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GEMSIS-Ionosphere

Quantitative Evaluation of Transmission of Electromagnetic Energy

We have quantitatively evaluated transmission of electromagnetic energy between the inner magnetosphere and low-latitude ionosphere during geomagnetic storms using global ground magnetometers, radars and satellite observations.

  • Simultaneity of Electric Field Transmission: We found that quasi-periodic magnetic field variations (DP 2), which appear simultaneously between the polar region and equator, are produced by two kinds of electric fields. One is the dawn-to-dusk convection electric field due to southward IMF. The other is the dusk-to-dawn shielding electric field generated by the inner magnetosphere. We confirmed this process based on the results of Hokkaido HF radar and ring current simulation. This result shows that the electromagnetic energy transmitted from the polar region to the equator is simultaneous within a few of seconds. This is an important result in understanding the propagation process of electromagnetic energy.
  • Response of the Magnetosphere Associated with Solar Wind Dynamic Pressure Enhancements: We conducted detailed statistical analysis of the long-term geomagnetic observation data from middle latitudes to the equator in order to clarify a global picture of three-dimensional current systems generated by sudden commencements (SCs) associated with solar wind dynamic pressure enhancements. As a result, we showed that the global magnetic field signature is produced by a pair of field-aligned currents (FACs) resembling region 1 FACs during SCs. The most important fact in our results is that the magnetic effect produced by the FACs reached the nighttime equatorial region.
  • Inhomogeneity of Transmission of Electromagnetic Energy: From a detail analysis of satellite (CRRES, etc.) observation data, we found that convection electric fields in the near-Earth region respond quickly with one-to-one correspondence to the IMF polarity while the response of the electric field in the plasma sheet region tends to be delayed by several minutes. We also verified that electromagnetic energy flows from the ionosphere to the magnetosphere. These important results have been presented at international and domestic meetings, and published in journals of the American Geophysical Union.

Reference: Kikuchi et al., JGR, 2008

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