Behavior of the nighttime ionosphere

Abstract

Measurements of columnar electron contents made at frequent time intervals throughout the night permit the determination of the rate at which the total content decays. It is found that at midlatitudes this rate is correlated with the geomagnetic activity index Kp, while such correlation is negligible at lower latitudes. An annual variation of the decay rate is observed, with a maximum around June. These results are consistent with the theory that the nighttime ionosphere is maintained in part by the downward flux of electrons from the protonosphere.

On the mechanism of the post-midnight winter <i>N<sub>m</sub>F<sub>2</sub></i> enhancements: dependence on solar activity

“…Nighttime N m F 2 enhancements (pre-midnight and postmidnight) are a typical phenomenon for the mid-to lowlatitude F 2 -region which has long been observed both in N m F 2 and TEC (Arendt and Soicher, 1964;Evans, 1965Evans, , 1974Da Rosa and Smith, 1967;Titheridge, 1968Titheridge, , 1973Bertin and Papet-Lepine, 1970;Young et al, 1970;Tyagi, 1974;Davies et al, 1979;Kersley et al, 1980;Jakowski et al, 1986Jakowski et al, , 1991Balan and Rao, 1987;Joshi and Iyer, 1990;Jakowski and FoÈ rster, 1995). A morphological study by Mikhailov et al (2000) of the N m F 2 nighttime enhancements on the latitudinal chain of the Eurasian ionosonde stations has revealed systematic variations with season and solar activity in the occurrence probability of the peaks, their amplitude and timing.…”

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

“…Night-time enhancements of electron concentration are typical phenomena of the F2-layer in middle latitudes that can be observed both in the maximum of electron concentration in the F2-layer (NmF2) and total electron content (TEC) (Arendt and Soicher, 1964;Evans, 1965;Da Rosa and Smith, 1967;Bertin and Papet-Lepine, 1970;Young et al, 1970;Titheridge, 1973;Tyagi, 1974;Davies et al, 1979;IvanovKholodny and Mikhailov, 1986;Balan and Rao, 1987;Joshi and Iyer, 1990;Lois et al, 1990;Jakowski et al, 1991;Jakowski and Förster, 1995;Mikhailov and Förster, 1999;Mikhailov et al, 2000a, b). Although NmF2 and TEC variations usually exhibit similar behaviour in the night-time ionosphere, there are some differences in the occurrence of these variations and in the treatment that has been applied to their analysis (Tyagi, 1974;Lois et al, 1990).…”

Peculiarities of the nighttime winter foF2 increase over Irkutsk

“…Nighttime increases of the midlatitude F2 region electron density, Ne, (critical frequency, foF2, maximum electron density, NmF2, and total electron content, TEC) are wellknown phenomena (Evans, 1965;Da Rosa and Smith, 1967;Rao et al, 1982;Krinberg and Tashchilin, 1984;Bailey et al, 1991;Jakowski and Fö rster, 1995;Mikhailov and Fö rster, 1999;Mikhailov et al, 2000aMikhailov et al, , 2000bRichards et al, 2000;Belehaki and Tsagouri, 2002;Farelo et al, 2002;Dabas and Kersley, 2003;Pavlov and Pavlova, 2005;Luan et al, 2008;Pavlov et al, 2008;Yakovets et al, 2009). These phenomena are called also anomalous enhancements/increases of electron density, since the solar EUV radiation as the major source of ion production is absent during the nighttime.…”