JP3J.6 RADAR OBSERVATIONS DURING NAME 2004 PART II: PRELIMINARY RESULTS Timothy J. Lang*, Rob Cifelli, David Lerach, Lee Nelson, Stephen W. Nesbitt, Gustavo Pereira, and Steven A. Rutledge Colorado State University, Fort Collins, Colorado David Ahijevych and Rit Carbone National Center for Atmospheric Research, Boulder, Colorado 1. INTRODUCTION Two-dimensional radar-based regional data products from NAME 2004, detailed in Part I of this study (Lang et al. 2005) - as well as case studies using 3-D volumes from the NCAR S-Pol radar - are being used to understand the climatology of convection in the heart of the North American monsoon in northwestern Mexico and the Gulf of California. In particular, the relative importance of large-scale forcing and the diurnal cycle in organizing and modulating convection is being studied. Ahijevych et al. (2005) note the typical diurnal behavior of convection along the sea breeze front over the coast, as well as over the complex terrain of the Sierra Madre Occidental (SMO), which peaks in the late afternoon as expected (“undisturbed” regime). In addition, they note very active days (“disturbed” regime) wherein the typical diurnal convection evolves into more organized systems and propagates from the SMO, to the coastal plain where it merges with any existing sea breeze convection, and finally out to sea over the Gulf of California. In this work, we present preliminary results linking the evolution and structure of precipitation systems to the effects of large- scale forcing and the diurnal cycle. In addition, we will show examples from in- progress case studies of the 3-D microphysical evolution of NAME storms, as well as intercomparisons between S-Pol and a nearby multi-frequency profiler network. 2. DIURNAL CYCLE ANALYSIS Precipitation features were identified within the Version 1 NAME regional radar composites (0.02° grid spacing) by identifying regions with contiguous pixels (including adjacent corner pixels) of radar reflectivity ≥ 15 dBZ. Nesbitt et al. (2000) used a similar approach identifying precipitation features within the TRMM precipitation radar swath. For this study, features were identified within each time the radar composites were available, and their time of occurrence, location, area, rainfall volume, and number of points greater than 40 dBZ were calculated and stored. In addition, an ellipse-fitting technique (Nesbitt et al. 2005) is employed on each feature whereby the major and minor axis lengths are calculated from the Eigenvalues of the mass distribution tensor of the raining points within each feature. Twice the major axis of the calculated ellipse is recorded as the feature’s maximum dimension (FMD). During the NAME EOP, 199609 features were identified within the composites. Future work will encompass tracking the features in time and space such that storms may be examined in the context of their individual life cycles. Figure 1 shows diurnal cycle results from the precipitation feature analysis. A proxy for convective fraction (ratio of 40 dBZ to 10 dBZ; Fig. 1a) suggests that convective fraction is highest in the late afternoon (~1700 LT), in accordance with diurnal heating over the SMO. The amplitude on this peak is very large compared to the rest of the cycle. The mean feature maximum dimension (Fig. 1b) shows somewhat different behavior, with the maximum coming later, at 1900 LT, and a small plateau in the early to mid-morning hours. The importance of large features or mesoscale convective systems (MCSs; *Corresponding Author Address: Timothy J. Lang, Dept. of Atmospheric Science, Colorado State Univ., Ft. Collins, CO 80523; e-mail: tlang@atmos.colostate.edu