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NASA NTRS1994

The natural thermoluminescence of meteorites. 7: Ordinary chondrites from the Elephant Moraine region, Antarctica

We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76 deg 17 min S, 157 deg 20 min E) of Antarctica. We use our data to identify fragmented meteorites (i.e., 'pairings'); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (less than 12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H-chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.

Benoit, P. H.↗

NASA NTRS1994

Deep VLA imaging of twelve extended 3CR quasars

A representative sample of 12 extended quasars from the 3CR catalog has been imaged at 4.9 GHz using the Very Large Array (VLA). These full synthesis observations typically achieve an rms noise of 20 micro-Jy per beam. Jets are detected on at least one side of every source. The jets are well collimated compared with those in less powerfull sources, but spreading is detected in most of them. The opening angles of several jets are not constant, but show recollimation after an initial regime of rapid spreading. Many of the jets contain quasiperiodic strings of knots, of which the knot closest to the central feature is usually the brightest (until the jet nears its hot spot). The degrees of linear polarization at the jet knots range from less than 5% to approx. 50%, but show no common trend with distance along the jets. In knots that are elongated in directions close to that of the jet, the E vectors tend to be orthogonal to the jet axis. The prominence of the inner, straighter jet segments relative to the extended lobes correlates significantly with the prominence of the milliarcsecond-scale central features, but the prominence of the more bent jet segments does not. Candidates for counterjet emission are detected in seven sources, but there is no unambiguous, continuous counterjet in any of them. Estimates of the flux density ratios between the straighter jet segments and the counterjets based on these tentative detections range from 1.2:1 to greater than 175:1. There is no evidence in this sample that counterjet detectability correlates with such putative inclination indicators as central feature prominence or projected linear size. There is also no evidence that the prominence of the counterjets anticorrelates with that of the jets as predicted by simple relativistic-beaming models for the jet/counterjet asymmetry. There is, however, strong evidence that large bends in the main jet favor counterjet detection, and there are no counterjet candidates opposite long, uninterrupted straight segments of the main jets. The detectability of the counterjets in these quasars may therefore be strongly influenced by interactions between the underlying beams and inhomogeneities in the surrounding material. We offer a new empirical definition of the term 'hot spot' that is intended to improve the distinction between such features and 'jet knots.' Both the compactness of hot spots and their position in the lobe are affected by whether they are fed by a detectable jet. When the hot spots differ significantly in compactness, the more compact one is always on the jetted side. Jetted hot spots are also more likely to be recessed deeply from the outer edge of their lobes than are their counterjetted counterparts. The jetted hot spot is less prominent relative to other extended emission if the jet bends through a large angle, particularly if a large bend occurs abruptly. The counterjetted hot spot is also less well defined if the jet is more bent. The lobes of several sources show considerable inhomogeneity, including filamentation.

Bridle, Alan H.↗

NASA NTRS1995

An infrared imaging study of galaxies in the local universe

This poster was a preliminary report on a survey of galaxies in the local universe at J and K using a NICMOS3 256 x 256 infrared photometric camera attached to the 61 inch telescope on Mt. Bigelow. Deep images are being obtained for a representative sample of galaxies in the Uppsala General Catalogue. Structural and color parameters are determined for a wide variety of galactic types. These data should prove to be valuable in characterizing stellar populations within disks and bulges, determining if IR-active galaxies have unusual global as well as- nuclear properties, and understanding the effects of evolution and redshift dimming in distant galaxies.

Grauer, Albert D.↗

NASA NTRS1995

The effects of space radiation on flight film

The Shuttle and its cargo are occasionally exposed to an amount of radiation large enough to create non-image forming exposures (fog) on photographic flight film. The television/photography working group proposed a test plan to quantify the sensitivity of photographic films to space radiation. This plan was flown on STS-37 and was later incorporated into a detailed supplementary objective (DSO) which was flown on STS48. This DSO addressed the effects of significant space radiation on representative samples of six highly sensitive flight films. In addition, a lead-lined bag was evaluated as a potential shield for flight film against space radiation.

