Dynamics of three dimensional ionospheric plasma clouds

Abstract

The first self-consistent, three-dimensional analysis of plasma cloud evolution in the ionosphere is presented. It is demonstrated that there is a preferred perpendicular scale size associated with 3D plasma clouds given by r c~-c(T e + Ti)/eB z V n r C y where r c is the cloud radius, T a is the temperature of the a species, B z is the ambient magnetic field, V" is the neutral wind speed, and T c < 1/V2. PACS numbers: 94.20.Vv For more than two decades, the evolution of artificial plasma clouds in the near-earth space environment has been of interest to space physicists. Research in this area continues to be exciting and vigorous, especially in light of the recent Active Magnetospheric Particle Tracer Explorer mission 1 and the upcoming Combined Release and Radiation Effects Satellite mission. 2 Originally it was thought that artificial clouds would simply be a diagnostic of ambient plasma conditions; it was soon discovered that they do not simply convect because of ambient fields or winds, but, for example, can become unstable and rapidly structure. The mechanism which causes the structuring of ionospheric clouds is the ExB gradient drift instability. 3 This instability has been extensively studied both theoretically 4-9 and computationally. 10 " 14 Although a considerable amount of research has been carried out on this instability, there are several deficiencies with regard to its application to ionospheric plasma clouds. First, the bulk of theoretical analysis has focused on the short-wavelength limit (i.e., kL » 1 where k is the wave number and L is the density-gradient scale length associated with the cloud boundary). However, observationally the gross structuring of barium clouds is clearly in the long-wavelength regime 11 (i.e., kL<C\). And second, until quite recently, the finite parallel extent of the cloud along the ambient magnetic field has been neglected, as well as any parallel dynamical effects. Progress is being made in this area 6 " 9 ; however, a selfconsistent, long-wavelength, three-dimensional analysis of plasma cloud evolution has been lacking.In this Letter we present the first fully three-dimensional study of plasma cloud dynamics in the longwavelength limit. We first develop an equilibrium based upon a waterbag model. We then perform a perturbation analysis on the equilibrium. The important result of this analysis is the derivation of a stability criterion for the large-scale structuring of ionospheric plasma clouds; i.e., clouds are stable for r < r c , where r is the radius of the cloud and a r c is the critical radius and function of the local plasma parameters.The general three-dimensional equations for a warm plasma cloud in a uniform magnetic field B=Z?e z and a uniform background neutral wind V" =V n e x (see Fig. 1) are given by 8 dn c ^ . v -T7 i 9 1 ----V0xz-Vrt + -at B dz erj t d(j> _ T e fin dz ne bz = 0, -V x -/iV ± 0 + Z)j. / Vi/! + -zxV,,-V/i + -^-1 B n, £1/ dz er\ e d<f> _ T e dn dz ne dz =0,(2) where /;<, = =m e v <? /7ze 2 is the parallel resistivity, v e -v e i + v ...

Implications of the equipotential field line approximation for equatorial spread F analysis

“…The solution of the polarization potential in the drifting frame of reference is given by The solution of the ambipolar potential gives where P 2 is the second‐order Legendre polynomial and the coefficients are given by A similar set of solutions was derived by Drake and Huba [1987] for ionospheric plasma clouds and applied to plasma cloud stability. Here, we analyze the potential around a plasma irregularity elongated along the magnetic field direction.…”

“…The remaining dimensionless variables are r c ∇ ⊥ → ∇ ⊥ , L z ∂/∂ z → ∂/∂ z , and n / n b → n , where n b represents the background density. With this new set of dimensionless variables, can be rewritten as [ Drake and Huba , 1987] We examine the potential solution of a waterbag plasma irregularity which is a sphere of unity radius in the dimensionless units, i.e., n ( r ) = 1 + MH (1 − r ), where H is the Heaviside step function and the constant M represents the ratio n ( r )/ n b inside the sphere.…”

“…, L z ∂/∂z → ∂/∂z, and n/n b → n, where n b represents the background density. With this new set of dimensionless variables, equation (1) can be rewritten as [Drake and Huba, 1987] r Á nr ? y ½ þ ∂n ∂y À G ∂ 2 n ∂z 2 ¼ 0:…”

“…A similar set of solutions was derived by Drake and Huba [1987] for ionospheric plasma clouds and applied to plasma cloud stability. Here, we analyze the potential around a plasma irregularity elongated along the magnetic field direction.…”

Three‐dimensional numerical simulations of equatorial spread F: Results and observations in the Pacific sector

“…This also accommodates the possible effects of drift waves and related instabilities that may play secondary roles in ESF [ Huba and Ossakow , 1979; LaBelle et al , 1986; Hysell et al , 2002]. For instance, the full 3‐D treatment of warm plasma shows that perturbations on the surface of ionospheric plasma clouds propagate and twist into a barber pole configuration [ Drake and Huba , 1987; Drake et al , 1988; Zalesak et al , 1990]. As a consequence, the phase of the corrugations varies strongly along B , the plasma cloud loses its flute‐like characteristic (i.e., k · B ≠ 0), and the resulting finite k ∥ has a dissipative influence on the instability.…”