Showing papers on "Thunderstorm published in 1969"

Spatial Correlations of Storm, Monthly and Seasonal Precipitation

Abstract: One approach to defining sampling requirements for precipitation measurement networks is through statistical correlation methods. Data from three dense raingage networks in Illinois were used with this method on rainfall measurements ranging from 1-min rates to total storm, monthly and seasonal amounts. Effects of rain type, synoptic storm type, and other factors on spatial correlations were studied. Correlation decay with distance, used to indicate sampling requirements, was greatest in thunderstorms, rainshowers and air mass storms. Conversely, minimum decay occurred with steady rain and the passage of low pressure centers. Seasonally, the decay rate is much greater in May–September storms than in cold season precipitation. Sampling requirements are extreme in measuring rainfall rates; thus, assuming a minimum acceptance of 75% explained variance between sampling points, a gage spacing of 0.3 mi is needed for 1-min rain rates compared with 7.5 mi for total storm rainfall in summer storms.

recent studies of urban effects on precipitation in the United States

Abstract: A review of recent research in the United States concerning urban effects on precipitation has revealed that relatively few studies have been performed. The lack of densely spaced precipitation stations with good historical records, inadequate instruments for airborne measurements of the mechanisms that affect precipitation systems, and the difficulties associated with separating orographic, maritime, and gage-exposure effects are the primary reasons for so little research. However, certain climatological studies of four variously sized cities in the midwest and two large cities in the east have shown apparent urban-produced increases ranging from 5 to 16% in annual precipitation and rain days, with 7 to 20% increases in summer thunderstorm days. Substantially greater increases in precipitation, thunderstorms, and hailfalls, 31 to 246%, have been shown in a recent study of an area downwind from a major steel mill complex. The available results show little evidence of urban effects on the occurrence of exc...

Charge distribution in thunderstorm clouds

Abstract: The negative charge involved in lightning flashes to ground is found to be distributed in a manner strongly dependent upon the direction of movement of the storm, and does not, in general, constitute a nearly vertical column as proposed by Malan and Schonland. Based on a study of electric field-changes measured at two stations 10 km apart involving 539 return strokes from 84 flashes in 10 storms, we conclude that the horizontal component of the in-cloud channel on the average exceeds the vertical component, and points in the direction of storm motion. An analysis is given of the five methods of Malan and Schonland, on the basis of which we suggest that significant horizontal components are also compatible with their observations of a vertical column, and that the ‘nearly vertical’ aspect of the charge distribution has been over-emphasized.

Convective Processes Resolved by a Mesoscale Rawinsonde Network

Abstract: Guidelines followed in designing and operating a special mesoscale rawinsonde network are discussed. Objective data reduction and analysis techniques are developed and applied to the wind, temperature and moisture data measured during a selected thunderstorm case. The goal is to appraise the sounding system's limitations and reliability for resolving the mesoscale circulations associated with convective processes. A consistent four-dimensional synoptic portrayal of the variables is achieved by accounting for balloon drift, differing station-to-station and sounding-to-sounding ascent rates, and departures from scheduled release time.Temporal variations in the spatial distributions of computed divergence and kinematic vertical motion are in good qualitative agreement with the location and intensity of thunderstorm radar echoes, after further objective adjustments are applied to compensate for the assumed character of wind measurement and analysis errors. For the purpose of assessing data and analyt...

Thunderstorm turbulence and its relationship to weather radar echoes.

Abstract: Thunderstorm turbulence relationship to weather radar echoes from storm penetrations in Oklahoma by instrumented aircraft

Interactions of the thunderstorm with a conducting atmosphere

Abstract: Vertical dipole charge configurations placed in an atmosphere where the conductivity increases exponentially with altitude have been calculated. The problem is divided into cases involving fast and slow time variations, so that quasi-stationary situations can be compared with the fast changes of lightning discharges. The calculations are presented in the form of graphs in such a way that they can be used for dipoles of all magnitudes. The calculations indicate possible convective motions that can regenerate the dipole charge configurations, and they also show that the potential difference between the ionosphere and the earth can be maintained by thunderstorms only by the pumping action produced by lightning discharges to the earth.

Electricity and rain

Abstract: THE GENERATION OF ELECTRICITY and the formation of rain in thunderstorms are closely related through the physical and electrical interactions among colliding cloud particles, raindrops and hail. Our understanding of these processes started with the observations of Benjamin Franklin and Lord Rayleigh, in the 18th and 19th centuries, that electric fields exist in thunderclouds and that charged raindrops can coalesce. Modern theories indicate that different fall velocities of large and small drops are responsible for the separation of charge in the interior of the cloud.

