scispace - formally typeset
Search or ask a question

Showing papers on "Thunderstorm published in 1975"


Journal ArticleDOI
TL;DR: In this article, the amplitude and phase of diurnal and semidiurnal cycles at each station in the United States were analyzed and the results were displayed on seasonal maps in a vectorial format that emphasizes the large scale geographical consistency of the diurnal variations.
Abstract: Hourly data on the frequencies of all types of precipitation events, heavy precipitation events, trace precipitation events and thunderstorms for more than 100 stations in the United States were processed to generate statistics on the amplitude and phase of the diurnal and semidiurnal cycles at each station. Results are displayed on seasonal maps in a vectorial format that emphasizes the large scale geographical consistency of the diurnal variations. During summer each of the four parameters listed above displays a distinctive geographical pattern of diurnal variations. Thunderstorm frequency tends to be the most strongly modulated by the diurnal cycle; trace precipitation the least strongly modulated. Over the central United States the maximum frequency of severe convective storms occurs during the early evening; thunderstorms exhibit their maximum frequency around midnight, while most precipitation falls later in the night. These amplitude and phase differences offer some insight into the relat...

540 citations


Journal ArticleDOI
TL;DR: In this paper, it was suggested that the observed periods were characteristics of the acoustic sources in thundercloud cells and that the smearing of the Doppler records was very common during the occurrence of the (summer) afternoon storms.

46 citations


Journal ArticleDOI
TL;DR: From video-tape recordings of lightning flashes to ground in convective daytime storms at the NASA Kennedy Space Center, Florida and near Ocala, Florida, statistical data are presented for the flash-time duration, the number of strokes per flash, the time between all strokes, and time between strokes having spatially separate channels as mentioned in this paper.
Abstract: From video-tape recordings of lightning flashes to ground in convective daytime storms at the NASA Kennedy Space Center, Florida, and near Ocala, Florida, statistical data are presented for the flash-time duration, the number of strokes per flash, the time between all strokes, and the time between strokes having spatially separate channels. A daytime video tape 'photograph' of a stepped leader is reproduced. Finally, statistical data are presented for 13 long horizontal lightning discharges occurring along a line of nocturnal thunderstorms near Gainesville, Florida. These discharges all propagated horizontally near the freezing level (4.5 km) at an apparent average velocity between 5600 and 11,000 m/s for a typical distance of 2 to 3 km. Eleven of the 13 horizontal discharges were preceded by or occurred within 16.7 ms of a glow in the cloud roughly 0.5 km above the horizontal channel.

44 citations


Journal ArticleDOI
TL;DR: In this article, the authors summarized the migration velocities of convective storms for six situations, with different environmental wind fields, and found that large-diameter (ca. 20-30 km) storms generally deviated to the right, in proportion to their sizes and to the veering of wind with height.
Abstract: Migration velocities of convective storms are summarized for six situations, with different environmental wind fields. Small-and medium-sized storms generally moved to left of the direction of, and at speeds somewhat less than, the vector mean wind in the troposphere. Large-diameter (ca. 20–30 km) storms generally deviated to the right, in proportion to their sizes and to the veering of wind with height. This behavior, and the tendency for large storms to move appreciably slower than the mean wind, are even more pronounced when giant clusters of thunderstorms are considered. An example is analyzed in which a multicellular storm, 80 km wide, moved 55° to right of the mean wind and with half its speed. This behavior results from a characteristic pattern of propagation, in which new cells tend to form on the general upwind side of the cluster, with the larger and more intense cells developing on its right flank. The individual cells move through the cluster, dissipating on approach to its advancing and left flanks. Preferential formation of cells toward the rear side of the cluster is shown to be compatible with the probable origin and trajectories (relative to the moving storm) of air ascending from the lower part of the subcloud layer. The sometimes-observed rapid movement of large multicellular storms to left of the mean wind is partly accounted for by an opposite (left forward flank) pattern of propagation.

34 citations


Journal ArticleDOI
TL;DR: In this paper, a Doppler velocity signature of large shear coincident with tornado location has been discovered in an Oklahoma thunderstorm, which is used to draw conclusions concerning vertical depth of the tornado vortex and its apparent descent from storm mid-levels to the surface.
Abstract: A Doppler velocity signature of large shear coincident with tornado location has been discovered in an Oklahoma thunderstorm. The gate-to-gate tangential shear (GGS) signature is used to draw conclusions concerning vertical depth of the tornado vortex and its apparent descent from storm mid-levels to the surface.

