Showing papers on "Thunderstorm published in 1974"

Lightning in volcanic clouds

Abstract: Positive charge is carried aloft by the clouds formed when molten lava comes in contact with seawater, and thus positive potential gradient values sometimes exceed 7000 V/m. Lightning flashes often occur, associated with the more violent steam eruptions; they effectively lower positive charge to earth in single strokes, apparently in single element discharges that are opposite the polarity of those observed in normal thunderstorms. As was inferred from the shape of the potential gradient changes and from time-lapse photographs, the charge appeared to be distributed in a vertical column extending upward from the sea to a height not exceeding about 100 m.

Lightning Incidence in Britain and the Solar Cycle

Abstract: Many thunderstorm observers have been used in Great Britain for obtaining data on the occurrence of storms. Some experimental data are given and theoretical considerations made to show that the relationships between the recorded number of thunderstorm days, the actual number of thunderstorm days and lightning incidence are likely to be complex.

Cloud-to-Ground Lightning Versus Radar Reflectivity in Oklahoma Thunderstorms

Abstract: Sferic pulse-train amplitudes and arrival times were used to locate lightning flashes and correlate cloud-to-ground (C–G) lightning with radar reflectivity in two typical Oklahoma storm systems. One system was a squall line lasting about 6 hr and producing detailed azimuthal displays of at least six individual storms with C–G lightning. The second system was a group of weaker air mass thunderstorms lasting about 3 hr. Although lightning counts per unit time varied widely between storms and within the same storm, the correlation of lightning counts with the radial extent of radar reflectivity factors ≥550 mm6 m−3 was fair. A rough correlation existed between C–G lightning counts and the amount of rainfall. The overall average rate of one cloud-to-ground flash per 1.6 × 1010 gm of rainfall found in a limited number of storms compares with Battan's report of one flash per 3 × 1010 gm. Even though there was some uncertainty about the rainfall measurements, the Oklahoma results support the opinion tha...

Discussion of Measurements inside High-Speed Thunderstorm Updrafts

Abstract: Four soundings taken in high-speed updrafts of severe thunderstorms indicate moist adiabatic ascent to mid-levels. This implies that the cores of strong updrafts are undiluted by environmental air. The Squires-Turner entraining jet model substantiates this conclusion. Comparison of model and observed vertical velocities indicates in one case that actual velocities may be reduced by adverse pressure gradient forces which are not included in the model. However, the data from the other cases are not sufficient to verify this hypothesis.

Measured electric field in the vicinity of a thunderstorm system at an altitude of 37 km

Abstract: A balloon-borne experiment to measure the atmospheric electric field was flown from the National Scientific Balloon Facility at Palestine, Texas, on July 10, 1973. The electric field and atmospheric conductivity were measured during ascent and for a 4-hour float period at 37-km altitude. Termination of the flight occurred near a thunderstorm line in west Texas. The perturbing influence of the thunderstorms on the electric field was observed at least 100 km from the storm line. The measured electric field is in reasonable agreement with calculations based on simple models of cloud structure and atmospheric conductivity. Large pulses in the measured electric field are interpreted as being the result of intracloud lightning.

The Derivation of Consistent Fields of Wind and Geopotential Height from Mesoscale Rawinsonde Data.

Abstract: With an attainable height resolution of no better than ±10 m from individual soundings, direct analysis of geopotential height gradient from mesoscale rawinsonde ascents could not be expected to produce reliable results. A method is presented for deriving a height field which incorporates the carefully analyzed horizontal winds measured by an upper air network specifically designed to study severe thunderstorms. Three-dimensional distributions of wind, temperature and moisture content are obtained as a function of time using a combination of subjective and objective analysis techniques, which take account of departure from scheduled release time, differing ascent rates, and the horizontal drift of balloons during ascent. The vertical component of air motion is computed from the kinematic approach. Adjustments are applied to divergence estimates to achieve physically realistic results for vertical motion in the upper troposphere. Errors in the horizontal wind components are likewise altered for co...

Weather and Climatic Patterns

Abstract: This chapter contains a brief outline of the salient features of the weather and climatic patterns in India, with a special reference to the behaviour of the monsoon and the incidence of other major phenomena like cyclonic storms, depressions, thunderstorms, etc., which also influence the seasonal and regional distribution of the annual rainfall in India. Some reference is also made to phenomena like cold and heat waves, frost, high wind, hailstorm, etc. (GOVINDASWAMY 1953, RAMDAS 1946, RAMDAS et al. 1954, RAMDAS 1960, 1968).

