Yz. Su et al., A MODELING STUDY OF THE LONGITUDINAL VARIATIONS IN THE NORTH-SOUTH ASYMMETRIES OF THE IONOSPHERIC EQUATORIAL ANOMALY, Journal of atmospheric and solar-terrestrial physics, 59(11), 1997, pp. 1299-1310
The Sheffield University Plasmasphere Ionosphere Model (SUPIM) has bee
n used to study the effects of neutral winds of the north-south asymme
tries in the ionospheric equatorial anomaly at longitudes 120 degrees
E, 200 degrees E, 283 degrees E and 330 degrees E. The model results o
btained for magnetically quiet equinoctial conditions at solar maximum
produce north-south asymmetries in the equatorial anomaly in agreemen
t with the observations. The study shows that the neutral wind causes
the north-south asymmetries and that the asymmetries have longitudinal
variation in accord with the longitudinal variations in the displacem
ent of the geographic and geomagnetic equators and in the magnetic dec
lination angle. At longitudes 120 degrees E and 283 degrees E, where t
he magnetic declination angle is small and the magnetic equators are l
ocated in opposite geographic hemispheres, the asymmetries in the anom
aly are caused mainly by the asymmetries in the meridional wind. On th
e other hand, at longitudes 200 degrees E and 330 degrees E, where the
geographic and geomagnetic equators are almost coincident and the mag
netic declination angles are eastward and westward, respectively, the
asymmetries in the anomaly arise mainly from the zonal wind. During da
ytime, in the hemisphere of stronger poleward wind, the crest values i
n TEC are weaker than in the conjugate hemisphere at all longitudes co
nsidered. The values of NmF2 can be stronger or weaker, depending on t
he competition between the effects of increased chemical loss rate and
the downward flow of plasma from the plasmasphere caused by the stron
ger poleward wind. At night, after the magnetic meridional wind has ch
anged direction and has been in that direction for some time, the stro
nger crests in both TEC and NmF2 occur in the hemispheres of stronger
equatorward wind. (C) 1997 Elsevier Science Ltd.