Relative sunspot number

relative sunspot number

A daily, calculated index of sunspot activity derived in part from the number of individual spots (umbrae), sunspot groups, and an applicable observatory factor. The standard international relative sunspot number (RI) is now derived at the World Data Center–Sunspot Index and Long-Term Solar Observations (SILSO) at the Royal Observatory of Belgium in Brussels.

Space Weather Prediction Center, 2018: Sunspots/solar cycke. Accessed 1 October 2018. Available at https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle.

Term edited 1 October 2018.

See numerical weather prediction, climate prediction;

A relatively dark area on the surface of the sun consisting of a dark central umbra surrounded by a penumbra, which is intermediate in brightness between the umbra and the surrounding photosphere.