a Norwegian physicist who developed, along with Samuel Eyde in 1903, an electric-arc process (the Birkeland-Eyde process) for nitrogen fixation, which was one of the first processes used in the large-scale manufacture of nitrogen fertilizer from atmospheric nitrogen. He also was among the early pioneers of plasma physics and space physics. He is famous for his early and prescient explanation of the aurora borealis in terms of energetic particles from the solar wind interacting with the earth's magnetosphere. The results of the Norwegian Polar Expedition, conducted from 1899 to 1900, contained the first determination of the global pattern of electric currents in the polar region from ground magnetic field measurements.