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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Return stroke velocities and currents using a solid state silicon detector system

A small, portable device has been developed to measure return stroke velocities. With the device, velocities from 135 strokes that consist of 92 natural return strokes and 43 triggered return strokes have been analyzed. The average return stroke velocity for longer channels, greater than 500 meters, is 1.2 + or - 0.3 x 10 to the 8th m/s for both natural and triggered return strokes. For shorter channel lengths, less than 500 m, natural lightning has a statistically higher average return stroke velocity of 1.9 + or - 0.7 x 10 to the 8th m/s than triggered lightning with an average return stroke velocity of 1.4 + or - 0.4 x 10 to the 8th m/s. Using the transmission line model of the return stroke, natural lightning has a peak current distribution that is log-normal with a median value of 19 kA. Return stroke velocities and currents were determined for two distant single stroke natural positive cloud-to-ground flashes. The velocities were 1.0 and 1.7 x 10 to the 8th ms/s while the estimated peak current for each positive flash was over 125 kA.

Mach, Douglas M.↗
NASA NTRS1989

Lightning rates relative to tornadic storm evolution on 22 May 1981

Lightning and Doppler radar data for two tornadic storms in Oklahoma on May 22, 1981 are used to analyze ground flash rates relative to the time of tornadoes. It is found that the ground flash rates had no obvious relationship with the tornado times, although the stroke rate in both storms was greatest after the tornadic stage ended. The variations in the cyclone shear and the intracloud flash rates within 10 km of the mesocyclone region are examined. The results suggest that most tornadic storms have an increase in total flash rates near the time of the tornado and that this increase is often dominated by intracloud flashes.

Macgorman, Donald R.↗
NASA NTRS1989

Electrical structure in two thunderstorm anvil clouds

Electrical structures in two thunderstorm anvil clouds (or 'anvils'), one in New Mexico, the other in Oklahoma, were investigated, using measurements of electric field by balloon-carried instruments and a one-dimensional model to calculate the time and spatial variations of electrical parameters in the clear air below the anvil. The electric field soundings through the two thunderstorm anvils showed similar charge structures; namely, negatively charged screening layers on the top and the bottom surfaces, a layer of positive charge in the interior, and one or two layers of zero charge. It is suggested that the positive charge originated in the main positive charge region normally found at high altitudes in the core of thunderclouds, and the negatively charged layers probably formed as screening layers, resulting from the discontinuity in the electrical conductivity at the cloud boundaries.

Marshall, Thomas C.↗
NASA NTRS1988

A comparison of the optical pulse characteristics of intracloud and cloud-to-ground lightning as observed above clouds

The optical-pulse characteristics of intracloud (IC) and cloud-to-ground (CG) lightning flashes were investigated. The time-resolved optical waveforms at 777.4 nm and electric-field changes produced by lightning flashes were measured aboard a U2 aircraft flying above clouds at the same time that ground-based lightning measurements were carried out. The pulse shapes and intensities of IC and CG flashes, as viewed from above cloud, were found to exhibit remarkably similar waveshapes, radiances, and radiant energy densities. The median radiance at cloud top was found to be about 0.007 W/sq m per sr, and the median energy density about 0.000003 J/sq m per sr.

Goodman, Steven J.↗
NASA NTRS1989

Mobile, high-wind, balloon-launching apparatus

In order to place instruments for measuring meteorological and electrical parameters into thunderstorms, an inexpensive apparatus has been developed which makes it possible to inflate, transport, and launch balloons in high winds. The launching apparatus is a cylinder of bubble plastic that is made by joining the sides of the cylinder together with a velcro rip strip. A balloon is launched by pulling the rip strip rapidly. This allows the balloon to pop upward into the ambient low-level wind and carry its instrumentation aloft. Different-sized launch tubes are constructed to accommodate particular sizes of balloons. Balloons have been launched in winds of about 20 m/s.

Rust, W. David↗
NASA NTRS1989

A photoelectric technique for measuring lightning-channel propagation velocities from a mobile laboratory

The present device for lightning channel propagation-velocity determination employs eight photodetectors mounted behind precision horizontal slits in the focal plane of a photographic camera lens. The eight photodetector pulses, IRIG-B time, and slow and fast electric field-change waveforms are recorded on a 14-track analog tape recorder. A comparison of the present results with those obtained by a streaking camera shows no significant differences between the velocities obtained from the same strokes with the two systems; neither is there any difference in pulse characteristics or in the velocities calculated from them.

