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<br />.-,.----.-.-... '---+'---""--'-p---~-'- --..-...----- - --~--~-..,.-
<br />
<br />APRIL 1978
<br />
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<br />
<br />505
<br />
<br />MELVIN J. SCHROEDER AND GERARD E. KLAZURA
<br />
<br />TABLE 5. Contents of the fixed length case study summary file.
<br />
<br />particular study case. Its most probable uses are for
<br />areal precipitation analysis and precipitation formation
<br />and evolution~ studi~s which also use aircraft data and
<br />numerical and conceptual model results. Analysis
<br />programs have already been written which access this
<br />file and create tim~height, vertical cross-section, multi-
<br />level constant-altitude PPI, three-dimensional repre-
<br />sentations, and total precipitation "footprints" of in-
<br />dividual precipitating cells that have been identified.
<br />
<br />2) CASE STUDY SUMMARY FILE
<br />
<br />This file contains location, area, volume, rain and
<br />motion information for cells that were identified and
<br />tracked. The reports described later are generated from
<br />this file which contains fixed length records. Table 5
<br />presents the radar echo information contained in the
<br />Case Study Summary File.
<br />A general information record contains the radar loca-
<br />tion and Z-R relationships used for the rainfall com-
<br />putations. A volume summary record, following the
<br />general information record, is written, for every 5 min
<br />voluni'e scan for every cloud entity. Since the 3600
<br />sweep at a constant antenna tilt is a basic sampling
<br />entity, an area summary record is generated summariz-
<br />ing case study areal data for each antenna elevation
<br />angle which contains echo information. A morphology
<br />record, written whenever a split, merger or termination
<br />takes place, precedes the volume summary record and
<br />follows the general information record.
<br />
<br />d. Report generation (RADLIST)
<br />
<br />Six reports are created by the report generator pro-
<br />gram from the case study summary file. Fig. 5 shows
<br />an example of each report for a cell that appears on the
<br />composite B-scan of Fig. 3.
<br />A case study area report relates echo intensity and
<br />area for each case study. Data are presented in square
<br />kilometers by date, time, and tilt for the total area
<br />covered by the case and normally from 20 dBZ to
<br />65 dBZ, in 5 dBZ increments. No accumulation is done
<br />for Z. categories below the lowest level requested. The
<br />area totals are cumulative to the lowest specified Z.
<br />category.
<br />
<br />TABLE 4. Contents of compressed Z. file.
<br />
<br />Parameter
<br />
<br />Units
<br />
<br />Site location
<br />. Case identification
<br />Date
<br />Time
<br />Antenna elevation
<br />Antenna azimuth
<br />Range gate interval
<br />Azimuth step
<br />Elevation step
<br />Range start and end
<br />Reflectivity values
<br />
<br />year, day
<br />h, min, s
<br />deg
<br />deg
<br />km
<br />deg
<br />deg
<br />km
<br />dBZ
<br />
<br />Parameter
<br />
<br />Units
<br />
<br />Case identification
<br />Date
<br />Time
<br />Tilt
<br />Volume
<br />Area
<br />Centroid, echo-top and maximum Z.'range
<br />Centroid, echo-top and maximum Z. azimuth
<br /><::entroid, echo-top and maximum Z. height
<br />Radar maximum tilt angle
<br />Cloud base height
<br />Average and maximum Z.
<br />Volume of 14 reflectivity categories
<br />Area of 14 reflectivity categories
<br />Average and maximum rainfall rates
<br />M-P rain flux
<br />Z-R relationships (2)
<br />Location and height of radar
<br />
<br />year, day
<br />h, min, s
<br />deg
<br />km3
<br />km2
<br />km
<br />deg
<br />km
<br />deg
<br />km
<br />dBZ
<br />km3
<br />km2
<br />mm h-1
<br />km3 (5 min)-l
<br />
<br />km
<br />
<br />The case study location report identifies several
<br />characteristics about a radar cloud. In addition to
<br />cloud base height (km), area (km2) and cloud volume
<br />(km3) for every case and associated volume scan, the
<br />report lists range (km), azimuth (degrees from true
<br />north of the radar) and height (kIn) of centroid, echo
<br />top, and maximum Z., average and maximum Z., and
<br />maximum tilt for the case.
<br />Centroid calculations are done in the Cartesian co-
<br />ordinate system, assuming the Z. value exists in the
<br />center of the originally recorded range bin. Each bin
<br />volume is weighted with the Z. contained in it and
<br />they are all accumulated for the specific study case.
<br />Height of the centroid is calculated using volumetric
<br />data of the study case. It is computed using the formula
<br />as developed by Greene (1971) and assumes an equiv-
<br />alent earth radius of 6370 kIn.
<br />Echo top and maximum Z. value, range, azimuth and
<br />height are determined employing the same technique
<br />as used for the centroid range, azimuth and height
<br />calcula tions.
<br />Since its first application to meteorology, radar has
<br />been used to observe the formation, growth, dissipation
<br />and movement of echo areas. Radar echo movement as
<br />determined by the centroid of the area is a convenient
<br />method of describing the propagation and translation of
<br />the echo. The cloud dynamics report lists the results
<br />of the motion calculations.
<br />Echo motion calculations are done in the rectangular
<br />(X,Y) coordinate system after conversion from the
<br />B-scan (r,O) system. Rate of change is determined by
<br />calculating the amount of time in seconds from the
<br />beginning of one volume scan to the beginning of the
<br />next volume scan, and it is presented for the following:
<br />
<br />1. Horizontal and vertical centroid motion
<br />2. Height change of cloud top and maximum Z.
<br />
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