Electron–ion–neutral temperatures and their ratio comparisons over low latitude ionosphere

• Plasma temperatures (Te and Ti) exhibit similar but neutral temperature Tn exhibit different diurnal features.
• Magnitude of Te and Ti reduces while that of Tn increases with increasing solar activity.
• Plasma cools faster than neutrals during nighttime.
• The ratio (Te/Tn, Ti/Tn and Te/Ti) comparisons show higher sensitivity of electrons over ions and neutrals.
• Deviation of Te, Ti and Tn from equilibrium reduces with increasing solar activity.

Annual variations in temperatures of plasma (electron–Te, ion–Ti) using SROSS-C2 satellite and neutral (Tn) using NRLMSIS-00 (neutral atmospheric model); have been investigated and their ratios have been compared over half solar cycle (year 1995–2000, F10.7 ∼ 72–190). The region under consideration spans over 5–35°N geog. latitude and 65–95°E geog. longitude in the Indian sector, at an average altitude of 500 km. Te and Ti exhibit similar, while Tn show completely different diurnal features. During nighttime Te, Ti and Tn attain equilibrium with each other, but plasma cools faster than neutrals. Magnitude of Te and Ti reduces, while that of Tn increases with increasing solar activity. Ratio comparisons (Te/Tn, Ti/Tn and Te/Ti) show higher sensitivity of electrons compared to ions and neutrals. Te/Tn, Ti/Tn exhibits linear/direct relationship with solar flux, while Te/Ti doesn’t. The deviation of Te, Ti and Tn from equilibrium temperature decreases with increasing solar activity.