Figure 6From: A long-term trend in the F2-layer critical frequency as observed at Alma-Ata ionosonde station Plot of foF2(12) 132 versus F10.7(12) 132 for periods: 1964-2007 (a), 1964-1967 (b), 1968-1979 (c), and 1980-2007 (d). Back to article page