Understanding how different types of clouds result from air motions

What's happening in the air to make different types of clouds?  Could they affect you?

Clouds move across the sky in all kinds of shapes and sizes.  When you look up at the clouds, you may feel connected to nature.  Relax and unwind with it.

Cloud types with descriptions

Clouds are interesting because they are always changing and can have a magical or spiritual quality. They can make people feel a sense of awe and wonder, and have been symbols of spirituality for many cultures.  Clouds can be a great source of inspiration for artists.

They can create beautiful art by painting the ever-changing colors, shapes, and patterns of clouds, and they can use clouds to add atmosphere and emotion to their artwork. Clouds can also represent freedom and adventure.

Clouds help keep our climate balanced by reflecting sunlight and heat to keep us cool, as well as trapping heat to keep us warm. They also provide us with rain and snow, which helps us grow food and stay hydrated.  

Clouds can affect how much sunlight and pollution reach the Earth. This can change how plants grow and how much energy we can make from the sun.  Scientists study clouds to help them better understand how the Earth's climate and weather work. They look at how clouds form and interact with the atmosphere to help them make better predictions about the future.

How different are these clouds?

Cirrus clouds are high-level clouds while stratus clouds are long, flat, and horizontal.  Depending on their altitude, they can be classified as cirrus and alto for high and medium level, respectively.  A cloud formation is called a nimbus when it produces precipitation.  

Other cloud types are more specialized - they can only be found under certain atmospheric conditions or in a limited geographic area. The lenticular "lens-shaped" clouds shown in the montage above are an example. They are found near mountains.

Clouds that are puffy, pillowy, or piled high are the most interesting. When they produce rain, they are referred to as cumulus or cumulonimbus (producing thunderstorms); there is that "nimbus" again.

In order to get a more descriptive cloud name, meteorologists often combine two of these words. Alto-cumulus, for example, are puffy clouds at mid-levels. Take a look at the three examples above. By combining combinations like this, we can identify more than just four kinds of clouds.

How do clouds get their shapes?  The properties of the air surrounding the clouds, known as the "air parcel" containing the clouds.  There is quite a bit of science behind cloud formation.  

Cloud Science - Cloud formation in the atmosphere is a complex process driven by physics, temperature, and moisture. They form when warm, moist air rises and cools, causing the moisture to condense into tiny droplets or ice crystals. The process is called condensation, and it's influenced by a lot of things like temperature lapse rate (the rate at which temperature decreases with altitude), moisture in the air, and particles that act as condensation nuclei.

For meteorologists and atmospheric scientists, tephigrams and skew-T diagrams are great tools for analyzing and understanding the atmosphere.  Tephigrams are graphs that show the vertical temperature profile of the atmosphere in meteorology, thus they plot temperature against height in the atmosphere  Can you deduce all the other parameters for an air parcel from pressure, temperature, and dew point?   Yes.  Based on these, meteorologists can figure out which curve on the thermodynamic graph to follow.

Clouds form based on altitude, temperature, and moisture conditions in the atmosphere. Low-level clouds, like stratus and cumulus, form near the ground, while high-level clouds, like cirrus and alto, form higher up.  A precipitation cloud forms when moisture droplets or ice crystals are big enough to fall as rain, snow, or other types of precipitation.   In the lee (downwind side) of mountains, lenticular clouds form when the wind is forced over the terrain and creates a standing wave pattern.

Warning:  technical lingo ahead

Take a look at the drawing in this sample, right below the thunderstorm photo.  It shows a portion of a skew-T, log-P chart.  When the humidity of the air reaches 100%, the air parcel traces a curved line sloping upwards to the right called a moist adiabat if the humidity of that air has reached 100%, enough to produce cloud.  In the sample, it follows the line labelled "saturation adiabat".  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 curved line for moist air only if cloud droplets are present, telling us it’s a saturated parcel.

Let's look at an ideal situation. Don't worry about air mixing, also known as entrainment.

Then, carry out temperature comparisons described in detail on this page. Doing so will tell you if it is stable, unstable or neutral.  How so?

Stability classifications and the different types of clouds that result from them

There's stable and there's "stable".  Some atmospheric conditions are more stable than others. Stability can be divided into a few categories:

Absolutely Stable - The external forces on a displaced packet of air (one that's moved upwards or downwards) automatically try to bring it back to its original level.  No matter how much moisture is in it.   These conditions usually bring clear skies, fog, stratus or high cirrus clouds.  More on this further below.

Absolutely Unstable  - The displaced parcel keeps going faster and faster.  No matter how wet or dry it is.  This structural concept is theoretical and remains virtually nonexistent in reality, with short-lived exceptions occurring during conditions of external forcing (such as within storms).  It sure would give different types of clouds if it were to actually occur and persist. We would get strong cumuliform clouds. Big deep piles.

Conditionally Unstable - In this section we look at stability that varies with whether the air is dry or saturated.  This is also called potential instability.  Most of our clouds form under this condition. 

Convective Instability of the Second Kind (CISK) – CISK happens when the rate of temperature increase with height (the environmental lapse rate) is less than the dry adiabatic rate.  In this situation, latent heat (stored in vapour) within a storm core comes off as sensible heat (measurable with a thermometer) as soon as any condensation occurs.  Heat and moisture build up lower down in the atmosphere near the earth's surface, which can lead to deep convective clouds and thunderstorms. 

This heat provides just enough power for storm development.  It gives rise (pun intended) to convection which would not otherwise occur.  There's often intense precipitation, strong winds, and lightning with CISK.  Surface heating, moisture, atmospheric stability, and wind patterns can all influence CISK, which may have contributed to this storm.

Cumulonimbus development from above

Neutral - This time, the air parcel stays the same temperature as the surrounding air.  We don't see much cloud under these circumstances either, though its stability depends on water content, too.

What else are stability calculations used for?  Pasquill-Gifford is a classification system devised by two scientists in the 1960s.  Subdivisions of stability are assigned capital letters A through F, denoting varying amounts of lapse (and thus stability).  They're 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.

Here's an interesting situation...turbulent air gets well mixed, go figure!   In the mixed parcel, the environmental lapse rate becomes neutral.  If unsaturated air moved up through, it wouldn't feel any forces from ambient air pushing it upwards or downwards, so we'd say it's neither stable nor unstable.

Since moist air is less stable than dry air, it will convect (move upwards) more easily.  Clouds form because of this upward motion.  Clouds are made of water droplets, so moist air has the water supply needed to produce them.

What about absolute instability?

How long do you think it'll last?   Not long at all.  There has to be a steady source of heat from below, like cold air moving over a warm lake, a forest fire or strong sunshine quickly warming the ground underneath.

We'll get auto-convection and even more different types of clouds with super-adiabatic lapses.  Then we get turbulence, followed by a neutral lapse rate.

Cloud formation and suppression go hand-in hand.  Just by looking at the clouds, a meteorologist can tell what the temperature and moisture structure in the air is like.

Do you like what you see here?  If you have any comments, please let us know.

Cloud Types | How Many Do You Know?

Different air motions produce different types of clouds.  We see clouds formed by air moving up and down.

Do you have concerns about air pollution in your area??

Perhaps modelling air pollution will provide the answers to your question.

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Thank you to my research and writing assistants, ChatGPT and WordTune, as well as Wombo and others for the images.

GPT-4, OpenAI's large-scale language generation model (and others provided by Google and Meta), helped generate this text.  As soon as draft language is generated, the author reviews, edits, and revises it to their own liking and is responsible for the content.