INVESTIGATION OF RAINFALL CHARACTERISTICS ASSOCIATED WITH TROPICAL STORMS BONNIE, FRANCES AND IVAN IN UPSTATE SOUTH CAROLINA DURING 2004 C. W. ULBRICH Clemson University Clemson, SC and L. G. LEE NWS, Greer, SC

RADAR MOSAIC IMAGES FOR TROPICAL STORM BONNIE 12 AUGUST Z TO 1900Z (0200 TO 1500 EDT)

RADAR MOSAIC IMAGES FOR TROPICAL STORM FRANCES 7-8 SEPTEMBER Z,9/7/04 TO 0300Z,9/8/04 (2000 EDT,9/6/04 TO 2300 EDT,9/8/04)

RADAR MOSAIC IMAGES FOR TROPICAL STORM IVAN SEPTEMBER Z,9/16/04 TO 1300Z,9/17/04 (0400 EDT,9/16/04 TO 0900 EDT,9/17/04)

RAINFALL DATA COLLECTED FOR ALL THREE OF THESE STORMS AND ANALYSIS IS UNDER WAY. TODAY, RESULTS OF ANALYSIS ONLY FOR TROPICAL STORM FRANCES WILL BE SHOWN. CONCLUSIONS DRAWN ARE VALID FOR ALL THREE TROPICAL STORMS.

PRINCIPAL INSTRUMENTS USED IN THIS WORK FOR ANALYSIS OF BONNIE, FRANCES AND IVAN. LOCATED AT THE C.A.R.L. STANDARD JOSS DISDROMETER IMPORTANT PARAMETERS DETERMINED FROM DISDROMETER DATA: 1.RAINFALL RATE R (mm h -1 ) 2.RADAR REFLECTIVITY FACTOR (dBZ) 3.AVERAGE PARTICLE SIZE D m 4.RAINDROP SIZE DISTRIBUTION N(D) OTHER INSTRUMENTS: TIPPING BUCKET RAINGAGES MISC. METEOR. INSTRUMENTS

LOCATED AT THE NWS, GREER, SC WSR-88D WEATHER RADAR KGSP GREER, SC PRINCIPAL PARAMETER OF INTEREST: RADAR REFLECTIVITY FACTOR Z (dBZ) IN THE NWS, THE RAINFALL RATE R (mm h -1 ) FOUND FROM RELATION Z = A R b POSSIBLE VALUES: A=300, b=1.4 (Default) A=250, b=1.2 (Tropical)

LOCATION OF THE C.A.R.L.

RESULTS FOUND FOR FRANCES FROM DISDROMETER DATA 09/07/04, FRANCES R Z DoDo

EMPIRICAL ANALYSIS TO DETERMINE Z-R RELATION DEFAULT TROPICAL ACTUAL Z R

EXPECTED ERRORS FROM USING Z-R RELATION +35% ERROR IN R -35% ERROR IN R Z R

COMPARISON OF RAINFALL DEPTHS COMPUTED FROM Z-R RELATIONS WITH THAT MEASURED BY DISDROMETER 9/07/04, FRANCES MEASURED BY DISDROMETER AT C.A.R.L. ACTUAL TROPICAL DEFAULT

COMPARISON OF RAINFALL AMOUNTS FOUND FROM WSR-88D DATA WITH DISDROMETER AMOUNTS REFLECTIVITY FACTORS Z WERE DETERMINED FROM LEVEL II DATA FOR THE KGSP WSR-88D RADAR OVER THE LOCATION OF THE C.A.R.L. AT THE LOWEST ELEVATION ANGLE SCANS AND CONVERTED TO RAINFALL RATES R USING Z = A R b VALUES OF A AND b USED IN THE ANALYSIS WERE A=300, b=1.4 (default relation used by NWS) A=250, b=1.2 (NWS relation for distinctly tropical rain) A=271, b=1.41 (actual relation for Frances) HEIGHT OF PULSE VOLUME ABOVE C.A.R.L. APPROX. 500 m

ACTUAL RAINFALL DEPTH MEASURED BY DISDROMETER EMPIRICAL TROPICAL DEFAULT 09/07/04, FRANCES RADAR UNDERESTIMATES RAINFALL DEPTH BY AT LEAST A FACTOR OF 2, PERHAPS MORE

POSSIBLE EXPLANATION OF RESULTS: DISDROMETER IS MISCALIBRATED AND IS OVERESTIMATING THE REFLECTIVITY FACTOR BY A LARGE AMOUNT. TO ADDRESS THIS POSSIBILITY, DATA FROM NOAA WEIGHING RAINGAGES FROM SEVERAL LOCATIONS HAVE BEEN USED TOGETHER WITH WSR-88D RADAR DATA OVER THE GAGES. RAINFALL AMOUNT MEASURED BY GAGE COMPARED WITH THAT COMPUTED FROM REFLECTIVITY FACTOR USING Z-R RELATION. GAGE AMOUNTS SPECIFIED EVERY HOUR. RADAR DATA SPECIFIED APPROXIMATELY EVERY 5 MINUTES. DATA FOR PICKENS RAINGAGE ARE REPRESENTATIVE:

COMPARISON OF RAINFALL AMOUNT MEASURED BY NOAA WEIGHING RAINGAGE WITH AMOUNT MEASURED BY RADAR USING Z-R RELATIONS NOAA WEIGHING RAINGAGE (HOURLY) RADAR UNDERESTIMATES RAINFALL AMOUNT BY AT LEAST A FACTOR OF 2

COMPARISON OF REFLECTIVITY FACTORS MEASURED BY DISDROMETER AND KGSP WSR-88D DISDROMETER KGSP WSR-88D 09/07/04, FRANCES

CONCLUSIONS AND SUGGESTED FUTURE RESEARCH 1.KGSP WSR-88D NOT CALIBRATED CORRECTLY. SOURCE OF CALIBRATION PROBABLY LIES IN AN INCORRECT ASSUMPTION ABOUT VALUE OF ANTENNA GAIN (Maybe). 2.TO VERIFY THE CONCLUSIONS OF THIS WORK DISDROMETER SHOULD BE SITUATED NEAR ANOTHER WSR-88D, SAY, KCAE, AND MEASUREMENTS LIKE THOSE DESCRIBED HERE REPEATED. 3.DEMONSTRATION GIVEN IN THIS WORK IMPLIES THAT A PROPERLY CALIBRATED WSR-88D COULD PRODUCE ACCURATE RESULTS FOR RAINFALL DEPTH.