The geomagnetic storm of March 17, 2015 – the so far strongest storm of the present solar cycle

Plasma originating from a coronal mass ejection at the surface of the sun impacted the geomagnetic field, which protects our planet. This resulted in a geomagnetic storm which was observed worldwide at the geomagnetic observatories operated by GFZ and other institutes. Data from the American satellite ACE (Advanced Composition Explorer) showed an unexpectedly high velocity of the plasma of almost 700km/s at about 11UT (universal time). About one hour later the associated interplanetary magnetic field turned southward to values of almost -40nT. The characteristics of the plasma and its associated field promote the integration of solar particle radiation in the magnetic field of the Earth.

The strength of a geomagnetic storm is measured by the Kp-index, on a scale from 0 to 9. The Kp-index is determined and distributed internationally by GFZ the German Research Centre for Geosciences. During the geomagnetic storm of March 17, 2015, Kp-values between 7 and 8 were reached throughout 12 hours. The equatorial Dst storm index, which describes the geomagnetic activity at low latitudes, reached -221nT at 23UT, and indicated the peak of the storm on Earth. For comparison, during the most recent super storm (October 30, 2003) the peak value of the Dst was -383nT.

The strength of the storm is likely to diminish during the next days. The southward component of the interplanetary field has levelled out around 0nT and the solar wind speed oscillates around 550km/s, the latter still at an elevated level compared to non-storm times.

Observing such storms provides important insights into geophysical and space physics as well as estimating the force of current and future geohazards associated with such space weather events. Space weather monitoring aims at determining the hazard potential due to induced currents that might damage power supply lines or pipelines, as well as potential disturbances or failures of satellite systems, e.g. Global Positioning System (GPS) satellites. The interaction between the solar wind and Earth’s magnetic field is not yet fully understood. The strength and geometric dimensions of the geomagnetic field will be important to understanding this interaction. GFZ’s section 2.3 “Earth’s Magnetic Field” investigates such storm events and the role of the geomagnetic field as a protecting shield.

More information (as of March 19, 2015): NEWS.

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