Topside and intelhemispheric ion flows in the mid-latitude plasmasphere

A modelling study has been carried out of field-aligned ion flows in the topside ionospheres of conjugate hemispheres under solstice conditions at mid to low latitudes. In the model calculations coupled time-dependent O⁺, H⁺ and electron continuity, momentum and heat balance equations are solved along dipole magnetic field lines at L = 1.5 and 3.0 Sunspot medium and sunspot minimum atmospheric conditions are considered.It has been found that thermal coupling between conjugate hemispheres gives rise to strong flows of O⁺ in the topside ionosphere of the summer hemisphere that are directed upwards at conjugate sunrise and directed downwards at conjugate sunset. At conjugate sunrise in the winter hemisphere there is a small upward-directed signature in the O⁺ field-aligned flux; there is no observable signature in the O⁺ field-aligned flux in the winter hemisphere at conjugate sunset. There are strong upward and downward flows of O⁺ at local sunrise and local sunset, respectively, in both the summer and winter hemispheres.At both L = 1.5 and 3.0 the 24 h time-integrated interhemispheric H⁺ flux is in the direction summer hemisphere to winter hemisphere. At L = 1.5 its magnitude is in good agreement with the magnitude of the 24 h time-integrated plasma (O⁺ + H⁺) field-aligned flux at 1000 km altitude; there are no such agreements at L = 3.0.A study of the roles played by the individual terms of the O⁺ momentum equation has demonstrated the complex structure of momentum balance. Certain of the terms may be orders of magnitude greater than the combined total of the individual terms, i.e. the O⁺ field-aligned flux.