School Delays across the Tennessee Valley

NASA study hopes to improve rainfall modeling

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Joe Wheeler Lodge (Image: Jay Anderson)

Some days are just rainy and you can pop open your umbrella to stay dry. Other days are drizzly and it seems impossible to keep yourself from getting damp.

As of now, we’re not exactly sure why sometimes we get rain and sometimes we get drizzle. A new NASA study could help us find the answer though.

Before this study the primary idea revolved around something called cloud condensation nuclei. Cloud condensation nuclei is simply whatever water vapor condenses onto to form a raindrop. This can be anything from ocean spray, to tiny particles of dirt, or aerosols.

The idea is that if you have more aerosols you have more water droplets that develop. The more water droplets that develop from one amount of water, the smaller the droplets will be. If the droplets are small enough, then we have drizzle.

The new study from NASA has brought up a new idea for consideration though. It was found that clouds over the ocean are more likely to produce drizzle, even though there are fewer aerosols over the ocean.

It was also found that the updrafts in clouds over the ocean are much weaker. An updraft is the upward moving air in clouds. So it could be that when updrafts are stronger, then raindrops must become heavier to fall.

We could use this information to create better weather models which would be able to resolve potential updraft strengths, and therefore helps us forecast drizzle.

So why does it matter if it’s rain or drizzle? Other than the fact that rain and drizzle can inconvenience us in different ways, it also matters for forecasters! Drizzle can have a bigger impact on weather measurements like temperature. When it rains it cools us down briefly, but drizzle can have a longer lasting effect on daytime temperatures. So, if what was supposed to be a rainy morning turns out to be a drizzly morning, it might be a cooler day ahead than expected too.

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