Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session C5: Atmospheric Physics I |
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Chair: Sonja Behnke, New Mexico Institute of Mining and Technology Room: Macey Center Agora |
Friday, October 26, 2012 1:15PM - 1:27PM |
C5.00001: High-time-resolution Imaging of Lightning with the Long Wavelength Array Jacob M. Hartman, Richard Sonnenfeld, Bill Rison The first station of the Long Wavelength Array (LWA1), located in central New Mexico, is a 10--87~MHz radio telescope composed of 258 electronically steerable crossed-dipole antennas. The LWA1 includes a software correlator capable of imaging the full sky in real time with a five second cadence, or offline with cadences as short as a few milliseconds. Although designed to detect astronomical transients, we serendipitously discovered that this all-sky imager also images lightning. With a 5~ms frame rate, it can resolve the motion of leaders during intracloud flashes. In conjunction with the existing lightning observatories around the nearby Langmuir Laboratory, the LWA1 may also reveal previously undetectable properties of channel formation or current flow in intracloud lightning channels. Looking forward, this work represents a promising new observational technology when applied to lightning research. It suggests that future radio telescopes such as the Square Kilometer Array should be designed with this additional capability in mind. [Preview Abstract] |
Friday, October 26, 2012 1:27PM - 1:39PM |
C5.00002: Turbulence Measurement at the Very Large Array Keith Morris, Bryan Butler, Richard Sonnenfeld The effects of Earth's atmosphere on the quality of seeing in optical astronomy are well known, but radio astronomy also suffers from atmospheric interference. As radio waves travel through the troposphere, their speed and direction vary due to fluctuations in refractive index, largely caused by fluctuations in water vapor content. To quantify this interference, the Atmospheric Phase Interferometer (API) measures the RMS phase difference of a geosynchronous satellite beacon at two dedicated antennas. The Very Large Array (VLA) uses this information, plus wind speed, to schedule observations during optimal seeing conditions. The API measures along a single 300m, mostly E-W baseline. To the extent that the turbulence is shear-driven, there is believed to be direction dependence to this measurement. The phase time series can be used to determine the refractive index structure function for the local atmosphere, but only in the direction of that baseline. An upgraded API system, under development, will provide two-dimensional measurements, at lengths up to 813m, spanning the N-S/E-W plane. This paper seeks to establish the correspondence between surface atmospheric parameters and measured phase instability, and investigate what we will expect from the upgraded system. [Preview Abstract] |
Friday, October 26, 2012 1:39PM - 1:51PM |
C5.00003: Feasibility of Using Integrated Cavity Output Spectroscopy (ICOS) for Laser Scattering Research Emily Sotelo ICOS is proving to be a successful method for accurately measuring the atmospheric absorbance of a laser beam in a simulated environment. It was hypothesized that ICOS could be sensitive enough to accurately measure Rayleigh scattering. If feasible, it would mean that instead of having to conduct open range propagation experiments, scattering losses could be determined using a small, controlled test bed. This would be advantageous because it is cumbersome to propagate a laser beam a long distance in open space, as most other methods require. This study, done by Emily Sotelo as a student intern at the Air Force Research Laboratory, will be applied to the ongoing research of the scalability potential of the DPAL laser. [Preview Abstract] |
Friday, October 26, 2012 1:51PM - 2:15PM |
C5.00004: New developments in geostrophic turbulence and its implications for climate modeling and weather predictability Invited Speaker: Joseph Tribbia One of the many areas in geophysical fluid dynamics that impacts how we model dissipation in the climate system is the theory of two-dimensional and quasi geostrophic turbulence and its impact on atmospheric flow. Upscale energy and and down scale enstrophy cascades have been observed in the atmosphere along with the -3 power law predicted in two-dimensional turbulence theory put forward by Batchelor and Kraichnan in the late 1960s. A consequence of this observational finding is the fact that, unlike three-dimensional turbulence in which the eddy turnover time decreases with eddy length scale, in two dimensional and quasi-geostrophic turbulence the eddy turnover time is constant independent of eddy length scale in the enstrophy cascading range. A further consequence of this is that the Rossby number is constant through the enstrophy cascade. This implies that instabilities which depend on ageostrophic processes are restricted because the scaling laws which imply balanced, quasi-geostrophic dynamics are valid at all length scales. Recent results show, however, even given that all of the above statements are true and maintained in the dynamics, there is a mechanism through which quasi-geostrophic turbulence becomes inconsistent and develops the seeds of its own destruction at small scales. [Preview Abstract] |
