Tropical rainfall associated with convective and stratiform clouds: Intercomparison of disdrometer and profiler measurements

The motivation for this research is to move in the direction of improved al gorithms for the remote sensing of rainfall, which are crucial for meso- an d large-scale circulation studies and climate applications through better d eterminations of precipitation type and latent heating profiles. Toward thi s end a comparison between two independent techniques, designed to classify precipitation type from 1) a disdrometer and 2) a 915-MHz wind profiler. i s presented, based on simultaneous measurements collected at the same site during the Intensive Observing Period of the Tropical Ocean Global Atmosphe re Coupled Ocean-Atmosphere Response Experiment. Disdrometer-derived quanti ties such as differences in drop size distribution parameters, particularly the intercept parameter N-0 and rainfall rate, were used to classify rainf all as stratiform or convective. At the same lime. profiler-derived quantit ies, namely, Doppler velocity, equivalent reflectivity, and spectral width, from Doppler spectra were used to classify precipitation type in four cate gories: shallow convective, deep convective, mixed convective-stratiform. a nd stratiform, Overall agreement between the two algorithms is Found to be reasonable, Giv en the disdrometer stratiform classification, the mean profile of reflectiv ity shows a distinct bright band and associated large vertical gradient in Doppler velocity, both indicators of stratiform rain. I;or the disdrometer convective classification the mean profile of reflectivity lacks a bright b and, while the vertical gradient in Doppler velocity below the melting leve l is opposite to the stratiform case. Given the profiler classifications, i n the order shallow-deep-mixed-stratiform, the composite raindrop spectra f or a rainfall rate of 5 mm h(-1) show an increase in D-o, the median volume diameter, consistent with the dominant microphysical processes responsible for drop formation. Nevertheless, the intercomparison does reveal some lim itations in the classification methodology utilizing the disdrometer or pro filer algorithms in isolation. In particular, 1) the disdrometer stratiform classification includes individual cases in which the vertical profiles ap pear convective, but these usually occur at times when the disdrometer clas sification is highly variable; 2) the profiler classification scheme also a ppears to classify precipitation too frequently as stratiform by including cases that have small vertical Doppler velocity gradients at the melting le vel but no bright band; and 3) the profiler classification scheme includes a category of mixed (stratiform-convective) precipitation that has some fea tures in common with deep convection (e.g., enhanced spectral width above t he melting level) but other features in common with stratiform precipitatio n (e.g., well-developed melting layer signature). Comparison of the profile r-derived vertical structure with disdrometer-determined rain rater reveals that almost all cases of rain rates greater than 10 mm h(-1) are convectiv e. For rain rates less than 5 mm h(-1) all four profiler-determined precipi tation classes are well represented.