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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Ionospheric S-shaped Doppler fluctuations produced by the tornadoes

A three-dimensional nine element HF-CW Doppler sounder array has been used to detect ionospheric disturbances which may be due to tornadoes. The typical events chosen in the present study occurred on November 20 and 27, 1973. Both events are apparently associated with tornadoes sighted in the Huntsville, Alabama area. The Doppler records show S-shaped waves rather than the quasi-sinusoidal waves observed in conjunction with and apparently due to thunderstorms. The wave-periods are in the range of 6 to 8 minutes instead of the 3 to 5 minute periods associated with thunderstorms. Dissipation of waves is mostly due to the evanescent effect and they cannot propagate very far from the path of the tornado center. A theory is presented which is in good agreement with the observations.

Hung, R. J.↗
NASA NTRS1974

Superoutbreak tornadoes of April 3, 1974 as seen in ATS pictures

A total of 122 confirmed tornadoes during the April 3-4 superoutbreak is studied by conducting an extensive aerial survey for mapping the precise paths and characteristics of individual tornadoes. Major conclusions are that the life of a tornado varies between 1 and 125 min, that 74% of the tornadoes can be grouped together into 30 tornado families with the mean family life about 5 times the mean individual life, that the identification of family-producing thunderstorms appears to be extremely useful in issuing a tornado alert, and that a tornado-producing thunderstorm within a 50-mile radar range often shows a hook echo on PPI scope as a probable tornado indicator.

Fujita, T. T.↗
NASA NTRS1975

Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity

A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.

Hung, R. J.↗
NASA NTRS1976

Estimates of the low-level wind shear and turbulence in the vicinity of Kennedy International Airport on 24 June 1975

A study was conducted to estimate the type of wind and turbulence distributions which may have existed at the time of the crash of Eastern Airlines Flight 66 while attempting to land. A number of different wind and turbulence profiles are predicted for the site and date of the crash. The morning and mid-afternoon predictions are in reasonably good agreement with magnitude and direction as reported by the weather observer. Although precise predictions cannot be made during the passage of the thunderstorm which coincides with the time of the accident, a number of different profiles which might exist under or in the vicinity of a thunderstorm are presented. The profile that is most probable predicts the mean headwind shear over 100 m (300 feet) altitude change and the average fluctuations about the mean headwind distribution. This combination of means and fluctuations leads to a reasonable probability that the instantaneous headwind shear would equal the maximum value reported in the flight recorder data.

Lewellen, W. S.↗
NASA NTRS1975

Observation of severe weather activities by Doppler sounder array

A three-dimensional, nine-element, high-frequency CW Doppler sounder array has been used to detect ionospheric disturbances during periods of severe weather, particularly during periods with severe thunderstorms and tornadoes. One typical disturbance recorded during a period of severe thunderstorm activity and one during a period of tornado activity have been chosen for analysis in this note. The observations indicate that wave-like disturbances possibly generated by the severe weather have wave periods in the range 2-8 min which place them in the infrasonic wave category.

Smith, R. E.↗
NASA NTRS1976

Economic benefits of improved meteorological forecasts - The construction industry

Estimates are made of the potential economic benefits accruing to particular industries from timely utilization of satellite-derived six-hour weather forecasts, and of economic penalties resulting from failure to utilize such forecasts in day-to-day planning. The cost estimate study is centered on the U.S. construction industry, with results simplified to yes/no 6-hr forecasts on thunderstorm activity and work/no work decisions. Effects of weather elements (thunderstorms, snow and sleet) on various construction operations are indicated. Potential dollar benefits for other industries, including air transportation and other forms of transportation, are diagrammed for comparison. Geosynchronous satellites such as STORMSAT, SEOS, and SMS/GOES are considered as sources of the forecast data.

Bhattacharyya, R. K.↗
NASA NTRS1977

Spearhead echo and downburst in the crash of an airliner

Meteorological conditions leading to the crash of an airliner short of the runway of a New York airport were studied. Thunderstorm downdrafts much stronger than those measured on the 1946-47 Thunderstorm Project were found. These exceptional downdrafts have been designated as 'downbursts'. The violent cloud systems that produce downburst cells can be identified in the form of forward extensions of radar echoes designed as 'spearhead echoes' which move with unusual speed. The development of downburst cells appears to be tied in with overshooting tops of clouds at the anvil level.

