The first CME in this movie was produced by an M4-class flare at 1129 UT. It departed the sun traveling 1259 km/s. The second CME was produced by an M1-class flare at 1923 UT. It departed even faster, traveling ~1700 km/s.
A NOAA computer model suggests that the second CME will overtake the first, merging into a single “Cannibal CME” before striking Earth’s magnetic field around 0300 UT on March 31st.
Cannibal CMEs are fast coronal mass ejections that sweep up slower CMEs in front of them. This NASA movie shows what happens. The mish-mash contains tangled magnetic fields and compressed plasmas that can spark strong geomagnetic storms.
If the NOAA model is correct, the density of solar wind plasma around Earth could increase 10-fold when the CME arrives, while the solar wind speed will top 700 km/s. These events would set the stage for G2– to G3-class geomagnetic storms.
Observing tips: North Americans should be alert for auroras after local nightfall on March 30th. For Europeans, the hours before dawn on March 31st are favored. When chasing auroras, dark skies are essential; go to the countryside. Urban glare can overwhelm auroras even during a strong geomagnetc storm. Aurora alerts: SMS Text.