An interhemispheric model of artificial ionospheric ducts

Abstract

A duct in Earth's ionosphere is characterized by density gradients perpendicular to the magnetic field, which enhance refractive indices and act as waveguides to whistler-range waves. Interhemispheric ducts along magnetic field lines have implications for the transmission of ELF radio waves across the globe. Strong HF ionospheric heating has been shown to create a depletion of electrons at the heated region and could lead to a pressure perturbation that propagates along the entire magnetic field line, potentially forming an artificial duct. Here we present results from an ionospheric numerical model used to study the effects of localized HF heating on an interhemispheric magnetic flux tube. The existing Sami2 is Another Model of the Ionosphere (SAMI2) ionospheric model has been modified to include a flexible source of strong HF heating that can be varied to mimic the fluctuations in HF heating efficiencies and ionospheric conditions. Our parametric study includes varying the heating source intensity and location along the magnetic field line, revealing both linear and nonlinear relationships connecting these source parameters to maximum pressure, temperature, and density perturbations; propagation velocity of density perturbations; and characteristic heating and cooling times of the irradiated region. After a transient state, the duct structure achieves a quasi-steady state, showing electron depletion at the heated region and density enhancements in the regions just below and above the heated region. The density perturbations propagate deep inside the plasmasphere to the conjugate F2 peak, with density enhancements along the traveling pulse boundary. The possibility of generating interhemispheric ducts is discussed. Copyright 2006 by the American Geophysical Union.