The Sun-Earth Connection

by Amara Graps

"It is true that from the highest point of view the Sun is only one of a multitude - a single star among millions - thousands of which, most likely, exceed it in brightness, magnitude, and power. It is only a private in the host of heaven. But it alone, among the countless myriads, is near enough to affect terrestrial affairs in any sensible degree; and its influence upon them is such that it is hard to find the word to name it." Charles Young 1896 (American astronomer who was the first to see the green spectral line of solar corona).

In Young's quote above: "to affect terrestrial affairs in any sensible degree" is an understatement. Our Earth, orbiting 93 million miles away from the energetic star at the center of the Solar System, receives only one-half of one-billionth of the Sun's energy output. Mere crumbs! Yet those "crumbs" are enough to nourish and power the whole planet.

Today, a hundred years after Young's quote, it is still hard to find the word to name the Sun's influence on our terrestrial affairs. Heat absorbed by the Sun circulates air currents, which influences ocean water evaporation which drives clouds and rain, which then adds to vast rivers that moderates climates. Plant photosynthesis, triggered by the sunlight, produces carbohydrates which, via the food chain, nourishes herbivores and carnivores and human beings.

More examples of the Sun's influence on the Earth can be seen via the interplanetary magnetic field and the solar wind. When the plasma from the Sun's corona, called the "solar wind," rushes out into interplanetary space, it contains an imprint of the Sun's magnetic field. As the Sun rotates, the magnetic field, one line fixed to the Sun, twists into an Archimedes Spiral shape, reversing its polarity every eleven years. The rippled sheet triggers aurora and other electromagnetic disturbances on the Earth as the planets ride the ripples above and below the solar plane of zero magnetism.

Coronal mass ejections (CME) also trigger aurora and other electromagnetic disturbances on the Earth. These dramatic discharges of coronal material contain up to 11,000 million tons of solar matter traveling at a million miles per hour.

These examples of the Sun's influence on terrestrial affairs still form an incomplete list. I hope that you can now see why it is difficult find a word that names the Sun's influence on our Earthly existence!

This article will show you a variety of Internet resources for the Solar-Earth Connection, from the research projects to the educational to the playful. Enjoy the ride.


The International Solar Terrestrial Physics (ISTP) program

http://www-spof.gsfc.nasa.gov/istp/

The International Solar Terrestrial Physics (ISTP) program is a joint project of the United States, ESA, and Japan to understand the fundamental processes of the Earth-Sun system. These processes include stellar convection, magnetic dynamo action, generation of stellar winds, gravity and fundamental particle physics.

ISTP can be considered a framework for solar-terrestrial science, since there is now a variety of spacecraft to study the Sun-Earth system. The spacecraft include SOHO, Geotail, Wind, Polar, and ground-based observatories. This system is beginning to function extremely well. One evidence of this efficient system is its ability to observe and quickly bring together the total picture of coronal mass ejections from the time that they leave the Sun to the time when they interact with the Earth's magnetosphere.

In 1997, the news media published reports about CMEs that left the Sun and were subsequently tracked by many spacecraft. Not only by the ISTP network, but also tracked by other spacecraft and observatories. The event in January was a particularly interesting one because it was the first time that a solar event had been tracked so thoroughly (from "cradle to grave," said Stephen Maran at NASA's Goddard Space Flight Center), and it may have caused the demise of an expensive AT&T satellite which malfunctioned during the time of the geomagnetic storm following the CME event. The ISTP link and figure below gives full information about that particular January CME event, including data, scientific investigations, pictures, and media reports.

http://www-istp.gsfc.nasa.gov/istp/cloud_jan97/event.html

The ISTP page is a good place to start for many Sun-Earth related information and sites. It is also invaluable to the researcher, because, not only can you download the latest data from that site, but they also provide some softare (written in IDL) with which to view and analyze the data. The ISTP site is also a great place to gather information on CME events, to learn meetings and reports in the fields related to Sun-Earth Connections, and finally, I liked their educational outreach links and their primer on the Earth's magnetosphere. I found a few educational links that I didn't know about, in particular, a lively and interesting WWW page about Earth's auroras; created by the San Francisco Exploratorium
( http://www.exploratorium.edu/learning_studio/auroras)

I give the ISTP page a 9.9 as an example of a useful, interesting, and educational site.

