Twenty Questions and Answers

1. What is a cloud?
   A cloud is a suspension of water droplets, ice crystals or both in the atmosphere. Clouds are made of tiny water droplets or ice crystals - often both water and ice are present together when temperatures are between freezing (32 degrees Fahrenheit and -32.8 degrees Fahrenheit (-36 degrees Celsius). If you have ever walked in fog you have walked in a cloud - a cloud that forms at ground level.

2. How big are cloud droplets?
   Cloud droplets are very small, about 10 to 20 microns or about .0004 to .0008 inches in diameter. This is at least 5 times smaller than the thickness of an average human hair. The droplets are so small they float in the air. In a thunderstorm it takes 30 minutes for cloud droplets to grow into raindrops - which are 100 times bigger than droplets.

3. What is super-cooled water?
   Water below 32 degrees F is called supercooled. This condition is common in clouds where water and ice often exist together when temperatures are below freezing. At -32.8 degrees Fahrenheit (-36 degrees Celsius) the droplets have been converted to all ice crystals. Very high ice crystal clouds are called cirrus. Cirrus are usually wispy clouds of ice crystals although it is believed cirrocumulus clouds may contain water droplets.

4. How many droplets or ice crystals are in a cloud?

5. How do clouds form?
   Water is always present in the atmosphere in the form of invisible water vapor. When air cools and its relative humidity rises to near 100% the water vapor condenses into tiny water droplets or ice crystals.

   The vapor condenses on to tiny particles called nuclei. The nuclei may be smoke particles from fires, volcanic eruptions, or human activity; also dust, wind blown soil, or ocean spray. Nuclei may be flat and as small as 1 millionth of an inch in diameter. Without the nuclei it would be much more difficult for rain or snow to fall.

6. What are the basic cloud forms?
   Clouds may be flat or layered, puffy, wispy or hair-like, or precipitating. Clouds that are mostly flat are called stratus. Clouds that are puffy are cumulus, clouds that are high and wispy are called cirrus. Precipitating clouds are called nimbus.

7. What are the cloud layers?
   There are three cloud layers; low, middle, and high. Some clouds are categorize as clouds with great vertical extent. They rise through two or more layers. Cumulonimbus (thunderstorm) is a cloud of great vertical extent. It is classified as a low cloud if its base is in the low layer or a middle cloud if its base is in the middle level of the atmosphere.

8. What are the principle cloud types?
   There are ten principle cloud types, based on their form and height.
   High clouds: cirrus, cirrocumulus, and cirrostratus.
   Middle clouds: altocumulus and altostratus.
   Low clouds: cumulus, stratus, stratocumulus, nimbus, cumulonimbus
   Notice that the basic forms are cumulus (puffy) and stratus (layer or flat) and nimbus.

9. How high are clouds?
   Cloud tops are lower in polar regions and highest in the tropics.

   Cloud Tops:
   Polar regions: 25,000 feet
   Temperate regions: 45,000 feet
   Tropics: 60,000 feet
   
   Cloud Bases
   High clouds: Above 16,500 feet (5,000 meters)
   Middle clouds: Between 6,500 and 20,000 feet (2,000 meters to 6,000 meters)
   Low clouds: Below 6,500 feet (2,000 meters)

   Cloud bases are generally lower in humid climates and higher in dry climates. This means cloud bases are lowest in humid tropical climates and highest in desert areas. Of course there are always exceptions based on local weather conditions.

10. What are the different forms of water?
    Water can exist in three forms on Earth: a solid (ice), liquid (water), or a gas (water vapor). Clouds (liquid or ice) shade us from the Sun but also slows the loss of heat to space. Whenever water changes from vapor to liquid or vapor to ice, or changes from water to vapor or or ice to vapor, or from liquid to ice or ice to liquid, heat is transferred. The transfer of heat is very important for weather and climate.

    11. What happens when water changes its form?

    When water evaporates it stores the heat used for evaporation. It is called latent heat because the heat moves with the water vapor without changing the air temperature. Latent heat can move for thousands of miles before being released into the air when the water vapor condenses to form clouds and precipitation.

    This is a very efficient way for heat to move from one place to another on Earth. Remember: evaporation captures heat and condensation releases heat. Movement of latent heat plays an important role in the formation of clouds and the Earth’s heat budget.

    12. How much does a cloud weigh?

    We won’t be able to put a cloud on a scale to weigh it but we can estimate the weight by doing a little math. Let’s imagine a cloud that is 1 kilometer by 1 kilometer by 1 kilometer (about 6 tenths by 6 tenths by 6 tenths of a mile). The cloud would look like a cube with equal sides. Researchers have estimated that a cumulus cloud of that size would weigh 500,000 kilograms or 1.1 million lbs which is about 551 tons! A more complete explanation can be found here:

    https://www.sciencealert.com/this-is-how-much-a-cloud-weighs

    13. Why does a cloud float?
    A cloud is less dense than the surrounding dry air. That is because the density of water vapor is less than the density of dry air and the water vapor displaces some of the dry air. If there is enough water vapor some of the vapor condenses into water droplets. A cloud is made of water vapor and water droplets mixed with dry air. That volume of air is lighter than just dry air because the water vapor weighs less than dry air. So a cloud is a mixture of water vapor and dry air floating in the atmosphere with tiny water droplets has heavier dry air (denser air) below the cloud and lighter (less dense) air is above it. The smallest droplets can float in the air. If there is sufficient rising motion with the cloud, the droplets can increase in size until they are too heavy to float. At that point the droplets fall faster than the upward motion can carry the droplets higher so precipitation (rain) begins to fall.

    14. UNDER CONSTRUCTION