Quasi-Analytic Model of OTHR Clutter from Equatorial Bubbles in the Ionosphere
Abstract
Ground clutter for the over-the-horizon radar (OTHR) sky wave becomes Doppler shifted because of the ionosphere through which the radio rays are propagating changes. One source of these changes is ionospheric bubbles, which rise vertically through a horizontally stratified plasma near the equator. The rising plume structures are formed when gravity, neutral winds, or external electric fields act on the F-region plasma. The effect of these ionospheric disturbances can be simulated by tracing rays through physics-based models of the equatorial bubbles. For the physics-based models, exact solutions for internal electric potentials are derived, assuming linear or circular symmetry to the density structures imbedded in the background plasma. A wide variety of analytic solutions for electric potentials are found for both density cavities and density enhancements. Quasi-analytic solutions for the transport of the bubbles are derived using the continuity equation for the plasma with production and loss terms neglected. The analytic models of the electric fields produce incompressible motion that transports the locations of "plasma cells" but do not change the density of the plasma in each cell. This Lagrangean approach employs a time-dependent, coordinate mapping of the undisturbed layer grid. Using internal electric potentials of the bubbles and external polarizations of the F-layer as a whole, a transport model yields tilted plasma plumes that move through the F-region. This time-dependent computer model provides useful plasma densities in a fraction of the time for fully numerical simulations. The electric potential derived in the models can be directly applied to the ray-trace computations to yield predictions for Doppler shifts in the unstable ionosphere.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 27, 2006
- Accession Number
- ADA447535
Entities
People
- P. A. Bernhardt
Organizations
- United States Naval Research Laboratory