Point processes of seasonal thunderstorm rainfall: 3. Relation of point rainfall to storm areal properties

Abstract: Following a two-part study of the stochastic nature of thunderstorm occurrence and the probability of daily rainfall depths, the importance of point rainfall information to areal rain distributions is indicated. A probabilistic expression is developed for the relationship between the point depth of rainfall, the local probability distribution of storm cell maximum depth, and the dimensionless expression of storm depth-area pattern. In a sample test the expression is successfully used to reproduce point rainfall depth probability from storm maximum depth distribution and depth area data from Tombstone, Arizona.

Influence of thunderstorms on environmental ozone

Abstract: Ozone observations in north Florida show that thunderstorms play a role in the daily amount of environmental ozone. Increases associated with thunderstorms occur more frequently in the late winter, spring, and early summer than in other months. The observations strongly suggest that ozone produced by the lightning stroke must be insignificant. Stratospheric ozone is indicated to be the principal source of ozone associated with thunderstorms. Stratospheric ozone is believed to be entrained into the thunderstorm at high levels, near or above the tropopause. It is transported into the low levels of the atmosphere by the storm's downdraft. Finally, observations show that increases of ozone associated with thunderstorms occasionally reach sufficient magnitudes in the atmospheric portion of the biosphere to have ecological consequences.

Determinism in Mesoscale Wind Spectra at Columbia, Missouri

Abstract: Power spectra of mesoscale eddies with periods ranging from 10 min to 8 hr were computed for the months of January and July from three years of surface wind data obtained at Columbia, Mo. To educe the degree of determinism in the spectra, their variability with time of year, time of day, wind speed and direction, and with the presence or absence of thunderstorms was measured. Diurnal spectra for January and July were found to be similar. A comparison of semidiurnal daytime and nighttime spectra showed that the former contained considerably more energy than the latter and that the difference was greater in July than in January. The eddy energy was shown to increase by a factor of approximately 7 at night in the presence of thunderstorms. No effect of wind direction could be found. Over a large portion of the lower mesoscale range the diurnal power spectra followed a −1 law, similar to that for “wall turbulence” in the layer of strong shear in the boundary layer over a flat plate.

Severe Storm Latent Heat Release: Comparison of Radar Estimate Versus a Numerical Experiment

Abstract: The time variation of mass-integrated liquid water and latent heat release for a severe thunderstorm in marked vertical wind shear is investigated for an actual Oklahoma storm and for a two-dimensional numerical modeling experiment. For the actual storm, an approximate continuity equation for liquid water variation is used together with profiles of radar reflectivity. Empirical relationships are utilized to determine the rainfall rate (flux) and liquid water content from the radar reflectivity profiles. Estimates of total storm water mass are obtained from the reflectivity profiles for the volume swept by the radar beam in the vertical. The downdraft evaporation rate is parameterized on the basis of a previous study which estimated this quantity as a residual in the continuity equation for liquid water mass. To estimate latent heat release and total liquid water mass from the numerical model, the two-dimensional cloud is extended to a three-dimensional region whose horizontal cross sections are e...

Acoustic radar investigations of boundary layer phenomena

Abstract: A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.

A preliminary study of the synoptic conditions associated with lightning flashes over Mt. San Salvatore, Lugano, Switzerland

Abstract: A preliminary analytical study has been made of the synoptic situations associated with thunderstorms that initiate upward-moving leaders from the towers on the Mt. San Salvatore near Lugano, Switzerland. Synoptic situations at the time of the lightning occurrences were divided into six categories based on the surface weather and flow pattern during the period 1967–1969 at Lugano. Cloud thicknesses were estimated from the LFC (Level of Free Convection) and LCL (Lifting Condensation Level) from the mean sounding at Milan. Large cloud thicknesses were found to be associated with the combined upward and downward discharges and smaller cloud thicknesses were associated with only upward discharges (flashes initiated by upward moving stepped leaders). Furthermore, the large cloud thicknesses were associated with the thunder-storms that had proportionally more flashes to the surrounding countryside than to the tower itself. We offer the speculation that the difference in upward and downward discharges to the towers with associated synoptic situations may be explained on the basis of a deficiency of large raindrops which are believed to be necessary for the initiation of downward discharges. DOI: 10.1111/j.2153-3490.1974.tb01627.x

Electrification in the atmosphere

Abstract: Atmospheric electricity presents a hazard to shipping and there have been several serious fires caused by lightning strikes on tankers There have also been a number of explosions during tanker cleaning It has been suggested that there are some similarities between electrical conditions in a thundercloud and themists in tankers This article attempts to clarify the situation by describing the electrical fields in fine weather and in thunderclouds, and it also discusses electrical charge generation and lightning discharge and damage Results of testing with man-made thunderstorms are described, and conclusions which the author feels would make tanker operations safer are also discussed

