METEOROLOGY FOR EVERYONE                                                                          Prepared by: Dr. Ahmet KILIÇ

CLOUDS
   
CLOUD CLASSIFICATION

Clouds are usually the most obvious feature of the sky. They both reflect weather patterns and play a role in what the weather does. In addition to their obvious role as sources of precipitation, clouds also can affect the temperatures of the places below them. Clouds not only block incoming sunlight during the day, which cools the air, but they can also block outgoing radiation from the Earth, which can warm temperatures. Many unanswered questions about Earth's climate revolve around the roles of clouds.

How do clouds form? Clouds form when warm air rises and cools down enough for some of the water vapour in it to Condense into tiny water droplets or ice crystals. Billions of these make up a cloud. Water vapour  can also condense on to smoke or dust specks in the air.  

Measuring cloud cover. The number of clouds covering the sky is measured in oktas. The number of oktas indicates how much the sky is covered by clouds. Oktas are measured on a scale of 0 to 8 ( 8 oktas means that the sky is completely covered). For example, a weather forecaster may describe the sky as having four oktas of cloud, which means that half the sky is obscured by clouds.

HIGH LEVEL CLOUDS
MIDDLE LEVEL CLOUDS
LOW LEVEL CLOUDS
MULTI-LAYER CLOUDS
OROGRAPHİC CLOUDS
OTHER SPECIAL CLOUDS
 

CLOUD CLASSIFICATION

Clouds are generally classified based on characteristics, such as, altitude, appearance, or origin.  Altitude distinctions apply to those clouds that fit in various layers of the atmosphere as follows.

 

High level clouds, their bases above 6,000 meters.

Middle level clouds, their bases between 2,000 to 6,000 meters.

Low low clouds,   their bases below 2,000 meters.

Multi level clouds, vertically thick spanning multiple layers

Orographic clouds,  distinct clouds that form via interaction between wind and mountainous terrain features.

Other special clouds

 

In appearance, clouds may be thick or thin, have well defined edges or be very diffuse, appear hairlike, cellular, towering, or in sheets, and be associated with fair weather or precipitation. Most clouds owe their existence to upward vertical motion of air, hence they are often associated with weather producing phenomena, such as fronts, troughs, and low pressure systems. However, topography can also help move air upwards and produce clouds.

 

HIGH LEVEL CLOUDS

High-level clouds form above 6,000 meters and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals.

Cirrus are high altitude wispy clouds. They are usually quite thin and often have a hairlike or filament type of appearance.

 

 

 

Cirrocumulus are high clouds that have a distinct patchy and/or wavelike appearance.

 

 

 

 

Cirrostratus are high clouds that usually blanket the sky in ill-defined sheets. These clouds are usually optically thin and the sun and moon can usually shine some light through

 

 

MIDDLE LEVEL CLOUDS

The bases of mid-level clouds typically appear between 2,000 to 6,000 meters. Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

Altocumulus have distinct cloud elements and are either in a patchy, scattered distribution or can appear in linear bands.

 

Altostratus have a more uniform and diffuse coverage where it is difficult to detect individual elements or features.

 

LOW LEVEL CLOUDS

Low clouds are of mostly composed of water droplets since their bases generally lie below 2,000 meters. However, when temperatures are cold enough, these clouds may also contain ice particles and snow.

Cumulus are usually puffy and often have very distinct edges and usually a noticeable vertical development. They often have a poporn-like appearance. Cells can be rather isolated or they can be grouped together in clusters.

 

Stratocumulus can be widely scattered but are usually concentrated closer together in clusters or layers and have very little vertical development.

Stratus are usually the lowest of the low clouds. Stratus often appear as an overcast deck (as shown), but can be scattered. The individual cloud elements have very ill-defined edges compared to most low cumuloform clouds (e.g. cumulus and stratocumulus).

 

 Fog can be considered as a low stratus cloud in contact with the ground.

 

 

MULTI-LAYER CLOUDS

Multi-layer clouds are the heavy precipitation producers. The depth of these clouds give precipitation hydrometeors a better environment to develop and grow.

Nimbostratus are considered multi-layer clouds because their vertical extent often goes well into the middle cloud region and these clouds often have even taller cumulonimbus clouds embedded within them. The clouds are very dark, usually overcast, and are associated with large areas of continuous precipitation.

 

Cumulonimbus are the clouds that can produce lightning, thunder, heavy rains, hail, strong winds, and tornadoes. They are the tallest of all clouds that can span all cloud layers and extend above 60,000 feet. They usually have large anvil-shaped tops (as shown) which form because of the stronger winds at those higher levels of the atmosphere.

 

 

Cumulonimbus Mammatus  indicates that the atmosphere is quite unstable and can also be an indicator of impending severe weather.

 

 

Cumulonimbus from space

 

 

 

 

 

OROGRAPHIC CLOUDS

Orographic clouds, as the name implies, are produced by the flow of air interacting with mountainous terrain.

Cap clouds form when air containing water vapor is uplifted on the windward slide of the slope and reaches saturation producing liquid water cloud droplets and a cloud which can "cap" the summit.

 

 

 

Lenticular clouds are lens-shaped clouds that can result from strong wind flow over rugged terrain.

 

 

 
OTHER SPECIAL CLOUDS

Instability Billow Clouds is one that can develop due to Kelvin-Helmholtz (K-H) instability waves.

 

 

 

Contrails,  can be formed from the vapor contained in the exhaust of a jet engine of an airplane when they are flying at high enough altitudes where cold temperatures cause the vapor to turn into ice crystals like cirrus clouds.