Holly, Mark H.↗

NASA NTRS1996

Towards the Interoperability of Web, Database, and Mass Storage Technologies for Petabyte Archives

At the San Diego Supercomputer Center, a massive data analysis system (MDAS) is being developed to support data-intensive applications that manipulate terabyte sized data sets. The objective is to support scientific application access to data whether it is located at a Web site, stored as an object in a database, and/or storage in an archival storage system. We are developing a suite of demonstration programs which illustrate how Web, database (DBMS), and archival storage (mass storage) technologies can be integrated. An application presentation interface is being designed that integrates data access to all of these sources. We have developed a data movement interface between the Illustra object-relational database and the NSL UniTree archival storage system running in a production mode at the San Diego Supercomputer Center. With this interface, an Illustra client can transparently access data on UniTree under the control of the Illustr DBMS server. The current implementation is based on the creation of a new DBMS storage manager class, and a set of library functions that allow the manipulation and migration of data stored as Illustra 'large objects'. We have extended this interface to allow a Web client application to control data movement between its local disk, the Web server, the DBMS Illustra server, and the UniTree mass storage environment. This paper describes some of the current approaches successfully integrating these technologies. This framework is measured against a representative sample of environmental data extracted from the San Diego Ba Environmental Data Repository. Practical lessons are drawn and critical research areas are highlighted.

Moore, Reagan↗

NASA NTRS1995

Phase-Dependent Observations of Intermediate Polars and The Broad Emission and Absorption Line Region in NGC 3516

The Intermediate Polars (IP's) constitute a class of Cataclysmic Variables (CV's), which are binary star systems in which mass is transferred from a late-type main-sequence star to a white dwarf via Roche lobe overflow. In the IP's, the inner accretion disk is evidently disrupted by the magnetic field of the white dwarf. High-temperature shocks at the white dwarf's magnetic poles (where accretion occurs) produce X-rays, which are reprocessed into photons over a broad energy band across the electromagnetic spectrum. Because the white dwarf typically spins rapidly (rotation periods a few 10s to a few 100s of seconds), the signals due to both the X-rays and reprocessed photons are pulsed. The shape of the spectrum of pulse amplitude as a function of wavelength yields information about both the temperature and size of the pulse-emitting region. It has been noted by several investigators that the optical pulsation amplitudes rise steeply toward short wavelengths. It is therefore a fair surmise that pulsation amplitudes peak in the ultraviolet. The scientific goal of this project was to observe a representative sample of IP's, using IUE, in search of the expected strong UV pulsations, and hence to further our understanding of pulse-producing mechanisms.

Koratkar, Anuradha↗

NASA NTRS1997

Thermal Cycling of Mir Cooperative Solar Array (MCSA) Test Panels

The Mir Cooperative Solar Array (MCSA) project was a joint US/Russian effort to build a photovoltaic (PV) solar array and deliver it to the Russian space station Mir. The MCSA is currently being used to increase the electrical power on Mir and provide PV array performance data in support of Phase 1 of the International Space Station (ISS), which will use arrays based on the same solar cells used in the MCSA. The US supplied the photovoltaic power modules (PPMs) and provided technical and programmatic oversight while Russia provided the array support structures and deployment mechanism and built and tested the array. In order to ensure that there would be no problems with the interface between US and Russian hardware, an accelerated thermal life cycle test was performed at NASA Lewis Research Center on two representative samples of the MCSA. Over an eight-month period (August 1994 - March 1995), two 15-cell MCSA solar array 'mini' panel test articles were simultaneously put through 24,000 thermal cycles (+80 C to -100 C), equivalent to four years on-orbit. The test objectives, facility, procedure and results are described in this paper. Post-test inspection and evaluation revealed no significant degradation in the structural integrity of the test articles and no electrical degradation, not including one cell damaged early as an artifact of the test and removed from consideration. The interesting nature of the performance degradation caused by this one cell, which only occurred at elevated temperatures, is discussed. As a result of this test, changes were made to improve some aspects of the solar cell coupon-to-support frame interface on the flight unit. It was concluded from the results that the integration of the US solar cell modules with the Russian support structure would be able to withstand at least 24,000 thermal cycles (4 years on-orbit).