29 citations



Journal ArticleDOI
TL;DR: In this paper, the three dimensional cloud structure over a strong cold front in the southeastern United States on 4 April 1968 was analyzed using three-dimensional stereo images from the Apollo 6 mission, and the analysis extended from near Tyler, Texas, eastward to the Georgia coast.
Abstract: Twenty-three overlapping photographs from the Apollo 6 mission were stereographically analyzed to determine the three dimensional cloud structure over a strong cold front in the southeastern United States on 4 April 1968. The analysis extended from near Tyler, Texas, eastward to the Georgia coast. Four major cloud regions were observed: a zone of altocumulus behind the front, a vigorous thunderstorm complex along and just ahead of the front, a chaotic region of multilayer clouds for a few hundred kilometers east of the thunderstorms and a large region of cloud streets parallel to the surface winds near the coast. The cloud top altitudes in the thunderstorm complex were extraordinary, reaching a maximum height of 22.375 km, whereas the tropopause was located at 12–13 km and the maximum tops reported by radar 30 min before the Apollo pass were at 12.5 km. An area of approximately 2 × 104 km2 was covered with maximum tops of ⩾ 18 km. The accuracy of the stereographic technique was confirmed with cloud top al...

23 citations


Journal ArticleDOI
TL;DR: In this paper, 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.
Abstract: 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.

22 citations


Journal ArticleDOI
TL;DR: In this paper, a cold front passed through the mesonetwork of the National Severe Storms Laboratory in central Oklahoma and produced more than 2 inches of rain at some points within the network.
Abstract: On 14 May 1970 a cold front passed through the mesonetwork of the National Severe Storms Laboratory in central Oklahoma. As it did so, intense convection developed and thunderstorms produced more than 2 inches of rain at some points within the network. On this date a total of 58 rawinsonde observations were made at nine stations within the network, 42 of them during the period from about 1 h prior to frontal passage to 2 h afterward. We have analyzed these as well as other data to arrive at a picture of the structure of the mesoscale system and of the thermodynamical processes operating in it. The front first encountered potentially unstable rnoist air as it passed through the network. As this air was lifted frontally the instability was released, with remarkable results. A mesoscale downdraft–updraft doublet developed in the warm air aloft, with peak speeds at 400 mb of 2–3 m sminus;1 over 10 km widths transverse to the front, the descent being above the surface frontal position and the ascent (...

21 citations


Journal ArticleDOI
TL;DR: A paradox has developed involving on one hand sizeable reductions during the last two years in federal support of weather modification, as opposed to major scientific-technical advances in the field plus strong recommendations for increased federal support from the scientific community.
Abstract: A paradox has developed involving on one hand sizeable reductions during the last two years in federal support of weather modification, as opposed to major scientific-technical advances in the field plus strong recommendations for increased federal support from the scientific community. The major recent advances include the capability to operationally dissipate cold fogs, to enhance snow from orographic clouds, and to increase rain from tropical clouds, plus the discovery of sizeable urban-related increases in rainfall. Other advances include special weather radars, aircraft with new cloud sensors and the capability to penetrate thunderstorms, new seeding materials and delivery systems, and new techniques for evaluation of projects. These have been coupled with the spread of weather modification around the world and with the initiation of major seeding projects in Colorado (NHRE, HIPLEX, and San Juan Project), Florida, South Dakota, and Illinois-Missouri (METROMEX). Several groups (NACOA, NAS, ICAS, NWC, ...

16 citations



01 Jan 1975
TL;DR: In this article, it is suggested that variations of the current in the global atmospheric electrical circuit can be produced through regulation of the resistance between the tops of thunderclouds and the ionosphere.
Abstract: It is suggested that variations of the current in the global atmospheric electrical circuit can be produced through regulation of the resistance between the tops of thunderclouds and the ionosphere. Long- and short-term changes in the conductivity of this region occur due to changes in the ionization rate resulting from solar activity. Previous suggestions that the phenomena might be due to conductivity variations in the fair weather part of the world or an influx of space charge to the upper atmosphere are discussed and considered unlikely. It might be possible to test the proposed mechanism by measuring the temporal variation of the ionospheric potential during distributed solar periods. Another approach would be to measure simultaneously the variation in ionization rate and electric current over thunderstorms. Several ways in which changes in atmospheric electrification might influence other meteorological phenomena are mentioned.

