A. R. Barakat

• Utah State University

We studied the effects of a geomagnetic storm on the behavior of the polar wind for different seasonal and solar activity conditions using a generalized polar wind model that extends up to 8 RE, with a fluid-like component at low altitudes and a macroscopic PIC component at high altitudes. The geomagnetic activity was represented by an idealized st...

At terrestrial high latitudes, the plasma flows along ``open'' field lines, gradually going from a collision-dominated region into a collisionless region. Over several decades, the (fluid-like) generalized transport equations, TE, and the particle-based Monte Carlo, MC, approaches evolved as two of the most powerful simulation techniques that addre...

At high latitudes the plasma escapes along geomagnetic field lines from the high pressure ionosphere into the low pressure magnetosphere. As the plasma flows upwards, it goes through transitions from collision-dominated to collisionless conditions, from subsonic to supersonic flows, and form O+-dominated to H+-dominated compositions. Meanwhile, the...

At terrestrial high latitudes, the plasma flows along "open" field lines from the high-pressure ionosphere into the low-pressure magnetosphere. At relatively high altitudes, the plasma is fully ionized and the dominant collision mechanism corresponds to the Coulomb interaction. As the plasma flows upward, it gradually goes from a collision-dominate...

Both the polar and solar winds were postulated to explain observations made before routine access to space was possible. Subsequently, significant limitations of the thermal plasma observations of the polar wind led to diverging approaches to modeling it. The hydrodynamic and kinetic approaches to modeling were able to explain the limited observati...

The dynamic behavior of the ``generalized'' polar wind is investigated using a three-dimensional (3-D) dynamic model. The model is composed of two components. The high-altitude component is based on a macroscopic particle-in-cell (mac-PIC) approach that extends from an altitude of 1200 km to several Earth radii. The lower boundary conditions of the...

The dynamic behavior of the "generalized" polar wind is investigated using a 3-D dynamic model that extends from an altitude of 90 km to several Earth radii. The relevant equations are solved along magnetic flux tubes that convect across the high latitude region. A large number (~ 1000) of plasma flux tubes are followed. The total number of simulat...

Because of its relevance to space plasma problems (such as the terrestrial polar wind), we investigated the diffusion of a minor ion species through a non-uniform background major ion species. A Fokker–Planck expression was used to represent the Coulomb collisions between the minor and the background ions. A change of variables was implemented in o...

The ability to forecast the geomagnetic activities is becoming more important as human activity in space becomes more prevalent. For example, early warning of geomagnetic storms could help mitigate their harmful effects on space electronics and on electrical power lines. Moreover, recently developed space weather algorithms that utilize physics-bas...

The overall goal of our NASA theory research is to trace the flow of mass, momentum, and energy through the magnetosphere-ionosphere-atmosphere system taking into account the coupling, time delays, and feedback mechanisms that are characteristic of the system. Our approach is to model the magnetosphere-ionosphere-atmosphere (M-I-A) system in a self...

The dynamic behavior of the "generalized" polar wind is investigated using a 3-D dynamic model. In this study, we simulate the behavior of a large number (~100 to 1000) of plasma-filled geomagnetic tubes. The model is composed of two components. The high-altitude component is based on a macroscopic particle-in-cell (mac-PIC) approach that extends f...

The auroral field lines represent an important channel through which the ionosphere and the magnetosphere exchange mass, momentum, and energy. When the cold, dense ionospheric plasma interacts with sufficiently warm magnetospheric plasma along the field lines (with upward currents), double layers form with large parallel potential drops. The potent...

The effects of low-altitude energization (LAE) of ions in the auroral region are investigated using a 3-D dynamic model. In this study, we simulate the behavior of a large number (~100 to 1000) of plasma-filled geomagnetic tubes. The model is composed of two components. The high-altitude component is based on a macroscopic particle-in-cell (mac-PIC...

We have used Monte Carlo simulations of O+ velocity distributions in the high latitude F-region to improve the calculation of incoherent radar spectra in auroral ionosphere. The Monte Carlo simulation includes ion-neutral O+ -- O resonant charge exchange and polarization interactions as well as Coulomb self-collisions O+ -- O+. At a few hundreds ki...

