Decrease of cosmic-ray intensity on February 11, 1958

An analysis has been made of the cosmic-ray data recorded by the IGY network of stations during the sudden decrease of intensity on February 11, 1958. The unusual rapidity of the decrease, which was followed by a temporary recovery, provides a critical test for existing solar-controlled modulating mechanisms. The main decrease, occurring practically simultaneously over the earth, was relatively energy-insensitive. The subsequent temporary recovery appeared to be associated with a spatial anisotropy. It is suggested that these variations can be interpreted as the result of disordering the outer geomagnetic field by the solar wind, as first pointed out by Parker.