On March 9, 1999, solar physicists discovered a new tool for predicting solar eruptions, known as coronal mass ejections (CME). It has been shown that where the magnetic field lines snake around each other and form the letter 'S', one can be fairly certain that a CME will follow. This has come to be called the "S marks the spot" discovery. The Sun is covered with intense magnetic fields. These fields confine and conduct the plasmas over the visible surface of the Sun. Prominences and filaments are just two of the many effects produced by these magnetic fields. It is not yet fully understood how these 'S' shapes are formed, but at some point the magnetic field lines reconnect rather than sliding past each other. Then everything snaps and approximately 10 billion tons of ionized gas is hurled into space at speeds ranging upto 3 million kilometers per hour. If this explosion goes off at the right place on the Sun, it will reach the Earth in about four days. This can then cause geomagnetic storms, possibly damaging satellites and causing shut downs of power grids. Using X-ray telescopes scientists have been able to see these S-shaped regions embedded in active regions for years. They have been recognized as the dividing line between the areas in the active region with different polarities. Drs. Canfield, Hudson, and McKenzie took two years worth of Soft X-ray Telescope data and discovered that regions with either the 'S' shape or the upside down 'S' were more likely to erupt than those without the twist.

REF: http://science.nasa.gov/newhome/headlines/ast09mar99_1.htm

On February 3, 1999, using the Solar and Heliospheric Observatory (SOHO) scientists identified regions on the Sun where the high speed solar wind appears to originate. The high speed solar wind moves as fast as 3 million kilometers per hour. As the wind flows past the Earth, it changes the structure and shape of the Earth's magnetic field. If these changes are dramatic enough they can damage satellites and disrupt both communications and electrical power systems. As we become increasingly dependent on advanced technology, understanding this potential hazard becomes increasingly important. ESA and NASA scientists have for the first time observed the solar wind flowing from the edges of honeycomb-shaped patterns of magnetic fields at the surface of the sun, pictured above. These observations are presented in more detail in the 5 February 1999 issue of Science magazine.

REF:http://sohowww.nascom.nasa.gov/gallery/ESAPR/info01.html/

The Transition Region and Coronal Explorer (TRACE) has made a variety of contributions to the solar physics community over the past year. TRACE observations have pointed towards a corona comprised of thin loops that are naturally dynamic and continually evolving. (Loops are bright coronal structures that are longer than they are wide.) These very thin loops are heated on a time span of minutes to tens of minutes, after which the heating stops or changes significantly. The heating appears to occur primarily in the lowest 10,000 to 20,000 km of the magnetic field lines in the coronal segments. There is strong evidence suggesting that the lower altitude heating is intermittent on time scales of a minute or less, suggesting that the loops are driven from somewhere near the loop footpoints.

Previously, spectrally resolved observations of the Sun have suggested that the plasma in the transition region is on average redshifted (i.e. flowing downwards). This is obviously not the case and scientists hope that TRACE will help solve this dilemma. The erratic changes in the rate of heating forces the loops to continuously change their internal structure. There is both the injection of hot material from below the loops and rapid cooling of the loop tops. There is speculation that there are also downflows at temperatures intermediate to those of the hot Extreme Ultraviolet (EUV) emitting plasma and the cool EUV absorbing plasma. The EUV observations made with TRACE have shown material at coronal temperatures, as well as cooler material no hotter than 20,000 Kelvin, moving upward from as low as a few thousand kilometers above the photosphere. If we can understand the processes leading to these injections of matter into the outer atmosphere, we may be able to fully understand the method of coronal heating.

TRACE observations have also shown that two nearby regions can be very detached while regions further away may be more closely linked. In general, this means that regions up to several hundred thousand kilometers away frequently respond to flares and or eruptions, while at other times loops near an explosive event are unaffected. The reasons for this odd and unexpected relationship are not yet clear.

