Three-dimensional simulation of equatorial spread-F with meridional wind effects

Abstract

Abstract. The NRL SAMI3 three-dimensional simulation code is used to examine the effect of meridional winds on the growth and suppression of equatorial spread F (ESF). The simulation geometry conforms to a dipole field geometry with field-line apex heights from 200 to 1600 km at the equator, but extends over only 4 degrees in longitude. The full SAMI3 ionosphere equations are included, providing ion dynamics both along and across the field. The potential is solved in two dimensions in the equatorial plane under a field-line equipotential approximation. By selectively including terms in the potential equation, the reduced growth predicted by Maruyama (1988) and the stabilization predicted by Zalesak and Huba (1991) are separately realized. We find that ESF is stabilized by a sufficiently large constant meridional wind (60 m/s in our example).

Equinoctial asymmetry of a low-latitude ionosphere-thermosphere system and equatorial irregularities: evidence for meridional wind control

“…In the March case, the upward drift velocity exceeded 300 m/s, and the ESF bubbles rose to an altitude of approximately 1100 km by the end of the 4-h simulation period (19:15-23:15 UT). Consistent with past results (Huba et al, 2008;Krall et al, 2009), the peak plasma drift velocity (∼350 m/s) exceeded the peak bubble velocity (∼80 m/s) during the non-linear phase of the instability. The initial growth times (e-folding times) of 31 min and 79 min were obtained for the March and September cases, respectively.…”

“…The transequatorial wind that increases the field line integrated Pedersen conductivity was proposed as a suppression mechanism of the instability (Maruyama and Matuura, 1984;Maruyama, 1988;Saito and Maruyama, 2006). In addition to the Pedersen conductivity term, a meridional wind component perpendicular to the magnetic field line was shown to suppress the instability growth rate (Zalesak and Huba, 1991;Krall et al, 2009). The ambient ionosphere-thermosphere conditions during the period between the E-region sunset and the most probable onset time, as discussed below, would strongly control the onsets of plasma bubbles.…”

“…For simplicity, this version of SAMI3 uses a non-tilted dipole for the model geomagnetic field. The simulations include the effect of a constant meridional wind (all other winds are set to zero) both in terms of the effect of the redistributed plasma on the field-line integrated conductivities (Maruyama, 1988) and the effect of the wind component perpendicular to the magnetic field (Zalesak and Huba, 1991;Krall et al, 2009). Two cases were simulated.…”

“…As in study of Krall et al (2009), the growth times are determined from the peak upward drift velocity V p,max during the linear phase of the instability. Plots of log 10 (V p,max ) are shown in Fig.…”

“…A modified version of the NRL 3-D global ionosphere code SAMI3 (Huba et al, 2000(Huba et al, , 2005 was used for this purpose. This version of SAMI3 was recently applied to ESF studies (Huba et al, 2008;Krall et al, 2009) and models a "wedge" of the post-sunset ionosphere; it was limited to 4 • in longitude with a periodic boundary condition in order to obtain sufficient resolution for ESF modeling. Further, the perpendicular electric field E ⊥ =−∇ was determined self-consistently to calculate the E×B drifts.…”