How often have you been frustrated that a weather report was wrong? I know I am certainly guilty of this. Meteorology is a difficult and evolving science. We put a lot of stock into weather forecasts and then are often disappointed if they are not spot-on. Recent research of raindrop velocity might throw meteorology a curve ball. Michael Larson, an atmospheric physicist at the College of Charleston in South Carolina, recently published evidence that showed raindrops moving faster than their terminal velocity. What?? You're right, this shouldn't happen, but apparently, it does. Larson and his team measured the velocity of 23 million individual raindrops during their study. They found that 3 out of every 10 of them dropped faster than their terminal velocity. Terminal velocity is what occurs when the downward force of gravity and the upward force of friction on a falling object are equal, therefore canceling each other out.
This is not the first time this phenomena has been observed. In 2009 researchers found that smaller raindrops seemed to travel faster than their terminal velocity. The study published by Larson's team in Geophysical Research Letters on October 1st was further evidence this phenomena was occurring. It is still unclear to scientists why this is happening. The speedy drops are all categorized as "small", or those smaller than 0.5 millimeters (0.02 inch). It could be that these smaller drops have broken off of larger drops on their way down and it is affecting our measurement of their velocity. This is yet to be determined. We understand how to calculate the terminal velocity of the larger drops, but maybe we need to recalculate to determine the terminal velocity of the smaller ones. Some scientists are arguing that these smaller drops are "drizzle" rather than regular raindrops, therefore needing different calculations.
Regardless of the mysterious reason these raindrops are speeding faster than we thought, this discovery could affect meteorology. If we are using the standard equations for velocity of raindrops to predict the amount of rainfall, we could be throwing off the numbers that drive our weather models. This new evidence could cause a shift in how meteorologists predict the weather.
Science News Digital: "Raindrops break terminal velocity: Droplets lack clear explanation, could alter weather forecasts"
Little Shop of Physics: Why do raindrops sometimes land gently and sometimes land with a splat? (Hands-on Experiment)