Kinematic, Microphysical, and Precipitation Characteristics of MCSs in TRMM-LBA Robert Cifelli, Walter Petersen, Lawrence Carey, and Steven A. Rutledge Department of Atmospheric Science Colorado State University Overview This study uses dual-Doppler and S-band polarimetric radar data to examine differences in the vertical structure of convection that were observed during TRMM-LBA. Two MCSs, occurring in distinct meteorological regimes (see Fig. 3 in Petersen et al. poster), were chosen for analysis. The first MCS occurred on 26 January 1999 in low-level easterly flow as a squall line with an intense leading line of convection and a trailing region of decaying convection and stratiform precipitation. In contrast, the second MCS event, 25 February 1999, occurred in low-level westerly flow. This system exhibited little apparent organization and was best characterized as widespread stratiform precipitation with embedded convection. This poster presents results showing significant differences between these MCSs in terms of kinematic and microphysical characteristics. Figure 4. Same as Fig. 3 except for water content. Ice (gm m -3 - thin solid lines), liquid (gm m -3 - color contours), mass weighted mean drop diameter (mm - heavy solid lines) Active mixed phase microphysics Copious ice in mid-upper troposphere Paucity of ice in mid-upper troposphere Water Content EasterlyWesterly Individual CAPPI’s and Cross Sections Composite Analysis Summary The two MCSs in this study, representing distinct meteorological regimes, have significant differences in terms of vertical structure characteristics. The easterly event was more intense in terms of overall reflectivity and kinematic structure (Figs. 6 and 7). The MCSs were sampled in similar lifecycle stages based on low-level reflectivity characteristics (Fig. 5) but displayed pronounced differences in terms of kinematic evolution (Fig. 10). Polarimetric data indicated large differences in the vertical distribution of hydrometeors. The easterly MCS showed evidence of a robust mixed phase region and large amounts of ice above 6 km that was largely absent in the westerly case (Figs. 3, 4, and 8). These observations can be used for validation of TRMM alogorithms and numerical models which utilize information on hydrometeor vertical structure to estimate latent heating (Tao et al. 1993; Olson et al. 1999). Method 2.5 (3.0) hours of continuous dual-Doppler and polarimetric radar data analyzed for the easterly (westerly) MCS at 10 minute resolution. Radar data partitioned into convective and non-convective components using reflectivity texture algorithm similar to Rickenbach and Rutledge (1998). Water contents and mean drop diameters calculated following methods of Carey and Rutledge (2000). Rainfall calculated over a 40,000 km 2 grid using optimization procedure among S-Pol Z H, Z DR, and K DP, similar to Chandrasekar et al. (1993) and Petersen et al. (1999). See Carey et al. handout for details. Acknowledgements This work is supported by the NASA TRMM Program TRMM-LBA Instrumentation Figure 1. Location of instrument platforms deployed during TRMM-LBA. NCAR S-Pol and NASA TOGA (C-band) radars used for analyses Dual-Doppler baseline ~ 60 km Radar data interpolated onto a km 2 cartesian grid Citation Flight Track Cross Section EasterlyWesterly Examples of Convective Organization Squall line with trailing stratiform and decaying convection Originated as outflow from previous convection Widespread stratiform with embedded convection MCS persisted over 8 hours Organization and evolution more complicated than easterly MCS Figure 2. Radar CAPPI of storm relative winds and reflectivity for the 26 January “easterly” MCS (left) and 25 February “westerly” MCS (right). Precipitation Characteristics Figure 8. Composite frequency histograms (left km height range) and mean profiles (right) of precipitation characteristics as determined from S-Pol observations of Z H and Z DR. (a) Precipitation ice mass (M i g m -3 ), (b) rain mass (M w g m -3 ), and (c) mass weighted mean drop diameter (D m mm). Large differences in ice content above 6 km suggest vertical drafts in the westerly case are not strong enough to levitate drops high and/or long enough for significant drop freezing to occur Reason for differences in location of peak D m above melt level are uncertain but may reflect differences in updraft strength and subsequent location of maximum collision-coalescence growth Larger D m for easterly MCS below melt level probably due to fallout and melting of large ice particles Height (km) Reflectivity (dBZ) Partitioned Reflectivity Figure 6. Composite CFAD’s of S-Pol reflectivity for the easterly MCS (top row) and the westerly MCS (middle row). Bottom row shows corresponding mean reflectivity profiles (easterly -red and westerly -blue). Columns from left to right are for the convective, non-convective, and total precipitation categories. ConvectiveNon-ConvectiveTotal Westerly convective profile has steeper gradient in mixed phase region Westerly has bright band signature in non-convective region Non-ConvectiveConvective Total Height (km) Vertical Air Motion (m s -1 ) Partitioned Vertical Air Motion Figure 7. Same as Fig. 6 except for vertical air motion. Modes of distributions for each MCS are nearly identical but mean profiles are different due to higher frequency of intense drafts in the easterly MCS Easterly convective profile ~100% larger below melt level Non-convective drafts have a significant impact on the total draft structure for the easterly MCS Non-convective drafts are insignificant (in the mean) for westerly MCS in lower tropossphere despite characteristic bright band signature (see Fig. 6) - lack of descent may reflect moist environment and reduced evaporation Significant differences in intensity and lifecycle characteristics 10 9 kg s -1 “Easterly” Convection “Westerly” Convection Time (UTC) Height (km) Vertical Mass Transport Figure 10. Time-height cross section of vertical mass transport Rain Rate Histogram Mean rain rate in easterly MCS is larger by a factor of 2 due to higher frequency of intense rain rates Easterly MCS Westerly MCS Rain rate (mm hr -1 ) Figure 9. Composite rain rate histogram for the easterly MCS (top) and westerly MCS (bottom). Easterly 10 m s -1 Westerly 5 m s -1 Figure 3. Cross sections of wind flow and selected polarimetric signatures for the easterly MCS (left) and westerly MCS (right). Locations of the respective cross sections are shown in Fig. 2. Radar reflectivity shaded as indicated, Z DR (blue) is contoured at 1 dB, incrementing at 1 dB. LDR (Red) contoured at -23, -21, and -19 dB. Note change in wind vector scale between panels. Polarimetric Comparison Easterly Z DR -LDR signature suggests hail production via drop freezing No evidence of significant mixed phase process in westerly MCS Convective Fraction Easterly MCS Westerly MCS Figure 5. Time series of convective fraction in each dual-Doppler synthesis volume for the easterly MCS (top) and westerly MCS (bottom). Time (UTC) Convective Fraction MCSs were in similar lifecycle stages during their respective sampling periods