The Rain's Maintained Speed Strain Is Now Explained

A study in the journal Geophysical Research Letters finds that some raindrops are falling faster than they "should" be, which means meteorologists may be overestimating the total amount of rainfall. Steve Mirsky reports.

Could it be that our understanding of rain was all wet? A new study says that some drops of rain are falling faster than they should be. Which ultimately means that it may be raining less than we think.

It's been assumed that large raindrops fall faster than smaller ones. A big drop’s size and heft give it a faster terminal velocity. Because it overcomes air resistance better than a small drop. But now researchers have found small raindrops falling faster than some bigger drops, and faster than what their terminal velocity should be. The finding appears in the journal Geophysical Research Letters.

Researchers used sophisticated optical equipment to study about 64,000 individual raindrops, and found the expeditious outliers. Which came in clusters. These superfast droplets probably come from the breakup of fast-moving large drops. Standard techniques to measure rain assume that fast drops are larger, and therefore overestimate the total precipitation. The scientists note that a third of the economy is influenced by weather forecasting, so even a small improvement in our understanding of rain would be more than a drop in the bucket.

—Steve Mirsky