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Series

2005

All Physics Faculty Publications

Articles 1 - 20 of 20

Full-Text Articles in Physics

Concurrent Ohimager And Sodium Temperature/Wind Lidar Observation Of Localized Ripples Over Northern Colorado, L. Tao, C. Y. She, B. P. Williams, Tao Yuan, R. L. Collins, L. Kieffabar, A. Peterson Jul 2005

Concurrent Ohimager And Sodium Temperature/Wind Lidar Observation Of Localized Ripples Over Northern Colorado, L. Tao, C. Y. She, B. P. Williams, Tao Yuan, R. L. Collins, L. Kieffabar, A. Peterson

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On 3 and 5 September 2002 the OH all-sky imager at Platteville, Colorado (40.2°N, 104.7°W), observed small-scale, wavelike patterns (known as ripples), with horizontal wavelengths of ∼9 km and ∼7 km and lifetimes of ∼9 min and ∼15 min, respectively. The Colorado State University sodium lidar at nearby Fort Collins, Colorado (40.6°N, 105°W), also made concurrent observations of temperature and zonal and meridional winds, which allowed us to determine the nature of the ripples observed. Our observations suggest that the 3 September ripple was induced by a convective instability located at 87.5 km and the 5 September ripple was induced …

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An Operational Data Assimilation Model Of The Global Ionosphere, Robert W. Schunk, L. Scherliess, Jan Josef Sojka, D. C. Thompson, L. Zhu May 2005

An Operational Data Assimilation Model Of The Global Ionosphere, Robert W. Schunk, L. Scherliess, Jan Josef Sojka, D. C. Thompson, L. Zhu

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Physics-based data assimilation models of the ionosphere were developed at Utah State University as part of a DoD Multidisciplinary University Research Initiative (MURI) program. The USU effort was called Global Assimilation of Ionospheric Measurements (GAIM). One of the USU Data assimilation models has been selected for operational use at the Air Force Weather Agency (AFWA in Omaha, Nebraska. This model is a Gauss-Markov Kalman Filter model, and it uses a physic-based model of the global ionosphere and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. The model has been designed to …

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State Of Utah Space Environment & Contamination Study (Suspecs) Misse-6 Payload To Investigate Their Effects On Electron Emission And Resistivity Of Spacecraft Materials, John R. Dennison, L. Pearson, L. Davis, J. W. Burns, R. S. Hyde, James S. Dyer, Tina Andrus, Andrew Jay Auman, Jeff Duce, Tim Neilsen, Rob Leishman Apr 2005

State Of Utah Space Environment & Contamination Study (Suspecs) Misse-6 Payload To Investigate Their Effects On Electron Emission And Resistivity Of Spacecraft Materials, John R. Dennison, L. Pearson, L. Davis, J. W. Burns, R. S. Hyde, James S. Dyer, Tina Andrus, Andrew Jay Auman, Jeff Duce, Tim Neilsen, Rob Leishman

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A study of the effects of prolonged exposure to the space environment and of charge-enhanced contamination on the electron emission and resistivity of spacecraft materials, the State of Utah Space Environment & Contamination Study (SUSpECS), is planned for flight aboard the MISSE-6 payload. The Materials International Space Station Experiment (MISSE-6) program is designed to characterize the performance of candidate new space materials over the course of approximately four to eight month exposure periods on-orbit on the International Space Station, with a target flight date of mid-2006. The study is conducted by the Utah State University Materials Physics Group, in cooperation …

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Strong Electric Fields From Positive Lightning Strokes In The Stratosphere, R. H. Holzworth, M. C. Mccarthy, J. N. Thomas, J. Chin, T. M. Chinowsky, Michael J. Taylor, O. Pinto Jr. Feb 2005

Strong Electric Fields From Positive Lightning Strokes In The Stratosphere, R. H. Holzworth, M. C. Mccarthy, J. N. Thomas, J. Chin, T. M. Chinowsky, Michael J. Taylor, O. Pinto Jr.