Fujita, T. T.↗
NASA NTRS1977

Measured electric field intensities near electric cloud discharges detected by the Kennedy Space Center's Lightning Detection and Ranging System, LDAR

For a summer thunderstorm, for which simultaneous, airborne electric field measurements and Lightning Detection and Ranging (LDAR) System data was available, measurements were coordinated to present a picture of the electric field intensity near cloud electrical discharges detected by the LDAR System. Radar precipitation echos from NOAA's 10 cm weather radar and measured airborne electric field intensities were superimposed on LDAR PPI plots to present a coordinated data picture of thunderstorm activity.

Poehler, H. A.↗
NASA NTRS1979

Solar-terrestrial coupling through atmospheric electricity

There are a number of measurements of electrical variations that suggest a solar-terrestrial influence on the global atmospheric electrical circuit. The measurements show variations associated with solar flares, solar magnetic sector boundary crossings, geomagnetic activity, aurorae, differences between ground current and potential gradients at high and low latitudes, and solar cycle variations. The evidence for each variation is examined. Both the experimental evidence and the calculations made with a global model of atmospheric electricity indicate that there is solar-terrestrial coupling through atmospheric electricity which operates by altering the global electric current and field distribution. A global redistribution of currents and fields can be caused by large-scale changes in electrical conductivity, by alteration of the columnar resistance between thunderstorm cloud tops and the ionosphere, or by both. If the columnar resistance is altered above thunderstorms, more current will flow in the global circuit, changing the ionospheric potential and basic circuit variables such as current density and electric fields. The observed variations of currents and fields during solar-induced disturbances are generally less than 50% of mean values near the earth's surface.

Roble, R. G.↗
NASA NTRS1979

Lightning as an indication of storm severity

There is a substantial case for the theory that cloud electrification is related primarily to strong convection and the sizeable relative air motion that it implies; therefore, the electrification and subsequent discharge rates can be related to the air motion environment of thunderstorms. The isoceraunic contour map used by the WMO for observing and measuring thunderstorm occurrence contains no information on flash rates, flash density, flash relationship to storm severity, or flash variation with meteorological environment. A constant-view geosynchronous lightning mapper would permit simultaneous studies of the lightning discharge patterns and the meteorological environment of storms, thus establishing whether or not there is a reliable enough relationship to use the observed flash rates and characteristics as supplemental guidance for storm forecast refinement.

Dodge, J. C.↗
NASA NTRS1980

The relationship of storm severity to directionally resolved radio emissions

Directionally resolved atmospheric radio frequency emission data were acquired from thunderstorms occurring in the central and southwestern United States. In addition, RF sferic tracking data were obtained from hurricanes and tropical depressions occurring in the Gulf of Mexico. The data were acquired using a crossed baseline phase interferometer operating at a frequency of 2.001 MHz. The received atmospherics were tested for phase linearity across the array, and azimuth/elevation angles of arrival were computed in real time. A histogram analysis of sferic burst count versus azimuth provided lines of bearing to centers of intense electrical activity. Analysis indicates a consistent capability of the phase linear direction finder to detect severe meteorological activity to distances of 2000 km from the receiving site. The technique evidences the ability to discriminate severe storms from nonsevere storms coexistent in large regional scale thunderstorm activity.

Johnson, R. O.↗
NASA NTRS1979

A quasi-static model of global atmospheric electricity. II - Electrical coupling between the upper and lower atmosphere

The paper presents a model of global atmospheric electricity used to examine the effect of upper atmospheric generators on the global electrical circuit. The model represents thunderstorms as dipole current generators randomly distributed in areas of known thunderstorm frequency; the electrical conductivity in the model increases with altitude, and electrical effects are coupled with a passive magnetosphere along geomagnetic field lines. The large horizontal-scale potential differences at ionospheric heights map downward into the lower atmosphere where the perturbations in the ground electric field are superimposed on the diurnal variation. Finally, changes in the upper atmospheric conductivity due to solar flares, polar cap absorptions, and Forbush decreases are shown to alter the downward mapping of the high-latitude potential pattern and the global distribution of fields and currents.

