Electrodynamics of the ionosphere

We review various important studies in the field of electrodynamics of the ionosphere. Four topics are presented; (1) conductivity, (2) wind and the dynamo theory, (3) drift and its effect on the ionosphere formation and (4) interaction between wind and electromagnetic field.We point out some important future problems. They are: (1) We need to consider in the dynamo theory of the geomagnetic daily variation the connection of the ionosphere of both hemispheres by lines of force of the geomagnetic field. (2) Non-periodic wind may be important for producing electric field. (3) Drift to cause interchange of ionization contained in tubes of the geomagnetic field lines, and diffusion of ionization in these tubes control dynamic behaviours of the F2 region. (4) Interaction between wind and electric current presents a new problem. (5) The ionosphere and the magnetosphere react to each other.     

A new eclipsing low-mass X-ray binary with a giant companion

We detected hard X-ray emission from the unidentified Galactic bulge source 1RXS J175721.2-304405 with ASCA. The observed absorption column, flux and power-law index led us to consider that 1RXS J175721.2-304405 may be a new low-mass X-ray binary located near the Galactic center. Furthermore, the X-ray light-curve shows a step-function-like time variability, which is likely due to the occultation of a companion star. Future follow-up observations by missions such as ASTROSAT may reveal a periodic eclipse from 1RXS J175721.2-304405 if it is covered long enough. Since the long orbital period suggests a giant companion, follow-up observations will give firm evidence that 1RXS J175721.2-304405 is a new and rare eclipsing low-mass X-ray binary with a giant companion.     

Simultaneous observations of the plasma density on the same field line by the CPMN ground magnetometers and the Cluster satellites

By applying the cross-phase method and the amplitude-ratio method to magnetic field data obtained from two ground stations located close to each other, we can determine the frequency of the field line resonance (FLR), or the field line eigenfrequency, for the field line running through the midpoint of the two stations. From thus identified FLR frequency we can estimate the equatorial plasma mass density (ρ)$(\rho )$ by using the T05s magnetospheric field model [Tsyganenko, N.A., Sitnov, M.I. Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms, J. Geophys. Res. 110, A03208, 2005] and the equation of Singer et al. [Singer, H.J., Southwood, D.J., Walker, R.J., Kivelson, M.G. Alfven wave resonances in a realistic magnetospheric magnetic field geometry, J. Geophys. Res. 86 (A6) 4589–4596, 1981].