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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Application of spatial Poisson process models to air mass thunderstorm rainfall

Eight years of summer storm rainfall observations from 93 stations in and around the 154 sq km Walnut Gulch catchment of the Agricultural Research Service, U.S. Department of Agriculture, in Arizona are processed to yield the total station depths of 428 storms. Statistical analysis of these random fields yields the first two moments, the spatial correlation and variance functions, and the spatial distribution of total rainfall for each storm. The absolute and relative worth of three Poisson models are evaluated by comparing their prediction of the spatial distribution of storm rainfall with observations from the second half of the sample. The effect of interstorm parameter variation is examined.

Eagleson, P. S.↗
NASA NTRS1988

Interior characteristics at mid-levels of thunderstorms in the southeastern United States

Data characterizing the vertical wind structure and hydrometeors within cumulonimbus clouds in the southeastern United States were collected by the armored T-28 aircraft during the 1986 Cooperative Huntsville Meteorological Experiment (COHMEX). Data analysis concentrated on the hydrometeor character and development, as well as the general microphysical and kinematic structure of the clouds penetrated. The high reflectivities which sometimes exceeded the usual 55 dBz limit set for the T-28, are not necessarily related to hail in the COHMEX storms. Instead, large numbers of millimeter-size particles were found, while the hail infrequently encountered was generally small. The fact that the larger hydrometeors were usually found in narrow and weak updrafts that appeared to be well mixed suggests that a coalescence mechanism was active in many of the storms. The depth of warm cloud (typically about 3.5 km) present in these storms apparently allows ample time for particles to reach the observed millimeter sizes. The presence of cloud droplets in the largest sizes measured supports this mechanism. Ice processes play a role in the precipitation, but hail was unable to grow very large in these storms probably because the high concentrations of observed growth centers suggest a natural beneficial competition process.

Musil, Dennis J.↗
NASA NTRS1988

Providing operational guidance for the development of sea breeze thunderstorms at the Kennedy Space Center - An experiment using a mesoscale numerical model

The effectiveness of a mesoscale numerical model to provide improved local forecast guidance is evaluated with respect to sea breeze convection storms at the Kennedy Space Center. The model and operational forecast guidance production are described. A case study is presented for sea breeze convection storms and lightning events on July 1, 1986. It is found that the mesoscale numerical model outperforms purely subjective predictions of sea breeze convection. The range of applications for the model are considered.

Lyons, Walter A.↗
NASA NTRS1989

Characterization of thunderstorm induced Maxwell current densities in the middle atmosphere

Middle atmospheric transient Maxwell current densities generated by lightning induced charge perturbations are investigated via a simulation of Maxwell's equations. A time domain finite element analysis is employed for the simulations. The atmosphere is modeled as a region contained within a right circular cylinder with a height of 110 km and radius of 80 km. A composite conductivity profile based on measured data is used when charge perturbations are centered about the vertical axis at altitudes of 6 and 10 km. The simulations indicate that the temporal structure of the Maxwell current density is relatively insensitive to altitude variation within the region considered. It is also shown that the electric field and Maxwell current density are not generally aligned.

Baginski, Michael Edward↗
NASA NTRS1991

Analysis of lightning field changes produced by Florida thunderstorms

A new method is introduced for inferring the charges deposited in a lightning flash. Lightning-caused field changes (delta E's) are described by a more general volume charge distribution than is defined on a large cartesian grid system centered above the measuring networks. It is shown that a linear system of equations can be used to relate delta E's at the ground to the values of charge on this grid. It is possible to apply more general physical constraints to the charge solutions, and it is possible to access the information content of the delta E data. Computer-simulated delta E inversions show that the location and symmetry of the charge retrievals are usually consistent with the known test sources.

Koshak, William John↗
NASA NTRS1991

Electrification in winter storms and the analysis of thunderstorm overflight

The emergence of 24 hr operational lightning detection networks has led to the finding that positive lightning strokes, although still much fewer in number than the normal negative strokes, are present in summer and winter storms. Recent papers address the importance of understanding the meteorological conditions which lead to a dominance of one polarity of stroke over another; the appearance of positive strokes at the end of a storm appeared to presage the end-of-storm downdraft and subsidence leading to downburst activity. It is beginning to appear that positive strokes may be important meteorological indicators. Significant research accomplishments on the following topics are addressed: (1) a study to verify that the black boxes used in the lightning networks to detect both negative and positive strokes to ground were accurate; (2) the use of slow tails to determine the polarity of distant lightning; (3) lightning initiation in winter vs. summer storms; (4) the upgrade of sensors for the measurement of electric field signals associated with lightning; (5) the analysis of lightning flash records from storms between 40 and 125 km from the sensor; and (6) an interesting aspect of the initiation process which involves the physical processes driving the stepped leader. The focus of current research and future research plans are presented.

