Probing the ionosphere with rockets and radio waves: Studies of plasma waves and instabilities in the upper atmosphere

Summary form only given. The ionosphere is a low temperature (0.1 eV) and low-beta plasma layer that surrounds the Earth and affects a wide range of radio systems that involve communications, navigation, and radar. The unmodified ionosphere is in an equilibrium state defined by the balance of production, transport and loss of plasma subject to variations in solar irradiation and other natural effects. Artificial perturbations caused by energetic chemical releases and high power radio waves can be used to drive this plasma out of equilibrium. This presentation will focus on experimental data and theoretical analysis of recent experiments using the Space Shuttle, sounding rockets and high power radio waves to cause local perturbations in the upper atmosphere. Artificial disturbances can trigger plasma instabilities leading to the generation of plasma waves. A single 10-second burn of the on-orbit engines on the Space Shuttle locally injects 1 GJoule of energy into the upper atmosphere. The hypersonic exhaust vapors charge exchange and collide with ambient ions to yield energetic ion beams, and to launch a wide range of plasma waves. The High Frequency Active Auroral Research Program (HAARP) transmitter in Alaska produces a 10 MHz radio beam with an effective radiated power (ERP) of 3.6 GW. These radio waves excite parametric decay instabilities that convert an electromagnetic wave into pairs of high and low frequency electrostatic waves that can couple into cyclotron and longitudinal resonances that accelerate electrons to energies greater than 25 eV, sufficient for neutral breakdown. Optical emissions, plasma density fluctuations, enhanced temperatures, and changes in composition may be detected during these experiments. Active ionospheric experiments employ instrumented satellites and ground-based radars, optical instruments, and radio receivers as diagnostics. These studies may ultimately lead to partial control of the environment for radio wave propagation in the ionosphere.