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1984

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Articles 91 - 108 of 108

Full-Text Articles in Physics

Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar Jan 1984

Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar

All Physics Faculty Publications

Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal ...


Nighttime Thermospheric Winds Over Sondre Stromfjord, Greenland, J W. Meriwether Jr., P Shih, T L. Killeen, Vincent B. Wickwar, R G. Roble Jan 1984

Nighttime Thermospheric Winds Over Sondre Stromfjord, Greenland, J W. Meriwether Jr., P Shih, T L. Killeen, Vincent B. Wickwar, R G. Roble

All Physics Faculty Publications

Observations of nighttime thermospheric neutral winds made at Sondre Stromfjord, Greenland, with optical and radar instrumentation, showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells. This abatement appeared primarily in the poleward observations. In contrast, however, the characteristic midnight “surge” was usually seen in the equatorward set of observations. The apparent acceleration of about 250 m/s or greater within 4.6° latitude we attribute, in part, to a merging of neutral jet streams generated by polar cap ion drag adjacent to the ...


Initial Millstone Hill, Sondrestrom, And Hilat Observations Of Thermospheric Temperatures And Frictional Heating, W L. Oliver, J C. Foster, J M. Holt, G B. Loriot, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, P F. Bythrow, D I. Meng, F J. Rich, R E. Huffman Jan 1984

Initial Millstone Hill, Sondrestrom, And Hilat Observations Of Thermospheric Temperatures And Frictional Heating, W L. Oliver, J C. Foster, J M. Holt, G B. Loriot, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, P F. Bythrow, D I. Meng, F J. Rich, R E. Huffman

All Physics Faculty Publications

Elevation scan observations made by the Millstone Hill and Sondrestrom incoherent scatter radars are combined to provide extended latitudinal coverage of thermospheric measurements. Maps of the latitudinal and temporal structure of the exospheric temperature are presented for two 24‐hour periods over the latitude range 45 to 72 degrees north. On the magnetically quiet June day the Millstone and Sondrestrom data formed a consistent picture of thermospheric structure. On the disturbed July day the two radars observed very different behavior, with Millstone Hill observing strong, long‐lived ion frictional heating events but Sondrestrom observing more quiescent behavior. Comparison with HILAT ...


Thermospheric Neutral Wind At –39° Azimuth During The Daytime Sector At Sondrestrom, Vincent B. Wickwar Jan 1984

Thermospheric Neutral Wind At –39° Azimuth During The Daytime Sector At Sondrestrom, Vincent B. Wickwar

All Physics Faculty Publications

Measurements with the Sondrestrom radar have been used to examine the daytime thermospheric neutral wind and to relate that wind to other geophysical parameters. Ion drag is found to be particularly important for determining the wind pattern. However, evidence is presented that the wind pattern is significantly influenced by soft particle precipitation and, possibly, by Joule heating.


Sondrestrom Overview, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, C A. Leger, F Steenstrup, C H. Dawson Jan 1984

Sondrestrom Overview, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, C A. Leger, F Steenstrup, C H. Dawson

All Physics Faculty Publications

This overview of the Sondrestrom radar provides background material to help understand the early scientific results discussed in the following series of papers. It describes the geophysical region probed by the radar, the data acquisition procedure, and the extensive set of physical parameters derived.


The Polar Ionosphere: Editorial, Vincent B. Wickwar, J W. Meriwether Jr. Jan 1984

The Polar Ionosphere: Editorial, Vincent B. Wickwar, J W. Meriwether Jr.

All Physics Faculty Publications

Editorial


The Meridional Thermospheric Neutral Wind Measured By Radar And Optical Techniques In The Auroral Region, Vincent B. Wickwar, J W. Meriwether Jr., P B. Hays, A F. Nagy Jan 1984

The Meridional Thermospheric Neutral Wind Measured By Radar And Optical Techniques In The Auroral Region, Vincent B. Wickwar, J W. Meriwether Jr., P B. Hays, A F. Nagy

All Physics Faculty Publications

Radar observations of ion velocities in the magnetic zenith over Chatanika, Alaska, were used to determine the geomagnetic meridional component of the thermospheric neutral wind. Corrections for molecular diffusion and molecular ion contamination of the pure O+ composition assumed for the ionosphere were included in the analysis. Comparison of the averaged diurnal variation of the meridional wind showed good agreement between the two measurement techniques. Good agreement was also found for several cases of simultaneous observations. The evidence suggested that differences were caused by gravity waves. The 7 years of radar meridional wind results were examined with respect to magnetic ...


