The height of the maximum ionospheric electron density over the MU radar

Ionospheric F-2-layer peak height h(m)F(2) variations, as measured over 198 6-1995 by the MU radar (34.85 degrees N, 136.1 degrees E) and as calculated with a theoretical model, are discussed. The diurnal variations of the mea sured peak height for different seasons and levels of solar activity are co mpared with those estimated from ionosonde M3000F(2) and IRI predictions. A lso given are the measured ion drift velocities and meridional neutral wind s needed to understand the dynamic behavior of the F-2-layer. It is found t hat: (1) h(m)F(2) is generally higher during periods of the solar maximum t han during periods of the solar minimum, and higher in summer than in winte r; (2) for the solar maximum, h(m)F(2) drops markedly in the morning and in the afternoon, while, for the solar minimum, the h(m)F(2) minimum occurs i n the morning during summer and usually in the afternoon during winter. In general, the measured h(m)F(2) is well reproduced by our model when we use the observed drift velocities and plasma temperatures as inputs. Our modeli ng study shows that the neutral wind contributes strongly to the diurnal va riation of h(m)F(2) in winter by lowering the ionization layer by day, part icularly for the solar maximum; it also helps to enlarge the daynight diffe rence of h(m)F(2) in summer. The northward electromagnetic drifts that usua lly cancel the neutral wind effect have only a minor effect for the locatio n of the MU radar. Other features of the observed h(m)F(2) variations, e.g. , the solar maximum-minimum difference, the summer-winter difference, and t he morning and afternoon drops, are explained by the basic processes of Oproduction, loss and diffusion, as influenced by the atomic oxygen concentr ation and neutral and plasma temperatures. (C) 2000 Elsevier Science Ltd. A ll rights reserved.