Note on “Sudden commencements” and other small characteristic impulses

Abstract

The recent publication by the United States Coast and Geodetic Survey of a first instalment of ¼‐size reproductions of daily magnetograms, January to June, 1946, from the Cheltenham Magnetic Observatory, provides some interesting data in connection with “Sudden Commencements” (SC) and other small trace‐movements that are being studied at Greenwich. In a paper dated August, 1946, from the Royal Observatory, certain unexpected characteristics of SC‐occurrence were derived from the Greenwich data 1879–1944.for two of the results given by the Greenwich analysis, the Cheltenham magnetograms provide a valuable comparison even for the short epoch of six months—a specially active six months, however, embracing some unusual solar phenomena.