Thunderstorm warning system

Abstract: A thunderstorm warning system wherein signals from various detectors individually providing representations of (1) the quasistatic electric field occuring between the electric charges of a thundercloud and ground and of (2) radiofrequency radiation pulses within the longwave radiofrequency spectral range that are transmitted from lightning discharges in fully developed thunderstorms and, if desired, of (3) pulses in another spectral range, preferably the optical range, are combined in an electronic logic system so as to result in a visible or audible alert or alarm indication, respectively, under specific predetermined conditions.

Optical polarization induced by electric fields of thunderstorms

Abstract: Optical polarization measurements were made on isolated mountain thunderstorms by the use of a device built to map simultaneously the incident, vertical, and horizontal intensities of the scattered sunlight reflected from the thunderstorm. Results showed that the electric field contained within the thunderstorm prior to and after a lightning discharge is imaged by the local degree of polarization produced by the sunlight reflected from oriented ice crystals on the surface of the storm. The polarization was pronounced enough in simple isolated storms so that one could predict with reasonable certainty the locations of either cloud-to-ground or cloud-to-cloud strokes.

Present status of cloud velocity computations from the ATS I and ATS III satellites.

Abstract: Cloud velocity computations from ATS 1 and 3 satellites spin-scan photographs for prediction of neph systems motion and thunderstorms

Structure of the leading edge of thunderstorm cold-air outflow

Abstract: Thunderstorm cold air outflow leading edge structure recorded by NASA meteorological tower at Kennedy Space Center

Satellite Studies of Clouds and Cloud Bands Near the Low-Level JET1

Abstract: TIROS-VII and -VIII photographs are used to study synoptic and mesoscale cloud patterns during 6 days with strong southerly flow in the Central United States. Cases with nocturnal thunderstorms show a tendency for thunderstorms to occur in the downstream portion of the jet. Through advection of moisture and turbulent breakdown of the nocturnal inversion, the low-level jet plays an important role both in the formation of stratus and in its manner of dissipation. Longitudinal cumulus cloud bands with spacing of 10 to 15 km occur with slightly superadiabatic lapse rates and moderate wind shear in agreement with theoretical results by Kuo.

Flight Hazards in Thunderstoms Determined by Doppler Velocity Variance

Abstract: Vertical velocity variance was measured by means of Doppler radar in a thunderstorm in which no hail fell on the ground. At least 5% of the variance measurements were too large to be accounted for by the spread of precipitation fallspeeds and by vertical gradients of vertical velocity. On this basis, turbulence and/or shear is inferred in the regions of high velocity variance, which were mostly clustered in the front part of the storm, near or on the flanks of major updrafts, at altitudes of 4.5-10 km. The greatest variance value, observed at 7.5 km, was equivalent to a horizontal shear in the updraft in excess of 0.1 sec-1. We conclude that a vertical velocity variance of 2 m2 sec-2 in a storm suggests small hail or light to moderate turbulence, while variances above 4 m2sec-2very likely indicate damaging hail or severe turbulence, or both.

“Hail” on a Mountain in Arizona

Abstract: Visual observations on several mountain peaks in the Santa Catalina Mountains in southeastern Arizona reveal that solid ice particles commonly fall from cumulonimbus clouds in the summer. Hailstones having diameters >2 cm occurred on only one day out of a total of 76 days over a four-summer period. On the other hand, on the top of a 2800-m peak, ice or snow pellets or hail fell on 18 out of 30 observational days during a two-summer period. It seems reasonable to speculate that virtually all thunderstorms in this area contain such particles at some stage in their development.

The Inference of the Charge Distribution in Thunderstorms from Airborne Measurements of the Electric Field

Abstract: A computer-oriented numerical method is developed that under certain physically acceptable assumptions appears to make possible the calculation of the charge distribution in thunderstorms and other clouds from the record of the electric field measured from an airplane that flies ȧ known straight path near the cloud. The method is illustrated with an assumed charge distribution, and its application to actual flight measurements is cited.

