Bulletin of the American Physical Society
Joint Meeting of the Four Corners and Texas Sections of the American Physical Society
Volume 61, Number 15
Friday–Saturday, October 21–22, 2016; Las Cruces, New Mexico
Session B1: Earth Systems Sciences |
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Chair: Rosa Fitzgerald, University of Texas, El Paso Room: Exhibit Hall 2 |
Friday, October 21, 2016 10:00AM - 10:24AM |
B1.00001: Why plate tectonics is rare and how it started on Earth Invited Speaker: Viatcheslav Solomatov Observations suggest that plate tectonics operates only on Earth. Theoretical studies point out that plate tectonics is difficult to start on any planet. A fundamental feature of plate tectonics is mechanical recycling of the lithosphere. Two major obstacles to this process include the formation of a buoyant crust and the high strength of relatively cold rocks near the surface. Both factors prevent mechanical recycling of the lithosphere. In principle, both the buoyancy and the strength of the lithosphere can be overcome by sufficiently large forces. A giant impact or a superplume can provide such forces but they are of relatively short duration. It is unclear how they can produce a long-lived plate tectonics. Forces that are readily available such as those associated with mantle convection are insufficient to initiate plate tectonics. One of the key limitations of the current models is that they consider a solid or nearly solid planet. The difficulties for plate tectonics initiation on a completely solidified planet lead to a hypothesis that on Earth plate tectonics may have started during the magma ocean epoch, at the end of planetary accretion. According to this hypothesis, plate tectonics is a continuation of convection in the magma ocean. [Preview Abstract] |
Friday, October 21, 2016 10:24AM - 10:36AM |
B1.00002: Using Seismic Amplitude Data to determine Crustal Seismic Attenuation Structure beneath China Thomas Hearn Seismic amplitude data can be directly measured to look at regional attenuation. I used amplitude data from the dense China network that were originally collected for magnitude measurements. These measured amplitudes are generally from the Lg and Sg seismic phases and are dominated by shear-waves. Frequency dependent exponential models are used. The tomography problem inverts for regional geometric spreading, station gains, source corrections as well as the varying attenuation. Using the log-amplitude of the amplitudes linearizes the problem, corrects the non-Gaussian noise back to Gaussian, and gives images of higher quality than that obtained from travel time data. Results show grabens and basins have high attenuation with Q values near 100. Crystalline surface rocks typically show low attenuation with Q values near 1000. Low Q values along the edge of the Tibetan Plateau may be due to phase blockage occurring as a result of the rapid change in crustal thickness. [Preview Abstract] |
Friday, October 21, 2016 10:36AM - 10:48AM |
B1.00003: Regional seismic wave attenuation in Northeast China Nishath Ranasinghe, Thomas Hearn, Andrea Gallesgos, James Ni, Eric Sandvol Study of regional seismic wave attenuation is an important aspect of global nuclear explosion monitoring and yield estimation. We studied, Pg and Lg seismic wave attenuation in Northeast (NE) China utilizing seismic data collected from 452 earthquakes that were recorded primarily by Northeast China Extended Seismic (NECESS) Array. A Pg attenuation map with an average Q$_{\mathrm{0}}$ of 299 was created at a central frequency of 1 Hz by implementing the Two Station Method (TSM). We observe low Pg Q$_{\mathrm{0}}$ values (\textless 400) in the majority of areas in NE china except in the central parts of the Songliao Basin and Great Xing'an Range. Lg attenuation is studied by implementing both TSM and Reverse Two Station Method (RTSM) at central frequencies of 0.5, 1, 2 and 3 Hz. Although both methods show similar frequency dependent factors ($\eta )$, RTSM method consistently shows higher Lg Q$_{\mathrm{0}}$ values compared to TSM. We observe most of the sedimentary basins in NE china show low Lg Q$_{\mathrm{0}}$ values (\textless 400) while granitic mountain ranges consistently show high Lg Q$_{\mathrm{0}}$ values (\textgreater 800). [Preview Abstract] |
Friday, October 21, 2016 10:48AM - 11:00AM |
B1.00004: Behind the Rapid Intensification of Hurricane Patricia, the Strongest Recorded Hurricane in History K. Ryder Fox, Falko Judt In October of 2015, Hurricane Patricia stormed through the eastern Pacific, becoming the strongest recorded hurricane in history. Within a twenty-four hour period, Patricia's maximum wind speed increased by 105 kt, while the sea level pressure decreased by 95 hPa. Operational weather prediction models failed to accurately forecast this intensity evolution, provoking questions about the factors behind this unparalleled case of hurricane rapid intensification.~ In this study, a high resolution numerical weather prediction model (WRF) was employed to simulate Hurricane Patricia. Analysis of the WRF model fields demonstrated that environmental variables such as vertical wind shear, sea surface temperature, and relative humidity were extremely favorable for intensification. Patricia's environmental conditions were compared with corresponding quantities from a 30$+$ year climatology of hurricanes in the Eastern Pacific, revealing that sea surface temperature and relative humidity values fell into the 99th percentile. This indicates that the storm environment played a substantial role in Patricia's intensity. It additionally suggests that potential future cases of extreme rapid intensification can be predicted if models are able to capture the environmental conditions. [Preview Abstract] |
