Wave-formed ripple Wave-formed ripple In sedimentology, wave-formed ripples or wave-formed ripple marks are a feature of sediments (sandstones, limestones, siltstones) and dunes. These ripple marks are often characterised (and thus distinguished from current ripples) by symmetric cross sections and long relatively straight crests, which may commonly bifurcate. Commonly, these crests can be truncated by subsequent flows. Their wavelength (periodicity) depends on the sediment grain size, water depth and water-particle orbits in the waves. On tidal flats the pattern of wave-formed ripples may be complicated, as a product of changing depth and wind and tidal runoff directions. Symmetrical ripples are commonly found in
Solar constant annual range). The solar constant does not remain constant over long periods of time (see Solar variation), but over a year the solar constant varies much less than the solar irradiance measured at the top of the atmosphere. This is because the solar constant is evaluated at a fixed distance of 1 Astronomical Unit (AU) while the solar irradiance will be affected by the eccentricity of the Earth's orbit. Its distance to the Sun varies annually between 147.1·10 km at aphelion and 152.1·10 km at perihelion. The Earth receives a total amount of radiation determined by its cross section (π·R²),