Monte G. Bateman

North Alabama Lightning Mapping Array (LMA): VHF Source Retrieval Algorithm and Error Analyses

Two approaches are used to characterize how accurately the north Alabama Lightning Mapping Array (LMA) is able to locate lightning VHF sources in space and time. The first method uses a Monte Carlo computer simulation to estimate source retrieval errors. The simulation applies a VHF source retrieval algorithm that was recently developed at the NASA Marshall Space Flight Center (MSFC) and that is similar, but not identical to, the standard New Mexico Tech retrieval algorithm. The second method uses a purely theoretical technique (i.e., chi-squared Curvature Matrix Theory) to estimate retrieval errors. Both methods assume that the LMA system has an overall rms timing error of 50 ns, but all other possible errors (e.g., anomalous VHF noise sources) are neglected. The detailed spatial distributions of retrieval errors are provided. Even though the two methods are independent of one another, they nevertheless provide remarkably similar results. However, altitude error estimates derived from the two methods differ (the Monte Carlo result being taken as more accurate). Additionally, this study clarifies the mathematical retrieval process. In particular, the mathematical difference between the first-guess linear solution and the Marquardt-iterated solution is rigorously established thereby explaining why Marquardt iterations improve upon the linear solution.

Precipitation charge and size measurements inside a New Mexico mountain thunderstorm

We measured the charge and size of precipitation particles with an instrumented free balloon in a convective mountain thunderstorm over Langmuir Laboratory in central New Mexico. Using an instrument that measured precipitation charge from 2 to 220 pC and equivalent particle diameters from 0.6 to 3.8 mm, we deduced that (1) the charge of the main positive charge region is carried by cloud particles, the charge of the main negative charge region is carried by a mixture of negative charge bearing cloud particles and precipitation particles, and the charge of the lower positive charge region is carried almost entirely by precipitation; (2) there was a mixture of both polarities of precipitation charge at nearly all altitudes; (3) there was no relationship between precipitation charge and size; (4) our charge data appear to support the noninductive ice-ice collisional charging mechanism; and (5) the sign of charge carried by the precipitation reverses with ambient temperature. In comparing these data to previous measurements that were collected in New Mexico mountain thunderstorms with different instrumentation, we found that in most ways our precipitation charge data are similar to the previous measurements. In comparing these data with data that we previously collected in the trailing stratiform regions of mesoscale convective systems, we found that there are substantial differences in the precipitation charge data between these different cloud types.

Electric Fields, Cloud Microphysics, and Reflectivity in Anvils of Florida Thunderstorms

into the interior, electric fields very frequently increased abruptly from � 1 to >10 kV m 1 even though the particle concentrations and radar reflectivity increased smoothly. The abrupt increase in field usually occurred when the aircraft entered regions with a reflectivity of 10–15 dBZ. We suggest that the abrupt increase in electric field was because the charge advection from the convective core did not occur across the entire breadth of the anvil and because the advection of charge was not constant in time. Also, some long-lived anvils showed enhancement of electric field and reflectivity far downwind of the convective core. Screening layers were not detected near the edges of the anvils. Comparisons of electric field magnitude with particle concentration or reflectivity for a combined data set that included all anvil measurements showed a threshold behavior. When the average reflectivity, such as in a 3-km cube, was less than approximately 5 dBZ, the electric field magnitude was <3 kV m 1 . Based on these

Precipitation charge and size measurements in the stratiform region of two mesoscale convective systems

We measured the charge and size of precipitation particles with instrumented free balloons in the trailing stratiform regions of two different mesoscale convective systems (MCSs) in Oklahoma. Each of these stratiform regions had a different type of vertical electric field structure, one of each of the two types commonly found in MCS stratiform regions. Using an instrument that measured precipitation charge from 4 to 400 pC and equivalent diameters from 0.8 to 8.0 mm, we found that (1) the particles measured were not the major charge carriers in these storms, implying that smaller particles were responsible for the measured field, (2) there was no obvious relation between precipitation charge and size or polarity and size, (3) the precipitation size distribution in and near the transition zone consisted of two independent populations, one centered at 2.6 mm and one at 4.9 mm, (4) the two lower charge layers in these storms were likely created by in situ charging processes, and (5) net precipitation charge density was small because nearly equal amounts of positive and negative precipitation charge existed at all altitudes measured.

A Low-Noise, Microprocessor-Controlled, Internally Digitizing Rotating-Vane Electric Field Mill for Airborne Platforms

This paper reports on a new generation of aircraft-based rotating-vane-style electric field mills designed and built at NASA’s Marshall Space Flight Center. The mills have individual microprocessors that digitize the electric field signal at the mill and respond to commands from the data system computer. The mills are very sensitive (1 V m 1 bit 1 ), have a wide dynamic range (115 dB), and are very low noise (1 LSB). Mounted on an aircraft, these mills can measure fields from 1Vm 1 to 500 kV m 1 . Once-per-second commanding from the data collection computer to each mill allows for precise timing and synchronization. The mills can also be commanded to execute a self-calibration in flight, which is done periodically to monitor the status and health of each mill.

