The magnetogram inversion technique (MIT) has been demonstrated as a powerful $quot;remote sensing tool$quot; in estimating ionospheric quantities, such as ionospheric current, field-aligned current, electric potential and Joule heating rate etc. Furthermore it is now possible to infer instantaneous patterns of such global distributions with a high time resolution (say, 5 min) through the numerical method. However, the electric potential distribution estimated from the MIT is very sensitive to the choice of ionospheric conductivity models. It is a serious drawback of the method, since the electric potential over the polar region is a very important quantity reflecting the efficiency of the solar wind-magnetosphere coupling. Thus a realistic conductivity distribution over the entire polar ionosphere is acute. In this paper, we introduce a general concept of ionospheric electric conductivity along with several methods of estimating it.

The magnetogram inversion technique (MIT) is a computational method for calculating the global pattern of ionospheric current using ground magnetic disturbance data as input. By assuming the ionospheric electric conductivity distribution, the technique makes it further possible to estimate the distribution patterns of such electrodynamic quantities as electric field, electric potential, field-aligned current and Joule heating rate. Although the MIT is an indirect method, it provides instantaneous electrodynamical pictures of the entire polar ionosphere with a high time resolution while more direct measurements by radar, rocket and satellite are vital to understand the ionospheric phenomena but they provide informations only over a limited area. Since the output of the MIT are very sensitive to the choice of the ionospheric conductivity distribution, a companion paper will be devoted to the topic. Various electrodynamic quantities over the polar ionosphere, which are now available through the magnetogram inversion technique, will be also discussed in another companion paper.

Korea Polar Research Institute (KOPRI) installed an ionospheric sounding radar system called Vertical Incidence Pulsed Ionospheric Radar (VIPIR) at Jang Bogo Station (JBS) in 2015 in order to routinely monitor the state of the ionosphere in the auroral oval and polar cap regions. Since 2017, after two-year test operation, it has been continuously operated to produce various ionospheric parameters. In this article, we will introduce the characteristics of the JBS-VIPIR observations and possible applications of the data for the study on the polar ionosphere. The JBS-VIPIR utilizes a log periodic transmit antenna that transmits 0.5–25 MHz radio waves, and a receiving array of 8 dipole antennas. It is operated in the Dynasonde B-mode pulse scheme and utilizes the 3-D inversion program, called NeXtYZ, for the data acquisition and processing, instead of the conventional 1-D inversion procedure as used in the most of digisonde observations. The JBS-VIPIR outputs include the height profiles of the electron density, ionospheric tilts, and ion drifts with a 2-minute temporal resolution in the bottomside ionosphere. With these observations, possible research applications will be briefly described in combination with other observations for the aurora, the neutral atmosphere and the magnetosphere simultaneously conducted at JBS.