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Gary L. Achtemeier

Abstract

Successive corrections objective analysis techniques frequently are used to array data from limited area without consideration of how the absence of data beyond the boundaries of the network impacts the analysis in the interior of the grid. The problem of data boundaries is studied theoretically by extending the response theory for the Barnes objective analysis method to include boundary effects. The results from the theoretical studies are verified with objective analyses of analytical data. Several important points regarding the objective analysis of limited-area datasets are revealed through this study.

  • Data boundaries impact the objective analysis by reducing the amplitudes of long waves and shifting the phones of short waves. Further, in comparison with the infinite plane response, it is found that truncation or the influence area by limited-area datasets and/or the phase shift of the original wave during the first pass amplified some of the resolvable short waves upon successive corrections to that first pass analysis.
  • The distance that boundary effects intrude into the interior of the grid is inversely related to the weight function shape parameter. Attempts to reduce boundary impacts by producing a smooth analysis actually draw boundary effects father into the interior of the network.
  • When analytical test were performed with realistic values for the weight function shape parameters, such as the GEMPAK default criteria, it was found that boundary effects intruded into the interior of the analysis domain a distance equal to the average separation between observations. This does not pose a problem for the analysis of large datasets bemuse sevens rows and columns of the grid can be discarded after the analysis. However, this option way not be possible for the analysis of limited-area datasets because there may not be enough observations.

The results show that, in the analysis of limited-area datasets, the analyst should be prepared to accept that most (probably all) analyses will suffer from the impacts of the boundaries of the data field.

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Gary L. Achtemeier

Abstract

Single- and multiple-Doppler radar systems are increasingly being used to monitor circulations within the clear-air boundary layer where the scatterers may be gradients of the refractive index or biota or a combination of both. When insects are the primary source of returned radar power, it must be assumed that the insects are either small and are being carried passively in the air, or are flying randomly so that the bulk velocity of all the insects contained within a pulse volume is zero relative to the air.

This study presents dual-polarization radar observations of the interaction between a gust flow and a deep cloud of insects within a relatively unstable air mass over North Dakota on 4 July 1987. These data are unique in that they reveal several meteorological conditions for which the preceding assumption is not valid. The boundary layer was not capped, and circulations rose above an apparent threshold altitude above which these insects were not flying. Temperatures near the threshold altitude were in the range of 10°–15°C. The top of the insect layer remained near 1800 m AGL regardless of circulations that could have carried insects to higher altitudes.

A biological hypothesis of flight response to strong updrafts was developed and tested with dual-polarization data. Localized decreases in differential reflectivity Z DR, interpreted as the result of reorientation of insects in evasive flight were coincident with strong updrafts identified from the analyses of the Doppler velocities.

This study shows that conditions exist for which the insects are not valid tracers of air motion. Therefore, care must be taken that combined insect and wind velocities are not taken as wind velocity alone.

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Gary L. Achtemeier and Paul T. Schickedanz

Abstract

Covariates derived from 1200 GMT tropospheric soundings taken for 13 June at Dodge City, Kansas, were compared with 3 h rainfall within the surrounding area. Correlation magnitudes decreased beginning with the first period for which precipitation lagged the soundings. There were larger decreases thereafter. It is suggested that the correlation magnitudes decrease because the measured environment is not representative of the environment within distant precipitation-producing migratory disturbances. This implies that atmospheric measurements should be taken simultaneously with the initiation of rainfall if maximum correlative power is to be attained.

Spatial analyses are presented as an alternative to frequent observations so that migratory precipitation-producing disturbances can be detected prior to the on-site rainfall. Covariates obtained from spatial fields gave higher correlations with 3 h rainfall than did the covariates obtained from single soundings.

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Stanley Q. Kidder and Gary L. Achtemeier

Abstract

No abstract available.

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Stanley A. Changnon, Griffith M. Morgan Jr., Gary L. Achtemeier, Neil G. Towery, and Ronald C. Grosh

Abstract

A description is given of a broad program to Design and Experiment to Suppress Hail (DESH) in Illinois. This program draws on results acquired during 17 years of extensive hail research in Illinois. There are two principal tasks to DESH: the determination of the desirability and the feasibility of hail suppression experimentation in Illinois and the Midwest. Socio-economic studies have led to an affirmative conclusion on the desirability issues. The feasibility decision appears affirmative and rests on certain key results. Airborne cloud base seeding in the humid midwestern environment is possible but will be more difficult and expensive than in less humid areas. Radar will be needed for short-term forecasting, aircraft operations, identification of potential hailstorms, and in the evaluation of seeding effectiveness. Weather forecasting by objective techniques will be valuable in both operations and evaluation, and adequate objective techniques have been largely developed. The overall shape of the proposed experiment is now clear. It will consist of an impact monitoring effort, which will make assessments of societal, environmental and economic impacts and communicate with the public; an operational effort to execute the experiment according to the final detailed design; and an evaluation effort combining a variety of surface, synoptic and radar data to assess the efficacy of the chosen seeding technique.

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