Friday, October 21, 2016 11:00AM - 11:12AM |
B1.00005: Study of Photolysis Rate Coefficients to Improve Air Quality Models Suhail Mahmud, Pema Wangchuk, Rosa Fitzgerald, William Stockwell The main objective of this work is to measure hemi-spherically integrated spectrally resolved solar photon flux between the wavelengths of 300 and 700 nm (actinic flux), and use the measured actinic flux to improve air quality simulations. Photolysis is the main driver of ozone production and this factor defines the significance of this research work. The actinic flux has been measured during the summer of 2015 in the El Paso-Juarez Airshed, at the UTEP location to calculate photolysis rate coefficients for nitrogen dioxide (NO2), ozone (O3) and formaldehyde (HCHO). The improved photolysis rate coefficients have been integrated into a photochemical airquality model (CAMx), and simulations for a selected modeling summer 2015 ozone episode have been performed in the El Paso-Juarez Airshed in an attempt to improve on air quality forecasting. We present inter-comparison results of the ozone concentrations using the standard photolysis rate coefficients and the modified photolysis rate coefficients. Although this novel methodology is applied in the El Paso-Juarez Airshed, it can be used in any US region. [Preview Abstract] |
Friday, October 21, 2016 11:12AM - 11:24AM |
B1.00006: What is lightning channel conditioning? Richard Sonnenfeld, Hugh Christian, Daniel Walker A cloud-to-ground lightning flash can last as much as a second and consist of one to 20 return strokes. Some return strokes retrace channels first created by earlier strokes. The leader for an initial channel is called a stepped leader and has a propagation velocity of $\simeq5\times10^5$ m/s. If another leader retraces that channel within 100 ms, it progresses much more rapidly, up to $\simeq1\times10^8$ m/s. It is said that the difference between a stepped leader and a dart leader is that the dart leader proceeds on a channel which has been ``conditioned'', by the prior stepped leader. What is conditioning? One might assume that the channel is still hot and thus has a high population of free electrons. Radar studies by Holmes that averaged over tens of km of space found electron recombination time constants of 3--20 ms. Spectroscopic studies have also suggested channel cooling times in the millisecond range. How then, can a dart leader occur 100 ms after a stepped leader? One idea is that the free electrons recombine with Oxygen atoms creating a temporary population of ${O_2}^-$ ions. The ionization potential of ${O_2}^-$ is less than 1.5 eV, compared to 12 eV for $O_2$. Thus, conditioning is perhaps a "chemical" rather than a thermal process. [Preview Abstract] |
Friday, October 21, 2016 11:24AM - 11:36AM |
B1.00007: Plasma Deflection Test Setup for E-Sail Propulsion Concept Allen Andersen, Jason Vaughn, Todd Schneider, Ken Wright The Electronic Sail or E-Sail is a novel propulsion concept based on momentum exchange between fast solar wind protons and the plasma sheath of long positively charged conductors comprising the E-Sail. The effective sail area increases with decreasing plasma density allowing an E-Sail craft to continue to accelerate at predicted ranges well beyond the capabilities of existing electronic or chemical propulsion spacecraft. While negatively charged conductors in plasmas have been extensively studied and flown, the interaction between plasma and a positively charged conductor is not well studied. We present a plasma deflection test method using a differential ion flux probe (DIFP). The DIFP measures the angle and energy of incident ions. The plasma sheath around a charged body can measured by comparing the angular distribution of ions with and without a positively charged test body. These test results will be used to evaluate numerical calculations of expected thrust per unit length of conductor in the solar wind plasma. [Preview Abstract] |
Friday, October 21, 2016 11:36AM - 11:48AM |
B1.00008: Ionospheric neutron content analyzer Juan Treto The Ionospheric Neutron Content Analyzer (INCA) is a 3U CubeSat being built by New Mexico State University students. INCA will study the latitude and time dependencies of the neutron spectrum in low earth orbit (LEO) for the first time. INCA will carry a directional neutron detector, developed by NASA's Goddard Space Flight Center and the University of New Hampshire. INCA's focus are albedo neutrons and solar neutrons. Albedo neutrons are produced by high energy particles interacting with the Earth’s ionosphere, and can cause single-event upsets in electronics. Albedo neutrons decay, within 15 minutes, into protons and electrons, which are then trapped in the Earth's magnetic field. Cosmic rays, solar flares, and coronal mass ejections all contribute to albedo neutron formation. INCA will also chart solar neutron flux relative to solar activity. This will let us extrapolate information about their subsequent air shower effects in earth’s atmosphere. Direct solar neutrons are a component of solar wind, which allows us to learn about how and where they are accelerated. The data gathered by a directional instrument on a low-mass platform will provide data that can significantly improve our understanding of space weather and the formation of Earth's radiation belts. [Preview Abstract] |
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