Global morphology of night-time <i>Nm</i>F2 enhancements

Abstract

Abstract. An overall statistical study of night-time enhancements of NmF2 has been carried out. All available foF2 observations since 1955 at 53 ionosonde stations distributed worldwide in the latitude range φ geom = 15 • − 60 • were used in the analysis. More than 200 000 station-nights of data were analysed. This large data base allowed us to study seasonal, solar cycle and spatial variations of the NmF2 nighttime enhancements. Both pre-midnight and post-midnight NmF2 peaks demonstrate distinct variations with geophysical conditions, indicating different physical mechanisms responsible for their formation.

Analysis of the winter and semiannual ionospheric anomalies in 1999–2009 based on GPS global International GNSS Service maps

“…It tends to be higher in winter than in summer at low geomagnetic latitudes. Our results show the NWA is larger at mid to low geomagnetic latitudes according to Farelo et al [2002] with maximum values recorded in the South American region. The reason of the premidnight peaks in winter is due to a strong equatorward thermospheric wind raising the F 2 layer to heights with lower recombination rate [Mikhailov et al, 2000].…”

“…They concluded that NWA could be explained by interhemispheric coupling via plasma fluxes along magnetic flux tubes. Mikhailov et al [2000] and Farelo et al [2002] found two peaks when studying the N m F 2 night variability. Both peaks, during premidnight and postmidnight, show different features linked to the different physical mechanisms responsible for their formation.…”

The impact of FORMOSAT-5/AIP observations on the ionospheric space weather

“…At ionosphere mid-latitudes, the nighttime electron density enhancement has been observed and reported by previous studies (e.g., Bailey et al 1991;Farelo et al 2002;Dabas and Kersley 2003;Luan et al 2008;Park et al 2008;Chen et al 2011Chen et al , 2012Chen et al , 2013Lin et al 2011;Rajesh et al 2016). This density-enhanced ionospheric feature appeared more frequently during solar minimum conditions (Bailey et al 1991), and it is suggested to be caused by larger downward plasma flux from the plasmasphere during the nighttime (Mikhailov et al 2000;Farelo et al 2002;Dabas and Kersley 2003).…”

“…This density-enhanced ionospheric feature appeared more frequently during solar minimum conditions (Bailey et al 1991), and it is suggested to be caused by larger downward plasma flux from the plasmasphere during the nighttime (Mikhailov et al 2000;Farelo et al 2002;Dabas and Kersley 2003). Because the plasma flux exchanges between the plasmasphere and ionosphere affect the ionospheric density structure, properly specifying the upper boundary conditions (e.g., electron heat and the O + fluxes) becomes an important factor for applying physically based ionosphere models.…”

Dusk-to-nighttime enhancement of mid-latitude <i>Nm</i>F2 in local summer: inter-hemispheric asymmetry and solar activity dependence

“…Thus, diurnal variation feature of the F layer electron density sometimes deviates from the diurnal trend of the Chapman theory owing to the effect of these factors. A most significant deviation from the Chapman theory is the nighttime enhancement of the electron density (e.g., Dabas and Kersley, 2003;Davies et al, 1979;Essex and Klobuchar, 1980;Evans, 1965;Farelo et al, 2002;Liu et al, 2013;Luan et al, 2008;Tsagouri and Belehaki, 2002). The nighttime enhancement refers to the phenomenon 1959 and 1970-1985 that the electron density increases during the local nighttime hours.…”