Radio atmospheric a distance where luminosity is visible and thunder can be heard (typically about 10 km), these electromagnetic impulses are the only sources of direct information about thunderstorm activity on the ground. Transients electric currents during return strokes (R strokes) or intracloud strokes (K strokes) are the main sources for the generation of impulse-type electromagnetic radiation known as sferics (sometimes called atmospherics). While this impulsive radiation dominates at frequencies less than about 100 kHz, (loosely called long waves), a continuous noise component becomes increasingly important at higher frequencies. The longwave electromagnetic propagation of sferics takes place within the Earth-ionosphere waveguide between
History of geophysics the waves reflected off the internal layers of the Earth, several theories developed as to what would cause variances in wave speed or loss of certain frequencies. This led to scientists like Inge Lehmann discovering the presence of the Earth's core in 1936. Beno Gutenberg and Harold Jeffreys worked at explaining the difference in Earth's density due to compression and the shear velocity of waves. Since seismology is based on elastic waves, the speed of waves could help determine density and therefore the behavior of the layers within the Earth. Nomenclature for the behavior of seismic waves was produced based