Hoffman, David J.↗

NASA NTRS1996

Sulfur, Chlorine and Fluorine Degassing and Atmospheric Loading by the Roza eruption, Columbia River Basalt Group, Washington

In this study we attempt to quantify the amount of S, Cl and F released by the 1300 cu km Roza member (approximately 14.7 Ma) of the Columbia River Basalt Group, which was produced by a moderate-size flood basalt eruption in the mid-Miocene. Our results are the first indication of the potential atmospheric SO2 yield from a flood basalt eruption, and indicate the mechanism by which flood basalt eruptions may have seriously affected the environment. Glass inclusions in phenocrysts and quenched glass in products from various stages of the eruption were analyzed for concentrations of S, Cl and F and major elements. Glass inclusions contain 1965 +/- 110 ppm S, 295 +/- 65 ppm Cl and 1310 +/- 110 ppm F. Groundmass glass of Roza dike selvages contains considerably lower concentrations: 1110 +/- 90 ppm S, 245 +/- 30 ppm Cl and 1020 +/- 25 ppm F. Scoria clasts from near vent deposits contain 665 +/- 75 ppm S, 175 +/- 5 ppm Cl and 950 +/- 20 ppm F, and the groundmass glass of lava selvages contains 520 +/- 30 ppm S, 190 +/- 30 ppm Cl and 890 +/- 55 ppm F. In crystalline lava, the concentrations are 195 ppm S, 100 ppm Cl and 830 ppm F. Volatile element concentrations in these samples represent the progress of degassing through the eruption and can be used to estimate the potential amount of the volatiles S, Cl and F released by the magma into the atmosphere, as well as to evaluate the amount liberated by various phases of the eruption. The total amount of volatiles released by the Roza eruption is estimated to have been approximately 12,420 MtSO2, approximately 710 MtHCI and approximately 1780 MtHF. The Roza magma liberated approximately 9620 MtSO, (77% of the total volatile mass released), approximately 400 MtHCI (56%) and approximately 1450 MtHF (81%) at the vents and lofted by the eruption columns to altitudes of 7-13 km. Degassing of the lava is estimated to have released an additional approximately 2810 MtSO2, approximately 310 MtHCI and approximately 330 MtHF. The Roza eruption is likely to have lasted for approximately 10 years, indicating an annual H2SO4-mass loading of approximately 1800 Mt. Thus, the atmospheric perturbations associated with the Roza eruption may have been of the magnitude predicted for a severe "nuclear" or "volcanic" winter, but lasting up to a decade or more.

Thordarson, Th.↗

NASA NTRS1996

Cosmic-Ray-Exposure Ages of Diogenites and the Collisional History of the HED Parent Body or Bodies

Cosmic-ray-exposure ages of meteorites provide information on the collisional history of their parent bodies and the delivery mechanism of meteorites to Earth. The exposure-age distributions of ordinary chondrites show distinct patterns for H, L, and LL types, consistent with their origin on different parent bodies. The exposure-age distributions of howardites, eucrites. and diogenites (HEDS) show a common pattern with major peaks at 22 Ma and 38 Ma This provides additional evidence for a common origin of the HED meteorites, possibly 4 Vesta, although orbital dynamics calculations showed that the delivery of meteorites from Vesta to Earth is difficult. However, the discovery of several kilometer-sized Vesta-like asteroids in the region between Vesta and the 3:1 resonance suggested that these seem more likely parent bodies of the HEDs than Vesta itself. This implies that the exposure-age clusters may represent samples of several parent bodies. Therefore, the near-absence of diogenites with ages <20 Ma might be of interest for the composition of these kilometer-sized fragments of Vesta. Here we present cosmic-ray-exposure ages of 20 diogenites, including 9 new meteorites. In addition, we calculate the probability for each peak to occur by chance, assuming a constant production rate of HED fragments.

Welten, K. C.↗

NASA NTRS2000

International Test Program for Synergistic Atomic Oxygen and VUV Exposure of Spacecraft Materials

Spacecraft in low Earth orbit (LEO) are subject to degradation in thermal and optical performance of components and materials through interaction with atomic oxygen and vacuum ultraviolet radiation which are predominant in LEO. Due to the importance of LEO durability and performance to manufacturers and users, an international test program for assessing the durability of spacecraft materials and components was initiated. Initial tests consisted of exposure of samples representing a variety of thermal control paints and multilayer insulation materials that have been used in space. Materials donated from various international sources were tested alongside a material whose performance is well known such as Teflon FEP or Kapton H for multilayer insulation, or Z-93-P for white thermal control paints. The optical, thermal or mass loss data generated during the test was then provided to the participating material supplier. Data was not published unless the participant donating the material consented to publication. This paper presents a description of the types of tests and facilities that have been used for the test program as well as some examples of data that have been generated. The test program is intended to give spacecraft builders and users a better understanding of degradation processes and effects to enable improved prediction of spacecraft performance.

