Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session B1: Earth Science and Atmospheric Physics |
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Chair: Rosa Fitzgerald, The University of Texas at El Paso Room: Union East, 3rd Floor Templeton |
Friday, October 17, 2008 10:30AM - 10:54AM |
B1.00001: Earthquake Amplitudes and Crustal Attenuation in Asia and the Globe Invited Speaker: Seismic amplitudes are routinely measured for the estimation of earthquake magnitude. These data can also be used to interrogate the Earth's attenuation structure using seismic amplitude tomography. Amplitude tomography produces maps of crustal attenuation and is similar to conventional seismic travel time tomography, which maps velocity variations. Seismic amplitudes are influenced by source size, geometrical raypath spreading, attenuation due to intrinsic absorption and scattering, and station site gain. These effects are all included in the tomographic inverse problem and applied to data from Asia and the Globe. Data are from the Chinese National Seismic Network and one international data set from the International Seismological Center. The Chinese data cover most of China. They are measurements for the ML and MS magnitude scales and represent the amplitudes of body-waves traveling through the crust and short-period surface waves guided through the top five to ten kilometers of crust. The body-waves geometrically spread at a super-spherical rate rather than the expected cylindrical spreading. The high rate of geometric spreading is due to the effects of dispersion and leakage from the crust into the uppermost mantle. Surface waves spread in a cylindrical manner as predicted by theory. Dispersion has little effect on their amplitudes. Station site gains and corrections to the event magnitudes are small for both the inversions. Regional seismic attenuation variations are associated with the ocean-continent transition and surface rock type. The water layer creates high attenuation. Crystalline intrusive or volcanic rocks show little attenuation while active basin and fold belts show high attenuation. Data from the International Seismological Centre are from long-period surface waves that cover most of the planet. They are primarily influenced by attenuation structure in the crust but little affected by crustal thickness. As with the Chinese surface wave data, they show nearly perfect cylindrical spreading and relatively small station site gains. High seismic attenuation occurs in subduction zones, ocean ridges, and sediments. Cratons and igneous terrains have little attenuation. [Preview Abstract] |
Friday, October 17, 2008 10:54AM - 11:18AM |
B1.00002: Understanding Charge Transport by Lightning Invited Speaker: The primary thing that a lightning flash does is move a roughly 10~C charge from one place to another. While the charge structure of a thundercloud is increasingly well understood, the actual transport of charge by a flash is crudely understood. To make progress in this area we developed a new instrument, the electric field sonde (or Esonde) which measures, at tens of kSamples/second, the vector electric field development during a lightning flash. This instrument flies into storms, allowing it to get closer than a ground-based instrument to a lightning leader. It can also sense the full vector-nature of the electric field. The measurement of E-field change in the frequency band up to 100~kHz can in principle measure how charges are transported by a lightning flash. The problem with interpreting such measurements is the ``inverse problem,'' of mapping measured E-fields to generating charge distributions. A new technology, the lightning mapping array (LMA) now provides a 3-D, time-resolved, measurement of the location of a lightning channel in the clouds. By combining measurement of electric-field change in the clouds simultaneous with the LMA radio-frequency data on the lightning channel development, we can draw new conclusions about lightning and charge. In our first analyzed storm, we could see negative charge being deposited on the developing leader, as well as the effects of the positive charge center supplying this charge. We also reproduced by new means the findings of Krehbiel, et al. that in a multi-stroke cloud-to-ground flash, the charge for subsequent strokes draws on untapped pockets of charge ever further from the location of the cloud-to-ground channel. We are in the process of augmenting our balloon-borne Esonde and LMA with a networked array of field-change stations surrounding the Langmuir Laboratory for Atmospheric Research in central New Mexico. [Preview Abstract] |
Friday, October 17, 2008 11:18AM - 11:30AM |
