Showing papers on "Thunderstorm published in 1980"

A Study of Tornadic Thunderstorm Interactions with Thermal Boundaries

Abstract: 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.

Airborne and ground‐based studies of thunderstorms in the vicinity of Langmuir Laboratory

Abstract: Flights through the central regions of thunderstorms were made over New Mexico on 6 and 15 August 1977 with the ONR/NMIMT Schweitzer aeroplane which carried equipment designed to measure all three components of the electric field, and the charge, Q, and diameter, d, of individual precipitation elements. On the earlier day, information was also obtained with: a rain-gauge network surrounding Langmuir Laboratory; a 3 cm radar; an acoustic system for locating lightning channels; a ground-based field-change meter. The first cell on 6 August produced precipitation at the ground but no lightning. Vertical fields, Ex, of up to about 50kVm−1 and precipitation charge densities ρ of up to −0.5 C km−3 were recorded within the cloud. The second cell, which grew as the first one decayed, produced 7 lightning strokes in 9 minutes during which time the radar revealed vigorous vertical growth in a narrow zone containing precipitation. Thunder reconstructions showed the acoustic sources for the first flash of this cell to be very near the top of the cloud at an altitude of 10 km a.s.1. The subsequent flashes produced acoustic signals from progressively lower in the cloud. When the radar echo reached its maximum height lightning activity ceased. Ex values of up to about 50kVm−1 and pp values of down to −1 Ckm−3 were measured. ρp was consistently negative, individual charges being less than ±40 pC. Q values were within the inductive limit for a thundercloud at breakdown but no systematic relation between Q and d was found. Six penetrations were made through the thundercloud of 15 August, which produced only two lightning strokes. The Ex records were indicative of a (±) dipole located near the cloud top, at around –13°C. Fields of up to about 100kVm−1 and ρp values (positive and negative) of around 5Ckm−3 were measured. Q values of up to ±250 pC were recorded, with charges around ±50 pC being commonly found. No systematic Q-d relation was revealed, and smaller precipitation particles frequently carried charges (positive or negative) in excess of the inductive limit. On both days estimated precipitation rates were of order 10mmh−1 and on most occasions the pilot reported precipitation particles to be either ‘ice’ or ‘mixed liquid water and ice’.

Evidence of Urban and Lake Influences on Precipitation in the Chicago Area

Abstract: A study of summer precipitation conditions in the Chicago area sought to discern evidence of urban influences on precipitation processes and rainfall magnitude by investigating cloud, radar echo, rainfall and thunderstorm data. The rainfall studies identified an area of 15% greater rainfall in central Chicago, considered largely a result of urban influences. The degree of change is less than found at St. Louis, possibly a result of the inhibiting lake influences at Chicago. With respect to the placement of the rain change, the synoptic weather conditions when rain changes occur (squall lines and zones), and the tendency for rain changes to exist in heavier rainfall conditions, the Chicago findings reveal good agreement with those at St. Louis. Limited causative studies suggest an urban enhancement of convective clouds over Chicago and southern Lake Michigan during late afternoon, and case studies of radar echo behavior showed maximum echo intensification repeatedly occurred over the city and at h...

Gravity Waves from Thunderstorms

Abstract: Gravity waves generated by severe thunderstorms in the eastern Ohio-Pennsylvania area were recorded by an array of microbarovariographs at Palisades, New York and by standard microbarographs across northeastern United States. The waves were associated with the cold mesohigh from the outflow of the thunderstorms. Along their path the waves apparently triggered new thunderstorms. The waves were observed to propagate with the velocity of the wind just below the tropopause. The long-distance propagation of the waves is explained by the presence of a dust associated with the critical level (steering level), in agreement with the derivations given by Lindzen and Tung (1976). The dust was directional and waves were absent to the west of the generating area. In the generating area wave-CISK might have been operating. Sharp vertical temperature gradients associated with the passage of the waves were observed by temperature sensors on a tower.

Synoptic-Scale Environments Associated with High Plains Severe Thunderstorms.

