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- Title
Solar Flux Dependence of Post‐Sunset Enhancement in Vertical Total Electron Content Over the Crest Region of Equatorial Ionization Anomaly.
- Authors
Kumar, A.; Chakrabarty, D.; Pandey, K.; Yadav, A. K.
- Abstract
Based on 10 years' of vertical total electron content (VTEC) data in solar cycle 24 from Ahmedabad (23.0°N, 72.6°E, dip angle 35.2°), a station under the crest region of equatorial ionization anomaly (EIA), it is shown that both the integrated residual and total post‐sunset enhancements in VTEC are conspicuous during Equinox and December solstice when solar flux level exceeds 110 solar flux unit (sfu) with the exception of the year 2012–2013. The post‐sunset enhancements are absent in June solstice at this local time even if the solar flux level exceeds 110 sfu. The integrated residual and total VTEC enhancements during post‐sunset hours are found to be linearly correlated with the solar flux level in Equinox and December solstice. It is noted that a parabolic fit works better for the integrated total VTEC enhancement during December solstice suggesting a possible saturation of VTEC enhancements at high solar flux levels. Based on these observations and Thermosphere Ionosphere Electrodynamics‐General circulation model (TIE‐GCM) outputs, it is argued that the pre‐reversal enhancement (PRE) in the equatorial F region zonal electric field works in tandem with latitudinal gradient in the F region plasma density to determine the degree of VTEC enhancement over the EIA crest region during post‐sunset hours. These results highlight the solar flux dependence of the post‐sunset enhancement of VTEC over the crest region and show that sudden stratospheric warming events in 2012–2013 suppressed these enhancements in December solstice even if solar flux levels exceeded 110 sfu. Plain Language Summary: The low latitude region is one of the most L‐band scintillation affected region in the whole globe. In addition, owing to the equatorial plasma fountain process, the low latitude F region ionosphere is also marked by steep latitudinal plasma density gradient during post‐sunset hours. It is shown that the evening plasma fountain driven by pre‐reversal enhancement of the zonal electric field controls the post‐sunset enhancement of the F region plasma density over the crest region of equatorial ionization anomaly (EIA) region with the assistance from the latitudinal plasma density gradient. This result is important to forecast the ionospheric condition over the EIA crest region during post‐sunset hours. Key Points: Post‐sunset enhancements in vertical total electron content (VTEC) over the equatorial ionization anomaly crest region are significant only above 110 solar flux unit level during December solstice and EquinoxPre‐reversal enhancement (PRE) of equatorial zonal electric field is shown to primarily drive the post‐sunset enhancements in VTECThermosphere Ionosphere Electrodynamics‐General circulation model simulations reveal the additional importance of latitudinal plasma density gradients over low latitudes
- Subjects
PLASMA density; LATITUDE; CIRCULATION models; SOLAR cycle; ELECTRONS; ELECTRIC fields
- Publication
Journal of Geophysical Research. Space Physics, 2022, Vol 127, Issue 5, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2021JA030156