One of the ISTP spacecraft is the SOHO spacecraft, which stares at the Sun continuously from a point 1 million kilometers in front of Earth. I won't go into detail about the large SOHO WWW site now, but I must mention SOHO because of the large role that the satellite plays in initial observations of any new solar event. They have a "ringside seat" on the action, in other words.

The SOHO people are aware of their role in initially spotting solar disturbances and how that information is used in predicting subsequequent geomagnetic disturbances on the Earth. They have put together a WWW page with the latest information from SOHO and links to pages set up with data from other ISTP spacecraft. You can find that page at: http://sohowww.nascom.nasa.gov/gallery/current/.


Space Weather

Space weather refers to condtions on the Sun and in the solar wind, Earth's magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based logical systems and can endanger human life of health.

The Space Environment Center

Many scientists today are working hard at forcasting space weather, which they aim at being able to predict at least as accurately as they forecast Earth weather. If scientists can warn a day or so in advance of an imminent geomagnetic storm, then satellite operators and power companies can try to protect equipment, averting millions of dollars in damage.

The Space Environment Center (SEC) in Boulder, Colorado is one of those groups that works hard at forcasting solar and geophysical events.

http://www.sec.noaa.gov/

They conduct research in solar-terrestrial physics, they develop techniques for forecasting solar and geophysical disturbances, and they provide real-time monitoring and forecasting of solar and geophysical events. This site is an important one because of the breadth of their offerings. Their offerings include solar-terrestrial data and images, a daily report of space weather, a report and forecast of Solar Geophysical Data in an online Web document: "The Weekly", a primer on the Space Environment with descriptions of the sun and various solar phenomena, and they have a "Glossary of Solar-Terrestrial Terms", as well.

One of the most creative educational aspects that I've seen at a solar physics site is SEC's instruction for making an origami model of the Sun. We hope that by putting together this model of the Sun, you can learn more about the Sun, in particular we hope that you will be able to answer questions such as "What kinds of cycles does the Sun have?", "What are the four types of radiation from the Sun?", "What are some solar features?".

I give this site a 9.9 because of the importance and value of their scientific offerings to the research and commericial communites. If this site went away, I can't think of another site that comes close enough to this one to fill its shoes.

The Space Weather Tutorial Page

The Space Weather Forecast Page in Lund, Sweden, aims at educating the nonscientist about space weather. My definition for space weather at the top of this section came from that site.

http://www.lund.irf.se/HeliosHome/forecastservice.html

This WWW site paints a broad picture of the Sun-Earth connection by touching briefly on each of the important aspects of the connection. They use a minimum of text and, instead try to teach using colorful images (in thumbnail form to aid those with slow connections).

The site says that it all starts with solar magnetic flux tubes rising by magnetic buoyancy. That results in sunspots, solar flares, prominences, coronal mass ejections, coronal holes, fast solar wind, and so on. Their images follow that theme. They start with a few brief descriptions about the interior of the Sun (for example, by providing descriptions and links to the field of helioseismology, i.e. studies the solar interior using sound waves.) Then they work outwards with descriptions and links to the solar chromosphere, the solar corona, out into interplanetary space, and finally to Earth.

Their last section on that page: "Space weather effects" gives a pictorial description about the effect of space storms on power systems, satellite systems, navigation systems, communication systems, manned space flights and the Earth's climate.