A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk Jan 1984

A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

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 ...


Pitch Angle Properties Of Magnetospheric Thermal Protons And Satellite Sheath Interference In Their Observation, Jan Josef Sojka, G. L. Wrenn, J.F. E. Johnson Jan 1984

Pitch Angle Properties Of Magnetospheric Thermal Protons And Satellite Sheath Interference In Their Observation, Jan Josef Sojka, G. L. Wrenn, J.F. E. Johnson

All Physics Faculty Publications

Cold proton observations from the geosynchronous GEOS 2 satellite are presented to show the pitch angle distribution of the refilling cold ion population found beyond the plasmapause. This refilling cold ion population flows into the depleted equatorial regions of the flux tubes from the topside ionosphere. This refilling is observed both day and night. The ions have energies between 0.5 and 3 eV. These energy characteristics are consistent with other recent observations. Although the observed angular distribution of these ions is highly complex, when allowance is made for the satellite sheath several conclusions can be made concerning the ion ...


Systematic Estimate Of Binding Energies Of Weakly Bound Diatomic Molecules, Linda L. Vahala, Mark D. Havey Jan 1984

Systematic Estimate Of Binding Energies Of Weakly Bound Diatomic Molecules, Linda L. Vahala, Mark D. Havey

Electrical & Computer Engineering Faculty Publications

There is often insufficient spectroscopic data for a full RKR inversion to yield a potential for weakly bound diatomic molecules. In these cases, parametrized functions such as the Morse or Thakkar potentials may be used to obtain estimates of the binding energy. The Thakkar potential is more flexible, and has been used successfully on some weakly bound systems. In the more usual case, the Thakkar parameter p, which determines long range behavior R-p, is chosen by p=-a1-1, where a1 is the first Dunham coefficient; p is usually noninteger. The authors present an alternative choice for ...


Dayside Red Auroras At Very High Latitudes: The Importance Of Thermal Excitation, Vincent B. Wickwar, W Kofman Jan 1984

Dayside Red Auroras At Very High Latitudes: The Importance Of Thermal Excitation, Vincent B. Wickwar, W Kofman

All Physics Faculty Publications

Extensive radar observations have been made from Sondrestrom of the F region in the daytime sector between 70 and 79° Λ. Regions of enhanced electron temperature and electron density are found in close association with the velocity reversal in the morning and afternoon convection cells. From the radar measurements, calculations are made of the contributions to the atomic oxygen emission at 6300A from dissociative recombination and thermal excitation. The latter mechanism, in particular, in the enhancement regions gives rise to intensities that are comparable to those observed at very high latitudes during the past decade.


Irreversible Random And Cooperative Processes On Lattices: Spatial Correlations, James W. Evans, D. R. Burgess, D. K. Hoffman Jan 1984

Irreversible Random And Cooperative Processes On Lattices: Spatial Correlations, James W. Evans, D. R. Burgess, D. K. Hoffman

Physics and Astronomy Publications

For processes where ‘‘filling’’ events occur irreversibly and, in general, cooperatively at the sites of a lattice, the minimal closed hierarchy of rate equations involves only probabilities for (effectively) connected subconfigurations of empty sites. Extended hierarchies of equations for (effectively) disconnected empty subconfigurations couple back to these. Here we consider a solution to the latter via previously developed exact and approximate truncation schemes based on a shielding property of empty sites. Numerical results for several processes are presented for correlation behavior in both autocatalytic and autoinhibitory rate regimes. The asymptotic large separation behavior of the spatial correlations is analyzed most ...


Dynamics Of Two-Point Spatial Correlations For Randomly Hopping Lattice Gases: One-Dimensional Models, James W. Evans, D. K. Hoffman Jan 1984

Dynamics Of Two-Point Spatial Correlations For Randomly Hopping Lattice Gases: One-Dimensional Models, James W. Evans, D. K. Hoffman

Physics and Astronomy Publications

We consider the randomization of correlated, translationally invariant distributions of indistinguishable particles on lattices by random hopping, possibly involving several jump distances with generally different rates (and where double occupancy is excluded). Probabilities for various subconfigurations of n empty sites satisfy infinite closed sets of linear equations (for each n) in which the generator of the dynamics is self-adjoint. We provide a detailed spectral analysis of this generator for the two-point probabilities (or corresponding correlations) on a one-dimensional lattice. For just nearest-neighbor (1NN) and second-nearest-neighbor (2NN) jumps, the dynamics changes smoothly as a function of the ratio of the 2NN- ...