The auroral field lines represent an important channel through which the ionosphere and the magnetosphere exchange mass, momentum, and energy. When the cold, dense ionospheric plasma interacts with sufficiently warm magnetospheric plasma along the field lines (with upward currents), double layers form with large parallel potential drops. The potent...

The dynamic behavior of the high-latitude plasma during a representative geomagnetic storm is investigated using a 3-D macroscopic particle-in-cell (mac-PIC) model. In this study, we simulate the behavior of a large number ( ˜100 to 1000) of plasma-filled geomagnetic flux tubes. Each flux tube extends from 1200 km to several Earth radii, includes ˜...

The effects of low-altitude energization (LAE) of ions on the dynamic behavior of the high-latitude plasma was investigated using a macroscopic particle-in-cell (mac-PIC) model. The model simulates the behavior of a plasma-filled flux tube as it drifts across the different high-latitude regions (cusp, polar cap, auroral, and subauroral regions). In...

The dynamic behavior of the high-latitude plasma during a representative geomagnetic storm was investigated using a macroscopic particle-in-cell (mac-PIC) model. Special attention was given to the ion outflow dependence on the season and solar activity. The model simulates the behavior of a plasma-filled flux tube as it drifts across the different...

A Monte Carlo simulation is used to study the effects of Kappa H+distributions in the polar wind. We consider the gravity, the polarization electric field, the divergence of geomagnetic field lines and Coulomb collisions of H+ in a background of O+ ions. The aim is to study the consequences of a velocity distribution function with an enhanced high...

The effects of wave–particle interactions (WPI) on the plasma outflows at high latitudes was the subject of several studies. Previous attempts to address this problem, for the most part, modeled the response of the plasma on a “stationary” field line to certain pre-specified boundary conditions. However, the horizontal plasma drift across the diffe...

The authors studied the extent to which Maxwellian and bi-Maxwellian series expansions can describe plasma flows characterised by non-Maxwellian velocity distributions. The problem they considered was the steady-state flow of a weakly ionised plasma subjected to homogeneous electric and magnetic fields, and both polarisation and hard-sphere collisi...

In the high-latitude F-region, the plasma horizontal drift can be comparable to, or greater than the neutral oxygen (O) thermal speed. As a result of the interplay between the ionospheric E×B drift and the O-O + collisions, the O + velocity distribution function, f o + (v), deviates significantly from Maxwellian. While the E×B drift velocity increa...

Theoretical descriptions of the terrestrial polar wind have taken a variety of forms. Fluid equations have long been used to provide a description of the plasma bulk flow parameters in the polar wind. More recently, particle-in-cell (PIC) models have been applied to the polar wind, yielding a description of far-from-Maxwellian features of the flow....

A time-dependent macroscopic particle-in-cell (mac-PIC) model was used to study the temporal evolution of the polar wind under the influence of a hot electron population. First, the steady state results of the mac-PIC model were found for a wide range of hot/cold electron temperature ratios and compared with the results of the well-established time...

The outflow of the polar wind along diverging geomagnetic field lines has been the subject of many modeling studies for the past 25 years. As the plasma drifts up and out of the topside ionosphere, it undergoes several transitions; for instance, its velocity changes from subsonic to supersonic and its velocity distribution changes from Maxwellian t...

The energization of charged particles, due to interaction with the ambient electromagnetic turbulence, has a significant influence on the plasma transport in space. The effect of wave-particle interactions on the outflow characteristics of polar wind plasma was investigated. The theoretical model included gravitational acceleration (g), polarizatio...

The flow of plasma along open field lines at high latitudes is highly variable and depends both on conditions in the underlying ionosphere and thermosphere and on the transport of particles and energy from the magnetosphere. Past attempts to model this time variability have, for the most part, examined the response of the plasma on a stationary fie...

The ionospheric convection electric fields that occur at high latitudes cause plasma to drift across the cusp region and the polar cap. Since the magnetic field at high latitudes is close to vertical, pointing downward (upward) in the northern (southern) hemisphere, the convecting plasma experiences a centrifugal acceleration as it crosses the pola...

