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Martin Setvák and Charles A. Doswell III

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Charles A. Doswell III and Joseph T. Schaefer

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Barry E. Schwartz and Charles A. Doswell III

Meteorologists, like most scientists, often use observational data assuming the necessary steps have been taken to ensure that the quality of the data has been properly controlled. Experience developing an archive of upper-air observations from historical and real-time data suggests that some of the steps necessary to assure the basic scientific integrity of these data have not, in fact, been taken. This is especially so in recent years, since the introduction of automation into data observing and processing. Some of the problems and issues related to the observation, collection, and archiving of upper-air data are discussed. The intent of this paper is to stimulate dialogue within the upper-air-data–user community about these issues so that appropriate action can be formulated and implemented.

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Michael L. Branick and Charles A. Doswell III

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Cloud-to-ground lightning data are presented from tornadic thunderstorms in Oklahoma, Kansas, and Nebraska on 13 March 1990. The tornadic storms from northern Oklahoma northward into Kansas and Nebraska produced an unusually high percentage of positive cloud-to-ground (+CG) flashes, whereas those in central and southern Oklahoma produced mostly negative flashes. Visual evidence indicates a distinct difference in structure between the northern storms, which produced high +CG rates, and the southern storms, which did not. The storms with high +CG rates possessed characteristics of storms in the low-precipitation (LP) portion of the supercell spectrum. In contrast, visual and radar characteristics indicate that the southern storms with lower +CG frequencies were in the high-precipitation (HP) portion of the supercell spectrum. These findings are consistent with another recent study linking high +CG rates with LP storms. Based on these observations, potential benefits of real-time lightning-strike data to forecast and warning operations are considered.

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Charles A. Doswell III and Sonia Lasher-Trapp

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Meteorological observing networks are nearly always irregularly distributed in space. This irregularity generally has an adverse impact on objective analysis and must be accounted for when designing an analysis scheme. Unfortunately, there has been no completely satisfactory measure of the degree of irregularity, which is of particular significance when designing artificial sampling networks for empirical studies of the impact of this spatial distribution irregularity. The authors propose a measure of the irregularity of sampling point distributions based on the gradient of the sums of the weights used in an objective analysis. Two alternatives that have been proposed, the fractal dimension and a “nonuniformity ratio,” are examined as candidate measures, but the new method presented here is considered superior to these because it can be used to create a spatial “map” that illustrates the spatial structure of the irregularities in a sampling network, as well as to assign a single number to the network as a whole. Testing the new measure with uniform and artificial networks shows that this parameter seems to exhibit the desired properties. When tested with the United States surface and upper-air networks, the parameter provides quantitative information showing that the surface network is much more irregular than the rawinsonde network. It is shown that artificial networks can be created that duplicate the characteristics of the surface and rawinsonde networks; in the case of the surface network, however, a declustered version of the observation site distribution is required.

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Charles A. Doswell III and Stanley L. Barnes

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Charles A. Doswell III and Lance F. Bosart

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Joseph T. Schaefer and Charles A. Doswell III

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A simple analysis of the position error inherent in double-theodolite pibal systems is presented. The quality of data collected by double theodolites is very sensitive to the geometric design of the system, and care must be taken in the interpretation of results.

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Charles A. Doswell III and Joseph T. Schaffer

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Charles A. Doswell III and Paul M. Markowski

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Basic concepts of buoyancy are reviewed and considered first in light of simple parcel theory and then in a more complete form. It is shown that parcel theory is generally developed in terms of the density (temperature) difference between an ascending parcel and an “environment” surrounding that parcel. That is, buoyancy is often understood as a relative quantity that apparently depends on the choice of a base-state environmental profile. However, parcel theory is most appropriately understood as a probe of the static stability of a sounding to finite vertical displacements of hypothetical parcels within the sounding rather than as a useful model of deep convection.

The thermal buoyancy force, as measured by the temperature difference between a parcel and the base state, and vertical perturbation pressure gradient force together must remain independent of the base state. The vertical perturbation pressure gradient force can be decomposed to include a term due to thermal buoyancy and another due to the properties of motion in the flow. Some thought experiments are presented to illustrate the ambiguous relevance of the base state.

It is concluded that buoyancy is not a relative quantity in that it cannot be dependent on the choice of an essentially arbitrary reference state. Buoyancy is the static part of an unbalanced vertical pressure gradient force and, as such, is determined locally, not relative to some arbitrary base state outside of a parcel. This has direct application to the diagnosis of buoyancy from numerical simulations—done properly, such a diagnosis must include not only the thermal buoyancy term but also the perturbation pressure gradient force due to buoyancy.

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