Seasonal variation and solar activity dependence of the quiet‐time ionospheric trough

摘要: We have conducted a statistical analysis of the ionospheric F region trough, focusing on its seasonal variation and solar activity dependence under geomagnetically quiet moderate conditions, using plasma parameter data obtained via Common Program 3 observations performed by European Incoherent Scatter (EISCAT) radar between 1982 2011. confirmed that there is major difference in frictional heating high- low-latitude sides EISCAT field view (FOV) at ~73°0′N–60°5′N (geomagnetic latitude) an altitude 325 km, which associated with trough formation. Our results show high-latitude midlatitude troughs occur FOV, respectively. Seasonal variations indicate dissociative recombination accompanied main cause formation sunlit regions. During summer, therefore, occurrence rate maintained 80–90% postmidnight owing to eastward return flow. Solar indicates field-aligned currents modulate during winter equinox seasons. In addition, becomes deeper caused increased ion temperature F10.7, least summer seasons but not winter.