Journal ArticleDOI
TL;DR: In this article, the internal airflow and radar reflectivity structure of a convective storm was determined using the dual-Doppler radar coplane method of scanning and data reduction, and the absence of significant cold air outflow and its attendant gust front at the surface was attributed to the appreciable inflow of slow moving air into the downdraft at the middle layers and the fact that the potentially coldest air was located too low to contribute significantly to a deep downdRAFT circulation.
Abstract: The dual-Doppler radar coplane method of scanning and data reduction has been used to determine the internal airflow and radar reflectivity structure of a convective storm. Cumulus convection growing in a moderately sheared wind environment resulted in a nonsteady, moderate intensity thunderstorm. Precipitation fallout and downward moving air are found downshear of an updraft inclined in the downshear direction. Rapid storm translation, vertical shear of the ambient wind, and slow subcloud ascent of inflow air act to establish this observed draft configuration. The absence of significant cold air outflow and its attendant gust front at the surface is attributed to (i) appreciable inflow of slow moving air into the downdraft at the middle layers and (ii) the fact that the potentially coldest air was located too low to contribute significantly to a deep downdraft circulation.

Journal ArticleDOI
TL;DR: In this paper, data were obtained for three High Plains thunderstorms in which penetrations were made of the weak echo region by an instrumented aircraft and the data from one of the cases are presented in detail.
Abstract: Data were obtained for three High Plains thunderstorms in which penetrations were made of the weak echo region by an instrumented aircraft. The data from one of the cases are presented in detail. Two of the storms were steady state, as revealed by chaff analysis and subsequent subcloud passes. The third storm dissipated during the penetrations. The three storms were each characterized by negatively buoyant air at cloud base. Chaff released into the updrafts of the storms did not decelerate below the level of free convection (LFC). A vertical pressure perturbation gradient, therefore, existed below the LFC and within the weak echo region which acted to accelerate the air parcels in the presence of negative buoyancy. The analysis of the equivalent potential temperature fields for the two steady storm cases revealed considerable entrainment of environment air into the weak echo region. The mixing of the entrained parcels probably caused the observed increase of turbulence with height.

Journal ArticleDOI
TL;DR: A particularly severe and long-lasting thunderstorm occurred 19-20 August 1973 as mentioned in this paper, which was followed through its life cycle by means of radar, satellite, and surface observations, and was noteworthy for its very strong winds, locally heavy rain, and the magnitude of the pressure jump associated with it.
Abstract: Intense thunderstorms, which frequent the desert Southwest of the United States in the summer months, have been known by several different names: chubasco, haboob, and Sonora storm. Prior to the advent of satellites and radar, the sparsity of observations in the desert Southwest precluded any determination of where these storms developed, as well as information on their areal coverage and life cycle. A particularly severe and long-lasting thunderstorm occurred 19–20 August 1973. This storm was followed through its life cycle by means of radar, satellite, and surface observations. This particular storm was noteworthy for its very strong winds, locally heavy rain, and the magnitude of the pressure jump associated with it. The converging of two separate mesohighs is believed to be the cause of the very intense storm that moved westward across the Imperial Valley of Southern California.

Journal ArticleDOI
TL;DR: In this paper, National Severe Storms Laboratory mesonetwork soundings were taken near thunderstorms and squall lines between 1966 and 1973, and thirty-four of these soundings sampled updrafts at various levels.
Abstract: Between 1966 and 1973, National Severe Storms Laboratory mesonetwork soundings were taken near thunderstorms and squall lines. Thirty-four of these soundings sampled updrafts at various levels. Because of instrumental noise and atmospheric fine structure, many of the individual soundings were hard to interpret. However, significant results were obtained from the data as a whole and from the four fastest updraft cases.

01 Jan 1975
TL;DR: In this paper, radar observations of 93 tornado families occurring on April 3, 1974 are discussed. Of the 93 tornadoes included in the sample, 81% were associated with hook-like echoes with appendages at least 40 degrees to the south of the echo movement.
Abstract: Radar observations of tornado families occurring on April 3, 1974 are discussed. Of the 93 tornadoes included in the sample, 81% were associated with hook-like echoes with appendages at least 40 deg to the south of the echo movement. At least one tornado was associated with 62% of the hook-like echoes observed. All of the tornadoes with intensities of F 4 and F 5 were produced by hook-like echoes; the mean intensity of all tornadoes associated with this type of echo was F 3, while the mean intensity of the remaining tornadoes was F1. The tornadic hook-like echoes moved to the right of the non-tornadic echoes forming a tornado line in advance of the squall line. Some tornadoes were associated with 'spiral' echoes.