The occurrence of shock waves in the terrestrial polar wind was predicted many years ago by a time-dependent three-dimensional model based on hydrodynamic equations. These shocks were seen to occur for counterstreaming ion populations and for cases when a convecting flux tube entered a region of sharply increasing electron temperature, such as the...

The polar wind is an ambipolar plasma outflow from the terrestrial ionosphere at high latitudes. As the ions drift upward along geomagnetic flux tubes, they move from collision-dominated (ion barosphere) to collisionless (ion exosphere) regions. A transition layer is embedded between these two regions where the ion characteristics change rapidly. A...

A Monte Carlo simulation was developed in order to study the effects of wave-particle interactions (WPI) on the plasma outflow in the polar wind. The simulation also considered the other mechanisms included in the ‘classical’ polar wind studies such as gravity, the polarization electrostatic field, and the divergence of geomagnetic field lines. Alt...

Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E×B drift and ion-neutral collisions. The majority of previous literature, in which the effect of ion self-collisions was neglec...

The escape of the polar wind plasma is an important element in the ionosphere-magnetosphere coupling. Both theory and observations indicate that the wave-particle interactions (WPI) play a significant role in the dynamics of ion outflow along open geomagnetic field lines. A Monte Carlo simulation was developed in order to include the effect of the...

A Monte Carlo simulation was used to study the steady state flow of the polar wind protons through a background of O+ ions. The simulation region included a collision-dominated region (barosphere), a collisionless region (exosphere), and the transition layer embedded between these two regions. Special attention was given to using an accurate collis...

In a wide variety of space physics problems (e.g. polar wind, solar wind), outflowing species pass through two different regions 1.(1) a collision-dominated region, in which hydrodynamic transport equations can be applied2.(2) a collisionless region, where kinetic models are applicable. These two regions are separated by a transition layer where mo...

A method presented by Wu et al. (1992) for computing the H(+) vertical velocity from the main ionospheric parameters measured by the EISCAT VHF radar is tested in a fully controlled sequence which consists of generating an ideal ionospheric model by solving the coupled continuity and momentum equations for a two-ion plasma (O(+) and H(+)). Syntheti...

EISCAT VHF radar was used to investigate the vertical flows of H(+) and O(+) ions in the topside high-latitude ionosphere. The radar transmitted a single long pulse to probe the ionosphere from 300 to 1200 km altitude. A calculation scheme is developed to deduce the H(+) drift velocity from the coupled momentum equations of H(+), O(+), and the elec...

The auroral ion velocity distributions were performed using a Monte Carlo computation scheme that was improved by using a very large electric field and a more sophisticated ion-neutral collision model than in the past, which included a detailed description of the polarization interaction between ions and neutrals, while allowing for the full veloci...

The objective of the research is to use the low-frequency wave spectrum measured by the Plasma Wave Instrument on the DE-1 spacecraft to include the wave-particle interaction (WPI) in the different polar wind models that are available at Utah State University. A Monte Carlo technique was used to simulate the ion diffusion in the velocity space due...

Semi-kinetic and kinetic models are powerful tools for attacking a range of flow conditions involving collisionless plasmas and they have been used for more than two decades to model the polar wind. With this approach, a Maxwellian ion velocity distribution is generally adopted at the lower boundary of the collisionless regime and the resulting dis...

The problem of the escape of a minor species through a major species for different mass ratios is considered. The gravitational force is simulated by a barrier that reflects particles that reach the upper boundary with an up-going velocity greater than an escape velocity. Different collision models (Maxwell molecule and hard sphere) and different v...

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-te...

The Quasi Neutrality (QN) equation is usually solved by an iterative procedure to obtain the electrostatic potential distribution in plasmas. A new numerical method to obtain the same result more efficiently, based on the numerical integration of the differential form of the QN equation, is presented. In the case when the QN approximation fails to...

Auroral ion distributions under the influence of large electric fields were obtained using the Monte Carlo approach and were compared to limited order polynomial expansion, for both the three-dimensional velocity space and one-dimensioanal ion distribution. It is shown that Monte Carlo simulations can provide velocity moments to high orders with a...

Monte Carlo simulations of ion velocity distributions in the high-latitude F region have been performed in order to improve the calculation of incoherent radar spectra in the auroral ionosphere. The results confirm that when the ion temperature becomes large due to frictional heating in the presence of collisions with the neutral background constit...