Abstract: Typical synoptic-scale features are described for summertime severe thunderstorms on the High Plains. Severe weather generally occurs on several days in succession, under conditions that are relatively benign in terms of conventional severe weather parameters. Low-level conditions strongly resemble previously described convective flash flood situations. Moderate westerly flow is indicated at mid- and upper-levels, with the jet stream axis typically across or north of the threat area. Preexisting mesoscale systems often play a significant role in organizing the activity. Examples are shown, including one involving a thunderstorm outflow boundary.

Electric fields, electron precipitation, and VLF radiation during a simultaneous magnetospheric substorm and atmospheric thunderstorm

Abstract: A balloon payload instrumented with a double-probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L=4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ..delta..B of approx.500 nT at approx.0930 UT. A single-cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from approx.1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one-half the fair weather value prior to 1000 UT; decreased to about one-quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation.more » Third, the data show a high probability that half-hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from the magnetosphere.« less

Discovery of frequent lightning discharges in clouds on Venus

Abstract: The analysis of the composition of the Venus atmosphere made by seven Soviet Venera-type spacecraft between 1967 and 1975 has resulted in speculation about the possible role of lightning in the formation of some minor atmospheric components similar to the Earth's atmosphere. The glowing of the Venus nightside, the ashen light, sometimes observed1 might also be explained by lightning in the Venus atmosphere. Calculations show, however, that there must be many lightning discharges to be visible from the Earth. Nevertheless, although some speculation has arisen about the existence of lightning in the atmospheres of the other planets until recently only lightning discharges in the Earth atmosphere were known.

Rainfall/Watershed Relationships for Southwestern Thunderstorms

Abstract: DEPTH-AREA relationships for thunderstorm rainfall were developed from 20 years of record from dense raingage networks in Arizona and New Mexico, using the National Weather Service method described in NOAA Atlas 2. The relationships are compared with similar previously published ones. Relationships also were developed to indicate the distribution of storm rain-fall over a watershed. This information could be valuable to agencies, groups, and individuals involved in water resources design and evaluation for climatologically similar areas.

A model for ball lightning

Abstract: An eyewitness sees ball lightning as a luminous sphere in regions of thunderstorm activity. There are many reports of ball lightning forming after a lightning discharge, existing for several seconds, and terminating suddenly and silently, or exploding with or without material damage1,2. Jennison3 has described ball lightning observed at close range inside a commercial aircraft shortly after a lightning discharge. As it drifted down the aisle of the passenger cabin, this ball lightning exhibited: (1) perfect equilibrium in a perfectly spherical shape with diameter 22±2 cm; (2) 5–10 W of optical radiation in blue-white light, but no heat radiation; and (3) an optically thick surface of almost solid appearance, devoid of polar or toroidal structure, but with some limb-darkening. It seems unreasonable to dismiss Jennison's ball lightning as an optical illusion4 (afterimage of the eye's retina). A physical explanation in terms of a microwave cavity5, a d.c. glow discharge6, chemical reactions7, nuclear reactions8 or annihilation of antimatter9 runs into difficulties since the all-metal airplane structure would act effectively as an air-tight Faraday cage. A plethora of excited atoms and molecules, and electromagnetic waves ranging from radio frequencies to X rays are produced in the channel of a lightning discharge, but only electric charge itself can enter the interior of an all-metal airplane without difficulty. Here a new model is presented which explains ball lightning in terms of electric charge.

Downbursts and microbursts - An aviation hazard

Abstract: Downburst and microburst phenomena occurring since 1975 are studied, based on meteorological analyses of aircraft accidents, aerial surveys of wind effects left behind downbursts, and studies of sub-mesoscale wind systems. It is concluded that microbursts beneath small, air mass thunderstorms are unpredictable in terms of weather forecast. Most aircraft incidents, however, were found to have occurred in the summer months, June through August. An intense microburst could produce 150 mph horizontal winds as well as 60 fps downflows at the tree-top level. The largest contributing factor to aircraft difficulties seemed to be a combination of the headwind decrease and the downflow. Anemometers and/or pressure sensors placed near runways were found effective for detecting gust fronts, but not for detecting downbursts. It is recommended that new detection systems placed on the ground or airborne, be developed, and that pilots be trained for simulated landing and go-around through microbursts.

