Once a cloud forms, how do we know what to call it? Clouds form in many environments and look different depending on those environments, and depending on whether they’re composed of liquid droplets or ice crystals. We’ll discuss this more in the following chapter on precipitation. A common one used in cloud seeding is called silver iodide, AgI. Materials with a hexagonal shape, like ice crystals, also make particularly good surfaces for ice to form on. In Earth’s atmosphere, aerosols are abundant, so water vapor does not struggle to find CCN to condense onto.Īnother type of aerosol that helps with the formation of cold clouds, or clouds composed of ice crystals, are called Ice Nuclei (IN). In laboratory studies with a clean atmosphere (with no aerosols) relative humidities up to 400% have been measured. If there were no aerosols in the atmosphere, relative humidities well over 100% would be needed for clouds to form. An aerosol that is hygroscopic, or “water-liking”, has the potential to be a cloud condensation nuclei. Anything that is small enough to be lofted and suspended in the atmosphere has the potential to be an aerosol. They can be composed of material from plant or organism life, like sulfates and nitrates or volatile organic compounds, or even phytoplankton.

They can also be composed of sea salt from the ocean, black carbon from fires, or sulfate from volcanic activity. They can be composed of earth matter like dust, clay, or soot. Aerosols are everywhere in the atmosphere. The surface is provided by tiny particulates in the atmosphere known as aerosols, or more generally, cloud condensation nuclei ( CCN).

However, water vapor requires a surface on which to condense. When air becomes saturated, excess water vapor in the atmosphere can condense to form liquid water. For example, a person’s breath on a cold day or jet contrails can both form clouds because of this mixing process. The mixture of two unsaturated air parcels can even cause saturation in the resulting mixture. In some cases, both moisturizing and cooling can happen at the same time. Saturation is typically achieved by either adding moisture until the dew point temperature is equivalent to the temperature or cooling until the temperature is lowered to the dew point temperature. Vortices, like wing tip vortices on aircraft, or tornados.Advection fog: air moving over cold ocean currents.Adding Moisture (or mixing with cool moist air).The list below describes the three ways air parcels can become saturated. To put this another way, we know that clouds form when the atmosphere is saturated. To become saturated, the air either needs to cool with the same moisture content (move left on a constant e 0 line), or increase the moisture content (move upward on a constant T line) until the air meets the saturation curve. Imagine a point on the right side of the line, at T=75 ☌, and e 0=12.5 kPa. temperature have an exponential relationship ( CC BY-SA 4.0). The Clausius-Clapeyron relationship showing that saturated vapor pressure vs. Sub-saturated air has a relative humidity below 100% and super-saturated air has a relative humidity above 100%. The region to the right of the line represents air that is sub-saturated, and the region to the left of the line represents air that is super-saturated. The line represents the vapor pressure at saturation for a given temperature. Recall from Chapter 4, the Clausius-Clapeyron diagram.

They are falling but they fall so slowly that they appear to be suspended in the air. The cloud droplets or crystals are so small that their terminal velocity, the highest velocity possible as an object falls through a fluid, is negligible. What is a cloud and how does it form?Ī cloud is a collection of suspended particles of water droplets and/or ice crystals in the atmosphere.

In addition to identifying the cloud, you should know the general altitude (low, mid, or high), cloud class (convective or stratiform) and whether or not it is a rain cloudĬumulus clouds (Photo by Shintaro Russell).

Differentiate between and identify major cloud types including cumulus, stratus, cirrus, altostratus, etc.

Describe the difference between cumuliform and stratiform cloud classes.

Describe the importance of cloud condensation nuclei in cloud formation.

By the end of this chapter, you should be able to:

Earthdesk sample high definition clouds