Chapter 21:

Space weather (including solar flares, aurorae, geomagnetic storms):

High-quality new pictures of the Sun, taken earlier this week from the Solar and Heliospheric Observatory (SOHO), have raised hopes that the mission may soon be returned to scientific operations. Engineers have successfully reactivated nine of the 12 instruments on the European Space Agency (ESA)/NASA SOHO mission, which has been out of commission for nearly four months after contact was lost on June 24.

Images from the Michelson Doppler Imager and the Extreme Ultraviolet Imaging Telescope on SOHO are posted on the Internet at: http://sohowww.nascom.nasa.gov

"Scientists on both sides of the Atlantic have waited anxiously for the recovery of SOHO," commented Roger Bonnet, ESA's director of science. "Thanks to the extraordinary determination and skill of ESA and NASA personnel, with industrial contractors and scientific teams also playing their part, the world has recovered its chief watchdog on the Sun. SOHO is needed more than ever, because the Sun is rapidly becoming stormier with a mounting count of sunspots."

"It's very exciting to see these images again after so many weeks of concern. We hope that all the SOHO scientific instruments can be returned to the same level of health, so we can resume normal scientific operations in the near future," said Dr. Joseph Gurman, the U.S. project scientist for SOHO, and co- investigator on the Extreme Ultraviolet Imaging Telescope (EIT).

"As of today, nine of the 12 instruments on board SOHO have been turned on. Four of them are already fully functional; the other five are still undergoing careful recommissioning activities. But so far no signs of damage due to thermal stress during the deep freeze have been detected. I tip my hat to the engineers who built this spacecraft and these sensitive but robust instruments," said Dr. Bernhard Fleck, the ESA project scientist for SOHO. The remaining three instruments will be switched on over the next few weeks..

The images are the latest success for the team during a complex, challenging recovery sequence. On July 23, SOHO was located using radar techniques with the 305-meter Arecibo, Puerto Rico, radio telescope of the U.S. National Astronomy and Ionosphere Center as a transmitter and a 70-meter dish of the NASA Deep Space Network as a receiver. SOHO first responded to radio transmissions on August 3, and telemetry from SOHO was received August 8, telling controllers the condition of the spacecraft and its instruments. The spacecraft's frozen hydrazine fuel was gradually thawed, and on September 16, SOHO's thrusters were fired to stop its spin and to place it in the correct orientation towards the Sun.

Prior to the interruption, instruments on SOHO had taken about two million images of the Sun, an activity representing over a terabyte (a trillion bytes) of data. After its launch on Dec. 2, 1995, SOHO revolutionized solar science by its special ability to observe simultaneously the interior and atmosphere of the Sun, and particles in the solar wind and the Sun's outer atmosphere.

SOHO observations have been the subject of more than 200 papers submitted to refereed, scientific journals. Apart from discoveries about flows of gas inside the Sun, giant "tornadoes" of hot, electrically charged gas, and clashing magnetic field- lines, SOHO also proved its worth as the chief watchdog for the Sun, giving early warning of eruptions that could affect the Earth.

SOHO operates at a special vantage point 1.5 million kilometers (about one million miles) out in space, on the sunward side of the Earth. The spacecraft was built in Europe and it carries both European and American instruments, with international science teams. SOHO was launched on an Atlas IIAS rocket and is operated from NASA's Goddard Space Flight Center in Greenbelt, Maryland.

In April 1998, SOHO's scientists celebrated two years of successful operations and the decision of ESA and NASA to extend the mission to 2003. The extension enables SOHO to observe intense solar activity, expected when the count of sunspots rises to a maximum around the year 2000.

