Showing papers on "Weather radar published in 1974"

The use of digital weather radar records for short‐term precipitation forecasting

Abstract: Weather radar may be used for forecasting the motion and development of precipitation patterns. A technique is described here which uses digital data sets and a computer pattern-matching programme to forecast storm motion for periods between one-half and 2 or 3 hours. The technique is able to track systems as they appear over the edge of the display by locking on to the leading edge features. Considerable attention has been given to evaluation techniques and more than 30 experiments involving seven different days of data from radars in Toronto and Montreal have been performed. It was found that although different classes of events had different forecastabilities, it was possible to obtain useful results for one hour forecasts on all the events studied.

The accuracy of radar-derived rainfall measurements in hilly terrain

Abstract: A weather radar has been used to measure rainfall over hilly terrain in north Wales. The radar was a standard Plessey Type 43S, which has a wavelength of 10 cm and a beam width to half power points of 2°. Measurements were compared with those based on a raingauge network consisting of 62 tipping bucket gauges distributed over 1,000 km2. This density of gauges was inadequate to define the hourly areal rainfall sufficiently accurately on some occasions and in these circumstances the radar-derived pattern was used to interpolate between the gauges so as to obtain an ‘optimum’ estimate of the actual sub-catchment rainfall which was then used to evaluate the accuracy of the radar measurement. Errors in the radar estimates were excessive unless the radar was calibrated hourly using raingauge measurements from one site. The accuracy was further increased when the horizontal drift of the rain in the wind between the radar beam and the calibration site was allowed for. Using these procedures, the mean percentage difference regardless of sign, Y, between the radar and optimum estimates of three-hourly rainfall over sub-catchments of typically 50 km2 varied from about 15% close to the calibration site to about 20% at a distance of 20 km. Differences decreased as the period of integration was increased; Y was 13% for 6 hour periods compared with 20% for 2 hour periods. Y also varied with the area of comparison. For point measurements hourly estimates differed by 37% but over an area of 500 km2 around the calibration site they differed by about 13%. The main causes of error in the radar measurements seem to be (i) variations in the drop size distribution relation, (ii) the spatial variation in the growth (or evaporation) which occurred between the beam and the ground and (iii) the horizontal drift of the rain in the wind. Probably all of these factors, but in particular (ii), are more important in the hilly terrain of this study than would be the case in flatter terrain. A further factor contributing to the differences between the radar and optimum estimates was the (unavoidable) error in each optimum estimate of the actual rainfall. The accuracy of the radar estimates decreased markedly if the beam intersected the melting layer. The increased errors were reduced by introducing an empirical correction factor which is a function of the range of the sub-catchment from the radar and the height of the melting layer, but the spatial and temporal variations of the melting layer were such that it was not possible to obtain the same accuracy as when the beam was entirely within rain.

Air navigation and landing aid system

Abstract: An air navigation and landing aid system wherein a pair of transponder beacons are located at known positions adjacent an airport runway. The aircraft carries a weather pulse radar system and an antenna for furnishing information affording a navigation aid during the flight stage. Switching means are inserted between the antenna and the weather radar for switching, during the landing stage, the received pulses relating to each beacon, in response to the interrogation of the weather radar, to a special receiver and a processing circuit which furnishes information affording a landing aid.

Applications of radar to meteorological operations and research

Abstract: Radar echoes from meteorological targets have existed almost from the time that radar was first used. In this paper, an equation is presented which relates the echo power to a characteristic of the cloud or precipitation particles within the radar pulse volume. Some examples of how radar has been used for operational purposes are given; these include a description of the utility of radar for storm detection, how radar can be used as an aid to weather forecasting for both the public and aviation interests, and also how radar can be applied to help solve some hydrological problems. Significant research results on the nature of atmospheric structure and processes as derived with the help of radar are presented. Doppler radar has played a prominent role in the investigation of storm dynamics, and high-power high-resolution radars have been used for studying the development and nature of clear-air turbulence and convective processes in the clear air. Recent trends in meteorological radars are indicated and suggestions are set forth which relate to the improved use of radar for operations.

