The weather this past week has been quite cloudy and rainy. Some of my runs and bike rides left me very wet, yet rejuvenated from listening to the rush of the raindrops falling in the trees and the water running all around. I don’t mind running or biking in the rain because it literally helps wash away the dust and dirt of life and leaves the mind with a clean perspective.
While running and biking this week, I watched the clouds come and go in different colors, shapes, and densities. Some of the changes occurred quickly with the clouds swirling in the wind. Other changes were slower, like when the clouds dissipated over the course of the morning to reveal a clear blue sky for a few hours in the afternoon. In observing these changes, I started to wonder about clouds, how they form, and what dictates their movements.
Clouds form when water vapor in the atmosphere condenses and clings to microscopic particles. The warmer, less-dense patches of air rise while the cooler, denser air patches fall. As water vapor rises, it experiences less atmospheric pressure, which allows it to expand. The expansion causes energy loss resulting in cooling of the air.
As the air cools and comes in contact with microscopic particles, condensation forms. The collection of condensation creates the visible cloud. The amount of condensation plays a part in the clouds’ appearance and color.
Where Clouds Form
Clouds form at different levels of the atmosphere. These levels are named based upon altitude:
The level of the atmosphere where the cloud forms helps distinguish the cloud type.
According to the National Oceanic and Atmospheric Administration, there are ten basic types of clouds.
These types include:
- Cirrus, which appear white, delicate and hair-like. These clouds form from ice crystals high in the atmosphere. They may appear bright yellow or red before sunrise and after sunset. Their transparency allows the sun’s light to still be seen.
- Cirrostratus, which appear as a thin veil or sheet spread across the sky. These clouds are considered high clouds since they form high in the atmosphere.
- Cirrocumulus, which appear thin, white, and grainy or rippled. This type is less common and formed from ice crystals high in the atmosphere.
- Altostratus, which appear gray or bluish in color and in layers or sheets. This type of cloud is formed in the middle atmosphere and is thin enough to let the sun’s light shine through, but not in vast rays. Instead, the sun looks more like a round ball when viewed among this type of cloud.
- Altocumulus, which appear white or gray like ripples or rolls. This is the most common mid cloud and it often appears with other cloud types. If the edge of this type of cloud passes in front of the sun or the moon, a corona will appear.
- Nimbostratus, which appear thick, dark gray, and layered so as to block out the sun’s light. This mid level atmosphere cloud is often called a rain cloud because it contains enough moisture to totally saturate the atmosphere and cause precipitation.
- Cumulus, which appear thick and white with sharp edges. This low level atmosphere cloud may look like a dome, mound, or tower with parts that look like cauliflower. Parts of these clouds that catch the sun’s rays appear brilliant white, but the bases are darker gray. Appearing in the morning, these clouds grow, fade throughout the day, and dissolve by evening.
- Stratus, which appear gray, layered, and uniform in the lower levels of the atmosphere. This cloud is capable of producing drizzling rain, ice, or grainy snow. The sun’s outline may be seen through this type of cloud, depending upon how thick the layer is.
- Cumulonimbus, which appear as heavy, dense towers and may produce thunderstorms, hail, and tornadoes. The top of this low level atmosphere cloud is usually smooth and flattened, shaped like an anvil or plume.
- Stratocumulus, which appear as gray or white patches, sheets, or layers in the lower levels of the atmosphere. These clouds often have a dark honeycomb appearance and may look like round masses or rolls.
Other Cloud Types
There are other types of clouds that appear in special circumstance or conditions. These clouds include:
- Mammatus clouds, which are typically seen in severe weather, hanging down from cumulonimbus clouds
- Lenticular clouds, which form from wind patterns near mountains
- Fog, considered as a cloud on the ground formed from tiny water droplets in the air.
- Contrails, clouds seen trailing air planes that are formed when the jet engine exhaust mixes with the atmospheric conditions.
- Fractus clouds, formed when wind shears apart larger clouds. They often appear jagged and in irregular patterns.
- Green clouds, often seen during severe weather in the Great Plains region of the United States.
The following chart offers a nice summary of cloud types and the levels of the atmosphere where they form:
The water vapor droplets that form clouds move with the wind or air streams around them. The droplets condense, grow into clusters, become saturated, and then lose moisture in the form of condensation (rain, snow, or hail). The size of the water droplets dictates how fast they can move. Larger droplets have more mass and move slower than smaller droplets with less mass.
The makeup of molecules and particles within the atmosphere constantly changes, which is why clouds come and go as time passes. Watching all these changes may not be high on one’s priority list in life, however, I have found contemplating the clouds and events of a given day to be quite educational. There is always something to be learned, taught, or conveyed with time’s help and nature’s changes.
Resources and Related Links
Cloud Movement – http://www.scientificamerican.com/article/why-do-clouds-float-when/
Condensation – http://water.usgs.gov/edu/watercyclecondensation.html
How Clouds Form – http://www.livescience.com/44785-how-do-clouds-form.html
Special Cloud Types – http://www.weatherwizkids.com/weather-clouds.htm