1. Contrasting Tropical Rainfall Regimes Using TRMM and Ground-Based Polarimetric Radar Steven A. Rutledge, Robert Cifelli, Timothy J. Lang Colorado State University, Fort Collins Steven W. Nesbitt University of Illinois at Urbana-Champaign Contact Info: Steven A. Rutledge, CSU Atmospheric Science, Ft Collins, CO 80523; (970) 491-8283, rutledge@atmos.colostate.edu This research is supported by NASA PMM Grant NNX07AD51G and NSF Grant ATM-0733396. Larry Carey contributed some of the LBA plots. 1. Introduction2. NAME (July-August 2004)3. TRMM-LBA (January-February 1999) > 1500 m 500-1500 m < 500 m Ocean/Gulf Mean a 232.215 242.532 258.158 261.074  a 16.95 23.53 33.41 38.31 Mean b 1.47 1.48 1.49 1.49  b 0.009 0.011 0.014 0.016 Mean Unc 0.250 0.206 0.154 0.083 R (mm/hr)  Unc R 0.138 0.153 0.143 0.094 Mean Cond 3.48 3.57 3.40 2.81 R (mm/hr)  Cond R 1.28 1.67 2.06 2.43 Mean R Freq 0.070 0.055 0.042 0.026  R Freq 0.027 0.031 0.030 0.021 S-Pol Near-Sfc D 0 via D 0 = 1.529*(Z DR ) 0.467 S-Pol Near-Sfc Z DR, D 0, and Z H S-Pol Near-Sfc R*, D 0, and Z H S-Pol Liquid & Ice Water Mass* S-Pol a in Z=aR 1.5 ** TRMM PR Statistics July-August 1998-2007 TRMM PR (JA 98-07) Reflectivity CFAD TRMM PR (JA 98-07) a in Z=aR b N1 N2 N3N4 N5 N6 N7 N8 In convection over the water, S-Pol shows smaller D 0 s (N1), particularly at higher reflectivities (N2) and rain rates (N3). This is associated with less ice mass aloft (N4). However, liquid water mass is large, suggesting the importance of warm rain instead of ice processes over the Gulf. Over land, the lowest elevations have the largest values of D 0 and ice mass aloft, and these values tend to decrease with increasing elevation. This is consistent with upscale growth of convection toward lower elevations (Lang et al. 2007). The net result is increasing a in Z=aR 1.5 from water to high elevations. However, this is not observed in the TRMM data (N6, N7), which shows an opposite trend. TRMM does support the inference of more vertically intense echoes over the low-elevation land, however (N8). Note: TRMM not yet partitioned by conv/strat like S-Pol. The TRMM satellite has provided unprecedented data for over 10 years. TRMM precipitation products have advanced our understanding of tropical precipitation considerably. There are many studies underway that seek to refine the precipitation products from the TRMM Precipitation Radar. In this work we build on previously identified influences on tropical precipitation in Amazonia and in Mexico, the latter associated with the N. American Monsoon system. Precipitation in Amazonia is strongly influenced by pronounced reversals in the low-level flow regime (easterly and westerly regimes, or continental-like vs. maritime-like) (I1, I2). In Mexico, precipitation characteristics vary markedly with terrain (I3), ranging from frequent showery rain over the high terrain of the Sierra Madre Occidental to more persistent, heavier rain over the coastal plains (I4). Even a broader contrast exists between land based convection and convection over the adjacent Gulf of California. We use polarimetric radar data from two field projects, TRMM-LBA and NAME (North American Monsoon Experiment) to characterize the physical nature of precipitation in these regions. We contrast these structures to statistics from the PR. It will be demonstrated that using regime-specific Z- R estimators could lead to improved rainfall estimates derived from the PR. TRMM-LBA Precipitation variability as a function of meteorological regime NAME Precipitation variability as a function of terrain I1. Easterly and westerly regimes in TRMM-LBA showing higher lightning flash rates in the east regime compared to the west regime. Mean CAPE is higher in the East regime compared to the West regime. I2. Diurnal cycle of rainfall for the east and west regimes during TRMM-LBA. I3. Terrain map for the NAME domain. Adapted from Lang et al. (2007). I4. Diurnal cycle of rain frequency and median rain rate for the NAME domain. Results are plotted as a function of elevation band and over water. Adapted from Rowe et al. (2008). * Methodology described in Cifelli et al. (2002) ** Methodology described in Bringi et al. (2004) 1.111.08Mean b (conv) 426531Mean a (conv) 2.85.6Mean Cond. R (all -mm/hr) WestEast 444485Mean a (all) 1.08 Mean b S-Pol Z-R Statistics via Pol-tuning** L7 S-Pol Near-Sfc D 0 via D 0 = 1.529*(Z DR ) 0.467 L1 S-Pol Near-Sfc Z DR, D 0, and Z H L2 S-Pol Near-Sfc R*, D 0 and Z H L3 L4 S-Pol Liquid Water Mass* L5 S-Pol Ice Water Mass* East regime precipitation is characterized by larger D 0 compared to the west regime (L1), especially at moderate reflectivities (L2). Above ~55 mm/hr, D 0 in both regimes is nearly constant, suggesting that the DSD approaches equilibrium (L3). East regime precipitation also contains larger liquid and ice water mass compared to the west regime (L4 and L5), consistent with the higher occurrence of large updrafts and mixed phase precipitation in the east regime (L6). The larger drops observed in the east regime are manifested in a higher “a” coefficient of the Z=aR b relation in convective precipitation. This indicates that different Z-Rs are required to accurately estimate the rainfall in each regime. Although previous studies (Petersen et al. (2002) have shown that TRMM can distinguish differences in east and west regime vertical structure (L8), future work is needed to determine whether TRMM is able to capture the regime-dependent variability in DSD characteristics observed by S-Pol. S-Pol Z H cumulative frequency distributions and mean profiles Height (km) East West L6 TRMM PR time series (Dec. 1998-Feb. 1999) of the cumulative frequency distribution of 30 dBZ echo top height in the LBA region (from Petersen et al. 2002). L8