Magnetic storm-induced enhancement in neutral composition at low latitudes as inferred by O(<sup>1</sup>D) dayglow measurements from Chile

Abstract

Abstract.We describe the effect of the 6 November 2001 magnetic storm on the low latitude thermospheric composition. Daytime red line (OI 630.0 nm) emissions from Carmen Alto, Chile showed anomalous 2-3 times larger emissions in the morning (05:30-08:30 Local Time; LT) on the disturbed day compared to the quiet days. We interpret these emission enhancements to be caused due to the increase in neutral densities over low latitudes, as a direct effect of the geomagnetic storm. As an aftereffect of the geomagnetic storm, the dayglow emissions on the following day show gravity wave features that gradually increase in periodicities from around 30 min in the morning to around 100 min by the evening. The integrated dayglow emissions on quiet days show day-to-day variabilities in spatial structures in terms of their movement away from the magnetic equator in response to the Equatorial Ionization Anomaly (EIA) development in the daytime. The EIA signatures in the daytime OI 630.0 nm column-integrated dayglow emission brightness show different behavior on days with and without the post-sunset Equatorial Spread F (ESF) occurrence.

Contributions of imaging Echelle spectrographs to daytime optical aeronomy

“…The results from this study also indicated a clear difference between the development of Appleton anomaly by 1400 LT on an ESF day and a non-ESF day as indicated by the post-sunset ionograms at Jicamarca on the respective days. This development in the disparity in the strength of the Appleton anomaly development on these two days were independently confirmed by the latitudinal TEC measurements at 1800 LT (Pallamraju et al, 2004a). The dayglow data from different locations show characteristic differences between magnetically disturbed and quiet days.…”

“…Even though there are many factors that affect the ESF-triggers, owing to the coupled nature of the equatorial phenomena, it is believed that the daytime ionosphere-thermosphere system prepares the equatorial ionosphere in making the background conditions conducive for triggering the ESF. In this regard, the development of Appleton anomaly, which demonstrates significant day-to-day variability, has been shown to play an important role in defining the background state of the ionospherethermosphere system for the occurrence of ESF (Raghavarao et al, 1988;Sridharan et al, 1994;Pallamraju et al, 2004a). This effect was also supported by the TEC measurements at sunset time over American longitudes (Mendillo et al, 2001;Valladares et al, 2001).…”

“…This effect was also supported by the TEC measurements at sunset time over American longitudes (Mendillo et al, 2001;Valladares et al, 2001). It is hypothesized that the ionization crests and the excess temperature therein become sources for the generation of cells of meridional and vertical winds that affect the occurrence of the ESF in the nighttime (Raghavarao et al, 1993;Sridharan et al, 1994;Jyoti et al, 2004;Pallamraju et al, 2004a). This is the motivation behind the daytime optical measurements from lowlatitudes.…”

“…2, middle panel) is the day that was affected by the magnetic storm of 6 November 2001. The enhancements in emissions on this day at different latitudes were caused by the redistribution of neutrals brought in from high-latitudes towards the low-and equatoriallatitudes and hence provided a clear evidence of the formation of latitudinal circulation cells in neutrals during severe geomagnetic storms (Pallamraju et al, 2004a) that were first proposed by Mayr et al (1978). The results from this study also indicated a clear difference between the development of Appleton anomaly by 1400 LT on an ESF day and a non-ESF day as indicated by the post-sunset ionograms at Jicamarca on the respective days.…”

Vertical coupling of atmospheres: dependence on strength of sudden stratospheric warming and solar activity

“…This plasma then diffuses along the magnetic field lines and accumulates at around ±15°latitudes off the magnetic equator, building up regions of enhanced densities (crests) in plasma, and this phenomenon is known as the EIA (Raghavarao et al 1988). The strength and latitude coverage of the EIA crest depends on season and lower atmospheric forcings of tidal nature (Immel et al 2006;Pallamraju et al 2004Pallamraju et al , 2010. Waves propagating from the lower atmosphere perturb the E-region dynamo electric field which is mapped to the F-region and thereby contribute to the redistribution of plasma.…”