April 28, 1999

Solar Events Affect Space Weather of Earth

1. Artist's depiction of a huge cloud of plasma gas ejected by the Sun in the direction of Earth (see text). Such an ejection is called a "coronal mass ejection" (CME). The various components shown here--Sun, CME, Sun-Earth distance, and the Earth and its magnetosphere--are not drawn to scale.

2. Artist's depiction of (a) the magnetic field lines of the Earth's magnetosphere, distorted by the arrival from the Sun of a CME plasma cloud, and (b) fountains of atmospheric gas (blue, bluish-green) streaming upward into the Earth's magnetosphere from above the Earth's north (N) and south (S) magnetic poles.

3. The bubble of a coronal mass ejection bursting into interplanetary space.

Click images for an enlarged view.

Image Credits: The scientific team of the Thermal Ion Dynamics Experiment (TIDE) onboard the Polar spacecraft and NASA (figures 1 and 2). Archives of the High Altitude Observatory (National Center for Atmospheric Research) and the Solar Maximum Mission (NASA) (figure 3).

The first of the above images illustrates a huge cloud of hot, ionized gas ejected from the Sun's corona. Such an ejection is called a "coronal mass ejection" (CME). If a CME cloud travels in the direction of the Earth and collides with our planet's magnetosphere, as illustrated in figure 1, the magnetic field lines of the magnetosphere become distorted and giant fountains of ionized gas stream upward from above our planet's magnetic poles. The upward-streaming gas comes from the Earth's ionosphere, the uppermost layer of our planet's atmosphere.

Such fountains of upward-streaming gas from the Earth's ionosphere occurred on September 24, 1998. The culprit was a coronal mass ejection that erupted on the Sun two days earlier and ejected a huge cloud of plasma toward the Earth.

Here is how a solar CME can affect the Earth's magnetosphere and trigger giant gas fountains.

The Earth's magnetic field resembles that of a bar magnet, with a north pole and a south pole. Typically, the Earth's magnetic field lines are fairly symmetric, except that the solar wind compresses them on the sunward side and pulls them into a magnetotail that stretches into interplanetary space on the antisun side.

When a cloud of hot, ionized gas from a CME collides with the Earth's magnetic field, it greatly increases the compression of the magnetic field lines on the Earth's sunward side and their elongation into the magnetotail on the opposite side as illustrated in figure 2. This temporary but severe distortion of the Earth's magnetic field squeezes ions and electrons in the polar regions of the ionosphere upward and creates the fountains that we have discussed. Due to their electric charges, the ions and electrons do not simply move radially upward and away from the Earth, but generally follow the magnetic field lines into the magnetotail.

Some of the ejected plasma gets trapped in Earth's magnetic tail and flows back toward the Earth, where it causes magnetic storms.

Atmospheric scientists have known since the early 1980s that the Earth's upper atmosphere leaks ions of hydrogen, nitrogen, oxygen, and other atoms into space. It was suspected that this loss had something to do with activities on the Sun. Scientists confirmed this connection between the Sun and Earth when NASA's Polar spacecraft flew through the fountains of upward-streaming gas during the event of September 24. The quantity of gas lost from the ionosphere in this event amounted to a few hundred tons. In comparison, the mass of the entire Earth atmosphere is approximately five thousand trillion (5 x 10¹⁵) tons.

More Cool Stuff

For more information on the collision of a CME plasma cloud with the Earth's magnetosphere and its consequences, go to a press release of December 1998 of the International Solar-Terrestrial Physics (ISTP) program and NASA:

http://www-istp.gsfc.nasa.gov/istp/news/9812/solarwind.html

Additional information on the Sun-Earth connection, the Earth's magnetosphere, space missions, news, and images can be accessed from the ISTP homepage and its outreach link:

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

We published other articles on the Sun and the Sun-Earth connection under the titles "Our Sun," "Why Is the Sun's Corona So Hot?", "The Key to Predicting Magnetic Storms?", "A Snapshot of the Sun's Magnetic Field," and "A Cloudy Day in Space":

http://observe.ivv.nasa.gov/nasa/exhibits/sun/sunframe.html
http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_971217/ob971217.html
http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960911/ob960911.html
http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960417/ob960417.html
http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960131/ob960131.html

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space and atmospheric sciences:

Windows to the Universe is a site created by the University of Michigan that offers access to information about the Sun and the other planets of the solar system.

http://www.windows.umich.edu/

Take an electronic field trip to the sun with Passport to Knowledge: "Live from the Sun."

http://passport.ivv.nasa.gov/sun/

Other LTP sites that are dedicated to the space and atmospheric sciences can be found at:

http://learn.ivv.nasa.gov/education/topics/space_sci.html

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_atmos.html