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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Use of the surface wind field as a predictor of thunderstorms and cloud-to-ground lightning at Kennedy Space Center

The convergence-lightning nowcasting method that began to be operationally tested and evaluated by USAF personnel at the KSC in 1986 uses surface convergence, especially the areal average, to identify the potential for new thunderstorm growth. When this areal method fails, normalized cell convergence, which is defined as the integral of cellular convergence with respect to its area, can be used as a complementary technique in association with the areal one. A detailed examination is conducted for one day, and the relationship of normalized cell convergence to lightning flash counts is examined in a 68-day ensemble.

Watson, Andrew I.↗
NASA NTRS1992

Ground level measurements of air conductivities under Florida thunderstorms

Values of the positive and negative polar conductivities under summer thunderstorms in Florida are highly variable and exhibit a significant electrode effect, but the total conductivity usually remains close to values found in fair weather, 0.4 to 1.8 x 10 exp -14 S/m. With these values a method proposed by Krider and Musser (1982) for estimating the total conductivity from changes in the slope of the electric field recovery following a lightning discharge will be extremely sensitive to small time variations in the local Maxwell current density and must be modified to include these effects.

Blakeslee, Richard J.↗
NASA NTRS1992

The use of VAS retrievals for thunderstorm forecasting at the Kennedy Space Center

A modified version of the current operational VAS retrieval methodology was used to examine preconvective environments over central Florida in the vicinity of NASA's Kennedy Space Center. The modifications to the retrieval algorithm are discussed, and results of a case study of 10-11 July 1989 are presented. The VAS retrievals detected mesoscale humidity and stability features that were not resolved by the operational radiosonde network. These features were closely associated with the locations of thunderstorm development.

Hoepner, Wayne A.↗
NASA NTRS1993

An alternative representation of the ice canopy for calculating microwave brightness temperatures over a thunderstorm

Passive microwave brightness temperatures (TBs) at 92 and 183 GHz from an aircraft thunderstorm overflight are compared with values calculated from radar-derived hydrometeor profiles and a modified proximity sounding. Two methods for modeling particles in the ice canopy are contrasted. The first is a 'traditional' approach employing Marshall-Palmer ice spheres. The second, or 'alternative', method partitions 20 percent of the ice water content into a Marshall-Palmer component for graupel and hail, and 80 percent into a modified gamma spherical particle size distribution function representing ice crystals. Results from the alternative approach are superior to those from the traditional method in the anvil and mature convective core. In the decaying convective region, the traditional approach yields better agreement with observed magnitudes. Neither method, however, matches the geometry of the observed TB depression associated with the decaying convective core. This is likely due to the presence of graupel, which is not detected as a special signature in radar reflectivity, but does diminish TBs through scattering. Brightness temperatures at the relatively high microwave frequencies considered are shown to be very sensitive to the ice-particle size distribution.

Muller, Bradley M.↗
NASA NTRS1942

The Electrical Structure of Thunderstorms

The time histories of thunderstorm charge distribution during three storms occurring during the summer of 1940 in the vicinity of the Albuquerque Airport were investigated by the use of eight synchronized recording electrometers arranged in a particular pattern over a field 1.6 kilometers above sea level.

Workman, E J↗
NASA NTRS1956

Summary of derived gust velocities obtained from measurements within thunderstorms

Available measurements of the derived gust velocities within thunderstorms are summarized for altitudes from 5,000 to 34,000 feet. The results indicate that the intensity of the derived gust velocity is essentially constant up to altitudes of 20,000 feet and that an approximate 10-percent reduction in the gust intensity occurs for altitudes from 20,000 to 30,000 feet.

