(NASA) A wave of plasma and magnetic fields from a Feb. 17 coronal mass ejection passed by Earth on Feb. 20, 2000. Geomagnetic activity is up, but this event may not cause significant aurora.

An interplanetary wave of ionized gas and magnetic fields passed by Earth on February 20, 2000 at 2100 UT. The shock front was caused by a full halo coronal mass ejection (CME) that erupted from the Sun on February 17, 2000. Geomagnetic activity has increased as a result of the interplanetary wave, but it appears there will be no significant aurora over the lower 48 U.S. states. The NOAA Space Environment Center forecasts a 30% chance of minor geomagnetic storm activity at middle latitudes today, decreasing to only 15% tomorrow.

When fast-moving material from a CME flows away from the Sun, it piles up against slower-moving gas that had been ejected earlier. This produces a sharp, dense shock front like the one ACE detected yesterday. When the shock wave passed ACE around 2100 UT, the solar wind density soared from 3 gm/cc to over 10 gm/cc.

About an hour later the shock wave reached Earth's magnetosphere, a region of space controlled by our planet's magnetic field. The magnetosphere forms a shield that helps protect Earth from solar wind storms. Yesterday's shock front carried with it a magnetic field with a strong southerly component. South-pointing magnetic fields are sometimes able to partially cancel the Earth's magnetic field at the point of impact and create a chink in our magnetic armor.

Plasma (ionized gas) can then enter the magnetosphere through this weak point. Aurora often follow such an injection of solar plasma. This time, however, the magnetic field of the disturbance flipped northward after only 4 hours. Mid-latitude aurora were not reported last night, and forecasters have downgraded the chances for aurora during the next 48 hours.

While this space weather event might not put on much of an auroral show, we could be in store for a dazzling display late this week or next. A large coronal hole is just approaching the Sun's central meridian. Coronal holes are regions of low magnetic field strength where high speed solar wind particles can escape into interplanetary space. When the energetic wind stream reaches Earth, it can buffet the magnetosphere and trigger aurora.

Mitch Battros
Producer - Earth Changes TV
http://www.earthchangesTV.com