The most recent event with which we tested our model is the June 06, 2000 CME. SOHO/LASCO and EIT observed a full halo CME on June 06, 2000 at 15:54 UT, surrounding the occulting disk. The plane-of-sky speed of the leading edge of the halo was measured to be about 908 km/s near the Sun. The halo is probably associated with an X2.3 flare and filament eruption in AR 9026, located at about N21 E15. This is an ideal event for testing our model, because it originated close to the disk center and headed towards Earth. Our model predicts a travel time of 2 1/2 days, so the CME was expected to arrive around 4 UT on June 09. The CME arrived at 22 UT on June 08. This is about 6 hours earlier than our prediction, but within our accuracy of 12 hours.
Solar Storm Warning Down To 12 Hours
Greenbelt - June 21, 2000 - The arrival from the Sun of billion-ton electrified-gas clouds that cause severe space storms can now be predicted to within a half-day, a great improvement over the best previous estimates of two to five days.

Scientists at the Catholic University of America, Washington, DC, and NASA's Goddard Space Flight Center, Greenbelt, MD, have created a model that reliably predicts how much time it takes for these clouds, called Coronal Mass Ejections (CMEs), to traverse the gulf between the Sun and the Earth, based on their initial speed from the Sun and their interaction with the solar wind.

The new model uses recent observations from the European Space Agency/NASA Solar and Heliospheric Observatory (SOHO) and the NASA WIND spacecraft. The model has been validated and made more accurate using historical observations from the Helios-1 (Germany/NASA), the Pioneer Venus Orbiter (NASA), and the Space Test Program P78-1 (United States Air Force) spacecraft.

Earth-directed CMEs cause space 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 (northern and southern lights), but space storms are occasionally harmful, potentially disrupting satellites, radio communications and power systems.

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Capturing Solar Snaps
Bozeman - June 21, 2000 - A decades-old mystery about the behavior of magnetic fields in solar flares may now be solved, thanks to careful observations by a pair of solar scientists.
"The new model more accurately predicts the arrival of Coronal Mass Ejections, and will greatly benefit people who operate systems affected by space storms," said lead author Dr. Natchimuthuk Gopalswamy of Catholic University, a Senior Research Associate at the National Academy of Sciences/National Research Council.

"The improved forecasts let operators of sensitive systems take protective action at the proper time and minimize the unproductive time when systems are placed in a safe mode to weather the storm."

Gopalswamy and colleagues will present this research today during a meeting of the Solar Physics Division of the American Astronomical Society at Lake Tahoe, Stateline, NV.

Coronal Mass Ejections leave the Sun at various speeds, ranging from 12 to 1,250 miles (about 20 to 2,000 kilometers) per second. Only the CMEs directed at Earth are potentially harmful; estimating when they will arrive is difficult because their speed changes due to interaction with the solar wind, a stream of electrically charged gas blowing constantly from the Sun at about 250 miles (about 400 kilometers) per second.

Just as a motorboat heading downstream will slow to the speed of the river's current if its motor is turned off, Coronal Mass Ejections starting out from the Sun more quickly than the solar wind eventually are slowed by the drag of this "stream."

If a boat pulls up anchor, it will gradually accelerate until it is moving at the speed of the current. Similarly, CMEs that start out more slowly than the solar wind are pulled along until they match the solar wind's speed.

Using data from solar-observing spacecraft, Gopalswamy and his team discovered how much the solar wind sped up or slowed down various Coronal Mass Ejections according to their initial speeds.

If the initial speed of a CME is known, the new model accurately accounts for the influence of the solar wind on the CME speed, and the CME arrival time at Earth can now be precisely estimated.

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