A Numerical modeling study of CII instability seeded by the pre-reversal vertical drift

The collisional interchange instability (CII) is known to lead to the equatorial plasma bubble (EPB) development when the ionosphere is raised to higher altitudes by the pre-reversal electric field or vertical drift (PRVD). The PRVD presents considerable longitudinal variation (with scale size ~ 15°) across the sunset terminator and this variation may act as a seeding perturbation as proposed by Woodman (1994) and Huang and Kelley (1996b). In the present work, we examine the efficiency of this longitudinal variation of the PRVD to act as a seeding for the CII and to give rise to EPB in the absence of any other kind of initial perturbation. To do so, we carried out the CII simulation at the equator in a plane perpendicular to the magnetic field. We consider a few simplified cases choosing a Gaussian-shaped longitudinal variation of PRVD with various possible minimum and peak values and finally consider a realistic case with a spatial-temporal configuration of PRVD obtained using SAMI2 model. Simulations with simplified cases show that the EPB develops only for minimum value greater than 20 m/s and amplitude (difference between the peak-to-minimum values) greater than 40 m/s. Simulation with a realistic case shows that the PRVD during high solar flux summer satisfies these threshold conditions and with the seeding scale ~ 15°, the EPB of longitudinal size ~ 2° is developed toward east of the PRVD peak.