February 19, 2014 Magnetic Disturbance - Peak Dst -95 nT

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Space Weather Events of February 19, 2014

This small-to-moderate, but highly complex, multiphase geomagnetic storm is related to a series of Earth-directed coronal mass ejections (CMEs) that launched from the sun starting on February 16th, accounting for the first significant/extended geomagnetic activity observed in nearly 8 months.

The initial phase exhibited no classical "sudden commencement", likely because a period of southward interplanetary magnetic field (IMF) had already initiated magnetospheric convection, slowly reducing USGS' 1-minute storm-time disturbance (Dst) index. The first CME reached the Earth's magnetopause shortly after 03:00Z on Feb. 19, and in spite of a rather weak shock, its northward orientation drove a moderate (~15nT) positive impulse in Dst. As the CME's magnetic flux rope rotated, IMF reoriented southward, eroding the magnetopause, driving strong magnetospheric convection, and ultimately reducing USGS Dst to nearly -100nT for the storm's main phase. A subsequent northward turning of the IMF (possibly another small CME) encouraged a quick recovery, returning Dst more than halfway to ambient conditions within ~8 hours. The Space Weather Prediction Center's (SWPC's) estimated planetary K index (Kp) rose to 6 during this period.

A second much stronger shock, likely associated with a solar filament eruption observed on February 18th, hit Earth's magnetopause shortly after 03:00Z on Feb. 20th. The IMF associated with the previous CME had been gradually weakening, and its orientation random, so the relatively strong (~25nT) positive impulse in Dst observed at 03:20Z was largely due to magnetopause (i.e., Chapman-Ferraro) currents. This was short-lived as IMF turned sharply southward, northward, then southward again, driving a double-dip storm-within-a-storm where USGS Dst fell back to -63nT and -75nT, respectively. IMF then returned to ambient conditions, and the geomagnetic storm (re)entered a slow recovery phase for almost 48 hours. Again, SWPC Kp rose to 6 during this period.

Finally, a third, slow-moving CME, likely launched from the sun on February 20th, arrived at Earth shortly after 07:00Z on Feb. 23rd. Increased solar wind density and a weakly northward IMF orientation drove a moderate (~17nT) positive impulse, before the IMF reoriented southward, reducing main phase Dst to -50nT. SWPC Kp only rose to 4 during this period.

Last Updated 2014-03-18 21:28:51 by E. J. Rigler