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A balloon payload launched in Brazil has measured vector electric fields from lightning at least an order of magnitude larger than previously reported above 30 km in the stratosphere. During the flight hundreds of lightning events were recorded, including several positive cloud to ground lightning strokes. A two stroke flash, with small (15 kA peak current) and moderate (53 kA) positive strokes at a horizontal range of 34 km, produced field changes over 140 V/m at 34 km altitude. On-board optical lightning detection, recorded with GPS timing, coupled with ground based lightning location gives high time resolution for study of …

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Polar F-Layer Model-Observation Comparisons: A Neutral Wind Surprise, Jan Josef Sojka, M. David, Robert W. Schunk, A. P. Van Eyken Jan 2005

Polar F-Layer Model-Observation Comparisons: A Neutral Wind Surprise, Jan Josef Sojka, M. David, Robert W. Schunk, A. P. Van Eyken

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The existence of a month-long continuous database of incoherent scatter radar observations of the ionosphere from the EISCAT Savlbard Radar (ESR) at Longyearbyen, Norway, provides an unprecedented opportunity for model/data comparisons. Physics-based ionospheric models, such as the Utah State University Time Dependent Ionospheric Model (TDIM), are usually only compared with observations over restricted one or two day events or against climatological averages. In this study, using the ESR observations, the daily weather, day-to-day variability, and month-long climatology can be simultaneously addressed to identify modeling shortcomings and successes. Since for this study the TDIM is driven by climatological representations of the …

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The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson Jan 2005

The Importance Of Accurate Computation Of Secondary Electron Emission For Modeling Spacecraft Charging, S. Clerc, John R. Dennison, C. D. Thomson

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Secondary electron emission is a critical contributor to the current balance in spacecraft charging. Spacecraft charging codes use a parameterized expression for the secondary electron yield δ(Eo) as a function of incident electron energy Eo. Simple three-step physics models of the electron penetration, transport and emission from a solid are typically expressed in terms of the incident electron penetration depth at normal incidence or range R(Eo ), and the mean free path of the secondary electron, λ(E). We recall classical models for the range R(Eo): a power law expression of the form b1Eon1 …

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Proposed Modifications To Engineering Design Guidelines Related To Resistivity Measurements And Spacecraft Charging, John R. Dennison, Prasanna Swaminathan, Randy Jost, Jerilyn Brunson, Nelson W. Green, A. Robb Frederickson Jan 2005

Proposed Modifications To Engineering Design Guidelines Related To Resistivity Measurements And Spacecraft Charging, John R. Dennison, Prasanna Swaminathan, Randy Jost, Jerilyn Brunson, Nelson W. Green, A. Robb Frederickson

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A key parameter in modeling differential spacecraft charging is the resistivity of insulating materials. This parameter determines how charge will accumulate and redistribute across the spacecraft, as well as the time scale for charge transport and dissipation. Existing spacecraft charging guidelines recommend use of tests and imported resistivity data from handbooks that are based principally upon ASTM methods that are more applicable to classical ground conditions and designed for problems associated with power loss through the dielectric, than for how long charge can be stored on an insulator. These data have been found to underestimate charging effects by one to …

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Behavior Of The Ionosphere And Thermosphere Subject To Extreme Solar Cycle Conditions, C. G. Smithtro, Jan Josef Sojka Jan 2005

Behavior Of The Ionosphere And Thermosphere Subject To Extreme Solar Cycle Conditions, C. G. Smithtro, Jan Josef Sojka

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A 1-D global average ionosphere and thermosphere (GAIT) model is used to examine the climatological behavior of the upper atmosphere, subject to both extremely low and high solar flux. These extremes are justified, in part, by the Maunder Minimum and Grand Maximum epochs described by J. A. Eddy, as well as other studies involving cosmogenic isotopes and Sun-like stars. As the irradiance falls below normal solar minimum levels, the concentration of O+ decreases rapidly relative to the molecular ions, such that the ratio ƒoF2/ƒoF1 approaches unity. When subject to exceptionally high solar …

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A New Global Average Model Of The Coupled Thermosphere And Ionosphere, C. G. Smithtro, Jan Josef Sojka Jan 2005

A New Global Average Model Of The Coupled Thermosphere And Ionosphere, C. G. Smithtro, Jan Josef Sojka

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A model representing the global average ionosphere and thermosphere (GAIT) is developed as a tool to explore the response of the coupled system to changes in the input solar irradiance between 3 and 360 nm. The GAIT model self-consistently solves the coupled continuity, momentum, and energy equations for the three major neutral species, N2, O2, and O, as well as minor neutral constituents important to the global energy budget. In the ionosphere the model includes five different ion species and two excited states of O+. The GAIT model also includes an approximate treatment of …

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Ionospheric Weather Forecasting On The Horizon, Robert W. Schunk, L. Scherliess, Jan Josef Sojka, D. C. Thompson, L. Zhu Jan 2005

Ionospheric Weather Forecasting On The Horizon, Robert W. Schunk, L. Scherliess, Jan Josef Sojka, D. C. Thompson, L. Zhu

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Models of the ionosphere using state-of-the-art data assimilation techniques are nearing operational use.