Brook, Marx↗
NASA NTRS1991

The spatial variations of lightning during small Florida thunderstorms

Networks of field mills (FM's) and lightning direction finders (LDF's) were used to locate lightning over the NASA KSC on three storm days. Over 90 percent of all cloud-to-ground (CG) flashes that were detected by the LDF's in the study area were also detected by the LDF's. About 17 percent of the FM CG events could be fitted to either a monopole or a dipole charge model. These projected FM charge locations are compared to LDF locations, i.e., the ground strike points. It was found that 95 percent of the LDF points are within 12 km of the FM charge, 75 percent are within 8 km, and 50 percent are within 4 km. For a storm on 22 Jul. 1988, there was a systematic 5.6 km shift between the FM charge centers and the LDF strike points that might have been caused by the meteorological structure of the storm.

Oram, Timothy D.↗
NASA NTRS1991

An assessment of VAS-derived retrievals and parameters used in thunderstorm forecasting

VAS satellite retrievals and derived parameters used in forecasting severe local storms were evaluated against corresponding radiosonde values. VAS products were also compared with the first-guess input to the retrieval algorithm. The evaluation methodology was to pair each radiosonde observation with the closest VAS retrieval within 50 km during a four-month period in 1986. VAS temperatures agreed closely with radiosonde values; dewpoints showed less agreement. Sounding differences were poorly correlated with the number of pixels from which the retrievals were prepared. VAS discrepancies usually were not well correlated with first-guess errors. Horizontal gradients of VAS products were stronger than those from radiosondes. VAS precipitable water agreed better with ground truth than did dewpoints at individual levels, but VAS thicknesses were not much improved. Results for severe storms forecasting parameters indicated that discrepancies increased with the amount of manipulation required during computation. The lifted index showed the best agreement; positive bouyant energy showed poor comparisons.

Fuelberg, Henry E.↗
NASA NTRS1990

A preliminary evaluation of short-term thunderstorm forecasting using surface winds at Kennedy Space Center

In 1987 NASA expanded its surface wind network onto the mainland west of Kennedy Space Center, increasing the network area from nearly 800 sq km to over 1600 sq km. Here, the results of this expansion are reported using three years of wind and lightning information collected during June, July, August, and September of 1987, 1988, and 1989. The divergence-lightning relationships and the importance of wind direction are addressed, and the verification is summarized.

Watson, Andrew I.↗
NASA NTRS1993

Electrification in winter storms and the analysis of thunderstorm overflight data

We have been focusing our study of electrification in winter storms on the lightning initiation process, making inferences about the magnitude of the electric fields from the initial pulses associated with breakdown, i.e., with the formation of the initial streamers. The essence of the most significant finding is as follows: (1) initial breakdown radiation pulses from stepped leaders prior to the first return stroke are very large, reaching values of 20-30 Volts/meter, comparable to return stroke radiation; and (2) the duration of the stepped leader, from the initial detectable radiation pulse to the return stroke onset, is very-short-ranging from a minimum 1.5 ms to a maximum of 4.5 ms. This past summer (June-August of 1991) we participated in the CAPE program at the Kennedy Space Center in order to acquire data on stepped leaders in summer storms with the same equipment used to get the winter storm data. We discovered that the vigorous leaders seen in winter so frequently were present in summer storms, although not as large in amplitude and certainly not as frequent.

Brook, Marx↗
NASA NTRS1993

The importance of short-term forecasting of thunderstorms to launch operations at Cape Canaveral

The local meteorological events leading up to the launch of the space shuttle Atlantis on 2 August 1991 were captured in full-resolution GOES visible data being archived for the Convection and Precipitation/Electrification Experiment. The postponement of the launch on 1 August, and the successful lift-off on the following day provide a good example of the important role played by nowcasting and short-term forecasting at Cape Canaveral. In this brief article, we discuss the local weather conditions prior to, during, and after the launch and demonstrate the importance of short-term forecasting capabilities around the cape during launch operations.