Rutledge, Sharon↗

NASA NTRS1999

Exploration of Uncertainty in Glacier Modelling

There are procedures and methods for verification of coding algebra and for validations of models and calculations that are in use in the aerospace computational fluid dynamics (CFD) community. These methods would be efficacious if used by the glacier dynamics modelling community. This paper is a presentation of some of those methods, and how they might be applied to uncertainty management supporting code verification and model validation for glacier dynamics. The similarities and differences between their use in CFD analysis and the proposed application of these methods to glacier modelling are discussed. After establishing sources of uncertainty and methods for code verification, the paper looks at a representative sampling of verification and validation efforts that are underway in the glacier modelling community, and establishes a context for these within overall solution quality assessment. Finally, an information architecture and interactive interface is introduced and advocated. This Integrated Cryospheric Exploration (ICE) Environment is proposed for exploring and managing sources of uncertainty in glacier modelling codes and methods, and for supporting scientific numerical exploration and verification. The details and functionality of this Environment are described based on modifications of a system already developed for CFD modelling and analysis.

Thompson, David E.↗

NASA NTRS2000

A Subsurface Explorer for Deep Underground Exploration on Mars

A subsurface explorer (SSX) is being developed at the Jet Propulsion Laboratory which is suitable for exploration of the deep underground environments on Mars. The device is a self-contained piledriver which uses a novel 'spinning hammer' technology to convert a small continuous power feed from the surface over a two-wire tether into a large rotational energy of a spinning mass. The rotational energy is converted to translational energy by a novel mechanism described here. The hammer blows propagate as shock waves through a nosepiece, pulverizing the medium ahead of the SSX. A small portion of the pulverized medium is returned to the surface through a hole liner extending behind the SSX. This tube is 'cast in place' from two chemical feedstocks which come down from the surface through passages in the hole liner and which are reacted together to produce new material with which to produce the hole liner. The lined hole does not need to be the full diameter of the SSX: approximately 100 kilograms of liner material can create a tunnel liner with a three millimeter inside diameter and a six millimeter outside diameter with at total length of four kilometers. Thus it is expected that core samples representing an overlapping set of three-millimeter diameter cores extending the entire length of the SSX traverse could be returned to the surface. A pneumatic prototype has been built which penetrated easily to the bottom of an eight meter vertical test facility. An electric prototype is now under construction. It is expected that the SSX will be able to penetrate through sand or mixed regolith, ice, permafrost, or solid rock, such as basalt. For pure or nearly pure ice applications, the device may be augmented with hot water jets to melt the ice and stir any sediment which may build up ahead of the vehicle. It is expected that an SSX approximately one meter long, three to four centimeters in diameter, and with a power budget of approximately 200 Watts will be able to explore up to approximately five kilometers deep at the rate of about ten meters per day.