Surface Measurements of the Electrical Properties of Warm Clouds over the Sea

Abstract: THE electrical properties associated with warm cloud precipitation have been measured routinely at Hilo, on the windward coast of the Island of Hawaii, for the past three years. Warm clouds in this locality typically form over the ocean east of the island and move inland with the north-east trade wind. The present series of measurements is part of a continuing investigation of the mechanism of charge separation in warm clouds and of how such processes may be related to thunderstorm electricity. It is important to study the electrical properties of non-freezing clouds, which consist only of liquid cloud droplets, to clarify the role of the liquid phase in the complex liquid-ice continuum of thunderstorms, and changes in electrical properties also are intimately associated with the dynamic behaviour of clouds. We believe that atmospheric electrical measurements will provide useful information on the growth and development of warm clouds.

Electrical processes in heavy rain in the tropics

Abstract: The thesis is based on research carried out in Sierra Leone over a period of several years. An asymmetric field mill and a 'wide-angle' shielded receiver have been developed for the measurement of electric field and precipitation current in tropical thunderstorms. A detailed field-mill theory is presented which analyses the effects of leakage currents, inadequate grounding, contact potentials, conduction current, 'pick-up' of fluctuating electric fields and noise in the amplifier. Principles are deduced for the optimum design of a precision field mill using either a phase sensitive detector or an asymmetric signal. Measurements of precipitation current and its response to step changes in the field show that turbulent diffusion of splash droplets probably constitutes an important, even dominant, electrical process in heavy rain. The response of precipitation current to a lightning flash, averaged over many flashes, is large and has a delay of a few seconds. From the analysis of various models considered as a mechanism to explain the results it is deduced that charge carried on splash droplets is being diffused upwards by turbulence, transported by wind and is itself precipitating into the rain receiver. An experiment was performed to measure the electric current due to evaporation. The results show that the current due to evaporation in the presence of an electric field is much smaller than that due to conduction in air. The observation of a 'warm' thunderstorm cloud is reported. A project was developed to make visual and electrical measurements simultaneously on the same cloud. A time lapse film of tropical clouds, together with some electric field measurements beneath them, are used to discuss the flow pattern associated with a tropical thunderstorm and the mechanism by which it becomes charged. Appendices include an analysis of the shielding effect of a vertical rod at ground potential, the description of some further instrumentation, including a data processing system designed by the author which uses a novel but effective method of detecting the occurrence of the peak of a signal, more detailed mathematical derivations of equations used in the main text and a filming schedule for the time-lapse photography.

Studies of hail damage at Chikugo District, Fukuoka Prefecture

Abstract: Remarkable damage was caused by a thunderstorm with hail in a south part of Fukuoka prefecture on 28th May 1967. The damage was observed over a zonal district extending from Tosu (Saga prefecture) toKuroki, through Kurume, Jyoyo. Especially, the damage to agricultural products was heavy. The author has investigated this hail damage form the following points:1. Hail damages in the past.The largest hailstorms recorded in the Fukuoka prefecture was seen on Feb. 19, 1684, in Kurume. The maximum size of the stones was about 7cm in diameter, weighing aobut 82 grams. The author made use of a 285-year period (1682-1967), for a total 31 haildamage days, to investigate the relation between hail storms and the months. Haildamage occurred preimarily in May (31%), and secondarily in April (21%).2. Synoptic weather condition of hailfall.Various ways have been employed for collecting data from radar observations, aerial observation by pilots through flights over the area of the hail path, Weather Bureau's upper soundings, surface observations by the persons in the storm area and the author took photographs of hail damage area. Also the data for crop loss of hail storm were supplied by the public offices.A 5.7cm radar set operated at the Seburi radar site can depict thunderstorm cells in the storm by PPI photographs, . This photograph as indicated in Fig 4, helps delineate the hail path, its movement, development, and orientation. It also delieates the hail boundary within a 100km radar range. The echo areas shown reveal that the thunderstorm under study developed as a clam shell shape, the first hail falling from the south western edge of east-southeastward moving thunder storm cell (see echo area Fig. 6).From analysis of upper (850-, 700-, 500-, and 300mb levels) and surface synoptic maps of May 28, 1967, it is evident that the thunderstorm and hailstorm developed along a meso low pressure, pushing forward across south central mountains of Fukuoka (Minou mountains). The 500-mb level jet stream appeared to be about 27m/s, probably responsible for the development of the storm through its vertical shear effects on the vertical movements of the individual storm cells along the meso low.3. Distribution of hail damage.The topographic effect on hail distribution is of importance, because it determines the speed and direction of local winds and, in turn, affects the distribution of hailstorms.The author has made investigation on the duration and the begining and ending hours of storms, as well as the degrees of the haildamage. Data included the time of hailing (begining), size distribution of hailstones from photograph, stone density on the ground, lightning, direction of destructive wind, and estimates of crop and property damage damage types. The analysed haildamage lines are showr in Fig-6.4. Condition of hail damage.Damage caused by the hailstorm is vast. For small animals, the damage is serious when the hailstones range from 3 to 6cm in diameter. Stones of about 3cm diameter are considered disastrous to crops in general.Theoretically, the degree of damage inflicted upon plants by hailstorms depends upon the stone size, areal density, depth of coverage, duration of the storm, falling velocity, area coverage, and age of the plants. Heavy rainfall and severe wind accompanying the hail cause considerable addintional damage.It has been found that the area of crop damage coincides fairly closely with the density of stones; in general, the damged crop area coincides with the areas of stone density of 100 or more per square meter. Factors other than stone density influencing crop damage were a maximum stone size above 3cm diameter a longer point duration than 10 minutes, and a surface wind exceeding 20m/s. Finally, in the isohyetal analysis, it was revealed that the rain core was generally associated with the hailstorm and with 10mm rainfall during the 3-hour period

