Raindrop size distribution during different monsoon periods over Metro Manila, Philippines

Abstract

The raindrop size distribution (DSD) characteristics over Metro Manila are investigated using rainfall measurements from the Science Garden Disdrometer station (14.6°N, 121.04°E). The DSD observations are grouped according to the onset and termination dates of the Southwest Monsoon (SWM) and Northeast Monsoon (NEM) periods. Results show that small raindrops dominate the NEM rainfall while large raindrops are more observed during the pre-SWM and SWM periods. The high values of intercept (Log₁₀ N_w), slope (Λ), and shape (µ) parameters observed during the NEM period indicate the high concentration of small raindrops. The Z-R relations obtained during the NEM period are found to deviate from the pre-, post-, and SWM periods and has important implications in radar operations. These findings suggest that the seasonal variability of DSD should be taken into consideration in developing algorithms for further advancements in quantitative precipitation estimation (QPE) in weather radars and cloud parameterizations in numerical prediction models.