4:15 PM - 4:30 PM
[PEM09-23] Investigation of the mid-latitude ionospheric response during substorm based on magnetic and electric field observations
Keywords:Substorm, Field aligned current, current wedge, ionospheric current
Investigation of the mid-latitude ionospheric response during substorm based on magnetic and electric field observations
The purpose of this study is to obtain a more comprehensive view and understanding of the formation process of global three-dimensional current system during auroral substorms.
It is known that there are two types of current systems in the polar ionosphere: the R1-current linked to the magnetospheric convection system and the R2-current linked to the pressure gradient region in the inner magnetosphere [Iijima and Potemra, 1976, 1978]. Substorms are caused by strong plasma injection in the near-earth region. The plasma vorticities that grow at the flow edge of the plasma injection forms a substorm current wedge (SCW) system of which current closure structure is the same of the R1 current system. At the lower latitude of the SCW system, the R2-type current system develops due to the increase in plasma pressure in the inner magnetosphere. Growth of the R2-type system and the SCW system don't always match. The R2-type current system causes not only a shielding effect that weakens the ionospheric current reaching low latitudes and equatorial regions due to the growth of the SCW system, but also an over-shielding effect that sometimes causes the growth of current systems in the opposite direction. (Kikuchi et al [1996]; Nishida [1968]).
The ground magnetic field disturbances observed during substorms are not only generated by the ionospheric currents, but also by the field-aligned currents (FACs) accompanied by the growth of the SCW. In the mid- and low-latitude regions, where this composite effect is particularly large, it is difficult to determine from the magnetic field data alone whether the magnetic field variation during substorms is due to the formation of the ionospheric current system or to the remote field effect of the current wedge current system. A direct comparison of ionospheric electric and magnetic field data is essential for a better understanding of the causes of magnetic disturbances.
In this presentation, we report the results of a study of mid-latitude ionospheric variability during auroral substorm using electric field data from the HF Doppler radar and magnetic field data from SuperMag and MAGDAS installed by Kyushu University in Palatunka, Russia. The analysis period was from October 2006 to May 2007, and the number of events was 100. As an initial result, two patterns of magnetic and electric field variations were identified in the mid-latitude night side. (i) A westward electric field was observed for 30 minutes to 1 hour after the magnetic and electric field fluctuation onset on the evening side of the SCW (14 out of 20 events). (ii) W-shaped oscillations and then westward electric field fluctuations were observed for 10 minutes before and after the SCW center magnetic field fluctuation and electric field fluctuation onset (4 out of 6 events). This may indicate the growth and extinction of the FAC pat of the SCW associated with the substorm. We report the results of a detailed global verification of this fact.
The purpose of this study is to obtain a more comprehensive view and understanding of the formation process of global three-dimensional current system during auroral substorms.
It is known that there are two types of current systems in the polar ionosphere: the R1-current linked to the magnetospheric convection system and the R2-current linked to the pressure gradient region in the inner magnetosphere [Iijima and Potemra, 1976, 1978]. Substorms are caused by strong plasma injection in the near-earth region. The plasma vorticities that grow at the flow edge of the plasma injection forms a substorm current wedge (SCW) system of which current closure structure is the same of the R1 current system. At the lower latitude of the SCW system, the R2-type current system develops due to the increase in plasma pressure in the inner magnetosphere. Growth of the R2-type system and the SCW system don't always match. The R2-type current system causes not only a shielding effect that weakens the ionospheric current reaching low latitudes and equatorial regions due to the growth of the SCW system, but also an over-shielding effect that sometimes causes the growth of current systems in the opposite direction. (Kikuchi et al [1996]; Nishida [1968]).
The ground magnetic field disturbances observed during substorms are not only generated by the ionospheric currents, but also by the field-aligned currents (FACs) accompanied by the growth of the SCW. In the mid- and low-latitude regions, where this composite effect is particularly large, it is difficult to determine from the magnetic field data alone whether the magnetic field variation during substorms is due to the formation of the ionospheric current system or to the remote field effect of the current wedge current system. A direct comparison of ionospheric electric and magnetic field data is essential for a better understanding of the causes of magnetic disturbances.
In this presentation, we report the results of a study of mid-latitude ionospheric variability during auroral substorm using electric field data from the HF Doppler radar and magnetic field data from SuperMag and MAGDAS installed by Kyushu University in Palatunka, Russia. The analysis period was from October 2006 to May 2007, and the number of events was 100. As an initial result, two patterns of magnetic and electric field variations were identified in the mid-latitude night side. (i) A westward electric field was observed for 30 minutes to 1 hour after the magnetic and electric field fluctuation onset on the evening side of the SCW (14 out of 20 events). (ii) W-shaped oscillations and then westward electric field fluctuations were observed for 10 minutes before and after the SCW center magnetic field fluctuation and electric field fluctuation onset (4 out of 6 events). This may indicate the growth and extinction of the FAC pat of the SCW associated with the substorm. We report the results of a detailed global verification of this fact.