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<br />335 <br /> <br />JOURNAL OF APPLIED METEOROLOGY <br /> <br />VOLUME 19 <br /> <br />bin volumes (whose associated reflectivity exceeded <br />the three thresholds) over the entire 3600 by 120 <br />antenna volume scan. The maximum total areas <br />were 'computed by accumulating all bin areas (whose <br />associated reflectivity exceeded the three thresholds) <br />over each 3600 by 10 antenna sweep within the <br />volume scans. The maximum of the 12 possible for <br />each volume scan was the value used. Usually the <br />10 or 20 sweep contained the largest echoing area. <br />Schroeder and Klazura (1978) include examples of <br />computer printouts which contain these variables as <br />well as further discussion of them. <br />The sounding variables were obtained from the <br />output of an operational computer program that is <br />routinely executed on project rawinsonde data. <br />Items 20 through 23 in Table 1 are stability <br />indexes. The lifted index and total totals index are <br />discussed by Galway (1956) and Millert, respectively. <br />The K index is the sum of the 85 kPa temperature <br />and dew point minus the sum of the 50 kPa tempera- <br />ture and the 70 kPa dew point depression: KI <br />= (Tsso + TDsso) - (Tsoo + T700 - TD700)' <br /> <br />3. Results <br /> <br />Correlation coefficients were first computed for <br />each predictor/dependent and predictor/predictor <br />variable pair. Many of the predictor variables were <br />highly cross correlated (see Table 2). Thus, before <br />proceeding with a stepwise multiple linear regres- <br />sion analysis, the 23 variables were first stratified <br />into five categories. The technique used for the <br />stratifications was a compromise between placing <br />highly correlated variables under the same category <br />and still have the categories define subdivisions <br />whose contents were generally physically related: <br />The five' categories and variables contained <br />therein are: <br /> <br />1) Temperature (Tsfe, LEV -20, LEV 0) <br />2) Water vapor and stability (EPTsoo, TDsfe, <br />PWsso, PW700, PWsoo, PWtot> MR, LllOo, L1so, <br />TTI, KI) <br />3) Upper level wind direction (WDIRaoo, WDIRsoo, <br />WDIR700) <br />4) Lower level wind direction (WDIRsso, <br />WSHEAR) <br />5) Wind speed (WSPDaoo, WSPDsoo, WSPD700, <br />WSPDsso). <br /> <br />Most of the variables within all but one category <br />were cross-correlated at a level higher than 0.50. <br />The exception was the wind-speed category in which <br />only the 30 and 50 kPa wind speeds were highly <br />correlated. The wind shear term, although calcu- <br /> <br />1 Miller, R. c., 1972: Notes on analysis and severe-storm fore- <br />casting procedures of the Air Force Global Weather Central. <br />Tech. Rep. 200, U.S. Air Force, 190 pp. <br /> <br />.......,- <br /> <br />TABLE I. Radar echo characteristics and sounding <br />variables chosen for study. <br /> <br />Dependent variables (radar echo characteristics) <br />I. TOPmax -maximum echo height <br />2. Zmax -maximum reflectivity factor . <br />3. VOLIO -maximum total volume> 10 dBZ <br />4. VOL30 -maximum total volume> 30 dBZ <br />5. VOL,o -maximum total volume> 40 dBZ <br />6. AREAIO -maximum total area> 10 dBZ <br />7. AREA30 -maximum total area> 30 dBZ <br />8. AREA,o -maximum total area> 40 dBZ <br />9. RVOLMP -maximum rain volume (5 min period) <br />[Marshall- Palmer] <br />10. RRATEMP-maximum rain rate [Marshall-Palmer] <br /> <br />Predictor variables (sounding variables) <br />I. EPT500 -equivalent potential temperature at 50 kPa <br />(500 mb) <br />2. LEV -20 -height of - 200C level <br />3. LEVo -height ofOoC level <br />4. T,rc -surface temperature <br />5. TD,rc -surface dew-point temperature <br />6. WDIR300 -30 kPa wind direction <br />7. WDIR500 -50 kPa wind direction <br />8. - WDIR700 -70 kPa wind direction <br />9. WDIR850 -85 kPa wind direction <br />10. WSPD300 -30 kPa wind speed <br />II. WSPD500 -50 kPa wind speed <br />12. WSPD700 -70 kPa wind speed <br />13. WSPD850 -85 kPa wind speed <br />14. WSHEAR-directional wind shear (WDIR300 minus <br />WDIR850) <br />-precipitable water (surface-85 kPa) <br />-precipitable water (surface-70 kPa) <br />-precipitable water (surface-50 kPa) <br />-precipitable water (total) <br />-mean mixing ratio (lowest to kPa) <br />-lifted index 10 kPA layer, mean mixing ratio, <br />adiabatic <br />-lifted index (5 kPa layer, mean mixing ratio <br />and temperature) <br />-total totals index <br />-K index <br /> <br />15. PW850 <br />16. PW700 <br />17. PW500 <br />18. PWtot <br />19. MR <br />20. LIlOo <br /> <br />21. LI50 <br /> <br />22. TTI <br />23. KI <br /> <br />lated from the difference between the 30 and 85 kPa <br />height intervals was very highly correlated with the <br />85 kPa wind direction and, therefore, was grouped <br />with it. <br />The variable within each category which had the <br />highest individual correlation coefficient was the <br />one allowed to be entered into the stepwise multiple <br />linear regression analysis process. The order in <br />which variables were entered during each of the 10 <br />stepwise regression phases (one for each dependent <br />variable) is shown in Table 3. The multiple correla- <br />tion coefficients (Mult R) are listed, as are the <br />individual correlation coefficients (Indiv R). <br />The number of cases analyzed for the 10 depend- <br />ent variables on the 1976 data set ranged from 23 <br />to 26. For all 10 dependent variables there always <br />was at least one variable which correlated better <br />than :to. 50, and five dependent variables had a pre- <br />dictor variable with a correlation coefficient higher <br />than :!:O.60. The highest individual correlation coef- <br />