Robert F. Dale

Time of Observation Temperature Bias and “Climatic Change”

Abstract Historical changes in time of once daily maximum and minimum temperature observations at cooperative climatological stations from 1905 to 1975 have introduced a systematic bias in mean temperatures. Unless corrected, this bias may be interpreted incorrectly as climatic “cooling” and may also affect the assessment of agricultural production potential and fossil fuel needs. Maximum and minimum temperature data for two years from the National Weather Service station at Indianapolis International Airport were used to evaluate the differences between mean temperatures obtained by terminating the 24 h period at the midnight observation and the mean temperatures obtained by terminating the 24 h period at 0700 and 1900 hours, typical observation times for AM and PM observing stations. The greatest mean temperature bias occurs in March when a 1900 observation day yields a monthly mean temperature 1.3°F above a midnight observation, and a 0700 observational day gives a −1.3°F bias. Since the number of AM o...

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...

Effect of Trend or Technology Variables and Record Period on Prediction of Corn Yields with Weather Variables

Abstract Reliable crop-weather-technology models are needed for yield prediction and for the determination of climatic risks in crop production. Accurate and timely information on crop yields would help both industry and government anticipate and more efficiently allocate food supply and create a more stable grain price for individual farm planning. Critical analyses of several multiple regression models for predicting county average corn (Zea mays L.) yields with weather information in Indiana showed that yield predictions are very sensitive to the trend variable(s) used to account for technology and also to the specific period of record used to estimate the regression parameters. Models using a function of year as the variable to represent technology trend showed great fluctuation in their parameter estimates and in their yield predictions from year to year. Predicted yields with average weather fluctuated up to 22 bushels per acre from one year to the next in the 1970s as each additional year was adde...

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...

Modeling Occurrences of Non-VFR Weather: A Case Study for Design of Flight Instruction Programs1

Objective methods in which climatology is considered are needed in the design of flight instruction programs. Weather conditions less than the minimum (LM) thresholds designated for Minimum Instructional Visual Flight Rules (MIVFR) were defined as those with 25 kt. The climatology of the LM conditions for four two-hour flight periods during the spring, fall, and summer semesters at Purdue University was generated. The negative binomial distribution was used to develop the expected LM probability deciles, which, for a fixed level of controllable resources, were used to predict the maximum number of students that should be enrolled in each semester. In the general aviation flight technology program at Purdue University, it was found that with present class enrollments in Visual Flight Rules (VFR) flight training, all students could be expected to complete their scheduled flying hours during a semester, without considerable makeup flight i...