Contributions of the low-latitude boundary layer to the finite width magnetotail convection model

Convection of plasma within the terrestrial nightside plasma sheet contributes to the structure and, possibly, the dynamical evolution of the magnetotail. In order to characterize the steady state convection process, we have extended the finite tail width model of magnetotail plasma sheet convection. The model assumes uniform plasma sources and accounts for both the duskward gradient/curvature drift and the earthward E × B drift of ions in a two-dimensional magnetic geometry. During periods of slow convection (i.e., when the cross-tail electric potential energy is small relative to the source plasma\u27s thermal energy), there is a significant net duskward displacement of the pressure-bearing ions. The electrons are assumed to be cold, and we argue that this assumption is appropriate for plasma sheet parameters. We generalize solutions previously obtained along the midnight meridian to describe the variation of the plasma pressure and number density across the width of the tail. For a uniform deep-tail source of particles, the plasma pressure and number density are unrealistically low along the near-tail dawn flank. We therefore add a secondary source of plasma originating from the dawnside low-latitude boundary layer (LLBL). The dual plasma sources contribute to the plasma pressure and number density throughout the magnetic equatorial plane. Model results indicate that the LLBL may be a significant source of near-tail central plasma sheet plasma during periods of weak convection. The model predicts a cross-tail pressure gradient from dawn to dusk in the near magnetotail. We suggest that the plasma pressure gradient is balanced in part by an oppositely directed magnetic pressure gradient for which there is observational evidence. Finally, the pressure to number density ratio is used to define the plasma “temperature.” We stress that such quantities as temperature and polytropic index must be interpreted with care as they lose their nominal physical significance in regions where the two-source plasmas intermix appreciably and the distributions become non-Maxwellian

On the possibility of quasi-static convection in the quiet magnetotail

Abstract The magnetotail is known to serve as a reservoir of energy transferred into the terrestrial magnetosphere from the solar wind. In principle, the stored energy can be dissipated impulsively, as in a substorm, or steadily through the process of steady adiabatic plasma convection. However, some theoretical arguments have suggested that quasi-static adiabatic convection cannot occur throughout the magnetotail because of the structure of the magnetic field. Here we reexamine the question. We show that in a magnetotail of finite width, downtail pressure gradients depend strongly on the ratio of the potential across half the tail to the ion temperature in the far tail (60 RE). For pertinent quiet time ratios (∼3), a Tsyganenko quiet-time magnetic field model is consistent with steady convection

Correlations and Renormalization of the Electron-Phonon Coupling in the Honeycomb Hubbard Ladder and Superconductivity in Polyacene

We have performed extensive density matrix renormalization group (DMRG) studies of the Hubbard model on a honeycomb ladder. The band structure (with Hubbard U=0) exhibits an unusual quadratic band touching at half filling, which is associated with a quantum Lifshitz transition from a band insulator to a metal. %SAK as a function of a third-neighbor hopping parameter. For one electron per site, non-zero $U$ drives the system into an insulating state in which there is no pair-binding between added electrons; this implies that superconductivity driven directly by the repulsive electron-electron interactions is unlikely in the regime of small doping, $x\ll 1$. However, the divergent density of states as $x\to 0$, the large values of the phonon frequencies, and an unusual correlation induced enhancement of the electron-phonon coupling imply that lightly doped polyacenes, which approximately realize this structure, are good candidates for high temperature electron-phonon driven superconductivity

Disentangling density and temperature effects in the viscous slowing down of glassforming liquids

We present a consistent picture of the respective role of density and temperature in the viscous slowing down of glassforming liquids and polymers. Specifically, based in part upon a new analysis of simulation and experimental data on liquid ortho-terphenyl, we conclude that a zeroth-order description of the approach to the glass transition should be formulated in terms of a temperature-driven super-Arrhenius activated behavior rather than a density-driven congestion or jamming phenomenon. The density plays a role at a quantitative level, but its effect on the viscosity and the structural relaxation time can be simply described via a single parameter, an effective interaction energy that is characteristic of the high temperature liquid regime; as a result, density does not affect the ``fragility'' of the glassforming system.Comment: RevTeX4, 8 pages, 8 eps figure

