Variations of the electric field distribution in the sub-auroral latitude and polar ionosphere during geomagnetic storms

Details Variations of the electric field distribution in the sub-auroral latitude and polar ionosphere during geomagnetic storms Variations of the electric field distribution in the sub-auroral latitude and polar ionosphere during geomagnetic storms

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa41a1395s&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SA41A-1395

Other

2712 Electric Fields (2411), 2730 Magnetosphere: Inner, 2760 Plasma Convection (2463), 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)

Scientific paper

In order to clarify time and spatial evolutions of the large-scale electric field in the middle-latitude, sub-auroral and polar cap ionosphere during the development of geomagnetic storms, we have performed statistical analysis of the long-term electric field observation of the Akebono satellite for about 7 years from March, 1989 to January 1996. In the present data analysis, we selected 1725 cases of geomagnetic storms during the above period. Here, we defined the phenomena of magnetic disturbances indicating the minimum value of less than -40 nT in the SYM-H index as the geomagnetic storm. Moreover, we defined the periods of dSYM-H/dt<0 and dSYM-H/dt>0 as the main and recovery phases of geomagnetic storms, respectively. We also identified the magnetically quiet condition periods when the SYM-H and Kp indices represent more than -10 nT and less than 2. On the other hand, in the electric field data analysis, we used the mapping method into the ionosphere proposed by Mozer [1970], using the IGRF90 model field. During a magnetically quiet condition, the electric field distribution in the high-latitude region of more than 60o shows a typical structure of the electric field indicating the two-cell convection pattern. In the polar cap region, the dawn-to-dusk electric field appears with the averaged magnitude of 10.0-20.0 mV/m. Moreover, in the auroral zone, the poleward electric field mainly distributes with strong dependence on magnetic local time, which shows that the electric field is directed equatorward and poleward in the local time sectors of 00-12h and 12-24h, respectively. On the other hand, in this case, the potential drop in the polar cap region can be estimated as about 26 kV. During the main phase, the averaged electric field intensity in the auroral zone and polar cap region increases by 2-3 times amplitude and the polar cap region expands into the low-latitude region, compared with that during the magnetically quiet condition. In this case, we can estimate the polar cap potential as about 62 kV. Moreover, a new component of the poleward electric field appears in the sub-auroral region in the local time sector between 18 and 24h with the averaged magnitude of 40-60 mV/m without the azimuthal component. On the other hand, the potential distribution of the electric field shows the negative potential stricture in the dawn sector between 03 and 06h with the potential drop of about 4-6 kV. During the recovery phase, the polar cap boundary moves into the high-latitude region from 70 to 74o and the poleward electric fields clearly appear with the double structure in the auroral zone and sub-auroral region in the dusk sector between 18 and 23h. The poleward electric field in the sub-auroral region can be identified as the SAID/SAPS phenomena. Moreover, in the equatorward region of the poleward electric field, the shielding electric field appears with the magnitude of 5-10 mV/m. The similar electric fields are found in the low-latitude (less than 42 degrees) dawn sector between 02 and 05h.

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