On the solar activity variations of nocturnal F region vertical drifts covering two solar cycles in the Indian longitude sector

Abstract

A comprehensive analysis of the seasonal and solar cycle variabilities of nighttime vertical drift over the Indian longitude sector is accomplished using ionosonde data located at the magnetic equatorial location, Trivandrum (8.5°N, 76.5°E). The analysis extends over a span of two decades . The representative seasonal variations based on the extensive data of nocturnal vertical drift during three different solar activity epochs is arrived at, for the first time. Seasonally, it is seen that maximum post sunset V d is obtained in vernal equinox (VE), followed by autumnal equinox (AE), winter solstice (WS), and summer solstice (SS) for high and moderate solar epochs, while for low solar epoch, maximum V d occurs in WS followed by VE, AE, and SS. Further, the role of sunset times at the magnetic conjugate points in modulating the time and magnitude of peak drifts during different solar epochs is ascertained. The equinoctial asymmetry in peak V d during high and moderate solar epochs is another significant outcome of this study. The solar activity dependence of vertical drift for a wide range of solar fluxes has been quantified for all the seasons. In the present era of GPS-based communication and navigation, these are important results that give a better handle in understanding essential factors that impact equatorial ionospheric phenomena.

Role of IMF By in the prompt electric field disturbances over equatorial ionosphere during a space weather event

“…Over Thumba, on the other hand, the F region vertical drifts were downward during the interval T 1 – T 2 , less downward (approaching zero) during T 2 –( T 2 + 00:35), and significantly upward (∼20 m/s) during the time interval ( T 2 +00:35)– T 3 . The drifts during ( T 2 + 00:20)– T 3 were in sharp contrast to the average vertical drifts (blue dashed line) at this local time reported by Madhav Haridas et al [] based on h'F observations. The deviation of the Thumba drift was above the uncertainty level (∼5 m/s) during the interval T 1 – T 2 , and it was consistently negative in contrast to the quiet time drifts suggesting a westward PP electric field influence during T 1 – T 2 .…”

“…The variations in (a) IMF B z (in red) and S Y M ‐ H (in cyan), (b) IMF B y (in blue), (c) solar wind pressure P , on 7 January 2005. These variations are compared with the (d) EEJ variations over Peruvian sector Δ H JIC ‐Δ H PIU , (e) vertical plasma drift from JULIA (in black) along with its four quiet day average prior to the event (in dashed blue), and (f) vertical drift data over Thumba (in black) after Chakrabarty et al [] along with its seasonal quiet time values from Madhav Haridas et al [] (in dashed blue). The Jicamarca and Thumba drifts have uncertainties of the order of 2 m/s and 5 m/s, respectively.…”

Evidence for the Significant Differences in Response Times of Equatorial Ionization Anomaly Crest Corresponding to Plasma Fountains During Daytime and Post‐Sunset Hours

“…(2018). Further, it may be noted here that observations from the Indian sector suggest that the PRE occurs about half an hour later in Equinox compared to December solstice (e.g., Madhav Haridas et al., 2015; Sripathi et al., 2016). This may reduce the response time of the EIA crest region during Equinox if one uses vertical drift observations from the dip equatorial station.…”

“…H and D a represent atomic Oxygen ion scale height and ambipolar diffusion coefficient respectively. The relevant plasma, neutral, geomagnetic field and meridional wind parameters used as inputs in Equation 1 are taken from IRI-16 (Bilitza et al, 2017), NRLMSISE-00 (Picone et al, 2002), IGRF-13 (Alken et al, 2021), and HWM-14 (Drob et al, 2015) Haridas et al, 2015;Sripathi et al, 2016). These results suggest that the F-region background conditions over low latitude do not support the reduced response time of the EIA crest region during post-sunset hours.…”

Electrodynamics of the equatorial evening ionosphere: 1. Importance of winds in different regions

“…On magnetically quiet days the vertical convection is generally upward during the day and downward at night, often with an enhancement of the upward velocity in the early evening before the reversal to downward velocity at later times, referred to as the prereversal enhancement (PRE) [ Woodman , ; Fejer et al , ; Fejer , ; Fejer et al , ; Scherliess and Fejer , ; Pacheco et al , ; Fejer , ; Madhav Haridas et al , ]. In addition to seasonal and longitudinal variations, the vertical velocity varies with the level of solar activity [e.g., Fejer et al , ; Fejer , ; Stoneback et al , ; Madhav Haridas et al , ]. In the evening the zonal convection in the upper ionosphere is generally eastward, increasing from sunset until about 22 magnetic local time (MLT) [ Coley and Heelis , ; Coley et al , ; Fejer et al , ].…”