Dependence of the probability of observing a middle-latitude trough and a lower-latitude subtrough in the concentration of He+ ions upon the season, local time, and magnetic activity
At. Karpachev et Ln. Sidorova, Dependence of the probability of observing a middle-latitude trough and a lower-latitude subtrough in the concentration of He+ ions upon the season, local time, and magnetic activity, GEOMAG AER, 40(2), 2000, pp. 23-33