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William D. Bonner

Abstract

This article describes the mission and organization of the National Meteorological Center (NMC), summarizes progress since the introduction of the CYBER 205 computers in 1983, and describes plans for NMC numerical prediction systems in the 1990s. Plans include the introduction of a new mewsoscale “storm” model on next generation computers, continued improvements in the resolution and physics of the NMC global model, and extension of daily forecasts from 5 to 7 days with a “week-two” forecast of average weather conditions.

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WILLIAM D. BONNER

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The relationship between the low-level jet and thunderstorm activity in the south-central United States is examined through mesoanalysis of surface data from Weather Bureau and NSSP stations. Separate squall systems moved through Kansas and Oklahoma during the night; the systems in Kansas persisted while those in Oklahoma died out. The most likely explanation for this is the synoptic-scale vertical velocities in the vicinity of the low-level jet.

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WILLIAM D. BONNER

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Geographical and diurnal variations in the frequency of occurrence of strong low level wind maxima are determined using 2 yr. of wind data from 47 rawinsonde stations in the United States. Maximum frequency of occurrence is found in the Great Plains at approximately 37°N. and 98°W. The vast majority of jets in this region occur with southerly flow. Southerly wind maxima appear on both morning and afternoon soundings but occur with much greater frequency, over a larger area, on the morning observations.

Twenty-eight morning jet cases are used to determine average synoptic-scale wind and temperature patterns in the vicinity of the jet. Diurnal wind oscillations are examined by comparisons of jet frequencies, speeds, and altitudes on four-times-daily observations. The oscillation is similar to that described by Blackadar; however, there is no apparent tendency for the latitudinal variation in period of the oscillation which Blackadar's model implies.

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WILLIAM D. BONNER and FRANK WINNINGHOFF

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TIROS-VII and -VIII photographs are used to study synoptic and mesoscale cloud patterns during 6 days with strong southerly flow in the Central United States. Cases with nocturnal thunderstorms show a tendency for thunderstorms to occur in the downstream portion of the jet. Through advection of moisture and turbulent breakdown of the nocturnal inversion, the low-level jet plays an important role both in the formation of stratus and in its manner of dissipation. Longitudinal cumulus cloud bands with spacing of 10 to 15 km occur with slightly superadiabatic lapse rates and moderate wind shear in agreement with theoretical results by Kuo.

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William D. Bonner and Ralph D. Petersen

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Kenneth H. Bergman and William D. Bonner

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Kenneth H. Bergman and William D. Bonner

Abstract

A simple numerical experiment demonstrates that if the errors in satellite-derived temperatures are correlated spatially, the error of an optimum interpolation objective analysis using such temperature data is increased. Moreover, increasing the density of such observations beyond a, threshold value (a spacing of about 400 km in the experiment) does not yield any significant improvement in analysis accuracy, in contrast to the cage of observations with spatially uncorrelated errors.

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WILLIAM D. BONNER and JAN PAEGLE

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Analysis of 1 week's data in August 1960 shows significant diurnal variations in surface geostrophic wind over the south-central United States. The oscillation in the southerly component (V g) is driven by the response of the thermal wind to the diurnal temperature cycle over sloping terrain. A smaller oscillation in U g derives from spatial variations in the amplitude of the diurnal pressure wave. The amplitude of the oscillation in V g is about 3 to 5 m sec–1 at the surface, decaying exponentially with height to near 0 at 2 km.

Examination of 11 yr of summertime rawinsonde data at Fort Worth, Tex., shows a very regular diurnal variation in boundary layer wind with maximum amplitude of about 3 m sec–1 at 600 m above the ground. This oscillation is forced by periodic variations in both eddy viscosity and geostrophic wind. Using a simplified model of the boundary layer, we obtain solutions for the diurnally periodic wind resulting from “reasonable” variations in eddy viscosity and “observed” variations in geostrophic wind.

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Owen E. Thompson, Philip A. Arkin, and William D. Bonner

Abstract

A comprehensive summary of diurnal wind variations in the midwestern region of the United States is presented. Analyses are based on seven summers of four per day soundings at Fort Worth, Tex., Topeka, Kan., and International Falls, Minn. It is found that the diurnal oscillations are most prominent at Fort Worth, of significant amplitude at Topeka, and, although of lesser amplitude, still detectable at International Falls. An analysis is made of the forcing required to account for that part of the wind oscillation which cannot be attributed to Coriolis effects. This analysis indicates that the forcing is comparatively small at Fort Worth when the wind oscillations are largest owing to a resonance there with natural inertial oscillations. Significant forcing is present at higher latitude stations even though the manifestation of the forcing in the wind field is somewhat smaller in amplitude. The data suggest that forcing mechanisms at low and high attitudes may propagate to cause wind oscillations in the middle levels.

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EXECUTIVE COMMITTEE, James R. Mahoney, William D. Bonner, Joanne Simpson, Roscoe R. Braham Jr., Robert J. Serafin, Paul D. Try, Richard E. Hallgren, and Kenneth C. Spengler
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