Moisture Convergence Using Satellite-Derived Wind Fields: A Severe Local Storm Case Study

Abstract: Five-minute interval 1-km resolution SMS visible channel data were used to derive low-level wind fields by tracking small cumulus clouds on NASA's Atmospheric and Oceanographic Information Processing System. The satellite-derived wind fields were combined with surface mixing ratios to derive horizontal moisture convergence in the prestorm environment of April 24, 1975. Storms began developing in an area extending from southwest Oklahoma to eastern Tennessee 2 h subsequent to the time of the derived fields. The maximum moisture convergence was computed to be 0.0022 g/kg per sec and areas of low-level convergence of moisture were in general indicative of regions of severe storm genesis. The resultant moisture convergence fields derived from two wind sets 20 min apart were spatially consistent and reflected the mesoscale forcing of ensuing storm development. Results are discussed with regard to possible limitations in quantifying the relationship between low-level flow and between low-level flow and satellite-derived cumulus motion in an antecedent storm environment.

Estimation of corona current beneath thunderclouds

Abstract: The intense electric field beneath a thunderstorm often produces corona discharge from bushes and trees. The average steady state corona current per unit horizontal area, Jc, is approximately proportional to the time rate of change of the electric field at the ground when the value of the field changes sign following a lightning flash. This paper derives this relationship and proposes that the contribution of corona discharge to the charge budget of a thunderstorm be evaluated from measurements of the electric field at many sites below a thunderstorm rather than from direct measurement of the corona current.

Observations of Two Colorado Thunderstorms by Means of a Zenith-Pointing Doppler Radar

Abstract: A description is given of the distributions of radar reflectivity, mean Doppler velocity, vertical air velocity and Doppler-velocity variance in two thunderstorms over eastern Colorado. A zenith-pointing Doppler radar was used to obtain data at height intervals of 152 m. It is shown that the storms were composed of a series of turbulent updrafts, resembling those observed in hailstorms in southeastern Arizona. On the basis of similarities with thunderstorms observed elsewhere, it is speculated that the variable nature of the radar reflectivities and updrafts are a characteristic feature of most thunderstorms and that they contribute significantly to the highly variable nature of hail.

Daylight spectra of individual lightning flashes in the 370-690 nm region

Abstract: An optical multichannel analyzer slit spectrometer coupled to a minicomputer was used to record lightning spectra. This is the first successful application of a slit spectrometer to the study of individual lightning flashes and it was accomplished in the daytime. Over 300 spectra were obtained in 1978 and 1979 and are correlated with other experiments in the Thunderstorm Research International Program (TRIP). The spectra duplicate previously published nighttime data but reveal for the first time the relative intensity of H-alpha (656.3 nm) and H-beta (486.1 nm) emissions above their daytime absorption features. These are the characteristic Fraunhofer C and F lines in the solar spectrum. This result suggests that the observation of lightning from space may be accomplished by monitoring the hydrogen emissions from lightning which occur on earth, or on other planets with hydrogen in their atmospheres, such as Jupiter and Venus where lightning recently has been reported.

Rain and Hail Extremes at Altitude

Abstract: A study of the literature was conducted to find the latest data on the rainfall and hail extreme ambient conditions at altitude for the purpose of reviewing the environmental operating conditions of aircraft turbine engines. A 0.1% probability of exceeding 20.96 g/m of water between 4 and 6 km was found for the rainiest month in the tropics, which gives a maximum water/air ratio of 3.18% at 6 km. There is a 0.1% probability of encountering a 2.4-in. (6.1-cm) or greater size hailstone along a 200-mile (320-km) route during the most severe month in the most severe area.

An airport wind shear detection and warning system using Doppler radar

Abstract: Two numerical models of aircraft performance are developed to relate atmospheric wind signals in wind-shear situations to aircraft response. Both models produce time histories of pitch angle, airspeed, height above the ground, and other parameters for simulating aircraft making precision approaches along a 3-deg glide slope to the runway. Simulations conducted using thunderstorm environment wind data indicate that the horizontal wind component is at least as important as the vertical component in determining aircraft response to wind shear. Obtaining quantitative measurements of aircraft approach or departure quality is found to depend on several factors, including the knowledge of winds along the expected flight track, clear-air detection in a quasi-horizontal path, and a near continuous estimate of approach deterioration due to shear conditions.

