On formation of Global Cowling channel in the ionosphere and the generalized Ohm's Law

Time-dependent generalized 3-fluids Ohm's law in the ionosphere is reconsidered. We explicitly show that difference between electric field and E.M.F. (Electro Motive Force, such as Lorentz force, friction force and pressure gradient force acting to electron fluid) become source for radiation of electromagnetic wave. In a spatiotemporal scale much slower than the electron plasma frequency and much larger than the electron inertial length, the electric field and E.M.F should converge to the same value. Thus the evolution of magnetic field in a time scale that we are interested in, is described by the Faraday's law driven by the E.M.F. After time scale that an inductive response is completing, the resultant electrostatic electric field distribution and associated current system is determined to satisfy the current conservation law with appropriate boundary conditions. Using this framework, possible mechanism for current closure from polar to equatorial ionosphere via global Cowling channel is discussed. The Cowling channel is formed by generation of secondary electric field in a cancelling process of accumulated charge caused by Hall current divergence. In our model, a global (primary) Hall current accompanied by two-cell type ionospheric convection induces polarization charge at the conductivity gradient region of dawn-dusk conductivity terminator and magnetic dip-equator. The secondary electric field accompanied by this induced charge generates the secondary Hall current flows along the dawn-side terminator line to the magnetic dip-equator. Resultantly, the global Cowling channel from polar to equatorial ionosphere via the terminator-line and magnetic-dip equator could be formed. Our model shows that enhancement of polar origin equatorial electrojet (EEJ) at morning side region, is due to the converging Hall current from polar to the dawn side dip-equator. Meanwhile, decaying of EEJ is due to the diverging Pedersen current from dusk-side dip-equator to the polar region. This mechanism can be applied to the EEJ disturbances accompanied by the solar wind variations such as DP2-type magnetic field disturbances and many phenomena associate the equatorial enhancement and/or depression of the geomagnetic field disturbances.