The first EIT image taken in the Fe IX/X line at 171 A is available at:
http://sohowww.estec.esa.nl/operations/Recovery/eit_171_981013.gif
and
http://sohowww.nascom.nasa.gov/operations/Recovery/eit_171_981013.gif
The MDI image can be found at:
http://soi.stanford.edu

The latest SOHO EIT images can be found on the Web at:
http://umbra.nascom.nasa.gov/eit/eit_full_res.html

Details about the operations and about SOHO in general, can be found at:
http://sohowww.estec.esa.nl
and
http://sohowww.nascom.nasa.gov

Information on the recovery of SOHO can be found at:
http://sohowww.nascom.nasa.gov/operations/Recovery//operations/Recovery/

SPACECRAFT IMAGES CAPTURE MAGNETIC ENERGY BURST ON SUN

The first images from NASA's Transition Region and Coronal Explorer (TRACE) spacecraft reveal activity in the solar atmosphere in stunning detail and include the first detailed observations of a magnetic energy release, called a magnetic reconnection.

The magnetic reconnection was observed on May 8, 1998, in a region of the solar atmosphere where two sets of perpendicular magnetic loops expanded into each other. Magnetic reconnection occurs when magnetic fields "snap" to a new, lower energy configuration, much like when a twisted rubber band unwinds or breaks. A magnetic reconnection can release vast amounts of energy and is responsible for explosive events on the Sun, such as flares, that can cause communication and power system disruptions on Earth.

High resolution movies of a relatively small but clear magnetic reconnection event and other spectacular solar activity observed by TRACE were presented today during the spring meeting of the American Geophysical Union in Boston.

"The TRACE spacecraft is unique in that it has both high spatial and temporal resolution in the extreme ultraviolet, wavelengths of light that reveal the multimillion degree temperature of the Sun," said Dr. Alan Title, TRACE Principal Investigator from the Stanford Lockheed Institute for Scientific Research (SLISR) in Palo Alto, CA. "We can image solar activity in finer detail than existing spacecraft, and we can take a new image once every few seconds. Both are necessary for our mission, which is to understand in great detail how energy is transported from the solar surface into the outer atmosphere. In the past, spacecraft of lower resolution were forced to average over much larger areas and periods of time. This made it difficult to get at the fundamental physics."

"In our magnetic reconnection movie, we can distinguish the fine details of the magnetic fields and see how they change during time periods of about a minute. TRACE has given us many surprises, and new ones occur nearly every observation. We found that even large areas of the Sun, some more than 60,000 miles long, can heat up or cool down significantly and thus appear and disappear in just a few minutes," said Title.

The TRACE spacecraft, launched from Vandenberg AFB, CA, on April 1, 1998, joins a multinational fleet of International Solar Terrestrial Physics project spacecraft studying the Sun during a critical period when solar activity is beginning its rise to a peak early in the new millennium. The Sun goes through an 11-year cycle from a period of numerous intense storms and sunspots to a period of relative calm and then back again. The coming months in the Sun's cycle will provide solar scientists with periods of intense solar activity interspersed with periods when the Sun is relatively passive and quiet. This will give TRACE the chance to study the full range of solar conditions, even in its relatively short planned lifetime.

TRACE is training its powerful telescope on the so-called "transition region" of the Sun's atmosphere, a dynamic region between the relatively cool surface and lower atmosphere regions of the Sun (about 10,000 degrees Fahrenheit) and the extremely hot upper atmosphere called the corona (up to three million degrees Fahrenheit). Using portions of the telescope sensitive to extreme-ultraviolet and ultraviolet wavelengths of light, TRACE is studying the detailed connections between the fine-scale surface features and the overlying, changing atmospheric structures of hot, electrically charged gas called plasma. The surface features and atmospheric structures are linked by fine-scale solar magnetic fields. The solar atmosphere is constantly evolving because the magnetic fields that dominate the corona are continuously displaced by the convective motions in the outer layers of the Sun just below the photosphere.

The TRACE science team also will study the evolution of events, such as massive flarings and huge eruptions, in the Sun's atmosphere. These events originate at the Sun's visible surface, the photosphere, and travel upward through its atmosphere (chromosphere and transition region), and then into its super-hot corona before speeding out into space, sometimes towards Earth.

