Sun takes another solar shot, this time at Earth
Posted: April 12, 2001

An angry Sun fired off another powerful X-class flare Tuesday. X-class flares are the most powerful classification, and this flare, rated X-2, was the most recent in a series that included one of the most powerful solar blasts in 25 years.

An eruption of electrified gas, called a Coronal Mass Ejection, or CME, was observed shortly after Tuesday's flare, and it is heading our way. Depending on the orientation of the magnetic field carried by the CME cloud, it may cause a magnetic storm when it impacts the Earth's own magnetic field.

This series of images follows the progress of a coronal mass ejection associated with the powerful solar flare on Tuesday. The images were made using observations from the Large Angle and Spectrometric Coronagraph (LASCO) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft. The LASCO instrument uses a coronagraph (blue disk in the middle of each image) to block direct light from the Sun so the much fainter solar atmosphere (corona) can be seen. The white circle in the middle of the coronagraph disk represents the apparent size of the Sun as viewed from SOHO's position in space. Photo: NASA and ESA
Tuesday's flare which was observed by the Solar and Heliospheric Observatory (SOHO) and NASA's Transition Region and Coronal Explorer (TRACE) occurred at 1:25 a.m. EDT and came from a region on the Sun designated active region 9415. This region is rotating with the Sun and currently points towards Earth. Active region 9415 includes a sunspot group and has generated three X-class flares this month, including an X-5 flare on April 6.

The front of the ejection cloud associated with Tuesday's flare hit Earth shortly after 9 a.m. EDT Wednesday. Moderate to strong storm levels, rated G2 - G3, will be possible during Wednesday and Thursday as the CME passes Earth, according to the National Oceanic and Atmospheric Administration's Space Environment Center (NOAA SEC), Boulder, CO.

"This is another in an exciting series of solar events during this maximum epoch of the current solar activity cycle," said Dr. Ernest Hildner, Director of the NOAA SEC. The NOAA SEC classifies flares according to their power and estimates, tracks, and evaluates the effects of solar activity on the space environment near Earth. The NOAA SEC is the federal agency responsible for making official space weather predictions.

Solar flares, among the solar system's mightiest eruptions, are tremendous explosions in the atmosphere of the Sun, capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds flares can accelerate solar particles to very high velocities - almost to the speed of light - and heat solar material to tens of millions of degrees.

CME eruptions, often associated with flares, are clouds of electrified, magnetic gas weighing billions of tons ejected from the Sun and hurled into space with speeds ranging from 12 to 1,250 miles per second. The CME associated with Tuesday's flare was thrown from the Sun at an estimated 1,000 miles per second. CMEs can be even more powerful than flares and the total energy in a good-sized ejection is about 100 times greater than that of the largest flares.

Depending on the orientation of the magnetic fields carried by the CME cloud, Earth-directed ejections can cause magnetic storms by interacting with the Earth's magnetic field, distorting its shape and accelerating electrically charged particles, electrons and atomic nuclei, trapped within. Severe solar weather is often heralded by dramatic auroral displays but the magnetic storms can also affect satellites, radio communications and power systems.

Active region 9415 is expected to produce more solar outbursts because it has a complex magnetic field structure. Active regions are areas near the Sun's visible surface where a concentration of distorted magnetic fields exists. Sunspots are often found in active regions because the strong magnetic fields there slow the flow of heat from the Sun's interior, keeping part of the region slightly cooler than its surroundings, which causes it to appear as a dark spot on the solar surface.

The SOHO project is an international cooperative program between NASA and the European Space Agency in the framework of the International Solar Terrestrial Science Program.