Tolefson, H B↗
NASA NTRS1993

The heating of suprathermal ions above thunderstorm cells

We estimate ion heating in the topside ionosphere directly over thunderstorm cells. The primary heating is due to lower hybrid waves excited through linear mode coupling as intense electromagnetic (EM) whistler mode radiation from lightning is scattered from small scale (2 - 20 m) magnetic-field-aligned plasma density irregularities in the topside ionosphere. For typical radiated EM fields, we find that suprathermal H+ ions in the 6 eV and greater energy range can be heated by 20 to 40 eV as a result of a single lightning discharge. We also show how the number density of 6 eV and greater H(+) ions is enhanced by preheating resulting from the absorption of proton whistlers in the 500-1000 km altitude range. For lightning discharge rates of one or more per second over a 10 exp 4 sq km area, our model predicts a total energy gain for the H(+) ions of 400 eV to 2 KeV and a perpendicular ion flux of about 10 exp 5 to 10 exp 6/sq cm sec. These fluxes should be observable on low altitude spacecraft using presently available instrumentation.

Bell, T. F.↗
NASA NTRS1994

Characteristics of luminous structures in the stratosphere above thunderstorms as imaged by low-light video

An experiment was conducted in which an image-intensified, low-light video camera systematically monitored the stratosphere above distant (100-800 km) mesoscale convective systems over the high plains of the central U.S. for 21 nights between 6 July and 27 August 1993. Complex, luminous structures were observed above large thunderstorm clusters on eleven nights, with one storm system (7 July 1993) yielding 248 events in 410 minutes. Their duration ranged from 33 to 283 ms, with an average of 98 ms. The luminous structures, generally not visible to the naked, dark-adapted eye, exhibited on video a wide variety of brightness levels and shapes including streaks, aurora-like curtains, smudges, fountains and jets. The structures were often more than 10 km wide and their upper portions extended to above 50 km msl.

Lyons, Walter A.↗
NASA NTRS1994

Observations of Nocturnal Thunderstorms and Lighting Displays as Seen During Recent Space Shuttle Missions

During the recent space shuttle flights the Mesoscale Lightning Experiment, an observational program to observe thunderstorms and lightning from space, was conducted. The low light level TV cameras located in the payload bay of the space shuttle were commanded from the ground and used to collect video images. Presented in this paper are some of the images and supporting information.

Vaughan, Otha H., Jr.↗
NASA NTRS1994

NASA Shuttle Lightning Research: Observations of Nocturnal Thunderstorms and Lightning Displays as Seen During Recent Space Shuttle Missions

A number of interesting lightning events have been observed using the low light level TV camera of the space shuttle during nighttime observations of thunderstorms near the limb of the Earth. Some of the vertical type lightning events that have been observed will be presented. Using TV cameras for observing lightning near the Earth's limb allows one to determine the location of the lightning and other characteristics by using the star field data and the shuttle's orbital position to reconstruct the geometry of the scene being viewed by the shuttle's TV cameras which are located in the payload bay of the shuttle.

Vaughan, Otha H., Jr.↗
NASA NTRS1998

The Behavior of Total Lightning Activity in Severe Florida Thunderstorms

The development of a new observational system called LISDAD (Lightning Imaging Sensor Demonstration and Display) has enabled a study of severe weather in central Florida. The total flash rates for storms verified to be severe are found to exceed 60 flashes/min, with some values reaching 500 flashes/min. Similar to earlier results for thunderstorm microbursts, the peak flash rate precedes the severe weather at the ground by 5-20 minutes. A distinguishing feature of severe storms is the presence of lightning "jumps"-abrupt increases in flash rate in advance of the maximum rate for the storm. ne systematic total lightning precursor to severe weather of all kinds-wind, hail, tornadoes-is interpreted in terms of the updraft that sows the seeds aloft for severe weather at the surface and simultaneously stimulates the ice microphysics that drives the lightning activity.

