Equatorial F region zonal plasma irregularity drifts under magnetospheric disturbances

Abstract

Abstract. Equatorial F region plasma drift velocities measured by a digital ionosonde (CADI) that was recently installed in Fortaleza, Brazil, are used to investigate magnetospheric disturbance effects in the vertical (zonal) and zonal (vertical) velocities (electric fields). For the first time we report evidence of large fluctuations in irregularity zonal drift velocities (-50-180 m/s) associated with magnetospheric disturbances. The fluctuations in the zonal velocity, anti correlated with those in vertical velocity, are unlikely to be produced by prompt penetration of disturbance meridional electric field of high latitude/magnetospheric origin. A mechanism is proposed to explain the velocity fluctuations that involves: (1) Hall polarization vertical electric field in the E-layer that is field line mapped on to F-layer, and (2) electric field caused by vertical current arising from divergence in field line integrated zonal Pedersen current; both produced by the primary disturbance zonal electric field. Enhanced nighttime E region conductivity with possible spatial gradients, a requirement for the functioning of this mechanism, is observed to be present from other simultaneous measurements, whose source is suggested to be particle induced ionization in the south Atlantic Magnetic Anomaly (SAMA) zone, as known also from previous studies.

Occurrence and zonal drifts of small-scale ionospheric irregularities over an equatorial station during solar maximum – Magnetic quiet and disturbed conditions

“…For instance, in the case of process (a) westward disturbance wind could suppress the normally eastward thermospheric wind that drives the ambient plasma, then resulting in a reduced eastward irregularity drift velocity or even a net westward drift (Abdu, 1997). For the mechanism (b), disturbance dynamo electric field and prompt penetration disturbance zonal electric field could impose an additional fluctuating field line mapped vertical Hall electric field, which in turn could cause zonal plasma/irregularity drift variations (Abdu et al, 1998b;. In another way, the process (c) could arise from spatial gradients in conductivity, giving rise to vertical current and electric field that might produce fluctuations in the observed zonal drift.…”

“…In another way, the process (c) could arise from spatial gradients in conductivity, giving rise to vertical current and electric field that might produce fluctuations in the observed zonal drift. At Brazilian longitude sector mechanisms (b) and (c) could, perhaps, be favored by modifications in the nighttime ionospheric conductivity caused by enhanced particle precipitation in the South Atlantic Magnetic Anomaly (SAMA) region (for more details see Abdu et al, 1998b).…”

“…Under disturbed circumstances the zonal drift of the ambient plasma and the irregularities can be affected by different possible sources of vertical electric field variations, such as: (a) thermospheric disturbance winds and the associated disturbance dynamo electric fields (Blanc and Richmond, 1980), (b) vertical Hall electric field (Abdu et al, 1998b) and (c) by divergence of horizontal currents in the lower F-region and E-layer (Haerendel et al,1992). For instance, in the case of process (a) westward disturbance wind could suppress the normally eastward thermospheric wind that drives the ambient plasma, then resulting in a reduced eastward irregularity drift velocity or even a net westward drift (Abdu, 1997).…”

Long-duration positive ionospheric storm during the December 2006 geomagnetic storm: Ionizing effect of forbidden electrons

“…Ionospheric effects of energetic particles, which can penetrate to the D, E, and F ionospheric regions from magnetosphere and interplanetary space, have been known for a long time as well as are studied now (e.g., Abdu et al, 1998;Suvorova et al, 2012Suvorova et al, , 2013Suvorova et al, , 2014Zigman et al, 2014;Zakharenkova and Astafyeva, 2015).…”

Electrodynamics of ionospheric weather over low latitudes

“…An important component of the short-term variability of bubble irregularities over any location concerns the zonal drift of the irregularities, which is eastward under quiet conditions, as is the background plasma drift driven by the dynamo action of the night-time eastward thermospheric wind. However, such drift can be modified drastically, even to reverse westward due to (1) storm time thermospheric zonal wind arising from auroral heating when equatorward disturbance winds acquire westward velocity at low and equatorial latitudes (see for example, Sutton et al 2005); (2) Hall electric field induced by the PPEF under enhanced night-time E layer conductivity and/ or by reduced F region density (Abdu et al 1998(Abdu et al , 2003. The aspect (2), which is relatively less well-known so far is briefly discussed further below.…”