Aircraft Observed Precipitation Characteristics during the DYNAMO Field Project

One of the NOAA P-3 instrumented aircraft was deployed during the DYNAMO (Dynamics of the Madden-Julian Oscillation) field experiment in November-December 2011 in the Indian Ocean. This platform offers a unique perspective of precipitating convective systems, recording data from a tail-mounted X-band, Doppler radar and in-situ cloud and precipitation laser-shadowgraph particle probes. The radar is a vertically scanning, dual plate radar system using a fore-aft alternating scanning technique. The system acquires a 360° scan approximately every 6 seconds (~12 s for a fore-aft pair). Due to the mobile nature of this platform, this translates into a spatial resolution of about 1.2-1.5 km. This allows an unprecedented view of precipitating systems during this project, revealing cellular life cycle at a finer temporal and spatial scale than that available with ground- and ship-based systems. During the DYNAMO project a number of radars were deployed in a quadrilateral configuration, with a primary objective being to study the cloud populations present in the climatological Madden-Julian Oscillation initiation region. Analyses of cloud populations employ the traditional convective and stratiform archetypes; using a chosen standardized methodology (e.g. horizontal textural algorithm on gridded data or new radar coordinate methodology). While this presentation does not look to develop these techniques explicitly, it is important to be aware of the fine-scale structure of the convective system population that may not be discernable via surface-based weather radar systems. Aircraft data was obtained primarily in stratiform precipitation with occasional penetrations of convective lines, typically near cloud base. Subjective classification was performed using time series of native radar data. Precipitation particle imaging probe data (PMS 2D-P) was also parsed into convective and stratiform populations using multiple techniques (e.g. rain rates magnitude and variability, and log10Nw-D0 scatter plots) to compare with subjective classification. These results compared favorably, however a number of subjectively identified stratiform points incorrectly fell into the convective type. Further analysis of radar data revealed that stratiform echo often exhibited reflectivity values (~40 dBZ) on par with convective echo, particularly near the melting level. Reflectivity characteristics were not as well defined in this maritime region, with many instances of growing or decay convective cells located under a brightband feature. These results suggest rapid evolution of precipitation processes and microphysical structure that could easily be missed with traditional convective-stratiform partitioning techniques with the potential to cause problems in numerical simulations.