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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Thunderstorm and lightning observations from Space Shuttle

A 16 mm camera equipped with a photocell optical sensor and a two-channel tape recorder will be used by Shuttle astronauts to obtain information on thunderstorms and lightning from orbital altitude. The camera will provide photographs of the lightning at night and of the convective structure of the storms during the day. The photocell sensor, which is capable of detecting and recording lightning by day and by night, will give information on the frequency and characteristics of the lightning that is occurring.

Vaughan, O. H., Jr.↗
NASA NTRS1979

Jet transport performance in thunderstorm wind shear conditions

Several hours of three dimensional wind data were collected in the thunderstorm approach-to-landing environment, using an instrumented Queen Air airplane. These data were used as input to a numerical simulation of aircraft response, concentrating on fixed-stick assumptions, while the aircraft simulated an instrument landing systems approach. Output included airspeed, vertical displacement, pitch angle, and a special approach deterioration parameter. Theory and the results of approximately 1000 simulations indicated that about 20 percent of the cases contained serious wind shear conditions capable of causing a critical deterioration of the approach. In particular, the presence of high energy at the airplane's phugoid frequency was found to have a deleterious effect on approach quality. Oscillations of the horizontal wind at the phugoid frequency were found to have a more serious effect than vertical wind. A simulation of Eastern flight 66, which crashed at JFK in 1975, served to illustrate the points of the research. A concept of a real-time wind shear detector was outlined utilizing these results.

Mccarthy, J.↗
NASA NTRS1980

Thunderstorm-environment interactions determined with three-dimensional trajectories

Diagnostically determined three dimensional trajectories were used to reveal some of the scale interaction processes that occur between convective storms and their environment. Data from NASA's fourth Atmospheric Variability Experiment are analyzed. Two intense squall lines and numerous reports of severe weather occurred during the period. Convective storm systems with good temporal and spatial continuity are shown to be related to the development and movement of short wave circulation systems aloft that propagate eastward within a zonal mid tropospheric wind pattern. These short wave systems are found to produce the potential instability and dynamic triggering needed for thunderstorm formation. The environmental flow patterns, relative to convective storm systems, are shown to produce large upward air parcel movements in excess of 50 mb/3h in the immediate vicinity of the storms. The air undergoing strong lifting originates as potentially unstable low level air traveling into the storm environment from southern and southwestern directions. The thermo and hydrodynamical processes that lead to changes in atmospheric structure before, during, and after convective storm formation are described using total time derivatives of pressure or net vertical displacement, potential temperature, and vector wind calculated by following air parcels.

Wilson, G. S.↗
NASA NTRS1980

Direct effects of lightning on an aircraft during intentional penetrations of thunderstorms

An armored T-28 aircraft was struck by lightning on two different days while participating in the 1979 severe environmental storm and mesoscale experiment in Oklahoma. The T-28, which is specially armored and instrumented, was making intentional penetrations of thunderstorms and was struck twice on 30 May and once on 5 June. Various degrees of damage, mainly in the form of large burn spots and holes, resulted to the aircraft.

Musil, D. J.↗
NASA NTRS1979

Flight through thunderstorm outflows

Computer simulation of aircraft landing through thunderstorm gust fronts is carried out. The 3 degree-of-freedom, nonlinear equations of aircraft motion for the longitudinal variables containing all two-dimensional wind shear terms are solved numerically. The gust front spatial wind field inputs are provided in the form of tabulated experimental data which are coupled with a computer table lookup routine to provide the required wind components and shear at any given position within an approximate 500 m x 1 km vertical plane. The aircraft is considered to enter the wind field at a specified position under trimmed conditions. Both fixed control and automatic control landings are simulated. Flight paths, as well as control inputs necessary to maintain specified trajectories, are presented and discussed for aircraft having characteristics of a DC-8, B-747, and a DHC-6.

Frost, W.↗
NASA NTRS1980

A study of tornadic thunderstorm interactions with thermal boundaries

A study of tornadic thunderstorm interactions with thermal boundaries using a model of subcloud wind profiles is presented. Within a hot, moist, and conditionally unstable air mass, warm thermal advection and surface friction cause the winds to veer and increase with height, while within a cool, moist air mass cool thermal advection and friction combine to produce a wind profile that has maximum speeds near the surface and veers little with height. The spatial distribution of different wind profiles and moisture contents within the boundary layer may act together to maximize mesoscale moisture contents, convergence, and cyclonic vorticity within a narrow mixing zone along the thermal boundary.

Maddox, R. A.↗
NASA NTRS1981

Spiral feature observed at top of rotating thunderstorm

A dark spiral feature is noted in the geosynchronous satellite visible image of the top of a thunderstorm which also has a Doppler radar-observed mesocyclone. Although the evidence is not conclusive, the feature may represent cyclonic rotation at cloud top associated with the pre-tornado mesocyclone.

