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R. G. Barry

The investigations of de Saussure on altitudinal effects on meteorological elements in the Alps during the 1780s are discussed. His ideas on the cause of cold in mountains and his attempts to determine evaporation and atmospheric transparency are especially notable and little known in comparison with the recognition of his contributions to developments in hygrometry.

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M. A. Palecki and R. G. Barry

Abstract

The statistical relationships between lake freeze-up/lake ice break-up dates and air temperature means over various time periods are analyzed for 63 lakes in Finland. Mean temperatures for the individual months before the lake event dates are strongly correlated with these dates; significant correlations hold for periods up to five months in length before freeze-up. Regression coefficients depend on location, but are consistent within regions. Latitude and distance from the coast are the most important sources of variation in the regression coefficients.

The regression coefficients are used to translate changes in lake freeze-up/break-up dates into estimated changes in air temperature. In southern Finland a five day change in freeze-up date would represent a 1.1°C change in November temperature of the same sign. A time series of November temperatures estimated from lake freeze-up dates is derived and compared with observations at Helsinki. The spatial pattern of temperature change over time is also examined using the freeze-up dates. Freeze-up/break-up dates provide a useful proxy for air temperature estimates in data-sparse regions of middle-high latitudes and could permit rapid satellite monitoring of climate perturbations.

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R. G. Barry and J. M. Clark

Abstract

An ERTS-1 Data Collection Platform instrumented with meteorological sensors has been operated for more than a year at 3536 m in the Front Range, Colorado.

The interface system and sensor performance are shown to operate well although the message interval is suitable only for certain types of parameter with the present interface system.

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R. G. Barry, R. C. Brill, and G. F. Estabrook

Abstract

The TAXIR information retrieval system, originally developed for taxonomic research, is described in the context of its application to climatological data. Data banks for four mountain stations in Colorado have been established and analysed using TAXIR and a package of statistical routines. The procedures and their cost effectiveness are evaluated.

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Jill Williams, R. G. Barry, and W. M. Washington

Abstract

The NCAR global circulation model has been used to simulate global atmospheric conditions using boundary conditions representing those of the present day and those of the Würm/Wisconsin glacial maximum at about 20,000 years ago, for January and July cases.

The mean zonal wind strength in the July ice age case in the middle latitudes of the Northern Hemisphere was comparable with present winter conditions. Also in the ice age cases, the upper westerlies were not apparently displaced south of the Laurentide ice sheet. The Icelandic and Aleutian lows in January were displaced 10° southward, the Siberian high remained unchanged from the control situation, and a new low center was found over eastern Europe and the European USSR. In July high pressure developed over most of Asia. Maps of cyclone frequency in a 30-day period showed the influence of major ice sheets and sea ice in displacing zones of cyclone activity southward in January. Frequent cyclones occurred over central North America and there was a continuation of cyclone activity in the North Atlantic and from eastern Europe into Asia. There was virtually no cyclonic activity near the Laurentide ice sheet in July.

Cloud cover and precipitation were also analyzed. Changes in precipitation for the glacial maximum cases are mainly quantitative rather than affecting its spatial distribution. The zonal averages show small changes for the Southern Hemisphere. In the Northern Hemisphere precipitation was decreased slightly in winter with most pronounced effects between 0–10N and 55–70N. The summer shows a dramatic reduction of precipitation north of 10N.

There is broad agreement between these paleo-climatological reconstructions and those of other studies using different models.

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L. D. Williams, R. G. Barry, and J. T. Andrews

Abstract

The variation over uneven terrain of the daily total of incident shortwave (global) radiation under cloudless conditions may be estimated by existing methods for calculating direct and diffuse solar radiation on a slope. A computer program for performing these calculations, incorporating a technique to determine when the direct rays of the sun are screened by the horizon at each point, is described. The adequacy of the approximation for diffuse radiation is considered by comparison with published data. Computations for an area of east Baffin Island, Northwest Territories, Canada, demonstrate that the occurrence of glaciers there is influenced both by elevation and by solar radiation. The potential of such computations as an aid in selecting station sites for climatological studies is also discussed.

