Just like snowflakes, raindrops, especially their sizes, can vary, which can also significantly matter. A satellite snapshot shows that the sizes of rain can be a huge factor in understanding storms and forecasting weather.
Earth science teaches us that liquids from different bodies of water evaporate to create clouds and fall back to earth in a process called precipitation. By then, they come in the form of rain, sleet, hail and snowflakes. They may also appear with strong winds and storms that can be very damaging.
Storm clouds, on the other hand, can have raindrops of different sizes — some big and small - depending on whether they collide or break apart. For example, droplets tend to be bigger if they collide with one another since they can accumulate.
Knowing their ratio is important to understand how much precipitation goes back to Earth, but it used to be a challenge since the data needed were limited.
With Global Precipitation Measurement (GPM), a core satellite by Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA), researchers have a more reliable method of collecting information. Launched in 2014 into space, it contains instruments that measure rainfall and varying degrees of precipitation in different parts of the world.
Using 3D pictures captured by GPM, scientists can now ascertain more accurately the drop size distribution, which is "one of many factors that determines how big a storm will grow, how long it will last and how much rain it will ultimately produce," said NASA's research meteorologist Joe Munchak.
In particular, the sizes of the raindrops can influence the rate in which it evaporates after falling in dry air. If the raindrops are small, they tend to evaporate more quickly, cool the air faster, and fall to the ground more strongly that the winds can pick up speed and strength. However, the downward flow can slow down or even dissipate the storm since it can disrupt the storm-related air as it goes up.
If these data are missing, "we can have a big error in how much rain we know fell and that can have some big implications for knowing long term accumulations which can help with flash flood predictions," he added.
The GPM can therefore improve both weather forecasting models and disaster preparedness, and with visual cues like blue and green to indicate small raindrops ranging 0.5 to 3 millimeters, understanding the weather is easier.