The power of the TRACE telescope to do detailed studies of the solar atmosphere makes this observatory unique among the current group of spacecraft studying the Sun. The spacecraft has roughly 10 times the temporal resolution and five times the spatial resolution of previously launched solar spacecraft. A Sun-synchronous orbit is uninterrupted by Earth's shadow for eight months at a time, allowing the mission the greatest chance to observe the random processes which lead to flares and massive eruptions in the Sun's atmosphere.

The TRACE core team consists scientists from Lockheed Martin Advanced Technology Center, Stanford University, NASA's Goddard Space Flight Center, the University of Chicago, Montana State University, and the Harvard-Smithsonian Center for Astrophysics. Images to support this story are available at:

FTP://PAO.GSFC.NASA.GOV/newsmedia/TRACE/

Lockheed master list of solar web sites

http://www.lmsal.com/solarsites.html

TRACE Satellite Launched

The Transition Region and Coronal Explorer spacecraft was successfully launched on April 1st to make high-resolution observations of these regions of the outer solar atmosphere. It is working well.

SOHO Summary

Therese Kucera of the NASA Goddard Space Flight Center summarized SOHO results at the American Association for the Advancement of Science meeting in February 1998. Other SOHO press releases deal with the magnetic carpet of coronal loops, coronal mass ejections and their effect on Earth, a jet stream near the pole, and helioseismology.

Solar Probe - An Update

For the first time in many years the Solar Probe has an excellent chance to become a flight mission ready for launch in Oct. 2002. The Solar Probe will address the fundamental question of solar wind acceleration which can only be answered by in-situ and remote sensing measurements close to the sun. This mission exploring the last uncharted region in the solar system will be among the first three in the Outer Planets/Solar Probe Line with the launch of the first planned for 2002/03 and subsequent launches expected at approximately two-year intervals. The process of determining the launch sequence of Solar Probe, Pluto-Kuiper Express and Europa Orbiter is now underway with thedecision expected in about 3 to 4 months. An essential part of this process will consist of assessing the scientific importance of these missions as expressed by members of the community through the Sun-Earth Advisory Subcommittee (SECAS), the Solar System Exploration Subcommittee (SSES) and members of the Science Board of Directors at NASA Headquarters. Other factors include technology readiness and overall cost. Congressional approval for a 2000 start of this new series of missions addressing the "Origins Theme" will soon be requested.

The current baseline Solar Probe mission addresses the basic questions of solar wind origin and solar surface topology over the poles with highly capable science instruments. Despite significant advances made in recent years, these questions can only be resolved with this mission. Flying a trajectory perpendicular to the Earth-sun line during its perihelion passage, Solar Probe will use in-situ and imaging measurements to provide the first three-dimensional viewing of the corona, direct high-resolution observations of solar polar regions and magnetic fields, and local sampling of the solar environment. High-data-rate measurements commence at 0.5 AU, ten days prior to perihelion at 4 solar radii, and encompass both polar passes, allowing for comparison of measurements at corresponding heliolatitudes. These primary observations are complemented by context- setting cruise measurements and Earth-based observations. Using a Discovery-class launch vehicle, the baseline mission will take 3.6 years to complete. On-hand technologies and low-risk development can enable the Solar Probe to reach the sun during the next solar minimum if it is launched as either the first or second of the three Outer Planets Missions. A second close flyby of the sun around solar maximum may be possible. This extension of the Solar Probe mission will be studied.

The goal of the Solar Probe Science Definition Team (SP SDT) is to ensure broad involvement of the SPA community in all phases of this once-in-a-lifetime mission. We welcome your comments and suggestions to help us achieve this goal.

For more information contact any member of the SP SDT or visit the Solar Probe Web site http://solarprobe2.jpl.nasa.gov/.

Yohkoh Public Outreach

I would like to take this opportunity to bring to your attention a web site that we have been putting together over the last two years as part of a public outreach and education project. The Yohkoh Public Outreach Project (YPOP) is a NASA funded educational outreach project designed to facilitate public access to high quality Yohkoh/SXT and other solar data via the Internet.

