Daytime altitude variations of the equatorial, topside magnetic field-aligned ion transport at solar minimum

摘要

Above the ion density peak, the interhemispheric transport of plasma plays an important role in shaping the spatial density distribution of the ionosphere. This study uses daytime observations of the ion drift, density, and composition near the geomagnetic equator from the Coupled Ion-Neutral Dynamics Investigation on board the Communication/Navigation Outage Forecasting System satellite, for the period of extremely low solar activity present in 2008 and 2009, to explore the altitude variation in interhemispheric transport at heights reaching up to the O~+/H~+ transition height. These observations revealed that the physical processes leading to interhemispheric transport do not change with altitude. These processes include forcing from the lower thermosphere, E×B drift, and chemical processes. Their longitudinal variations combine with the structure of the geomagnetic field to cause the differences in interhemispheric transport seen in different longitude regions. At all longitudes, the quantity of plasma crossing the geomagnetic equator depends strongly on ion density, which causes large changes to the altitude variations of the field-aligned plasma drift speed. Key Points Flux tracks altitude changes in interhemispheric transport better than velocity Transport drivers are the same throughout the topside ionosphere Altitude and latitude density variations influence the transport strength