Behaviour of the low-latitude ionosphere-plasmasphere system at long deep solar minimum

The behaviour of the low-latitude ionosphere-plasmasphere system during the long deep solar minimum between solar cycles 23 and 24 is presented using the physics based model SUPIM and FORMOSAT-3/COSMIC satellite data. Using the vertical ion drift velocity measured by C/NOFS satellite, and neutral densities and wind velocities obtained from MSIS and HWM, SUPIM calculates the electron and ion (O⁺, H⁺, He⁺, N₂⁺, O₂ ⁺, and NO⁺) densities and temperatures and plasma fluxes within ±40° magnetic latitudes and 150-2000 km heights for Indian longitudes at equinox (F10.7 = 68, Ap = 4). FORMOSAT-3 measures the corresponding electron density up to 600 km height. The data and model show the ionosphere contracting to a thin layer during the long deep solar minimum. During daytime, the ionosphere has a half-width of only about 250 km over the equator and 150 km at EIA crests with a peak density of about 10⁶ cm^-3 and O⁺/H⁺ transition height at around 750 km. At night, the ionosphere reduces to a cold thinlayer of half-width less than about 150 km at the crests with a peak density of about 10⁵ cm^-3, and transition height about 500 km where the ion densities reduce to about 10⁴ cm^-3. Plasma density in theplasmasphere (above transition height) remains nearly constant at about 10⁴ cm^-3 during both day and night, and decreases only very slowly with height. However, the temperatures increase rapidly at sunrise at all heights to reach about 2500 K (electron) and 2250 K (ion) at 0800 hrs LT at 2000 km height(at EIA crests), which decrease by a maximum of only 250 K until sunset. After sunset, both electronsand ions cool rapidly until about midnight and then decrease slowly to nearly constant temperatures at all heights to about 650 K prior to sunrise. SUPIM predictions and FORMOSAT-3 data agree also withC/NOFS and CHAMP satellite observations.