An l-nu Diagram

An <i>l</i>-nu Diagram

. The frequency, nu, of sound waves is plotted as a function of the spherical harmonic degree, l, for just eight hours of high-resolution data taken with the SOHO MDI instrument. A frequency of 3 milliHertz, or 0.003 cycles per second, corresponds to a wave period of five minutes. The degree, l, is the inverse of the spatial wavelength, or surface size; an l of 400 corresponds to waves on the order of 10 million meters in size. The oscillation power is contained within specific combinations of frequency and degree, demonstrating that the surface oscillations are due to standing waves confined within resonant cavities. (Courtesy of the SOHO MDI/SOI consortium. SOHO is a project of international cooperation between ESA and NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University