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<br />Normalized dBZ profiles: 7128-Bold; COARE-light; GATE-dash <br />14 <br />13 <br />12 <br />11 <br />10 <br />9 <br />~ 8 <br />7 <br />i 6 <br />:I: 5 <br />4 <br />3 <br />2 <br />1 <br />o <br /> <br /> <br />, <br />":~...., <br />, <br />, <br />, <br />, <br />, <br />, <br /> <br />o <br /> <br />0,2 <br /> <br />0,4 0,6 0,8 <br />Norm.aRenectlvity <br /> <br />1 <br /> <br />FIG, 16, Height profiles of nonnalized radar reflectivity (nor, <br />malized to profIle maxima) for the FCL case (bold, solid line), and <br />the mean convective profiles from the TOGA eOARE (light, <br />solid; DeMott and Rutledge 1998) and GATE (dashed; Szoke and <br />Zipser 1986) tropical oceanic regimes. Short solid horizontal <br />(dash) lines indicate the heights of the 00 and -200e temperature <br />levels for the (tropical oceanic) FeL environment. <br /> <br />siluated near and jusI above the height of the OOC level. <br />Reflectivities of 35 dBZ extended to temperatures <br />colder than -lOoC al this time, with the first detected <br />CG lightning occurring 15 min later, Cross sections <br />of 2;,R and Kop in Fig, 17a combined with the cross <br />section of radial velocity in Fig, 17b suggest that 2- <br />3-mm diameter raindrops (Zo.'s approaching 2 dB, <br />with Kop's of 2.5" km-I; e,g" Bringi et ai, 1996) were <br />being formed between the 2- and 3-km levels (x <br />= I km, Fig, 17b) in the updraft located on the eastern <br />edge of the convective core (x = 0.5-1.5), The verti- <br />cal extent of ZOR values> I dB and Kop values <br />> 10 km-I also suggests that millimeter-sized raindrops <br />were being lofted by the updraft to temperatures colder <br />than OOC, followed by freezing (Bringi et ai, 1996), as <br />indicated by reflectivities near 50 dBZ in the updraft <br />and a rapid falloff in the ZOR and Kop above the 4-km <br />level. To investigate this drop freezing process further, <br />we calculated the reflectivity-weighted ice fraction (f) <br />using ZH and ZOR as outlined in Carey and Rutledge <br />(1996), As shown in Fig, 17c,J;increased from 0,1 to <br />0.5 just above the 4-km level in the updraft However, <br />mixed-phase precipitation existed up to at least 5 km <br />as indicated by the 0,9 ice fraction line (and hence 0,1 <br />rain fraction), This observation is further supported by <br />the presence of an "LDR cap" of -23 to -24 dB over- <br />lapping the top of the ZOR core, consistent with drop <br /> <br />208 <br /> <br />1.2 <br /> <br />freezing in a mixed-phase environment (e,g" Bringi <br />et al, 1996; Bringi et al, 1997; Jameson et ai, 1996), <br />The raindrops were lofted through the freezing <br />level along a northwestward trajectory and as they <br />froze likely underwent substantial accretional growth <br />prior to descending on the northwest side of the convec- <br />tive core, The location of the 57 dBZ reflectivity core <br />near and just above the 3,8-km level, situated in horizon- <br />tal gradients of radial velocity, ZOR and Kop' suggests <br />that the descending ice particles were likely growing <br />by accretion before they melted, Microphysically, the <br />observations for the FCL case seem conceptually simi- <br />lar to that of an "accumulation wne" model of precipi- <br />tation production, This concept, which involves <br />efficient precipitation production through a coupling <br />of wann-rain and ice-particle accretion processes, has <br />been previously invoked to explain hail growth (e,g" <br />Sulakvelidze et ai, 1967) and microphysical observa- <br />tions of rainfall production in tropical cumulonimbi <br />(e,g" Takahashi 1990; Takahashi and Kuhara 1993), <br />A similar microphysical process was proposed by <br />Bringi et al, (1996) in their multiparameter radar study <br />of a storm that produced heavy rain, hail, and minor <br />flooding in Fort Collins in June 1992, <br />A horizontal cross section of Zw ZOR' and Kop at <br />1.2 km AGL (Fig, 18a) during the time correspond- <br />ing to Figs, 17a-<: reveals interesting microphysical <br />structure that is relevant to the radar estimation of rain- <br />fall (Fig, 18b), Cells of high reflectivity exceeding <br />50 dBZ were approximately collocated with cores of <br />elevated 2;,R > 1.5 dB, suggesting the presence of drops <br />in excess of 3 mm (Herzegh and Jameson 1992), <br />Comparison of Figs, 17b and 18a reveals that these <br />cells containing large raindrops, likely resulting from <br />a collision-<:oalescence process, were located in the <br />updraft along the leading edge of the convective com- <br />plex, In contrast, the largest values of Kop (<': 1.50 km-I) <br />were centered primarily in the downdraft and further- <br />more were displaced to the northwest of the peak val- <br />ues of ZH and ZOR in the updraft by 1-4 km, This <br />juxtaposition between maxima in Kop and Z.lZOR has <br />important implications for storm microphysics and the <br />radar estimation of rainfall, as further discussed below, <br />The corresponding horiwntal cross section of radar- <br />derived rainfall rate is presented in Fig, 18b, We uti- <br />lize the NEXRAD Z-R and a blended R(f4,p, 2;,R)/Z-R <br />algorithm utilizing CSU-CHILL polannetric data (cf, <br />section 7d), The blended R(Kop, 2;,R) estimate pro- <br />duced peak rain rates of 110 mm h-I, while the peak <br />rain rate from the Z-R alone is only 75 mm h-t, In ad- <br />dition, the region of heavy rain (R> 50 mmh-I) is sig- <br /> <br />" <br /> <br />Vol, 80, No, 2, Februory 1999 <br />