Journal ArticleDOI
TL;DR: In this article, the feasibility of using artificial earth satellites to monitor thunderstorm activity was evaluated using the measurements made with the earth-oriented vee antenna of the Radio Astronomy Explorer (RAE 1) satellite in the frequency range 0.2-9.2 MHz.
Abstract: A study was made to determine the feasibility of using artificial earth satellites to monitor thunderstorm activity. The nighttime noise-temperature measurements made with the earth-oriented vee antenna of the Radio Astronomy Explorer (RAE 1) satellite in the frequency range 0.2-9.2 MHz were correlated with reported surface thunderstorm activity. Analysis shows that the minimum nighttime HF noise level (in the absence of surface thunderstorms) at an altitude of 5850 km over the United States is fixed by man-made noise. When thunderstorms are active below the satellite, the noise level is increased by about 6-12 dB. The highest level is associated with the most intense storms. It is concluded that thunderstorm regions can be detected by an orbiting satellite using HF radio techniques, but ionospheric effects must be taken into account.

Journal ArticleDOI
TL;DR: In this paper, the trajectories of hypothetical dropsondes are calculated in thunderstorm circulations and resultant vertical wind speed profiles as a function of height are constructed for each of the sondes.
Abstract: The trajectories of hypothetical dropsondes are calculated in thunderstorm circulations and resultant vertical wind speed profiles as a function of height are constructed for each of the sondes. Motion fields are a) calculated by a time-dependent two-dimensional thunderstorm model and b) constructed based upon observed environmental winds. Model-calculated vertical wind speed profiles are compared with observations for the northeastern Colorado storm of 22 July 1972. Agreement is shown between certain basic features; additionally, other calculations point to various potential features of dropsonde trajectories and vertical wind speed profiles. Possible application of similar methods to the hail growth problem is discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors used the numerically calculated height of a convective plume, which relies on the entire sounding of temperature and humidity above the assumed cloud base, is considered to be a measure of the thermodynamic predisposition of the atmosphere to convective overturning.
Abstract: The numerically calculated height of a steady-state model of a convective plume, which relies on the entire sounding of temperature and humidity above the assumed cloud base, is considered to be a measure of the thermodynamic predisposition of the atmosphere to convective overturning. The plume height is evaluated as a predictor of summer thunderstorms at Tampa, Fla., and is found to contain more forecast skill than a combination of two simpler and more familiar predictors, the Showalter Index and the precipitable water depth. In absolute terms, however, the skill is modest. Skill is somewhat improved when a simple measure of the zonal geostrophic flow over the Florida penninsula is considered as a predictor together with the height of the model plume, but it is suggested that a major portion of skill, not yet within reach, resides in prediction of the mesoscale systems in wwhich convection is organized.


Journal ArticleDOI
01 Feb 1975-Tellus A
TL;DR: In this article, the authors describe a case study of progressive gravity waves in the troposphere and deduce their propagation speed and direction, and their dispersive characteristics, from surface spectra of wind and pressure.
Abstract: In this paper we describe a case study of progressive gravity waves in the troposphere. We deduce their propagation speed and direction, and their dispersive characteristics, from surface spectra of wind and pressure. We compare the results with direct measurements of the waves made over an array of spaced pressure sensors using cross spectrum techniques and an algorithm developed by one of us (Young). The agreement is very satisfactory and demonstrates the feasibility of monitoring atmospheric wave conditions in almost real time using only sensors (high quality) in use at standard weather observation stations. The waves in the case we describe were highly dispersive and apparently were generated by a violent thunderstorm some 100 km west of the site of observation. DOI: 10.1111/j.2153-3490.1975.tb01651.x

Journal ArticleDOI
TL;DR: In this paper, the advantages and potential for the use of hourly surface static energy (cpT+gz+Lw) analysis to readily detect and monitor areas affected by thunderstorm outflow air are presented.
Abstract: The advantages and potential for the use of hourly surface static energy (cpT+gz+Lw) analysis to readily detect and monitor areas affected by thunderstorm outflow air are presented. A comparison between the delineation of thunderstorm-produced meso- or bubble highs by conventional pressure analysis and static energy analysis is made using the 15 May 1968 severe storm day as an example.

01 Jan 1975
TL;DR: In this paper, a study was conducted to identify the sequence of processes that lead from some change in solar input to the earth to a change in tropospheric circulation and weather.
Abstract: A study was conducted to identify the sequence of processes that lead from some change in solar input to the earth to a change in tropospheric circulation and weather. Topics discussed include: inputs from the sun, the solar wind, and the magnetosphere; bremsstrahlung, ionizing radiation, cirrus clouds, thunderstorms, wave propagation, and gravity waves.

