From sun to Earth: Tracking a new storm 

On April 7, the day before the meeting began, another large solar outburst blazed forth, blasting Earthward a blob of gas and magnetic energy at a speed of 1.6 million kilometers an hour. Researchers called the resulting storm, which didn't reach Earth's vicinity until 3 days later, relatively mild. There were no reports of problems with spacecraft or electric power outages on Earth. Ground-based detectors, however, measured sizable increases in the energy of electrons in Earth's ionosphere, and skywatchers as far south as Boston were treated to a dazzling auroral display.

 As they had for the January eruption, the researchers relied on an armada of spacecraft to track the disturbance, known as a coronal mass ejection because it originates in the sun's outer atmosphere, or corona. This time, an ultraviolet camera aboard the SOHO spacecraft, which continuously monitors the sun, was in operation, and researchers could view the disturbance deeper in the corona than ever before.

"If the last event was [captured] from cradle to grave, this one was from birth to grave," says Nicola Fox of Goddard.

 Like the earlier outburst, which researchers classify as a magnetic cloud, the blob of material ejected on April 7 forced the interplanetary magnetic field around it to point south, allowing it to dump energy efficiently into the oppositely oriented magnetic domain of Earth.

 Despite similarities, the April event was much more complex, says Charles C. Goodrich of the University of Maryland at College Park. Researchers predicted, from January's records, that the material would strike Earth's vicinity late on April 9. That night came and went, however, with no sign of the blob's arrival.

 Scientists worried that they had miscalculated. In fact, says Fox, the material had plowed into an unusually slow solar wind, the stream of charged particles blowing out from the sun. The expanding blob "had to go through molasses to get to us," Fox says.

 In addition, says Goodrich, this material does not qualify as a magnetic cloud because it abruptly switched the direction of its magnetic field and did not show a drop in temperature.