On May 27, 1998, scientists analyzing data from the Michelson Doppler Imager (MDI), an instrument on board SOHO, were able to show that flares produce seismic waves in the Sun's interior. "The researchers observed a flare-generated solar quake that contained about 40,000 times the energy released in the great earthquake that devastated San Francisco in 1906. The flare took place on July 9, 1996". Dr. Alexander G. Kosovichev, a senior research scientist from Stanford University, and Dr. Valentina V. Zharkova from Glasgow University (United Kingdom) were responsible for finding the seismic properties in MDI data from the Sun's surface. (This finding was reported in the May 28, 1998 issue of the journal NATURE.) The quake produced what appears to be large ripples spreading through the Sun's surface. In an hour, the waves traveled a distance ten times that of the Earth's diameter. The waves accelerated from 22,000 miles per hour to 250,000 miles per hour as they traveled outward and disappeared into the photosphere. Kosovichev and Zharkova developed a theory that predicts the nature and magnitude of these shock waves. However, their theory did not predict the strength of these waves correctly. In fact the actual wave was ten times stronger than they had predicted. Kosovichev predicts that as they travel throughout the Sun's interior they actually recombine on the opposite side of the Sun from where the flare erupted. This then creates a faint duplicate of the original ripple like pattern. The SOHO scientists believe that the seismic waves will allow them to verify interior solar conditions by studying the pattern of the waves as they travel through the interior, emerging at the surface.

REF:http://soi.stanford.edu/press/agu05-98/press-rel.html

For over 55 years scientists have been unable to explain why the corona is three million degrees when the visible surface of the Sun is only eleven thousand degrees Fahrenheit. On November 5, 1997 SOHO scientists released information concerning what they believe to be the cause of this huge temperature gradient.The thermal transfer of energy from a cooler surface to something much hotter is not physically possible. This implies that the energy transfer must be in the form of waves or magnetic energy. Dr. Alan Title of the Stanford-Lockheed Institute for Space Research, Lockheed Martin Advanced Technology Center, Palo Alto, CA, said "We now have direct evidence for the upward transfer of magnetic energy from the Sun's surface toward the corona above. There is more than enough energy coming up from the loops of the 'magnetic carpet' to heat the corona to its known temperature." The corona can be seen reacting to these evolving magnetic fields in images of the Sun's surface produced by the Extreme Ultraviolet Imaging Telescope (EIT), the Coronal Diagnostic Spectrometer (CDS), and the Transition Region and Coronal Explorer (TRACE). SOHO's Michelson Doppler Imager (MDI) provided very detailed and calibrated movies of the magnetic fields on the visible surface of the Sun. These movies showed rapidly changing properties of the Sun's "magnetic carpet" which can be described as a sprinkling of tens of thousands of magnetic concentrations. Analysis of the appearances and disappearances of these small concentrations on the the surface showed that after a "typical small magnetic loop emerges, it fragments and drifts around and then disappears in only 40 hours" said Title. These quickly evolving magnetic structures could very well produce the needed energy to raise the coronal temperature up to three million Kelvin.

REF:http://soi.stanford.edu/press/ssu11-97/ssu.html

The Michelson Doppler Imager (MDI) is an instrument on board the Solar and Heliospheric Observatory (SOHO). MDI has three basic helioseismology programs: Medium-l, Low-l and Dynamics. Helioseismology's principal goal is to determine the structure and dynamics of the Sun's interior from the oscillation frequencies of normal modes. MDI's Medium-l Program has the ability to provide continuous observations of oscillation modes of angular degree. The measurements made by MDI of the noise in the Medium-l oscillation power spectrum is lower than in ground-based measurements. Observations made with MDI have also revealed an existing asymmetry of oscillation spectral lines. A drastic change right at the edge of the core can be inferred from the sound-speed profile. Both radial and latitudinal variations of the sound speed are depicted in the diagram above, created by A.G. Kosovichev. The positive variations or hotter regions are shown in red and the negative variations or cooler regions are shown in blue.The Helium contained in a thin layer just above the convection zone is less abundant than originally predicted. Using MDI, one can also predict a significant rotational shear in this thin layer.

REF: http://soi.stanford.edu/results/sspeed.html

On August 18, 1997, scientist who used the Solar and Heliospheric Observatory (SOHO) released the discovery of jet streams beneath the surface of the Sun. Jet streams are rivers of hot, electrically charged gas (plasma). They have also discovered something similar to trade winds which appear to transport energy beneath the Sun's surface. These observations were made by the Solar Oscillations Investigation (SOI) group at Stanford University, Palo Alto, CA. It is believed that these discoveries willl help solar physicists to understand the sunspot cycle. The jet streams are found near the poles and cannot be seen at the surface. The jets are small compared to the Sun as a whole and are made of oval regions that are flattened. They measure about 17,000 miles across.