Proceedings ArticleDOI
01 Oct 1975
TL;DR: F ive ty p es of sh ie ld e d co m m u n ica tio n c a b le s (w ith an o u te r in su la t in g c o v e r) , 180 f t.
Abstract: F ive ty p es of sh ie ld e d co m m u n ica tio n c a b le s (w ith an o u te r in su la t in g c o v e r) , 180 f t . in len g th , w e re su b je c te d to the induced e le c tro m a g n e t ic f ie ld s due to a n e a rb y s im u ­ la te d l ig h tn in g s t ro k e . T he ligh tn ing s t r o k e w as an e l e c t r i ­ c a l a r c to g ro u n d due to th e d is c h a rg e of a h igh v o ltag e M a rx g e n e ra to r . M e a su re m e n ts of induced sh ie ld c u r r e n t , and s ig n a l co n d u c to r c u r r e n t s and v o lta g e s w e re m ad e fo r a s e r i e s o f cab le te rm in a t io n c o n d itio n s . T he co m m u n i­ c a tio n c a b le s te s te d w e re 50 p r . and 100 p r . te lephone c a b le s , 6 p r . and 12 p r . sh ie ld e d , t w i s t e d p a i r , a r m o r e d c a b le , and R G -11A /U c o ax ia l c ab le . E x tra p o la t in g the r e s u l t s of th e s e t e s t s , p e r fo rm e d w ith 11, 000 a m p e re s t r o k e s , to the l a r g e s t l ik e ly l ig h tn in g s t ro k e s (of 2 0 0 ,0 0 0 a m p e re s ) in d ic a te th a t the c o m m u n ica tio n cab le o u te r sh e a th (o r a r m o r ) m ay e a s i ly have ind u ced c u r r e n t s in th e 1000 a m p e re ra n g e . Induced v o ltag e m ay r e a c h 1000 v o lts b e tw een an in n e r co n d u c to r and g ro u n d and b e tw een c o n ­ d u c to rs of a tw is ted p a i r .

Journal ArticleDOI
TL;DR: In this article, a model of a nonthermal mechanism for low pressure centers in thunderstorms is developed which scales from the laboratory to the atmosphere using a turbulence Reynolds number, a velocity ratio and the diameter of the updraft.
Abstract: Within the thunderstorm there is an extensive region of collision between airflows having different transports of momentum. The inflow-updraft should interact with cloud layer environmental wind to produce counter-rotating vortex pairs somewhat like those produced in the laboratory by a jet in a crossflow. Atmospheric evidence of vortex pairs for severe thunderstorms is shown from measurements made by aircraft and by radar. A model of a non-thermal mechanism for low pressure centers in thunderstorms is developed which scales from the laboratory to the atmosphere using a turbulence Reynolds number, a velocity ratio and the diameter of the updraft. Central pressure deficits and vorticity of lee vortices scaled up from the laboratory observations are consistent with the few available thunderstorm measurements. The model is used to explain deviate motion of thunderstorms as well as to suggest a mechanism for tornado development and movement.

Journal ArticleDOI
TL;DR: In this paper, the authors used half-wave-length dipole antennas to measure the VHF radiation from nearby lightning discharges and found that the intensity ratios of horizontal to vertical polarizations for each lightning flash are very scattered and ranged mostly between −2 and +8 dB.
Abstract: Polarizations of VHF radiation from nearby lightning discharges were observed by using half-wave-length dipole antennas. The intensity ratios of horizontal to vertical polarizations for each lightning flash are very scattered and ranged mostly between −2 and +8 dB. On the average, the horizontal to vertical ratios for cloud flashes are 2 or 3 dB higher than ground flashes. This is probably due to the difference in height between the VHF sources in both types of flashes. Active thunderstorms which generate frequent flashes give relatively high horizontal to vertical ratios. These results suggest that the fundamental process generating VHF radiation is a group of minute discharges of almost random orientation in a cloud.



01 Jan 1975
TL;DR: In this paper, the authors presented a method for severe storm identification based on satellite data, where the top of huge thunderstorms in satellite images often appear as vast areas of extensive cirrus cloud; they consist of clusters of anvil clouds, each generated by vigorous thunderstorm circulation.
Abstract: Ideas are presented for severe storm identification based on satellite data. The tops of huge thunderstorms in satellite pictures often appear as vast areas of extensive cirrus cloud; they consist of clusters of anvil clouds, each generated by vigorous thunderstorm circulation. The overshooting tops observed in satellite pictures are located where the subanvil updrafts are the strongest. Learjet experiment results show that an overshooting top varies either quickly or slowly, depending on the characteristics of individual clouds. When an overshooting top collapses, a small segment of the anvil cirrus jumps upward in the wake of the overshooting top. Also discussed is the monitoring of vertical motions from satellites and tornado-producing thunderstorms from geostationary altitude. A very high-resolution imagery of both infrared and visual spectral bands makes it possible to infer vertical motions beneath the anvil top. A combination of cloud velocity and anvil expansion rate will permit, in the future, determining the location of severe storms within the vast areas of anvil clouds.