A Comparison of Two Ground-Based Lightning Detection Networks against the Satellite-Based Lightning Imaging Sensor (LIS)

AbstractLightning stroke data from both the World Wide Lightning Location Network (WWLLN) and the Earth Networks Total Lightning Network (ENTLN) were compared to lightning group data from the Lightning Imaging Sensor (LIS) from 1 January 2010 through 30 June 2011. The region of study, from 39°S to 39°N latitude, chosen based on the orbit of LIS, and 164°E east to 17°W longitude, chosen to approximate the possible Geostationary Lightning Mapper (GLM) longitude, was considered in its entirety and then divided into geographical subregions. Over this 18-month time period, WWLLN had an 11.0% entire region, 13.2% North American, 6.2% South American, 16.4% Atlantic Ocean, and 18.9% Pacific Ocean coincidence percent (CP) value. The ENTLN CP values were 28.5%, 63.3%, 2.2%, 3.0%, and 2.5%, respectively. During the 18 months, WWLLN CP values remained rather consistent but low and often higher over ocean than land; ENTLN CP values showed large spatial and temporal variability. With both networks, North America had le...

A Balloon-Borne Instrument for Measuring the Charge and Size of Precipitation Particles inside Thunderstorms

Abstract A new balloon-borne instrument created by the authors and referred to as the q-d instrument that measures the charge q and size d of precipitation particles is discussed. The instrument measures charge with an induction cylinder size with an optical sensor, and fall speed by the time difference between the two. A second induction cylinder at the top serves as the entry point and detects precipitation that splashes off the entry. In this way, particles contaminated by splashing are removed from the data. It is capable of measuring particle sizes ranging from 0.8 to 8.0 mm in diameter and charges ranging from ±4 to ±400 pC. Since the size is measured optically, one can detect uncharged particles and measure their size. The q-d instrument does not show evidence of corona at its extremities until the electric field is as large as 100 kV m−1 at 700 mb.

On the Magnitude of the Electric Field near Thunderstorm-Associated Clouds

Abstract Electric-field measurements made in and near clouds during two airborne field programs are presented. Aircraft equipped with multiple electric-field mills and cloud physics sensors were flown near active convection and into thunderstorm anvil and debris clouds. The magnitude of the electric field was measured as a function of position with respect to the cloud edge to provide an observational basis for modifications to the lightning launch commit criteria (LLCC) used by the U.S. space program. These LLCC are used to reduce the risk that an ascending launch vehicle will trigger a lightning strike that could cause the loss of the mission or vehicle. Even with fields of tens of kV m−1 inside electrically active convective clouds, the fields external to these clouds decay to less than 3 kV m−1 within 15 km of cloud edge. Fields that exceed 3 kV m−1 were not found external to anvil and debris clouds.

Retrieving Storm Electric Fields from Aircraft Field Mill Data. Part II: Applications

Abstract The Lagrange multiplier theory developed in Part I of this study is applied to complete a relative calibration of a Citation aircraft that is instrumented with six field mill sensors. When side constraints related to average fields are used, the Lagrange multiplier method performs well in computer simulations. For mill measurement errors of 1 V m−1 and a 5 V m−1 error in the mean fair-weather field function, the 3D storm electric field is retrieved to within an error of about 12%. A side constraint that involves estimating the detailed structure of the fair-weather field was also tested using computer simulations. For mill measurement errors of 1 V m−1, the method retrieves the 3D storm field to within an error of about 8% if the fair-weather field estimate is typically within 1 V m−1 of the true fair-weather field. Using this type of side constraint and data from fair-weather field maneuvers taken on 29 June 2001, the Citation aircraft was calibrated. Absolute calibration was completed using the...

Automated storm tracking and the lightning jump algorithm using GOES-R Geostationary Lightning Mapper (GLM) proxy data

This study develops a fully automated lightning jump system encompassing objective storm tracking, Geostationary Lightning Mapper proxy data, and the lightning jump algorithm (LJA), which are important elements in the transition of the LJA concept from a research to an operational based algorithm. Storm cluster tracking is based on a product created from the combination of a radar parameter (vertically integrated liquid, VIL), and lightning information (flash rate density). Evaluations showed that the spatial scale of tracked features or storm clusters had a large impact on the lightning jump system performance, where increasing spatial scale size resulted in decreased dynamic range of the systems performance. This framework will also serve as a means to refine the LJA itself to enhance its operational applicability. Parameters within the system are isolated and the systems performance is evaluated with adjustments to parameter sensitivity. The systems performance is evaluated using the probability of detection (POD) and false alarm ratio (FAR) statistics. Of the algorithm parameters tested, sigma-level (metric of lightning jump strength) and flash rate threshold influenced the systems performance the most. Finally, verification methodologies are investigated. It is discovered that minor changes in verification methodology can dramatically impact the evaluation of the lightning jump system.