Unusual nighttime impulsive foF2 enhancements at low latitudes: Phenomenology and possible explanations

摘要: Abstract This paper is focused on unusual nighttime impulsive electron density enhancements that are rarely observed at low latitudes a wide region of South America, under quiet and medium/high geomagnetic conditions. The phenomenon investigation very peculiar because besides being brief duration, it characterized by pronounced compression the ionosphere. was studied analyzed using both F2 layer critical frequency (foF2) virtual height base F (h′F) values recorded five ionospheric stations widely distributed in space, namely: Jicamarca (−12.0°, −76.8°, magnetic latitude −2.0°), Peru; Sao Luis (−2.6°, −44.2°, +6.2°), Cachoeira Paulista (−22.4°, −44.6°, −13.4°), Jose dos Campos (−23.2°, −45.9°, −14.1°), Brazil; Tucuman (−26.9°, −65.4°, −16.8°), Argentina. In more restricted over Tucuman, also investigated total content (TEC) maps computed measurements from 12 GPS receivers. A detailed analysis isoheight ionosonde plots suggests traveling disturbances (TIDs) caused gravity wave (GW) propagation could play significant role causing for activity; latter case however recharging fountain effect, due to electric fields penetrating magnetosphere, joins TID plays an as much enhancements.