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Semi-Relativistic Approximation To Gravitational Radiation From Encounters With Non-Spinning Black Holes, Jonathan R. Gair, Daniel J. Kennefick, Shane L. Larson Jan 2005

Semi-Relativistic Approximation To Gravitational Radiation From Encounters With Non-Spinning Black Holes, Jonathan R. Gair, Daniel J. Kennefick, Shane L. Larson

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The capture of compact bodies by black holes in galactic nuclei is an important prospective source for low frequency gravitational wave detectors, such as the planned Laser Interferometer Space Antenna. This paper calculates, using a semirelativistic approximation, the total energy and angular momentum lost to gravitational radiation by compact bodies on very high eccentricity orbits passing close to a supermassive, nonspinning black hole; these quantities determine the characteristics of the orbital evolution necessary to estimate the capture rate. The semirelativistic approximation improves upon treatments which use orbits at Newtonian order and quadrupolar radiation emission, and matches well onto accurate Teukolsky …

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Coherent State Path Integral For Linear Systems, Charles G. Torre Jan 2005

Coherent State Path Integral For Linear Systems, Charles G. Torre

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We present a computation of the coherent state path integral for a generic linear system using "functional methods'' (as opposed to discrete time approaches). The Gaussian phase space path integral is formally given by a determinant built from a first-order differential operator with coherent state boundary conditions. We show how this determinant can be expressed in terms of the symplectic transformation generated by the (in general, time-dependent) quadratic Hamiltonian for the system. We briefly discuss the conditions under which the coherent state path integral for a linear system actually exists. A necessary -- but not sufficient -- condition for existence …

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Climatology Of Short-Period Gravity Wavesobserved Over Northern Australia During The Dawex Campaign And Their Dominant Sourceregions, Pierre-Dominique Pautet, Michael J. Taylor, A. Z. Liu, G. R. Swenson Jan 2005

Climatology Of Short-Period Gravity Wavesobserved Over Northern Australia During The Dawex Campaign And Their Dominant Sourceregions, Pierre-Dominique Pautet, Michael J. Taylor, A. Z. Liu, G. R. Swenson

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The Darwin Area Wave Experiment (DAWEX) was designed to investigate the generation and propagation of gravity waves from intense regions of localized convection that occur regularly over northern Australia (in the vicinity of Darwin) during the premonsoon period. This multinational program was conducted during the austral spring 2001 using a range of coordinated optical, radar, and in situ balloon measurements. As part of this program, all-sky image observations of short-period gravity wave events in the near infrared OH nightglow emission (altitude ∼87 km) were made from two well-separated sites in northern Australia: Wyndham (15.5°S, 128.1°E) and Katherine (14.5°S, 132.3°E), over …

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Terdiurnal Wave Signatures In The Upper Mesospherictemperature And Their Association With The Wind Fields At Low-Latitudes (20°N), A. Taori, Michael J. Taylor, S. Franke Jan 2005

Terdiurnal Wave Signatures In The Upper Mesospherictemperature And Their Association With The Wind Fields At Low-Latitudes (20°N), A. Taori, Michael J. Taylor, S. Franke

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A novel investigation of terdiurnal (8-hour) oscillations in the mesosphere and lower-thermosphere temperature and wind field over Maui, Hawaii (20.8°N, 156.2°W) has been performed. Coincident observations using a mesospheric temperature mapper and a meteor wind radar were obtained since May 2002 as part of the Maui Mesosphere and Lower Thermosphere (Maui MALT) program to investigate the seasonal structure and dynamics of the low-latitude middle atmosphere. This study focuses on a 10-day period in July 2002 when a persistent ∼8-hour oscillation was identified in dual measurements of the OH (6,2) and O2 (0,1) nocturnal rotational temperatures sampled at nominal altitudes of …

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Comparison Of Simultaneous Na Lidar And Mesospherictemperature Mapper Measurements And The Effects Of Tides On The Emission Layer Heights, Y. Zhao, Michael J. Taylor, X. Chu Jan 2005

Comparison Of Simultaneous Na Lidar And Mesospherictemperature Mapper Measurements And The Effects Of Tides On The Emission Layer Heights, Y. Zhao, Michael J. Taylor, X. Chu

