Theory 
Clouds| CONTENT - A useful description of the varied clouds types you may observe. A tutorial in our series about the Earth |
Clouds are the main visible elements of the weather which is taking place in the troposphere. Clouds are ensembles of microscopic water droplets or icy crystals. Clouds are an important step in the water cycle at Earth as they are the result of the condensating moisture coming from soil and as they are eventually turning water into precipitations falling back Earth. On the other hand clouds are an important actor of the Earth's energy budget as clouds top is reflecting the solar radiation while clouds base is trapping re-radiated heat from the surface. Thus clouds are an element of the natural greenhouse effect. Clouds are among the most important mediators of heat reaching Earth's surface. Where clouds are absent, darker surfaces like the ocean or vegetated land absorb heat, but where clouds occur their white tops reflect incoming sunlight away, which can cause a cooling effect on Earth’s surface. A cloud forms when the air temperature and pressure are favorable for the vapor to condense into ice. The vapor and the ice reach a balance point that is determined by the air temperature and pressure. 'Nucleation' generally is what causes ordinary clouds with airborne specks of dust and even living microbes can serve like loci where moisture aggregate. Tiny ice crystals, drops of water, and snowflakes grow around these particles, falling to Earth if and when they become heavy enough. A recent view is that bacteria or fungi, diatoms and algae as swept up into the skies might be the seed to raindrops or snowflakes in clouds rather that minerals or other particulates. Some bacteria further likely help ice, like for hailstones, to form a temperatures above the freezing point of water due to a special proteine which binds water molecules in a closer proximity. That specificity is used by such bacteria to crack open into a plant through cold as some scientists think that those bacteria might use its journey into the clouds like a life cycle. Updrafts in low-lying clouds keep drizzle droplets aloft until they cannot hold them up any longer as drizzle then falls like full-sized raindrops (that is truer still for such clouds over a water body, where droplets fall like drizzle because updrafts are even weaker). In terms of droplets' size, a typical cloud condensation nucleus is 0.0002 millimeters, a typical cloud droplet around 0.02 mm and have not enough mass to fall. A typical drizzle droplet is 0.5 mm as it is just heavy enough to fall, and a typical raindrop is about 2 mm. Clouds sort into four main categories depending on the altitude of their base. Various main types are sub-dividing the categories. More than 100 types of clouds exist. Clouds types present at a given location depend on the weather fronts existing there
Altitude clouds are composed of icy crystals and found above 20,000 ft (6 km)
Middle altitude clouds are composed of water droplets or of icy particles if temperature is appropriate. They are found between 2 and 4 miles (3-6 km)
Low clouds are composed of water droplets but they may turn into icy crystals or snow temperature permitting. They are found under 1 mile of altitude (1.6 km)
Multi-level clouds are ranging in altitude from less than 1 mile to more than 8 miles (1.6-13 km)
