Local time dependent response of postsunset ESF during geomagnetic storms

Abstract

[1] Development or inhibition of ESF during magnetically active periods has been an important space weather topic of interest during the recent past in view of its applications in the satellite based navigational systems. Particularly, the postsunset period exhibits significant variability for storm time development of ESF versus longitude. In this paper, we report the results of a multi-instrumental (ground based and space-borne) and multistation study on the development/inhibition of postsunset ESF during five moderate to intense geomagnetic storms occurred during the low and descending phase of the solar activity period, [2004][2005][2006]. It has been observed that, the prompt penetration of eastward electric fields into low latitudes and subsequent development of ESF occurred in all longitudinal sectors where the local time corresponds to postsunset hours during the entire main phase of the storm. In this paper, we show the development of plasma bubble irregularities over a wide longitudinal extent of 92°owing to the dusk time penetration of eastward electric fields into low latitudes. Either the sudden increase in AE-index and/or a marked decrease in Sym-H index may be used as proxies to determine the occurrence as well as the time of penetration of electric fields into equatorial and low latitudes. However, in such cases where the AE-index does not represent any sudden increase, the dSymH/dt seems to be the better index to determine the time of penetration. In this paper, is also presented an interesting case where the prompt penetration eastward electric fields dominated the existing strong westward electric fields and subsequently caused the onset of spread-F and scintillations at both VHF (244 MHz) as well as L-band (1.5 GHz) frequencies.

Low-latitude ionospheric-thermospheric response to storm time electrodynamical coupling between high and low latitudes

“…The second huge plume at 0045 LT, significant L-band scintillation at AREQ and GLPS around midnight provides evidence for the penetration of intense eastward electric fields associated with the northward turning of IMF Bz over the equator which prevailed over the ambient westward electric fields leading to development of strong ESF after midnight. This corroborates with the previous report by Tulasi Ram et al [2008]. Using the data from different longitude sectors, they explained the role of storm time prompt penetration of electric field in the occurrence of ESF.…”

“…The geomagnetic storm can initiate ESF in the post midnight sector because of abnormal upward reversals in the vertical plasma drift under the action of eastward electric fields of ionospheric disturbance dynamo (IDD) [Kelley and Maruyama, 1992;Hysell and Burcham, 1998] and also often because of penetration of eastward electric fields associated with northward turning of IMF Bz . There are ample of studies reported which explain the development/inhibition of ESF during geomagnetic storm and the role of storm time perturbation electric fields during last three decades [Aarons, 1991;Sastri et al, 1993;Abdu et al, 1995;Fejer et al, 1999;Basu et al, 2001bBasu et al, , 2005Sobral et al, 2001;Huang et al, 2005, Huang andChen, 2008;Tulasi Ram et al, 2008].…”

Unseasonal development of post-sunset F-region irregularities over Southeast Asia on 28 July 2014: 1. Forcing from above?

“…Another source of westward electric fields is the disturbance dynamo, which is caused by a westward neutral wind enhancement from mid-latitudes to the equator that occurs a few hours following an increase of geomagnetic activity (Blanc and Richmond 1980). The eastward penetration electric field that enhances the PRE is known as the "under-shielding" electric field (or the "promptpenetration electric field, " PPEF) that follows a sudden southward turning of the IMF (e.g., Huang et al 2005;Tulasi Ram et al 2008).…”

Effect of magnetic activity on plasma bubbles over equatorial and low-latitude regions in East Asia

“…Taking into consideration the added penetration or dynamo electric field tends to enhance or diminish the effect of PRE near sunset, and determines the favorable or unfavorable conditions for the development of plasma bubbles, many authors have made efforts to examine the influence of magnetic activity on the occurrence of ionophseric irregularities (e.g. Singh et al, 1997a;Martinis et al, 2005;Tulasi Ram et al, 2008). Earlier studies of the effects of geomagnetic storms on the development or inhibition of ionospheric irregularities have shown that there is a general consensus that magnetic activity tends to suppress the generations of spread-F or plasma bubbles in the pre-midnight period, whereas the possibility of observing spread-F or plasma bubbles during the postmidnight period increases with magnetic activity.…”