CORONAL MASS EJECTIONS

AND ERRUPTIVE

PROMINENCE

بسم الله الرحمن الرحيم" يا معشر الجن واإلنس إن

استطعتم أن تنفذوا من أقطار السموات واألرض

فانفذوا ال تنفذون إال فبأى آالء ربكما (34بسلطان )

يرسل عليكما (35تكذبان ) ونحاس فال شواظ من نار

( فبأى ءاآلء 36تنتصران )" ( 37ن )ربكما تكذبا

سورة الرحمن

(55)

Which of your Lord's marvels can you deny?

• O assembly of the jinn and the men! If you are able to pass through the regions of the heavens and the earth, then pass through; you cannot pass through but with authority (33). Which of your Lord's marvels can you deny?(34)

Fig 1: A huge coronal mass ejection (about twice the size of the visible sun) seen in this coronagraph image on February 2000. About one hour before this image was taken, another SOHO instrument, the Extreme ultraviolet imaging spectrometer EIT ,detected a filament eruption lower down near the solar chromosphere.

1- It is a giant magnetic bubble that rapidly expands to exceed the sun in size and pushes billions of tons of million degree gas into interplanetary space at speeds of about 4X10 *5m/s reaching the earth in about four days. Their associated shock propel vast amount of high speed particles ahead of them.2- CMEs erupt from the sun as self-contained structures of hot material and magnetic loops. They apparently result from a rapid large scale restructuring of magnetic fields in the low corona.3- They are detected on routine visible light cronagraphs.4- They where discovered in 1971, but since then, thousands CMEs have been identified

5- The LASCO instrument on SOHO observes the sun from 1.1 to 30 solar radii..6- frequency of occurrence 3.5 events per day (activity maximum) and 0.2 events per day (activity minimum).7- The amount of energy liberated in CME is comparable to solar flare energy, it is used in expelling the mass and in lifting it against gravity., while flare energy is used in accelerating particles and emitting X and radio waves.8- Near activity minimum, CMEs are largely confined to equatorial regions , but near maximum they are observed at all solar latitudes.9- When it hits the earth, a mass ejection can produce powerful geomagnetic storms, intense auroras, electrical power blackouts etc.10- About 70% of CME are associated with and followed by eruptive promimences.

Fig 2:Coronal mass ejection, planets and Pleiades A coronal mass ejection, four planets and bright stars of the Peiades cluster are all captured in this image from SOHO, taken with the LASCO instrument on 25 May 2000. Four of the five naked eye planets are seen in rare alignment as bright discs bisected by a line which is an instrumental effect caused by the intense sunlight reflected from the planets.

Fig 3: Eruptive prominence: This large eruptive prominence was observed in the extreme ultraviolet light of ionized helium(He II 3040 Aº on 24 July 1999. The comparison image of the Earth shows the enormous extent of the prominence. The inset full disk solar image indicates that the eruption looped out for a distance almost equal to the sun's radius.

magnetic interaction: A pair of oppositely directed twisted coronal loops come in contact, releasing magnetic energy to power a solar flare. Arrows indicate the directions of the magnetic field lines and the sense of twist. Such magnetic encounter can occur when newly merging magnetic fields rise through the photosphere to merge with preexisting ones in the corona, or when the twisted coronal loops are forced together by underlying motion.

The fields partially innailates each other. The magnetic field lines are never permanently broken and they simply reconnect into new magnetic configuration. The explosive instability has been compared to an earthquake. According to this analogy , the moving roots or foot points of magnetic loop resemble two tectonic plates , they grind against each other and build up stress and energy. When the stress is pushed to the limit, the two plates cannot slide further and the accumulated energy is released as an earthquake. That part of the fault line then returns to its original equilibrium position. After an explosion on the sun., the magnetic fields similarly regain their composure , fusing together

Solar flare Model: Explosions are frequently triggered in compact structures just above the tops of coronal loops,. Magnetically fields of opposite magnetic polarity are probably driven together there. During an impulsive solar , the free magnetic energy released during magnetic reconnection is converted to charged particles kinetic energy . In less than a second, electrons are accelerated to the speed of light at a site above the top of the loop shown schematically here, generating a burst of radio energy as well as impulsive hard x-ray emission. Some of these non thermal

electrons are channeled down the loop and strike the chromosphere at nearly the speed of light emitting hard X-rays by bremsstrahlung at the loop footpoints. When beams of accelerated protons enter the dense lower atmosphere, they cause nuclear reactions that result in gamma- ray spectral lines and energetic neutrons. Material in the chromosphere is heated very quickly and rises into the loop, accompanied by a slow increase in soft X-ray radiation. This upwelling of heated material is called chromospheric evaporation.

