EATS1011 Lecture 8

Clouds

• Clouds to fall but then they fall into warmer air and evaporate
  
• CCN: 100%
  
  • Cloud condensation Nuclei (CCN)
    
• Newton's first law
  
  • The droplet of radius r
    
  • The droplet's going down
    
  • And friction of particles in the air
    
  • Eventually balance out
    
  • Friction force
    
    • 6πR(eta) V
      
      • Eta is viscosity (missing symbol)
        
  • Gravitational force
    
    • M*g
      
      • M ass of the droplet
        
      • G ravity
        
      • = 4/3πR³
        
  • These two forces equal each other out
    
  • Get formulas from website
    
  • This only applies to 'small' droples (< 100microns)
    
  • Terminal Velocity
    
    • 
      
    • 
      
    • 
      
  • 
    
  • V_T = 6x10³ R(m) m/s (R> 100 mm)
    
• Condenstation -> growth
  
  • 1/R
    
• 1) collision and coalescence
  
  • Warm
    
• 2) bergeon process
  
  • Mixed phase clouds
    
    • (liquid water + ice)
      
  • The difference in vapour pressure drives the growth of the droplets
    
• Size spectrum
  
  • 1 micron -> 5 microns -> 10 microns – 15 microns – 50 microns
    
  • The small ones fall slower than the large ones
    
  • The large one sweep up the smaller ones under them
    
    • Until the droplet gets even bigger and falls faster
      
    • If there are enough small particles you can see how we get very large droplets