Ionospheric modification - An outdoor laboratory for plasma and atmospheric science


  • A. Y. Wong,

  • R. G. Brandt


With the ability to induce large-scale changes in the ionosphere by high-power ground-based HF transmitters, laboratory-like experiments can be performed repetitively in space plasmas. Using satellites and rockets, as well as ground-based magnetometers, optical and radar diagnostics, this large-scale plasma has been investigated. The absence of walls and the long confinement time make this plasma distinctively different from conventional laboratory plasmas. Particle and energy transports can be studied in this large-scale well-confined plasma. Significant changes in density profiles and velocity distributions can be brought about by modest incident EM wave intensity because the wave fields are resonantly enhanced and the perturbations are cumulative in the same plasma over a long time. Free energy sources can further enhance the excitation of waves. Experimental methods are reviewed together with major experiments performed at the Platteville, Arecibo, Max Planck, and HIPAS observatories. The ionospheric plasma with a rich source of free energy is highly variable especially in the auroral zone, and fast temporal resolution techniques used in laboratory experiments have been introduced to these outdoor experiments to observe caviton collapse and other fast processes. High-frequency and low-frequency wave phenomena are observed to be excitable simultaneously and coupled by non-linear processes. Laboratory experiments, computer simulation, and analytic theories are used to interpret and to guide field experiments. Future experiments include the studies of the formation of potential double layers and ion acoustic shocks from density cavities and their coupling to free energy sources in the ionosphere. Active experiments are desirable in the atmosphere whose response to a known perturbation such as the controlled heating of electrons and neutrals and the formation of negative ions can be quantified. With higher focusing of the available power, there is the exciting possibility of generating a steady state ionospheric plasma and an opening to a new era in controlled atmospheric experiments and long-range communications.