Cnoidal wave is the wave height, "λ" is the wavelength, "c" is the phase speed and "η" is the trough elevation. Further cn is one of the Jacobi elliptic functions and "K"("m") is the complete elliptic integral of the first kind; both are dependent on the elliptic parameter "m". The latter, "m", determines the shape of the cnoidal wave. For "m" equal to zero the cnoidal wave becomes a cosine function, while for values close to one the cnoidal wave gets peaked crests and (very) flat troughs. For values of "m" less than 0.95, the cnoidal function can be approximated with trigonometric
Shock wave of sound, so that the sound waves leaving the aircraft pile up on one another, similar to a traffic jam on a motorway. When a shock wave forms, the local air pressure increases and then spreads out sideways. Because of this amplification effect, a shock wave can be very intense, more like an explosion when heard at a distance (not coincidentally, since explosions create shock waves). Analogous phenomena are known outside fluid mechanics. For example, particles accelerated beyond the speed of light in a refractive medium (where the speed of light is less than that in a vacuum, such as