Mach, Douglas M.↗
NASA NTRS1989

Photoelectric return-stroke velocity and peak current estimates in natural and triggered lightning

Two-dimensional photoelectric return stroke velocities from 130 strokes are presented, including 86 negative natural, 41 negative triggered, one positive triggered, and two positive natural return strokes. For strokes starting near the ground and exceeding 500 m in length, the average velocity is 1.3 + or - 0.3 X 10 to the 8th m/s for natural return strokes and 1.2 + or - 0.3 X 10 to the 8th m/s for triggered return strokes. For strokes with lengths less than 500 m, the average velocities are slightly higher. Using the transmission line model (TLM), the shortest segment one-dimensional return stroke velocity, and either the maximum or plateau electric field, it is shown that natural strokes have a peak current distribution that is lognormal with a median value of 16 kA (maximum E) or 12 kA (plateau E). Triggered lightning has a medium peak current value of 21 kA (maximum E) or 15 kA (plateau E). Correlations are found between TLM peak currents and velocities for triggered and natural subsequent return strokes, but not between TLM peak currents and natural first return stroke velocities.

Mach, Douglas M.↗
NASA NTRS1989

Polarization radar and electrical observations of microburst producing storms during Cohmex

The life cycles of two electrified, microburst-producing storms that occurred on July 19 and 20, 1986 near Huntsville, Alabama are described and compared. The kinematic and microphysical development of the storm clouds is examined. Lightning activity prior to the onset of the microburst is studied. It is observed that ice phase precipitation particles are important in the electrification of the storm and in the formation of the strong downdraft, and the vertical distribution and movement of mass have a role in determining the total lightning activity and type of flashes.

Goodman, Steven J.↗
NASA NTRS1990

New instruments for solar research

In fulfilment of its goal to develop early detection and warning of emerging solar magnetic fields, the Center for Applied Solar Physics (CASP) has designed and constructed a solar vector magnetograph (VMG) that will provide unique data on the sunspot regions where flares originate. The instrument is reportedly beginning to approach its goals of measuring all three components of the solar magnetic field with a sensitivity of 50 to 100 G and a spatial resolution on the sun of about 700 km (1 arcsec). Importance of new high-resolution capabilities is stressed and the interpretation of VMG measurements is discussed. The performance of the solar VMG, installed in a 6-m dome at the National Solar Observatory at Sacramento Peak in Sunspot, New Mexico, and its construction and environment are described; particular attention is given to the use and function of the filters. Initial results are examined, including a description and analysis of a magnetogram obtained after installation of an improved blocking filter.

Rust, David M.↗
NASA NTRS1992

BATSE spectroscopy analysis system

The Burst and Transient Source Experiment (BATSE) Spectroscopy Analysis System (BSAS) is the software system which is the primary tool for the analysis of spectral data from BATSE. As such, Guest Investigators and the community as a whole need to know its basic properties and characteristics. Described here are the characteristics of the BATSE spectroscopy detectors and the BSAS.

Schaefer, Bradley E.↗
NASA NTRS1991

Electric field soundings through thunderstorms

Twelve balloon soundings of the electric field in thunderstorms are reported. The maximum magnitude of E in the storms averaged 96 +/-28 kV/m, with the largest being 146 kV/m. The maximum was usually observed between vertically adjacent regions of opposite charge. Using a 1D approximation to Gauss' law, four to ten charge regions in the storms are inferred. The magnitude of the density in the charge regions varied between 0.2 and 13 nC/cu m. The vertical extent of the charge regions ranged from 130 to 2100 m. None of the present 12 storms had charge distributions that fit the long-accepted model of Simpson et al. (1937, 1941) of a lower positive charge, a main negative charge, and an upper positive charge. In addition to regions similar to the Simpson model, the present storms had screening layers at the upper and lower cloud boundaries and extra charge regions, usually in the lower part of the cloud.

Marshall, Thomas C.↗
NASA NTRS1990

Electrical and kinematic structure of an Oklahoma mesoscale convective system

The case study examines the dynamics and kinematics of a mesoscale convective system (MCS) by comparing its meteorological parameters with in situ electrical measurements. Conventional MCS characteristics are reported including a rear inflow jet, wake low, and a bipolar cloud-to-ground pattern, but some nonclassical conditions are also reported. Horizontally long cloud-to-ground electrical strikes are noted which demonstrate that cloud-to-ground electrical data alone cannot entirely characterize stratiform electrification in MCSs.

