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Norman, OK, United States

Bruning E.C.,Texas Tech University | Macgorman D.R.,National Severe Storms Laboratory
Journal of the Atmospheric Sciences | Year: 2013

Previous analyses of very high frequency (VHF) Lightning Mapping Array (LMA) observations relative to the location of deep convective updrafts have noted a systematic pattern in flash characteristics. In and near strong updrafts, flashes tend to be smaller and more frequent, while flashes far from strong vertical drafts exhibit the opposite tendency. This study quantitatively tests these past anecdotal observations using LMA data for two supercell storms that occurred in Oklahoma in 2004. The data support a prediction from electrostatics that frequent breakdown and large flash extents are opposed. An energetic scaling that combines flash rate and flash area exhibits a 5/3 power-law scaling regime on scales of a few kilometers and a maximum in flash energy at about 10 km. The spectral shape is surprisingly consistent across a range of moderate to large flash rates. The shape of this lightning flash energy spectrum is similar to that expected of turbulent kinetic energy spectra in thunderstorms. In line with the hypothesized role of convective motions as the generator of thunderstorm electrical energy, the correspondence between kinematic and electrical energy spectra suggests that advection of charge-bearing precipitation by the storm's flow, including in turbulent eddies, couples the electrical and kinematic properties of a thunderstorm. © 2013 American Meteorological Society. Source

Mote T.L.,University of Georgia | Brooks H.E.,National Severe Storms Laboratory
Journal of Applied Meteorology and Climatology | Year: 2014

This research compares reanalysis-derived proxy soundings from the North American Regional Reanalysis (NARR) with collocated observed radiosonde data across the central and eastern United States during the period 2000-11: 23 important parameters used for forecasting severe convection are examined. Kinematic variables such as 0-6-km bulk wind shear are best represented by this reanalysis, whereas thermodynamic variables such as convective available potential energy exhibit regional biases and are generally overestimated by the reanalysis. For thermodynamic parameters, parcel-ascent choice is an important consideration because of large differences in reanalysis low-level moisture fields versus observed ones. Results herein provide researchers with potential strengths and limitations of usingNARRdata for the purposes of depicting climatological information for hazardous convective weather and initializing model simulations. Similar studies should be considered for other reanalysis datasets. © 2014 American Meteorological Society. Source

Mazur V.,National Severe Storms Laboratory | Ruhnke L.H.,University of Oklahoma
Journal of Geophysical Research: Atmospheres | Year: 2014

Current cutoff in lightning channels, which takes place in the development of both intracloud and cloud-to-ground flashes, is still poorly understood. A new evaluation of the conditions leading to current cutoff, and also of the two existing hypotheses of the cutoff mechanism, is the main objective of the paper. We reviewed the literature with results of measurements and modeling of free-burning arcs in a laboratory (the closest analogs of lightning leaders) focusing on the relationship between the internal electric field and current. This relationship governs the leader's behavior in the current cutoff. In our analysis of the mechanisms leading to current cutoff, we identify the two types of current cutoff in lightning channels: the current cutoff in a single, unbranched leader channel, which occurs as the result of reaching the threshold conditions for leader propagation; and the current cutoff in branched leaders, when screening by the leader branches alters the ambient electrical environment, thus diminishing the leader current and causing cutoff at a branching point or at the base of the straight channel that preceded branching. We advance the electrostatic model of the screening effect of branching on current cutoff, introduced by Mazur and Ruhnke (1993), and we provide the evidence of this mechanism from lightning observations. We also critically evaluate the concept of lightning-channel instability, proposed by Heckman (1992), as a suggested mechanism leading to current cutoff. We show that the fundamentals of this concept and therefore the concept in its entirety are invalid. © 2014 American Geophysical Union. All Rights Reserved. Source

Lewis J.M.,National Severe Storms Laboratory | Lewis J.M.,Desert Research Institute
Bulletin of the American Meteorological Society | Year: 2014

Mathematicians and physicists at Los Alamos developed the so-called Monte Carlo method in the late 1940s to deal with the uncertainty of branching events in the life of elementary particles. Mathematicians and physicists at Los Alamos developed the so-called Monte Carlo method in the late 1940s to deal with the uncertainty of branching events in the life of elementary particles. While at AFCRC, he took a leadership role in the investigation of stratospheric ozone through use of ground-based infrared radiance measurements. He developed a mathematical inversion technique to convert infrared radiance measurements into ozone profiles. Epstein's limited knowledge of the earlier work aside, he wrote a prospectus that described his research plan for SDP in meteorology. The plan rested on phase-space representation as opposed to physical-space representation: that is, spectral as opposed to gridpoint representation. Source

Li Y.,University of Oklahoma | Zhang G.,University of Oklahoma | Doviak R.J.,National Severe Storms Laboratory
IEEE Transactions on Signal Processing | Year: 2014

Polarimetric weather radars provide additional measurements that allow better characterization of the targeted medium. Because ground clutter has different polarimetric characteristics from weather echoes, dual-polarization measurements can be used to distinguish one from the other. Ground clutter and weather signals also have different statistical properties which can be utilized to distinguish one from the other. A test statistic, obtained from the generalized likelihood ratio test (GLRT), and a simple Bayesian classifier (SBC), with inputs from the mean and covariance of the received signals, are developed to detect ground clutter in the presence of weather signals. It is found that the test statistic produces false detections caused by narrow-band zero-velocity weather signals while the SBC can effectively neutralize them. This work is aimed at detecting ground clutter based solely on data from each resolution volume. The performances of the test statistic and SBC are shown by applying them to radar data collected with the University of Oklahoma-Polarimetric Radar for Innovation in Meteorology and Engineering. © 1991-2012 IEEE. Source

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