Lightning causes $10B of damage every year (in the USA), kills hundreds worldwide, poses a danger to air traffic, and scares the heck out of you when you’re driving. Numerically modeling these waves is requires the most advanced techniques available. Complicating these studies, however, is the fact that the propagation of radio waves in complex media such as the plasma in the Earth’s lower ionosphere is one of the most fundamentally difficult ones in electromagnetism, violating nearly every convenient simplifying assumption like homogeneity, linearity, symmetry, and anisotropy. Measurements of properties of the D region are extremely difficult, since those altitudes are too high for balloons, yet too low for satellites, so this is a useful ability. ELF/VLF waves also penetrate into seawater, which has led to their use over the past several decades for communication with submerged submarines at long distances.įrom a scientific perspective, though, the reflectivity of the D region at these frequencies make ELF/VLF a unique tool for remote sensing of the D region, which responds to a variety of inputs like solar activity, lightning energy, electron precipitation from the radiation belts, cosmic gamma-rays, and earthquakes. These are called radio atmospherics, or sferics. For instance, if you set up a radio receiver just about anywhere on Earth, you can pick up short bits of radiation from lightning strikes literally halfway around the world.
Why are ELF/VLF Waves Useful for Engineers and Scientists?ĮLF/VLF waves are useful scientifically because they largely reflect at the D region of the Earth’s ionosphere (60-90 km altitude), and are thus efficiently guided in the Earth-ionosphere waveguide to global distances.
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