5.3 Cloud formation and types

Clouds are the visible manifestation of atmospheric moisture, forming through condensation around tiny particles. This section explores the process of cloud formation, including key elements like water vapor and cooling mechanisms, as well as the physics behind it.

Cloud types are classified by altitude and appearance, ranging from low-level stratus to high-level cirrus. We'll examine various cloud formations, their characteristics, and how they serve as indicators of weather conditions and potential severe weather events.

Cloud formation process

Condensation and key elements

Top images from around the web for Condensation and key elements

• 

  Clouds: formation – Classroom Partners View original

  Is this image relevant?

• 

  Thunderstorms | Physical Geography View original

  Is this image relevant?

• 

  ACP - Cloud condensation nuclei characteristics during the Indian summer monsoon over a rain ... View original

  Is this image relevant?

• 

  Clouds: formation – Classroom Partners View original

  Is this image relevant?

• 

  Thunderstorms | Physical Geography View original

  Is this image relevant?

1 of 3

Top images from around the web for Condensation and key elements

• 

  Clouds: formation – Classroom Partners View original

  Is this image relevant?

• 

  Thunderstorms | Physical Geography View original

  Is this image relevant?

• 

  ACP - Cloud condensation nuclei characteristics during the Indian summer monsoon over a rain ... View original

  Is this image relevant?

• 

  Clouds: formation – Classroom Partners View original

  Is this image relevant?

• 

  Thunderstorms | Physical Geography View original

  Is this image relevant?

1 of 3

• Cloud formation occurs when water vapor condenses into liquid water droplets or ice crystals around tiny particles (condensation nuclei)
• Three key elements required for cloud formation
  • Water vapor
  • Cooling of air to its dew point
  • Presence of condensation nuclei
• Adiabatic cooling leads to cloud formation as air rises and expands in the atmosphere
• Lifting mechanisms cause air to rise and cool
  • Convection
  • Frontal lifting
  • Orographic lifting (mountains)
  • Convergence

Physics of cloud formation

• Clausius-Clapeyron equation describes relationship between air temperature and water-holding capacity
  • Crucial for understanding cloud formation process
  • Explains why warmer air can hold more water vapor
• Supersaturation occurs when relative humidity exceeds 100%
  • Allows continued growth of cloud droplets
  • Growth mechanisms include collision and coalescence
• Latent heat release during condensation affects atmospheric stability
  • Can lead to further lifting and cloud development

Cloud types: Altitude vs Appearance

Low and mid-level clouds

• Low-level clouds (0-2 km altitude)
  • Stratus: flat, layered appearance (fog when touching the ground)
  • Stratocumulus: patchy, often in rows or waves
  • Nimbostratus: thick, dark, associated with continuous precipitation
• Mid-level clouds (2-6 km altitude)
  • Altostratus: gray or white sheets, often covering entire sky
  • Altocumulus: white or gray patches, sometimes in a mackerel sky pattern

High-level and vertically developed clouds

• High-level clouds (5-13 km altitude)
  • Cirrus: thin, wispy, composed of ice crystals (mare's tails)
  • Cirrostratus: thin veil-like layer, can create halos around sun or moon
  • Cirrocumulus: small, round white puffs in a pattern (mackerel sky)
• Vertically developed clouds (span multiple altitude levels)
  • Cumulus: puffy, cotton-like appearance (fair weather cumulus)
  • Cumulonimbus: towering thunderstorm clouds with anvil-shaped top

Cloud classification systems

• World Meteorological Organization's International Cloud Atlas
  • Provides comprehensive classification system
  • Includes ten basic cloud types and various subtypes
• Additional cloud formations
  • Mammatus: pouch-like structures underneath cloud base
  • Lenticular: lens-shaped clouds formed by orographic lifting
• Cloud cover measurement uses oktas (eighths of sky covered)

Clouds and weather conditions

Clouds as weather indicators

• Stratus and stratocumulus indicate stable atmospheric conditions
  • May bring light precipitation or drizzle (mist, fog)
• Cumulus cloud development signals atmospheric instability
  • Small cumulus suggest fair weather
  • Large, towering cumulus may develop into cumulonimbus
• Nimbostratus associated with continuous moderate to heavy precipitation
  • Often linked to warm fronts or occluded fronts
• Cirrus clouds often precede warm fronts
  • May indicate approaching weather system (24-48 hours in advance)

Severe weather and cloud types

• Cumulonimbus clouds indicate potential for thunderstorms and severe weather
  • Associated with heavy precipitation, lightning, and strong winds
  • Supercell thunderstorms have rotating updrafts (mesocyclones)
• Mammatus clouds, while not a distinct type, often indicate severe weather
  • Associated with turbulence and potential for tornadoes
• Wall cloud formation in severe thunderstorms
  • Lowered cloud base that may precede tornado development
• Shelf clouds and roll clouds indicate gust fronts
  • Associated with strong outflow winds from thunderstorms

Aerosols and cloud formation

Types and sources of aerosols

• Aerosols are tiny solid or liquid particles suspended in the atmosphere
  • Serve as condensation nuclei for cloud droplet formation
• Natural sources of aerosols
  • Sea spray (salt particles)
  • Dust from deserts or volcanic eruptions
  • Biological particles (pollen, spores)
• Anthropogenic sources of aerosols
  • Industrial emissions (sulfates, nitrates)
  • Biomass burning (smoke particles)
  • Vehicle exhaust (soot, organic compounds)

Aerosol impacts on cloud properties

• Size, composition, and concentration of aerosols influence cloud properties
  • Affect droplet size distribution and cloud albedo
• Twomey effect describes impact of increased aerosol concentration
  • Leads to more numerous but smaller cloud droplets
  • Can alter cloud reflectivity and lifetime
• Hygroscopic aerosols readily absorb water
  • Particularly effective as cloud condensation nuclei (salt particles)
• Aerosol-cloud interactions crucial for understanding climate change
  • Can lead to both warming and cooling effects
  • Represent a significant source of uncertainty in climate models