Roble, R. G.↗
NASA NTRS1980

Analysis and prediction of severe storms environment

Using the special data set collected in Project SESAME (1979), an analysis and modeling efforts to test the hypothesis that a unique combination of terrain, boundary layer processes, and synoptic-scale circulations result in a preferred region of latent instability that determines the location of severe thunderstorm outbreaks are described. Because the relevant circulations are large scale, it is hypothesized that a model that contains the necessary physics will be able to predict the location of these severe storms at least 24 h in advance. Through detailed analysis of the SESAME data set and a series of numerical forecasts, the above hypothesis is being tested and it is hoped that quantitative understanding of the processes leading to the development of severe thunderstorms in the midwestern United States will be gained.

Carlson, T. N.↗
NASA NTRS1980

Doctor Fujita's microburst analysis at Chicago

Doppler radar measurements of an intense wind shear occurance are discussed. The data suggest the presence of an incredibly strong low level jet outflow component of the microburst event, reaching 60 knots only 50 meters above the surface. Evidence also suggests that microbursts more typically occur in very weak thunderstorms that have hardly reached thunderstorm stage.

Mccarthy, J.↗
NASA NTRS1981

Stereographic observations from geosynchronous satellites - An important new tool for the atmospheric sciences

Observations of cloud geometry using scan-synchronized stereo geostationary satellites having images with horizontal spatial resolution of approximately 0.5 km, and temporal resolution of up to 3 min are presented. The stereo does not require a cloud with known emissivity to be in equilibrium with an atmosphere with a known vertical temperature profile. It is shown that absolute accuracies of about 0.5 km are possible. Qualitative and quantitative representations of atmospheric dynamics were shown by remapping, display, and stereo image analysis on an interactive computer/imaging system. Applications of stereo observations include: (1) cloud top height contours of severe thunderstorms and hurricanes, (2) cloud top and base height estimates for cloud-wind height assignment, (3) cloud growth measurements for severe thunderstorm over-shooting towers, (4) atmospheric temperature from stereo heights and infrared cloud top temperatures, and (5) cloud emissivity estimation. Recommendations are given for future improvements in stereo observations, including a third GOES satellite, operational scan synchronization of all GOES satellites and better resolution sensors.

Hasler, A. F.↗
NASA NTRS1981

On the reliability of hook echoes as tornado indicators

A study of radar echoes associated with the tornadoes of the 3 April 1974 outbreak was performed to evaluate the usefulness of echo shape as an indicator of tornadic thunderstorms. The hook shape was usually successful in characterizing an echo as tornadic, with a false alarm rate of 16%. Because hook echoes were relatively rare, however, a less restrictive shape called distinctive was more successful at detecting tornadic thunderstorms, identifying 65% of the tornadic echoes. An echo had a distinctive shape if it possessed a marked appendage on its right rear flank or was in the shape of a spiral, comma or line echo wave pattern (LEWP). Characteristics of the distinctive echo are given.

Forbes, G. S.↗
NASA NTRS1981

Operational procedures relative to severe weather

Severe weather impact on both safety and the economics of all types of aviation, and reduction of elimination are discussed. The functions and responsibilities of the dispatcher are outlined. All surface weather reports showing inclement weather, SIGMET REPORTS, forecasting turbulence or icing, convective SIGMETS: (1) tornadoes; (2) hail 3/4 of an inch or greater; (3) imbedded thunderstorms; (4) squall lines or (5) an area of level four or greater thunderstorms. This information along with PIREPs of severe weather are relayed to affected flights. It is concluded that operational procedures must be timely and well conceived to assure the least amount of impact on airline operations.

Sullivan, J. F.↗
NASA NTRS1981

The Joint Airport Weather Studies Project

A block diagram of the joint airport weather studies program is presented. Background leading to the development of the program is reviewed. Basic studies, aircraft performance, and detection and warning techniques used to develop fine scale structure of thunderstorm dynamics and kinematics in the vicinity of a major airport; effect of thunderstorm low level wind shear on aircraft performance; and development of real time testing of flow level wind shear detection and warning techniques and displays are described.

Mccarthy, J.↗