Application of Radar to Measurement of Surface Precipitation

Abstract: : The report contains two major sections. In the first, consideration is given to the accuracy and practicality of measuring surface precipitation by radar. The second summarizes studies which have been made regarding mesoscale precipitation patterns and their relation to larger-scale circulations. It is concluded that for convective storms a properly instrumented 10-cm radar can provide more accurate measurements of rainfall over an area than can a network of gauges. A wave length as short as 3 cm is shown to be unsatisfactory for measuring precipitation because of attenuation. In widespread storms appreciable errors, occasionally a factor of two or three, may result from differences between the precipitation in the volume sampled by the radar and that reaching the surface. Observations of such effects are presented and discussed. Advantages and liabilities both of the radar and of a network of gauges for measuring precipitation over an area are illustrated by experiments in which simultaneous measurements by the two methods are compared. The second section of this report presents detailed descriptions of the structure and behavior of mesoscale precipitation areas and convective cells both in extratropical cyclones and in thunderstorm complexes. These descriptions will serve as a basis for physical and numerical studies of mesoscale phenomena.

Electric Fields in the Vicinity of Lightning Strokes

Abstract: New data have been added to the information available on the electric fields during thunderstorms. The new data consist of records of the potential gradients that exist on the earth's surface in the vicinity of lightning strokes. Records have been obtained within 150-200 feet of known stroke locations. To the best of the authors' knowledge this has not been accomplished before. Based on the information obtained, a relation has been derived between the estimated gradient and the distance from the stroke. Also, an estimate is made of the potentials induced by nearby lightning strokes in a conductor at the height of a typical distribution system.

Meteorological satellite study on the development of tornado-producing thunderstorms

Abstract: Tornado producing thunderstorms using conventional surface and upper air data combined with ATS-III data, discussing mesoscale disturbances and momentum exchange

Turbulence measurements at lower levels around a squall line

Abstract: : The NAE T-33 was operated out of Tinker Air Force Base from April 22 to May 10, 1968 on a co-operative program of storm turbulence measurement. Control of the aircraft was exercised from the National Severe Storms Laboratories at Norman, Oklahoma. The object of the program was to explore turbulence intensities around thunderstorms and through radar 'gaps' in squall lines between 5,000 and 15,000 feet. On May 7, a squall line southeast of Oklahoma City was investigated, the T-33 being directed through essentially echo-free holes in the line. Moderate to severe turbulence was encountered in these gaps. Time histories and power spectra of the turbulence are presented and some conclusions are drawn as to the implication of the results to airline operations at these lower heights in severe storm situations. (Author)

Frequency and Duration of Thunderstorms in the Cape Kennedy Area

Abstract: This report presents a detailed statis­ tical analysis of thunderstorm occur­ rence at or in the immediate vicinity of Cape Kennedy, Florida based on 13 years of record through the year 1967 • Em­ pirical thunderstorm probabilities are derived for any given time of the day, for any day of the year for time periods ranging up to seven days duration. Pre­ sented also are data on multiple thun­ derstorm occurrence on single days, probability of thunderstorm nonoccurrence, thunderstorm duration, "runs" of thunderstorm days and con­ ditional thunderstorm probabilities.