5.2 Cloud formation processes and classification

Clouds form through condensation, coalescence, and ice nucleation. These processes depend on factors like adiabatic cooling, atmospheric stability, and moisture availability. Understanding cloud formation is key to predicting weather patterns and precipitation.

Clouds are classified by altitude, shape, and composition. Different cloud types are associated with specific weather phenomena. For example, nimbostratus clouds bring steady rain, while cumulonimbus clouds can produce thunderstorms. Recognizing cloud types helps forecast weather conditions.

Cloud Formation Processes

Processes of cloud formation

Top images from around the web for Processes of cloud formation

• 

  ACP - Modelling the effect of condensed-phase diffusion on the homogeneous nucleation of ice in ... View original

  Is this image relevant?

• 

  ACP - The temperature dependence of ice-nucleating particle concentrations affects the radiative ... View original

  Is this image relevant?

• 

  ACP - The ice-nucleating ability of quartz immersed in water and its atmospheric importance ... View original

  Is this image relevant?

• 

  ACP - Modelling the effect of condensed-phase diffusion on the homogeneous nucleation of ice in ... View original

  Is this image relevant?

• 

  ACP - The temperature dependence of ice-nucleating particle concentrations affects the radiative ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Processes of cloud formation

• 

  ACP - Modelling the effect of condensed-phase diffusion on the homogeneous nucleation of ice in ... View original

  Is this image relevant?

• 

  ACP - The temperature dependence of ice-nucleating particle concentrations affects the radiative ... View original

  Is this image relevant?

• 

  ACP - The ice-nucleating ability of quartz immersed in water and its atmospheric importance ... View original

  Is this image relevant?

• 

  ACP - Modelling the effect of condensed-phase diffusion on the homogeneous nucleation of ice in ... View original

  Is this image relevant?

• 

  ACP - The temperature dependence of ice-nucleating particle concentrations affects the radiative ... View original

  Is this image relevant?

1 of 3

• Condensation
  • Water vapor cools and condenses into liquid water droplets
  • Requires presence of condensation nuclei (dust, salt particles) for water vapor to condense upon
  • Occurs when air becomes saturated and relative humidity reaches 100%
• Coalescence
  • Water droplets collide and merge to form larger droplets
  • Larger droplets fall faster than smaller ones, causing collisions and combining
  • Essential for growth of cloud droplets into raindrops (precipitation)
• Ice nucleation
  • Formation of ice crystals in clouds
  • Requires presence of ice nuclei (dust particles, bacteria) for ice crystals to form around
  • Two processes:
    1. Homogeneous nucleation: Temperatures below -40℃, water droplets freeze spontaneously
    2. Heterogeneous nucleation: Temperatures between 0℃ and -40℃, ice nuclei facilitate formation of ice crystals

Factors in cloud development

• Adiabatic cooling
  • Decrease in temperature when air parcel rises and expands without exchanging heat with surroundings
  • Causes relative humidity of rising air to increase, potentially leading to condensation and cloud formation
  • Dry adiabatic lapse rate ~9.8℃/km, moist adiabatic lapse rate varies with moisture content
• Atmospheric stability
  • Atmosphere's resistance to vertical motion
  • Stable conditions suppress vertical motion and cloud development, unstable conditions promote them
  • Determined by comparing environmental lapse rate (ELR) with adiabatic lapse rates:
    • Absolute stability: ELR < Moist adiabatic lapse rate
    • Conditional instability: Moist adiabatic lapse rate < ELR < Dry adiabatic lapse rate
    • Absolute instability: ELR > Dry adiabatic lapse rate
• Moisture availability
  • Amount of water vapor present in atmosphere
  • Higher moisture increases likelihood of condensation and cloud formation
  • Sources: evaporation from water bodies, transpiration from plants, advection from other regions

Cloud Classification and Characteristics

Classification of clouds

• Cloud classification by altitude
  • Low-level clouds (surface to 2 km)
    • Stratus (St)
    • Stratocumulus (Sc)
    • Cumulus (Cu)
  • Mid-level clouds (2 km to 6 km)
    • Altostratus (As)
    • Altocumulus (Ac)
    • Nimbostratus (Ns)
  • High-level clouds (6 km to 18 km)
    • Cirrus (Ci)
    • Cirrostratus (Cs)
    • Cirrocumulus (Cc)
• Cloud classification by shape
  • Cumulus: Puffy, cauliflower-like appearance with flat bases
  • Stratus: Flat, featureless, often covering entire sky
  • Cirrus: Thin, wispy, composed of ice crystals
• Cloud classification by composition
  • Water clouds: Composed entirely of liquid water droplets (cumulus, stratus)
  • Ice clouds: Composed entirely of ice crystals (cirrus)
  • Mixed-phase clouds: Contain both liquid water droplets and ice crystals (nimbostratus)

Cloud types vs weather phenomena

• Precipitation
  • Nimbostratus clouds associated with steady, prolonged precipitation
  • Cumulonimbus clouds can produce heavy rainfall, hail, and snow
• Thunderstorms
  • Cumulonimbus clouds responsible for thunderstorms due to strong vertical development and unstable atmospheric conditions
  • Thunderstorms require moisture, instability, and lifting mechanism (fronts, orographic lifting, convective heating)
• Frontal systems
  • Warm fronts: Sequence of cloud types from high-level cirrus to mid-level altostratus and nimbostratus, then low-level stratus
  • Cold fronts: Often accompanied by cumulonimbus clouds, leading to thunderstorms and heavy precipitation
  • Occluded fronts: Mix of cloud types and precipitation patterns depending on occlusion type (warm or cold) and atmospheric stability