Tan, J H; Cohen, M; Inan, U S; Scherrer, P H; Scherrer, D

"VLF Remote Sensing of the Lower Ionosphere: Solar Flares, Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares"

Stanford University Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via ELF/VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas of a couple of meters in size, the sensitivity of these instruments allows the measurement of magnetic fields as low as several tens of femtoTesla per root-Hz, in the frequency range of ~30 Hz to 50 kHz. This sensitivity well exceeds that required to detect any event above the ambient atmospheric noise floor, determined by the totality of lightning activity on the planet. In recent years, as cost of production, timing accuracy (due to low cost GPS clocks), and data handling flexibility of the systems has improved, it has become possible to distribute many of these instruments in the form of arrays, to perform interferometric and holographic imaging of the lower ionosphere. In the context of the IHY in 2007, the ELF/VLF receiver can used extensively as part of the United Nations initiative to place scientific instruments in developing countries. Stanford University's past experiences setting up arrays of ELF/VLF receivers include an interferometer in Alaska, the Holographic Array for Ionospheric and Lightning research (HAIL) consisting of instruments at 13 different high schools in mid-western United States, a broader set of ELF/VLF receivers in Alaska, and various receivers abroad, including in France, Japan, Greece, Turkey, Ireland, and India. A global network of ELF/VLF receivers offer possibilities for a wide range of scientific topics, as well as serving as a means for educational outreach. These goals will be achieved using the newest version of the Stanford VLF receiver, known as AWESOME: Atmospheric Weather Educational System for Observation and Modeling of Electromagnetics. This new version is substantially lower in cost, and easier to set-up and use. Nevertheless, the receivers offer the same ultimate levels of resolution in time, sensitivity and dynamic range, as well as ease of handling of data that is used by researchers conducting cutting edge ionospheric and magnetospheric research. In this context, the placement of these systems at underdeveloped host countries provides an open-ended potential for exploration, limited only by the imagination and drive of the users. AWESOME monitors can be placed at schools, or universities, where they will serve the dual purpose of advancing scientific research, as well as providing a valuable tool for scientific education. Data collected can be pooled and publicly available to all the sites, strengthening the potential for both cooperative education and collaboration on the science between various regions and locations.