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DAVID B. SPIEGLER

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David B. Spiegler

Abstract

An objective layer of maximum-wind (LRMW) analysis technique which is described and evaluated, has two main features: 1) a categorization procedure that sorts wind profiles into nine jet-stream categories, for the derivation of regression equations to generate initial-guess fields of six LRMW parameters; and 2) an analysis technique that locates jet cores between grid points and generates “observations” along these cores from horizontal-jet profile models.

Initial-guess fields are generated for thickness of the LRMW, wind speed maximum, mean height and wind direction of the LRMW, and vector shears below and above the LRMW, providing a three-dimensional picture of the wind field.

The initial-guess LRMW equations are stable in tests with independent data and are capable of specifying very well the general characteristics of the LRMW profile. They also provide realistic values for the LRMW parameters over no-data areas that are consistent with the entire analysis area.

Over data areas, where objective and subjective analyses could be compared, the objective LRMW analyses compare favorably with subjective analyses.

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DAVID B. SPIEGLER

Abstract

A detailed analysis of conventional and aircraft reconnaissance data and satellite pictures for two unnamed Atlantic Ocean cyclones during 1970 indicates that the storms were of tropical nature and were probably of at least minimal hurricane intensity for part of their life history.

Prior to becoming a hurricane, one of the storms exhibited characteristics not typical of any of the recognized classical cyclone types [i.e., tropical, extratropical, and subtropical (Kona)]. The implications of this are discussed and the concept of semitropical cyclones as a separate cyclone category is advanced.

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DAVID B. SPIEGLER

Abstract

The 24-hour 500-mb. barotropic forecasts prepared by the Joint Numerical Weather Prediction Unit (JNWPU) have been investigated in 30 cases of rapid sea level cyclogenesis. Composite error maps are presented for the region of cyclogenesis. The 500-mb. errors are found to be significantly larger when the solenoidal field at that level is strong than when it is weak.

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DAVID B. SPIEGLER
and
GEORGE E. FISHER

Abstract

Melted precipitation and snowfall data from eight winters were used to develop a snow and melted precipitation prediction model associated with 850-mb cyclones along the Atlantic Seaboard. Results indicate that the major potential for heavy snow exists in a band extending from 75 to 225 mi to the left and from 350 to about 1,000 mi ahead of the 850-mb cyclone in the 12-hr period beginning 6 hr after routine upper air observation time. Application of the prediction model of snow amounts to some storms from the 1968–1969 winter season indicate they provide valuable guidance to the forecaster during periods of East Coast storms.

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George H. Milly
,
John T. Ball
, and
David B. Spiegler

Abstract

An examination is made of the hypothesis that the inconclusive or marginal effects of many cloud seeding operations are due, at least in part, to an inhomogeneous distribution of freezing nuclei resulting in great ranges of concentration and extensive areas of overseeding and underseeding over the target region. Distributions of silver iodide nucleus concentrations arising from ground based generators were computed using a Gaussian plume diffusion model. Meteorological conditions and the number, locations, and yield of ground based generators were varied in a series of numerical experiments which bracketed conditions typical of many cloud seeding operations. The results indicated that effective seeding concentrations of nuclei can be achieved over a significant portion of the target area only by carefully considering initial atmospheric conditions as they affect nucleus diffusion and activity, and by accordingly designing and deploying the system of silver iodide generators.

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