Exactly Solvable Irreversible Processes On Bethe Lattices, James W. Evans Jan 1984

Exactly Solvable Irreversible Processes On Bethe Lattices, James W. Evans

Physics and Astronomy Publications

We consider the kinetics of processes where the sites of a Bethe lattice are filled irreversibly and, in general, cooperatively by monomers, dimers, or polyatomics. For nearest neighbor and sometimes more general cooperative effects (including random filling as a special case), we show that the infinite hierarchy of rate equations for probabilities of empty subconfigurations can be exacty truncated and solved using a shielding property of empty sites. We indicate, in certain cases, a connection between these Bethe lattice solutions and certain approximate truncation solutions for corresponding processes on ‘‘physical’’ 2‐D and 3‐D lattices with the same coordination ...


The Kinematic Apse And Jz‐Preserving Propensities For Nonreactive, Dissociative, And Reactive Polyatomic Collisions, D. K. Hoffman, James W. Evans, D. J. Kouri Jan 1984

The Kinematic Apse And Jz‐Preserving Propensities For Nonreactive, Dissociative, And Reactive Polyatomic Collisions, D. K. Hoffman, James W. Evans, D. J. Kouri

Physics and Astronomy Publications

We consider the generalization of the kinematic apse to nonreactive polyatom–polyatom impulsive collisions, dissociative atom–molecule impulsive collisions,and (partially) impulsive reactive atom–diatom collisions. Appropriate generalizations of the kinematic apse are obtained along which there is a classical propensity for preserving the projection of the total intrinsic spin. In the case of reactive scattering, we discuss several different situations for which such a propensity occurs. For reactive systems in which no such propensity exists, the analysis may still provide a basis for classifying reactions.


Hamiltonian Interpretation Of Anomalies, Philip C. Nelson, Luis Alvarez-Gaumé Jan 1984

Hamiltonian Interpretation Of Anomalies, Philip C. Nelson, Luis Alvarez-Gaumé

Department of Physics Papers

A family of quantum systems parametrized by the points of a compact space can realizeits classical symmetries via a new kind of nontrivial ray representation. We show that thisphenomenon in fact occurs for the quantum mechanics of fermions in the presence ofbackground gauge fields, and is responsible for both the nonabelian anomaly and Witten’sSU(2) anomaly. This provides a hamiltonian interpretation of anomalies: in the affectedtheories Gauss’ law cannot be implemented. The analysis clearly shows why there are nofurther obstructions corresponding to higher spheres in configuration space, in agreementwith a recent result of Atiyah and Singer.


Exactly Solvable Irreversible Processes On One‐Dimensional Lattices, N. O. Wolf, James W. Evans, D. K. Hoffman Jan 1984

Exactly Solvable Irreversible Processes On One‐Dimensional Lattices, N. O. Wolf, James W. Evans, D. K. Hoffman

Physics and Astronomy Publications

We consider the kinetics of a process where the sites of an infinite 1‐D lattice are filled irreversibly and, in general, cooperatively by N‐mers (taking Nconsecutive sites at a time). We extend the previously available exact solutionfor nearest neighbor cooperative effects to range N cooperative effects. Connection with the continuous ‘‘cooperative car parking problem’’ is indicated. Both uniform and periodic lattices, and empty and certain partially filled lattice initial conditions are considered. We also treat monomer ‘‘filling in stages’’ for certain highly autoinhibitory cooperative effects of arbitrary range.


Competing Irreversible Cooperative Reactions On Polymer Chains, James W. Evans, D. K. Hoffman, D. R. Burgess Jan 1984

Competing Irreversible Cooperative Reactions On Polymer Chains, James W. Evans, D. K. Hoffman, D. R. Burgess

Physics and Astronomy Publications

We analyze model processes involving competition between several irreversible reactions at the sites of a 1D, infinite, uniform polymer chain. These reactionscan be cooperative, i.e., the corresponding rates depend on the state of the surrounding sites. An infinite hierarchy of rate equations is readily derived for the probabilities of various subconfigurations. By exploiting a shielding property of suitable blocks of unreacted sites, we show how exact hierarchy truncation and solution is sometimes possible. The behavior of solutions is illustrated in several cases by plotting families of ‘‘reaction trajectories’’ for varying ratios of reactant concentrations ...