What causes rain or snow? It’s all because of the water cycle! The Sun’s heat causes the water from the different parts of the Earth, like oceans, seas, lakes, rivers, even water from wet clothes you dry outside your house, to rise into the air and turn into water vapor.
Water vapors join together and form into clouds, and when they become too heavy to stay suspended in the clouds, they condense in the form of rain or snow. (click here for more details)
One moment you see the clouds and then they disappear. It is because evaporation and condensation is a continuous process in the atmosphere. However, most of the condensed water does not fall as precipitation because their fall speed is not large enough to overcome updrafts which support the clouds.
It’s not only water that causes precipitation to happen. The tiny droplets of water must condense on even smaller dust, salt, or smoke particles, which act as a nucleus. Additional water vapor causes water droplets to grow as the particles collide. And enough collisions are needed to produce a droplet with a fall speed that exceeds the cloud updraft speed to fall as precipitation. Do you know that millions of cloud droplets are required to create a single raindrop? Yes. Moreover, through the Bergeron-Findeisen process, ice crystals rapidly grow at the expense of the water vapor present in a cloud. This is a more efficient mechanism for producing precipitation-sized drops that fall as snow or melt and fall as rain. (click here for more details)
The shape of a raindrop and the different sizes
We are always fascinated at imagining things. Maybe even with what really is the shape of the raindrops and how big they are. From TV advertisers to illustrators of children’s books, we are always taught that raindrops look like a teardrop, but they bear scant resemblance to it. Alister Frasier explained that small raindrops (with less than 1mm radius) are spherical like a ball. As they collide and grow larger, they more likely to have a shape of a hamburger bun, and the bottom of the drop begins to be affected by the resistance of the air it is falling through. When they reach about 4.5mm, they rapidly become distorted and look more like a parachute with a tube of water around the base, and it is when they usually break up into smaller drops. (click here for more details)
How raindrops fall in various sizes
Because of the surface tension of water, raindrops start to form in a roughly spherical structure. This surface tension serves as the “skin” of a body of water that makes the molecules stick together due to the weak hydrogen bonds that occur between water molecules.
The surface tension is stronger on smaller raindrops than in larger drops because of the airflow around the drop. There is greater airflow on the bottom of the water drop than at the top due to small air circulation disturbances that create less air pressure. It is also the surface tension that maintains the drop’s spherical shape while the bottom becomes more flattened out.
Even as a raindrop is falling, it often collides with other raindrops and thus increasing its size. And once it becomes too large, it will eventually break apart in the atmosphere as smaller drops. (click here for more details)
When it rains, it pours
Everyone seems to be interested in extremes, including weather, “therefore, creating a database of professionally verified records is useful in that fact alone,” says Randall Cerveny from the World Meteorological Organization (WMO).
- Greatest rainfall in one minute.
On July 4, 1956, at Unionville, Maryland, 1.22 inches (31.2 millimeters) of rain fell in one minute. A record highest rainfall in just a minute.
- Greatest rainfall in 24 hours
Cyclone Denise in Foc-Foc, La Réunion, was the biggest rainfall that occurred in a day. It happened on an island in the southern Indian Ocean. Some 1.825 meters (71.8 inches) of rain fell over 24 hours, from January 7 to 8, 1966. (click here for more details)
How are raindrops measured?
A circular funnel with a 203mm (8inch) diameter is the standard instrument used to measure rainfall. The rain is collected into a graduated and calibrated cylinder that can record up to 25mm of precipitation.
But, a Tipping Bucket Rain Gauge (TBRG) in modern automatic weather stations is employed. It also has an aperture of 203mm. (click here for more details)
Every time it rains, you will remember how they are formed and how they exactly look. And you just smile that they don’t burst as one giant drop of water falling altogether, because if they do, the umbrellas that we have now, won’t work.