Williams, Earle↗
NASA NTRS1999

High-Altitude Aircraft-Based Electric-Field Measurements above Thunderstorms

We have developed a new set of eight electric field mills that were flown on a NASA ER-2 high-altitude aircraft. During the Third Convection And Moisture EXperiment (CAMEX- 3; Fall, 1998), measurements of electric field, storm dynamics, and ice microphysics were made over several hurricanes. Concurrently, the TExas-FLorida UNderflights (TEFLUN) program was being conducted to make the same measurements over Gulf Coast thunderstorms. Sample measurements will be shown. Our new mills have an internal 16-bit A/D, with a resolution of 0.25 V/m per bit at high gain, with a noise level less than the least significant bit. A second, lower gain channel gives us the ability to measure fields as high as 150 kV/m.

Bateman, M. G.↗
NASA NTRS1999

Optical Transient Detector (OTD) Observations of a Tornadic Thunderstorm

Total lightning observations made by the Optical Transient Detector (OTD) of a tornadic thunderstorm that occurred over Oklahoma 17 April 1995 are presented. The average flash rate of the tornadic storm during the 3.2 min observation period was 45 flashes min.with a flash rate density of 1.16 x 10(exp -4)/s sq km. The total flash rate was almost 18 times higher than the cloud-to-ground rate measured by the National Lightning Detection Network (NLDN). In addition. total lightning rates were observed to decrease prior To tornadic development.

Buechler, D. E.↗
NASA NTRS1999

High-Altitude Aircraft-Based Electric-Field Measurements Above Thunderstorms

We have developed a new set of eight electric field mills that were flown on a NASA ER-2 high-altitude aircraft. During the Third Convection And Moisture EXperiment (CAMEX-3; Fall, 1998), measurements of electric field, storm dynamics, and ice microphysics were made over several hurricanes. Concurrently, the TExas-FLorida UNderflights (TEFLUN) program was being conducted to make the same measurements over Gulf Coast thunderstorms. Sample measurements are shown: typical flight altitude is 20km. Our new mills have an internal 16-bit A/D, with a resolution of 0.25V/m per bit at high gain, with a noise level less than the least significant bit. A second, lower gain channel gives us the ability to measure fields as high as 150 kV/m.

Bateman, M. G.↗
NASA NTRS1999

Thunderstorm and Lightning Development: Modeling and Observations

We use results of a numerical model of convective clouds with a lightning parameterization to examine thunderstorm development and the location of lightning initiation in a Florida storm. These results are compared with radar observations and interferometric measurements of VHF emissions from both intra-cloud (IC) and cloud-to-ground (CG) lightning flashes. Observed rate and mean duration of flashes are analyzed through model results, and we comment altitudes of VHF sources given by the ONERA 3D interferometric system.

Solomon, Robert↗
NASA NTRS1999

Optical Transient Detector (OTD) Observations of a Tornadic Thunderstorm

Total lightning observations made by the Optical Transient Detector (OTD) of a tornadic thunderstorm that occurred over Oklahoma on 17 April 1995 are presented. The average flash rate of the tornadic storm during the 3.2 min observation period was 45 flashes/min, with a flash rate density of 1.16 x 10(exp -4)/s sq km. The total flash rate was almost 18 times higher than the cloud-to-ground rate measured by the National Lightning Detection Network (NLDN). In addition, total lightning rates were observed to decrease prior to tornadic development.

Buechler, D. E.↗
NASA NTRS2002

Thunderstorms Characteristics Observed By TRMM

The goal of the present study is to begin a more comprehensive examination of the spectrum of storm types and their attributes worldwide, and as a function of season, location, and convective regime using the observed lightning, microwave scattering, and reflectively signatures. A global, multi-year data set (1998-2000) is being assembled to further our understanding of convective processes in different climatological regimes. We find that the deepest thunderstorms (having reflectively in excess of 50 dBZ at 9 km altitude) occur in all the sub-tropical continents and occasionally over the open ocean. The most intense storms have the greatest lightning rates, lowest brightness temperatures and greatest depth of reflectively-all indicative of strong updrafts and a well-developed volume of precipitation-sized ice particles.

Goodman, Steven J.↗