The Radar Backscatter from Selected Agricultural Crops

Abstract: To study the possible use of the radar backscatter coefficient for purposes of vegetation inventory a series of measurements was undertaken on radar ground returns. Single vegetation species were studied. Use was made of stable platforms (television towers) with the radar at an altitude of 75 m above the terrain. The influence of weather and season was investigated. It was shown that a single vegetation type behaves as a Rayleigh scatterer. The radar backscatter coefficient as a function of frequency and polarization proves to be the only usable classifier to classify vegetations with the aid of radar.

Causes for Precipitation Increases in the Hills of Southern Illinois

Abstract: Studies involving precipitation in Illinois have shown the presence of 10 to 15 percent more precipitation in the average annual precipitation pattern in the Shawnee Hills area of southern Illinois than in nearby ftatlands Three methods differing in scale and time were used to delineate the hill anomaly and to determine the reasons for it First, a series of climatic studies of precipitation distribution considering daily, monthly, and seasonal data for comparison of hill and fladand stations were performed during 1960-1963 Next, a 5-year project involving analysis of data from a special raingage network on the basis of individual rain periods, months, and seasons during 1965-1969 was planned to define the areal extent of the hill high Finally, the results of these two studies were used to design a 1-month field study involving a weather radar, 3 cloud cameras, 5 weather (temperature-humidity) stations, 1 pilot balloon site, and aircraft sampling flights Results of the three major studies show that the hill enhancement of precipitation is the addition of moisture due to greater evapotranspiration from the forested hills and the convergent wind field created over the western hills caused by the configuration of the hills and valleys Reference: Jones, Douglas M A, Floyd A Huff, and Stanley A Changnon, Jr Causes for Precipitation Increases in the Hills of Southern Illinois Illinois State Water Survey, Urbana, Report of Investigation 75, 1974 Indexing Terms: Cloud condensation nuclei, convection, diurnal differences, hill effect, Illinois, precipitation, radar echoes, wind

A Computer-Generated -Dimensional" Graphic Display for Weather Radar Data.

Abstract: The use of a minicomputer to generate “four-dimensional” graphic displays of quantitative weather radar data by employing three-dimensional graphic techniques is described. The time dimension is added by using a video disc recorder to record and play back a time series of the displays. These displays succeed in portraying the radar reflectivity structure of individual storms or storm cells in a meaningful way.

Operational Techniques for Radar Set AN/TPS-41.

Abstract: : The report provides techniques for use with the mobile Weather Radar Set AN/TPS-41. The techniques will permit the meteorologically untrained radar operator to interpret the radar signal in terms of weather parameters and to communicate the weather information. Since the radar set is intended to be moved on occasion, particular attention is given to the problems of siting the radar at new locations. The means for obtaining an optimum return signal is discussed. A simplified description of types of rainfall to be observed is given. A method is presented for calculating rainfall rate by a nomogram. Techniques are described for interpreting echoes in terms of rainfall intensity and presenting the resultant information to the user.

Case Studies of Coastal Convective Storms as Observed by Doppler Radar.

Abstract: : The life cycles of coastal convective storms are studied utilizing a Doppler weather radar. The cases presented involve storms triggered by the sea breeze front. Horizontal and vertical scanning as well as fixed vertical pointing were utilized to observe the storms. Analyses of the observations suggest that convective storms move with the source of the updraft rather than the environmental wind and that the interaction between the vertically moving air and the environmental flow determines the time history of the storm structure. (Author)

Effect of rain on 4 GHz troposcatter radio paths

Abstract: The letter discusses field-strength measurements made with a narrow-beam scanning receiving aerial on an occasion when widespread rain embraced two 4 GHz transhorizon radio paths, the modification to the angular distribution of the troposcatter energy brought about by the rain being used to indicate the presence of rain scatter. A weather radar and rain gauges distributed along the paths aided the interpretation of the results. It is suggested that rain on such paths is not likely to contribute significantly to the path-loss statistics, but rain may cause significant changes in the mean direction of arrival of the scatter signals, whereas clear-air inhomogeneities in the refractive index produce somewhat smaller changes.