Abstract
Abstract. In the auroral lower-E and upper-D region of the ionosphere, plasma clouds, such as sporadic-E layers and meteor plasma trails, occur daily. Large-scale electric fields, created by the magnetospheric dynamo, will polarize these highly conducting clouds, redistributing the electrostatic potential and generating anisotropic currents both within and around the cloud. Using a simplified model of the cloud and the background ionosphere, we develop the first self-consistent three-dimensional analytical theory of these phenomena. For dense clouds, this theory predicts highly amplified electric fields around the cloud, along with strong currents collected from the ionosphere and circulated through the cloud. This has implications for the generation of plasma instabilities, electron heating, and global MHD modeling of magnetosphere-ionosphere coupling via modifications of conductances induced by sporadic-E clouds.
Highlights
At lower-E/upper-D ionospheric altitudes, roughly between 80 and 120 km, high density meteor plasma trails and sporadic-E layers develop within a lower density background plasma
Neutral winds with a component perpendicular to the magnetic field produce an effective external electric field in the neutral frame of reference. Such external fields polarize the highly conducting cloud, redistribute the electrostatic potential within it and in the background ionosphere, and form a large-scale current system. This can be important for generation of plasma instabilities, electron heating, electrodynamic coupling between the ionospheric E and F regions, and, through modified ionospheric conductance, even for global ionospheremagnetosphere coupling
We have studied the 3-D electrodynamic interaction of an external electric field with a dense plasma cloud embedded in the lower-E/upper-D ionosphere
Summary
At lower-E/upper-D ionospheric altitudes, roughly between 80 and 120 km, high density meteor plasma trails and sporadic-E layers develop within a lower density background plasma. Shalimov et al (1998) and Shalimov and Haldoupis (2005) applied ideas similar to those from the seminal papers by Farley (1959, 1960) by including ionospheric current closure and using a more realistic 3-D slab model Their theory relied on approximate scaling arguments rather than on a rigorous solution of the underlying differential equations. Yokoyama et al (2004) performed 2-D and 3-D numerical simulations of cloud polarization, current closure, and E-F region coupling, including the recently predicted sporadicE instability (Cosgrove and Tsunoda, 2002b, 2004; Tsunoda et al, 2004; Tsunoda, 2006) These simulations give spatial distributions of the electric field but, being performed for particular cases only, provide no parameter dependencies as we will provide. Appendix A presents the mathematical details of coordinate transformations, while Appendix B discusses an extended (rod-like) cloud, such as, e.g., a meteor plasma trail and finds the plasma density restriction for the elongated-structure solution as presented in Dimant et al (2009)
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