Please note that thiswas the reason for studying the selected drop sizes.
For some applications (e.g. raindrop shape studies related to radar rainfall
estimations), however, equilibrium shaped drops that fall at nonterminal
velocities (i.e. Zone II) would be sufficient. In such cases, rain
towers of approximately 6 m are adequate for studying the entire raindrop
size spectrum.
As our experimental observations for Zone II indicate, drops can attain
equilibrium shapes before achieving terminal velocities although
the velocity and pressure fields are not fully developed. There may be
different plausible explanations for this observation. One explanation
is that the changes in the velocity and pressure fields may have insignificant
effect on the drop shape during this acceleration phase. Another
explanation is that the hydrodynamic and the aerodynamic forces
may vary in such a way that the shape remains almost constant. An
accurate explanation for this observation requires a comprehensive
investigation, which is beyond the scope of this study.