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A detailed comparative study of two new mesospheric temperature data sets, measured by different remote-sensing techniques, has been performed as part of a long-term investigation of low-latitude mesospheric dynamics. Coincident observations using the University of Illinois Na wind/temperature lidar and the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) were conducted from the summit of Haleakala Crater, Maui, Hawaii (20.8°N, 156.2°W, ∼3000 m) as part of the Maui-MALT program. High-quality joint measurements were obtained during four lidar campaign periods, and 16 nights of data, spanning the interval January 2002 to October 2003, are presented here as example observations during each …

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Importance Of Accurate Computation Of Secondary Electron Emission For Modelingspacecraft Charging, Sebastien Clerc, John R. Dennison Jan 2005

Importance Of Accurate Computation Of Secondary Electron Emission For Modelingspacecraft Charging, Sebastien Clerc, John R. Dennison

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The secondary electron yield is a critical process in establishing the charge balance in spacecraft charging and the subsequent determination of the equilibrium potential. Spacecraft charging codes use a parameterized expression for the secondary electron yield δ(Eo) as a function of incident electron energy, Eo. A critical step in accurately characterizing a particular spacecraft material is establishing the most efficient and accurate way to determine the fitting parameters in terms of the measured electron yield data and physics-based theoretical models. Simple two- or three- step physics models of the electron penetration, transport and emission from a solid are typically expressed …

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Evolution Of The Electron Yield Curves Of Insulators As A Function Ofimpinging Electron Fluence And Energy, Alec Sim, John R. Dennison, Clint Thomson Jan 2005

Evolution Of The Electron Yield Curves Of Insulators As A Function Ofimpinging Electron Fluence And Energy, Alec Sim, John R. Dennison, Clint Thomson

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Electron emission and concomitant charge accumulation near the surface of insulators is central to understanding spacecraft charging. We present a study of changes in electron emission yields as a result of internal charge build up due to electron dose. Evolution of total, backscattered and secondary yield results over a broad range of incident energies are presented for two representative insulators, KaptonTM and Al2O3. Reliable yield curves for un-charged insulators are measured and quantifiable changes in yields are observed due to fluences. We find excellent agreement with a phenomenological argument based on insulator charging predicted by …

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Universe Interactive: Static Displays With Active Components, Michelle B. Larson Jan 2005

Universe Interactive: Static Displays With Active Components, Michelle B. Larson

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As the World Year of Physics (WYP) approaches, the AAPT WYP Committee would like to encourage everyone to consider ways to engage those around us in celebrating the science that makes us the proud geeks we are. The geek sentiment is my own, and does not necessarily reflect the views and opinions of the committee. This paper offers simple and inexpensive astronomy-related ideas for a bulletin-board-type display. The particular ideas presented below are hands-on classroom activities that I've adapted for display purposes. The display is static in that once constructed it does not require a personal facilitator, but each component …

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Experimentally Derived Resistivity For Dielectric Samples From The Crres Internal Discharge Monitor, Nelson W. Green, A. Robb Frederickson, John R. Dennison Jan 2005

Experimentally Derived Resistivity For Dielectric Samples From The Crres Internal Discharge Monitor, Nelson W. Green, A. Robb Frederickson, John R. Dennison

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Resistivity values were experimentally determined using charge storage methods for six samples remaining from the construction of the Internal Discharge Monitor (IDM) flown on the Combined Release and Radiation Effects Satellite (CRRES). Three tests were performed over a period of four to five weeks each in a vacuum of ~5×10-6 torr with an average temperature of ~25 ºC to simulate a space environment. Samples tested included FR4, PTFE, and alumina with copper electrodes attached to one or more of the sample surfaces. FR4 circuit board material was found to have a dark current resistivity of ~1×1018 Ω-cm and a moderately …

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Measuring Charge Storage Decay Time And Resistivity Of Spacecraft Insulators, Jerilyn Brunson, John R. Dennison Jan 2005

Measuring Charge Storage Decay Time And Resistivity Of Spacecraft Insulators, Jerilyn Brunson, John R. Dennison

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An informal discussion of how accurate measurements of resistivity and increasing understanding of the behavior of insulating materials used on spacecraft is fundamental to advancing the design and utility of the spacecraft. Build up of charge can vary between different areas of the spacecraft, with excess charge accumulating and leading to functional anomalies or component failure. The most important parameter in determining how charge will decay through an insulator is the resistivity of the material. Current industry standards for measuring resistivity have been shown to be inconsistent with actual phenomena, and new methods of measuring resistivity must be developed and …

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