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Full-Text Articles in Physics

Image Measurements Of Short Period Gravity Waves At Equatorial Latitudes, Michael J. Taylor, W. R. Pendleton Jr., S. Clark, H. Takahashi, D. Gobbi, R. A. Goldberg Nov 1997

Image Measurements Of Short Period Gravity Waves At Equatorial Latitudes, Michael J. Taylor, W. R. Pendleton Jr., S. Clark, H. Takahashi, D. Gobbi, R. A. Goldberg

All Physics Faculty Publications

A high-performance, all-sky imaging system has been used to obtain novel data on the morphology and dynamics of short-period (<1 hour) gravity waves at equatorial latitudes. Gravity waves imaged in the upper mesosphere and lower thermosphere were recorded in three nightglow emissions, the near-infrared OH emission, and the visible wavelength OI (557.7 nm) and Na (589.2 nm) emissions spanning the altitude range ∼80–100 km. The measurements were made from Alcantara, Brazil (2.3°S, 44.5°W), during the period August-October 1994 as part of the NASA/Instituto Nacional de Pesquisas Espaciais “Guara campaign”. Over 50 wave events were imaged from which a statistical study of the characteristics of equatorial gravity waves has been performed. The data were found to divide naturally into two groups. The first group corresponded to extensive, freely propagating (or ducted) gravity waves with observed periods ranging from 3.7 to 36.6 min, while the second group consisted of waves of a much smaller scale and transient nature. The later group exhibited a bimodal distribution for the observed periods at 5.18 ± 0.26 min and 4.32 ± 0.15 min, close to the local Brunt-Vaisala period and the acoustic cutoff period, respectively. In comparison, the larger-scale waves exhibited a clear tendency for their horizontal wavelengths to increase almost linearly with observed period. This trend was particularly well defined around the equinox and can be represented by a power-law relationship of the form λ h = ( 3.1 ± 0.5 ) τ ob 1.06 ± 0.10 , where λ h is measured in kilometers and τob in minutes. This result is in very good agreement with previous radar and passive optical measurements but differs significantly from the relationship λ h ∝ τ105 ob inferred from recent lidar studies. The larger-scale waves were also found to exhibit strong anisotropy in their propagation headings with the dominant direction of motion toward the-NE-ENE suggesting a preponderance for wave generation over the South American continent.


Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces, R. E. Davies, Jr Dennison Nov 1997

Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces, R. E. Davies, Jr Dennison

All Physics Faculty Publications

Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition--e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces can and generally do undergo significant evolution ...


Observational Evidence Of Wave Ducting And Evanescence In The Mesosphere, J. R. Isler, Michael J. Taylor, D. C. Fritts Nov 1997

Observational Evidence Of Wave Ducting And Evanescence In The Mesosphere, J. R. Isler, Michael J. Taylor, D. C. Fritts

All Physics Faculty Publications

A collaborative radar and imaging study of gravity waves over the Hawaiian Islands was performed during October 1993 as part of the Airborne Lidar and Observations of Hawaiian Airglow 1993/Coupling and Dynamics of Regions Equatorial (ALOHA-93/CADRE) campaign to investigate the propagation characteristics of short-period (<1 hour) waves at nightglow altitudes. The horizontal wavelengths and apparent phase speeds of quasi-monochromatic wave events were measured in four separate nightglow emissions using data obtained by a high-resolution CCD imager. This information was correlated with simultaneous MF radar wind measurements over the same height interval (∼80–100 km) to infer intrinsic wave parameters in each case. Correlating the two data sets allowed the determination of the local vertical wavenumber for each event, in particular whether it be real (indicative of freely propagating waves) or imaginary (indicative of ducted or evanescent waves). The results of this study indicate a preponderance of ducted or evanescent waves at 80–100 km during the time of the observations, with up to ∼75% of the events recorded exhibiting ducted or evanescent behavior. Also noted was a tendency for ducted behavior to be more prevalent among waves with shorter horizontal wavelengths, in agreement with Doppler ducting theory. These results suggest that ducted waves are relatively common in the upper mesosphere and lower thermosphere region, at least over the mid-Pacific Ocean. As small-scale waves which are ducted have the potential to travel much longer horizontal distances than freely propagating waves, the frequency of their occurrence should be taken into account in efforts to quantify gravity wave effects at these altitudes.


