Day‐to‐day variability of the equatorial ionization anomaly and scintillations at dusk observed by GUVI and modeling by SAMI3

Abstract

[1] The day-to-day variability in ionospheric irregularity generation giving rise to equatorial scintillation has remained an unresolved issue over many decades. We take a fresh look at the problem utilizing the global imagery provided by the Global Ultraviolet Imager (GUVI) instrument on NASA's Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite. GUVI has been acquiring images of 135.6-nm emission in the Earth's ionosphere-thermosphere system since 2001. These GUVI disk images at dusk have been used to identify cases where the equatorial ionization anomaly (EIA) crests lie near the magnetic equator over a relatively narrow longitude range, so that the anomaly looks collapsed. A 16-month period of GUVI data collected during evening at solar maximum is used to study the morphology of these so-called collapses, since the EIA collapse is shown to be linked to the suppression of equatorial plasma bubbles and scintillations. In particular, we look at the June solstice, during which the Atlantic and Pacific show very different climatology and EIA collapses are most frequent in the GUVI data. On the other hand, EIA collapses are a relatively rare occurrence during the equinox period when scintillations are most prevalent globally. We obtained a few dramatic examples of day-to-day variability in EIA behavior and scintillations over India. The Sami3 is Also a Model of the Ionosphere (SAMI3) model was used to investigate the conditions during the evening collapse of the anomaly in the Indian longitude sector, where measurements of total electron content (TEC) and scintillations and estimates of the daytime vertical drifts and those at dusk were available. Results from SAMI3 show that the observed collapse of the anomaly at dusk can be simulated by a reversal of the upward vertical drift in midafternoon in agreement with the drift estimates from magnetometer observations. Such reversed vertical drifts at this time of the day are generally seen during counterelectrojet events. Introduction of neutral winds into SAMI3 better approximates the dusk behavior of TEC at low-latitude stations in India. This study reveals that the longitudinally confined EIA collapse may explain some of the differences in day-to-day variability of scintillations at different locations around the globe.

Features of theF3layer in the low-latitude ionosphere at sunset

“…A similar case was investigated by Zhao et al [2008] for the East Asian region, which suggests that planetary waves modulating the semidiurnal tide might be responsible for the corresponding anomaly enhancement of EIA in the postsunset period. Basu et al [2009] revealed the fact that a counter-electrojet (CEJ) event in the afternoon may contribute to the inhibition of EIA. The cause of the day-today variability of the E × B drift corresponding to the PRE remains unresolved as the information regarding altitude, latitude, longitude, and local time variations of the ion drifts, the neutral winds, and the electric fields are only starting to become available.…”

Low Latitude Ionospheric Electrodynamics

“…These include airglow observations by the IMAGE (Immel et al 2004(Immel et al , 2007) and TIMED satellites (e.g., Basu et al 2009), and ion drift, density and composition measurements on board the Defense Meteorological Satellite Program (DMSP) (Basu et al 2001;Hartman and Heelis 2007), and Republic of China Satellite (ROCSAT-1) (e.g., Kil et al 2007;Fejer et al 2008a) satellites. In addition, total electric content (TEC) has been obtained from TOPEX satellite data (e.g., Scherliess et al 2008), and magnetic field, plasma density and TEC data have been derived from measurements on board the Challenging Minisatellite Payload (CHAMP) satellite (e.g., Lühr et al 2004).…”

Ionospheric scintillations at Guilin detected by GPS ground-based and radio occultation observations

“…Before the reversal of the drift from upward to downward, there exists an upward drift enhancement named prereversal enhancement (PRE), which is driven by an enhanced eastward electric field lasting about an hour after sunset. At the time of sunset, the F region zonal neutral wind and conductivity gradient caused by the sunset terminator interact to develop an enhanced eastward electric field on the dayside of the terminator and a westward electric field on the nightside (Basu et al, 2009). A clear relation exists between the magnitude of the prereversal enhancement of the vertical plasma drift velocity and the occurrence of post-sunset equatorial spread F (ESF): when a strong prereversal enhancement presents, the irregularities are more likely to develop (Li et al, 2008).…”