Hunter, Steven M.↗
NASA NTRS1993

A Compact Imaging Detector of Polarization and Spectral Content

A new type of image detector will simultaneously analyze the polarization of light at all picture elements in a scene. The integrated Dual Imaging Detector (IDID) consists of a polarizing beam splitter bonded to a charge-coupled device (CCD), with signal-analysis circuitry and analog-to-digital converters, all integrated on a silicon chip. The polarizing beam splitter can be either a Ronchi ruling, or an array of cylindrical lenslets, bonded to a birefringent wafer. The wafer, in turn, is bonded to the CCD so that light in the two orthogonal planes of polarization falls on adjacent pairs of pixels. The use of a high-index birefringent material, e.g., rutile, allows the IDID to operate at f-numbers as high as f/3.5. Other aspects of the detector are discussed.

Rust, D. M.↗
NASA NTRS1992

Electric and kinematic structure of the Oklahoma mesoscale convective system of 7 June 1989

Balloon soundings of electric field in Oklahoma mesoscale convective systems (MCS) were obtained by the National Severe Storms Laboratory in the spring of 1989. This study focuses on a sounding made in the rearward edge of an MCS stratiform rain area on 7 June 1989. Data from Doppler radars, a lightning ground-strike location system, satellite, and other sources is used to relate the mesoscale attributes of the MCS to the observed electric-field profile.

Hunter, Steven M.↗
NASA NTRS1993

Two-dimensional velocity, optical risetime, and peak current estimates for natural positive lightning return strokes

Velocities, optical risetimes, and transmission line model peak currents for seven natural positive return strokes are reported. The average 2D positive return stroke velocity for channel segments of less than 500 m in length starting near the base of the channel is 0.8 +/- 0.3 x 10 exp 8 m/s, which is slower than the present corresponding average velocity for natural negative first return strokes of 1.7 +/- 0.7 x 10 exp 8/s. It is inferred that positive stroke peak currents in the literature, which assume the same velocity as negative strokes, are low by a factor of 2. The average 2D positive return stroke velocity for channel segments of greater than 500 m starting near the base of the channel is 0.9 +/- 0.4 x 10 exp 8 m/s. The corresponding average velocity for the present natural negative first strokes is 1.2 +/- 0.6 x 10 exp 8 m/s. No significant velocity change with height is found for positive return strokes.

Mach, Douglas M.↗
NASA NTRS1993

Continued Development of an Ultra-Narrow Bandpass Filter for Solar Research

The objective of work under this task was to develop ultranarrow optical bandpass filters and related technology necessary for construction of a compact solar telescope capable of operating unattended in space. The scientific problems to which such a telescope could be applied include solar seismology, solar activity monitoring, solar irradiance variations, solar magnetic field evolution, and the location of targets for narrow-field specialized telescopes. We have demonstrated a Y-cut lithium-niobate Fabry-Perot etalon. This filter will be used on the Flare Genesis Experiment. We also obtained solar images with a Z-cut etalon. The technical report on etalon filters is attached to this final report. We believe that work under this grant will lead to the commercial availability of a universal optical filter with approximately 0.1 A bandwidth. Progress was made toward making a suitable 1-2 A tunable blocker filter, but it now appears that the best approach is to make a double-cavity etalon that will not require such a narrow blocker. Broader band blockers are commercially available.

Rust, David M.↗
NASA NTRS1993

Space Storable Rocket Technology program (SSRT). Option 1 program

The Space Storable Rocket Technology (SSRT) Option 1 Program was initiated in October 1991 after completion of the Basic Program. The program was restructured in mid-July 1992 to incorporate a Rhenium Technology Task and reduce the scope of the LO2-N2H4 engine development. The program was also extended to late February 1993 to allow for the Rhenium Technology Task completion. The Option 1 Program was devoted to evaluation of two new injector elements, evaluation of two different methods of thermal protection of the injector, evaluation of high temperature material properties of rhenium and evaluation of methods of joining the rhenium thrust chamber to the columbium injector and nozzle extension. In addition, critical experiments were conducted (Funded by Option 2) to evaluate mechanisms to understand the effects of GO2 injection into the chamber, helium injection into the main LO2, effect of the splash plate and effect of decreasing the aspect ratio of the 120-slot (-13a) element. The performance and thermal models were used to further correlate the test results with analyses. The results of the work accomplished are summarized.

Chazen, Melvin L.↗