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C. S. Hanson, R. G. Barry, and C. R. Stearns
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Barry A. Bodhaine, Norman B. Wood, Ellsworth G. Dutton, and James R. Slusser

Abstract

Many different techniques are used for the calculation of Rayleigh optical depth in the atmosphere. In some cases differences among these techniques can be important, especially in the UV region of the spectrum and under clean atmospheric conditions. The authors recommend that the calculation of Rayleigh optical depth be approached by going back to the first principles of Rayleigh scattering theory rather than the variety of curve-fitting techniques currently in use. A survey of the literature was conducted in order to determine the latest values of the physical constants necessary and to review the methods available for the calculation of Rayleigh optical depth. The recommended approach requires the accurate calculation of the refractive index of air based on the latest published measurements. Calculations estimating Rayleigh optical depth should be done as accurately as possible because the inaccuracies that arise can equal or even exceed other quantities being estimated, such as aerosol optical depth, particularly in the UV region of the spectrum. All of the calculations are simple enough to be done easily in a spreadsheet.

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Barry E. Schwartz, Stanley G. Benjamin, Steven M. Green, and Matthew R. Jardin

Abstract

As part of an investigation into terminal airspace productivity sponsored by the NASA Ames Research Center, a study was performed at the Forecast Systems Laboratory to investigate sources of wind forecast error and to assess differences in wind forecast accuracy between the 60-km Rapid Update Cycle, version 1 (RUC-1), and the newer 40-km RUC-2. Improved knowledge of these errors is important for development of air traffic management automation tools under development at NASA Ames and elsewhere. This information is also useful for operational users of RUC forecast winds. To perform this study, commercial aircraft reports of wind reported through Aircraft Communications, Addressing, and Reporting System (ACARS) were collected in a region over the western and central United States for a 13-month period, along with RUC-1 and RUC-2 wind forecasts. Differences between forecasts and ACARS observations and estimates of ACARS wind observation error itself were both calculated.

It was found that rms vector differences between observations and forecasts from either version of the RUC increased as wind speed increased, and also as altitude increased and in winter months (both associated with higher wind speed). Wind errors increased when thunderstorms were nearby and were smaller in wintertime precipitation situations. The study also showed that considerable progress has been made in the accuracy of wind forecasts to be used for air traffic management by the introduction of the RUC-2 system, replacing the previous RUC-1 system. Improvement was made both in the intrinsic accuracy as well as in the time availability, both contributing to the overall improvement in the actual wind forecast available for air traffic management purposes. Using 3-h forecasts, RUC-2 demonstrated a reduction in mean daily rms vectors of approximately 10% over that for RUC-1 based on accuracy improvements alone. This error reduction increased to about 22% when time availability improvements were added. It was also found that the degree of improvement from the RUC-2 increased substantially for periods with a large number of significant wind errors. The percentage of individual vector errors greater than 10 m s−1 was reduced by RUC-2 from 8% (RUC-1) to 3% overall and from 17% to 7% during the worst month. Such peak error periods have a strong impact on air traffic management automation tools. Last, it was found that the estimated trajectory projection errors from the RUC-2 using 1–2-h forecasts averaged 9 s for ascent/descent flight segments of approximately 15 min, and about 10 s for en route segments of the same duration.

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Stanley G. Benjamin, Brian D. Jamison, William R. Moninger, Susan R. Sahm, Barry E. Schwartz, and Thomas W. Schlatter

Abstract

An assessment is presented on the relative forecast impact on the performance of a numerical weather prediction model from eight different observation data types: aircraft, profiler, radiosonde, velocity azimuth display (VAD), GPS-derived precipitable water, aviation routine weather report (METAR; surface), surface mesonet, and satellite-based atmospheric motion vectors. A series of observation sensitivity experiments was conducted using the Rapid Update Cycle (RUC) model/assimilation system in which various data sources were denied to assess the relative importance of the different data types for short-range (3–12 h) wind, temperature, and relative humidity forecasts at different vertical levels and near the surface. These experiments were conducted for two 10-day periods, one in November–December 2006 and one in August 2007. These experiments show positive short-range forecast impacts from most of the contributors to the heterogeneous observing system over the RUC domain. In particular, aircraft observations had the largest overall impact for forecasts initialized 3–6 h before 0000 or 1200 UTC, considered over the full depth (1000–100 hPa), followed by radiosonde observations, even though the latter are available only every 12 h. Profiler data (including at a hypothetical 8-km depth), GPS-precipitable water estimates, and surface observations also led to significant improvements in short-range forecast skill.

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