Density enhancements associated with equatorial spread <I>F</I>

Abstract

Abstract. Forces governing the three-dimensional structure of equatorial spread-F (ESF) plumes are examined using the NRL SAMI3/ESF three-dimensional simulation code. As is the case with the equatorial ionization anomaly (IA), density crests within the plume occur where gravitational and diffusive forces are in balance. Large E × B drifts within the ESF plume place these crests on field lines with apex heights higher than those of the background IA crests. Large poleward field-aligned ion velocities within the plume result in large ion-neutral diffusive forces that support these ionization crests at altitudes higher than background IA crest altitudes. We show examples in which density enhancements associated with ESF, also called "plasma blobs," can occur within an ESF plume on density-crest field lines, at or above the density crests. Simulated ESF density enhancements reproduce all key features of those that have been observed in situ.

Topside signature of medium-scale traveling ionospheric disturbances

“…Pimenta et al (2007) presented plasma blobs associated with equatorial plasma depletions during a geomagnetic storm using ground-based airglow imaging and in situ plasma observations from the Defense Meteorological Satellite Program (DMSP). Likewise, Krall et al (2010) demonstrated through modeling that the blob phenomenon could be attributed to equatorial plasma bubble activity. However, the specific plasma blob phenomenon investigated in the present report is not considered to be directly associated with equatorial plasma depletion activity (Kil et al, 2011;Choi et al, 2012).…”

Equatorial spread <I>F</I> fossil plumes

“…1 and 2 but with the instability seeded via random fluctuations in the O + density, temperature, and velocity. As in Krall et al (2010a) these initial fluctuations are based on the observed amplitudes of traveling ionospheric disturbances as reported in Hocke and Schlegel (1996, see Fig. 17 therein).…”

“…This is indicated by ion flow vectors that extend outward across field lines (the dots in each left-hand panel are arrayed along geomagnetic field lines), by ρ values within the bubble that are lower than background values, and by a strong zonal gradient in the electrostatic potential. As noted in Huba et al (2009b) and Krall et al (2010a), a "super fountain effect" acts within an ESF bubble, producing density crests at altitude 600 km and latitude ±16 • that are analogous to the background "Appleton anomaly" ionization crests. In the middle row of contour plots (01:17 UT), the bubble has nearly halted its upward motion.…”

“…In this simulation there are no winds (V nφ = 0). This simulation was described in Krall et al (2010a), where it was shown that the upward motion of the bubble stops when ρ at the upward edge of the bubble is the same as that of the nearby background ionosphere at the same height. Here we describe this result in further detail.…”

“…Recently, the use of sophisticated three-dimensional computer simulation models (Huba et al, 2008;Retterer, 2010) has increased our basic understanding of ESF. Computer simulations have provided newly detailed explanations of numerous ESF-related phenomena including compositional and temperature signatures of ESF, ESF stabilization by meridional winds Maruyama et al, 2009;Abdu et al, 2006), the effect of zonal winds on ESF plume morphology (Huba et al, 2009c), ESF airglow , and ESF-related "plasma blobs" (Krall et al, 2010a).…”