Mapping the duskside topside ionosphere with CINDI and DMSP

Abstract

The CINDI plasma instrument package on board the C/NOFS spacecraft performs in situ measurements of the velocity, temperature, composition, and density of ionospheric ions. In a 402 by 849 km orbit with a 13° inclination its apogee reaches the topside ionosphere at the same altitude as the polar-orbiting DMSP spacecraft that also carry similar plasma measurement packages. Over the course of about 66 days the apogee of C/NOFS' orbit cycles once through all solar local times. This paper presents the apogee observations from the CINDI instruments between 21 August and 5 September 2008 when the C/NOFS' apogee passed through the orbital planes of the duskside equatorial crossings of the four operational DMSP spacecraft. Combining the data from all five spacecraft reveals the spatial distribution of the total ion density, the ion temperature, and the ion composition at these altitudes. Comparisons of these observed distributions from CINDI and DMSP are used to check the agreement between the new CINDI instruments and the long-operating DMSP instruments. The results of the density and temperature measurements show good agreement, however there are two regions where the composition and temperature measurements show discrepancies that result from the limitation of the plasma instruments in an environment of extremely low density plasma composed of over 85% light ions (H+ and He+). Copyright 2010 by the American Geophysical Union.