Terannual variation in the F2 layer peak electron density (NmF2) at middle latitudes

摘要: Ionosonde data from 33 stations in three longitude sectors 1969 to 1986 have been used study the seasonal variations of ionospheric F-2 layer peak electron densities (NmF2). We found that there is a periodic oscillation daytime NmF2 with period 4 months (terannual). Our analysis shows very good phase match between annual and semiannual oscillations terannual oscillations. These vary solar activity same way: large amplitudes during maximum. The amplitude also correlated product suggest might be related nonlinear interaction In addition, stronger midlatitude region Northern Hemisphere than Southern Hemisphere. Furthermore, are differences nighttime. No obvious signature seen nighttime layer.