North-South Asymmetry in N_mF2 at Mid-Latitude Conjugate Ionosphere Produced by Asymmetrical Thermospheric Winds

抄録

Effects of the asymmetrical thermospheric winds on N_mF2 at the latitudes 25°N, 35°N, 45°N and their geographically conjugate points have been computed for equinox conditions to study diurnal and longitudinal variations of the north-south differences in N_mF2. In our calculations, the asymmetrical wind model of ILL et al. (1975) has been used. Although the effects of the winds on N_mF2 are almost equal at latitudes 45°N and S, they give a significant effect on the north-south differences of N_mF2 at lower latitude, namely N_mF2 at latitudes 25°S and 35°S become about 30 percent greater than those at latitudes 25°N and 35°N between 02 and 08 LT (Local Time). This north-south asymmetry is most pronounced at each longitude around 06 LT. During the daytime, the maximum electron density of the F2-layer in the northern hemisphere becomes comparatively greater than the maximum electron density of the F2-layer in the southern hemisphere by the winds. In the evening, N_mF2 at latitudes 25°S, 35°S, and 45°S are greater than N_mF2 at their northern conjugate points in the longitude range 0°-120°E, reverse hold true in other longitude ranges. The computed differences in N_mF2 between at latitudes 25°N, 35°N, 45°N and at their geographically conjugate points are in agreement with observational differences obtained by the ISS-B satellite, except during the nighttime at the longitude range 180°E-60°W. It is shown that the diurnal and longitudinal variations in the differences between N_mF2 at mid-latitude point and those at its geographically conjugate point are well explained by considering the effects of the asymmetrical winds which focus toward the area of 02-05 LT, 35°N-40°N.