Adler, R. F.↗
NASA NTRS1980

Doppler radar observation of the evolution of a thunderstorm

Triple-Doppler radar observations of the evolution of the three-dimensional structure of a thunderstorm on May 19, 1978 are analyzed. Continuous data were taken over a long period of the non-severe storm's lifetime as it passed through the radar and the portable automated mesonet network. A fairly low cloud top of 10 km and high reflectivities were observed, and horizontal rotations developed in the middle troposphere, which never reached lower levels. The cyclonic and anticyclonic circulations at mid-levels intensified after the maximum cell height was reached, and a high reflectivity maximum lasted 15-20 min aloft, with the core descending to the surface because of rapid fallout from the largest precipitation particles. Due to the fairly small scale of the updrafts, future use of smaller grid spacings is considered a necessity.

Heymsfield, G. M.↗
NASA NTRS1980

Doppler radar observations of the three-dimensional turbulent structure of a quasi-steady thunderstorm

The spatial patterns and temporal evolution of Doppler radar-inferred turbulence within a quasi-steady, left-moving thunderstorm are reported. An organized downdraft circulation was observed, which maintained a persistent, continuously-propagating, anticyclonic and turbulent updraft. The updrafts attained peak speeds of 25 m/s, and maximum estimated reflectivity factors exhibited peak magnitudes of 50-55 dBZ. Mechanical and buoyant production appeared to be the primary generators of turbulence, although buoyancy generation may have also significantly contributed, since turbulent and dynamic entrainment into the vertically accelerating updraft was appreciable below the strongest turbulent activity at 7 km. Patterns of the radial shears of radial velocity exhibited a significant decrease in strength and areal coverage as the storm weakened, which is attributed to decreased activity of large turbulent eddies and the diminution of large-scale mean wind gradients produced by vertical exchanges of horizontal momentum and strong updraft gradients.

Knupp, K. R.↗
NASA NTRS1981

Evolution of downdrafts and rotation in an Illinois thunderstorm

Multiple-Doppler radar observations of a non-severe Illinois thunderstorm with nearly rectilinear vertical wind shear and storm motion related to the wind at a height of 2.5 km are discussed. The cell examined had a radar top of 10 km, and reflectivities of 60 dB(Z). Attention is given the evolution of updraft, downdrafts, and vorticity in this cell, where typical magnitudes were 12 m/sec, 8 m/sec and 0.005/sec, respectively. The main downdrafts were found to be the upshear downdraft during the growth period of the cell, and the left bank downdraft during the mature and downdraft periods. The location of upshear downdraft at mid to upper levels resembles the Lennon and Doswell (1979) conceptual model, as well as three-dimensional cloud model results of severe storms.

Heymsfield, G. M.↗
NASA NTRS1981

Thunderstorm hazards flight research - Program overview

The NASA thunderstorm hazards research program, designed to study the effects of lightning strikes on the design and operation of aircraft, is described. An all-weather F-106B is instrumented to document the EM characteristics of direct and nearby strikes, measure the field parameters and analyze the ambient atmospheric content, and film the strikes; X-ray detectors are also on board, along with instrumentation for determining the frequency of visible light waveforms. Data is either recorded on-board or sent by telemetry to base, while ground based telemetry is used to direct the pilot and craft into regions of optimal lightning activity. The sensing apparatus is described, and ongoing programs to correlate different storm parameters are reviewed, along with operational procedures and safety precautions. Continued use of the craft through 152 storms and 16 direct hits, with no fatalities or circuit breaker throw, confirms the ability of metal skinned aircraft to withstand lightning strikes; data gathered from flights during 1980 are provided.

Deal, P. L.↗
NASA NTRS1982

An intense, quasi-steady thunderstorm over mountainous terrain. I - Evolution of the storm-initiating mesoscale circulation

The evolution of mesoscale systems that eventually lead to the formation of large quasi-steady storm systems is investigated. The morphological and turbulent structure of the quasi-steady storm is described. Data obtained during the South Park Area Cumulus Experiment from surface meteorological stations, rawinsondes and tethered balloons, conventional and Doppler radars, powered aircraft, and satellites, indicate that on July 19, 1977, a north-south oriented line of intense convective cells formed and remained within South Park. Elevated surface heating created a region of low-level convergence, importing Pacific moisture from west of the Rockies. The mesoscale thunderstorm line formed over this convergence zone, and a single large convective cell was observed to grow on the southern end of the mesoscale line, exhibiting supercell characteristics and substantial modifications of the environmental flow.

