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Howard B. Bluestein

The University of Oklahoma (OU) Severe Storms Intercept Project—1979 was conducted in conjunction with the spring field program of the National Severe Storms Laboratory (NSSL), Norman, Okla., and the Severe Environmental Storms and Mesoscale Experiment (SESAME ‘79). The purposes of the project were to provide NSSL with ground-based visual observations, in the field, of thunderstorms that were observed simultaneously by Doppler radar; to document and photograph severe-storm phenomena and related damage; and to obtain high-quality movies of tornadic debris clouds.

A ground-based intercept crew consisting of four members operated from 1 April 1979 to 15 June 1979. The itineraries of the chase crews were usually determined jointly by the NSSL forecaster and the OU crew on the basis of conventional data from the service “A” and “C” teletypewriters, the National Facsimile Circuit (NAFAX), interpretation of satellite photographs, and data from both a conventional and a Doppler radar.

Although the total number of missions was small (11), tornadoes were filmed on 2 chases, and severe events were documented on a total of 6 chases; 2 missions were damage surveys. On only 3 out of 11 missions were no severe storm-related phenomena observed. On 2 May the chase crew obtained spectacular, high-quality, normal-speed movies of the entire history of the multiple-vortex stage of a tornado and associated debris west of Orienta, Okla. Other highlights include normal-speed movies of the tornado in Seymour, Tex. on 10 April, time-lapse movies on 6 June of a storm complex that had a Doppler radar-observed mesocyclone signature, and documentation of the occurrence of “staccato” lightning near Buffalo Springs, Tex., on 20 May.

The data collected during this project, along with other types of data gathered simultaneously by others, will lead to a better understanding of the kinematics and dynamics of severe thunderstorms and tornadoes. Furthermore, the photographs will help spotters recognize potentially dangerous storms, and thereby provide more reliable warnings to the public.

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Howard B. Bluestein

Abstract

Satellite-observed tropical and extratropical cloud bands often look alike. It is hypothesized that synoptic-scale deformation and tropical cloud band orientation are related, since the axis of dilatation associated with the former is related to extratropical frontal cloud band orientation.

This study finds the following evidence for the hypothesis:

  1. The orientations of climatological bands of cloudiness in tropical oceanic areas are for the most part well-correlated with the respective climatological, gradient-level, axis-of-dilatation orientations.
  2. Significant correlations were found between the cloud-band and axis-of-dilatation orientations of the objectively analyzed nondivergent wind at 950, 850 and 700 mb during BOMEX Phase IV. The objective analyses made use of synchronous and asynchronous data. The significance decreased with height, and was very small at 450 mb. On days when cloud bands were zonally oriented, the average axis-dilatation orientation was zonal; when cloud bands were nonzonally oriented, the average axis-of-dilatation orientation was nonzonal.
  3. The orientation of a spectacular cloud band during GATE was well-correlated with the axis of dilatation of the subjectively analyzed 850 mb wind.
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Howard B. Bluestein

Abstract

Photographs are presented that illustrate the various forms in which “flanking lines” exist in nature. Flanking lines may appear not only as the commonly observed sloping line of cumulus congestus, but also as erect towers with a vertical face, and as a line of altocumulus castellanus above and parallel to a band of stratocumulus lenticularis. It is suggested that the slope of the tops of the flanking-line towers with respect to the ground is related to a quantity that is similar in form to the bulk Richardson number, and that the orientation of the flanking line is a function of the mean wind in the lowest 6 km and storm motion. These hypotheses need to be verified when high-resolution, rapid-scan, visible and infrared satellite imagery become available on a daily basis.

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Howard B. Bluestein

Abstract

Photographic evidence is presented of funnel clouds pendant from the bases of convective clouds whose updrafts appear to be rooted well above the boundary layer. These funnel clouds occur in environments supportive of severe convective storms, under dissipating cumulus humilis, cumulus congestus, and low-precipitation cumulonimbus, and on the rear side of supercell and multicell convective storms. Since these funnel clouds do not become tornadoes, spotters should learn to distinguish them from the potentially tornadic funnel clouds that occur under convective clouds that are rooted in the boundary layer.

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Howard B. Bluestein

Abstract

This is a case study of a mesoscale area of convection which began at night over western Kansas on 2 September 1982 and lasted until the afternoon of 3 September. Evidence from analyses of surface, upper-air, radar, and satellite observations suggests that the thunderstorms probably formed in response to the lifting of an elevated layer of conditional instability. The lifting can be attributed qualitatively to quasi-geostrophic ascending motion resulting from a shallow layer of warm advection near 60 kPa. Two possible sources of moisture were midlevel moisture which had been advected around an upstream ridge and a localized area of turbulent transport of water vapor from below. The convective event could not have been forecast with synoptic-scale, mandatory-level analyses alone; it was difficult to explain even with detailed analyses at other levels.

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Howard B. Bluestein

Abstract

The TOTO (Totable Tornado Observatory) device was field tested in the Southern Plains by a severe-storm intercept team from the University of Oklahoma from late May through early June 1981. The results from two intercept missions and a gust-front intercomparison at the National Severe Storms laboratory are discussed. Measurements are presented of wind speed, wind direction, pressure and temperature made underneath a rotating wall cloud and within 1.5 km of two tornadoes. A damage survey and a Doppler-radar observed mesocyclone-signature track were used in conjunction with the TOTO data to obtain an estimate of the maximum wind speed inside one of the tornadoes.

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Howard B. Bluestein

Abstract

The rare occurrence of a tornado in the Sierra-Nevada region of California is documented. The synoptic-scale wind and pressure field and the thermodynamic structure of the environment are discussed.

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Howard B. Bluestein

Abstract

Tornadoes are often reported as tropical cyclones make landfall. In this note I present photographic evidence of a possible funnel cloud in the eye of Hurricane Norbert in the Eastern Pacific, far from landfall.

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Howard B. Bluestein

Abstract

Photographs of several severe storm related phenomena are described. A double wall cloud having a double vortex structure evolved from a single wall cloud, and subsequently turned back into a single wall cloud and produced a tornado. In addition, a double funnel cloud was observed under a curved, high-based cloud extending eastward and southeastward from the wall cloud region.

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Howard B. Bluestein

Faculty and students from the School of Meteorology at the University of Oklahoma and staff members from the Atmospheric Technology Division at the National Center for Atmospheric Research (NCAR) participated in a special course given during the last two weeks of May 1992. The purpose of the course was to give students the opportunity to use the NCAR mobile CLASS (Cross-Chain LORAN Atmospheric Sounding System) in the field and to interpret data they collected themselves in the context of material learned earlier in a lecture setting. Soundings were obtained in parts of Texas and Oklahoma in the environment of multicell storms, in supercells, in a gust front, and on the cold side of a cold front.

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