July 24

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Frozen clouds in the freezer and in the sky

By Juman Hijab

July 24, 2021

clouds, white color

Ice cube "clouds"need frozen water 

And quick freezing temperatures

Clouds in ice cubes are due to disorganized air bubbles that reflect a lot of white color back to us. 

The ice cube shown below on the left has a white rod in it, with surrounding clarity. It was probably produced by having even cooling and very cold temperatures symmetrically around the cube. This gives the water the ability to freeze quickly entrapping air bubbles in a rod formation in the center of the cube. 

It is possible to create clear ice cubes commercially. At home,  the best techniques rely on slower freezing, and a means of having the top of the cube freeze last. This allows the slowly freezing water to push the air bubbles to the top before they get embedded in the frozen water. 

ice cube with white rod

Ice cube with white rod

Stack of clear ice cubes

White clouds in the sky need frozen water vapor, an updraft, and a change in pressure

A major difference is how the air bubbles are trapped

  • A similarity between the clouds in ice cubes and the white clouds in the sky is that the whiteness is due to disorganized air bubbles.
  • A difference between the two is that:
    • The ice cube "clouds"  are due to air bubbles entrapped in freezing liquid water;
    • In white clouds in the Troposphere, the air bubbles are entrapped in freezing water vapor.

In addition, there are 3 more differences that are important to be aware of. Without those 3 elements, clouds would look like gray fog or steam. 

Tea kettle boiling water

Tea kettle boiling water

fog over the mountainside

Fog over the mountainside

Boiling water from Geyser

Boiling water and steam from Geyser

1. Adding air to cooling water vapor

First, the element needed to create  all clouds and fog is water vapor. Cooling water vapor is necessary - but not sufficient - to create white clouds. 


For example, cooling water vapor after a hot shower or  from a steam kettle does not look as white as a cumulus cloud. To look white, one needs to add quite a bit of air.


Here's how it works: 


Cooling water vapor will cause condensation of the vapor into droplets as well as create a webbing of interconnected water vapor molecules that holds everything in place. 


This creates the fogginess of cooling water vapor, just like when you blow out your breath on a cold day. This is the first step. 


However, when you add a lot of air into the mix, you increase the whiteness. Look at the difference between the fog developing over the mountainside and the steam spewing out from a Geyser. The latter has a lot of air mixed in increasing the whiteness of the "cloud". 


Cumulus clouds

Whipped egg whites

Beaten egg whites

White bubbles beer

Head of beer pint

Soapy foam on man's hand

Soapy foam

2. Strong water vapor connections

Second, a strong netting is needed to entrap the air pockets so that cumulus clouds look pure white. The cumulus clouds shown on the left are proud, tall, well-defined, and pure white (except at their flat-bottomed surfaces).


When the netting is weak, the clouds can look ragged and fuzzy, like fog or steam. The thing is that if clouds don't have a sturdy web holding all the air molecules, water droplets, and the churning air drafts within the cloud, they would look pretty ragged, like the steam coming out of the Geyser above.    


Other objects that create a strong well-defined white presence have a strong net that holds the air/gas pockets in place. For example, egg whites, beer head, soap bubbles, and sea foam create white structures because the sturdy netting holds the pockets of air in place in a disorganized jumble. 


In the same way, clouds need a strong netting to hold a lot of air pockets in place. How else would they produce a towering cumulonimbus?


The strong netting comes from very strong hydrogen bonds. When water vapor molecules come together in the cold Troposphere they join hands into ice crystals. The colder the molecules, the stronger the hydrogen bonds. 


In reality, the ice crystals in the cloud are entrapping air pockets Just like snow does on the ground.

Cumulonimbus

Cumulonimbus

San Francisco Fog

San Francisco fog

Huge soap bubble

Soap bubble with stormy sky

Giant soap bubble

Giant Soap bubble

3. An updraft to moves the cloud  from high to low pressures

Having cold temperatures really helps; but the defining feature of cumulus clouds - particularly the cumulonimbus - is how white they are as they grow in height.  Doesn't the cumulonimbus on the left look as stiff as beaten egg whites?

