R. H. Shaw

A Comparison of Solar Radiation and Net Radiation

Daily values of solar and net radiation at Ames, Iowa were compared for the period, late June through November, 1954. It was found that by dividing the data into two groups, clear days and cloudy d...

CLIMATOLOGICAL ANALYSIS OF FREEZE DATA FOR IOWA

A set of freeze thresholds is defined which replaces the loosely defined element “killing frost.” Freeze series are tested and found to be random. This makes it possible to fit frequency distributions. It is hypothesized that these distributions are normal and a test of significance verifies this. A hypothesis that the variance parameter is constant over Iowa is tested and found to be true. It is shown that spring and fall freeze are independent and this results in a simple form of freeze-free period distribution. The calculation of probabilities of freeze and freeze-free season are explained.

The Climatology of Soil Moisture, Atmospheric Evaporative Demand, and Resulting Moisture Stress Days for Corn at Ames, Iowa

Abstract The average seasonal march and frequency of soil moisture in the corn root zone at Ames, Iowa, during a 30-yr period was estimated for a well-drained 5-ft soil profile holding 9 inches of available water at field capacity. Average seasonal marches of soil moisture in the top 5 ft were also prepared from simulated water balance computations for soils with three different available field capacities (6, 9 and 12 inches) and, for each capacity, three different 1 April soil moisture profiles (20, 60 and 100 per cent of available field capacity) from which to begin the moisture budget calculations. The average seasonal march and frequencies of evaporation from a Weather Bureau Class A evaporation pan and from corn with soil moisture not limiting were estimated. Using an experimentally derived atmospheric-soil moisture stress relation for corn, the climatology of potential evapotranspiration from corn was expressed as the soil moisture necessary in the corn root zone to prevent moisture stress in corn o...

Low-Level Stability and Pollutant-Trapping Potential for a Rural Area

Abstract Temperature and wind speed measurements over a 6-year period from a 32 m tower located in a primarily rural area are used to assess the pollutant-dispersive characteristics of a rural site. A monthly comparison of a crude pollution-trapping index shows July through September the most favorable, and December through February the least favorable, months for the trapping of contaminants emitted from ground-based sources in rural areas.

Field Plant Physiology

Publisher Summary This chapter discusses the relation between plants and its environment. The environmental elements that affect the growth of plants include radiant energy, temperature, water, and humidity. Analysis of light relationships in plant communities is complicated. Under field conditions, the intensity of solar illumination is not static, but varies erratically, frequently from minute to minute. In addition, the diurnal light cycle and the yearly seasonal light rhythm both impart predictable aberrations that are related to latitude. The intensity and wavelength components of light environment are markedly altered by these factors, but within the plant canopy, even more important are the factors such as the quantity and quality of plant parts that absorb, reflect, and transmit the incident radiation. Crop production research on plant–temperature relations falls into three general categories: the optimum temperature regime for the various crop species; the maximum temperature endured by the crop species without either reduced dry matter accumulation or death of the plant; and the lowest temperature tolerated by the crop species. In crop production, plant–soil–water relations are of paramount importance. Under field conditions, water loss is due both to evaporation from the soil surface and transpiration from plant surfaces. A plant may undergo water stress even when soil moisture is near field capacity and, likewise, encounter little moisture stress even though soil moisture is low, depending on atmospheric conditions. The internal water status of a plant is a function of water absorption versus transpiration.

Determination of Acceptable Sampling Rates for Recording Wind-Speed Data

ABSTRACT A cup anemometer approved by the National Weather Service was used to collect wind-speed data at a nominal sampling rate of 60 samples/min. Acceptable rates for sampling from a cup anemometer were deter-mined. The study indicated that for the particular wind data studied the standard deviation of the percentage difference between an hourly average wind speed obtained by 1 sample/min and the reference of 60 samples/ min was 1.5 percent. A 1-min average from the hour (representing the National Weather Services method of determining hourly average wind speeds) had a standard deviation of the percentage difference from the reference wind speed of 13.6 percent, indicating that the 1-min average from the hour may be a poor representation of an hourly average wind speed.

Low Precipitation Observational Bias at Cooperative Climatological Stations

An upward bias exists in probabilities of 0 or trace weekly total precipitation since small amounts often occur undetected and are recorded as 0 or trace at climatological stations where observatio...

Crop Adaptation and Climate

Publisher Summary Crop adaptation essentially refers to the relationships between the principal environmental factors and the growth response of crop plants. Largely ecological in character, this branch of plant science can be considered a synthesis of important elements of geography, physiology, genetics, meteorology, and agronomy. It is noted that because of its direct relationship to food production, the adaptation of crops is of vital concern to all. High on the list of important relationships are those dealing with the climatic elements, precipitation, temperature, and light, as they relate to the adaptation of old varieties of crops and to the development of new ones. This chapter reviews the contributions to the development of principles on which these relationships are based.

Bibliography of Agricultural Meteorology

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An Evaluation of Dew Point Fluctuations in the Microclimatic Layer

Measurements of the diurnal and height variation of the dew-point temperature in three types of ground cover (corn, soybeans and bare ground) were made in 1948 at Ames, Iowa, using a photoelectric dew-point hygrometer. The variations are expressed as the standard deviation of a frequency distribution of the dew-point temperatures taken at half-second intervals during a minute run.