Bulletin of the American Physical Society
2019 Annual Meeting of the APS Four Corners Section
Volume 64, Number 16
Friday–Saturday, October 11–12, 2019; Prescott, Arizona
Session L02: Atmospheric Physics / Geophysics |
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Chair: Stacy Palen, Weber State University Room: AC1 115 |
Saturday, October 12, 2019 11:00AM - 11:24AM |
L02.00001: Simple Physics Explains a Common Temperature Minimum in Thick Atmospheres of Planets and Large Moons Invited Speaker: Tyler Robinson Atmospheric temperature minima are fundamental for understanding many planetary processes. Inversions in the upper atmospheres of Earth, Jupiter, Saturn, Titan, Uranus, and Neptune lead to temperature minima that, remarkably, all occur near 0.1 bar, despite very different radiation environment, atmospheric composition, gravity, and internal heat flux. We examined the atmospheric thermal structure of these worlds with an analytic 1-D radiative-convective model, which assumes gray thermal transfer of radiation. We find that tropopause temperature minima always lie in the radiative regime, above the radiative-convective boundary. Thus, the shared 0.1 bar tropopause arises from the common physics of infrared radiative transfer. Our findings imply that the common 0.1 bar tropopause levels seen in the solar system atmospheres are more universal. Thus, we hypothesize that many worlds orbiting other stars (exoplanets) will possess a 0.1 bar tropopause temperature minimum. [Preview Abstract] |
Saturday, October 12, 2019 11:24AM - 11:48AM |
L02.00002: Seismic evidence for long-lived elevated temperatures beneath Earth’s mantle transition zone Invited Speaker: Lauren Waszek The Earth’s mantle comprises a series of discontinuities that result from mineralogical phase transitions as pressure and temperature increase with depth. Global discontinuities at 410-km and 660-km depth delimit the mantle transition zone (MTZ). In conjunction with seismic tomography models, properties of the MTZ help quantify regional thermochemical variations, to constrain mass and heat fluxes between the upper and lower mantle. While both discontinuities are detected in precursors to the mantle shear phase SS, the ‘660’ is typically absent for the compressional equivalent, PP. Notably, the 660 transition selectively impedes up and downwelling flow. Here, we reveal from mineralogical modelling that a visible P660P corresponds to a dominant garnet transition at temperatures >1800 K; geodynamically, this promotes flow through the MTZ. We use comprehensive datasets of SS and PP precursors and a refined stacking approach based on Voronoi tessellations to generate global observations. We show that high temperatures, and hence efficient transportation through the MTZ, occur in only a small fraction (~0.6\%) of the globe. Broad regions of long-lived elevated temperature beneath the Pacific are consistent with impeded mantle upwellings, with implications for surface volcanism. [Preview Abstract] |
Saturday, October 12, 2019 11:48AM - 12:00PM |
L02.00003: Topology of Earth's Magnetic Shield: Modeled Properties and Applications David Smith, Jan Sojka The open-closed boundary (OCB) defines the region where geomagnetic field lines transition from being closed to open. A closed field line has both foot points at or near Earth in opposing hemispheres. An open field line has one foot point at Earth while the other maps to the interplanetary magnetic field (IMF). Charged particles are able to follow these open field lines into Earth's upper atmosphere. The altitude to which these charged particles penetrate is a function of particle energy and latitude and is known as the energy cutoff latitude (CL). Given sufficient energy, these charged particles may reach the D-region of the ionosphere (about 100 km), causing increased absorption of HF radio signals, especially over polar regions. So-called polar cap absorption (PCA) events can, therefore, wreak havoc on HF communications near the polar cap boundary. It has been estimated that in excess of 7000 transpolar commercial flights occur each year. Hence, it is an important public safety issue that reliable means exist to anticipate HF communication conditions. Using the Tsyganenko model of the geomagnetic field (T96) we were able to show that the OCB experiences a UT-dependent variation. We are now prepared to demonstrate that this same UT-effect is inherent in the CL. Understanding this UT-dependent variability is critical to being able to accurately model HF communications disruptions due to PCA events. [Preview Abstract] |
Saturday, October 12, 2019 12:00PM - 12:12PM |
L02.00004: Prediction of Seismic Wave Arrivals Using a Convolutional Neural Network Jorge Garcia, Lauren Waszek Seismology uses energy from earthquakes to image the deep interior of Earth. Large amounts of seismic data are required in order to obtain detailed observations of the its internal structure; typical datasets comprise over 100,000 seismic records. With the exception of some basic processing methods, compilation of the data is performed by hand using simple visualization software. The most significant and time-consuming task is the identification and picking of seismic phases. Previous attempts at automating this procedure involve algorithms that generally underperform compared to a human expert. However, even among human-compiled datasets, consistency of phase arrival across and within datasets is a problem. The variation in decisions results in disagreement between obtained images, and subsequent interpretation of Earth’s structure and processes. We employ a Convolutional Neural Network (CNN) to predict the arrival time of the mantle shear-wave phases in a seismogram in an effort to accelerate and make consistent the task of data processing. We expand on this by implementing a committee of multiple CNNs to predict both the correct arrival time and the polarity of an arriving seismic phase. We compare the results obtained from the model to those of an experienced seismologist. [Preview Abstract] |
Saturday, October 12, 2019 12:12PM - 12:24PM |
L02.00005: A new regional seismic velocity model of the inner core beneath the Pacific Ocean Rashni Anandawansha, Lauren Waszek Despite the inner core's relatively small size, it plays an important role in governing Earth's dynamics. Seismically, the inner core is characterized by complex features; the dominant structures being an east-west asymmetry in seismic velocity and attenuation, and cylindrical anisotropy, with various regional differences. Origin(s) of these features of is still unknown. Anisotropy appears weak at the inner core boundary, but stronger at depths; this also varies on regional length scales. The structure of the inner core is not well constrained at depths of 0 -- 15 km, and 100 - 200 km beneath the inner core boundary. This is because several seismic waves arrive at the same time and interfere. In order to separate and identify the phases, we use a combination of array stacking techniques and synthetic seismogram modeling. We extract the arrival times of several P waves which travel in similar paths through the mantle. Consequently, the measured arrival times then allow us to explore the seismic velocity structure. We initially focus on the region in the vicinity of the hemisphere boundary beneath the Pacific Ocean, which has previously been observed to display complicated lateral variations. Our results will allow us to better constrain the evolution of the hemispheres and anisotropy with depth and hence over time. [Preview Abstract] |
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