Cotton, W. R.↗
NASA NTRS1982

An intense, quasi-steady thunderstorm over mountainous terrain. III - Doppler radar observations of the turbulent structure

The evolution of the turbulent structure of the intense, quasi-steady thunderstorm that occurred on July 19, 1977, over South Park, Colorado, is examined. Doppler radar estimates of turbulent kinetic energy dissipation rates and radial shears of raw radial velocity are used, and a comparison is made between turbulent patterns and mean storm airflow. Turbulent intensity and activity peaked at mid to upper storm levels, and the primary storm updraft was almost turbulence-free at low levels. It is suggested that buoyancy and wind shear acted together to generate turbulent eddies at middle storm levels, and at mid to upper levels, maximum estimated dissipation rate estimates approached 0.15 sq m/cu s.

Knupp, K. R.↗
NASA NTRS1982

The life cycle of thunderstorm gust fronts as viewed with Doppler radar and rawinsonde data

This paper presents the time-dependent analysis of the thunderstorm gust front with the use of Project NIMROD data. RHI cross sections of reflectivity and Doppler velocity are constructed to determine the entire vertical structure. The life cycle of the gust front is divided into four stages: (1) the formative stage; (2) the early mature stage; (3) the late mature stage; and (4) the dissipation stage. A new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground, while carrying some of the smaller precipitation ahead of the main echo core of the squall line. This feature is called a 'precipitation roll'. As determined from rawinsonde data, the cold air behind the gust front accounts for the observed surface pressure rise. Calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow. The equation governing the propagation speed of a density current accurately predicts the movement of the gust front.

Wakimoto, R. M.↗
NASA NTRS1983

The NASA Thunderstorm Overflight Program (TOP): Research in atmospheric electricity from an instrumented U-2 aircraft platform

An overview of the NASA Thunderstorm Overflight Program (TOP) is presented. The various instruments flown on the NASA U-2 aircraft, as well as the ground instrumentation used to collect optical and electronic signature from the lightning events, are discussed. Samples of some of the photographic and electronic signatures are presented. Approximately 6400 electronic data samples of optical pulses were collected and are being analyzed.

Vaughan, O. H., Jr.↗
NASA NTRS1982

Medium-range objective predictions of thunderstorms on the McIDAS/CSIS interactive computer system

Until recently, all operational meteorological data has been made available to forecasters in a variety of different forms. Predictions based upon these different data formats have been complicated by the inability of forecasters to easily assimilate, in real-time, all data to provide an optimum decision regarding future weather occurrences. By March 1980, a joint NASA/NOAA effort had been initiated to develop the Centralized Storm Information System (CSIS). The primary objectives of this joint project are related to an improvement of the overall severe storm forecast and warning procedure and to a demonstration of the operational utility of techniques developed within the applied research community. CSIS is to utilize the Man Computer Interactive Data Access System (McIDAS). The present investigation is concerned with one of the first attempts to employ the CSIS system for the evaluation of a new research technique involving the prediction of thunderstorms over a forecast period of 12-48 hours.

Wilson, G. S.↗
NASA NTRS1983

In situ aircraft measurements of enhanced levels of N2O associated with thunderstorm lightning

A series of measurements of enhanced levels of atmospheric N2O associated with thunderstorm lightning are reported. The data were gathered by instrumentation on-board an aircraft operated as part of the NASA Storm Hazards Project. Air samples were taken both during storms and in clear conditions to have a basis for comparisons; sample bottles were filled at altitudes from 11,000-40,000 ft. Gas chromatography was employed for sample composition analyses, revealing clear air N2O concentrations of about 310 ppbv, while storm concentrations reached, for example, 490, 729, and 393 ppbv. Although the measurements did not precisely characterize the actual lightning contributions, the enhancements being present during electrically active storms did confirm that trace gases are produced by lightning. Calculations are presented to demonstrate that the 3 to greater than 12 keV X rays detected in storm clouds are of sufficient energy to drive the production of N2O from the reaction of metastable nitrogen with molecular oxygen.

Levine, J. S.↗
NASA NTRS1983

Heavy thunderstorms observed over land by the Nimbus 7 scanning multichannel microwave radiometer

Brightness temperatures obtained through examination of microwave data from the Nimbus 7 satellite are noted to be much lower than those expected on the strength of radiation emanating from rain-producing clouds. Very cold brightness temperature cases all coincided with heavy thunderstorm rainfall, with the cold temperatures being attributable to scattering by a layer of ice hydrometeors in the upper parts of the storms. It is accordingly suggested that brightness temperatures observed by satellite microwave radiometers can sometimes distinguish heavy rain over land.

Spencer, R. W.↗