Cooper, Harry J.↗
NASA NTRS1991

Sensor fusion techniques for predicting thunderstorm evolution using lightning and radar networks

A pattern recognition scheme that is used to generate initial seeds or 'first guess' fields for clustering the discrete lightning discharges into storm cells is presented. The clustering process is critically dependent on the prior accuracy of the lightning location estimates. The generation of subsequent storm life-cycle time series (for extrapolation forecasting) also relies on the cluster analysis procedure assigning the correct number of lightning discharges (objects) to the proper storms (groups). The advantages and limitations of different clustering strategies for storm identification and tracking are examined. Storm identification with lightning data alone is compared to storm identification with radar alone, and some synergies for sensor fusion are explored.

Goodman, Steven J.↗
NASA NTRS1999

Characteristics of Thunderstorms and Lightning Flashes Which Produce Mesospheric Transient Luminous Events

A six year record of optical observations of lightning-induced mesospheric transient luminous events (TLEs) is available from the Yucca Ridge Field Station (YRFS) near Ft. Collins, CO. Climatological analyses reveal sprites and elves occur in a variety of convective storm types, but principally mesoscale convective systems (MCSs) and squall lines. Severe supercell storms rarely produce TLEs, except during their dissipating stage. Few TLEs are observed during storms with radar echo areas <7,500 sq km. Above this size there is a modest correlation with radar areal coverage. A typical High Plains storm produces 45 TLEs over a 143 interval. Sprites and most elves are associated with +CGs. The probability of a TLE increases with peak current. In six storms, 5.1% of +CGs produced TLEs, the number increasing to 32% of +CGs with >75 kA and 52% of +CGs with >100 kA peak current.

Lyons, W. A.↗
NASA NTRS1999

Global Lightning Variations Caused by Changes in Flash Rate and by Changes in Number of Thunderstorms

Observations from the Optical Transient Detector in space are used to examine the response of the number of storms and the total flash rate to thermodynamic forcing of deep convection on the diurnal and annual time scales. On the diurnal time scale, the flash rate appears to track with cloud buoyancy, and storm numbers dominate later in the cycle. On the annual time scale, almost all of the total lightning response is due to changes in the number of storms, with a negligible contribution from flash rate.

Williams, E.↗
NASA NTRS2000

Lightning Activity within a Tornadic Thunderstorm Observed by the Optical Transient Detector (OTD)

The first storm-scale, total lightning observations during tornadogenesis from space are presented. The NASA (National Aeronautics and Space Administration) OTD (Optical Transient Detector) overpass of an Oklahoma supercell, just minutes prior to tornado touchdown on 17 April 1995, detected a lightning flash rate of 45 flashes/ min. The total lighting activity was at least 15 times greater than the cloud-to-ground lightning activity detected by the National Lightning Detection Network (NLDN), indicating most of the lightning was intracloud. Total lightning rates were decreasing rapidly prior to tornadic touchdown. These observations are consistent with the limited results from recent ground based measurements of total lightning activity in tornadic storms, suggesting significant intracloud lightning and rapidly decreasing flash rates prior to tornado touchdown.

Buechler, D. E.↗
NASA NTRS2000

Lightning Activity within a Tornadic Thunderstorm Observed by the Optical Transient Detector (OTD)

The first storm-scale, total lightning observations from space during tornadogenesis are presented. During the overpass of an Oklahoma supercell, just minutes prior to tornado touchdown on 17 April 1995, the NASA (National Aeronautics and Space Administration) OTD (Optical Transient Detector) detected a total of 143 flashes during approximately 3 minutes of observation time. The estimated total flash rate ranges from 45 (raw counts) to 78 (corrected for detection efficiency) flashes min-1. This total flash rate was at least 17 times greater than the cloud-to-ground lightning rate detected by the National Lightning Detection Network (NLDN), indicating most of the lightning was intracloud. Cloud-to-ground lightning at this time was also dominated by positive polarity flashes. In addition, total lightning rates were decreasing rapidly prior to touchdown. These OTD observations are consistent with the limited results from recent ground based measurements of total lightning activity in tornadic storms and corroborate that such storms have unusually high total flash rates, are dominated by intracloud lightning, and that the total flash rates are observed to decrease rapidly in the minutes prior to touchdown.

Buechler, D. E.↗