Biographical Memoirs V.74

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Scott Ellsworth Forbush

April 10, 1904 - April 4, 1984

By James A. Van Allen

Scott Forbush laid the observational foundations for many of the central features of the now huge field of solarinterplanetary-terrestrial physics. The heart of his research was the patiently meticulous and statistically sophisticated analysis of the temporal variations of cosmic-ray intensity, as measured by ground-based detectors at various latitudes and altitudes, and the correlation of such variations with presumptively causative or at least related geophysical and solar phenomena. Among the latter were magnetic storms, solar activity, rotation of the Earth, and rotation of the Sun.

Working almost alone with only technical assistance, Forbush either discovered or put on a reliable basis for the first time the following fundamental cosmic-ray effects:

The quasi-persistent 27-day variation of intensity;
The diurnal variation of intensity;
The absence of a detectable sidereal diurnal variation of intensity;
The sporadic emission of very energetic (up to several GeV) charged particles by solar flares;
Worldwide impulsive decreases (Forbush decreases) of intensity followed by gradual recovery;
The 11-year cyclic variation of intensity and its

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