Two-Dimensional Spectral Analysis Of Mesospheric Airglow Image Data, F. J. Garcia, Michael J. Taylor, M. C. Kelley Oct 1997

Two-Dimensional Spectral Analysis Of Mesospheric Airglow Image Data, F. J. Garcia, Michael J. Taylor, M. C. Kelley

All Physics Faculty Publications

A technique to analyze short-period (<1 hour) gravity wave structure in all-sky images of the airglow emissions is described. The technique involves spatial calibration, star removal, geographic projection, regridding, and flat fielding of the data prior to the determination of the horizontal wave parameters (wavelength, velocity, and period), by use of standard two-dimensional Fourier analysis techniques. The method was developed to exploit the information that is now available with wide-field solid state imaging systems. This technique permits interactive and quantitative investigations of large, complex data sets. Such studies are important for investigating gravity wave characteristics, their interaction with the airglow emissions, and their geographic and seasonal variability. We study one event of this type here and present possible evidence of a nonlinear wave–wave interaction in the upper atmosphere.


Nonlinear Front Evolution Of Hydrodynamic Chemical Waves In Vertical Cylinders, J. W. Wilder, D. A. Vasquez, Boyd F. Edwards Sep 1997

Nonlinear Front Evolution Of Hydrodynamic Chemical Waves In Vertical Cylinders, J. W. Wilder, D. A. Vasquez, Boyd F. Edwards

All Physics Faculty Publications

The nonlinear stability of three-dimensional reaction-diffusion fronts in vertical cylinders is considered using the viscous hydrodynamic fluid equations in the limit of infinite thermal diffusivity. A nonlinear front evolution equation is presented and used to examine the transition from nonaxisymmetric to axisymmetric convection observed in experiments performed in cylinders. Comparisons with experiments show excellent agreement in both the shape and speed of the front.


High Resolution Oi (630 Nm) Image Measurements Of Fregion Depletion Drifts During The Guara Campaign, Michael J. Taylor, J. Labelle, J. A.H. Sobral Jul 1997

High Resolution Oi (630 Nm) Image Measurements Of Fregion Depletion Drifts During The Guara Campaign, Michael J. Taylor, J. Labelle, J. A.H. Sobral

All Physics Faculty Publications

A high performance, all‐sky, imaging system has provided data on the evolution and drift motions of F‐region depletions above the magnetic dip equator at Alcântara, Brazil, (2.3°S, 44.5°W). Monochromatic images of depletions in the OI(630 nm) nightglow were recorded on eight nights during 1‐16 October, 1994, as part of the Guará campaign. The drift motions of the depletions were typically 80–100 m/s eastward prior to local midnight and reduced to a minimum of ∼30–50 m/s in the morning hours, in accord with previous observations. However, on October 2 ...


Numerical Simulations Of Gravity Waves Imaged Over Arecibo During The 10-Day January 1993 Campaign, M. P. Hickey, R. L. Walterscheid, Michael J. Taylor, W. Ward, G. Schubert, Q. Zhou, F. Garcia, M. C. Kelley, G. G. Shepherd Jun 1997

Numerical Simulations Of Gravity Waves Imaged Over Arecibo During The 10-Day January 1993 Campaign, M. P. Hickey, R. L. Walterscheid, Michael J. Taylor, W. Ward, G. Schubert, Q. Zhou, F. Garcia, M. C. Kelley, G. G. Shepherd

All Physics Faculty Publications

Recently, measurements were made of mesospheric gravity waves in the OI (5577 Å) nightglow observed from Arecibo, Puerto Rico, during January 1993 as part of a special 10-day campaign. Clear, monochromatic gravity waves were observed on several nights. By using a full-wave model that realistically includes the major physical processes in this region, we have simulated the propagation of two waves through the mesopause region and calculated the O(1 S) nightglow response to the waves. Mean winds derived from both UARS wind imaging interferometer (WINDII) and Arecibo incoherent scatter radar observations were employed in the computations as were the ...


Empirical Studies Of Ionospheric Electric Fields, Ludger Scherliess May 1997

Empirical Studies Of Ionospheric Electric Fields, Ludger Scherliess

All Graduate Theses and Dissertations

The first comprehensive study of equatorial- to mid-latitude ionospheric electric fields (plasma drifts) is presented, using extensive incoherent scatter radar measurements from Jicamarca, Arecibo, and Millstone Hill, and F-region ion drift meter data from the polar orbiting DE-2 satellite. Seasonal and solar cycle dependent empirical quiet-time electric field models from equatorial to mid latitudes are developed, which improve and extend existing climatological models. The signatures of electric field perturbations during geomagnetically disturbed periods, associated with changes in the high-latitude currents and the characteristics of storm-time dynamo electric fields driven by enhanced energy deposition into the high-latitude ionosphere, are studied. Analytical ...


