that coronal holes are regions of open magnetic field lines that extend out into the solar wind rather than coming back down to the Sun's surface as they do in other parts of the Sun., along which coronal gas can flow outward into interplanetary space in the form of the solar wind. Coronal holes rotate at the poles with a constant 27 day period.
Polar plumes are long straight, spoke-like streamers that project outward from the Sun's north and south poles where much of the fast wind comes from. We often find bright areas at the footpoints of these features that are associated with small magnetic regions on the solar surface. These structures are associated with the "open" magnetic field lines at the Sun's poles.
Earlier results from SOHO established that the gas of the fast wind leak through magnetic barriers near the Sun's visible surface. Previously, the gas of the fast wind was thought to stream out from the gaps between the plumes.
Now observations suggest that most of the fast wind leaves the Sun via the plumes themselves, which are denser than their surroundings. Gas can rise at 60 kilometres per second to a height of 250 000 kilometres above the Sun's visible surface. The fast wind is subsequently accelerated mysteriously to 750 kilometres per second.
The slower wind, half the speed of the fast wind, which comes from the Sun's equatorial regions leaks from helmet streamers, which are plainly seen protruding into the Sun's atmosphere during a solar eclipse. Coronal mass ejections also contribute to the solar wind in the equatorial zone of the Sun. the fast wind predominates in the heliosphere often colliding with the slow wind creating shock waves which agitate the Earth's space environment.
Kinks in the Sun's magnetic field caused by Alfven waves travel down the magnetic fields that emanate from the Sun. Where polar plumes occur, the magnetic field isn't kinked, but instead forms long, thin, straight tubes. This means that the Alfven waves don't operate in these regions, though scientists don't yet know why.
The Sun's polar plumes stretch out past the orbit of Mars and maybe farther. These plumes can be so thin and so long at the same time. The thin, straight tubes are diagnostic of Birkeland currents, which have an outer twisted filament or rope-like form taken by electric current flowing in plasma. The Alfven waves are therefore more likely to be the structure of the magnetic field associated with Birkeland currents.
The correlation between sunspot number and auroral sightings hints at a relationship between solar activity and geomagnetism. Also, changes in the solar luminosity effects climatic variability on Earth. Certain portions of the solar spectrum, in particular the ultraviolet, vary drastically throughout the solar cycle.
Solar astronomers of the nineteenth century recognized that flares observed on the Sun were followed by disturbances in magnetic instruments on Earth.
Large flares and coronal mass ejections often trigger geomagnetic storms; coronal material blown outward from the Sun at speeds exceeding that of the normal quasi-steady solar wind steepens into shocks, which pass by the Earth, interacting with and perturbing the protective cocoon of magnetic field called the magnetosphere.
It normally protects us from the energetic particles in the solar wind. But during a coronal mass ejection radiation the particles interact with the Earth's magnetic field at the poles to produce the auroras (borealis, australis).
Solar flares can also disrupt communications. The radiation and particles ionize the atmosphere and prevent the movement of radio waves between satellites and the ground. The ionized particles in the atmosphere can induce electric currents in power lines and cause power surges. These power surges can overload a power grid and cause blackouts.
Please now go to: The Magnetosphere Part 7
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