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Articles 1 - 12 of 12
Full-Text Articles in Physical Sciences and Mathematics
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 …
Theoretical Study Of The Seasonal Behavior Of The Global Ionosphere At Solar Maximum, Jan Josef Sojka, Robert W. Schunk
Theoretical Study Of The Seasonal Behavior Of The Global Ionosphere At Solar Maximum, Jan Josef Sojka, Robert W. Schunk
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A time-dependent, three-dimensional, multi-ion numerical model of the global ionosphere was used to study the asymmetry in large-scale ionospheric features between the northern and southern hemispheres. The comparisons were done for June and December solstice conditions at solar maximum for quiet geomagnetic activity. Simple conditions and diurnally reproducible ionospheric features were established in order to elucidate the intrinsic hemispherical differences that are associated with the different displacements between the geomagnetic and geographic poles and the different atmospheric conditions. In comparing the ionospheric densities in the northern and southern hemispheres for a given season, we found the following: (1) The winter …
A Theoretical Study Of The Lifetime And Transport Of Large Ionospheric Density Structures, Robert W. Schunk, Jan Josef Sojka
A Theoretical Study Of The Lifetime And Transport Of Large Ionospheric Density Structures, Robert W. Schunk, Jan Josef Sojka
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Large-scale density structures are a common feature in the high-latitude ionosphere. They have been observed in the dayside cusp, polar cap, and nocturnal auroral region. Relative to background densities, the perturbations associated with large-scale structures vary from about 10% to a factor of 100. The lifetime and transport characteristics of “large” ionospheric structures (factor of 10 to 100) were studied with the aid of a three-dimensional time-dependent ionospheric model. Both density depletions and enhancements were considered. A density structure was created at a specific location in the high latitude F region and the subsequent evolution was followed for different seasonal …
Theoretical Study Of The Effect Of Ionospheric Return Currents On The Electron Temperature, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline
Theoretical Study Of The Effect Of Ionospheric Return Currents On The Electron Temperature, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline
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An electron heat flow can occur in a partially ionized plasma in response to either an electron temperature gradient (thermal conduction) or an electron current (thermoelectric heat flow). The former process has been extensively studied, while the latter process has received relatively little attention. Therefore a time-dependent three-dimensional model of the high-latitude ionosphere was used to study the effect of field-aligned ionospheric return currents on auroral electron temperatures for different seasonal and solar cycle conditions as well as for different upper boundary heat fluxes. The results of this study lead to the following conclusions: (1) The average, large-scale, return current …
Theoretical Study Of The High-Latitude Ionosphere’S Response To Multicell Convection Patterns, Jan Josef Sojka, Robert W. Schunk
Theoretical Study Of The High-Latitude Ionosphere’S Response To Multicell Convection Patterns, Jan Josef Sojka, Robert W. Schunk
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It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. When the interplanetary magnetic field (IMF) is southward, plasma convection at F region altitudes displays a two-cell pattern with antisunward flow over the polar cap and return flow at lower latitudes. However, when the IMF is northward, multiple convection cells can exist, with both sunward flow and auroral precipitation (theta aurora) in the polar cap. The characteristic ionospheric signatures associated with multicell convection patterns were studied …
Theoretical Study Of The Electron Temperature In The High-Latitude Ionosphere For Solar Maximum And Winter Conditions, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline
Theoretical Study Of The Electron Temperature In The High-Latitude Ionosphere For Solar Maximum And Winter Conditions, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline
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The electron temperature (Te) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, Te hot spots develop, and …
A Theoretical Study Of The Production And Decay Of Localized Electron Density Enhancements In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk
A Theoretical Study Of The Production And Decay Of Localized Electron Density Enhancements In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk
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The origins, transport, and decay of large-scale (≳ 10 km) F region density irregularities were theoretically studied using a high-latitude time dependent ionospheric model. Such density irregularities (blobs) have been found both in the polar cap and the auroral zone. The model study, which focuses on blobs being produced by auroral precipitation, shows that the observed energy fluxes can readily account for the blob densities if a plasma flux tube is exposed to the precipitation for 5-10 min. Once the flux tube is transported away from the source, the F region density profile recovers its shape on a time scale …
Theoretical Study Of Anomalously High F Region Peak Altitudes In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk
Theoretical Study Of Anomalously High F Region Peak Altitudes In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk
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During the last solar maximum period several observations of anomalously high F region peak altitudes have been made by the high latitude incoherent scatter radars. The observations indicate that there are several distinctive features associated with these high hmF2 ionospheric profiles: (1) they are observed near midnight with the plasma flowing out of the polar cap, (2) NmF2 ranges from 105 to 106 cm−3, (3) hmF2 ranges from 400 to 500 km, (4) below 300 km the profile is devoid of ionization, and (5) the observations are for solar maximum conditions. …
A Theoretical Study Of The Global F Region For June Solstice, Summer Maximum, And Low Magnetic Activity, Jan Josef Sojka, Robert W. Schunk
A Theoretical Study Of The Global F Region For June Solstice, Summer Maximum, And Low Magnetic Activity, Jan Josef Sojka, Robert W. Schunk
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We constructed a time-dependent, three-dimensional, multi-ion numerical model of the global ionosphere at F region altitudes. The model takes account of all the processes included in the existing regional models of the ionosphere. The inputs needed for our global model are the neutral temperature, composition, and wind; the magnetospheric and equatorial electric field distributions; the auroral precipitation pattern; the solar EUV spectrum; and a magnetic field model. The model produces ion (NO+, O2+, N2+, N+, O+, He+) density distributions as a function of time. For our …
A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk
A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk
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The response of the polar ionosphere to magnetospheric storm inputs was modeled. During the “storm,” the spatial extent of the auroral oval, the intensity of the precipitating auroral electron energy flux, and the plasma convection pattern were varied with time. The convection pattern changed from a symmetric two-cell pattern with a 20-kV cross-tail potential to an asymmetric two-cell pattern with enhanced plasma flow in the dusk sector and a total cross-tail potential of 90 kV. During the storm there were significant changes in the ion temperature, ion composition, and molecular/atomic ion transition height. The storm time asymmetric convection pattern produced …
A Theoretical Study Of The High Latitude F Region’S Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk
A Theoretical Study Of The High Latitude F Region’S Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk
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The response of the polar ionosphere to magnetospheric storm inputs was modeled. During the storm the two major processes that couple the F region to the magnetosphere, namely the electric field distribution and the particle precipitation from the magnetosphere, undergo drastic modification on relatively short F region time scales. These time-dependent changes are not simply related to the F region storm time dependent changes. The lower F region responds on a time scale of only minutes to the storm associated changes in the auroral precipitating electron flux, owing to the dominance of chemistry production-loss mechanisms over transport processes. At higher …
A Theoretical Study Of The High-Latitude Winter F Region At Solar Minimum For Low Magnetic Activity, Jan Josef Sojka, W. J. Raitt, Robert W. Schunk
A Theoretical Study Of The High-Latitude Winter F Region At Solar Minimum For Low Magnetic Activity, Jan Josef Sojka, W. J. Raitt, Robert W. Schunk
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We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at solar minimum for low magnetic activity. Our numerical study produced time dependent, three-dimensional ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. The main result we obtained was that high-latitude ionospheric features, such as the ‘main trough,’ the ‘ionization hole,’ the ‘tongue of ionization,’ the ‘aurorally produced …