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Dynamical Effects Of Ionospheric Conductivity On The Formation Of Polar Cap Arcs, L. Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
Dynamical Effects Of Ionospheric Conductivity On The Formation Of Polar Cap Arcs, L. Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
All Physics Faculty Publications
By using a magnetosphere-ionosphere (M-I) coupling model of polar cap arcs [Zhu et al., 1993], a systematic model study of the effects of ionospheric background conductivity on the formation of polar cap arcs has been conducted. The variations of the ionospheric background conductivity in the model study cover typical ionospheric conditions, including solar minimum, solar maximum, winter, and summer. The simulation results clearly indicate that the ionospheric background conductivity can dynamically affect the mesoscale features of polar cap arcs through a nonlinear M-I coupling process associated with the arcs.
Multiple Polar Cap Arcs: Akebono (Exos D) Observations, T. Obara, T. Mukai, H. Hayakawa, K. Tsurda, A. Matsuoka, A. Nishida, H. Fukunishi, L. Zhu, Jan Josef Sojka, D. J. Crain
Multiple Polar Cap Arcs: Akebono (Exos D) Observations, T. Obara, T. Mukai, H. Hayakawa, K. Tsurda, A. Matsuoka, A. Nishida, H. Fukunishi, L. Zhu, Jan Josef Sojka, D. J. Crain
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Akebono (Exos D) observations demonstrate that polar cap arcs sometimes have a fine structure, that is, multiple (double or triple) arcs with spacing of a few tens of kilometers. The multiple polar cap arcs are dominantly observed in the nightside polar cap region, suggesting that low background conductance favors the appearance of the structured arcs. A relationship between the spacing and the average energy of the precipitating electrons is investigated. Results show that a higher energy leads to a wider spacing. Akebono observations also show the existence of a downward current region embedded between upward current regions (arcs). Comparison of …
Model-Observation Comparison Study Of Multiple Polar Cap Arcs, Lie Zhu, Cesar E. Valladares, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
Model-Observation Comparison Study Of Multiple Polar Cap Arcs, Lie Zhu, Cesar E. Valladares, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
All Physics Faculty Publications
A quantitative model-observation comparison of multiple polar cap arcs has been conducted by using a time-dependent theoretical model of polar cap arcs. In particular, the electrodynamical features of multiple polar cap arcs with various spacings are simulated and the results are compared with the images obtained from the All-Sky Intensified Photometer at Qaanaaq. The results show that the observed and simulated arcs are quite similar, both spatially and temporally. The results support the theory proposed by Zhu et al. [1993a, 1994b] that the structure of polar cap arcs is mainly determined by the magnetosphere-ionosphere (M-I) coupling processes and that …
Modelling Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu
Modelling Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu
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We present results of a new model of the time-dependent ionospheric response to a generalized steady state Sun-aligned (SA) arc structure. The thermal and plasma structure of a “prototype” arc is compared to the general features of observed SA arcs. We find that the general features of electron density, Ne , electron temperature, Te , and ion temperature, Ti , are determined by the distribution of the particle precipitation and E × B convection associated with the SA arc. The model results are extended to predict the possible variation of Ne, Te , and …
Model Study Of Multiple Polar Cap Arcs: Occurrence And Spacing, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
Model Study Of Multiple Polar Cap Arcs: Occurrence And Spacing, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
All Physics Faculty Publications
A new scenario for the formation of multiple polar cap arcs is proposed based on the results from a time‐dependent electrodynamic model of polar cap arcs developed by Zhu et al. [1993]. The results suggest that the appearance of multiple polar cap arcs may not be due to multiple structures in the magnetospheric source region, but instead, may primarily be determined by the coupled magnetosphere‐ionosphere system in which the ionosphere plays an active role. It was found that with the same magnetospheric driver, a strong ionospheric background convection and an ionospheric background Hall conductance in the range of from 0.5 …
Theoretical Study Of Polar Cap Arcs: Time-Dependent Model And Its Applications, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
Theoretical Study Of Polar Cap Arcs: Time-Dependent Model And Its Applications, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
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A time-dependent theoretical model of polar cap arcs developed during the Coupling, Energetics, and Dynamics of Atmospheric Regions/High-Latitude Plasma Structures (CEDAR/HLPS) campaigns in the past two years is briefly described. In the model the electrodynamics of the polar cap arcs are treated self-consistently in the frame of the coupled magnetosphere-ionosphere system. The preliminary simulation results of the temporal evolution and spatial structure of the polar cap arcs for both winter and summer conditions are presented. The model can be used to conduct both the model-observation study of specific features of the polar cap arcs and the quantitative theoretical study of …
Parameterized Study Of The Ionospheric Modification Associated With Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu
Parameterized Study Of The Ionospheric Modification Associated With Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu
All Physics Faculty Publications
Sun-aligned (SA) arcs are a prevalent feature of the polar cap ionosphere during northward interplanetary magnetic field conditions. These arcs are, like the auroral arc, a complex electrodynamic system coupling the ionosphere and magnetosphere. The electron precipitation and convection electric field associated with this system modify the polar cap ionospheric plasma distribution. In the past decade, a wealth of observational information has indicated the complexity of these ionospheric modifications, but only a limited number of model studies have been carried out to elucidate the changes associated with SA arcs. In this investigation, an extensive parametric study has been conducted to …
A Time-Dependent Model Of Polar Cap Arcs, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
A Time-Dependent Model Of Polar Cap Arcs, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain
All Physics Faculty Publications
A two-dimensional time-dependent model of polar cap arcs has been developed. The electrodynamics of the polar cap arcs are treated self-consistently in the frame of the coupled magnetosphere-ionosphere system. The focus of this paper is to introduce the physics and mathematical formulation of the model and describe the features of the spatial structure and temporal evolution of the polar cap arcs. The modeling results indicate that the time constant for the formation of the polar cap arcs is around 10 min. It is found that an initial single-arc precipitation pattern associated with a polar cap arc tends to split into …