Every snowflake is unique, but did you know that raindrops come in different sizes? The Global Precipitation Measurement (GPM) satellite mission, a joint venture between NASA and the Japan Aerospace Exploration Agency, allowed scientists to take three-dimensional images of raindrops and snowflakes as they fall and even beforehand, measuring for the first time the sizes and locations of individual drops within storms.
“The drop size distribution 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 Joe Munchak, a research meteorologist at NASA’s Goddard Space Flight Center.
“We’ve never been able to see how water droplet sizes vary globally until now.” GPM’s predecessor, the Tropical Rainfall Measuring Mission, used radar and microwave imaging to measure the amount of precipitation in layers of storm clouds in the tropics. The experiment was successful but less comprehensive than GPM’s, which observes both rain and snowfall worldwide with significantly more detail via a single main satellite observatory and a network of partner satellites.
Observing individual raindrops will allow scientists to better understand how storms work and the “precipitation microphysics” behind them. There are a variety of sizes of drops in each cloud (which later fall as rain or snow): clouds with ice in them produce larger drops, and drops from the cloud’s edge are smaller than those from the middle. As raindrops fall through dry air, water evaporates. Smaller drops evaporate more quickly than larger ones, making the air around them cooler and damper. This can cause strong, cold winds close to
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