Depending on the force that drives the wave, solar waves can be classified into three different modes: acoustic (p-mode), gravity (g-mode) and surface gravity (f-mode).
Acoustic waves have the force of pressure behind them and are determined by the speed of the solar sound waves. These high-frequency waves are often known as five-minute oscillations because that is the approximate length of their cycle; they are visible and take place in patches on the surface of the Sun.
Gravity waves are driven by that force and have low frequency; these waves cannot be seen on the surface as they occur below the convection zone in the Sun’s interior. Surface gravity waves, meanwhile, occur in the photosphere. There may be millions of overlapping modes within each type.
Together this data can be analysed to make inferences about the Sun’s interior and even what’s occurring on the side facing away from us.