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  • 1
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    Diffusion model for lightning radiative transfer (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A one-speed Boltzmann transport theory, with diffusion approximations, is applied to study the radiative transfer properties of lightning in optically thick thunderclouds. Near-infrared (lambda = 0.7774 micrometers) photons associated with a prominent oxygen emission triplet in the lightning spectrum are considered. Transient and spatially complex lightning radiation sources are placed inside a rectangular parallelepiped thundercloud geometry and the effects of multiple scattering are studied. The cloud is assumed to be composed of a homogeneous collection of identical spherical water droplets, each droplet a nearly conservative, anisotropic scatterer. Conceptually, we treat the thundercloud like a nuclear reactor, with photons replaced by neutrons, and utilize standard one-speed neutron diffusion techniques common in nuclear reactor analyses. Valid analytic results for the intensity distribution (expanded in spherical harmonics) are obtained for regions sufficiently far from sources. Model estimates of the arrival-time delay and pulse width broadening of lightning signals radiated from within the cloud are determined and the results are in good agreement with both experimental data and previous Monte Carlo estimates. Additional model studies of this kind will be used to study the general information content of cloud top lightning radiation signatures.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; D7; p. 14,361-14,371
    Format: text
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  • 2
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    Aircraft electric field measurements: Calibration and ambient field retrieval (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An aircraft locally distorts the ambient thundercloud electric field. In order to determine the field in the absence of the aircraft, an aircraft calibration is required. In this work a matrix inversion method is introduced for calibrating an aircraft equipped with four or more electric field sensors and a high-voltage corona point that is capable of charging the aircraft. An analytic, closed form solution for the estimate of a (3 x 3) aircraft calibration matrix is derived, and an absolute calibration experiment is used to improve the relative magnitudes of the elements of this matrix. To demonstrate the calibration procedure, we analyze actual calibration date derived from a Lear jet 28/29 that was equipped with five shutter-type field mill sensors (each with sensitivities of better than 1 V/m) located on the top, bottom, port, starboard, and aft positions. As a test of the calibration method, we analyze computer-simulated calibration data (derived from known aircraft and ambient fields) and explicitly determine the errors involved in deriving the variety of calibration matrices. We extend our formalism to arrive at an analytic solution for the ambient field, and again carry all errors explicitly.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; D11; p. 22,781-22,792
    Format: text
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  • 3
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    Analysis of lightning field changes produced by Florida thunderstorms (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new method is introduced for inferring the charges deposited in a lightning flash. Lightning-caused field changes (delta E's) are described by a more general volume charge distribution than is defined on a large cartesian grid system centered above the measuring networks. It is shown that a linear system of equations can be used to relate delta E's at the ground to the values of charge on this grid. It is possible to apply more general physical constraints to the charge solutions, and it is possible to access the information content of the delta E data. Computer-simulated delta E inversions show that the location and symmetry of the charge retrievals are usually consistent with the known test sources.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-TM-103539 , NAS 1.15:103539
    Format: application/pdf
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  • 4
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    A linear method for analyzing lightning field changes (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A constrained, least-squares method for analyzing multiple-station measurements of lightning field changes (delta Es) is introduced. Previous methods have attempted to fit the spatial pattern of lightning delta Es using nonlinear models, such as a point charge (Q) or a point dipole (P) model. With the linear method, the delta Es are described not by models but by a general volume charge distribution that is deposited on a large (40 x 40 x 20 cu km) Cartesian grid above the measuring network. A linear system of equations is used to relate the measured delta Es to the charges that are deposited at each grid point. With this approach, the information content of the measurements can be quantified by an eigenanalysis of the covariance matrix of the linear system. Constraints can be used to reduce the infinity of possible solutions to the linear system and also to reduce systematic biases that can be introduced by the method of solution. It is shown that a Landweber iterative method, derived from the general method of steepest descent, can be used to solve the linear system and that the resulting volume charge distributions are generally consistent with computer-simulated charge sources, when these sources are over the measuring network. The Landweber iteration has also provided solutions for natural lightning events that are consistent with Q- and P-model results.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 51; 4; p. 473-488
    Format: text
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  • 5
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    Analysis of lightning field changes during active Florida thunderstorms (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A computer algorithm for deriving accurate values of lightning-caused changes in cloud electric fields under active storm conditions was developed and applied to data obtained during two thunderstorms from a network of ground-based electric field mills at the NASA Kennedy Space Center and the Cape Canaveral Air Force Station. The resulting field changes were analyzed using a least-squares optimization procedure and point-charge (Q) and point-dipole (P) models. The values and the time variations of the Q-model parameters under active storm conditions were found to be similar to those reported by Maier and Krider (1986) for small storms, when the computations were carried out with the same analysis criteria and comparable biases. The parameters of the P solutions were found to vary with time within the storm interval and from storm to storm.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 1165-118
    Format: text
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  • 6
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    Time-averaged current analysis of a thunderstorm using ground-based measurements (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The amount of upward current provided to the ionosphere by a thunderstorm that appeared over the Kennedy Space Center (KSC) on July 11, 1978, is reexamined using an analytic equation that describes a bipolar thunderstorm's current contribution to the global circuit in terms of its generator current, lightning currents, the altitudes of its charge centers, and the conductivity profile of the atmosphere. Ground-based measurements, which were obtained from a network of electric field mills positioned at various distances from the thunderstorm, were used to characterize the electrical activity inside the thundercloud. The location of the lightning discharges, the type of lightning, and the amount of charge neutralized during this thunderstorm were computed through a least squares inversion of the measured changes in the electric fields following each lightning discharge. These measurements provided the information necessary to implement the analytic equation, and consequently, a time-averaged estimate of this thunderstorm's current contribution to the global circuit was calculated. From these results the amount of conduction current supplied to the ionosphere by this small thunderstorm was computed to be less than 25% of the time-averaged generator current that flowed between the two vertically displaced charge centers.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; D5; p. 10,653-10,661
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  • 7
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    Estimates of the Lightning NOx Profile in the Vicinity of the North Alabama Lightning Mapping Array (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Marshall Space Flight Center Lightning Nitrogen Oxides Model (LNOM) is applied to August 2006 North Alabama Lightning Mapping Array (NALMA) data to estimate the (unmixed and otherwise environmentally unmodified) vertical source profile of lightning nitrogen oxides, NOx = NO + NO2. Data from the National Lightning Detection Network (Trademark) (NLDN) is also employed. This is part of a larger effort aimed at building a more realistic lightning NOx emissions inventory for use by the U.S. Environmental Protection Agency (EPA) Community Multiscale Air Quality (CMAQ) modeling system. Overall, special attention is given to several important lightning variables including: the frequency and geographical distribution of lightning in the vicinity of the NALMA network, lightning type (ground or cloud flash), lightning channel length, channel altitude, channel peak current, and the number of strokes per flash. Laboratory spark chamber results from the literature are used to convert 1-meter channel segments (that are located at a particular known altitude; i.e., air density) to NOx concentration. The resulting lightning NOx source profiles are discussed.
    Keywords: Environment Pollution
    Type: M10-0569 , M10-0443 , 21st International Lightning Detection Conference (ILDC)/Vaisala; Apr 18, 2010 - Apr 22, 2010; Orlando, FL; United States
    Format: application/pdf
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