Different types of clouds explained

What kinds of atmospheric structure give us different types of clouds?

You can often put two of these words together to get a cloud name. You can have altocumulus for mid-level puffy clouds. See the three examples above. We can then identify more than just four cloud types.

What gives the different types of clouds their shapes? The properties of the air parcel containing the clouds.

Can you deduce all other relevant parameters for an air parcel from pressure, temperature and dew point? Yes. And from these we easily decide which curve on a thermodynamic graph to follow if this air moves up or down. Take a look at this sample.

The trace made by the air parcel goes up the moist adiabat, the curved line labelled "saturated adiabat" if saturated. If it is not saturated it follows the dry adiabat, the straight line going up to the left. When the air is moving downwards, follow the moist only if cloud droplets are present.

Let's be ideal here. Do not worry about air mixing, known as entrainment.

Then do the temperature comparisons described on this page. This will tell us if it is stable, unstable or neutral.

Stability classifications.

• Absolutely Stable - The external forces on a displaced packet of air try to return it to its original level. Regardless of moisture content. We often see no cloud, fog or stratus or high cirrus clouds under these conditions.
• Absolutely Unstable - The displaced parcel keeps going, faster and further. No matter how moist or dry it is. This theoretical concept is virtually nonexistent in reality but it sure would give different types of clouds if it were to actually occur. We would get strong cumuloform clouds. Big piles.
• Conditionally Unstable - Stability depends on whether it is dry or saturated. We also call this potential instability. This condition gives us most of our clouds.
• Neutral - This time the air's temperature remains the same as the surrounding air temp. Sometimes called equilibrium, it depends on water content as well. Regardless, we don't see much cloud under these circumstances either.

Two scientists got together in the 1960’s and devised the Pasquill-Gifford system of classifications. They defined stability subdivisions and assigned them capital letters A through F. The system and its concepts are still used in air quality modeling today.

Air quality is greatly affected by atmospheric stability. Why? Because stable air traps pollution and different types of clouds near the ground or even in elevated layers.

















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An interesting situation

Since moist air is less stable than dry air, it will convect, that is move upwards, more easily. It is this upward motion that leads to clouds. And moist air has the water supply needed for the production of different types of clouds, since they're made of water.

What about absolute instability?

Stability and cloud formation or suppression go hand-in hand. An experienced meteorologist can tell what the temperature and moisture structure is like above just by examining the clouds.

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