Contribution of time-dependent electric and magnetic fields to the dynamics of magnetic storms Original Research Article

The evolution in time of the ion pressure distribution in a time-dependent magnetic field is simulated, the drift current density is calculated and the Biot-Savart law is used to obtain ground magnetograms during one hour growth of a synthetic magnetic storm. The disturbance is at the level of −17 nT near midnight. Hydrogen and oxygen ions picked out of the storm pressure distribution are traced backwards in time to identify the source location and its energetic characteristics. The time-dependent magnetic field, convection, corotation and induced electric fields are applied in the tracing procedure. It follows from the study, two regions are distinguished as source sites for the storm ions: near-midnight near tail (r > 10 RE) region activated by the induced electric field, and the dawn side region activated by the corotation and convection electric fields. Tail ions contribute to ϵ < 60 keV component of the storm ring current while dawn ions become the 100 – 200 keV component of the current. The study yields arguments supporting the idea that the necessary condition for a storm to be fast and intense is either active high-latitude ionosphere supplying 10 – 50 keV ions to near-equatorial regions on the morning side or an electric field able to push energetic ions towards the Earth to radial distances 5 – 6 RE. The contribution of the time-dependent magnetic and electric fields to the dynamics of magnetic storm consists in activating the near tail and in extracting ions from the high-latitude ionosphere.