As part of this project we were charged with the production of a high quality version of Yohkoh/SXT long-term movie. Over 5 years of the Yohkoh mission are now online with a cadence of approximately 1 frame per 6 hours. This provides a quick-look data access facility for use by the solar community as well as educators and the general public. The movie can be accessed via

http://www.lmsal.com/YPOP/FilmArchives/data_access.html

Another feature you might find of interest is the weekly Yohkoh science nugget from the SXT Chief Observer at ISAS. This can be found at

http://www.lmsal.com/YPOP/

The general outreach site can be accessed via http://www.lmsal.com/YPOP/

and is full of interesting activities and information. The YPOP pages are being continually updated and improved but please have a look at our site and if you have any comments or suggestions let us know.

New San Fernando Observatory Web Site

The San Fernando Observatory has recently reorganized its Web site. In particular, daily updated photometric full-disk solar images in two wavelengths are available. In the near future, we plan daily postings of sunspot number, area, and location, and facular areas. A downloadable archive of SFO's twelve years' worth of photometric full-disk solar images is being developed, and should be partially in place by the end of 1998.

The site is located at http://davinci.csun.edu/~astro/sfo.html.

Williams Expeditions Featured on Web Pages

Take a look at http://www.stellarimages.com/kidseclipse and http://www.williams.edu/Astronomy/eclipse98.

SOHO Works on the Solar Magnetic Field

Scientists using SOHO reported in November about observations of magnetic loops and their possible role in magnetic heating.

Common Misconceptions

Incorrect
SOHO stands for Solar Helioseismology....
Correct
SOHO stands for Solar and Heliospheric, where the heliosphere is the sphere around the sun (Helios).

Incorrect
The Sun has a radioactivity zone.
Correct
The Sun has, inside its convection zone, a radiation zone, that is, a zone in which energy is transported by radiation instead of by convection. Radioactivity, the decay of nuclear particles, is not a phenomenon that takes place in or on the Sun.

Incorrect
Scientists study helioseismology by studying wavelengths.
Correct
Scientists study helioseismology by studying waves on the surface of the Sun. The periods with which these waves oscillate are different for waves that penetrate the Sun to different distances.

Incorrect
To use helioseismology, scientists send waves into the Sun.
Correct
To use helioseismology, scientists observe waves that are naturally generated by the Sun.

Incorrect
The chromosphere, seen every day by looking straight at the Sun, has emission lines because it is hotter than the photosphere.
Correct
The chromosphere is too transparent to add emission lines to the solar absorption lines. Only when we see it at the edge of the Sun (known as the "limb") do we detect emission lines, because then we see the chromosphere in silhouette against dark sky. We can see the chromosphere and prominences in this way every day with telescopes on Earth that use H-alpha filters or without filters at the times of total solar eclipses.

Cluster to fly again

The European Space Agency is planning to replace the four Cluster satellites to study the solar wind that were lost in an explosion during launch in 1996.

Eclipse, Satellite Solar Slides

Eight radial-filter eclipse images from the National Center for Atmospheric Research and a variety of coronal images from the Solar Maximum Mission are viewable on the Web and can be ordered as slides.

SOHO reveals solar circulations

Observations taken from SOHO show the flow of gases about 20 thousand kilometers under the solar surface. Belts of gas, like the Earth's trade winds or the winds that form the bands of Jupiter, circulate some 16 km/hour relative to their surroundings. Sunspots form between neighboring belts, perhaps because the relative motion of the belts is twisting the magnetic fields there. The opposite possibility should also be considered: that the strong magnetic fields at these positions keep the gas from flowing freely, leading to the presence of the bands.
Further, the bands slowly migrate toward the equator, as the sunspots are observed to do in the butterfly diagram.
In addition, the outer layer of the sun folows at 80 km/hour from the equator to the poles.
Finally, also released at a late August 1997 NASA press conference, jet streams circulate at 75 degrees latitude.