抄録
The sunspot number (R) dependence of the E region maximum electron density (Nm) near noon is studied under the form Nm=N00√1+ρeR (cosχ)(1+Γ)/2, based on f0E obtained at 28 stations around the world. It is found that (1) the N00 for intermediate latitudes is lower than that for low latitudes, and greater in winter than in summer, (2) the N00 for high latitudes is much lower, (3) two groups having different N00's exist in low latitudes, and (4) the ρe always increases with χ irrespective of seasons and latitudes. Based on some theoretical investigation, the difference in atmospheric temperature due to seasons and latitudes is discussed and some arguments are given on the height dependence of the effective recombination coefficient. Finally, empirical formulae to give Nm as a function of R and χ for different seasons and latitudes are tentatively given.
