Exploring the Possible Physical Origins of Raindrops falling at Non-Terminal Fallspeeds

Abstract:

Raindrops with fall speeds deviating from their expected terminal velocity have been observed in many precipitation studies. Not all measurements show clear evidence for the existence and ubiquity of non-terminal raindrops; consequently, some have dismissed the observed non-terminal drops as instrumental artifacts.

Here, we interrogate this data record in detail to determine if the non-terminal drop detections are real and -- if so -- to understand the possible physical origin of the non-terminal drops. Using data from several years of 2DVD observations, we show that non-terminal drops are omnipresent in the data record. We find that the immediate environment around super-terminal and sub-terminal drop detections is measurably different. Additionally, the data record reveals differing relationships between rain rate and super/sub-terminal drop abundances.