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<br />many of these various error sources in a "bulk" fashion. This may have therefore precluded any <br /> <br />perceived need to manually tweak the l-R parameters or the rain rate threshold during the event, <br /> <br />a task that would be difficult to do operationally with any consistent success given our current <br /> <br />less-than-complete understanding of the cloud microphysical (or other) processes affecting these <br /> <br />parameters, Both the rain rate and l-R parameters likely change over relatively small spatial and <br /> <br />temporal scales in ways not fully understood, and they may be a function of atmospheric <br /> <br />temperature and/or moisture sounding variables on any given day (Kelsch 1989), Optimizing <br /> <br />these parameters as a function of storm type, geographic location, season, etc. across the entire <br /> <br />U.S. is a necessary but daunting task, and the transportability of locally-optimized parameter <br /> <br />values from one time or location to another is questionable at best. <br /> <br />This is one area where dual polarization radar technology has potential due to its <br /> <br />increased ability to distinguish hydrometeor sizes and types such as rain vs. hail. As a result, the <br /> <br />dilemma of determining appropriate rain rate thresholds and/or l-R parameters associated with <br /> <br />the WSR-88D PPS single polarization rainfall estimation technology may be partially side- <br /> <br />stepped when using dual polarization data because other more robust rainfall estimation <br /> <br />techniques become available that are less sensitive to elusive raindrop size distributions, for <br /> <br />example, those that use differential phase measurements (Ryzhkov and lrnic' !996a,b). <br /> <br />8. Basin-averaged rainfall <br />Point measurements of radar and gauge rainfall have been compared thus far. This <br /> <br />section will briefly examine the basin-averaged rainfall as derived from the PPS. Time series of <br /> <br />basin-average and basin-maximum reflectivity, rain rate, one-hour rainfall and storm-total <br /> <br />21 <br /> <br />./ <br /> <br />y' <br />