In Table 1, we summarize our findings on shape and fall velocity
of free-falling water drops. Our experimental results reveal that terminal
velocity is the stringent criterion for free-fallingwater drops to
achieve both the equilibrium shape and the constant fall velocity, i.e.
Zone III conditions. For a given application that requires laboratory
rainfall simulations under Zone III conditions, rain towers of approximately
12 m would be sufficient to adequately simulate the entire
raindrop size spectrum. Though only three raindrop sizes were studied,
we can assume some overall conclusions for the entire raindrop
size spectrumbecauseWang and Pruppacher (1977) showed in their
theoretical calculations that drops ranging approximately from
2.5 mm to 5 mm in diameter requires the longest fall distances (drops
with approximately 3.6 mm diameter requiring the longest fall distance)
to achieve terminal velocity in the entire raindrop size spectrum.