Solar Activity:
The output of the Sun in all forms, light, solar wind, and energetic particles, is not constant. It varies with both time (seconds to centuries!) and position on the Sun. These changes are called solar activity and are probably reflections of changes below the Sun's surface. (Scientists can study the output and how it varies to study the workings of the Sun).
Solar Wind:
Most planets are surrounded by the flow of hot, magnetized, solar wind plasma (in a plasma the electrons are pulled free from the atoms and can move independently. The individual atoms are charged, even though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality) flowing out of the Sun carrying a large amount of kinetic and electrical energy. The solar wind shock waves are formed in front of the planets (see bow shock in the diagram below) that have their own magnetic fields.
- For more information about effects of the Solar Wind visible on Earth, see the Educational Brief: Earth's Invisible Boundaries, Auroras at: http://education.gsfc.nasa.gov/experimental/all98invProject.Site/Pages/science-briefs/ed-overington-tupis/solar.html
Terrestrial magnetosphere: (from the Oulu Space Physics Textbook)
The auroral oval from space: http://www-spof.gsfc.nasa.gov/Education/wpcap.html
http://www-spof.gsfc.nasa.gov/Education/Figures/de_ful_s.gif
Cameras aboard satellites can look down at the aurora and snap an instantaneous picture. What they see (above) is a roughly circular strip, centered a little nightward of the magnetic pole, known as the auroral oval. During large magnetic storms the oval grows in size and may even reach the population centers of Europe and America, giving people there a rare opportunity to watch auroras from their own backyards.
CMEs (Coronal Mass Ejections):
One of the most important scientific advances of the space age is the discovery of one type of solar activity, coronal mass ejections. Coronal mass ejections (CMEs) are powerful eruptions in which as much as 100 billion kilograms of plasma from the Sun’s atmosphere is blown into interplanetary space at one time. Traveling outward from the Sun and heading towards Earth at speeds up to 1000 kilometers per second, CMEs can create major disturbances in the magnetic fields of interplanetary space and trigger severe magnetic storms on Earth. CMEs aimed at the Earth can be responsible for enhanced auroral activity, satellite damage, and power station failures by driving interplanetary shock waves and accelerating particles to “near light” speeds, all of which come crashing into the Earth’s magnetic environment. Usually the Earth’s magnetosphere acts as a protective blanket, channeling most of the magnetic particles around the Earth, not allowing many of the particles to reach the Earth.
But if conditions are right, big changes occur which can wreak havoc on our technology. As a society we have come to depend on satellites, electrical power, and radio communication, all of which can be affected by these electric and magnetic forces. Since so much information is relayed by satellites- from ATM machines and broadcast signals to disaster warning systems- CMEs pose a technological hazard to our civilization.
For more detailed information see:
1. CMEs: Satellites in Peril at http://hpcc-k12.gsfc.nasa.gov/gessep/serverhome/gessep98/earth-sunconnections/inv3/cme.abstract.html
2. Solar Storms and Their Human Impacts at: http://image.gsfc.nasa.gov/poetry/storm/storms.html from the Public Outreach, Education, Teaching and Reaching Youth website.
3. Solar events information may be found at: Space Weather: http://helios.gsfc.nasa.gov/weather.html
4. See Blackout: at http://image.gsfc.nasa.gov/poetry/storm/black1.html
(http://www.gsfc.nasa.gov/ace/cmesoon.tif)
Sunspots:
Sunspots, temporary disturbances in the Sun's photosphere, are the most visible advertisement of the solar magnetic field. They appear dark because temperatures are considerably lower than in surrounding areas.
Solar Flares:
A solar flare is an enormous explosion in the solar atmosphere. It results in sudden bursts of particle acceleration, heating of plasma to tens of millions of degrees, and the eruption of large amounts of solar mass. Large flares can cause electromagnetic problems for spacecraft, but are not thought to be responsible for geomagnetic storms.
There are two types of flares: impulsive and gradual. Impulsive flares accelerate mostly electrons, with some protons. They last minutes or hours and the majority appear near the solar equator. Impulsive flares occur at a rate of about 1000 per year during solar maximum.
Gradual flares accelerate electrons, protons, and heavy ions to near the speed of light, and the events tend to last for days. They occur mainly near the poles of the Sun and happen about 100 times per year.
Solar Plumes:
Solar plumes are long, feathery jets that extend from near the poles of the Sun to more than 13 million miles into space. Solar plumes expel a high-speed stream of hot plasma from the corona that can reach one million degrees! The base of the plume contains churning magnetic fields and solar gases. At its base, a plume is about 2500 km (1580 miles).
Coronal Holes:
Coronal holes are large areas in the corona of the Sun that are less dense and cool than the surrounding areas. Coronal holes allow plasma to stream away from the Sun.
Solar Cycle:
The number of solar event occurrence varies from maximum (more active) to minimum (less active) following a fairly regular 11-year cycle.
Solar Activity and ACE:
The matter which makes up the hair on our heads to the toes on our feet is made of the same particles as the Earth, the Sun, the Milky Way galaxy, and the galaxies beyond. These particles all had their origin in the Big Bang (the lighter elements) or in stars (the heavier elements). It is the purpose of the ACE (Advanced Composition Explorer) spacecraft to sample the matter that comes near the Earth from the Sun, the space between the planets, and the Milky Way galaxy beyond the solar system.
Measuring particles from solar activity allows us to better understand and prepare for its effects on Earth. The ACE spacecraft is positioned about one million miles sunward of the Earth. The instruments on board ACE, measuring solar plasma flow rates and the composition of the plasma, can give us early notice of disruptive solar events that are headed towards the Earth.
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