Showing papers on "Weather station published in 1990"

Radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions

Abstract: Research was conducted into the estimation of radiation absorbed by a vertical cylinder in complex outdoor environments under clear sky conditions. Two methods of estimation were employed: a cylindrical radiation thermometer (CRT) and model developed by Brown and Gillespie (1986), and the weather station model. The CRT produced an integrated temperature reading from which the radiant environment could be estimated successfully given simultaneous measurements of air temperature and wind speed. The CRT estimates compared to the measured radiation gave a correlation coefficient of 0.9499, SE=19.8 W/m2, α=99.9%. The physically-based equations (weather station model)require the inputs of data from a near by weather station and site characteristics to estimate radiation absorbed by a vertical cylinder. The correlation coefficient for the weather station model is 0.9529, SE=16.8 W/m2, α=99.9%. This model estimates short wave and long wave radiation separately; hence, this allowed further comparison to measured values. The short wave radiation was very successfully estimated:R=0.9865, SE=10.0 W/m2, α=99.9%. The long wave radiation estimates were also successful:R=0.8654, SE=15.7 W/m2, and α=99.9%. Though the correlation coefficient and standard error may suggest inaccuracy to the micrometeorologist, these estimation techniques would be extremely useful as predictors of human thermal comfort which is not a precise measure buut defined by a range. The reported methods require little specialized knowledge of micrometeorology and are vehicles for the designers of outdoor spaces to measure accurately the inherent radiant environment of outdoor spaces and provide a measurement technique to simulate or model the effect of various landscape elements on planned environments.

Near Real Time Irrigation Scheduling Using Heat Unit Based Crop Coefficients

Abstract: An interactive computer program (SCHEDPEN) which utilizes growing-degree-day based crop coefficients for irrigation scheduling was developed and tested on cotton during 1988 and 1989 at two locations in Arizona. The program can directly accept weather data files from Arizona's automated agricultural weather station network (AZMET) via phone access. At both locations the program was compared to two other methods of irrigation scheduling and while yield and water use were not significantly different among the three methods, some algorithmic errors were found in SCHEDPEN which have been corrected. The program continues to be developed for additional crops and incorporation of additional management information.

Winter Offshore/Onshore Wind Differences in Southeastern Hudson Bay, Canada

Abstract: Acquisition of two 38-day wind data sets collected over a fast-ice shelf and at a nearby coastal weather station (Kuujjuarapik) in Hudson Bay allowed the calculation for the first time of an offshore/onshore wind speed ratio for an ice-covered environment. Mean wind over the ice was 29% higher than at the coast, compared to values of 65% for open ocean locations. This reflects the effect of the higher drag coefficient of the sea ice that more strongly attenuates the wind than does the sea surface. The data set also allowed the evaluation of the change in the wind field by local topography. Thus, a strong orographic effect was found in the SW quadrant, as winds of less than 5 m/s were deflected toward the SE and NW.

Comparisons of Temperature Measurements from Local Weather Stations and the Tomato Plant Canopy: Implications for Crop and Pest Forecasting

Abstract: Additional index words. Lycopersicon esculentum, Heliothis zea, Spodoptera exigua, agrometeorology, degree day models Abstract. Temperatures recorded by weather stations and within the canopy of tomato (Lycopersicon esculentum Mill.) crops were compared in fields near Davis, Calif., during Summer 1983 (60 days) and 1987 (50 days). For both years, the average maximum and minimum temperatures, daily temperature ranges, degree days per day, and total accumulated degree days were compared. In 1983, the mean maximum temperature at the weather station did not differ significantly from that in the canopy, but the mean minimum temperature at the weather station was signifi- cantly lower than that in the canopy. In 1987, the mean maximum temperature at the weather station was significantly higher than that in the canopy, but mean minimum temperatures did not differ significantly. Temperature ranges were significantly narrower for the weather station toward the end of the 1983 season, and significantly wider for the weather station at midseason 1987. Comparisons of degree days per day showed significant differences between means at the weather station and in the canopy in 1983, and among those at the weather station and the two degree day calculation methods used for temperatures recorded in the canopy. Total accumulated degree days based on temperature records at the weather station were lower than those in the canopy in 1983 but higher in 1987. In 1987, the single sine degree day calculation method overestimated degree days compared to the 2-hr triangulation method. The phenology of the tomato crop as predicted by weather station temperatures indicated that tomato maturation was underestimated in 1983 and overestimated in 1987. The rate of development for hypothetical populations of Heliothis zea (Boddie) and Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) within the tomato crop was again underestimated in 1983 and overestimated in 1987, as based on temperature data of the weather station. The developmental rates of crops, their pests, and associ- ated natural enemies are regulated by the temperatures en- countered through the course of a growing season (Willmer, 1986). As a result, the concept of physiological time (degree days) is now widely used as a driving variable for predictive phonological models used in agricultural systems. The cal- culation of degree days can be accomplished using a variety of techniques, but most assume that the growth rate of the crop or arthropod is linearly related to ambient temperature within the limits of specified lower and upper developmental thresholds (Wilson and Barnett, 1983). One popular method, which uses daily maximum and minimum temperatures, is the single sine method of Baskerville and Emlin (1968). An- other method of calculating degree days is the triangulation or trapezoidal technique (Lindsey and Newman, 1956). Both methods can be adapted for use as 24-hr (single) methods that calculate degree days based on one maximum and one mini- mum temperature per day, or as 12-hr or smaller interval methods if maximum and minimum temperatures are recorded at more frequent intervals. Increasing the frequency at which temperature data are collected will improve the precision of both techniques (Wilson and Barnett, 1983). Fundamental to the accuracy of degree day calculations is the accuracy of the temperature data used. Temperature data may