B1.00003: Analytic representations of high-altitude auroral H$^{+}$ and O$^{+}$ densities, flow velocities and temperatures in terms of drivers for incorporation into global magnetospheric models James Horwitz, Wen Zeng As new methods of describing multiple fluid species and other advances enhance the capability of global magnetospheric models to simulate the dynamics of multiple ion species, they also allow more accurate incorporation of ionospheric plasma outflows as source populations into these large scale models. Here, we shall describe the distilled results of numerous physics-based simulations of ionospheric plasma outflows influenced by auroral driving agents in terms of compact analytic expressions in terms of precipitation electron energy flux levels, characteristic energy levels of the precipitating electrons, the peak spectral wave densities for low-frequency electrostatic waves which transversely heat ionospheric ions, and solar zenith angle. The simulations are conducted with the UT Arlington Dynamic Fluid Kinetic (DyFK) ionospheric plasma transport code. We present these analytic expressions for ionospheric origin O$^{+}$ and H$^{+}$ densities, temperatures and field-aligned flow velocities at the 3 R$_{E}$ altitude inner boundaries of typical magnetospheric models. [Preview Abstract] |
Friday, October 17, 2008 11:30AM - 11:42AM |
B1.00004: The interplay of Alfv\'{e}n waves and energized electrons with auroral ionospheric plasma James Horwitz, Fajer Jaafari, Sam Jones, Yi-Jiun Su, Wen Zeng Replace this text with your abstract body. Alfv\'{e}n waves propagating along magnetic field lines in the auroral ionosphere-magnetosphere system involve parallel electric fields which can accelerate auroral electrons. Here, we examine the propagation of Alfv\'{e}n waves within O$^{+}$ and H$^{+}$ auroral ionosphere-magnetosphere density profiles from the UT Arlington Dynamic Fluid-Kinetic (DyFK) ionospheric plasma transport model, and explore the energization of Alfv\'{e}nic electrons and their effects on the ionosphere-magnetosphere plasma system. A linear one dimensional gyrofluid code is used for the Alfv\'{e}n wave description, incorporating electron inertia, electron pressure gradient and finite ion gyroradius effects. This allows determination of the characteristics of the propagating Alfv\'{e}n waves which generate the inertial parallel electric field responsible for energizing electrons. Using a test particle we simulate the response of a distribution of electrons to these Alfv\'{e}n wave electric fields. These electrons are incorporated into the DyFK model to produce the associated ionization and thermal electron heating. [Preview Abstract] |
Friday, October 17, 2008 11:42AM - 11:54AM |
B1.00005: Plasmasphere Plume-associated Storm-Enhanced Densities (SED) as Suppliers of Ionospheric Outflows to the Magnetosphere James Horwitz, Wen Zeng, John Foster, Robert Strangeway, Mark Adrian, Thomas Moore Elevated ionospheric density regions which evidently have been convected from the subauroral plasmaspheric region toward the noon sector cleft ionosphere have been reported. Here, the possibility that these so-called Storm Enhanced Density (SED) regions could serve as ionospheric plasma source populations for cleft ion fountain outflows is explored. The UT Arlington Dynamic Fluid Kinetic (DyFK) code is employed to simulate the entry of a high-density ``plasmasphere-like'' flux tube entering the cleft region and subjected to an episode of wave-driven transverse ion heating. Initial comparisons of these modeling results with SED-outflow-plasmasphere plume observations will also be presented. [Preview Abstract] |
Friday, October 17, 2008 11:54AM - 12:06PM |
B1.00006: Spectroscopic Distance Measurements of Atmospheric Continuum Light Sources (e. g. Marfa lights) Sagar Ghimire, Karl Stephan Our research is based on data we collected during a 20-night investigation of a phenomenon known as ``Marfa lights'' using a Schmidt-Cassegrain telescope and a CCD-array spectrometer. Although no objects we sighted met all the criteria of ``true'' Marfa lights, we collected spectra of headlights at different locations, some of which could have been false positives for a light of unknown origin. Spectroscopic analysis of the visible oxygen absorption band near 13121 per cm (760 nm) was used to estimate distances to headlights, which emit a continuum spectrum. Comparisons of spectroscopic distance data with independent geographical information system (GIS) distance data shows that distance estimates obtained with spectroscopy agree within +/- 1.4 KM or better for distances greater than 4 KM. The technique adopted involves computation of the experimental transmittance function and the expected transmission function for the 760 nm band. The RMS error between these two transmission functions is computed over various distances, and the minimum-error distance gives us the best estimate of the actual distance. [Preview Abstract] |
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