Ion temperature and density relationships measured by CINDI from the C/NOFS spacecraft during solar minimum

Abstract

The Ion Velocity Meter (IVM), a part of the CINDI instrument package on board the C/NOFS spacecraft, makes in situ measurements of plasma temperature, composition, density, and velocity. The 16 April 2008 launch of C/NOFS coincided with the deepest solar minimum since the space age began with F10.7 cm radio fluxes in the 60–70 solar flux unit range. Because of the 13° inclination of the orbit the location of the perigee advances through all local times in about 66 days. This allows seasonal sampling of ionospheric temperature, density, and composition as a function of local time, magnetic latitude, and altitude. Measurements taken near the spacecraft's 402 km perigee altitude indicate an unusually cold low‐density ionosphere with nighttime ion temperatures at the magnetic equator reaching as low as 600 K with an [O+]/[H+] ratio of 4 and maximum daytime temperatures of 1300 K. The O+ to H+ transition height is very low and at the highest altitudes measured H+ comprises over 75% of the ionospheric plasma at all local times. We compare average values of the measured parameters with those from the International Reference Ionosphere and with incoherent scatter radar measurements from Jicamarca.

Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

“…Since the level of solar activity under which C/NOFS has operated has varied from unusually low to moderate, this mission has provided an extension to the climatological database on the topside ionospheric region during conditions of an extremely contracted ionosphere (Heelis et al, 2009;Coley et al, 2010). This means that C/NOFS was effectively operating further above the primary altitudes of E and F region dynamo activity than other equatorial spacecraft and that the neutral winds responsible for the F region dynamo are generally well below the spacecraft altitude.…”

Climatology of ionospheric upper transition height derived from COSMIC satellites during the solar minimum of 2008

“…Direct measurements of upper transition height are typically made by in situ ion observations of satellites or ground based incoherent scatter radar (e.g., Coley et al, 2010;Gonzá lez and Sulzer, 1996;Heelis et al, 2009;Hysell et al, 2009). However, these direct observations of upper transition height are not enough to give us a comprehensive understanding of its dependence on solar activity, local time, season, and location (Bilitza, 2001).…”

Does theF10.7index correctly describe solar EUV flux during the deep solar minimum of 2007-2009?

“…Therefore, special attention should be paid to this when developing ionospheric models. In fact, some works [e.g., Bruinsma and Forbes, 2010;Coley et al, 2010;Lühr and Xiong, 2010] have pointed out that some ionospheric and thermospheric models driven by F 10.7 overestimate electron concentration and neutral density during the recent Smin.…”