The Laser Lightning Rod System: Domestication

Abstract: An unusual application of the laser, namely protection of life and property from lightning, is described. The device relies on multiphoton ionization in mode-locked beams, rather than on collisional (avalanche) electron production. Feasibility is demonstrated numerically, and relevant principles explained. A method of mobile deployment is mentioned, by which economic (as opposed to scientific) feasibility might be achieved. The Laser Lighting Rod System (LLRS) is a modelocked' laser that produces large scale multiphoton ionization (MPI) 2 in the right places at the right times. Calculations indicate that it will have a useful range of a few kilometers and be capable of predetermining the paths of stepped leader (and hence lightning channel) development throughout a volume determined by this range. To the extent that Vonnegut's electrical theory of tornadoes 3 may be valid, the LLRS may permit the destructive force of tornadoes to be diminished (by providing an alternative path to ground for the lightning currents that would otherwise serve to heat the tornado core). Helicopterborne, and periodically grounded in a scheme to be described elsewhere, pairs of such systems could give hot pursuit to active thunderstorm cells throughout their lifetimes, diverting all cloud-to-ground strikes harmlessly to ground, even over forested terrain too rugged for surface vehicle penetration or helicopter landing. In contrast to lightning abatement schemes based on chaff dispersal the LLRS does not litter the landscape, does not require that aircraft go near (or blindly penetrate deep into) the thundercloud, can respond much more quickly to changing conditions, and is better matched to thunderstorm cell drift velocities. A classical prerequisite for collisional ionization in a laser beam is that the amplitude of free electron motion, as induced by the alternating optical frequency electric field, shall be comparable with the electron mean free path. In the laser-induced long spark demonstrations of Basov 5 and Hagen, 6 the electron mean-free path exceeded the amplitude of

Models of spatial and temporal distribution of thunderstorm rainfall

Abstract: A simplified stochastic model based on airmass thunderstorm rainfall data from the 58-square-mile Walnut Gulch Experimental Watershed in south eastern Arizona is being developed at the Southwest Watershed Research Center, Tucson, Ariz. Records from the 95 rain gage network on this watershed pro vide valuable information on airmass thunderstorm rainfall in the Southwestern United States. Proba bility distributions are being used to model random variables—number of cells, spatial distribution of the cells, and cell center depths—of thunderstorms in a summer rainy season. A computer program produces synthetic thunderstorm rainfall based on these distributional assumptions. The synthetic data are compared, with respect to storm center depths and isohyetal map characteristics, with data from the dense rain gage network on Walnut Gulch. The daily and hourly chances of occurrence of seasonal airmass thunderstorm rainfall are modeled. Efforts are being made to model the temporal dis tribution of rainfall from individual cells within the airmass thunderstorm. Finally, the question of model transferability to other regions and locations is tied to defining regional meteorology and local topography.

Visual Observations of a Tornadic Thunderstorm

Abstract: (1974). Visual Observations of a Tornadic Thunderstorm. Weatherwise: Vol. 27, No. 6, pp. 256-258.

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

Abstract: 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.

Application and Applicability of Hydrodynamic Instability Theories to the Formation of Severe Thunderstorms: Free Circulation

Abstract: The feasibility of applying various hydrodyanmic instability theories, previously found applicable in the development of tropical cyclone vortices, to the formative stage of a severe thunderstorm when a meso-low-pressure cell is the dominant circulation feature of the storm's immediate environment is investigated. A consistent grid of meteorological data representative of a meso-low-pressure cell is generated using a model previously described by Lin and Martin. Stability theory of atmospheric vortices is then involved to reflect certain characteristic qualities of an assumed superimposed perturbation upon the generated mesoscale data. The resultant growth-rate equation indicates the determining factors for severe thunderstorm development to be the dimensions of the perturbation and the stability characteristics of the meso-low-pressure cell upon which that perturbation is superimposed. The static stability term representative of the meso-low-pressure cell, in particular, appears to dominate to t...

Acoustic sounding in the planetary boundary layer

Abstract: Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the boundary between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.

The velocities of charged hydrometeors and the production of high fields in thunderstorms [presentation]

Abstract: Calculations of the terminal velocities of charged hydrometeors in the presence of electric fields have been confirmed experimentally. They have formed the basis of computations of the charging current J flowing through a thundercloud as a result of the operation of a precipitative mechanism of cloud electrification. Values of J were calculated for a range of values of field strength E, precipitation rate p 0, precipitation content L, cloud water content C, charge distribution, total separated charge, and the fraction f of the small particles that have undergone a charging event.