The third element necessary to produce really white clouds (or white fog as shown in the San Francisco bay area) is the change in pressure felt by the updraft of air.


When there is an updraft pushing the air molecules and water vapor higher in altitude, the cloud mass experiences the lower pressures of higher altitudes. Under lower pressures there is expansion of the air. This expansion leads to cooling. 

The cloud mass experiences stretching of the water vapor crystal netting followed by cooling followed by re-freezing. This is not unlike blowing a soap bubble.  When the soap bubble connections are strong, we can continue to blow air into the bubble breaking and reforming the water/phospholipid layers. The soap bubble lining that holds the entrapped air in place.


Sometimes humongous soap bubbles can be produced by adding corn syrup to the soapy mixture.

Keep in mind that the netting that holds air bubbles in place - in soap, beer malt, or egg whites - contains a layer of water. When one incorporates a sugary molecular substance into that water layer, everything becomes many times more cohesive.

Similarly, as the water vapor net is expanded and then forced into lower pressure altitudes, it breaks down and then reforms. Additional water vapor molecules are added as the supercooled liquid water in the higher reaches of the cloud sublimate in the lower pressure Troposphere.

Moist updrafts allows ongoing replenishment of the water vapor netting as the cloud expands higher. The net result is that the tops of towering clouds are smooth and pure white. 


How white is white?

The whiter the color of the object means that there is a higher percentage of white light that is reflected back. The higher the percentage, the starker the whiteness.  


In summary; an updraft of air into a cloud does several things that help a cloud become white:

  • It raises the warm and moist air to altitudes that are much colder
  • It allows water vapor to freeze into ice crystals; this creates a web of frozen water vapor is produced with strong, cold hydrogen bonds
  • It supplies air to the cloud
  • It creates a high--> low pressure situation that forces expansion of the cloud mass; this leads to further cooling of the air, sublimation of water droplest/ice crystals back into vapor, refreezing the vapor with even stronger and colder hydrogen bonds.

Thus, an updraft of air is a strong part of the reason that we get cumulus (white fluffy clouds) versus stratus clouds (shapeless  dark grey clouds).

The stronger the netting, the smoother the curves of the cloud, just like the smoothness of the bubbles in a soapy mix. Weakening of the water vapor bonds in a cloud - say because there is no more updraft - will create the ragged edges of a dissipating cumulus cloud.


Picture credits:

  1. Michael Himbeault. Structure . Cracks showing up in the ice cube as it is warming up; air is seen bubbling up through the cracks to the top of the ice cube, Aug 21, 2010.
  2. Antoni BCN. ice_cube_1024, Nov 1, 2011.
  3. Hijab, J. Clear ice cubes formed at home, 2019.
  4. By Jorge Salcedo. Red kettle steaming hot isolated on black background, ID: 6234364.
  5. Nathalie Owen. Fog o'er the Mountainside, Dec 27, 2013.
  6. Phillip Stewart. Boiling water flowing into Firehole River , Sep 15, 2010.
  7. Images by John 'K'. "Flat bottomed clouds". Flickr photo-sharing, taken on March 4, 2009.
  8. Scott Mindeaux. whipped_egg_whites. Flickr photo-sharing. Taken July 6, 2005.
  9. Martin Garrido. Beer. Flickr - photosharing. Taken on Dec 27, 2011.
  10. By jocic. Soapy foam on man's hand, ID: 160713749.
  11. Bernard DUPONT. Cumulonimbus Cloud, Somewhere above, Nov 14, 2015. 
  12. Chris Ballance. Golden Gate - Evening Fog rolling in, Jan 10, 2014.
  13. kismihok. Bubble: Giant soap bubble and the sky before storm. Flickr photo-sharing. Taken July 17, 2012.
  14. elPadawan. Giant Soap Bubble: Giant soap bubble outside the New Yorker shop, Můstek subway station, Prague. July 12, 2012.

Juman Hijab

About the author

Juman is a retired physician after having been in clinical practice for more than four decades. Her lifelong interest has been in the chemistry of life.

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