The formation of an electron hole in the topside equatorial ionosphere

In this letter we report new modeling results that show the formation of an electron hole (depletion) in the topside equatorial ionosphere. The reduction in the electron density occurs in the altitude range 1500 - 2500 km at geomagnetic equatorial latitudes. The hole is produced by transhemispheric O+ flows that collisionally couple to H+ and transport it to lower altitudes, thereby reducing the electron density at high altitudes. The transhemispheric O+ flows are caused by an interhemispheric pressure anisotropy that can be generated by the neutral wind, primarily during solstice conditions. The formation of the electron hole has a seasonal and longitudinal dependence. This result has been found with a new low-latitude ionospheric model that has been developed at the Naval Research Laboratory: SAMI2 (Sami2 is Another Model of the Ionosphere).