Showing papers on "Weather station published in 1983"

Comparison of weather station snowfall with winter snow accumulation in high arctic basins

Abstract: Most water balance studies in the High Arctic indicate that the weather stations underestimate annual precipitation, but the magnitude of such error is unknown. Based on up to seven years of field measurements, this study provides a comparison of snowfall at weather stations with the winter snow accumulation in their nearby drainage basins. Snowfall is the major form of precipitation in the polar region for nine months every year. Without vegetation, snowdrift is controlled by the local terrain. By establishing the snow characteristics for different terrain types, total basin snow storage can be obtained by areally weighting the snow cover for various terrain units in the basin. Such a method was successfully employed to compute total winter snowfall in the drainage basins near Resolute, Eureka and Mould Bay. Results show that the basins had 130 to 300per cent more snow than the weather stations recorded. Using revised snowfall values that are reinforced by Koerner's snow core measurements from i...

Weather Station Siting and Consumptive Use Estimates

Abstract: The environment of a weather station site is important in estimating consumptive use by irrigated crops. Consumptive use may be overestimated when air temperature and vapor pressure data from a weather station with an arid local environment are used without modification. To document the effect of weather station aridity on consumptive use estimates, three sites in irrigated areas and two sites in nonirrigated, arid rangeland in southern Idaho were instrumented with weather stations during 1981. Air temperatures were higher and vapor pressures were lower at the arid sites. Use of air temperatures and dewpoint estimates from arid sites caused an overestimation of ETr by 17% (210 mm) over the irrigation season. Results indicate the importance of weather site evaluation and adjustment of siting effects and weather before consumptive use estimates are made. A procedure is outlined for adjusting historical temperature data to reflect an irrigated condition.

Heat balance of the surface layer of the sea at ocean weather station T

Abstract: Heat balance of the upper 200 m of the sea south of Japan is studied, by the use of marine meteorological and oceanographic data at Ocean Weather Station T (29°N, 135°E), intensively obtained from June 1950 to November 1953. Local time change of the heat content in the surface layer and the net heat flux through the air-sea interface are calculated directly from these data, and the heat convergence in the sea is estimated from their residuals. Regarding the relative importance of one- and three-dimensional processes, it is found that, on a time scale of a few days to one month, the variation of heat content depends on heat convergence in the sea, while on a seasonal time scale, the heat content is determined primarily by the heat flux through the sea surface in December through February, by heat convergence within the sea from March to May, and by both processes from June to November. It is inferred that the heat convergence in the sea is caused by advection of water masses which are bounded by sharp fronts. Spectral analysis of sea surface temperature indicates that they typically take 2 to 3 days to pass the station, and their typical size is estimated as around 20 km by assuming the typical advection velocity of water masses to be 10 cm s−1.

A quantitative approach to the Pruitt and Doorenbos version of the Penman equation

Abstract: The Pruitt and Doorenbos version of the Penman equation developed from information given in Appendix II of FAO Irrigation and Drainage Paper No. 24 is calculated mainly from tables and is based on measurements made over a grass surface. Procedures are presented here to quantify these relationships, such as the calculation of net radiation, and to extend this approach to measurements made over alfalfa (Medicago sativa, L.). The latter was achieved by using a wind function that takes into account the height of the alfalfa and the use of mean rather than maximum relative humidity to calculate the correction factor used to take into account day and night weather conditions on calculated reference crop evapotranspiration. Using the above procedures, calculated values of evapotranspiration overestimated measured values from alfalfa by 13%. From data collected with an automated weather station near Broadwater, Nebraska, a much better agreement was obtained between these general procedures and a Penman equation with a locally derived- wind function. With greater utilization of low cost, automated weather stations for agricultural use, the procedures given for calculating reference crop evapotranspiration can easily be implemented in irrigation scheduling programs.

Factors Affecting Simulated Crop Yield Spatial Extrapolation

Abstract: ROP models are increasingly being used to estimate large area yields and generate information for regional agricultural crop/weather advisories. Utilizing models for these purposes requires an understanding of the factors affecting spatial extrapolation of estimates of crop growth and yield. This paper examines the influence of distance, elevation and monthly precipitation on variations of simulated corn and sorghum yields using meteorological data from a distant site for two plant extractable soil water levels. Daily maximum and minimum temperatures, radiation, and precipitation were used for yield simulations at sites in Kansas, Oklahoma, and Texas. Yield errors (defined as the yield difference between a distant and centrally located reference site) were calculated for each year. Mean simulated yields over all years were approximately the same within each area for corn and sorghum (i.e., the arithmetic mean yield errors were close to zero). Root mean square yield errors were correlated with geographical and meteorological variables. Errors were always most highly correlated with the logarithm of the distance from the centrally located site for the different plant extractable soil water levels and crop models. The addition of precipitation and elevation differences in the regression equation only slightly increased the percentage of explained variation and also increased the complexity of the relationship needed to explain the degree to which point estimates of yield could be spatially extrapolated. Regression slopes between errors and distance were similar across sites, water levels, and models. These results have significance for determining weather station densities required in using crop models for large areas yield estimates or as input for agricultural weather advisories.