Investigation of enhanced E-region activity and intermediate meteoric ion layers over Arecibo

Sporadic-E (Es) layers are a frequent phenomena over Arecibo, and almost occur every night with varying intensity. The seasonal dependence, as well as their formation mechanisms have been studied intensively in the past. These can be detected using several instruments that include ionosondes, Incoherent Scatter Radar, and by calcium ion (Ca+) resonance lidars. In this work, we focus on the sudden increase in meteoric Ca+ with values exceeding 500 ions/cm-3 on the night of 30 Nov 2016, while average concentrations were in the range of 5 – 30 ions /cm-3. On this night, the average Es altitude was ~ 98 km before 3:00 AM (LT) or 7 UT, with the occurrence of Kelvin-Helmholtz like features suggestive of strong wind shears during pre-midnight hours. During pre-dawn hours, Es exhibited sudden uplift with layer ascending to altitudes ~ 115 km with marked enhancement in the densities. Remarkably, the F-region displayed a sudden drop in electron concentration values as the Es strength increased. HmF2 exhibited oscillatory behavior during this time, while the delay in the Es enhancement and F-region densities occurred in the order of a few tens of minutes. Additionally, Ca+ ions were detected above the meteoric ablation zone, and appeared to be co-located with the intermediate descending layers. In this paper, we compare local E- and F-region over Arecibo on three consecutive nights, and a possible connection with equatorial spread-F that could possibly be responsible for meteoric Ca+ between 120 – 180 km altitudes. Thus, this meteoric ion is an excellent tracer for probing the least explored region of the ionosphere-thermosphere system.