Abstract
In order to quantitatively evaluate the collection efficiencies of raindrops captured by videosondes at altitudes of 2500m or less, the collection efficiencies were calculated by statistical method with disdrometer as the true value. The synchronized observation using videosondes, disdrometer, and polarimetric radar was conducted during Baiu season in Okinawa Islands. When the change of the raindrop particle size distribution due to differences in time, space and case is small, the influence of variation of collection efficiencies on the relationship between the number of samples captured by videosondes and the slope parameters of particle size distributions was evaluated through random number experiments.
The 50th percentile of collection efficiencies was approximately 0.2 when the raindrop diameter(D) was 0.5 to 2.4 mm. When D was 1.5 mm or more, the variation of the collection efficiency was large. It was shown that the number of particles of more than 100 for videosonde observation is required to estimate slope parameter(Λ) of particle size distribution. It was found that there is a possibility of estimating the raindrop particle size distributions in the air from the videosonde if the optimum collection efficiencies for the large particle size class are clarified.
