Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session B8: Atmospheric Physics |
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Chair: Pace VanDevender Room: MU224 |
Friday, October 16, 2015 10:50AM - 11:02AM |
B8.00001: High Speed Sprite Imaging Geoff McHarg, Hans Stenbaek-Nielsen Streamers observed in the middle atmosphere located above positive cloud to ground lightning strikes are referred to as sprites. Sprite streamers initiate between 70 and 80 km and are observed to propagate first downward and then sometimes upward, at speeds up to one-third the speed of light. We report on the use of high speed (up to 15,000 frames per second) imaging to resolve the structure, dynamics, and spectral content of the visible light emitted by sprites. We compare our observations to models developed of the initiation, propagation, splitting and brightness of sprite streamers. [Preview Abstract] |
Friday, October 16, 2015 11:02AM - 11:14AM |
B8.00002: Lightning Trends and ELVES Near the Pierre Auger Observatory Cody Doyle, David Grisham, Lawrence Wiencke Emissions of Light and Very low frequency perturbations due to Electromagnetic pulse Sources (ELVES), are transient luminous events that occur above some lightning storms. The fluorescence detectors at the Pierre Auger Observatory are well suited to detecting and characterizing this radiation. Data from the Lightning Imaging Sensor and World Wide Lightning Location Network were examined for temporal and spacial correlation to these events in an attempt to learn more about the characteristics of lightning that cause ELVES. While searching for causal events, many seasonal and geographic patterns in South American storm systems were uncovered. [Preview Abstract] |
Friday, October 16, 2015 11:14AM - 11:26AM |
B8.00003: Instrument to Measure Lightning Electric Fields Integrated with a Small Unmanned Aircraft Richard Sonnenfeld, Daniel Jensen, Graydon Aulich, Brian Argrow, James Mack For lightning research an unmanned aircraft (UAS) can provide rapid and reliable (compared to balloons), and safe (compared to manned craft) access to severe storms, hurricanes and tornados. Our first UAS project seeks to measure vector electric fields aloft from nearby lightning. Integration of an electric field sonde (Esonde) with a UAS required weight reduced from 6 to 2 pounds and diameter decrease from 6 to 2.5 inches (compared to our balloon-borne Esondes). A custom data system streaming 16-bits at 500 kSamples/s to SD cards aided this reduction. Four channels of induced charge are measured by electrodes on the streamlined Esonde pod now mounted atop a Tempest UAS airframe. $\vec{E}$-field is derived from linear combinations of charges induced on each of the four electrodes. The linear coefficients are calculated by solving $\nabla^2 \phi =0$ for $\phi$ and $\vec{E}$ on the Esonde geometry. For balloon-borne sondes, approximate analytical solutions exist for a long cylinder in a constant $\vec{E}$-field. In contrast, the airframe mere inches from the Esonde pod necessitates numerical simulations for Laplace's equation (using COMSOL). While we found the fiberglas airframe to be only half as disruptive as a metal aircraft would be, its effect is still significant. [Preview Abstract] |
Friday, October 16, 2015 11:26AM - 11:38AM |
B8.00004: Rapidly rotating flow in an oscillating split cylinder Paloma Gutierrez-Castillo, Juan M. Lopez The flow in a rapidly rotating cylinder is studied numerically via spectral methods. The cylinder of radius $a$ and length $h$ is completely filled with fluid of kinematic viscosity $\nu$. It is split in two at its half height, and the rapid rotation in the two halves is modulated periodically. The modulations set up thin oscillatory boundary layers on the endwalls and the sidewall. From the corners where endwalls and sidewall meet, as well as from the split in the two halves, inertial wave beams are emitted into the interior following the characteristic directions dictated by the dispersion relation. Due to finite viscosity and nonlinear flow conditions, the wave beams produce intricate patterns, formed by to constructive and destructive interferences as they self intersect, which vary with the modulation frequency. [Preview Abstract] |
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