In the classical picture of the polar wind, the H/sup +/ flow becomes supersonic and collisionless, and the H/sup +/ velocity distribution becomes anisotropic and asymmetric at altitudes above about 3000 km. Previously, the stability of the classical polar wind was studied and found to be stable for a wide range of electron temperatures. However, t...

The hydrodynamic transport equations are solved for H(+) and O(+) with allowance made for the important dynamic, collisional, and chemical effects that operate in the F region ionosphere below regions of ion acceleration. It is found that the total ion flux demand imposed on the ionosphere by the higher altitude acceleration region is an important...

In this paper, the hydrodynamic transport equations for H(+) and O(+) are solved, including the important dynamic, collisional, and chemical effects that operate in the F region ionosphere below regions of ion acceleration. It is found that the most important parameter controlling the amount of O(+) in plasma outflows is the total ion flux demand i...

The classical polar wind is an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. At altitudes above about 3000 km, the H(+) flow becomes supersonic and collisionless, and the H(+) velocity distribution becomes non-Maxwellian. The non-Maxwellian features include a temperature anisotropy, with the parallel H(+) te...

A semikinetic model was used to study the steady state, collisionless, polar wind outflow from the Jovian polar caps. H(+)-escape fluxes and energies were calculated for a range of conditions, including several values of the ambient electron temperature, different hot electron populations, and both with and without the effects of the centrifugal fo...

A semikinetic model is used to describe the steady state collisionless flow of H(+), O(+), and electrons along diverging geomagnetic field lines in the high-latitude topside ionosphere. The effect that hot electron populations have on the polar wind is emphasized. Several such populations are considered, including the polar rain, polar showers, and...

O(+) density and flux profiles are calculated for a steady state polar wind flow of O(+) ions and electrons along geomagnetic field lines in the polar cap. Profiles are computed both with and without allowance for accidentally resonant charge exchange (ARCE) between O(+) and H. It is found that ARCE acts to reduce the limiting O(+) escape flux by l...

Contents: Introduction. Currents and conductivities. Thermospheric winds and plasma transport. Plasma convection. Polar wind. Conclusions.

A semikinetic model was used to describe the steady state collisionless flow of the polar wind along diverging geomagnetic field lines at high latitues. Emphasis was given to studying the behavior of O(+) ions for a wide range of boundary conditions at the baropause (4500 km). The main result obtained was that for high electron temperatures Te = ab...

A semikinetic model was used to describe the steady state collisionless flow of the polar wind along diverging geomagnetic field lines at high latitudes. Emphasis was given to studing the behavior of O** plus ions for a wide range of boundary conditions at the baropause (4500 km). The main result obtained was that for high electron temperatures (T/...

fields greater than about 30 mV m-1 and that these nonMaxwellian distributions have an important effect on the high-latitude ionosphere. The calculated velocity distributions were obtained from closed form solutions to Boltzmann's equation for a simple relaxation collision model and from series solutions to Boltzmann's equation for more rigorous co...

A wide variety of plasma flow conditions is found in aeronomy and space plasma physics. Transport equations based on an isotropic Maxwellian vilecity distribution function can be used to describe plasma flows which contain 'small' temperature anisotropies. However, for plasma flows characterized by large temperature anisotropies, transport equation...

An attempt is made to present a unified approach to the study of transport phenomena in multicomponent anisotropic space plasmas. In particular, a system of generalized transport equations is presented that can be applied to widely different plasma flow conditions. The generalized transport equations can describe subsonic and supersonic flows, coll...

First, I attempt to present a unified approach to the study of transport phenomena in multicoponent anisotropic space plasmas. In the limit of small temperature anisotropies this system of generalized transport equations reduces to Grad's 13-moment system of transport equations. In the collisionless limit, the generalized transport equations accoun...

For application to aeronomy and space physics problems involving strongly magnetized plasma flows, we derived momentum and energy exchange collision terms for interpenetrating bi-Maxwellian gases. Collision terms were derived for Coulomb, Maxwell molecule, and constant collision cross-section interaction potentials. The collision terms are valid fo...