Browsing by Subject "Solar wind"

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Analysis of geomagnetic storms and substorms with the WINDMI model
(2006) Spencer, Edmund Augustus; Horton, Wendell; Hallock, G. A.
A family of nonlinear dynamical models called WINDMI is developed to analyze the behaviour of geomagnetic storms and substorms. This set of plasma physics based descriptions of the interaction of the solar wind and the earth’s magnetosphere is aimed at understanding the key processes that influence geomagnetic activity, and consequently develop a reliable space weather prediction system. The global WINDMI-RC model is a system of eight nonlinear ordinary differential equations that describe the solar wind-magnetosphere-ionosphere coupling and the interaction of basic energy components in the nightside magnetosphere. The WINDMI-SR model is a spatially resolved version of the global WINDMI-RC model that decomposes the nightside magnetosphere into sections, with a system of differential equations attached to each section. The lowest order mode of the WINDMI-SR model corresponds to the behaviour of the WINDMI-RC model. The higher order modes describe electromagnetic pulses propagating along the geotail. The global model is computationally optimized using a genetic algorithm (GA) and used to analyze two large geomagnetic storm events. The GA optimization results show that the model is able to predict the storm time Dst index reliably and captures the timing and periodicity of the sawtooth signatures in the auroral Electrojet AL index reasonably well for both storm events. The spatially resolved model is used to study the propagation of electromagnetic pulses along the geotail and the response along the length of the nightside magnetosphere with changing solar wind activity.
Plasma turbulence in the equatorial electrojet observations, theories, models, and simulations
(2015-12) Hassan, Ehab Mohamed Ali Hussein; Morrison, Philip J.; Horton, Wendell; Fitzpatrick, Richard; Bengtson, Roger; Humphreys, Todd
The plasma turbulence in the equatorial electrojet due to the presence of two different plasma instability mechanisms has been observed and studied for more than seven decades. The sharp density-gradient and large conductivity give rise to gradient-drift and Farley-Buneman instabilities, respectively, of different scale-lengths. A new 2-D fluid model is derived by modifying the standard two-stream fluid model with the ion viscosity tensor and electron polarization drift, and is capable of describing both instabilities in a unified system. Numerical solution of the model in the linear regime demonstrates the capacity of the model to capture the salient characteristics of the two instabilities. Nonlinear simulations of the unified model of the equatorial electrojet instabilities reproduce many of the features that are found in radar observations and sounding rocket measurements under multiple solar and ionospheric conditions. The linear and nonlinear numerical results of the 2-D unified fluid model are found to be comparable to the fully kinetic and hybrid models which have high computational cost and small coverage area of the ionosphere. This gives the unified fluid model a superiority over those models. The distribution of the energy content in the system is studied and the rate of change of the energy content in the evolving fields obeys the law of energy conservation. The dynamics of the ions were found to have the largest portion of energy in their kinetic and internal thermal energy components. The redistribution of energy is characterized by a forward cascade generating small-scale structures. The bracket of the system dynamics in the nonlinear partial differential equation was proved to be a non-canonical Hamiltonian system as that bracket satisfies the Jacobi identity. The penetration of the variations in the interplanetary magnetic and electric fields in the solar winds to the dip equator is observed as a perfect match with the variations in the horizontal components of the geomagnetic and electric fields at the magnetic equator. Three years of concurrent measurements of the solar wind parameters at Advanced Composition Explorer (ACE) and Interplanetary Monitoring Platform (IMP) space missions used to establish a Kernel Density Estimation (KDE) functions for these parameters at the IMP-8 location. The KDE functions can be used to generate an ensemble of the solar wind parameters which has many applications in space weather forecasting and data-driven simulations. Also, categorized KDE functions ware established for the solar wind categories that have different origin from the Sun.
Stability analyses of auroral substorm onset and solar wind
(2019-12) Derr, Jason Robert; Breizman, Boris N.; Horton, C.W. (Claude Wendell), 1942-; Hazeltine, Richard D.; Shapiro, Paul R.
Pertaining to the stability analysis of auroral substorm onset, a geometric wedge model of the near-earth nightside plasma sheet is used to derive a wave equation for low frequency shear flow-interchange waves which transmit E x B sheared zonal flows along magnetic flux tubes towards the ionosphere. Discrepancies with the wave equation result used in Kalmoni et al. (2015) for shear flow-ballooning instability are discussed. The wedge wave equation is used to compute rough expressions for dispersion relations and local growth rates in the midnight region of the nightside magnetotail where the instability develops, forming the auroral beads characteristic of geomagnetic substorm onset. Stability analysis for the shear flow-interchange modes demonstrates that nonlinear analysis is necessary for quantitatively accurate results and determines the spatial scale on which the instability varies. The Rice Convection Model-Equilibrium (RCM-E) is used to provide background fields for a global magnetospheric wedge wave equation, from which the growth rates and dispersion relations can be calculated for the shear flow-interchange instability. Mapping of this growing traveling wave back to the magnetosphere yields the auroral bead projections of the instability. The cause of magnetic substorm onset by comparison with the beads, and its location in the magnetotail, is determinable once more suitable simulation run is performed. The linear stage of the marginally stable instability is discussed in detail. Subsequent nonlinear relaxation properties of the auroral arc, including saturation value of instability amplitudes, are determined. Shear flow-interchange instability appears to cause magnetic substorm onset, insofar as auroral beads are its signature. Pertaining to the stability analysis of jet microstreams, fast solar wind streams are known to be dominated by Alfvénic turbulence, i.e. large amplitude magnetic field and quasi-incompressible velocity fluctuations with a correlation corresponding to waves propagating away from the Sun. In addition, the Ulysses spacecraft has shown that microstreams, persistent long period (1/2-2 days) fluctuations in the radial velocity field are ubiquitous in the fast wind. This contribution explores the possible causal relation between microstreams and Alfvénic turbulence. We carry out a parametric study setup for the linear and nonlinear stability of the microstream jets to Kelvin-Helmholtz (KH) instabilities: starting from the profiles of density, radial speed and magnetic field observed in the solar wind, we aim to investigate both at what distance from the Sun KH instabilities may be triggered and the nature of the ensuing nonlinear dynamics.