Static magnetic field models consistent with nearly isotropic plasma pressure

Using the empirical magnetospheric magnetic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By “inverting” the magnetic field, we determine what distributions of an anisotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohydrostatic equilibrium condition, J × B = ∇ · P. The TU model, parameterized for different levels of geomagnetic activity by the Kp index, provided the magnetic field values from which J × B was numerically evaluated. A best fit solution was found that minimized the average difference between J × B and ∇ · P along an entire flux tube. Unlike previous semi-empirical models, the TU models contain magnetic stresses that can be balanced by a nearly isotropic plasma pressure with a reasonable radial gradient at the equator

Avoided Critical Behavior in a Uniformly Frustrated System

We study the effects of weak long-ranged antiferromagnetic interactions of strength $Q$ on a spin model with predominant short-ranged ferromagnetic interactions. In three dimensions, this model exhibits an avoided critical point in the sense that the critical temperature $T_c(Q=0)$ is strictly greater than $\lim_{Q\to 0} T_c(Q)$. The behavior of this system at temperatures less than $T_c(Q=0)$ is controlled by the proximity to the avoided critical point. We also quantize the model in a novel way to study the interplay between charge-density wave and superconducting order.Comment: 32 page Latex file, figures available from authors by reques

Relative timing of substorm onset phenomena

[1] In this paper we examine the temporal ordering of midtail flow bursts, Pi2 pulsations, and auroral arc brightening at substorm onset. We present three substorm events for which the Geotail spacecraft was situated at local midnight, near the inner edge of the plasmasheet. We show that high-speed, convective Earthward directed plasma flows observed by Geotail occurred 1–3 min before auroral onset as observed by the Polar Visible Imaging System and Ultraviolet Imager auroral imagers on board the Polar spacecraft. We also show that the onsets of both nightside Pi2 pulsations and magnetic bay variations were simultaneous with auroral onset. We argue that these observations lend strong support to the flow burst-driven model of magnetotail dynamics. We also examine a high-latitude magnetic precursor to onset and show that it is likely due to the currents expected from the passage of a flow burst through the plasmasheet prior to substorm onset. Finally, we calculate an analytic expression for this current and show that it is unlikely to generate discrete auroral structures

On inward motion of the magnetopause preceding a substorm

Magnetopause inward motion preceding magnetic storms observed by means of OGO-E magnetomete

Magnetospheric plasma pressures in the midnight meridian: Observations from 2.5 to 35 RE

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) were statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12–35 RE) magnetotail plasma sheet. The observed plasma pressure, assumed isotropic, was mapped along model magnetic field flux tubes (obtained from the Tsyganenko and Usmanov [1982] model) to the magnetic equator, sorted according to magnetic activity, and binned according to the mapped equatorial location. In regions (L ≳ 12 RE) where the bulk of the plasma pressure was contributed by particles in the energy range of the FPE (70 eV to 40 keV for ions), the statistically determined peak plasma pressures vary with distance similarly to previously determined lobe magnetic pressures (i.e., in a time-averaged sense, pressure balance normal to the magnetotail magnetic equator in the midnight meridian is maintained between lobe magnetic and plasma sheet plasma pressures). Additional plasma pressure data obtained in the inner magnetosphere (2.5 \u3c L \u3c 7) by the Explorer 45, ATS 5, and AMPTE CCE spacecraft supplement the ISEE 2 data. Estimates of plasma pressures in the “transition” region (7–12 RE), where the magnetic field topology changes rapidly from a dipolar to a tail-like configuration, are compared with the observed pressure profiles. The quiet time “transition” region pressure estimates, obtained previously from inversions of empirical magnetic field models, bridge observations both interior to and exterior to the “transition” region in a reasonable manner. Quiet time observations and estimates are combined to provide profiles of the equatorial plasma pressure along the midnight meridian between 2.5 and 35 RE