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6: Clouds

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    9567

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    Clouds have immense beauty and variety. They show weather patterns on a global scale, as viewed by satellites. Yet they are made of tiny droplets that fall gently through the air. Clouds can have richly complex fractal shapes, and a wide range of sizes (The World Meteorological Organization (WMO) updated their International Cloud Atlas in 2017 (WMO-No. 407). It is an excellent resource that you can access online at www.wmocloudatlas.org). Clouds form when air becomes saturated. Saturation can occur by adding water, by cooling, or by mixing; hence, Lagrangian water and heat budgets are useful. The buoyancy of the cloudy air and the static stability of the environment determine the vertical extent of the cloud. Fogs are clouds that touch the ground. Their location in the atmospheric boundary layer means that turbulent transport of heat and moisture from the underlying surface affects their formation, growth, and dissipation.

    • 6.0: Homework Exercises
      This page comprehensively explores cloud classification and fog formation, detailing various cloud types, their characteristics, and the environmental conditions influencing their formation. It emphasizes the importance of thermodynamic diagrams for analyzing temperature and dew point and includes practical exercises for understanding fog dynamics and atmospheric phenomena.
    • 6.1: Processes Causing Saturation
      This page explains how clouds form through air saturation via cooling, moisture addition, or mixing. Cooling reaches the dew point temperature, while added moisture raises the dew point. Both processes can occur simultaneously. Mixing unsaturated air parcels can also result in saturation, exemplified by jet contrails. It details calculations for determining the temperature and moisture content necessary for saturation, along with sample applications to aid understanding.
    • 6.2: Cloud Indentification
      This page provides an overview of cloud classifications, focusing on cumuliform and stratiform clouds. Cumuliform clouds, linked to atmospheric instability, can lead to thunderstorms, while stratiform clouds appear as horizontal layers associated with warm fronts. The page details specific types like nimbostratus, which brings precipitation, and stratocumulus, formed from surface turbulence. It also covers pyrocumulus clouds created by heat and anthropogenic clouds like contrails.
    • 6.3: Cloud Organization
      This page covers cloud organization in various weather conditions, highlighting cloud streets and mesoscale cellular convection (MCC). It explains how cloud streets arise in specific winds and the broader patterns of MCCs that can go unnoticed. Additionally, it incorporates Richard Feynman's views on scientific integrity, stressing the necessity of transparency in research for valid outcomes.
    • 6.4: Cloud Classification
      This page provides an overview of cloud classification according to shape, as established by the World Meteorology Organization. It outlines the system of genera, species, varieties, and supplementary features, detailing ten main cloud genera and their characteristics. Additionally, it discusses cumulus towers formed by larger clouds like cumulus congestus and cumulonimbus, along with the concept of "velum," a thin cloud veil that affects cloud structures.
    • 6.5: Sky Cover (Cloud Amount)
      This page discusses sky cover in oktas, a measurement of cloud coverage. It outlines the World Meteorological Organization's classification system for cloud amounts and symbols used in weather reporting. The page also explains how obscurations like fog or haze affect cloud visibility and defines the aviation term 'ceiling' as the height of the lowest significant cloud layer, with obscurations impacting vertical visibility reporting.
    • 6.6: Cloud Sizes
      This page discusses the characteristics of cumuliform clouds, noting their size correlation between diameter and depth, ranging from 1 km for fair weather to 10 km for thunderstorms. It explains the lognormal distribution of cloud sizes, highlighting the prevalence of medium-sized clouds and the rarity of larger ones, influenced by temporal and spatial factors.
    • 6.7: Fractal Cloud Shapes
      This page explores fractals, focusing on their unique patterns and dimensions relevant to meteorology, such as clouds and lightning. It differentiates between Euclidean geometry's integer dimensions and fractal geometry's non-integer dimensions, with a fractal dimension indicating a shape's spatial filling ability, illustrated by examples like crumpled newspaper.
    • 6.8: Fog
      This page explores various types of fog, primarily focusing on advection and radiation fog, detailing their formation mechanisms and the environmental conditions required for their development. It highlights the mathematical models for estimating fog formation, including factors like temperature, moisture, and boundary layer conditions.
    • 6.9: 6.9. Review
      This page covers the processes of water vapor condensation that lead to cloud and fog formation, focusing on the roles of cooling, moisture addition, and mixing. It describes how buoyancy affects cloud types, distinguishing between cumuliform and stratiform clouds based on air stability. The page also details cloud classification by altitude and appearance, outlines different fog types, and introduces heat and moisture budget equations for weather forecasting in ideal conditions.

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    This page titled 6: Clouds is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Roland Stull via source content that was edited to the style and standards of the LibreTexts platform.