The site is a nicely comprehensive site. They conclude, by summarizing everything on the Space Weather Tutorial Page (a nice touch!), links to animations, a glossary of space weather terms, and a bibliography list for further reading. I thought that the site was very carefully designed, it was concise, and it portrayed alot of information in small portions and in a colorful and interesting way. Rating; 9.9

The Solar Guide

The Solar Guide is an Web "users guide" for how to use Geophysical Alert Broadcasts. The author is David Rosenthal. The guide is based on information made available by NOAA and the Space Environment Services Center (site described above). The 45-second Geophysical Alert Broadcasts are primarily intended for users in North America and the Pacific, and outline the current nature of the solar-terrestrial environment.

Updated every three-hours beginning at 0000 UTC, the Geophysical Alert Broadcasts are concerned with two primary types of Earth-Sun interaction: electromagnetic radiation and geomagnetic activity (which includes effects from solar sub-atomic particle emissions).

If you are a researcher in this field or a commercial vendor operating equipment that could be affected by solar and geomagnetic events, then you would benefit by knowing about the space weather predictions and how to interpret the space weather forecasts. This guide well help you in understanding the lingo of the field. Rating: 9.5

Daily Solar Data

If you are a researcher or an an educator or just simply curious about how many sunspots are on the Sun today, you can go to this site which shows daily solar data:

http://umbra.nascom.nasa.gov/images/latest.html

At this site you can download images from some of the major solar observatories: SOHO, Yohkoh, the National Solar Observatories, and the High Altitude Observatory, for example. It is a valuable site for the solar researcher, and it is a valuable site for educators wishing to show their students the many faces of the Sun. I give it a rating of 9.9 for high content and convenience value.

The Sun

The following WWW site is an educational site by Davison E. Soper at the University of Oregon about basic aspects of the Sun. It's a simple, clean, no-frills, high-school level site that is my favorite example of how the Web should be used for science education.

http://zebu.uoregon.edu/~soper/Sun/sun.html

The page at first looks like a sparse page of text and numbers about the Sun, for example:

Distance: 1 AU ~ 150 x 106 km. 
Size: radius ~ 0.7 x 106 km. 
Mass: ~ 2 x 1030 kg. 
Density: ~ 1400 kg/m3. 
Composition: 74% H, 25% He, 1% other (by mass). 
Temperature: at photosphere ~ 6000 K. 
Luminosity: ~ 4 x 1026 W. 
But the viewer quickly notices that on that page are links with descriptions about how we know those particular parameters and values. For example, clicking on the above "Distance" word brings you to another page that describes astronomical units, and the motion of planets in elliptical orbits. Clicking on "Luminosity" brings you to a page with a diagram of the definition of luminosity, an equation and what number results when one plugs numbers into the simple equation.

I really can't say enough good things about this particular WWW site. I will mark .1 points off because of the dreary Netscape gray background, but I wish all sites were full of this much content! Rating: 9.9


Auroras

Auroras are beautiful light shows visible from those living in Earth's higher latitudes. The light shows arise from a mixing of trapped solar charged particles, the Earth's magnetic field, and the Earth's atmosphere. Charged particles in space from the Sun become pulled into Earth's magnetic field and are trapped. Once they are trapped, the particles spiral towards the Earth's magnetic poles, where the particles hit the gases in the Earth's atmosphere. These collisions give off energy that we see as colored light.

Many different kind of solar events, such as CMEs can trigger auroras. During the well-publicized CME events of this last Winter and Spring, the auroral activity was quite high. There is little doubt at those times that the activity was caused by the solar storms passing by.

The Aurora Page

http://www.geo.mtu.edu/weather/aurora

This WWW page at Michigan Technological University, Houghton, Michigan about auroras may be the most comprehensive aurora WWW page on the Web. Here you will find information, links, and images about auroras. In particular, you will find easy reading on the subject, auroral forecasts, many auroral images from the Earth and from space, auroral sounds, and a long list of other aurora sites. They tie in to the Sun-Earth connection by providing space and space weather links, as well. A very useful site for researchers and educators both! Rating 9.9

Watch the skies!


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Last Modified by PK in July 2008.