Solar and lunar variations in total electron content at Tokyo

354-361Total electron content (TEC) data at Tokyo (subionospheric dip lat. 23.2°N) for the period 1977 to 1980 have been subjected to harmonic analysis to derive the solar diurnal variation and its higher harmonics. The daily mean value A0 and the diurnal and semi-diurnal amplitudes A1 and A2 respectively show a semi-annual variation. The times of maxima of these harmonics show an annual variation. A1 and A2 linearly increase with sunspot number RZ with a tendency for saturation and looping at RZ > 160. The lunar monthly tide has predominant monthly component (M1) with an amplitude varying from 0.8 to 12.3 TEC units, maximizing in winter at solar hour 12 noon. The semi-monthly component (M2) is ~ 50% of M1 amplitude. The lunar diurnal amplitude (L1) maximizes at ~ 2.5 TEC units in winter, while the semi-diurnal amplitude (L2) is 0.9 TEC units which is opposite to observations at low latitudes. These results are compared with earlier results at Low latitudes and discussed in term of (a) possible tidal effects in neutral wind at mid-latitudes, (b) increased production and increased thermospheric temperature as the solar activity progresses, and (c) seasonal changes in neutral composition and temperature