Equatorial broad plasma depletions associated with the enhanced fountain effect

Abstract

[1] Broad plasma depletions (BPDs), plasma depletions whose longitudinal width is over several hundred kilometers, have been detected in the equatorial F region by low-earth-orbit satellites during both magnetically quiet and magnetically disturbed periods. A few hypotheses were suggested to explain the creation of BPDs, but the underlying mechanism of this phenomenon is still under debate. We investigate the origin of BPDs by analyzing the simultaneous in situ and optical observations of the ionosphere on 30 May 2003 (Kp = 8 + ), 24 April 2012 (Kp = 7 À ), and 31 October 2012 (Kp = 0 + ). BPDs on 30 May 2003 were detected by the Republic of China Satellite-1 at an altitude of 600 km, and BPDs on the other days were detected by the Communication/Navigation Outage Forecasting System satellite near an altitude of 400 km. Our results show that the detection of BPDs is closely associated with background ionospheric morphology; BPDs are detected on the days when the equatorial ionization anomaly (EIA) is intense and the crests of the EIA have moved poleward. Measurements of upward plasma motion support the existence of ionospheric uplift at BPD locations. These observations and the detection of BPDs near the magnetic equator lead to the interpretation that the satellite detection of BPDs during those 3 days is likely related to the uplift of the F peak height above the satellite orbits.

Equatorial broad plasma depletions associated with the evening prereversal enhancement and plasma bubbles during the 17 March 2015 storm

“…BPDs seem to occur in association with large storms, and their creation mechanism is considered to be different from the creation mechanism of bubbles. BPDs are the phenomena identified by in situ satellite observations [Basu et al, 2001[Basu et al, , 2007Burke et al, 2000Burke et al, , 2009Greenspan et al, 1991;Huang et al, 2011;Kil and Lee, 2013;Lee et al, 2014;Su et al, 2002].…”

Broad plasma depletions detected in the bottomside of the equatorial F region: Simultaneous ROCSAT‐1 and JULIA observations

“…Lee et al . [] pointed out that a BPD has either smooth walls or steep walls depending on the presence of bubbles. If multiple and large bubbles developed as a consequence of the uplift of the ionosphere, then a satellite in the bottomside would detect a deeper and wider BPD in that region than in the region where bubbles were absent.…”

“…Plasma depletions whose zonal widths are greater than several hundred kilometers occasionally occur, and we call them broad plasma depletions (BPDs). BPDs have been detected by satellites near the magnetic equator in the altitude range of 350–840 km [ Basu et al ., , ; Burke et al ., , ; Greenspan et al ., ; Huang et al ., , ; Kil and Paxton , ; Kil and Lee , ; Kil et al ., ; Lee et al ., ; Su et al ., ]. The BPD phenomenon has been considered to be associated with geomagnetic storms because most studies reported the BPDs observed during magnetically disturbed periods.…”

“…The hypotheses regarding the source of BPDs are divided largely into two categories. One category explains the BPD phenomenon in terms of the relative altitudes of satellites and F region [ Basu et al ., , ; Greenspan et al ., ; Kil and Lee , ; Lee et al ., ; Su et al ., ]. According to this hypothesis, the occurrence of BPDs along a satellite orbit is related to the sampling of the ionosphere in the bottomside of the F region.…”

“…The BPD phenomenon has been considered to be associated with geomagnetic storms because most studies reported the BPDs observed during magnetically disturbed periods. However, BPDs also occur during magnetically quiet periods when the satellite altitude is low (~400 km) [ Lee et al ., ].…”