Wilcox, B. H.↗

NASA NTRS1996

Spinoff 1996

By their challenging nature, NASA programs are particularly demanding of technological input. Meeting the aeronautical and space goals of the past four decades has necessitated leading edge advancements across a diverse spectrum that embraces virtually every scientific and technological discipline. Technology is simply knowledge and, like other forms of knowledge, it is often broadly applied and transferable. For that reason, the vast storehouse of technology NASA has built is a national resource, a bank of knowledge available for commercial applications and enhancements to the quality of life-"spinoff"-to new products and processes of benefit to the national economy, industrial efficiency and human welfare. Multiple use of technology has never been more important. Budgetary stringency is reducing the amount of government funding available for new research and development, but at the same time intensifying international competition demands increasing technological innovation to strengthen the U.S. posture in the global marketplace. Reuse of technology offers a relatively inexpensive supplementary means of partnering with industry focused on bringing new products and processes to the market. More than a thousand of spinoff products and processes have emerged from reapplication of technology developed for NASA mission programs. Each has Contributed some measure of benefit to the national economy, productivity or lifestyle; some bring only moderate increments of gain, but many generate benefits of significant order with economic values in the millions of dollars. Other technologies with moderate economic return have added measurably to the quality of life of U.S. citizens. Collectively, they represent a substantial dividend on the national investment in aerospace research. By Congressional mandate, it is NASA's responsibility to promote expansion of spinoff in the public interest. Through its Technology Transfer Program, NASA seeks to encourage greater use of its technological resources by providing a link between the technology and those who might be able to put it to advantageous use. The program's aim is to broaden and accelerate the transfer accomplishments and thereby to gain national benefit in terms of new products, services, and new jobs. This publication is an instrument of-and documents the outcome of-that purpose. It is intended to heighten awareness of the technology available for transfer and its potential for public benefit. Spinoff 1996 is organized in three sections: Section 1, summarizes NASA's current mainline programs, whose objectives require development of new technology and therefore replenish and expand the bank of knowledge available for reapplication. Section 2, the focal point of this volume, contains a representative sampling of spinoff products and processes that resulted from secondary application of NASA technology. Section 3, describes the various mechanisms NASA employs to stimulate technology transfer and lists, in an appendix, contact sources for Further information about the Technology Transfer Program.

Haggerty, James J.↗

NASA NTRS1995

Spinoff 1995

Recognizing the great potential of the technology bank, Congress charged NASA with stimulating the widest possible use of this valuable resource in the national interest. NASA's instrument of that purpose is the Technology Transfer Program, which seeks to broaden and accelerate the spinoff process. Its intent is to spur expanded national benefit, in terms of new products and new jobs, by facilitating the commercial application of the technology; it encourages greater use of the storehouse of knowledge by providing a channel linking the technology and those who might be able to put it to advantageous use. In July 1994, NASA implemented an Agenda for Change - a new way of doing business in partnership with the private sector. This Agenda marks the beginning of a new focus to further improve our contributions to America's economic security through the pursuit of aeronautics and space missions. This publication is an implement of the Technology Transfer Program intended to heighten awareness among potential users of the technology available for transfer and the economic and social benefits that might be realized by applications of NASA technology to US commercial interests. Spinoff 1995 is organized in three sections. Section 1 outlines NASA's mainline effort, the major programs that generate new technology and therefore replenish and expand the bank of technical knowledge available for application. Section 2, the focal point of this volume, contains a representative sampling of spinoff products and processes that resulted from applications of technology originally developed to meet NASA aerospace goals. Section 3, describes the various mechanisms NASA employs to stimulate technology transfer and lists, in an appendix, contact sources for further information about the Technology Transfer Program.

Haggerty, James J.↗

NASA NTRS2000

Microphysical Modelling of Polar Stratospheric Clouds During the 1999-2000 Winter

The evolution of the 1999-2000 Arctic winter has been examined using a microphysical/photochemical model run along diabatic trajectories. A large number of trajectories have been generated, filling the vortex throughout the region of polar stratospheric cloud (PSC) formation, and extending from November until the vortex breakup, in order to provide representative sampling of the evolution of PSCs and their effect on stratospheric chemistry. The 1999-2000 winter was particularly cold, allowing extensive PSC formation. Many trajectories have ten-day periods continuously below the Type I PSC threshold; significant periods of Type II PSCs are also indicated. The model has been used to test the extent and severity of denitrification and dehydration predicted using a range of different microphysical schemes. Scenarios in which freezing only occurs below the ice frost point (causing explicit coupling of denitrification and dehydration) have been tested, as well as scenarios with partial freezing at warmer temperatures (in which denitrification can occur independently of dehydration). The sensitivity to parameters such as aerosol freezing rates and heterogeneous freezing have been explored. Several scenarios cause sufficient denitrification to affect chlorine partitioning, and in turn, model-predicted ozone depletion, demonstrating that an improved understanding of the microphysics responsible for denitrification is necessary for understanding ozone loss rates.