Coronal mass ejection are also probably energized and expelled by similar process.

PREDICTING EXPLOSIONS ON THE SUN

Coronal loops are magnetically reconfigured as they twist in response to internal differential rotation and convective motions. Yet, the coiled magnetic fields hold their energy in place, and remain without substantial change for days, weeks and even months at a time, like a rattlesnake waiting to strike. Then they suddenly and unpredictably go out of control, explodes and tears the magnetic cage apart.The solar explosions emit energetic particles, intense radiation, powerful magnetic fields and strong shocks that can have enormous practical implications when directed toward the earth. They can disrupt radio navigation and communication systems, pose significant hazards to astronauts, satellites and space stations near earth, and interfere with power transmission lines on the ground. National space environment centers and defence agencies therefore continuously monitor the sun from the ground and space to forecast threatening activity.

The ultimate goal is to learn enough about solar activity to predict when the sun is about to have an explosion. Such space weather forecasts will probably involve magnetic changes that precede solar flares and coronal mass ejections, especially in the low corona where the energy is released or at lower levels in the photosphere where we can watch internal motions pulling and twisting the magnetism about.

When the bright X-ray emitting coronal loops are distorted into a large, twisted S or inverted S configuration, a coronal mass ejection from that region becomes more likely. In other words, the magnetism gets stirred up into a complex , stressed and twisted situation before it explode, and relaxes to a more stable configuration after the outburst.

Before CME After CME

after

Will the CME hit the Earth?

It is critically important to know if the material sent out from the solar outbursts is headed toward earth.

-CMEs that are expelled from near the visible edge of the sun are not likely to impact earth, but threaten other parts of space.-Mass ejections are most likely to hit the earth if they originate near the center of the solar disk as viewed from earth. And are sent directly toward the planet. It is critically important to know if the material sent out from the solar outbursts is headed toward earth. -CMEs that are expelled from near the visible edge of the sun are not likely to impact earth, but threaten other parts of space.

Halo coronal mass ejections

-Mass ejections are most likely to hit the earth if they originate near the center of the solar disk as viewed from earth. And are sent directly toward the planet. -As previously noted, the outward rush of such a mass ejection appears appears in coroagraph images as a ring or halo around the occulting disk. -The earth directed ones may be preceded by coronal activity at ultraviolet and X-ray wavelengths near the center of the solar disk as viewed from the earth. -The mass ejection is itself sometimes associated with waves running across the sun, like tidal waves or tsunami going across the earth.

-As previously noted, the outward rush of such a mass ejection appears appears in coroagraph images as a ring or halo around the occulting disk. -The earth directed ones may be preceeded by coronal activity at ultraviolet and X-ray wavelengths near the center of the solar disk as viewed from the earth. -The mass ejection is itself sometimes associated with waves running across the sun, like tidal waves or tsunami going across the earth.

Which high energy electrons hit the earth

The high energy electrons that accompany solar flares follow the spiral pattern of the interplanetary magnetic field, so they must be emitted from active regions near the west limb and the solar equator to be magnetically connected with the earth.

Solar flares emitted from other places on the sun are not likely to hit earth but they could be headed toward interplanetary spacecraft,the moon ,mars or other planets.

SEEING THE BACK SIDE OF THE SUN

Nowadays scientists can use sound waves to see right through the sun to its hidden, normally invisible back side , enabling them to monitor active regions before they rotate to to face the earth. The new technique, dubbed helioseismic holography, examines a wide ring of sound waves that emanate from a region on the side of the sun facing away from the earth(the far side) and reach the near side that faces the earth.. When a large active is present on the back side of the sun, its intense magnetic fields compress the gases there, making them slightly lower and more dense than the surrounding material. A sound wave that normally takes 6 or 7 hours to travel from the near side to the far side of the sun and back again takes approximately 12 seconds less when it bounces off the compressed active regions on the far side. When the near side photosphere oscillations are examined by SOHO Micheson Doppler imager or MDI, they can detect the quicker return of these sound waves.

Solar astronomers might be able to use this technique to to monitor the structure and evolution of large regions of magnetic activity as they cross the far side of the sun and revealing the regions that are growing in magnetic complexity and may be the site of explosions.Since the solar equator rotates with a period of 27 days , when viewed from the earth, this can give at least seven days extra warning of possible bad weather in space.