Development of an Integrated View of Plasma Instability Processes in the Lower Ionosphere

Earth's ionosphere is a mixture of neutral gas and charged particles. The ionosphere is generally broken out by layers, defined according to the wavelengths of the radiation most commonly absorbed. The E-region extends from 90-150 km and is ionized through X-ray and ultraviolet radiation. The F-region (150-600 km) is ionized by extreme ultraviolet radiation. Although waves and disturbances ("structuring") occur throughout the ionospheric medium ("plasma"), studies often focus on; either the E or F layer owing in part to limitations of experimental and theoretical; techniques employed. As a result, development of a unified view of ionospheric plasma structuring processes remains incomplete. This proposal will fill this gap by (1) developing a unified plasma instability theory applicable in the broad range of altitudes including the previously unexplored transitional valley region between the E and F region peaks and (2) observing the valley region with a radar that routinely receives returns from a broad range of altitudes. The proposed research leverages NSF assets and knowledge synthesis to contribute fundamentally to the theory of plasma instability and structuring. This knowledge is relevant to the communication and navigation industries, and therefore to society. The integrated theory will be incorporated into UAF plasma physics classes, that currently rely primarily on original journal publications rather than teaching modules. The proposal will also fund a new Ph.D. student. The proposed research will address the fundamental question of what combination of destabilizing and stabilizing factors results in the plasma perturbations growing in amplitude and producing ionospheric structures. The actual proposal activity consists of three interconnected projects: 1. Development a unified theory of ionospheric plasma instabilities including thermal, inertial, and gradient effects for arbitrary altitude and propagation; 2. Determination of the critical gradient length required to destabilize plasma in the non-isothermal case for arbitrary altitude; 3. Analysis of SuperDARN and ISR data to investigate small-scale irregularity occurrence in the previously unexplored transitional "valley" region (~150 km). These measurements are expected to provide support for a theory that strong gradients are required to make plasma unstable in the valley at small scales. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.