Laserfiche WebLink
<br />AUGUST 1984 <br /> <br />DONEAUD, IONESCU-NISCOV AND MILLER,JR. <br /> <br />1603 <br /> <br /> <br />.. <br /> <br />Woodley technique (GWT) developed empirical re- <br />lationships between the life history of satellite-deter- <br />mined visible cloud area and gage-radar measured <br />rainfall over southern Florida. Griffith et al. considered <br />average rain rates for two categories of echoes, those <br />growing in areal extent and those decaying. An <br />extended scheme for partitioning the total rain volume <br />of cloud segments (nine categories of rain rates were <br />established) was constructed by Woodley et al. (1980) <br />and modified by Augustine et al. (1980). The GWT <br />has also been applied to the United States High <br />Plains (Griffith et al., 1981). These authors mentioned <br />that rain rates vary drastically with synoptic conditions <br />and location. <br />There exists an increased interest in using visible <br />and infrared satellite data to estimate rain volumes <br />over larger regions. Although a roughly constant <br />average rai,n rate' has often been used by satellite <br />researchers to compute rain volumes, a study of the <br />variability of rain rates during and among storms has <br />not yet been performed, at least for the semiarid <br />climate of the northern United States High Plains. <br />The purpose of this study is to investigate the <br />evolution of rain rates during storms in a semiarid <br />climate, and particularly the extent to which the <br />average rain rate can be used to estimate rain volume <br />in convective storms. <br />There is a need for knowledge of spatial and <br />temporal distributions of rainfall, as well as total <br />volumetric rainfall for many hydrologic, agricultural <br /> <br />1060 <br /> <br />49 <br /> <br />.'--"-.. <br />~N1: <br /> <br />410 <br /> <br />E.fl <br />0" <br />s~ <br />o~ <br />,," <br />o(E. <br /> <br />45 <br /> <br />and other applications. As long as the floating-ta~get <br />storms are moving within a basin area (very low <br />speed), the hydrologic applications of the work are of <br />primary interest; otherwise, agricultural as well as <br />climatological interests predominate. <br /> <br />2. Sow'ce and processing of data <br /> <br />Data from the 1980 and 1981 summer operations <br />of the North Dakota Cloud Modification Project <br />(NDCMP) were used in this study. The NDCMP is <br />a cloud seeding program in North Dakota with the <br />dual objectives of rain enhancement and hail suppres- <br />sion. The data were collected at two field . locations, <br />Bowman (District 1) and Parshall (District 2). Figure <br />I illustrates the geographic location of the two radar <br />sites. The radars were 5.4 cm WR-lOO units manu- <br />factured by Enterprise Electronics Corporation and <br />equipped with digital data recording systems. Details <br />concerning the data recording, calibration and pro- <br />cessing procedures are given by Doneaud et al. (1984). <br />Low-tilt PPI products were the basic data used in <br />this analysis. From these products, echo clusters <br />(storms) were identified and time histories of various <br />radar parameters where computer generated. The <br />small mesoscale areas of Austin and Houze (1972), <br />or the mesoscale cloud systems described by Super <br />and Heimbach (1980) as cells bigger than a cumulus <br />cloud but smaller than a typical mesoscale convective <br />complex, are included. . <br /> <br />I 40 <br /> <br />1020 <br /> <br />go <br /> <br />10 <br /> <br />FIG. 1. Locations of the two radar sites in the 1980 and 1981 NDCMP. <br /> <br />100" <br /> <br /> <br />{. <br />