Statistical Characteristics of Multipeak Raindrop Size Distributions at the Surface and Aloft in Different Rain Regimes

Abstract

Two years (∼672 h) of lower-atmospheric wind profiler (LAWP) and 4 yr (∼733 h) of Joss–Waldvogel disdrometer measurements are utilized to study the multipeak (MP) occurrence statistics at the surface and aloft. For the first time, an attempt has been made to address several key questions regarding MPs: their occurrence statistics and their dependency on height, season, and type of precipitation. MPs are not exceptional; rather, they are observed at all altitudes, albeit with different occurrence percentages. The occurrence of MPs seems to be height dependent, and this dependency varies with the type of rain system. The occurrence percentage of bimodal echo (two peaks) is high above (below) the melting level (ML) in convection (in other types of rain). The percentage occurrence of bimodal echo in warm rain is similar to that in cold rain, but only below the ML. The spectrum with more than two peaks appears to be predominantly in convection, particularly above 4 km. The MP statistics on the surface DSD derived from disdrometer data also support the profiler statistics qualitatively (occurrence is more likely in convection); however, the magnitudes of the percentage of occurrence are different at the surface and aloft. The peaks in the raindrop size distribution (DSD) spectra exist predominantly in drop diameter ranges of 0.45–0.65 and 0.9–1.3 mm in all types of rain, consistent with earlier numerical and observational studies. The MP occurrence does not have seasonal dependence aloft, but shows some variation at the surface with a larger percentage of the occurrences in the southwest monsoon. However, peaks in the surface DSD exist at same diameters in both monsoon seasons.