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A Rare Cloud Formation In Australia.

When residents of Wonthaggi in south-eastern Australia saw a huge footprint in the sky with a rainbow across it, rumors started flying about aliens and paranormal activities. People took to social media websites like Twitter to share their pictures.

However, there is a perfectly logical explanation. These formations are aptly named hole-punch clouds because it looks like someone punched a hole through the clouds.

So, what is the secret behind these holey clouds?

First, A Look At Precipitation

We all know about the cycle of water. Water evaporates and becomes water vapor when the air is warm. As the warm air rises in the sky, it cools (condensation) and form tiny droplets of water. When enough of these droplets collect together in the sky, clouds form. If the clouds are big enough and have enough water droplets, the droplets bang together and form even bigger drops.

For it to rain, temperatures inside the cloud need to be sub-zero, or below freezing point of water. When these super-cooled water droplets in the clouds meet specks of dust, salt or sand, they form small ice crystals. When these crystals become too heavy to stay afloat, they fall as rain because of gravity. This is known as precipitation which we see and feel as rain.

Did you know that millions of cloud droplets are required to produce a single raindrop!

How Hole-punch Clouds Form?

When temperatures fall in a small part of the cloud, it causes localized rain or snowstorm. This creates a hole in the cloud. The spectacular rainbow in the hole was formed in Australia, because sunlight streaming through, was diffracted by tiny water crystals suspended in the air.

Did you know that when airplanes take off or land, they can also cause hole-punch clouds to form? Under normal conditions, clouds at temperatures between 0 and minus 40 degrees Celsius contain suspended, super-cooled droplets of liquid water. An airplane, powered by jet engines or propellers, "seeds" clouds like these by expanding and cooling the air that flows under its wings or through its propellers. This cooling creates ice, which attracts the super-cooled water droplets. Together, they grow heavier and create snow or rain.

Sometimes, clouds can be intentionally seeded to alter weather. To cause rains, clouds are sprayed with silver iodide which causes water droplets to freeze. It is an expensive process that is done in parts of China. However, this practice is criticized because we are tampering with nature and there is concern about the effects of silver iodide.

Here is an explanation for another such cloud formation a few years back.

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Title Annotation:Our Earth
Geographic Code:8AUST
Date:Nov 7, 2014
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