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James B. Harrington and Thomas R. Heddinghaus

Abstract

Power spectra of mesoscale eddies with periods ranging from 10 min to 8 hr were computed for the months of January and July from three years of surface wind data obtained at Columbia, Mo. To educe the degree of determinism in the spectra, their variability with time of year, time of day, wind speed and direction, and with the presence or absence of thunderstorms was measured.

Diurnal spectra for January and July were found to be similar. A comparison of semidiurnal daytime and nighttime spectra showed that the former contained considerably more energy than the latter and that the difference was greater in July than in January. The eddy energy was shown to increase by a factor of approximately 7 at night in the presence of thunderstorms. No effect of wind direction could be found.

Over a large portion of the lower mesoscale range the diurnal power spectra followed a −1 law, similar to that for “wall turbulence” in the layer of strong shear in the boundary layer over a flat plate.

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Thomas R. Heddinghaus and Ernest C. Kung

Abstract

Eigenvector and harmonic analyses have been performed with monthly mean values of upper air parameters of the Northern Hemispheric circulation for the period from April 1955 to December 1974. The parameters used involve the 700 and 500 mb temperatures, the 700–500 mb thickness, the 300 mb kinetic and eddy kinetic energies, and the 700, 500 and 300 mb zonal/meridional flow indicators. The zonal/meridional flow indicator is defined as the ratio |u|/|v|, where the bar indicates the monthly mean.

The first eigenvectors of the normalized parameters are associated with the annual variation of the basic patterns. For the temperature field the first eigenvector overwhelmingly dominates. It reflects the annual variation of temperature in the mid and higher latitudes with an effect of the land-ocean configuration. The second eigenvector shows a land-ocean contrast. The long-term variation of temperature in the lower latitudes also stands out. For the kinetic energy and zonal/meridional flow indicator the first eigenvectors are not as dominant as that of temperature. They reflect the subtropical jet and other hemispherical-scale circulations. The third eigenvector of kinetic energy and second eigenvector of the zonal/meridional flow indicator appear to be associated with the semiannual oscillations of the large-scale wind systems including summer and winter monsoons. It also appears that high-numbered eigenvectors of kinetic energy and zonal/meridional flow indicators are associated with long-term variations in the lower latitudes and short-term variations in the mid to high latitudes.

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Thomas R. Heddinghaus and Arthur F. Krueger

Abstract

Four years of satellite observations of the outgoing longwave radiation have been used to study the distribution of cloudiness and rainfall over the tropics. Annual and interannual variations are described, partially with the help of an eigenvector analysis. Interannual variations in the outgoing longwave radiation are particularly interesting since they tend to follow the Southern Oscillation. Consequently, it can be used to monitor changes in the large-scale circulation over the tropics.

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Thomas R. Heddinghaus and Douglas M. Le Comte

Publication of a national weekly weather summary called the Weekly Weather Chronicle began in 1872. This summary was the precursor of today's Weekly Weather and Crop Bulletin (WWCB), a publication that reports global weather and climate conditions relevant to agricultural interests, as well as current national activities and assessments of crop and livestock conditions. The WWCB is produced by the Joint Agricultural Weather Facility (JAWF), a world agricultural weather information center located in the U.S. Department of Agriculture (USDA) headquarters in Washington, D.C., and jointly staffed by units of the National Oceanic and Atmospheric Administration's Climate Analysis Center and USDA's World Agricultural Outlook Board and National Agricultural Statistics Service. Besides featuring charts and tables (e.g., temperature and precipitation maps and crop progress and condition tables), the WWCB contains summaries and special stories highlighting significant weather events affecting agriculture, such as droughts, torrential rains, floods, unusual warmth, heat waves, severe freezes, heavy snowfall, blizzards, damaging storms, and hurricanes.

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Raymond P. Motha and Thomas R. Heddinghaus

The Joint Agricultural Weather Facility (JAWF), a cooperative effort between the Climate Analysis Center, NMC/NWS/NOAA (National Meteorological Center/National Weather Service/National Oceanic and Atmospheric Administration) and the World Agricultural Outlook Board, U.S. Department of Agriculture (USDA), focuses on weather anomalies and their effects on the crop-yield potential in major international crop areas. The basic mission is to provide an objective procedure for translating the flow of global weather information into timely and accurate assessments of growing-season conditions which ultimately impact on global agricultural production and trade. Daily monitoring of satellite weather images and meteorological data provides the framework for agricultural weather analysis. Daily, weekly, and seasonal summaries are processed and merged with historical weather and crop data for evaluation of the crop-yield potential. Information is disseminated at routine briefings, in written summaries, and through informal discussions.

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George Ohring, Philip F. Clapp, Thomas R. Heddinghaus, and Arthur F. Krueger

Abstract

Maps are presented showing the mean annual sensitivities of longwave and net radiation at the top of the atmosphere to changes in cloud amount for the region 60°N to 60°S. The maps are based on an analysis of a 45-month set of monthly mean radiation budget data for the years 1974–78 derived from the NOAA satellite scanning radiometers. The analysis technique is based on the regression method of Ohring and Clapp (1980), with some minor modifications. Both regionally and globally, the maps show that the albedo effect of clouds is greater than their greenhouse effect. The maps also suggest that the longwave sensitivity parameter might serve as a useful measure of the geographical distribution of effective cloud heights.

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