Studies Of Mid-Lattitude Mesospheric Temperature Variability And Its Relationship To Gravity Waves, Tides, And Planetary Waves, Kenneth C. Beissner May 1997

Studies Of Mid-Lattitude Mesospheric Temperature Variability And Its Relationship To Gravity Waves, Tides, And Planetary Waves, Kenneth C. Beissner

All Graduate Theses and Dissertations

Temperature observations of the middle atmosphere have been carried out from September 1993 through July 1995 using a Rayleigh backscatter lidar located at Utah State University (42°N, lii0W). Data have been analyzed to obtain absolute temperature profi les from 40 to 90 km. Various sources of error were reviewed in order to ensure the quality of the measurements. This included conducting a detailed examination of the data reduction procedure, integration methods, and averaging techniques. eliminating errors of 1-3%. The temperature structure climatology has been compared with several other mid-latitude data sets. including those from the French lidars, the SME ...


Wind Climatology At 87 Km Above The Rocky Mountains At Bear Lake Observatory--Fabry-Perot Observations Of Oh, V. B. Wickwar, I K. Monson, C M. Vadnais, D Rees Apr 1997

Wind Climatology At 87 Km Above The Rocky Mountains At Bear Lake Observatory--Fabry-Perot Observations Of Oh, V. B. Wickwar, I K. Monson, C M. Vadnais, D Rees

Reports

This paper presents the neutral -wind climatology at approximately 87-km 53 altitude from Utah State University's Bear Lake Observatory (BLO). a mid-latitude site 54 situated in the middle of the Rocky Mountains. The winds were determined using a very 55 sensitive Fabry-Perot interferometer (FPI) observing the OH Me inel (6-2) PI (3) line al 56 843 nm. The climatology. determined from monthly averages of the nightly evolution of 57 the geographic meridional and zonal wind components over forty· five months, has three 58 distinct seasonal patterns: winter (November- February), summer (May-Jul y), and late 59 Slimmer (August and September ...


Thermoconvective Instability Of Paramagnetic Fluids In A Uniform Magnetic Field, J. Huang, Boyd F. Edwards, D. D. Gray Feb 1997

Thermoconvective Instability Of Paramagnetic Fluids In A Uniform Magnetic Field, J. Huang, Boyd F. Edwards, D. D. Gray

All Physics Faculty Publications

The effect of a uniform oblique magnetic field on a laterally unbounded insulating paramagnetic fluid layer heated from below is studied using a linear stability analysis of the Navier–Stokes equations supplemented by Maxwell’s equations and the appropriate magnetic body force. Two-dimensional rolls in an arbitrary vertical plane are considered. Longitudinal rolls with axes parallel to the horizontal component of the field are the rolls most unstable to convection. The corresponding critical Rayleigh number and critical wavelength for the onset of such rolls are less than the well-known Rayleigh–Bénard values in the absence of magnetic fields. Vertical fields ...


Model Study Of Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, P. Gifford, Jan Josef Sojka, Robert W. Schunk Jan 1997

Model Study Of Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, P. Gifford, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

We conducted a model study of ground magnetic signatures of traveling convection vortices (TCVs) that included both the ionospheric conductivity enhancement associated with the TCVs and the ground induction effect. We found that the localized conductivity enhancement can cause a significant distortion of the TCV current system and lead to a distortion of the ground magnetic disturbance patterns. The patterns of all three magnetic components are asymmetric, mainly in the E-W direction, and the patterns of the Z component show the strongest asymmetry (20–30%). We also found that the effect of induction currents on ground magnetic signatures of the ...


Driving A Physical Ionospheric Model With A Magnetospheric Mhd Model, Jan Josef Sojka, Robert W. Schunk, M. D. Bowline, J. Chen, S. Slinker, J. Fedder Jan 1997

Driving A Physical Ionospheric Model With A Magnetospheric Mhd Model, Jan Josef Sojka, Robert W. Schunk, M. D. Bowline, J. Chen, S. Slinker, J. Fedder

All Physics Faculty Publications

This is the first study in which a physical ionospheric model (time-dependent ionospheric model (TDIM)) has been driven through a substorm using self-consistent magnetospheric convection electric field and auroral electron precipitation inputs. Both of these were generated from a simulation of a real substorm event using the MHD model [Fedder et al., 1995b]. Interplanetary magnetic field (IMF) data were available for 1.5 hours until the substorm breakup. Hence the substorm growth and expansion dynamics is captured in a 1.5-hour time period. As a reference against which to compare this TDIM substorm simulation, a typical climatological TDIM simulation was ...