Lightning protection for aircraft

Abstract: Reference book summarizes current knowledge concerning potential lightning effects on aircraft and means available to designers and operators to protect against effects. Book is available because of increasing use of nonmetallic materials in aircraft structural components and use of electronic equipment for control of critical flight operations and navigation.

Short-interval SMS wind vector determinations for a severe local storms area

Abstract: Short-interval SMS-2 visible digital image data are used to derive wind vectors from cloud tracking on time-lapsed sequences of geosynchronous satellite images. The cloud tracking areas are located in the Central Plains, where on May 6, 1975 hail-producing thunderstorms occurred ahead of a well defined dry line. Cloud tracking is performed on the Goddard Space Flight Center Atmospheric and Oceanographic Information Processing System. Lower tropospheric cumulus tracers are selected with the assistance of a cloud-top height algorithm. Divergence is derived from the cloud motions using a modified Cressman (1959) objective analysis technique which is designed to organize irregularly spaced wind vectors into uniformly gridded wind fields. The results demonstrate the feasibility of using satellite-derived wind vectors and their associated divergence fields in describing the conditions preceding severe local storm development. For this case, an area of convergence appeared ahead of the dry line and coincided with the developing area of severe weather. The magnitude of the maximum convergence varied between -10 to the -5th and -10 to the -14th per sec. The number of satellite-derived wind vectors which were required to describe conditions of the low-level atmosphere was adequate before numerous cumulonimbus cells formed. This technique is limited in areas of advanced convection.

Airborne lightning characterization

Abstract: A WC-130 aircraft was instrumented with wideband electromagnetic field sensors and flown near active thunderstorms to obtain data on the characteristics of nearby and direct strike lightning. An electric field ground station and time-of-arrival network provided time correlated data to identify the three dimensional locations of the discharge and the different events in the lightning flash. A description of the sensors, calibration procedures, and recording equipment is presented. Data are presented on return stroke characteristics in the 5 to 50 km range.

Characteristics of VLF atmospherics during tropical thunderstorms

Abstract: Thunderstorm associated atmospherics during the monsoon, premonsoon and postmonsoon seasons over the tropical station Calcutta show some typical characteristics. In all the cases gradual rise of atmospherics (GRA) and steady recovery of atmospherics (SRA) have been found. In between the above two changes, there is the sudden enhancement of atmospherics (SEA) which is some times composed of two components SEA1 and SEA2. All the above facts of the integrated field intensity of atmospherics (IFIA) observed at 10 and 20 kHz have been critically examined here in relation to monsoon, premonsoon and postmonsoon thunderstorms. The results exhibit that the precipitation is associated with the steady recovery of IFIA during the monsoon and postmonsoon thunderstorms while that during premonsoon thunderstorms is associated with the second sudden enhancement. These anomalies have been interpreted in terms of charge separation within thunderclouds. Moreover, the difference of the respective amplitudes at 10 and 20 kHz of the different variations of IFIA have also been critically focussed.

Characteristics of lightning from frontal system thunderstorms

Abstract: A slowly rotating streak-camera array was used to photograph lightning flashes to ground from thunderstorms associated with 13 large frontal systems. Photographs of 139 flashes were obtained at Kansas City, Missouri, during 1979. Comparison of the frequency distributions of flash duration between frontal thunderstorms and air mass thunderstorms over nonmountainous terrain showed little difference between the two. However, comparison of the distributions of the number of strokes per flash indicated that frontal thunderstorms produce a greater percentage of high-order multiple stroke ground flashes than do air mass thunderstorms.

Environmental conditions and structure of some types of convective mesosystems observed over Venezuela

Abstract: A classification of storms in squall lines, thunderstorm clusters, and isolated thunderstorms was made using radar data collected during the second phase of the Venezuelan International Meteorological and Hydrological Experiments (VIMHEX-1972). The near-environmental conditions in advance of these types of storms are examined. The modification of the environment, as deduced from the dry static energy, moist static energy, latent heat content and relative winds is also studied, and a conceptual model for the storms is presented. Finally, some aspects of storm movement are described.