Drdla, Katja↗

NASA NTRS1995

Ames Research Center Mars/Pathfinder Heat Shield Design Verification ARC-JET Test

Design verification tests were performed on samples representing the aerobrake of the Mars/Pathfinder vehicle. The test specimens consisted of the SLA-561V ablator bonded to the honeycomb structure. The primary objective was to evaluate the ablation materials performance and to measure temperatures within the ablator, at the structural bondline and at the back sheet of the honeycomb structure. Other objectives were to evaluate the effect of ablative repair plug material treatment and voids in the heat shield. A total of 29 models were provided for testing in the Ames 60MW arc-jet facility. Of these, 23 models were flat-faced and six remaining models were curved edge ones, intended to simulate the conditions on the curved rim of the forebody where the maximum shear occurred. Eight sets of test conditions were used. The stagnation point heating rates varied from 47 to 240 W/cm2 and the stagnation pressures from 0.15 to 0.27 atm. (The maximum flight values are 132 W/cm2 and 0.25 atm) The majority of these runs were made at a nominal stagnation pressure of 0.25 atm. Two higher pressure runs were made to check the current (denser) ablation material for spallation, or other forms of thermal stress failure. Over 60% of the flatfaced models yielded good thermocouple data and all produced useful surface recession information. Of the five curved-edge models that were tested, only one gave good data; the remaining ones experienced model-holder failure. The test results can be summarized by noting that no failure of the ablative material was observed on any model. Also, the bondline temperature design limit of 250 C was never reached within an equivalent flight time despite a stagnation point heat load that exceeded the maximum flight value by up to 130%. At heating rates of over 200W/cm2 and stagnation pressures of 0.25 atm, or greater, the average surface recessions exceeded 0.5 cm on some models. The surface roughness increased dramatically at pressures above 0.25 atm and was four times greater at 0.27 atm than at 0.25 atm. Procured repair plug material performed much better than room-temperature cured plugs, as observed in the previous tests. Voids in the ablator did not increase local temperatures and gaps did not grow during testing.

Tran, Huy K.↗

NASA NTRS2003

Isothermal Microcalorimetric Evaluation of Compatibility of Proposed Injector Materials with High-Test Hydrogen Peroxide Propellant

High-test hydrogen peroxide (HTP) is receiving renewed interest as a monopropellant and as the oxidizer for bipropellant systems. HTP is hydrogen peroxide in concentrations ranging from 70 to 98%. All surfaces wetted by HTP must be evaluated for compatibility with the fluid. In the case of tanks, lines and valves compatibility is required to preserve the HTP oxygen and energy content and to avoid overpressurization due to decomposition. With injectors and regenerative cooling passages shorter exposure time reduces these concerns. However, phase changes from fluid to gas impact heat transfer and become the dominant compatibility concern. Isothermal microcalorimetry (IMC) provides a convenient and reproducible means to observe the decomposition of HTP when exposed to structural materials and therefore the compatibility of those materials'. The instrument provides heat flow values in terms of watts that may be converted to a reaction rate given the heat of reaction for the decomposition of hydrogen peroxide. These values are then converted to percent active oxygen loss per week (%AOL/wk) to preserve an earlier convention for quantifying HTP compatibility. Additionally, qualitative designations of compatibility have been assigned to these values. This scheme consists of four classes with Class 1 being the most compatible. While historical compatibility data is available its current applicability is in question due to subtle changes in the compositions of both HTP and structural materials. Trace levels of molecules can have significant influence on compatibility. Therefore representative samples of materials must be evaluated with current HTP formulations. In this work seven materials were selected for their strength characteristics at high temperature as expected in a HTP injector. The materials were then evaluated by IMC for HTP compatibility.

Gostowski, Rudy↗

NASA NTRS2003

Objective Classification of Radar Profile Types, and Their Relationship to Lightning Occurrence

A cluster analysis technique is used to identify 16 "archetypal" vertical radar profile types from a large, globally representative sample of profiles from the TRMM Precipitation Radar. These include nine convective types (7 of these deep convective) and seven stratiform types (5 of these clearly glaciated). Radar profile classification provides an alternative to conventional deep convective storm metrics, such as 30 dBZ echo height, maximum reflectivity or VIL. As expected, the global frequency of occurrence of deep convective profile types matches satellite-observed total lightning production, including to very small scall local features. Each location's "mix" of profile types provides an objective description of the local convective spectrum, and in turn, is a first step in objectively classifying convective regimes. These classifiers are tested as inputs to a neural network which attempts to predict lightning occurrence based on radar-only storm observations, and performance is compared with networks using traditional radar metrics as inputs.

Boccippio, Dennis↗