An Embedded Ring Approach To The Vibrational Dynamics Of Amorphous Materials, Jr Dennison, T. E. Doyle Jan 1997

An Embedded Ring Approach To The Vibrational Dynamics Of Amorphous Materials, Jr Dennison, T. E. Doyle

All Physics Faculty Publications

A theoretical approach has been developed to model the vibrational modes of amorphous, two-dimensional materials. The method considers that the vibrational density of states is composed primarily of states originating from embedded ring structures of medium-range order. The materials are modeled as continuous random networks comprised of a statistical distribution of symmetric, planar rings with four to eight members. The rings are treated as local structural units embedded in the material, similar to molecules within a solid. The ring potentials are approximated with a valence force model (bond-stretching and bond-angle-bending force constants) modified by a third harmonic, effective force constant ...


Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock Jan 1997

Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock

All Physics Faculty Publications

Global topological defects produce nonzero stress energy throughout spacetime, and as a result can have observable gravitational influence on surrounding matter. Gravitational effects of global strings are used to place bounds on their cosmic abundance. The minimum separation between global strings is estimated by considering the defects' contribution to the cosmological energy density. More rigorous constraints on the abundance of global strings are constructed by examining the tidal forces such defects will have on observable astrophysical systems. The small number of observed tidally disrupted systems indicates there can be very few of these objects in the observable Universe.


Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson Jan 1997

Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson

All Physics Faculty Publications

First-order semiclassical perturbations to the Schwarzschild black hole geometry are studied within the black hole interior. The source of the perturbations is taken to be the vacuum stress-energy of quantized scalar, spinor, and vector fields, evaluated using analytic approximations developed by Page and others (for massless fields) and the DeWitt-Schwinger approximation (for massive fields). Viewing the interior as an anisotropic collapsing cosmology, we find that minimally or conformally coupled scalar fields, and spinor fields, decrease the anisotropy as the singularity is approached, while vector fields increase the anisotropy. In addition, we find that for massless fields of all spins, the ...


Why Quantum Mechanics Is Complex, James Thomas Wheeler Jan 1997

Why Quantum Mechanics Is Complex, James Thomas Wheeler

All Physics Faculty Publications

The zero-signature Killing metric of a new, real-valued, 8-dimensional gauging of the conformal group accounts for the complex character of quantum mechanics. The new gauge theory gives manifolds which generalize curved, relativistic phase space. The difference in signature between the usual momentum space metric and the Killing metric of the new geometry gives rise to an imaginary proportionality constant connecting the momentumlike variables of the two spaces. Path integral quantization becomes an average over dilation factors, with the integral of the Weyl vector taking the role of the action. Minimal U(1) electromagnetic coupling is predicted.


The Global Ionosphere-Polar Wind System During Changing Magnetic Activity, Robert W. Schunk, Jan Josef Sojka Jan 1997

The Global Ionosphere-Polar Wind System During Changing Magnetic Activity, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

A time-dependent, three-dimensional, multi-ion model of the global ionosphere-polar wind system was used to study the system's response to an idealized geomagnetic storm for different seasonal and solar cycle conditions. The model covered the altitude range from 90 to 9000 km for latitudes greater than 50° magnetic in the northern hemisphere. The geomagnetic storm contained a 1-hour growth phase, a 1-hour main phase, and a 4-hour decay phase. Four storm simulations were conducted, corresponding to winter and summer solstices at both solar maximum and minimum. The simulations indicated the following: (1) O+ upflows typically occur in the cusp and ...


Ionospheric Response To An Auroral Substorm, R. W. Schunk, L. Zhu, Jan Josef Sojka, M. D. Bowline Jan 1997

Ionospheric Response To An Auroral Substorm, R. W. Schunk, L. Zhu, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

The response of the ionosphere to a representative auroral substorm was simulated. The response was found to be significant at all altitudes in a large spatial region near midnight magnetic local time. In this midnight region, there were Te and Ti hot spots, substantial O+ → NO+ composition changes, non‐Maxwellian velocity distributions, transient ion upwellings, a large‐scale lowering of the F‐layer, ionization peaks that occur in the E‐region, and sharp horizontal gradients. Also, during the expansion phase, the E‐region densities increase due to auroral precipitation, while the plasma densities above 300 km decrease due ...


Spinors, Jets, And The Einstein Equations, Charles G. Torre Jan 1997

Spinors, Jets, And The Einstein Equations, Charles G. Torre

All Physics Faculty Publications

Many important features of a field theory, e.g., conserved currents, symplectic structures, energy-momentum tensors, etc., arise as tensors locally constructed from the fields and their derivatives. Such tensors are naturally defined as geometric objects on the jet space of solutions to the field equations. Modern results from the calculus on jet bundles can be combined with a powerful spinor parametrization of the jet space of Einstein metrics to unravel basic features of the Einstein equations. These techniques have been applied to computation of generalized symmetries and “characteristic cohomology” of the Einstein equations, and lead to results such as a ...