Friday, October 26, 2012 2:15PM - 2:27PM |
C5.00005: Intracloud Lightning Flashes Can Be Similar in Detail Richard Sonnenfeld, William Winn, Gaopeng Lu, Harald Edens, Steven Hunyady, Jeff Lapierre The unpredictable shape of the channel from cloud to ground in lightning is well known. However, when we mapped repeated intra-cloud (IC) lightning flashes, we in some cases see a repeatable path over 15 minutes. A storm, on 8/18/2004 near Langmuir Lab in New Mexico, spawned six flashes between 19:52:30 and 20:06:41 UTC exhibiting remarkable similarity. When corrected for winds (i.e., when shown in a coordinate system relative to their air-parcel) all flashes originated within a roughly 1~km radius. We introduce ``lightning nursery'' to describe these fecund regions of atmosphere. The first three of these flashes were the most similar. They formed branching structures roughly 30~km in size in which the branches coincided with each other over substantial lengths to a precision of a kilometer. Several conclusions can be drawn from this. 1) When the pre-flash electric field is sufficiently strong, the distribution of charge in a thunderstorm completely determines the path of the flash, over tens of kilometers. 2) Over a period of a couple of minutes, a storm recharges itself to a very similar configuration. 3) This observation validates the use of lightning mapping techniques to deduce the charge structure of storms not just as layers, but as 3-dimensional forms. [Preview Abstract] |
Friday, October 26, 2012 2:27PM - 2:39PM |
C5.00006: Combined Current Measurements and Lightning Mapping Array Observations of Rocket-Triggered Lightning at Langmuir Lab Jacob Trueblood Over the 2011 storm season at Langmuir Lab, several rocket-triggered lightning flashes were observed by Langmuir's Lightning Mapping Array (LMA) and by current viewing resistors (CVR). The LMA data allows us to calculate the velocity of the positive leaders from the flashes. The CVR is attached to the wire that is towed behind the rocket allowing us to measure the current at the base of the lightning flash. We are able to compare the current measurements and velocity calculations from the LMA data to provide insights into stages of a triggered flash. We discuss one flash from August 11 as a case study, were we found positive leader velocities to range from 1.4 to 2.4x10$^{4}$ m s$^{-1}$ The faster speeds were found during the initial continuous current (ICC). [Preview Abstract] |
Friday, October 26, 2012 2:39PM - 2:51PM |
C5.00007: Analysis of Electric Field Change, Interferometric, and Lightning Mapping Data to Study Intra-Cloud Lightning Jeff Lapierre, Mike Stock, Manabu Akita, Richard Sonnenfeld, Paul Krehbiel, William Rison, Zen Kawasaki, Harald Edens While return stroke and leader waveforms are increasingly well understood in cloud-to-ground flashes, the precise origin of recoil leaders, K-changes, and M-components remains uncertain. Also, the structure of the electric field change from intra-cloud flashes remains poorly understood. Considerable progress has been made via comparing electric field data to Lightning Mapping Array (LMA) data (Winn et al. 2011), but the fast changes in electric field, such as K-changes, are only coarsely resolved in LMA data. In order to better resolve such fast electric field changes, we used the recently upgraded Continuous Broadband Digital Interferometer (Continuous DITF) in unison with the Langmuir Electric Field Array (LEFA) and the LMA to better understand the sharp features in electric field waveforms. The LMA provides 3D localization of sources detected by the Continuous DITF and, when synchronized with LEFA data, reveals how charges move during a flash. Features in the electric field corresponding to recoil leaders in intra-cloud flashes have already been detected, and we expect continued studies will allow us to investigate recoil leaders, K-changes, and M-components. Winn, W. P., G. D. Aulich, S. J. Hunyady, K. B. Eack, H. E. Edens, P. R. Krehbiel, W. Rison, and R. G. Sonnenfeld (2011), Lightning leader stepping, K changes, and other observations near an intracloud flash, \textit{J. Geophys. Res.}, 116, D23115, doi:10.1029/2011JD015998. [Preview Abstract] |
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