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Water in the Atmosphere (Water Cycle (How the water cycle works (The light…

- - - - Air can hold moisture in the form of water vapour
      - Water vapour in the air is expressed as relative humidity (RH)
      - Warm air can hold more water vapour than cold air can
      - When the air can hold no more water vapour, it is said to be saturated. Any extra water vapour will then undergo condensation ( it will change into tiny droplets that make up cloud)
    - - Cirrus clouds
        
        Are very high in the sky
        
        look like delicate brush-strokes
      - Cumulus clouds
        
        Are at medium altitudes
        
        Look like fluffy 'castles in the sky'
        
        Some dark cumulus clouds bring showers
      - Stratus clouds
        
        Are low in the sky
        
        Occur in thick layers
        
        Can bring long spells of percipitation
    - - Rain
        
        Rain is the most common form of precipitation
        
        Occurs when moisture-laden air is forced to rise
        
        Three types
        
        Relief rain
        
        Occurs when air is forced to rise over mountains, resulting in rain on the windward side
        
        Moisture-laden winds blow in from the sea 2. Air rises over mountains and is cooled 3. Water vapour condenses to form cloud and rain on the windward side of the mountains 4. When the air moves down the leeward (sheltered) slope, it has already lost most of its moisture. So the leeward side gets little rain. It is called a rain shadow area
        
        Is common in western mountains of Ireland, such as those in Kerry and Donegal
        
        Convectional rain
        
        Occurs when air rises from a warm land surface
        
        the sun heats the earth's surface 2. Air over the hot land is warmed. It expands and rises rapidly 3. As the air rises, it is cooled 4. Water vapour condenses to form cumulus cloud and heavy, thundery showers
        
        Is common in Ireland only on hot, summer days, but it occurs frequently in some regions near the equator
        
        Cyclonic (frontal) rain
        
        This is associated with low pressure systems such as depressions. They contain warm and cold air masses. Forms where these air masses meet
        
        Warm air is light, so it tends to rise over heavier, cool air. 2. Warm air cools 3. Water vapour condenses to form stratus cloud and rain
        
        is very common in Ireland