Initial direct strike lightning data

Abstract: Data waveforms of the rate of change of electric flux density obtained during two lightning strikes to an aircraft specially instrumented for lightning electromagnetic measurements are presented. The aircraft was operating in a thunderstorm environment to elicit strikes. The instrumentation system configuration, flight conditions, and strike scenario showing probable lightning path on the aircraft are described. The waveforms, which were obtained at a 10 nanosecond sample interval, indicate significant excursions of the rate of change of electric flux density occurred over few hundred nanoseconds time interval.

Faa radars and their display of severe weather (thunderstorms)

Abstract: : The relative performances of FAA ASR and ARSR Air Traffic Control radars are compared with the WSR-57 weather radar using simple models of time-dependent reflectivity profiles from severe thunderstorms. Results show the relatively wide vertical beams of FAA radars are helpful for early detection of new rain cells developing aloft. This better detection depends on range and is most useful within 65 n.mi. (120 km). Beyond 110 n.mi. (204 km), the FAA ARSR radars receive less returned signal and therefore underestimate storm strength more than the WSR-57, especially when the first heavy precipitation and hail have reached the ground. Because the FAA radar antennas are tilted and the beam axis is usually several degrees above the horizon, the return tends to maximize during storm development, but may decrease below severe weather indications while severe weather is occurring. be separated using high resolution FIMS. The precision of the proposed analysis method was evaluated with an authentic jet fuel sample, and it was found that the coefficient of variation of minor components averaged 6 percent while that of larger components was 2 or 3 percent. The use of high resolution FIMS together with a batch inlet system and computerized data collection and analysis system appears to be a highly promising technique for providing detailed quantitative data on the chemical composition of middle distillate fuels. (Author)

Airborne Lightning Warning Systems: A Survey.

Abstract: : Lightning warning systems for airborne use may be classified in accord with their application as near-zone warning systems, and distant warning systems. The near-zone systems considered here are essentially electrostatic field detectors (field mill, radioactive probe, and corona point) that can warn of the presence not only of thunderstorms but of high electric fields associated with nonthundery clouds that may nevertheless cause triggered strikes to aircraft (far outnumbering strikes due to natural lightning, according to pilot reports). Lightning-strike and high-field statistics, and associated corona effects, are discussed in connection with triggering of strikes. The distant warning systems considered, aside from airborne weather radar, include RF electric and magnetic sferics detectors, as well as optical systems and the above-mentioned near-zone detectors modified to also detect sferics. The sferics detectors sense electromagnetic fields radiated by lightning and pre-lightning discharges, and may be classified according to their applications as single-station bearing detectors (crossed loops-wideband or narrowband, multiple loops, time-of-arrival and interferometer systems), and as single-station range detectors (crossed loops, 500-KHz-pulse-height, spectral-amplitude-ratio/group-delay-difference, electric amplitude, e.g. 1/r-cubed, and ratio-of-magnetic-to-electric-amplitude systems). Many of the systems surveyed have virtues warranting their consideration, as individuals or in combinations, for airborne warning and avoidance application. However, they all have advantages and disadvantages that require further investigation, careful testing and evaluation.

The diuranal distribution of large hail over the united states

Abstract: The diurnal course of large hail varies over the United States. The time of maximum of large hail changes from near 1500 hours on the east coast to between 1800 and 1900 hours on the Great Plains. The north-to-south differences are smaller except near the Gulf Coast, where secondary maxima occur. In some areas the time of maximum of large hail differs from the maxima times of tornadoes, heavy rain, and thunderstorms.

Outflow from a Nocturnal Thunderstorm

Abstract: : An investigation of a dry nocturnal gust front moving over a dense network of meteorological instruments in east central Illinois is presented The outflow was generated out of an eastward moving, organized storm system passing north of the network Although no precipitation was measured in the network, a change from ambient to outflow air was observed in other meteorological parameters more than 100 km south of the point at which the outflow is estimated to have initiated (Author)